Abstract- In this paper two swastik slots are loaded near the edges of rectangular microstrip antenna. Here, partial ground plane is used. Substrate is made up of fire redundant epoxy (FR4). The antenna is simulated by using HFSS simulation software. The effect of variation in feeding position, length of partial ground plane and height of the substrate on antenna bandwidth is analyzed. This antenna design gives impedance bandwidth of 10.7 GHz operating over a frequency range of 4.1 to 14.8 GHz with VSWR < 2. These characteristics make the designed antenna suitable for Satellite applications.
Keywords: – Microstrip Antenna, Swastik Slot, Partial ground plane, Satellite Communication.
I. INTRODUCTION
Antenna, simply a metallic device for sending and receiving radio waves. Antennas are widely used in mobile and satellite applications but these applications required some specifications of antenna such as light in weight, economic with thin profile and conformal to a shaped surface. Microstrip antenna posses all these specifications required for satellite and mobile applications. But it has certain disadvantages like narrow bandwidth and lower gain. There are various methods to improve the bandwidth and gain of microstrip antenna such as by using parasitic patches either on another layer or on the same layer but in this method there are some drawbacks such as increase the thickness of antenna whereas parasitic patches on the same layer increase the lateral size of antenna. This drawback can be overcome by using partial ground plane [1][2].
Various satellite communications are used in direct broadcast satellite for Europe (11.7-12.5GHz) and fixed satellite services for Europe (10.7-11.7 GHz for downlink and 14-14.8 GHz for uplink). Satellite communication also used for military purposes (X-band for 8-12 GHz) such as defense tracking and
vehicle speed detection for law enforcement. It is also used in maritime vessel traffic control.
In this paper, double swastik-slot loaded rectangular microstrip antenna is designed and analyzed. Two swastik slot reduces the overall impedance of microstrip antenna for much extend. By doing this impedance of antenna brings closer to characteristic impedance of microstrip feed line. Therefore, the value of VSWR become lesser and we get higher bandwidth because impedance bandwidth of antenna inversely proportional to VSWR.
Fig.1.shows the design of double swastik slot loaded rectangular microstrip patch antenna with partial ground plane and glass as a substrate. Microstrip line is used for feeding.
ANTENNA DESIGN
Fig.1. Design of Double Swastik-Slot loaded Microstrip Antenna
Table 1 shows the dimension of various parameters of antenna
TABLE 2
DIMENSIONS
S.No Parameters Dimensions Material
1 Substrate Wsub=30 mm
Lsub=30 mm
Hsub= varying FR4
2 Rectangular patch Lp= 16 mm
Wp= 11.964mm Copper
3 Ground Plane Wg= 16 mm
Lg= varying Copper
4 Swastik Slot-1 Ls= 5mm
Ws= 5mm
Wsw= Varying –
5 Swastik Slot-2 LHs= 5mm
Ws= 5mm
Wsw= Varying –
6 Feed line Wf= 3.01mm
Lf = 8 mm Copper
II. MATHEMATICALFORMULATION
Width and length of microstrip antenna is simply given in [1]. In microstrip antenna, radiation occurs due to the fringing effects. Due to fringing effects electrical length of patch is greater than its physical length. This fringing depends on the width of patch and height of substrate [2].
Let h be the height of substrate, Weff be the effective width of feed line and ??r be the relative permittivity of dielectric substrate. The width of microstrip line in microstrip antenna is given as follows:
For
and for
Where, A and B are given as follows
Impedance of vertical slot is given as follow
And impedance of horizontal slot is given as follow
Here,
Rr and XA =Real and Imaginary Part of Impedance [6]
III. ANTENNA DESIGN
In this paper, double swastik slot loaded micostrip antenna is designed by using Ansoft HFSS software. Length of rectangular patch is 16 mm and breadth of patch is 11.964 mm. FR4 substrate is used which is 30mm wide and 30mm long. Its thickness is kept varying and then we see its effect on bandwidth of antenna. The different values of thickness of substrate are 0.5mm, 0.75mm, 1mm, 1.25mm and 1.5mm. Feeder position is also varied about the symmetrical position. The different values of feeding positions are 0mm, 0.5mm, 1.5mm, 2mm, 2.5mm, 3mm.Ground plane having width 30mm and varying length at 7.2 mm, 7.4mm, 7.6mm, 8mm, 8.4mm, 8.8mm, 9mm. Two swastik-slots near the edges of patch is used to decrease the overall impedance.
IV. RESULTS AND DISCUSSION
In HFSS, rectangular patch and partial ground plane are made up of PEC (Perfect Electrical Conductor) and vacuum can be used for the radiation box.
