Antennas for Modern Small Satellites

Antennas for Modern Small Satellites

s. Gao1, K. M. U n w i n 2

, J. Z a c k r i s s o n 3, W. A. S h i r o m a 4

, J. M. A k a g f , K. M a y n a r c f ,P. Garner2, L. B o c c i a 5

, G. A m e n d o / a 5, G. Massa5

, C. U n d e r w o o d 1, M. B r e n c h l e y ,

M. Pointer2, a n d M. N. S w e e t i n g 1

1Surrey Space CentreUniversity of Surrey, Guildford, UK

Tel: +44 14683 682226; E-mail: [email protected]

2Surrey Satellite Technology Ltd.Gulldford, UK

3RUAG Aerospace SwedenSweden

"Universlty of Hawaii at ManoaHawaii, USA

5University of CalabriaCalabria, Italy

Abstract

Modem small satellites (MSS) are revolutionizing the space industry. They can drastically reduce the mission cost, and canmake access to space more affordable. The relationship between a modern small satellite and a "conventional" large satelliteis similar to that between a modern compact laptop and a "conventional" work-station computer. This paper gives an overviewof antenna technologies for applications in modem small satellites. First, an introduction to modern small satellites and theirstructures is presented. This is followed by a description of technical challenges in the antenna designs for modern smallsatellites, and the interactions between the antenna and modern small satellites. Specific antennas developed for modernsmall-satellite applications are then explained and discussed. The future development and a conclusion are presented.

Keywords: Antennas; satellite antennas; small satellites; micro satellite; cube-sat; GPS antennas; nano-sat

1. Introduction

T he general trend for conventional satellites is larger, heavier,

higher power, higher data rate, and multi-functional payloads

that are capable of offering better RF performance in terms of

EIRP, G/T, and spatial and polarization isolations. However, this

makes the satellites very expensive and time-consuming to

develop. Modem small satellites are typically one-tenth to one-one

hundredth of the mass and cost of their "big brothers." The devel

opment of modem small satellites is mainly driven by two sets rea

sons: the first consists of the financial and political needs to reduce

the cost; the other set is comprised of the technological advances in

low-power micro-electronics and digital signal processing (DSP)

[1-3]. Very-large-scale integration (VLSI) makes it possible to

build sophisticated circuits into small volumes, with low mass and

low power consumption. Modem technologies make it possible for

a constellation of modem small satellites to realize many sophisti

cated functions. The development of modem small satellites thus

leads to a significant reduction of cost for satellite industries.Another advantage of using modem small satellites is the short

time scale: conventional satellites may take over five years from

the proposal to final launch, while modem small satellites can be

developed within one year. For example, UoSAT-2, developed by

the University of Surrey in 1984, took only six months [1-3].

The term "modem small satellite" denotes several types of

satellites, including mini, micro, nano, pico, and femto-satellites.

Table 1 shows the classification of each satellite, and the corre

sponding mass and cost [2, 3]. As shown, significant savings in

mass, cost, and development time can be achieved by using mod

em small satellites compared to conventional large satellites.

The University of Surrey has been developing modem small

satellite technology since starting its UoSAT program in 1978.

UoSAT-l, developed by Surrey, was launched in 1981 [1-3]. Thiswas followed by UoSAT-2 in 1984. UoSAT-l continued to operate

for eight years, while UoSAT-2 was still operational after 18 years

in orbit. During the past 30 years, the University of Surrey's spin

off company, Surrey Satellite Technology Ltd. (SSTL), together

with Surrey Space Centre (SSC), have successfully designed,

developed and launched 32 modem small satellites for various

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Table 1. Classification of satellites by mass and cost.

TypeMass Cost Time of Development

(kId (US $) from Proposal to Launch

Conventional large satellite >1000 0.1-2 B >5 years

Medium satellite 500-1000 50-100 M 4 years

Mini-satellite 100-500 10-50 M 3 years

Micro-satellite 10-100 2-lOM year

Nano-satellite 1-10 0.2-2M year

Pico-satellite <1 20-200 k <1 year

Femto-satellite <0.1 0.1-20 k <1 year

Figure 1a. A schematic ofthe SSTL modular micro-satellite.

This paper is a significant expansion 0[[5] . It is organized as

follows: Section 2 describes the structure of typical modem small

satellites and some recent examples. Section 3 presents the challenges of antenna design for modem small satellites. Section 4

gives an overview of antennas developed for different functions in

modem small satellites, including telemetry, tracking, and com-

Figure lb. A photo of an SSTL micro-satellite [2).

2. Modern Small Satellites

2.1 The Structure of Micro-Satellites

The micro-satellite is a representative type of modem small

satellite. A modular design of a multi-mission micro-satellite plat

form was developed at Surrey in 1986, to accommodate a varietyof payload customers within a standard launcher envelope, to pro

vide increased packing density, improved electromagnetic com-

mand (TTC), high-speed payload data downlink, Global Positioning System (GPS)/global navigation satellite systems (GNSS),

inter-satellite cross links, etc. Various antennas for modem small

satellite applications will be presented. Conclusions and the futuredevelopment are presented at the end.

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Earthobservation

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I10. Payload module

9. ADCS module

8. OBDHmodule

7.TICmodule

6. Propulsionsystemmodule

5. Thermal control module

4. Power systemmodule

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J I Attach fitting I GPS I L

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countries around the world. Nowadays, many organizations aroundthe world are working on modem small satellites, and the progress

in modem small satellites can be found from the small-satellite

conference held annually at Utah [4]. These modem small satellitesare useful for various applications, including telecommunications,space science, Earth observation, mitigation and management of

disasters (floods, fire, earthquake, etc.), in-orbit technology verifi

cation, military applications, education, and training. However, it isto be noted that small satellites can never replace conventional

large satellites for fixed satellite service (FSS), broadcasting satel

lite services (BSS), and broadband services that demand very high

power (15 kW), high-gain antennas (30 to 50 dBi), aggregate EIRPvalues of more than 70 dBW, heavier mass, and precision satellite

pointing of 0.10 or less. It is difficult for small satellites to meet

these requirements and the high isolation requirements in otherservice areas, as demanded by FSS and BSS satellites, and also theextensive frequency reuse ofconventional satellites.

IEEE Antennas and Propagation Magazine, Vol. 51, No.4, August 2009 41


patibility (EMC), low-cost manufacture, and ease of integration.

Here, the electronic modules actually form the primary structure ofthe satellite. Figure Ia shows the schematic of an early SSTL

modular micro-satellite. It has a series of identical-outline

machined-modular boxes, stacked one on top of the other, to formthe satellite's body [3]. The modules are held together by tie-rods

that pass through the whole stack, and allow some dissipation of

vibrational energy. As shown, the micro-satellite consists of various subsystems (or modules), including batteries; uplink;

downlink; power system; thermal control; propulsion system;telemetry, tracking, and command; onboard data handling

(OBDH); the attitude-determination and control system (ADCS);

and the payload module (an Earth-observation compartment, in this

example).

Several stacked module trays form a cubic structure with

body-mounted solar panels on four faces. Some small, low-cost

micro-satellites have limited attitude control, usually confined topassive alignment to the local magnetic field, achieved via perma

nent magnets. The use of low-gain omnidirectional antennas meansthe satellites do not need accurate and costly pointing control.

However, high-speed downlinks for payload data will need high

gain antennas, where accurate pointing control is needed. This isusually achieved by a combination of gravity-gradient boom,

momentum wheel, and closed-loop active damping, using electro

magnets operated by an onboard computer, and even station-keep

ing propulsion systems. Attitude determination is provided by the

sun, geomagnetic-field sensors, and star-field cameras. The orbitalposition is determined to within ±I5m by on-board GPS receivers.

