A Planar Reconfigurable Yagi-Uda Antenna With End-fire Beam Scan

7/18/2019 A Planar Reconfigurable Yagi-Uda Antenna With End-fire Beam Scan

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A Planar Reconfigurable Yagi-Uda Antenna

with End-Fire Beam Scan

Huan-Chu Huang1, 3

, and Powen Hsu*2

1Graduate Institute of Communication Engineering and

2 Department of Electrical Engineering

National Taiwan University, Taipei 10617, Taiwan 3 HTC Corporation, Taoyuan 33068, Taiwan

4 Tel: +886-2-33663654, Fax: +886-2-23651744 E-mail: [email protected]

Abstract — A novel planar reconfigurable antenna on a thindielectric substrate based on the Yagi-Uda design rationale isproposed. This design not only can provide the end-fire beamscan with high directivities (at least 7.6 dBi) over a 60° coveragebut also can operate at a fixed frequency without frequency shiftwhen beam scans. The efficiencies of the antenna in all scanningscenarios are better than 78.5% or −1 dBi in terms of the 3D

average gain. Index Terms — Reconfigurable antennas, planar antennas,

Yagi-Uda antenna, end-fire, beam scan.

I. I NTRODUCTION

Due to the increasing demand for portable devices with

GPS functions, the embedded GPS antennas have gained

more and more attractiveness. For better communication

with GPS satellites, the radiation patterns of the embedded

GPS antennas should direct to the sky [1]-[2]. Because of the

complex environment and weak GPS signal, reconfigurable

patterns with high directivities from the embedded GPS

antennas can enhance the GPS communication qualities.

Antennas with reconfigurable patterns in the broadside have

been well studied [3]-[4]; however, the planar antennas with

end-fire reconfigurable patterns will be more suitable to the

portable devices because of low profile and better

conformability [5]. A new planar reconfigurable Yagi-Uda

antenna with end-fire beam scan is hence designed especially

for the GPS functions in mobile devices, such as smartphones,

GPS navigators, Notebooks, or Ultra-Mobile PCs (UMPCs).

In addition, a WLAN access point or a smart antenna system

(SAS) with better scanning resolution can also be attained by

adequately placing the antennas in a special arrangement,

such as a triangle, a square, a pentagon, and so on.

II. PRINCIPLES

To achieve a highly directive pattern scanning in the end-

fire direction instead of the broadside one, a Yagi-Uda design

is used. In Fig. 1, this planar antenna consists of a driven

dipole, a reflector, a director, two floating arms, and six

switches. Besides, a phase shifter is designed to maintain the

target frequency workable without the significant return loss

degradation due to the frequency shift when the beam scans.

scans.return loss degradation because of the frequency shift

wh

(a) Top metal layer

(b) Bottom metal layer

(c) Tilted view (assuming the dielectric substrate is transparent)

Fig. 1. Geometry of the proposed antenna.

x

y

L9

W16

W12

W10 L6

L8

L5 SW2

W15 L8

W14

W11

W13

W9

z

yx

Top-layer

side director

Bottom-layer

side director

Bottom-layer

reflector

Top-layer

reflector

Front director

Driven

dipole

Phase shifter Port

Via

x

y

L4

L2

W4

L1

L3

W2

SW5

SW6

SW3

SW4

SW1W3

W1

W8

W6 W5

W7

978-1-4244-2802-1/09/$25.00 ©2009 IEEE1914



In this design, the truncated ground on the bottom metal

layer and the two long strips on the top metal layers are

connected through the vias with 0.4 mm in radius, which

function as the role of the reflector behind the driven dipole.

Besides the purpose of electrical connection between top and

bottom layers, the vias can also enhance the reflection due to

the metal properties and thus improve the directivity and the

front-to-back ratio (F/B). Meanwhile, the two floating arms

located beside the front director as shown in Fig. 1 act as two

additional side directors which will lead to beam scanning as

long as the statuses of the two switches, SW1 and SW2, are

skillfully controlled. Due to the preliminary study, the on

status of a switch is simulated by a shorted metal path, while

the off status is done by an open one.

