Comparative study of the performance of microstrip circular patch antenna with and without slots

REETIKA1, RAJESH KR. VISHWAKARMA2 and K.K.VERMA3

DEPARTMENT OF PHYSICS& ELECTRONICS, Dr. R.M.L.AVADH UNIVERSITY, FAIZABAD-224001(U.P) INDIA.1,3

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGG, JAYPEE UNIVERSITY OF ENGINEERING AND TECHNOLOGY, GUNA, M.P, INDIA.2

Abstract

The present paper reports on the simulation studies of microstrip circular patch antenna with and without slot. The antennas have been designed for 2-8 GHz frequency band. Bakelite with dielectric constant of 4.5 has been chosen as substrate. The feed locations of (3.5, 1) and (1, -9.5) are the optimized values for circular patch without and with slots respectively. It has been observed that the BW increased slightly in the case of slotted patch and antenna efficiency remains almost constant for both cases. It has been concluded that the conventional circular patch resembled better performance compare to slotted patch having equal slots length.

Index terms – Circular patch, slots, efficiency, gain, directivity, bandwidth.

1. Introduction

The rapid advancement in mobile communication and wide ranging applications in the area of wearable antenna, GPS, RFID, WiMAX, telemedicine etc. has led to the compactness of the device which in turn requires a small, compact and robust antenna for integration with the compact device[1, 2] . Keeping in view this, microstrip patch holds significance due to its low weight, low volume and ease to interconnect with the device. This is also robust because of the fact that it is contained in a plastic cover over the radiating elements to provide protection from heat, rain, physical damage [3]. Although various shapes of microstrip patch antenna [4, 5] have been studied so far but the circular patch holds significance due to its high directivity [6], lesser area which ultimately reduces the cost and also because of circular polarization. The main advantage of Circular Polarization is that regardless of receiver orientation, it will always able receiving a component of the signal. In the present era where multiple usages of frequency band by a device have becoming popular; the design of microstrip patch is challenging area of research. In microstrip patch antenna dual frequency behaviour is obtained by introducing a reactive loading to single patch, including stubs [7], notches [8], pins [9], capacitors [10] and slots [11]. In the present simulation studies, effort has been focused on the circular microstrip patch with and without slots for multiple frequency behaviour.

2. Design of circular microstrip patch antenna

In the present paper, radiation performance of a circular patch antenna with four slots is considered and is compared with a conventional circular patch antenna without slots. Antenna is simulated by using IE3D software. In my design Bakelite substrate (ɛr=4.5, h=1.59, tanδ=0.001) is used. The schematic diagram and the simulated diagram are as shown in figure fig 1(a) and 1(b)

Figure 1(a)

(without slots) (with slots)

figure 1 (b) : simulated diagram with and without slots

3. Circular Patch Radius and Effective Radius

There is various design parameters for circular patch have been calculated by a formulae as given below for εr=4.5, fr =3 GHz, h= 1.59mm.

a= F

1+ 2hπ εr F [[ ln( πF2h )+1.7726]]

12

…………………………………………(1)

Where “a” is radius of circular patch and F is a factor whose value is as given below

F=8.791×109

f r√ε r

F= 8.791×109

3×109 √4.5

F= 1.3814

By putting all the values in equation (1), we get the value of a= 13.325mm.

The effective radius of patch due to fringing effect

ae =a 1+2hπ εr a [ ln( πa2h )+1.7726]

1/2

……………………………………………..(2)

From equation (2) value of ae obtained is 13.56mm.

4. Simulation results:

The table-I below shows different values of circular patch without slots for different feed locations. It has been observed that the feed location (3.5, 1) seems to be the optimized one in view of input impedance(50Ω) and the values of various parameters as obtained are listed in table-I. The table-II shows the corresponding values for circular patch with slots. The remarkable result noticed is that the BW of slotted circular patch has been found to be increased from 8.32% to 9.81%. On the basis of the simulated results, the feed location (-9.5, 1) seems to be the optimized one. It has been found that the circular microstrip patch with slots exhibited multiple frequency behaviour compared to dual frequency behaviour for circular microstrip patch without slots.

TABLE-I

Design No.

Feed point

Center freq(GHz)

Return loss(dB)

VSWR Real Z(Ω)

Radiation efficiency(%)

Antenna efficiency(%)

Gain(dBi) Directivity(dBi) BW(%)

D1 (3, 1) 3.036.182

-18.75-22.24

1.2611.168

39.6543.91

80.3212 68.4698 4.71615 6.36116 8.312

D2 (-3, 1) 3.036.182

-23.24-23.73

1.1481.139

45.7847.47

80.3793 63.3893 4.37526 6.3551 8.212

D3 (-3, -1) 3.036.182

-18.76-22.22

1.2611.168

39.6743.85

80.3212 68.4692 4.7161 6.36115 8.11

D4 (3, -1) 3.036.182

-18.31-22.19

1.2771.168

39.1943.85

80.3134 63.3893 4.37526 6.3551 8.21

D5 (3.5, 1)

3.036.182

-22.38-19.44

1.1641.239

50.1340.8

80.5640 69.4276 4.37526 6.3551 8.32

D6 (-3.5, 1)

3.036.182

-21.97-19.51

1.1731.236

49.6840.88

80.5528 69.8284 4.80177 6.36145 8.11

D7 (-3.5 -1)

3.036.182

-22.38-19.43

1.1641.239

50.2440.81

80.5658 69.4018 4.77468 6.36098 8.01

D8 (4 , 1) 3.036.182

-15.18-22.56

1.4221.161

61.556.56

80.7279 68.2208 4.70103 6.36186 8.32

TABLE-II

Design no.