Electrical power is typically generated by four body-mounted GaAssolar array panels, and stored in several lithium-ion rechargeable

batteries. Figure 1b shows a photo of a 65 kg micro-satellite devel

oped by SSTL [2].

2.2 Examples of Recent

Modern Small-Satellite Projects

2.2.1 Disaster-Monitoring Constellation

(DMC)

The DMC, developed by Surrey, consists of a constellation ofsix remote-sensing micro-satellites . It is the first low-cost and inte

grated Earth-observation constellation dedicated to monitoring and

mitigation of man-made and natural disasters [1, 2].

The DMC is operated for the Algerian, Nigerian, Turkish,Thailand, UK, and Chinese governments. Each satellite has a mass

of about 90 kg. It provides 32 m multi-spectral Earth-observationimaging, and covers a vast 600 x 600 km, anywhere on the Earth.

The images cover 10 times more area, compared with images of

less than 200 x 200 km currently available from other civilian

Earth-observation satellites. The six micro-satellites in the DMC

provide daily imaging worldwide, capable of monitoring any rap

idly changing phenomenon.

The DMC has monitored the effects and aftermath of the

Indian Ocean tsunami in December 2004, Hurricane Katrina in

August 2005, and many other floods, fires, and disasters. It offers

global monitoring with daily re-visitation at low cost. Figure 2

shows a conceptual view of the DMC, where a constellation of

micro-satellites is shown.

42

2.2.2 Orbiting Pico-Satellite

Automated Launcher (OPAL)

The OPAL is Stanford University's first student-built satel

lite, launched on a Minotaur rocket in 2000 [6]. It operates as an

experimental test bed in a sun-synchronous 750 km low Earthorbit. OPAL is a 23 kg hexagonal prism, made of aluminum hon

eycomb. It explores a new mission architecture to perform distributed sensing in space. In this architecture, a main spacecraft, called

the "mother-ship," deploys a number of smaller spacecraft, called"daughter-ships," to remote locations of interest to perform the

required distributed sensing. It has three primary payloads, includ

ing the mother-ship/daughter-ship mission, the magnetometer test

bed, and the accelerometer test bed.

The communication system uses packet-radio protocols

(AX.25) over amateur radio frequencies. It operates half-duplex on437.1 MHz at 9.6 kbaud. Four omnidirectional antennas arelocated on the OPAL's exterior. For the attitude-determination and

control system, rough attitude information is determined from themagnetometer measurements and solar-panel currents. The primary

power is supplied via GaAs solar panels, mounted on seven of

OPAL's eight external sides. Secondary power is provided by a

NiCd battery pack. OPAL's onboard data-handling system is basedon the Motorola 68332 microcontroller, running at 16 MHz with

I MB of onboard RAM. OPAL uses a modular, three-tray

approach. The mission was successfully operational for 30 months.

Figure 2. The configuration of DMC (2).

IEEE Antennas and Propagation Magaz ine, Vol. 51, No.4, August 2009


2.2.3 The University Nano-Satellite

Program (UNP) and SNAP-1

The nano-satellite is a type of modem small satellite having a

mass below 10 kg. The UNP is a collaborative program of student

built nano-satellites, started in 1999. The US Air Force Office of

Scientific Research (AFOSR) and the National Aeronautics and

Space Administration (NASA) jo intly funded 10 US universities in

designing and assembling nano-satellites, and conducting creat ive

low-cost space experiments, such as formation flying [7]. As a part

of the UNP, the Three-Comer Sat project is a joint effort among

Arizona State University, University of Colorado at Boulder, and

New Mexico State University. Three identical nano-satellites were

built by each univers ity to form a constellation, and to demonstrate

stereo imaging, formation flying, cellular phone communications,

and an innovative onboard data-handling system . The formation

flying is a cooperative effort between satellites operating as a net

work , where targeting and data acquisition are accomplished and

results transmitted to the ground segment and to the other satellites

via communication links, without the need for strict physical

proximity of the satellites. The three nano-satellites fly in a linear

follow-formation, with relative constant separation from each

other.

The EMERALD project, a collaboration between Stanford

University and Santa Clara Universi ty, is a low-cost, two-satellite

mission for validating formation-flying technologies, including

GPS-based positioning, inter-satellite communication, advanced

colloid micro-thrusters, and simple passive position-control

devices. Other parts of the UNP include ionospheric observation

nano-satellite format ion.

Such research activities have also taken place in Europe and

Asia . One example is the SPUTNIK-40, which weighed 3 kg and

was built in 1997 by l 'Aeroclub of France and the Russ ian Aero

nautical Federation. The first UK-built nano-satellite was SNAP-I.

It has a mass of 6.5 kg, and was designed and built at Surrey in just

nine months [1, 2].

2.2.4 The Cube-Sat

The Cube-Sat is a kind ofpico-satellite, having a cubic shape,

a standardized size of lO x lO x 10 cm, and a mass below 1 kg.

Nowadays, it has become a hot topic of research around the world .

The US Cube-Sat Program is an international collaboration of over

40 universities, high schools, and private firms, developing Cube

Sats containing scientific, private, and government payloads. Many

research projects on Cube-Sat also take place in Europe (Germany,

Surrey), Canada, and Japan.

One example of Cube-Sat is PolySat, developed by students

at California Polytechnic [8]. Figure 3 shows the PolySat with

deplo yed antennas. The structure, having a mass of 0.3 kg, is made

of aluminum, and is strong enough to survive launch loads . As in

Surrey's modular micro-satellites, electronic trays and battery sup

ports are located inside the satellite, and contribute to the structural

integrity of the satellite. Mounting points for antennas are located

on the exterior of the satellite. The antennas are rolled around the

satellite before deployment, and held in place with monofilament

secured using a short length of Nichrome wire inside the satelli te.

Upon deployment, a current is passed through the Nichrome wire,

which heats and melts the monofilament, and releases the antennas.

IEEE Antennas and Propagation Magazine , Vol. 51, No.4, August2009

The communication system uses amateur-radio frequency bands,

with a downlink at 440 MHz and an uplink at 144 MHz . The total

mass of PolySat is about 0.8 kg.

Modem small satell ites are designed and constructed with

rapid timescales at low cost. To achieve sophisticated functionality,

they make use of state-of-the-art commercial-off-the-shelf (COTS)

components, which are developed for terrestrial applications, but

are here adapted to space applications. Advances in low-power

microelectronics and digital signal processing can make the satel

lites smaller, smarter, fa ster, and cheaper [1-3].

3. Challenges of Antenna Designs for

Modern Small Satellites

3.1 Functions and Basics of Antennas in


Modem small satellites need antennas for realizing different

functions: 1.) telemetry, tracking, and command, which includes

both uplink and downlink, at different frequencies ; 2.) high-speed

downlink for payload data, e.g., in Earth-observation missions; 3.

GPS/GNSS receiver; and 4. inter-satellite cross links . These func

tions often requ ire several different antennas.

Typical coverages utilized for the antennas are from low-gain

hemispherical, isoflux, and fill-in to medium-gain antennas. The

basic radiator designs used are normally helices, monopoles,

patches, and patch-excited cups (pEC), depending on frequenc y

range , coverage requirements, and application.

Common for all helix designs is that they are lightweight

designs, with broad coverage and low cross polarization. A major

benefit of using quadrifilar-helix antennas (QHA) is that it is pos

sible to shape the radiation pattern to obtain the desired coverage.

