Phi Shape UWB Antenna with Band Notch Characteristics

In this paper a novel band notch antenna in UWB frequency range is designed using split rings. Split rings are overlapped with designed monopole to give phi shape. The slit gap gives band-notch operation from 5.1GHz to 6.29GHz and from 4.94GHz to 5.91GHz for SPSSR and SPSCR antennas respectively. Simulated and measured results are in good agreement. Keywords-monopole; split ring resonator; band-notch; UWB antenna; VSWR


INTRODUCTION
For a wireless communication system, large bandwidth is an important requirement.Although UWB antenna gives large bandwidth of 7.7GHz (3.1GHz to 10.6GHz), it faces many challenges of interference with existing systems in UWB range.To avoid this interference with existing systems like WLAN, HIPPERLAN, WiMAX, C-band satellite communication etc., band notch antennas are nowadays becoming popular and necessary for communication.In this paper a novel band notch antenna is designed by merging a monopole antenna with a square or circular split ring resonator.This proposed antenna shape looks like the Greek letter Phi (φ) hence is named as split Phi shape square ring (SPSSR) antenna and split Phi shape circular ring (SPSCR) antenna.Both antennas give single band notch operation in UWB band.Monopole is designed at 3GHz.The parameters for the SPSSR antenna are designed, optimized and applied to the SPSCR antenna.It is found that both antennas give the same response hence the same design can be extended to any other shape as well.In proposed antennas, by varying the split gap of rings, band notch frequency can be tuned to the desired band.The length and width of split ring resonator gives inductance, and the gap between two rings and the slit gap of the rings gives the capacitance.The gap between the rings and the slit gap is optimized to give UWB antenna with notch band characteristics.At slit gap of 1.1mm the UWB operation in with band notch at 5.87 and 5.47GHz is achieved for SPSSR and SPSCR respectively.
Many antennas with band-notch characteristics are reported.Band-notch characteristics are achieved by inserting different slots in the radiating patch [1-3].In [4,5] antennas with etching slots shapes such as H, M, W etc. slots in the ground plane are reported.A band notch antenna by etching a narrowband dual resonance fractal binary tree in the radiation element of the conventional UWB antenna is reported in [6], but the antenna manufacturing and structure are complex.The band-notched characteristics are obtained by adding a stepped impedance resonator (SIR) or a split ring resonator (SRR) on the feed line or cutting slots in the ground plane [7,8].A bandnotch antenna is designed by etching a nested CSRR inside the ground plane in [9].
Another technique to obtain band-notch characteristics is by adding the parasitic elements in the form of printed strips placed in the radiating aperture of the planar antenna at the top and bottom layer.They are employed to suppress the radiation at certain frequencies within an ultra-wide frequency band [10,11].By inserting the U-shaped parasitic element on the bottom plane of the basic planar monopole antenna [12] or by using a pair of arc shaped parasitic elements around the patch, an excellent notched frequency band for rejecting the WLAN band (5-6GHz) can be obtained [13].The electromagnetic coupling of the SRR with the CPW yields the frequency notch [14].There are many more techniques used to obtain bandnotch operation in UWB range.The proposed antenna is simple to design and implement.By changing the slit gap of the antenna the desired band-notch frequency can be tuned.Additional varactor diode can be implemented with the antenna as a future scope to give variable capacitance and the same antenna can be used to tune different frequency bands.The proposed antenna was carefully fabricated and measured.The return loss, VSWR, and impedance are measured to certify the performance.Results show acceptable discrepancy between simulation and measurement due to the influence of the SMA connector for testing and the indoor measurement environment.

CHARACTERISTICS
Initially a monopole antenna at 3GHz frequency is designed.The height of monopole antenna will be λ/4.Heights of monopole antenna and ground plane dimensions are fixed by optimization.Designed square and circular shape split ring resonators are overlapped with monopole to form the proposed phi shape antennas.The proposed SPSSR and SPSCR antennas for band notch applications in UWB range are shown in Figure 1.The length of the outer ring is 38mm and the ring width is

SPSSR a GHz
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Fig. 2 From the em gure 2, L1 is th d C2 are cap ner rings and C onopole on le equency of the to considerati rcuit is given b Fig. givin Fig. 8.4G

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Parameters uency Range (