Feed point

CenterFreq(GHz)

Return loss(dB)

VSWR Real Z(Ω) Radiation efficiency (%)

Antenna efficiency(%)

Gain (dBi)

Directivity (dBi)

BW(%)

SD1 (1 -9) 4.9766.485

-13.83-14.11-13.93

1.41.6171.499

51.9558.3845.38

67.729 67.7896 3.35575 5.32028 9.21

SD2 (1 -9.5) 4.9766.485

-14.93-13.86-11.9

1.4731.501.681

47.2750.3334.39

67.8608 67.8139 3.62403 5.31085 9.32

SD3 (1 -10) 4.9766.485

-15.56-12.55-14

1.41.6171.499

51.9558.3845.38

67.9993 67.8875 3.6282 5.3103 9.51

SD4 (1 -10.5)

4.9766.485

-16.72-11.21-15.2

1.4731.6081.32

60.852.1142.39

68.211 67.3812 3.6121 5.3012 9.67

SD5 (1 -11) 4.975.9396.485

-14.35-12.64-16.98

1.4741.6091.33

60.9952.1442.49

68.223 67.4015 3.59434 5.30764 9.81

SD6 ( 1 -8) 4.9766.545

-9.772-10.00-13.71

1.9611.9261.52

32.9426.5133.23

67.8608 67.8139 3.62403 5.31085 9.01

Fig. 2(a) Return loss (D5) Fig. 2(b) Return loss(SD2)

From fig. 2(a) shows a plot of return loss for circular patch antenna without slots showing its value <-10 dB for two center frequencies of 3.03GHz and 6.182 GHz i.e dual band operation and fig. 2(b) shows the corresponding plot for circular patch antenna with slots showing its values as -14.93dB, -13.86dB, -11.9dB for center frequencies of 4.97GHz, 6GHz and 6.485 GHz respectively.

Fig. 3(a) VSWR versus frequency plot (D5) Fig.3 (b) VSWR versus frequency plot (SD2)

Fig. 3(a) represents VSWR versus Frequency plot for circular patch without slots and values are 1.164 and 1.239 respectively for 3.03 GHz and 6.182 GHz center frequencies.Fig.3(b) represents VSWR versus frequency plot for circular patch with slot and values are 1.473, 1.50 and 1.681 for center frequencies of 4.97GHz, 6GHz and 6.485GHz respectively which are nearly equal to 1.

Fig .4(a) Real Z plot (D5) Fig. 4(b) Real Z plot (SD2)

Fig. 4(a) and Fig. 4(b) represent the plots of real impedance for patch without slots and with slots respectively and the values of real impedance are found to be nearly ~ 50 Ω.

Fig.5 (a) Smith chart (D5) Fig.5 (b) Smith chart (SD2)

Fig.4 (a) and Fig.4 (b) represent the corresponding smith chart for circular patch without and with slots. These represent both inductive and capacitive nature of patch.

Fig.6 (a)2D Radiation Pattern (D5) Fig.6 (b) 2 D Radiation pattern (SD2)

Fig .6(a) and Fig.6 (b) show the radiation patterns without and with slots for optimized feed locations of (3.5, 1) and (1, -9.5) respectively.

Fig. 7(a) Current distribution Fig.7 (b) Current distribution

Fig.7 (a) and fig.7 (b) show the current distribution of circular patch with and without slots.

Fig. 8(a) 3D Pattern (D5) Fig. 8(b) 3D pattern (SD2)

Fig. 8(a) and fig.8 (b) represent 3 D pattern of circular patch with and without slots. The comparative study of these two 3D patterns reveal that the circular patch without slots is having more directivity and gain compare to that of the circular patch with slots when the slot length is nearly equal.

Conclusion

In this paper, detailed analysis of effect of feed locations and slots on circular microstrip patch a have been studied by IE3D simulation software. We observed that slots of equal length do not have pronounced effect on the antenna performance compare to that of circular patch without slot. The feed locations of (3.5, 1) and (1, -9.5) are the optimized values for circular patch without and with slots. It has been found that the microstrip circular patch resembled better performance compare to slotted (equal slots length).

Acknowledgement The authors are grateful to Department of Electronics & Communication Engineering, Jaypee University of Engineering and Technology, Guna. Discussions with Dr. B.T.P. Madhav, K.L University, Dr. D. Arya, IET Alwar, Mr. Ambika Singh, KIITE, Udisha and Dr. V.S. Tripathi, MNIT Allahabad are highly acknowledged. The authors are also thankful Prof. R K Malaviya to provide for simulation and testing of microstrip antenna through Antenna Test & Measurement Society (ATMS), Ahmadabad.

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