Depending on the coverage and bandwidth requirements, they are

conical, or resonant, or something in between. Helices can be real

ized in different ways : self-supporting metallic wires, machined

out of one metall ic piece, metallic tubes or wires using dielectric

supports, or etched on dielectric cones or tubes .

However, for some applications the quadrifilar-helix antenna

type may be too tall for modem small satellites. In these cases

other antenna types, such as patches or patch-excited cups , must be

used .

- :

Figure 3. The PolyS at with deployed antennas [8].

43


3.2. Challenges of Antenna Designs for


Due to the special environment in space and the requirements

of modem small satellites, antenna designs for modem small satel

lites have many challenges. The main challenges include:

Antennas must be highly reliable, as it is difficult to

replace the antenna in space.

Antennas must be very small, have low mass, be highly

efficient, and be low cost, due to the stringent requirements of small size, low mass, and low cost of modem

small satellites.

Antennas must be mechanically robust, and able to sur

vive both random vibration and shock during the

launch.

The thermal design of the antennas must be carefully

evaluated. The antennas are designed to perform over a

wide temperature variation, typically from -150° C to

+150°C. The normal thermal design for wide-coverage

antennas is passive. Some designs must operate even

down to below -200° C. No multi-layer insulation

(MLI) or other thermal hardware is used.

Antennas must be able to survive the harsh radiationenvironment in space, such as ionizing radiation, cos

mic radiation, and solar energetic particles.

Effects of atomic oxygen need to be considered for

LEO (low-Earth-orbit) missions. This can be handled

by using a germanium-coated single-layer-insulation

protective cover on the antenna, or by using a resistant

surface treatment directly on the antenna [9].

Materials for the antennas need to be chosen carefully,considering the effects ofvacuum and micro-gravity.

High data rates require a high antenna gain. However,

the very limited space available on modem small satel

lites makes it difficult to accommodate a high-gain

antenna, which usually consists of bulky and compli

cated reflector antennas or antenna arrays. Costly

pointing will also be needed for high-gain antennas. A

tradeoffhas to be made.

As many antennas are fitted in a small space, EMC and

mutual coupling amongst these antennas, the payloads,

and circuits need to be carefully considered.

A major consideration for antenna design is the interac

tion between antennas and the modem small-satellite

structures. The spacecraft's structure can cause electro

magnetic scattering, as well as have blockage effects on

the antenna's radiation patterns. The scattering can

interfere with the antenna's radiation pattern, and can

cause severe degradation in gain performance and

sidelobes. This degradation will have a major influence

on a communication-link system's performance, and

needs to be assessed.

44

Antennas have to be located (as far as possible) on the

spacecraft in such a way that they can provide accept

able performance and, at the same time, do not disturbor interfere with other antennas, subsystems, or the

allowed outer physical envelope of the satellite (i.e.,

they must fit under the fairing of the launcher used).

As the antenna interaction with modem small satellites is a

major concern, more discussion is given in the next section.

3.3. Discussions on Antenna Designs and

Antenna Interactions with


The design of a small satellite antenna starts with the mission

requirements and the link budget. During the early phases of theproject, the quantity of data produced is established, and the needs

for separate telemetry, tracking, and command and payload links

are investigated. Simple missions may use a single link for all traf

fic, while more-advanced operations may separate the relatively

low-speed telemetry, tracking, and command functionality from the

high-speed data links. This allows the use of low-gain omnidirec

tional antennas for satellite-bus traffic, and high-gain antennas with

narrower beamwidths for the payload antennas. In the case of non

nominal attitude, the payload link will thus be interrupted, but the

telemetry, tracking, and command traffic can be maintained toensure that commanding of the satellite can continue, such that

nominal attitude can be reestablished.

For telemetry, tracking, and command antennas, the key

requirements are omnidirectional coverage, with associated low

gain, mechanical robustness, and resistance to environmental

effects, such as ultraviolet light, radiation, deep dielectric charging,

and differential surface charging. To achieve near omnidirectional

coverage, more than one antenna is often required. By simply

inspecting the beam pattern of a single antenna, one can be misled

into thinking that multiple antennas will produce a similarly

smooth radiation pattern. This is incorrect, and can be demon

strated by examining the simulations for both single (Figure 4) and

double (Figure 5) practical S-band monopole antennas (with asso

ciated mountings). The latter antennas were operated in opposite

directions and separated from one another by ten wavelengths.

The single monopole has a classical doughnut-shaped radia

tion pattern, distorted by the practical mounting mechanics. The

pattern of the double monopole has significant peaks and nulls. Ifthe nulls are of sufficient depth, they will equate to undesirable

communication blackouts.

This simple case is further exacerbated when one adds the

more-complex structure of the satellite. The body of the spacecraft

itself modifies the antenna's pattern, while the effects of adjacent

antennas, cameras, booms, sun sensors, and solar panels further

compound the problem. The resultant radiation pattern is far from

the desired smooth hemispherical shape, and is bound to have areas

of higher and lower gain. The relative phase of the signals fed toeach of the antennas will further modify the coverage. Figure 6

shows the result of placing two S-band tracking, telemetry, and

command (TT&C) monopole antennas on a 100 kg small satellite.

Although the pattern looks somewhat unsuitable, the type of com-

IEEE Antennas and Propagation Magazine, Vol. 51, No.4, August 2009


GIIl_v.ldllJ10zs00·20

·00.]3

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Figure 4. The radiation pattern of a single monopole antenna.

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Figure S. The radiation pattern of two monopoles separated bylOA..


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Figure 6. The collective gain pattern for two S-band monopolesmounted on a small satellite.

45


munication link needs to be considered. The telemetry system on

small satellites often comprises digital packets. If a packet is lost

due to the ground-station's transit through a propagation null, or

due to the satellite's tumbling during the commissioning phase, it

can simply be resent, thus maintaining the overall message integ

rity.

The placement of antennas for optimum coverage and

antenna-performance assessment can be found by using electro

magnetic (EM) simulation, by measurements, or by a combination

of both. The selection of the method or combination of methods is

either driven by the actual size being considered (i.e., if items such

as solar panels or foldable booms or other appendages exist), or by

whether the antenna is integrated or flush-mounted in the space

craft's body. In more recent years, affordable and accurate EM

simulation programs have become widespread. Once the sub-com

ponents of the satellite have been modeled, they can be quickly

configured to try out different positions to minimize radiation-pat

tern perturbations. It is now standard practice to simulate the entire

satellite during the design phase, to evaluate different types of

antennas and to optimize their radiation patterns.

It has been shown that in order to design an antenna

configuration suitable for a small satellite, the entire mission

objectives must be considered. The bulk of payload data required

and the transmission rate, along with the available satellite power,

helps to define the gain of required for the antenna. High-gain

antennas infer the need for an antenna-pointing mechanism, while

specific satellite-pointing requirements, such as for imaging, will

place specifications on the pointing mechanism, itself. Successful

configurations must be simulated in the design phase, and must

take into account the effects of limited ground planes, adjacent

structures, and co-located antenna systems.

Figure 7 shows the results from a typical low-profile antenna

installation on a spacecraft. As can be seen, the current magnitude

is high in the close vicinity to the antenna element, as expected.

4. Overview of Antennas Developed for


4.1 Antennas for TTC of


4.1.1 General Requirements

for this Application

During the initial acquisition period, following the satellite's

separation from the launcher, the satellite's stabilization has not

been achieved. Omnidirectional or wide-coverage antennas are

thus required for communication between space and ground.

