bandwidth and gain enhancement of proximity coupled...

The 7th National Radar Seminar and The 2ndInternational Conference on Radar, Antenna, Microwave, Electronics and Telecommunications (ICRAMET)

Surabaya – Indonesia | 27 – 28 March 2013

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Bandwidth and Gain Enhancement Of Proximity Coupled Microstrip Antenna Using Side Parasitic Patch

Taufal Hidayat, Fitri Yuli Zulkifli, Basari, Eko Tjipto Rahardjo

Antenna Propagation and Microwave Research Group (AMRG) Department of Electrical Engineering, Faculty of Engineering, Universitas Indonesia

Kampus Baru UI Depok, Indonesia Tel: 021-7270078, Fax: 021-7270077

Email: [email protected], [email protected], [email protected], [email protected]

Abstract—In this paper, a single element proximity coupled rectangular patch antenna is designed for future radar application, where high gain and wide bandwidth is required. A proximity coupled fed antenna is used to enhance the antenna’s gain and bandwidth. The gain of the single patch antenna is 4.22 dBi. By adding side parasitic patch, the bandwidth of the antenna can be improved up to 375%. The antenna works from 2.8 to 3.1 GHz this band is used for air surveillance radar. Moreover The gain of the side parasitic patch antenna is 5,57 dBi

Keywords—Proximity coupled, microstrip antenna, bandwidth enhancement, high gain, parasitic side patch

I. INTRODUCTION Some applications in telecommunication need high gain

antenna for their system, such us for radar application. Many high gain radar applications have relied upon parabolic reflectors. But these antennas have drawbacks especially for its bulky and heavy weight. For low profile antenna, to mitigate the disadvantages of parabolic reflector antenna, the microstrip array antenna can be used.

However, the microstrip antenna has also several drawbacks, especially the ability to achieve high gain with wide bandwidth. To solve these drawbacks, the first step is to characterize the single element to achieved wide bandwith and high gain antenna. Some techniques can be used to achieve high gain antenna. Some paper have been proposed to enhanced bandwidth and gain of a single element antenna, one of that is by using aperture coupled patch with hour glass slot [1]. But these methods do not achieve optimum performance for bandwidth and gain of single element.

There are numerous and well-known methods to increase the bandwidth of antennas, such as increase of the substrate thickness [2], the use of a low dielectric substrate [2], the use of various impedance-matching and feeding techniques [3], the use of multiple resonators [4]–[8], and the use of slot antenna geometry [9]. However, the bandwidth and the size of an antenna are generally mutually conflicting properties, that is, improvement of one of the characteristics normally results in degradation of the other.

Some methode can be used to enhance the bandwith of the antenna, one of that is by using parasitic patch [10], Some

papers have discussed about these methods, such as direct parasitic [11], indirect coupled parasitic [12], but they are of only implemented for direct feeding technique. In this paper a proximity coupled microstrip antenna using side parasitic patch is designed to enhance bandwidth and antenna gain.

II. PROXIMITY COUPLED MICROSTRIP ANTENNA There are several feeding techniques used for microstrip

single antenna which is shown in Fig 1. The shaded area refers to the copper sheet and the white area is the dielectric material of the substrate.

(a) (b)

(c) (d) Figure 1. Feeding techniques in microstrip antenna : (a) probe feed (b)

microtrip line feed (c) aperture coupled feed (d) proximity coupled feed

Among all of these techniques, proximity coupled has the best performance in term of wider bandwidth and higher antenna gain. The performance comparison can be shown in Table 1.



