Frequency agile monopole antenna using a reconfigurable bandpass filter

A novel microstrip monopole antenna with a reconfigurable -10 dB impedance bandwidth is proposed in this paper for cognitive radios. The antenna is fed by a microstrip line integrated with a stub coupled multiple-mode-resonator (MMR) filter. The reconfiguration of the filter makes the circular disc monopole antenna operate at either a wideband state from 3.8 to 6.9 GHz or a narrowband state by using a PIN diode. For the narrowband state, two varactor diodes are employed to change the antenna operating frequency from 4.3 to 6.6 GHz with a minimum 40 MHz bandwidth. Preliminary simulated results on input reflection coefficients for different states of the antenna are discussed in the paper.