Sometimes, more than two such antennas are mounted on different

sides of the satellite, to provide better coverage for the telemetry,

tracking, and command link, as well as for redundancy. Several

omnidirectional antennas at different frequencies, e.g., UHF and

VHF bands, are usually used for telemetry, tracking, and command

uplink and downlink, respectively.

46

4.1.2 Antenna Examples

Various monopole antennas, printed inverted-F-shaped anten

nas (PIFAs), microstrip-patch antennas, helices, and patch-excited

cup antennas, have been developed for telemetry, tracking, and

command of modern small satellites in the UHF, VHF, S, C, and Xbands. These antennas are simple, cheap, easy to fabricate, and

have wide radiation-pattern coverage; the satellite thus does not

need accurate control ofattitude.

Figure 8 shows a photo of the S-band microstrip-patch

antenna used at SSTL [2]. It employs a circular microstrip patch,

fed by a 50 {} probe feed at the bottom. It can operate within a tun

able frequency range of 2.0-2.5 GHz. Left-hand or right-hand cir

cular polarization can be achieved by using a single feed combined

with patch perturbation, or a 900 microstrip hybrid combined with

a circular patch. It achieves a maximum gain of about 6.5 dBi, has

a size of 82 x 82 x 20 mm, and a mass of less than 80 g. It can

operate within -200 C to +500 C, is radiation tolerant to 50 kRad,

and qualified to 50 g rms random vibration on three axes for 60 s,

Figure 9 shows RUAG Aerospace Sweden's S-band quadrifi

lar-helix antennas. They can be used for both the telemetry, track

ing, and command function, and for data downlink. They exhibit

an isoflux type pattern.

To respond to the need for single-frequency low-profile and

low-weight hemispherical or near-hemispherical antennas, working

Figure 7b. A mock-up of a typical spacecraft.

Figure 8. An S-band patch antenna at SSTL [21.



Figure 9. S-band quadrifilar-helix antennas at RUAG Aerospace Sweden (two antennas and test hats).

-- --.......',• .

... "

" . ..,;/-,-,' .. ....- ' "' -

't:.= ,

,..,... - '".

.

Figure 10. An X-band patch-excited cup antenna.

at S, C, or X band, patch-excited cup antennas were developed at

RUAG Aerospace Sweden . They consist of a short cylindrical cup,

with a circular cross section and an exciter. The cup is excited

using a stacked circular dual-patch element , or a single patch. The

lower patch or the single patch is fed at one point, and the patch

has two oppos ite perturbations for generating circular polarization.

The antennas have special features to minimize their coupling to

the surrounding spacecraft environment, as this is a common

problem for low-gain antennas of this type, and it has an effect on

the installed performance. The antenna's diameter is 60 for the C

band antenna, and 40 mm for the X-band antenna. The mass is less

than 90 g for the C-band antenna, and less than 20 g for the X-band

antenna. They are both almost all metal antennas (which is a pre

ferred property), with dielectric material only in the interface con

nector. Figure 10 shows the X-band patch-excited cup antennas

that can be used for the telemetry, tracking, and command function,

and Figure 11 shows the radiation patterns . The blue and red

curves in Figure II show the co- and cross-polar radiation patterns ,

IEEE Antennas and Propagation Magazine , Vol. 51, No.4, August2009

respectively. They exhibit a near-hemispherical type of radiation

pattern, and can be used, for example, when a helical type of

antenna is too tall.

4.2. Antennas for High-Speed Downlink of

Payload Data from Modern Small Satellites



After the satellite's stabilization has been achieved, large

quantities of payload data need to be transmitted at a high speed. A

compact high-gain antenn a is thus required. The wide-coverage

antennas discussed above can function as a backup for this high

gain antenna for the case where the satellite loses control of atti

tude. However, the antenna gain of modern small satellites can not

be too high, since a high-precision attitude control and determina

tion system (ACDS) is typically not used in small satellites. A gain

of about 12 dBi or lower is usually required for such antennas ,

depending on the specific mission requirements. Antennas with

higher gain can be used, if one uses an antenna-pointing mecha

nism on a modern small satellite.


Figure 12a shows a photo of the S-band quadrifilar-helix

antenna at SSTL [2]. A quadrifilar-helix antenna consist of four

helices fed with relative phases of 0°, 90°, 180°, and 270° . The

antenna shown operates in a frequency range of 2.025-2.11 GHz

for uplink , or 2.2-2.29 GHz for downlink. Left-hand (or right

hand) circular polarization and very low cross-polar levels can be

achieved with a conical beam. This antenna shapes the gain pattern

to offset the change in path loss, so as to provide a constant power

flux density at the ground station at each pass, i.e., range compen

sation . It has a size of 100 x 100 x 500 mm, and a mass of less than

500 g. It can operate within -20° C to +50° C, is radiation tolerant

to 5 kRad, and qualified to 15 g rms random vibration. It is suitable

for moderate-rate transmission in LEO missions. Figure 12b shows

the gain pattern for a single S-band quadrifilar-helix antenna as a

payload antenna mounted on a satellite. In this case, the antenna

pattern contained considerably fewer peaks and nulls than the

equivalent tracking, telemetry, and command-antenna configura

tion, and the effects of the satellite were not so pronounced.

A possible alternative to helix antennas is represented by the

shorted-annular-patch (SAP) radiators [10]. Shorted rings possess

radiation characteristics similar to those of circular patches, as the

equivalent magnetic-current distribution flowing on the two exter

nal boundaries is identical. However, the shorted-annular-patch

inner border, being shorted, does not radiate, and can be used to

tune the antenna's resonant frequency. The external radius can be

chosen to achieve narrower radiation patterns and higher directiv

ity. These effects are clearly shown in Figure 13, where the antenna

gain is presented for different shorted-annular-patch geometries

and different ground-plane sizes. Simulations were conducted by

taking the antenna's external radius in the range of 34-46 mm, and

adjusting the inner radius to make the patch resonate at a frequency

of 2.425 GHz. As shown, when the outer boundary was enlarged,

the gain increased up to about 11.5 dB. For larger ring radii,

sidelobes appeared, deteriorating the radiation pattern and reducing

the antenna's gain.

47


4644

!:10(

lo(

38 40 42SAP outer radius a [mm)

36

-- Infinite Ground plane

200mm X 200mm

-e- 140mm X 140mm

11.5 - 110mm X 110mm

11 r Gain

I [dBi]

',:'(,'//,.... ......>---__ I

y ,,-9.5 i I I j ;

9 !. f34

An example of this high-gain compact antenna was given in

[11], which proposed a stacked shorted-annular-patch design for

the European Student Earth Orbiter (ESEO) small-satellite mis

sion. It achieved a broadside radiation pattern, with a maximum

gain of 12.1 dB and a size of 110 x 130 x 10Omm, while the massdid not exceed 200 g. It should be noted that the maximum gain

achieved with the ESEO high-capacity antenna was limited by the

physical constrains of that mission. Indeed, when a 2AX2A ground

plane is considered, the maximum antenna gain increases to

14.2 dB. Even further enhancement can be reached when theantenna is placed into a metallic cup.

To support higher-data-rate payloads, the link budget dictates

either higher output power from the spacecraft's transmitters, or

higher antenna gains. The de power is usually a limiting factor onsmall satellites, and high antenna gains are usually selected. Typically, horn antennas or parabolic reflectors are adopted; however,

for LEO satellites, this adds the complication of requiring a track

ing system. Modern Earth-observation micro-satellites are requiredto slew the satellite to image a particular target, while simultane

ously transmitting the resultant data to the ground station. This canplace significant constraints on the antenna and on the pointing

mechanism. These include weight, slew rate, pointing accuracy,

power consumption, thermal stability, and mechanical jitter (high

magnification cameras are very sensitive to repetitive mechanical

resides on the back side of the antenna, and it can be coupled with

the radiating element through slots.