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TABLE 1. PERFORMANCE COMPARISON OF SEVERAL FEEDING TECHNIQUES

Performance Feeding technique

probe feed

microstrip line

aperture coupled

proximity coupled

frequency (GHz)

2.971 - 3.045

2.962 - 3.011 2.973 - 3.036 2.937 - 3.038

bandwidth (MHz) 74 49 63 101

directivity (dBi) - 6.274 6.339 6.378

gain (dB) - 2.884 3.53 3.921 azimuth HPBW (degree)

- 95.3 95.7 92.3

elevasi HPBW (degree) - 94.4 91.8 94.9

side lobe level (dB) - -14.3 -13.9 -14.6

Figure 1d shows the geometry of the basic proximity coupled patch antenna. The Antenna consists of two layer substrate. The radiating microstrip patch element is etched on top of the first layer substrate, while the microstrip feed line is etched on the top of the second layer substrate with the ground plane on the bottom of the second layer substrate. The thickness and dielectric constants of these two substrates may thus be chosen independently to optimize the distinct electrical function of radiation and circuity. The proximity coupled microstrip antenna is influenced by many variation of parameters such as microstrip patch length, microstip patch width, feed line width, etc.

The size of the patch can be calculated by using equation (1) to (4) as follows [5]:

푊푝 =

(1)

퐿푝 = − 2∇퐿 (2)

∇퐿 = ℎ × 0.412. .

. (3)

휀 = (4)

where, λ0 is free space wavelength and c is speed light in free space 3 x 108 m/s. Wp and Lp correspond to the width and the length of the patch.

III. ANTENNA DESIGN Before designing a side parasitic patch, a single rectangular

patch element antenna is designed to resonate at 3 GHz using Fr-4 substrate (εr = 4.6 and tan δ = 0.0009) with height 1.6 mm. Both of the patch and feed substrate consist of the same material and size, which is separated by a ground plane made from copper.

The software CST Microwave Studio has been used to model the single patch antenna with proper boundary condition. Using equation (1) to (4), the calculation result yields Lp by 15 mm and Wp by 23 mm.

The structure of the antenna is depicted in Fig. 3.

Figure 3. Design of single patch antenna with proximity coupled feed

Based on the structure and performance of the single patch

antenna design, to broaden the bandwidth, therefore the parasitic patch is added in the right and left side of the main patch. The structure of the side parasitic patch antenna is shown in Fig 4.

Figure 4. design of side parasitic patch antenna with proximity coupled

feed

The dimension of the single patch antenna and the side parasitic patch antenna is shown in Table 2.



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TABLE 2. DIMENSION OF ANTENNA STRUCTURE

label dimension

Single patch (mm)

Parasitic patch (mm)

Lsb 75 75

Wsb 75 75

Lp 15 8

Wp 23 24.2

Lp1 - 3

Wp1 - 24.2 Lp2 - 7

Wp2 - 24.2

Hp 1.6 1.6

Hf 1.6 1.6

Lf 37.5 37.5

Wf 1.33 1.33

IV. SIMULATION RESULTS By using the finite integration technique with the CST

software, the simulation results will be discussed in this section.

The first design, the single patch antenna with proximity coupled shows return loss characteristic in Fig. 5. The result excites 3% of fractional bandwidth for VSWR<1.5 from 2.91 GHz to 2.99 GHz.

Figure 5. Return loss of the single patch antenna

The radiation pattern of the single patch antenna is

depicted in Figure 6. From the simulation result, it can be seen that the single patch antenna has gain of 4.23 dBi width side lobe level -17.5 dB and half power beamwidth of 84.90.

Figure 6. Radiation pattern of the single patch antenna

The simulation result of the side parasitic patch antenna is depicted in Figure 7 and Figure 8. Figure 7 shows that the antenna resonates at 3 GHz with the fractional bandwidthof 10% from 2.8 GHz to 3.1 GHz for VSWR < 1.5. This result satisfies the required bandwidth for the air surveillance radar. Comparing the bandwidth result from the single patch antenna of 80 MHz to the side parasitic patch antenna of 300MHz, therefore, the side parasitic patch antenna has improved the bandwidth up to 375%.