Firstly, the effect of varying length of partial ground plane on bandwidth of antenna is analyzed. Fig. 2 shows return loss v/s frequency curve at different lengths of ground plane. Substrate height is taken to be 1.5 mm.
Fig. 2 Return loss v/s frequency curve for varying length of ground plane
Table 2 shows that an optimum bandwidth is achieved when length of partial ground plane is kept 7.4 mm.
TABLE 2
BANDWIDTH AT DIFFERENT LENGTHS OF GROUND PLANE
Length of ground plane Lg
( mm) Range of frequency
( GHz) Bandwidth
( GHz) Fractional Bandwidth
(%)
7.2 4.1-13.9 9.8 136.111
7.4 4.1-14.8 10.7 148.611
7.6 4.1-14.1 10 138.888
8 4.13-13.7 9.57 132.916
8.4 4.2-10.1 5.9 81.944
8.8 4.0-6.7 2.7 37.5
9 4.1-5.6 1.5 20.833
Now, the effect of varying feeding position about the symmetrical position on bandwidth of antenna is analyzed. Fig. 3 shows return loss v/s frequency curve at different feeding position.
Fig. 3 Return loss v/s frequency curve for varying feeding position
Table 3 shows that an optimum bandwidth is achieved when feeding position is 2.5mm about the symmetrical position.
TABLE 3
BANDWIDTH AT DIFFERENT FEEDING POSITION
Feeding from the symmetrical position(mm) Range of frequency
( GHz) Bandwidth
( GHz) Fractional Bandwidth
(%)
0 4.7-7.3 2.6 36.11
0.5 4.5-9.9 5.4 75
1.5 4.39-14.02 9.63 133.75
2.0 4.2-13.9 9.7 134.72
2.5 4.1-13.8 9.7 134.72
3.0 4.1-13.4 9.3 129.166
Next, the effect of changing height of substrate on bandwidth of antenna is observed. Fig. 4 shows return loss v/s frequency curve at different height of substrate.
Fig. 4 Return loss v/s frequency curve for varying height of substrate
Table 4 shows that an optimum bandwidth is achieved when height of the substrate is 1.5mm.
TABLE 4
BANDWIDTH AT DIFFERENT HEIGHT OF SUBSTRATE
Height of substrate ( mm) Range of frequency
( GHz) Bandwidth
( GHz) Fractional Bandwidth
(%)
0.5 7.3-8.5 1.2 16.66
0.75 6.4-8.36 1.96 27.222
1.0 5.5-10.609 5.1 70.95
1.25 4.2-13.8 9.6 133.333
1.5 4.1-13.8 9.7 134.722
Finally, antenna having ground plane length 7.4 mm, feeding position 2.5 mm from symmetrical position, substrate height is 1.5mm and substrate material is FR-4 epoxy. For this antenna design return loss is less than -10 dB in frequency range 4.1-14.8 GHz. Figure 5 shows return loss v/s frequency curve.
Fig. 5 Return loss v/s frequency curve for optimum antenna design
Figure 6 shows 2D E-plane radiation pattern at different frequencies with in the band 4.1-14.8 GHz.
Fig.6a 2D E-plane Radiation Pattern at 5 GHz
Fig.6b 2D E-plane Radiation Pattern at 10 GHz
Fig.6b 2D E-plane Radiation Pattern at 14 GHz
Figure7 shows 2D H-plane radiation pattern at different frequencies with in the band 4.1-14.8 GHz
Fig.7a 2D H-plane Radiation Pattern at 4 GHz
Fig.7b 2D H-plane Radiation Pattern at 10 GHz
Fig.7c 2D H-plane Radiation Pattern at 14 GHz
Figure8 shows 3D radiation pattern at different frequencies with in the band 4.1-14.8 GHz.
Fig.8a 3D H-plane Radiation Pattern at 5 GHz
Fig.8b 3D H-plane Radiation Pattern at 10 GHz
V. CONCLUSION
It is observed that two swastik slot loaded microstrip antenna provided optimum bandwidth when length of partial ground plane is 7.4mm (4.1-14.8 GHz i.e 10.7 GHz), feeding position is 2.5mm from symmetrical position (4.1-13.8 GHz i.e. 9.7 GHz) and height of substrate 1.5mm (4.1-13.8 GHz i.e. 9.7 GHz). Finally, we design antenna having ground plane length 7.4mm, height of substrate 1.6mm , feeding position 2.5 mm from symmetrical position, substrate material is FR-4 epoxy then we get bandwidth (S11<-10 dB) 10.7 GHz ( 4.1-14.8 GHz). The proposed design of the antenna can be used for a variety of satellite applications.
REFERENCES
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