Figure 12a. An S-band quadrifilar-helix antenna at SSTL (2).

Although shorted-annular-patch antennas can be designed tohave a gain considerably higher than other patch radiators, a further

gain increment can be easily achieved by means of a reflectorstacked on the shorted patch, and placed at about a half-wavelength

from the lower patch. As the literature shows, this method is gen

erally valid for all patch antennas. However, in the case of shortedrings, it is very easy to implement, and it results in higher gain val

ues. In fact, the upper radiator can be chosen to be a shorted patchcoaxial to the lower radiator, with the same inner radius. Similarly

to the single shorted-ring case, the stacked patches can thereby be

easily fabricated entirely in metal, using the central short as a supporting element for the whole structure (Figure 14), thus ensuring

mechanical robustness. As a further advantage, it should be considered that for the case of space applications, the inner short offers

a natural path to convey electrostatic discharges (ESD), avoiding

the use of dedicated circuits. In addition to the radiation-patternflexibility, the stacked shorted-ring antenna can be easily designed

for single, dual, or circular polarization, since the feed circuitry

Figure 13. The gain of the shorted-annular-patch antenna as a

function of the outer radius, for four different ground-planesizes. The antenna height was h = 1.5mm, while the dielectric

permittivity was cr = 1.

SAP -

Ground plane _ .

Dielectric -

Feed network

Figure 14. An exploded view of the high-gain shorted-annularpatch antenna (from (11)).

48 IEEE Antennasand Propagation Magazine , Vol. 51, No.4, August 2009


Figure 7a. An analysis model of a typical spacecraft.

Figure 12b. The gain pattern of the antenna in Figure 12a.

"-Band Anlenna , Gain, f = 6.9 GHz

'r-t----r-t- ....--,

150·150

o

; , ; ..

XIlA70 •• RHCP, Gain. f= 8.16 GHz

·15

·20

.50

..... .... . .• • . . ... ... . .

. ; : : .

5 _..

o ; :- ! .

-=lD

......

·10

Figure 11. Patch-excited cup-antenna radiation patterns (blue:co-polarization, red: cross-polarization).

Figure 19. X-band helix radiation patterns (700 degree edge-ofcoverage types) (blue: co-polarization, red: cross-polarization).

IEEE Antennas and Propagation Magazine , Vol. 51, No.4, August 2009 49


Figure 15. An antenna-pointing mechanism with an associated

horn antenna at SSTL.

Figure 16. An S-band patch-excited cup antenna at RUAG.

perturbations). SSTL has recently perfected an X-band mechani

cally steered high-gain hom-antenna mechanism (Figure 15), due

for launch in 2009. The circularly polarized hom has a gain of

15 dBi along boresight, and a 3 dB beamwidth of 27°. The associ

ated antenna-pointing mechanism weighs 2.7 kg, moves ±270° in

azimuth and ±110° in elevation with a pointing accuracy of < 1° ,

and consumes less than 3.2 W.

Figure 16 shows the S-band patch-excited cup antenna,

developed at Saab Space [9]. It consists of three patches , mounted

within a thin aluminum cup with a rim height of about a quarter

wavelength. Two lower patches form a resonant cavity, allowing

broadband or double tuning. The top patch acts as a reflector that

affects the illumination of the aperture, and is used to improve the

aperture efficiency. To achieve circular polarization, the lower

patch is fed in phase quadrature at four points by a stripline net-

50

work. It achieves a maximum again of about 12 dBi. A recent

patch-excited cup antenna development performed at Saab Space is

the update of the antenna in Figure 16, to be used for other mis

sions . It has a radiator tower that is modified compared to the

original design . It is now an all-metal design, and has a new feed

network configuration, an isolated four-point feed design. The

antenna is shown in Figure 17.

RUAG Aerospace Sweden has developed an innovative X

band helical antenna design for isoflux coverage. It is a small,

compact, and lightweight antenna solution, which was developed

to respond to the need for cost-effective antennas for the down

linking of data from LEO satellites. It features an innovative design

of the radiator part, which can be adapted to specific customer

requirements regarding gain, coverage, polarization, and frequency

band . While reducing the size and weight compared to the nor

mally used reflector or bi-cone antennas, the new antenna retains

the favorable characteristics of the traditional helical antenna : large

bandwidth and good RF performance. Currently, one radiator for

60° edge of coverage (EOC) and several antennas for 70° edge of

coverage are available. More than 15 flight antennas have been

delivered, and further antennas are in production. Figure 18 shows

Figure 17. S-band patch-excited cup medium-gain datadownlink antennas at RUAG.

Figure 18. X-band helical antennas at RUAG (70° edge-ofcoverage types).

IEEE Antennas and Propagation Magazine, Vol. 51, No.4, August2009


a waveguide-fed helical antenna, which has few parts, and there

fore low-cost production and stable performance with small prod

uct variations. It features an all-metal design of the radiator part,

which can be adapted to a variety of performance requirements .

This part is combined with a radome and a generic septum polar

izer, creating a modular system. Figure 19 shows the radiation

pattern for a 70° edge-of-coverage antenna, where the blue line is

the co-polarization and the red line is the cross-polarization pat

tern. It operates at X band, achieves a maximum gain of about

5 dBi for a 60° edge-of-coverage antenna, and about 35 dBi for a

70° edge-of-coverage antenna, and weighs less than 400 g.

CubeSats at practically every university have operated in the

UHF through S-band ranges. While sufficient for current CubeSat

missions, future data-intensive missions will require higher fre

quencies to provide greater data-transmission rates. However,

higher frequencies require a larger transmitter power due to the

greater link loss, making it necessary to use higher-power semi

conductor devices. Unfortunately, the RF output power available

from semiconductor devices drops off with a 1/f to 1/f2 fre

quency dependence, making it necessary to employ some form of

power-combining scheme to provide adequate transmitter power.

Although a variety of power combiners based on conventional cir

cuit techniques have been developed, they occupy large amounts of

area, and are inefficient for combining large numbers of devices,

making them impractical for use in a CubeSat. Figure 20 shows a

prototype active antenna developed at the University of Hawaii for

a CubeSat [12], using a novel power-combining scheme packaged

in a compact, low-profile structure that can be mounted on the side

of a cube. Known as a grid oscillator, it consists of an array of

semiconductor devices embedded in a metal grid that serves as a

de-bias distribution circuit, RF-embedding circuit, and radiating

structure . The grid is printed on a dielectric substrate, backed bythe metal CubeSat structure, which serves as a mirror to provide

the feedback necessary for oscillation. The vertical leads of the

grating serve as antennas, and the horizontal leads as de-bias lines.

If properly designed, the bias lines do not affect the high-frequency

performance of the active grid, as the radiated electric field is ver

tically polarized .

When de bias is applied, oscillation is triggered by transients

or noise, and each device oscillates at a different frequency. A non

coherent wave radiates from the grid, reflects off the mirror, and

injection locks the oscillating devices. At the onset of oscillation,

different modes of the cavity compete, as in a laser. The higher

order modes lose most of their power to diffraction, resulting in a

single-frequency, self-locked, coherent oscillation. The output

power from each device is combined in free space, making this

power-combining scheme quite efficient. Unlike typical phased

array antennas, the spacing between devices is only on the order of

a tenth of a free-space wavelength, making it very compact at

microwave frequencies. Because of its built-in redundancy, a grid

oscillator is also tolerant to single-point failures: about 10% of the

transistors can fail with minimal performance degradation.