Figure 7. Return loss of the antenna

The simulated radiation pattern and gain of the antenna is

shown in Figure 8. The result shows that the antenna gain is 5.57 dBi at the center frequency 2.836 GHz. The antenna beam is broadside direction with the half power beamwidth is 86º. In addition, the first side lobe level (FSLL) is -17.3 dB below the main lobe. Moreover, the side parasitic patch antenna has improved the antenna gain from 4.23 dBi to 5.57 dBi.



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Figure 8. Radiation pattern of the side parasitic pacth antenna

V. CONCLUSION A single element proximity coupled rectangular patch

antenna has been designed for future air surveillance radar application in Indonesia. A proximity coupled feed with additional side parasitic patch is used to enhance the antenna’s gain and bandwidth. The simulated S-parameter has a fractional bandwidth of 10%. As for the absolute gain, it is 5.57 dBi with only a single element. This preliminary research satisfies the required bandwidth of air surveillance radar, however to achieve the complex specification requirement for the antenna radar, more research has to be conducted.

REFERENCES

[1] H. Taufal and Y.Z. Fitri, “Pengembangan Antena Mikrostrip dengan Pencatuan Aperture Coupled pada Frekuensi S-Band”, Proceeding Seminar Nasional Microwave, Antena dan Propagasi (SMAP), 3 Oktober 2012

[2] D. H. Schaubert, D. M. Pozar, and A. Adrian,“Effect of microstrip an-tenna substrate thickness and permittivity: Comparison of theories and experiment,”IEEE Trans. Antennas Propag., vol. AP-37, pp.677–682, Jun. 1989.

[3] H. F. Pues and A. R. Van De Capelle, “An impedance matching technique for increasing the bandwidth of microstrip antennas,”IEEE Trans. Antenna Propag., vol. AP-37, no. 11, pp. 1345–1354, Nov. 1989.

[4] D. M. Pozar and D. H. Schaubert, Microstrip Antennas. New York:IEEE press, 1995, pp. 155–166.

[5] G. Kumar and K. C. Gupta, “Broad-band microstrip antennas using additional resonators gap-coupled to the radiating edges,”IEEE Trans. Antennas Propag., vol. AP-32, pp. 1375–1379, Dec. 1984.

[6] G. Kumar and K. C. Gupta, “Nonradiating edges and four edges gap-coupled multiple resonator broad-band microstrip antennas,” IEEE Trans. Antennas Propag., vol. AP-33, pp. 173–178, Feb. 1985.

[7] F. Crop and D. M. Pozar, “Millimeter-wave design of wide-band aperture-coupled stacked microstrip antennas,”IEEE Trans, Antennas Propag., vol. 39, no. 12, pp. 1770–1776, Dec. 1991.

[8] S.-H. Wi, Y.-B. Sun, I.-S. Song, S.-H. Choa, I.-S. Koh, Y.-S. Lee, and J.-G. Yook,“Package-Level integrated antennas based on LTCC tech-nology,”IEEE Trans. Antenna Propag., vol. 54, no. 8, pp. 2190–2197, Aug. 2006.

[9] S.-H. Wi, J.-M. Kim, T.-H. Yoo, H.-J. Lee, J.-Y. Park, J.-G. Yook, and H.-K. Park,“Bow-tie-shaped meander slot antenna for 5 GHz applica-tion,”in Proc. IEEE Int. Symp. Antenna and Propagation, Jun. 2002, vol. 2, pp. 456–459

[10] C. Wood, “Improved bandwidth of microstrip antennas using parasitic elements,” Proc. Inst. Elec. Eng., MOA, vol. 127, no. 4, pp. 231-234, Aug. 1980

[11] G. Kumar and K. C. Gupta.: ‘Broadband microstrip antennas using additional resonators gap coupled to the radiating edges’, IEEE Trans. Antennas Propagation,1984, 32, pp.1375-1379

[12] G. Kumar and K. C. Gupta.: ‘Non radiating edges and four edges gap coupled with multiple resonator, broadband microstrip antennas’, IEEE Trans. Antennas Propagation, 1985, 33, pp. 173-178

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bandwidth and gain enhancement of proximity coupled...

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