AWR Connected™

Application Note

INTRODUCTIONAutomated synthesis of microwave devices has been gaining in popularity in CAE

applications over the past decade. Antenna Magus now brings this capability to the

fi eld of antenna design. Antenna Magus provides a structured catalog of antennas

(monitor image below) with concise documentation, robust design algorithms, and

export models. The documentation is researched, structured, referenced, and

maintained to ensure that documentation on each antenna is well suited to the task at

hand. The design algorithms produce working parameter sets based on user-defi ned

objectives almost instantly. Antennas designed in Antenna Magus can be exported as

models to AWR’s Microwave Offi ce™/AXIEM® software for analysis and integration

with circuits and other system components. All models are fully parametric and can be

optimized together with other project components. This truly integrates the design of

the antenna into the overall design of the device and the system.

A DESIGN FLOW FOR ANTENNA SYNTHESISThe advantages of having access to information as well as various automated design

algorithms and export models can be enormous, enabling the engineer to quickly

evaluate different antenna topologies and choose an appropriate topology for the

task at hand. This application note shows how Antenna Magus can be used to explore

various antenna options during the early stages of the design and how specifi c designs

can be exported from Antenna Magus and integrated into Microwave Offi ce/AXIEM.

Design Flow for Base Station Antenna

The “Find” view within Antenna Magus software expedites antenna selection.

The “Find” view within Antenna Magus software expedites antenna selection.

EXAMPLE 1: EARLY ANTENNA

EXPLORATION AND DESIGNConsider for purposes of this example a

WAN base station antenna. The objective

is to ensure adequate signal coverage for

several homes in an area using a single

base station. Design engineers working

without Antenna Magus would typically

start by considering a selection of antenna

topologies with which they are familiar and

deciding if one of them would be a sensible

choice for the design at hand. With

Antenna Magus, engineers can search

for and explore a variety of different

options, reading about and comparing

them effi ciently, including antennas that

they have never seen before. Antenna

Magus also includes a toolbox of utilities,

like a free space path loss calculator

(Friis equation), to aid in deriving antenna

requirements from system specifi cations. System and antenna requirements such as

operating frequency, gain, bandwidth, impedance, required form factor, and cost form

the specifi cations that are used together with Antenna Magus to select an appropriate

antenna topology.

The calculation (Figure 1) in this example shows that if -60dBm power is required

from a 16dBi receive antenna at a 1km distance from a 5mW transmitter, then a

transmit antenna with a gain of 18dBi in the directions of required coverage will be

needed. In order to provide the required coverage, the pattern shape of the transmit

antenna is distinctive – a high gain fan-shaped beam would be ideal. The database

can be prioritized for suitable topologies using the keywords “fan beam” and “high

gain” (defi ned as antennas with gain

typically above 15dBi). This instantly

provides six topology options. As shown

in Figure 2, a summary of performance

information for four of the six probable

antennas is shown. Based on data from

the quick-summary information page, the

“linear resonant waveguide slot array”

and “resonant series-fed rectangular

microstrip patch array” antennas could

be candidates for further investigation,

as they appear to provide suffi cient gain

and the correct pattern shape.

Using the Antenna Magus Information

Browser, a side-by-side comparison of

these two antennas can be obtained

(Figure 3). The information in the

comparison highlights the advantages,

Figure 1: Information panel.

Figure 2: Select subset of topologies.

Figure 3: Two possible antenna topologies.

Select subset of topologies.

Figure 4: Performance data.

Figure 5: Capacitive disc-fed patch.

disadvantages, and capabilities of the topologies, helping the user select the best option.

In order to gain even deeper insight into the antennas, designs can be performed with

the click of a button for specifi c performance objectives for each of the antennas and

the specifi c physical dimensions and performances can be compared. This is illustrated

by the screenshot of the design of the linear resonant waveguide slot array (Figure 4).

The next step in the investigation and design process is to then export the model into

Microwave Offi ce/AXIEM for further analysis and optimization.

EXAMPLE 2: DESIGN AND EXPORTING OF AN ANTENNAOften a design engineer uncovers that the initial design provides insuffi cient

performance bandwidth. Usually the solution to this problem is to then construct

a larger structure such that it resonates over the entire band. But when additional

constraints like beam uniformity, size, and manufacturing costs are added, the

challenge becomes more perplexing. In this example, Antenna Magus is again used

to address the design challenge. The specifi cation now requires a planar antenna

with a gain of 6dBi that operates between 2.4GHz and 2.6GHz. Generally speaking,

pin-fed patch antennas have narrow bandwidth and would not be able to achieve this

specifi cation. Yet when searching through the Antenna Magus database for a

moderate bandwidth patch antenna, some EM-coupled feed options are suggested.

One such option is the “capacitive disc-fed rectangular patch antenna” (Figure 5).

In this antenna’s information document, the feed-disc is described to be capacitively

coupled to the patch along a radiating edge, effectively adding a capacitive component

to the input impedance and cancelling out the inductance of the feed-pin. This allows

Figure 6: The results for a patch designed on a 1.5mm FR4 for the top substrate and 6mm (—) and 8mm (—) air for the bottom substrate.

the use of thicker substrates (typically two layers), which in turn lowers the effective

dielectric constant, thus increasing the bandwidth of the patch antenna. It should be

noted that designing such an antenna without Antenna Magus is not a trivial task, as the

effective dielectric constant of a two-layer dielectric needs to be calculated and fi nding

the correct feed spacing for a good match will essentially be an optimization problem.

With Antenna Magus, the user is able to specify the bottom substrate height and all the

top substrate parameters, and the antenna can be designed within a few seconds.

The performance of a design can easily be estimated and the results from different

designs can be compared on the same graph. Figure 6 shows the estimated

performance for two different design cases where the top substrate properties were

kept constant, while the required height of the bottom air substrate was increased

from 6mm to 10mm. The refl ection coeffi cient graph clearly shows how the bandwidth

increases with the bottom substrate thickness. At this point

engineers can be confi dent that the antenna will operate within

specifi cation and that the design is ready to be exported to the

AWR Design Environment™. The exported model (Figure 7)

contains all the parameter values within the EM schematic.

The mesh settings are defi ned to give

accurate results in a reasonable time.

Certain general graphs and measure-

ments, such as S11 vs. frequency, gain

vs. frequency, etc., are predefi ned. The

project is therefore ready to run and all

parameters are available if changes are

necessary. Because all parameters are

defi ned in Microwave Offi ce/AXIEM, the

feed spacing, for instance, can be directly

edited in the AWR Design Environment

model defi nition to try and achieve a

higher input resistance.

CONCLUSIONAntenna Magus is ideal for quickly finding a first order design, assessing its

performance and easily exporting parameterized models to Microwave Office/

AXIEM, where parameters can be edited and simulated to find the best possible

solution for a wide range of problems.

Figure 7: 3D EM view and S11 results in AWR for the exported model.

Copyright © 2012 AWR Corporation. All rights reserved. AWR and AXIEM are registered trademarks and the AWR logo, AWR Connected, Microwave Offi ce and AWR Design Environment are trademarks of AWR Corporation. Other product and company names listed are trademarks or trade names of their respective companies. AN-AM-2012.11.26

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