4.3. Antennas for GPS/GNSS



Surrey pioneered the use of GPS and global navigation satel

lite systems (GNSS) in space. A GPS receiver can provide accurate


Figure 20. A prototype C-band grid oscillator, consisting of 36Agilent ATF-36077 pHEMT transistors, each occupying a

6 x 6 mm unit cell.

Figure 21a. A GPS antenna for the UK DMC satellite at SSTL

[2].

Figure 21b. A GPS patch-excited cup antenna at RUAG.

51


position, velocity, and time for LEO satellites. For this application,the antenna needs to be compact, low profile, able to operate at

GPS frequencies in the Ll (1.575 GHz) and L2 (1.227 GHz) bandswith stable performance, and produce low backward radiationtowards the small satellite body (to minimize the interactions with

the satellite). For more precise measurement, the optimum antenna

location on the satellite must be found, balancing the antenna'scoverage against spacecraft interference and multipath errors.Antenna phase variations must also be reduced.


A medium-gain antenna, shown in Figure 21a, was launched

on the UK-DMC satellite of SSTL for the purpose of collecting

reflected GPS signals in orbit [2]. This satellite has begun to col

lect reflected signals under a variety of sea conditions, and overland and ice. The antenna is a three-element, circularly polarizedmicrostrip-patch array with a gain of 12 dBi [2]. Antenna-design

challenges remain in terms of further reducing antenna size,improving the antenna's efficiency, multi-band (LlIL21L5 band)

operation, constant phase center, multipath mitigation, etc.

Figure 21b shows the patch-excited cup antenna developed at

RUAG Aerospace Sweden. It consists of two patches placed in a

circular cup. To obtain a stable antenna covering two GPS fre

quency bands (Ll, L2), the bottom patch was capacitively fed byfour probes and an isolated feed network. The antenna achieved acoverage out to 80° in zenith angle, and low backward radiation.

The antenna's diameter is 160 mm, and the mass is 345 g.

In [13-14] it was demonstrated how shorted-annular-patchantennas can achieve high-accuracy GPS/GNSS performance with

out compromising the physical constrains. These antennas can

indeed be designed to have reduced lateral and back radiation, with

adequate polarization purity and phase uniformity, in both GPS

bands [15]. This can be accomplished without the employment of

ground-plane extensions of choked rings. As a result, they offerperformance compatible with high-accuracy GNSS applications,but with sizes and weights compatible with small-satellite applica

tions.

To reduce the antenna's size, Surrey also worked with

Sarantel to bring out a space version of Sarantel's Geohelixceramic-loaded quadrifilar-helix antennas. The ceramic loading

leads to a smaller-size quadrifilar-helix antenna, compared to stan

dard quadrifilar-helix antennas. The reduced size of this antennaleads to a low antenna gain, but it is a practical solution for nanosatellites.

4.4. Antennas for Inter-Satellite

Cross Links and Others

One of the challenges in designing a distributed small-satellite network - especially a dynamically reconfigurable network,

consisting of satellites too small to contain an attitude-control system - is in establishing and maintaining a reliable crosslink with

other satellites in the network, without a priori knowledge of theirpositions.

Omnidirectional antennas are the obvious choice for crosslinking satellites that are subject to constant repositioning, but this

52

leaves the network susceptible to eavesdropping by unauthorized

ground stations, as well as by satellites outside the network but still

within range of the constellation. Omnidirectional antennas arealso inefficient, as power is radiated in all directions, not just in thedirection of the receiver. In security-sensitive networks, direct

cross links using dynamically beam-steered directional antennas

can prevent signal interception. However, these systems require

phase shifters or digital-signal-processing algorithms, addinganother layer of complexity to the system and negating the advan

tages of the simple, low-cost nature of small satellites.

For pico-satellite applications, an attractive alternative to

dynamic beam steering is a self-steering retrodirective array, whichpermits secure cross-link communications between satellites mov

ing randomly in space [16]. Retrodirective antennas are able to

sense the direction of an incoming radio transmission and send a

reply in that same direction, without the complexities associatedwith phase shifters in conventional phased arrays, or digital signal

processing in smart antennas. As with any directive antenna, thedirectivity not only improves network security, but also improves

the communication-link efficiency by minimizing power consumption.

Most retrodirective antennas have been implemented using a

conventional heterodyne phase-conjugation technique, requiring a

local oscillator (LO) that is twice the frequency of the interrogatingRF signal. This has the disadvantage of requiring a high-frequency

LO, which is sometimes impractical where de power and cost

budgets place restrictions on the design. Undergraduate students atthe University of Hawaii developed a 10 GHz, circularly polarized,two-dimensional, phase-conjugating array (Figure 22), based onquadruple sub-harmonic mixing, which relaxes the local-oscillatorfrequency requirement [17]. The method uses the fifth-order mixing product, requiring an LO frequency that is half the RF. Antiparallel diodes suppress the second harmonic of the LO, which is at

the same frequency as the RF.

For a network containing multiple satellite nodes, each satel

lite would have both an onboard omnidirectional interrogator andretrodirective transponder. The link is initiated by one satellite'somnidirectional interrogating signal, which is coded for an

intended receiver. That receiver then sends a retrodirective signalback to the interrogator, whereupon it switches to retrodirective

Figure 22. A circularly polarized, cross-shaped, mlcrostrippatch retrodirective array mounted on one face of a l.5DCubeSat. The resonant frequency was 10.5 GHz (from (17)).



Retrodirective Array

with PLLs

Outgoing RF Signal

veoRef

Phase Detector

Incoming Pilot Signal

Down Up

r----------------------------- -- ------------, 0

,

,,,

University of Hawaii students further extended the phase

detect ion concept from [18] to two-d imensional retrodirectivity

[19]. In addition to the power-loss reduction from 1/ R4 to 1/ R

2,

the heterodyne-scanning architecture eliminates the need for indi

vidual phase shifters at each radiating element , and reduces steer

ing control to a single voltage-controlled oscillator (VeO) per

steering dimension. Similar to [18], when the system in [19] is

interrogated, the E-plane phase detector outputs an error voltage

proportional to the E-plane-detected phase difference at its input.

Simultaneously, the H-plane phase detector outputs an error volt

age proportional to the H-plane-phase detected at its input. Each

error voltage is then passed as an input to the control-circuit mod

ule, which contains two independent steering-control circuits: an

LO phase-shifting network, and an IF phase-shifting network,

shown in Figure 25. The control circuit creates phase gradients in

each phase-shifting network by varying the veo tuning voltage,

based on the input phase-detector error voltage. A phase-addition

circuit, shown in Figure 26, is then used to add the E- and H-plane

phase gradients from the LO and IF networks to steer the two-

reducing the efficiency of the system. This is especially important

for a small-satellite application, where available power is already

limited. By decoupling the retrodirective signal from the interro

gating signal, a strong and constant retrodirected power level will

be transmitted back to the source (Figure 23b). This reduces the

loss of the system , with the power of the signal now approx imately

proportional to 1/ R2

•

The design of a retrodirective array capable of maintaining a

constant transmitted power is shown in Figure 24. Unlike the con

ventional Van Atta and heterodyne-based phase-conjugating

designs, the design in [18] used a phase detector to determine the

incoming angle of the interrogating signal. The resultant error volt

age is fed to a phase shifter, which directs the beam of the trans

mitting array back in the direction of the source . The power of the

transmitting signal is determined by the power of the RF source,

and is completely independent of the power from the interrogator.

