Reconfigurable UWB Circularly Polarized Slot Antenna with Three Modes of Operation and Continuous Tuning Range

In this paper, a tunable circularly polarized antenna with a reconfigurable integrated feed network is proposed for cognitive radio applications. The integrated feed network is composed of an ultra-wideband (UWB) band-pass filter (BPF), a continuously tunable T-shaped resonator, and an L-shaped microstrip line. The feed network employs 3 PIN diodes to switch between different RF paths, resulting in 3 modes of operation: an ultra-wideband mode (3.5-8.5 GHz), a narrowband bandpass (BP) mode and a narrowband bandstop (BS) mode. The continuous tuning range of the bandpass/bandstop narrowband mode is realized by two DC-controlled varactor diodes. The stand-alone antenna attains a -10 dB impedance bandwidth of 92.3 % (3.5-9.5 GHz), while it attains an Axial Ratio (AR) bandwidth of 88.3 % (3.1-8 GHz) in its wideband mode. The overlapped bandwidth (matching and AR) of the reconfigurable antenna is 78.2 % (3.5-8 GHz). The communicating state covers 80% of the sensing spectrum while maintaining circularly polarized radiation. The measured peak realized gain values for the wideband mode range from 2 to 3.2 dBic while the maximum gain for the narrowband mode ranged from 1.95 to 3.1 dBic. The measured results show that the proposed filtenna is suitable for UWB cognitive radio systems.