UWB Microstrip-Fed Monopole Antenna With Single And Dual Band Notch Characteristics

A planer monopole ultra wideband (UWB) antenna with single and dual band notched characteristics are presented in this article. Proposed antenna consists of simple rectangular shaped patch with sequential notches which is inserted in two lower corners. In order to obtain band notched properties ‘U’ shaped conductor backed plane (CBP) is embedded. Multiple ‘U’ shaped CBP can realize multiple frequency band notched charecteristics.To validate this concept two prototypes are designed, simulated and fabricated for single and dual band notched UWB Antenna. Notched band can be controlled by adjusting the parameters of U shaped CBP. Proposed antennas exhibit almost Omni directional radiation pattern over an operating bandwidth of (2.62 11) GHz. Key words: Band notch characteristics, conductor backed plane, ultra wideband antenna. INTRODUCTION: Ultra wideband (UWB) technology is expanding rapidly in wireless communication systems covering the frequency range from 3.1-10.6 GHz allocated by The Federal Communication Commission (FCC) [1].several monopole Antenna configuration have been designed so far for UWB operation[2-5].However in practical application WIMAX(3.3-3.6 GHz),WLAN(5.15-5.825 GHz),C band satellite communication service( downlink:3.7-4.2GHz,uplink:5.9-6.4GHz) and X band satellite communication service ( 7.25-8.39 GHz) are also operating in the UWB frequency range. Therefore UWB communication systems may generate interference with these bands. So it is desirable to design the UWB monopole antenna with multiple band stop characteristics. Different techniques for band rejection have been adopted such as embedding of slots on patch[6] or ground plane[7].or insertion of tuning stubs in ground plane.[8].or the band rejection by EBG structure.[9]. Addition of parasitic patches with antenna can also used for band stop characteristics. [10].another approach to realize the band notch function by the insertion of H shaped [11] or I shaped [12] parasitic element on the rear side of the substrate. In this article the simple monopole UWB antenna with a smaller size (24mm×24 mm×1.6 mm) is proposed. The realization of single or dual band notched features can be achieved by introducing a single or a pair of ‘U’ shaped parasitic elements. Two prototypes are designed and measured to confirm single and dual band notch response to verify the proposed antennas. Both simulated and measured results of VSWR and radiation pattern are presented and discussed. DESIGN OF MONOPOLE UWB ANTENNA WITH SINGLE BAND-NOTCHED CHARECTERISTICS The geometry of Proposed UWB antenna with single band-notched characteristics is illustrated in fig 1 which is constructed with a substrate made of FR4 with permittivity 4.4 and thickness 1.6 mm.The width of microstrip feed line is fixed at 2 mm to achieve 50Ω characteristic impedance. The length of ground plane is 6 mm printed on the back surface of the substrate along with a‘U’ shaped conductor backed plane (CBP). CBP acts as a half wavelength parasitic element. At the notch frequency the current flows are more dominant around the parasitic element create attenuation. The rectangular patch dimension is (12 × 15.5) m.m with two pairs of notches on the patch surface. Each notch of size(1× 2) m.m. The sequential discontinuities due to the notches on the patch generate several resonances which adjust the impedance band width over UWB frequency band and on the other hand at notch frequency, large impedance mismatch 275 is produced which leads to the better band notch performance as well as small increment in rejection bandwidth. Optimum gap between the radiator and the ground plane is kept at 2 m.m.Notched band can be controlled by varying the parameters of ‘U’ shaped CBP,which is characterized by Wi,Wo,D and d, while the width of ‘U’ shaped CBP is 0.5 m.m.The notch frequency where maximum VSWR is obtained is given as fn= c 2Ln ∈reff , ∈!"##= √(∈r +1) 2 Ln= λg/2 and c = speed of light, Ln is optimized length in this design where Ln= (D-d) + Wi/2 for Wi ≥ WP--------(i) and Ln= (D-­‐d) + Wo/2 for Wi< WP-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐ (ii) where WP is the patch width fixed at 12 mm. Fig 1: Geometry of proposed antenna with single band notch characteristics RESULTS AND DISCUSSION OF MONOPOLE UWB ANTENNA WITH SINGLE BAND-NOTCHED CHARECTERISTICS Simulation results of proposed antenna obtained byAnsys HFSSsimulator[13]. From simulated results in fig2 it is clearly seen that impedance bandwidth improves and covers the range from 2.62 11 GHz (VSWR<2) and on the other hand at rejection band peak VSWR increases with the insertion of the pair of notches with patch. From the simulation result in fig 3 it is observed that band notched frequency varies with the variation of D.The results predictedby HFSS simulator are compared to the ones calculated by equation (i) and (ii) as shown in fig.4(a) and 4(b) for different value of wi. It is seen that nature of slopes in the two sets of results are almost similar against the frequency. Fig 2: VSWR characteristics with notch effect Fig 3: VSWR characteristics for various D