Interrogator

Signal

InterrogatorSignal

Retrodirective Array

TTTT

TTTT

Interrogato r

Signal

TA Retrodirected

Signal

Figure 23b. The relative power levels, represented by thethickness of the arrows (l.e., a thicker arrow represents astronger signal) of the interrogator and retrodirected signalsfor a retrodirective array where the interrogator and retrodirective signals are decoupled (from (18)).

Figure 23a. The relative power levels, represented by thethickness of the arrows (l.e., a thicker arrow represents astronger signal) of the interrogator and retrodirected signalsfor a conventional retrodirective array.

Figure 24. A retrodirective array using phase detection andshifting (from (18)).

mode and the link is established. The use of coded signals prevents

unauthorized third-party interrogation, and helps in setting up mul

tiple links between nodes .

One of the limitations in many retrodirective array architec

tures is the power dependence of the retrodirected signal on the

interrogating signal. Since the signal must travel a distance R to the

retrodirective array and back, the power level of the signal will be

proportional to approx imately 1/R4 (Figure 23a), significantly

,

Angl e Detecting Arr ay, ,L • I

RF Source

TransmiUer Arr a y

IEEE Antennas and Propagation Magazine , Vol. 51, No.4, August2009 53


IF Out

(2.5 GHz)

Figure 25. A photo of the prototype IF phase-shifting network(from (19)).

IF Ports(2.5 GHz)

Figure 26. A photo of the four-element phase-addition circuit.

The sixteen-element phase-addition circuit is made up of four

of these four-element boards (from [19)).

dimensional heterodyne-scanned array back toward the interroga

tor's direction.

Many other antennas have also been developed, e.g., deploy

able reflectors [20]. Surrey has also worked with European Anten

nas Ltd. to design a circularly-polarized high-gain patch array for

GPS in higher orbits.

5. Conclusion and Future Work

This paper has given an overview of antenna technologies for

modern small satellites . Many antennas for modern small-satellite

applications have been explained and discussed. An introduction to

modern small satellites and their structures has been presented. The

technical challenges of antenna designs for modern small satellites

have also been explained .

The designs of modern small satellites are strictly constrained

in size, mass, and power. Much research work is going on to make

small satellites even smaller, smarter, faster, and cheaper. Recent

examples at Surrey include printed-circuit-board (PCB)-Sat, where

54

the whole satellite is built on a single PCB, as well as Chip-Sat,

where the satellite is built in a single chip [1,21]. Both are being

developed at SSC. Such satellites will be useful for future distrib

uted-satellite space missions, where hundreds or even thousands of

small satellites will be launched simultaneously, and will form a

cooperative network to realize sophisticated functions. There is

also ongoing work related to compact sensors, micro-electro

mechanical systems (MEMS), micro-propulsion systems, gravity

gradient stabilization, a three-axis attitude-control system, and

solar sails, which will make small satellites more capable.

To satisfy the requirements for next-generation modern small

satellites, more work is needed. Examples include active integratedantennas for modern small satellites, compact high-gain antennas,

the integration of antennas with solar panels, low-cost phased-array

antennas, smart antennas, low-cost deployable high-gain antennas

for modern small satellites, and antennas for satellite clusters.

Active antennas can further reduce the size, power consumption,

and cost of RF front-ends [22, 23]. These compact low-cost anten

nas with improved performance will enable future modern small

satellites to become smarter, smaller, and more flexible. Some

interesting antennas for spacecraft can also be found in [24].

6. Acknowledgement

The authors are thankful for the helpful comments from the

reviewers.

7. References

1. Surrey Space Centre home page: http://www.ee.surrey.ac.uk/

sSC/.

2. Surrey Satellite Technology Ltd. home page: http://www.sstl.co.uk.

3. M. N. Sweeting and C. 1. Underwood, "Small-Satellite Engi

neering and Applications," in P. Fortescue et al. (eds.), Spacecraft

Systems Engineering, West Sussex, John Wiley & Sons Ltd., 2003,

Chapter 18.

4. Utah State University Annual Small Satellite Conference Web

page: http://www.smallsat.org/proceedings.

5. S. Gao, M. Brenchley, M. Unwin, C. Underwood, K. Clark, K.

Maynard, L. Boland, and M. N. Sweeting, "Antennas for Small

Satellites," Proceedings of Loughborough Antennas and Propaga

tion Conference, March 2008, UK, pp. 66-69.

6. J. Cutler and G. Hutchins, "OPAL: Smaller, Simpler, and Just

Plain Luckier," Proceedings of 14th Annual AIAAlUSU Confer

ence on Small Satellites, Logan, UT, September 2000.

7. M. Martin, et al., "University Nanosatellite Program," Proceed

ings of IAF Symposium, Redondo Beach, California, USA, April

1999.

8. J. P. Suari, C. Turner and W. Ahlgren, "Development of the

Standard Cube-Sat Deployer and a Cube-Sat Class Pico-Satellite,"

http://cubesat.atl.calpoly.edulmediaIDocuments/Papers/cubesat-pa

per.pdf.



9. J. Zackrisson, "Wide Coverage Antennas," Proceedings of 21st

Annual AIANUSU Conference on Small Satellites, Utah, USA,

August 2007, paper no. SSC07-XIII-7.

10. G. Mazzarella and G. Di Massa, "Shorted Annular Patch

Antenna," Microwave and Optical Technology Letters, 8, March

1995, pp. 222-226.

11. E. Amieri, L. Boccia, G. Amendola, and G. Di Massa, "A

Compact High Gain Antenna for Small Satellite Applications,"

IEEE Transactions on Antennas and Propagation, AP-55, 2, Feb

ruary 2007, pp. 277-282.

12. T. S. Fujishige, A. T. Ohta, M. A. Tamamoto, D. S. Goshi, B.

T. Murakami, 1. M. Akagi, and W. A. Shiroma, "Active antennas

for CubeSat Applications," 16th Annual AIANUtah State Univer

sity Conference on Small Satellites, Logan, UT, August 2002.

13. L. Boccia, G. Amendola, and G. Di Massa, "Performance

Evaluation of Shorted Annular Patch Antennas for High-Precision

GPS Systems," lET Microwaves, Antennas & Propagation, 1, 2,

April 2007, pp. 465-471.

14. L. Basilio, R. L. Chen, J. T. Williams, and D. R. Jackson, "A

New Planar Dual-Band GPS Antenna Designed for Reduced Sus

ceptibility to Low-Angle Multipath," IEEE Transactions on Anten

nas and Propagation, AP-55, 8, August 2007, pp. 2358-2366.

15. L. Boccia, G. Amendola, and G. Di Massa, "A Dual Frequency

Microstrip Patch Antenna for High-Precision GPS Applications,"

IEEE Antennas and Wireless Propagation Letters, 3, 2004, pp.

157-160.

16. B. T. Murakami, M. A. Tamamoto, A. T. Ohta, G. S. Shiroma,

R. Y. Miyamoto, and W. A. Shiroma, "Self-Steering Antenna

Arrays for Distributed Picosatellite Networks," 17th Annual

AIAA/Utah State University Conference on Small Satellites,Logan, UT, August 2003.

17. T. J. Mizuno, J. D. Roque, B. Murakami, L. Yoneshige, G.

Shiroma, R. Miyamoto, and W. A. Shiroma, "Antennas for Dis

tributed Nanosatellite Networks," Proceedings of the IEEE/ACES

International Conference on Wireless Communications and

Applied Computational Electromagnetics, Honolulu, HI, April

2005, pp. 606-609.

