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EFFECTS OF PARASITIC PATCH SIZES UN MULTI-LA ELECTRUMAGNETICALLY COUPLED PATCH ANTENNA

R. 4. Lee* NASA Lewis Research Center, Cleveland, OH 44

ER

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K. F. Lee Department o t Electrical Engineering

The University of Toledo, Toledo, OH 43606

INTRODUCTION

Multi-layer electromagnetically coupled patch (EMCP) antennas have been studied extensively for broadband applications. For a two-layer EMCP antenna consisting of a parasitic patch and a fed patch of different sizes, significant increase in impedance bandwidth has been reported 11,21. In a recent study of the same antenna with identical patches, it was found that in addition to the large bandwidth region which occurs when the separation between the antenna layers is less than 0.15h, there exist also a high-gain region with separation exceeding 0 . 3 A C31. The broadband region, with closely spaced parasitic patch, behaves like coupled multiple tuned resonant circuits, while the high-gain region, characterized by large separation and narrow bandwidth, is reminiscent of a Yagi antenna. 111

this paper, the effects of parasitic patch size 011

two-layer and three-layer antennas are examined. Results for the resonant frequency, resonant input impedance and bandwidth for the broadband and high-gain regions are presented.

EXPERIMENTAL RESULTS

The geometry of the rectangular patch antenna and the two-layer EMCP antenna are shown in Fig. 1. The rectan- gular patch of dimensions a=1.5 cm and b=1.0 cm was fabricated on a Cuf I o n substrate with E r = 2 . 1 7 . The upper patch is parasitic and the lower patch is fed with a coaxial probe at x/a=0.75 and y/b=0.25. In the experi- ment, the dimensions of the fed patch was fixed at a=1.5 cm and b=1.0 cm, while dimensions a and b of the parasitic patch were reduced in steps of 0.5 cm. A total of nine sizes of the parasitic patch were tested with the largest being 1.55 cm x 1.05 cm and the small- est being 1.15 cm x 0.6 cm. Teflon spacers of 0.0254 cm and 0.15 cm were inserted between antenna layers f o r operating in the broadband and high-gain regions re- spectively. For simplicity, the three-layer EMCP anten- na has identical parasitic patches which are placed at

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equal spacings over. a fed patch. T h e effects oi reduc- ing the size of the parasitic patch relative t o the fed patch on the resonant frequency, resonant input imped- ance and bandwidth were measured using a HP8510 auto- matic netwurk analyzer. The results for the two-layer EMCP antenna are shown in figures 2-4, and those for the three-layer are shown in figures 5-7. It is seen that reductions i n t h e dimensions a and b of the para- sitic patch result in the following changes:

1. The resonant frequency of the two-layer EMCP antenna increases S I ightly in both the broadband and high-gain regions when the size difference between the fed and parasitic patches is more than f0.5 cm. For size dif- ference less than i0.5 em, the resonant frequency in the broadband region exhibits large variation ancl is minimum for parasitic and fed patches of identical size.

2. The resonant input resistance of the two-layer EMCP antenna increases in the broadband region but decreases i n Lhe high gain region. In each case, there is a certain size of the parasitic patch which yields a value of about 50 ohms.

3 . The bandwidth of the two-layer EMCP antenna in- creases slightly in the high-gain region, but decreases in the broadband region. For size variation of f0.5 cm or less, the bandwidth region displays resonant charac- teristics with a maximum bandwidth of over 9%. The iniaximuro bandwidth occurs where the resonant frequency is minimum.

4. The results fur the three-layer EMCP antenna exhib- its similar characteristics. In the broadband region, the rnaxiinum bandwidth is over 15% when the size of the parasitic patch relative to the fed patch is 0.5 cm or less. I n the high-gain region, the bandwidth is about 0.85% f o r identical patches, and is increased to 2.8% when a aild b of the parasitic patch are both reduced by 0.35 cm.

CONCLUSION

It is found experimentally that reducing the size of the parasitic patch can significantly change the reso- nant frequency, resonant input impedance and bandwidth uf the two-layer and the three-layer EMCP antennas. For ailtennas operating in the broadband region, the band- width is maximum when the parasitic and the fed patches are approximately equal in size. For operating in the high-gain region, the bandwidth is maximum when a and b of the parasitic patch are both reduced by 0.35 cm.

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REFERENCES:

1. G. Dubost, J. Rocquencourt, G. Bonnet, ‘Influence of Director Size Upon A Microstrip Patch Bandwidth’. 1987 leee AP/S International Symposium Digest, pp940-943.

2. R. T. Cock, C. G. Christodoulou,’Design of A Two- Layer, Capacitively Coupled Microstrip Patch Antenna Element For Broadband Application’. 1987 IEEE A P / S International Symposium Digest, pp936-939.

3. R. Q. Lee, K. F. Lee, J. Bobinchak,’Characteristics of A Two-Layer Electromagnetically Coupled Rectangular Patch Antenna’,Electronics Letters, V o 1 . 2 3 , - N o . 2 0 , 1987, pp1070-1073.

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--- Iromdbmd Region I Uigh-Gain legion

Pig. 4 Bandwidth .B a function of the reductions Of dimennions of the par.sltic patch f o r P tvo-layer W P antenna. tl-tpO.OZ54cm

d

~ i m s i 0 ~ 1 Change* in A and B (I)

Fig. 5 Fiesonant frequency as a function of the reduction. i n dimensions of the p a r a s i t i c patch f o r a three-layer WEP .ntenM.

e *-----

- Brodbmd Region

- Uigh-Gain Begion

9 0 9 . 5 -1.0 -1.5 -2.0 -1.5 -3.0 -1.5

g Im c

0

~ i m f i i o n a l Changes in A and B (d

Pig. 6 Resomaor input resistance a8 a function of the reductions of the paraa l t ic patch fmr a three-layer WEP antenna.

Broadband Region

- Uigh-hin Begion

I '0.0 4 . 5 -1.0 -1.5 -2.0 -2.5 -3.0 -,.,

dimensions

~ i r n s i o n d Changes i n A and B (I)

/ \, I- Broadband Region I \ - Uigh-C.in Bepion

F i g . 7 Bandwidth 8s a function of the reduCtioM io d h l u i o n . of the paramitie patch for a three-layer BlcP ante-.

*. '- 0 ' 0.0 4 . 5 -1.0 -1.5 -2.0 -2.5 -3.0

D i r n s i o n n l Change. i n A and B (d

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