To make sure the ability to keep the same target operation

frequency, the switches in the phase shifter should beactivated according to the statuses of SW1 and SW2. In

addition, SW3 and SW4 are designed to operate

synchronously, so as SW5 and SW6, because only one

feeding path will be activated at one time. In other words,

both SW3 and SW4 will be turned off as long as SW1 and

SW2 are turned on together. Otherwise, SW5 and SW6 will

be cut off to allow the fed signal through the SW3 and SW4.

Additionally, to achieve qualified return losses (|S11| ≦−10

dB) when beam scans in different switching scenarios, two

notches on the bottom metal layer are made to enable a better

impedance match.

When the switches SW1 and SW2 are both off, that is, thescenario of three isolated and floating directors in front of the

driven dipole, the main beam will direct to the end-fire

direction on the plane of θ= 90°. This phenomenon roots

from the cancellation of two vector dragging forces from the

two side directors, and consequently the net directing effect

will lead the main beam to radiate in the end-fire direction.

However, when one of SW1 and SW2 is turned on, the

corresponding isolated director, in other words, one of the

side directors, will connect with the front director and hence

form a long metal strip. This long metal strip actually

behaves more like another reflector instead of a director in

addition to the original reflector. Therefore, the newly

formed reflector will retard the propagation of radiated

energy, so the main beam will be guided by the remaining

isolated short director and the beam veers.

Moreover, when both of the two mentioned switches, SW1

and SW2, are turned on, that is, the scenario of a single

longer metal strip existing before the driven dipole, a new

longer reflector consequently forms. In such situation,

relatively more energy as compared with the previously said

scenarios will be retarded by this new and the original

reflectors and the main beam will be split into two ones and

squeezed toward the directions of θ= 0° and θ= 180°. As a

result, the directivities in these two mentioned orientations

will be better than those of the former analyzed cases.

III. SIMULATION R ESULTS

Simulation of the proposed design is performed by the

simulator Ansoft HFSS . The substrate used is FR4 with

relative dielectric constant of 4.4, loss tangent of 0.02, and

thickness of 0.8 mm. Besides, the metal’s conductivity is set

at 5.8×107 S/m. The target designed operation frequency is

the GPS’s frequency, 1575 MHz. Furthermore, based on Fig.

1, the dimensions of this designed geometry are clearly listed

in Table I.

In Figs. 1 (a) and 1(b), the white part is the FR4 dielectric

substrate. The grayish areas represent the top metal layer, andthe charcoal gray ones stand for the bottom metal layer.

Furthermore, the tilted view of the structure is shown in Fig.

1(c), in which for clearer and more complete sight of the

whole metal layout, the FR4 dielectric substrate is set to be

transparent.

For different switching schemes, the 2D and 3D directivity

patterns are correspondingly shown in Fig. 2 to Fig. 5. The

antenna characteristics, such as the return loss (or |S11|),

bandwidth, main beam angle, directivity, front-to-back ratio,

and efficiency are listed in Table II.

TABLE I

A NTENNA’S DIMENSIONS

Structure Symbol Value (mm) L5 33.0

L1 33.0 W9 3.0

W1 3.0

Bottom-Layer

Front Director

W10 24.9

Top-Layer

Front Director

W2 24.9 L6 65.0

L2 65.0 W11 3.0

W3 3.0

Bottom-Layer

Side Director

W12 41.3

Top-Layer

Side Director

W4 41.3 L7 38.6

L3 38.6 W13 3.0

W5 26.0

Bottom-Layer

Driven Dipole

W14 21.4

W6 3.0 L8 3.5

Top-Layer

Driven Dipole

W7 3.0 L9 236.0

Top-Layer L4 113.5

Bottom-Layer

Reflector

W15 5.0

Reflector W8 5.0 W16 55.0

1915



From Table II, the maximum directivity of 8.6 dBi occurs

in the case of three isolated directors, i.e., both SW1 and

SW2 are turned off. Moreover, beam scan angles can reach

±30° in the end-fire direction with high directivities (at least

7.6 dBi) and acceptable return losses (|S11| ≦−10 dB). The

efficiencies in different scenarios are better than 78.5%, i.e.,

−1 dB in terms of the 3D average gain. In addition, the F/B

of the design is defined by the ratio of the directivity of the

direction of the maximum radiation to that of the direction of

the maximum lobe in the range of ±60° from the opposite

direction [6]. Moreover, when SW1 and SW2 are turned on

at the same time, from Fig. 5 (c), stronger powers are directed

to θ= 0° and θ= 180° and hence can enable the better

transmitting and receiving quality in the broadside direction

compared with previous three cases. In other words, although

this scenario cannot provide high directivity, it can offer a

broader coverage shown in Fig. 5 (d).