18. G. S. Shiroma, R. Y. Miyamoto, and W. A. Shiroma, "A Full

Duplex Dual-Frequency Self-Steering Array Using Phase Detec

tion and Phase Shifting," IEEE Transactions on Microwave Theory

and Techniques, MTT-54, 1, January 2006, pp. 128-134.

19. M. K. Watanabe, R. N. Pang, B. O. Takase, J. M. Akagi, G. S.

Shiroma, and W. A. Shiroma, "A 2-D Phase-Detecting/Heterodyne

Scanning Retrodirective Array," IEEE Transactions on Microwave

Theory and Techniques, MTT-55, 12, December 2007, pp. 2856

2864.

20. R. Barrett, et aI., "Deployable Reflectors for Small Satellites,"

21st Annual AIANUSU Conference on Small Satellites, Utah,USA, August 2007, paper no. SSC07-Xill-4

21. D. Barnhart, T. Vladimirova and M. N. Sweeting, "Very Small

Satellite Design for Distributed Space Missions," Journal of

Spacecraft and Rockets, 44, 6, December 2007, pp. 1294-1299.


22. Y. Qin, S. Gao, and A. Sambell, "Broadband High-Efficiency

Circularly-Polarized Active Antennas and Arrays," IEEE Transac

tions on Microwave Theory and Techniques, MTT-54, 7, July

2006,pp.2910-2916.

23. S. Gao, and P. Gardner, "Integrated AntennaIPower Combiner

for LINC Radio Transmitters," IEEE Transactions on Microwave

Theory and Techniques, MTT-53, 3, March 2005, pp. 1083-1089.

24. W. A. Imbriale (ed.), Spaceborne Antennas for Planetary

Exploration, New York, John Wiley & Sons, 2006.

Introducing the Feature Article Authors

Steven Gao (BSc, MSEE, PhD) was born in Anhui, China.

He is a Senior Lecturer and Head of the Antennas and RF Systems

Group at Surrey Space Centre, University of Surrey, UK. His

research work has led to over 100 technical papers published in

international journals and conferences, and six book chapters. He

has been a TPC member, invited speaker, and technical session

chair of some international conferences in antennas, RF/microwave

circuits, electromagnetics, and satellite communications. His

research interests include satellite antennas, smart antennas, active

integrated antennas, reconfigurable antennas, GPS antennas,

RF/microwave power amplifiers, small satellites (micro-, mini-,

and nano-satellites), EM modeling, and communication systems.

Keith Clark received a BSc degree in EEE in 1984 from the

University of Surrey, and an MSc in RF and Microwave Engi

neering in 1989 from the University of Bradford. Since 1991, he

has worked at Surrey Satellite Technology, Ltd., as a Principal

Engineer, developing a wide variety of RF and microwave subsys

tems for small satellites. His areas of interest are practical small

satellite antennas, high-efficiency power amplifiers, and X-band

transmitters.

Martin Unwin received the BSc degree from Lancaster Uni

versity, UK, and the PhD degree from University of Surrey, UK.

He is Head of the GPS team at Surrey Satellite Technology Ltd.,

responsible for spaceborne GPS receiver design and operation.

Jan Zackrisson received the BS degree in Electrical Engi

neering in 1977. He has also studied master courses in physics,

microwaves, antennas, space technology, economics, and business

administration, between 1982 and 1996. Since 1992, he has been

with RUAG Aerospace Sweden (previously Saab Space), Gothen

burg, Sweden, where his current position is Senior Engineer

responsible for antenna-measurement techniques and for wide-cov

erage antenna products.

Wayne A. Shiroma received the BS degree from the Univer

sity of Hawaii at Manoa in 1986, the MEng degree from Cornell

University, Ithaca, NY, in 1987, and the PhD degree from the Uni

versity of Colorado at Boulder in 1996, all in Electrical Engineer

ing. In 1996, he joined the University of Hawaii at Manoa, where

he is currently an Associate Professor of Electrical Engineering and

Co-Director of the Hawaii Space Flight Laboratory. His research

interests include microwave circuits, antennas, and small satellites.

55


Justin M. Akagi received the as degree in Electrical Engi

neering from the University ofHawaii at Manoa in 2005. He is cur

rently working towards the MSEE at the same university. His

research includes microwave circuits, phased arrays, and small sat

ellites.

Kevin Maynard received an HNC in Electronic Engineering

from Guildford College of Technology in 1990, and an HND inElectronics and Electrical Engineering from Famborough College,

in 1993. Since joining SSTL in 1990, he has worked on RF sys

tems as a Principal Engineer, working on a wide variety of RF sub

systems and antennas for small satellites. He has been involved in

over 30 small satellites and numerous technology-transfer pro

grams. His areas of interest are implementation and simulations of

communication systems, components, and antennas.

Luigi Boccia received the Information Technology Engineering degree from the University of Calabria, Rende, Italy, and the

PhD degree from the University "Mediterranea" of Reggio

Calabria, Italy, in 2000 and 2003, respectively. He is Assistant Pro

fessor in the Dipartimento di Elettronica, Informatica e Sistemis

tica of the University of Calabria. His research interests include

microstrip antennas and microwave circuits.

Giandomenico Amendola received the Electrical Engineering degree from the University of Calabria, Rende, Italy. He is currently with the University of Calabria as an Associate Professor.

His main research interests are in the areas of microstrip antennas,

conformal antennas, microwave and millimeter-wave circuits.

Giuseppe Di Massa received the Laurea degree as Doctor in

Electronic Engineering from the University of Naples. He is a full

Professor at the University of Calabria. His main research interests

56

are focused on applied computational electromagnetic, microstrip

antennas, microwave integrated circuits, Gaussian-beam solutions,

millimeter-wave antennas, and near-field measurements.

Craig Ian Underwood (BSc, PGCE, PhD, MIEEE, FBIS) is

a Reader in Spacecraft Engineering and also Deputy Director of

Surrey Space Centre, University of Surrey, UK. He heads the

Planetary Environments Group within the Surrey Space Centre. His

current research activities include the development of miniaturized

instrumentation for ionizing-radiation detection, UV-VIS-NIR and

thermal-IR satellite remote sensing, micro-satellite-based bistatic

synthetic-aperture radar (SAR) imaging, and nano-/pico-satellite

technologies.

Prof. Sir Martin Sweeting (OBE, FRS) is the Executive

Chairman of Surrey Satellite Technology Ltd. (SSTL) and Direc

tor of Surrey Space Centre, University of Surrey, UK. Sir Martinpioneered the concept of rapid-response, low-cost, and highly

capable small satellites utilizing modem terrestrial commercial-off

the-shelf devices to "change the economics of space." In 1985, he

formed a spin-off university company (SSTL), which has designed,

built, launched, and operates in orbit a total of 32 nano-, micro-,

and mini-satellites, including the international Disaster Monitoring

Constellation, and the GIOVE-A Galileo satellite for ESA. He is

also Director of the Surrey Space Centre, leading a team of 60 fac

ulty and doctoral researchers investigating advanced small-satelliteconcepts and techniques. He is a Fellow of the Royal Society and a

Fellow of the Royal Academy of Engineering. In 1995, he was

awarded an OBE in HM Queen's Birthday Honours, and was

knighted by HM Queen in the 2002 New Year Honours, for ser

vices to the small-satellite industry. He was awarded the Royal

Institute of Navigation Gold Medal in recognition of the successful

GIOVE-A mission for the European Galileo system, and featured

in the UK's "Top Ten Great Britons." @)

IEEE Antennas and Propagation MagaZine, Vol. 51, No.4, August 2009
