Design of a Compact Reconfigurable Filtering Antenna Using π-shaped Microstrip Filter

A compact reconfigurable planar filtering monopole antenna with switchable band characteristics has been proposed in this paper. The filter cum antenna structure comprises two parts, a circular shaped planar monopole antenna with UWB characteristics and a π-shaped microstrip filter connected to the feedline. The design has been carried out in two phases. The initial structure has been optimized using microstrip discontinuity models and Random Drift Particle Swarm Optimizer has been used to achieve impedance matching over the desired frequency range. Subsequently, frequency reconfigurability has been introduced by considering switches at three junctions where the stubs meet the feedline and the portion where the feedline connects with the monopole antenna. For simplicity, the operation of the switches has been implemented by assuming short and open circuits for switch ON and OFF conditions respectively. Considering 3 switches, there are eight possible combinations of switching states and each of them corresponds to different frequency and pattern characteristics. The reported antenna can be used for Wi-Max, WLAN and UWB applications without any interference caused by nearby systems. The circular shaped planar monopole antenna without the filtering network operated in the UWB frequency range from 2 GHz - 10GHz. With the introduction of the π-shaped microstrip filter the frequency selectivity is achieved at 4.28GHz, 3.52GHz, 3.94GHz, 5.184GHz and 2.94GHz with the S11 values of -16.938dB, -29.32dB, -18.5dB, -50.6dB and -48.5dB respectively, corresponding to different combinations of switching states. The radiation characteristics also indicate high gain at the center frequencies corresponding to different switching states.