TABLE II

A NTENNA’S PERFORMANCE

SW1

Status

SW2

Status

|S11| @ 1575 MHz

Bandwidth

(|S11|≦ -10 dB)

Main Beam Angle Directivity F/B Efficiency

off off -15.7 dB 80 MHz θ= 90°, φ= 90° 8.6 dBi 13.5 dB 79.8%

off on -12.9 dB 105 MHz θ= 90°, φ= 60° 7.6 dBi 10.8 dB 84.1%

on off -24.9 dB 85 MHz θ= 90°, φ= 120° 7.6 dBi 10.3 dB 80.5%

on on -10.2 dB 65 MHz θ= 0° & θ= 180° 3.7 dBi 1.4 dB 78.7%

Fig. 3. Directivity patterns at 1575MHz when SW1 is off and SW2 is on.

Fig. 2. Directivity patterns at 1575MHz when SW1 is off and SW2 is off.

(b) θ= 90° (a) 3D pattern (d) φ= 90°(c) φ= 0°

(a) 3D pattern (c) φ= 0° (d) φ= 90°(b) θ= 90°

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IV. CONCLUSION

The proposed novel planar reconfigurable Yagi-Uda

antenna with high directivities when beam scans can achieve

more scan angles or finer angular resolutions by employing

more side directors. Besides, the size of the antenna can be

further reduced by clever transformation of the arms of the

driven dipole, such as the meander type. Furthermore, to

broaden the scanning coverage, the shape of the ends of the

driven arms can be tilted or curved. Last, by employing more

such proposed antennas in an appropriate arrangement, asimple smart antenna system (SAS) can be attained.

ACKNOWLEDGEMENT

The work was support by the National Science Council,

Taiwan, under Contract NSC 97-2221-E-002-061-MY3.

R EFERENCES

[1] M. Sanad, and N. Hassan, “Mobile Cellular/ GPS/ Satellite

Antennas with Both Single-Band and Dual-Band FeedPoints,”in Proc. IEEE Antennas & Propag. Society Int. Symp.,Jul. 2000, vol. 1, pp. 298-301.

[2] K. Yegin, “AMPS/ PCS/ GPS Active Antenna for EmergencyCall Systems,” IEEE Antennas & Wireless Propag. Lett., vol.6, pp. 255-258, 2007.

[3] S. Zhang, G. H. Huff, J. Feng, and J. T. Bernhard, “A PatternReconfigurable Microstrip Parasitic Array,” IEEE Trans. Antennas & Propag., vol. 52, no. 10, pp. 2773-2776, Oct. 2004.

[4] M. J. Slater, H. K. Pan, and J. T. Bernhard, “PreliminaryResults in the Development of a Compound ReconfigurableAntenna,” in Proc. IEEE Antennas & Propag. Society Int.Symp., Jul. 2008, pp. 1-4.

[5] G. Yao, Z. Xue, and W. Li, and Z. Liu, “Multi-Feed Comparedwith Single-Feed End-Fire Antenna,” in Proc. IEEE Antennas, Propag. & EM Theory Int. Symp., Nov. 2008, pp. 240-243,.

[6] N. Honma, T. Seki, K. Nishikawa, K. Tsunekawa, and K.Sawaya, “Compact Six-Sector Antenna Employing ThreeIntersecting Dual-Beam Microstrip Yagi-Uda Arrays withCommon Director,” IEEE Trans. Antennas & Propag., vol. 54,no. 11, pp. 3055-3062, Nov. 2006.

Fig. 4. Directivity patterns at 1575MHz when SW1 is on and SW2 is off.

Fig. 5. Directivity patterns at 1575MHz when SW1 is on and SW2 is on.

(c) φ= 0° (d) φ= 90°(a) 3D pattern (b) θ= 90°

(d) φ= 90°(a) 3D pattern (b) θ= 90° (c) φ= 0°

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A Planar Reconfigurable Yagi-Uda Antenna With End-fire Beam Scan