Realisation of highly compact planar lowpass filter for UWB RFID applications

A novel compact microstrip lowpass filter is described that exhibits an quasi-elliptical function response with high out-of-band rejection for integration in ultra-wideband (UWB) chipless radio frequency identification (RFID) receivers. The filter´s characteristics include a wide-stopband and low passband insertion loss with a passband ripple of 0.03 dB. Out-of-band attenuation of 30 dB is achieved up to about four times the cutoff frequency (4f_c), and 20 dB up to about seven times the cutoff frequency (7f_c). In addition, the proposed filter structure offers a high figure-of-merit of 8657 that exceeds the lowpass planar filters with an equal cutoff frequency reported in the literature to date.