Design of Broad Band Microstrip Shorted Patch Antenna ... - IEEE Xplore

2009 International Conference on Emerging Trends in Electronic and Photonic Devices & Systems (ELECTRO-2009)

Design of Broad Band Microstrip Shorted Patch Antenna With Semicircular Cut on Non Radiating Edge Pramod Kumar, Rashid Mahmood Department of Electronics engineering Galgotia’s College of Engineering and Technology, Gr. Noida, U.P, India [email protected], [email protected]

Jugul Kishor

A.K.Shrivastav

Department of Electronics engineering ITS Engineering College Gr. Noida,U. P., India [email protected]

Antenna division SAMEER-CEM Chennai,India

plane is h=12.8mm, and the radiating patch is short-circuited to the ground plane by using two identical shorting plates of width d placed at two ends of one of the patch’s radiating edges. At the center of the patch edge with shorting plates, a 50ohm microstrip feed line is used to directly feed the radiating patch.

Abstract—Here we design a compact size air suspended

microstrip line fed patch antenna with semi circular cut on non radiating edge. This antenna has wide band width. The fractional bandwidth is approximately 20 % of 1.82 GHz. Without semicircular cut on each non radiating edge its aspect ratio is greater then 2 by which cross polarization occur, but using this technique the aspect ratio maintain up to 1.04 which avoid cross polarization & broaden more impedance bandwidth by air suspended antenna. Keywords -shorted Patch, cross polarisation,base station antenna.

I.

INTRODUCTION

Fig 1. Geometry of Shorted Patch antenna

A low-cost microstrip-line-fed shorted patch antenna [1] suitable for base-station applications in DCS cellular communication systems has been studied. The geometry of the antenna is described in Figure1. Which is modeled on HFSSV10. Both the shorted patch and the 50-ohm microstrip feed line have an air substrate, and the material cost is thus reduced to a minimum. By using a pair of shorting plates [2] of proper widths for short-circuiting the radiating patch to the antenna’s ground plane this antenna can be directly fed by the 50ohm microstrip feed line, which greatly simplifies the antenna’s impedance matching design. II.

The signal strip of the microstrip feed line has a width wf and is connected to the radiating patch, at the patch’s shorted edge, by using a conducting strip of the same width wf. Note that both the microstrip feed line and the shorted patch have an air substrate and have different heights of t and h respectively, which provides more freedom in the antenna design. By selecting a suitable value of h, and semi circular cut on non radiating edge of 11 mm radius r, a wide impedance bandwidth suitable for applications in a DCS base station can be obtained, and good impedance matching of the proposed antenna is easily achieved by adjusting the width d of the two shorting plates. For DCS base-station application, design parameters of this antenna were chosen to be L = 23.5 mm, W = 58 mm, h = 12.8 mm, t = 3.2 mm, d = 5.5 mm, and wf = 16 mm. Aspect ratio of conventional antenna

DESIGN AND SIMULATION

The radiating patch has a length L and a width W and is supported by plastic posts (not shown in the figure) above a ground plane. The distance of the radiating patch to the ground

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58 W = = 2.46 and after cut L 23.5 36 W − ΔW aspect ratio is ≈ = 1.04 3.14 × 11 L + ΔL

RETURN LOSS

without circular cut is

0 -5 -10 S11(dB)

-15 -20

SIMULATED

-25

MEASURED

-30 -35 -40 -45 1.65

1.7

1.75

1.8

1.85

1.9

1.95

2

FREQUENCY (GHz.)

Fig. 3. Simulated & Measured return loss for this microstripline-fed shorted patch antenna; L = 23.5 mm, W = 58 mm, h = 12.8 mm, t = 3.2 mm, wf = 16 mm, d = 5.5 mm, and ground-plane size =100 ×100 mm2 .On patch half circle cut of 11mm radius in both sides to minimize the equivalent length so aspect ratio is less then 1.6 to avoid cross polarization Fig. 2. Simulated Model of Antenna III. RESULT DISCUSSION Figure 3 shows the measured return loss against frequency. It is clearly seen that an impedance bandwidth (1:2 voltage standing wave ratio [VSWR]) of larger than 20% covering the bandwidth requirement of the 1820-MHz band (1708– 1910 MHz) is obtained. Typical measured radiation patterns at 1725, 1800, and 1900 MHz are presented in Figure 4. Good broadside radiation patterns are obtained. Again, relatively greater cross-polarization radiation is reduced in the H-plane patterns, which is observed in conventional patch antennas with a thick air substrate. It is also possible that this cross-polarization radiation can be greatly reduced in practical base-station design with a 1× N (N =2, 4, 6, . . .) array configuration in which two adjacent patches are fed out of phase using a simple microstrip T network having a half guided-wavelength difference in length between its two output feed lines. In this case, the cross-polarization radiation owing to the higher order modes of two adjacent antennas can be canceled and reduced cross-polarization radiation can be expected. Measured antenna gain against frequency is shown in Figure 5

Fig. 4. Measured E- and H-plane radiation patterns for the antenna studied in Figure 1. (a) f1 = 1725 MHz, (b) f2 = 1800 MHz, (c) f 3= 1900 MHz A peak antenna gain of about 6.8 dBi is obtained, with a small gain variation of less than 0.6 dBi. The results show that the antenna studied has a low cost of construction and is suitable for applications in DCS base stations.

Fig. 5. Measured antenna gain in broadside direction for the antenna studied in Figure 1.

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IV.

VI.

CONCLUSION [1]

By using the recent technique we design wide band antenna for cellular base station with minimum cross polarization. Without disturbing the current distribution along length of patch antenna we achieve linear polarization and maintain aspect ratio. The measured return loss S11 (dB) has good agreement with simulated result. Electrical size is same but physical size is reduced so overall performance is same with conventional patch antenna without half circular cut. V.

[2] [3] [4]

ACKNOWLEDGEMENT

[5]

This work is supported by Antenna Div., SAMEER-CEM, Chennai. All measurement work had completed by using SAMEER resources

[6]

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REFERENCES

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