Miniature high selectivity filters using grounded spiral resonators

A novel miniature high selectivity filter designed using a metamaterial resonator based on four grounded spirals (ForeS) is presented. This enables extreme size reduction together with high out-of-band rejection and low insertion loss. A fabricated third-order filter has overall dimensions of lambda_g/4 by lambda_g/15, a 3 dB bandwidth of 3.7% at 1.63 GHz, insertion loss of -3 dB, attenuation greater than 75 dB in the lower stopband and greater than 40 dB up to 2.6 times the centre frequency.