Design of microstrip interdigital bandpass filter with suppression of spurious responses for L-band wireless communication applications

In the present paper, a compact L-band microstrip interdigital bandpass filter (BPF) with spurlines is designed. In the proposed microstrip interdigital BPF, spurious responses are suppressed and stopband attenuation is better than -14 dB everywhere upto 8 GHz excepting that near centre frequency of 4.87 GHz. The 3-dB bandwidth of the proposed BPF is 970 MHz (0.99 - 1.96 GHz) with a centre frequency of 1.475 GHz. The insertion loss value of the proposed BPF varies from 0.16 dB to 0.61 dB over the frequency range of 1.04 - 1.91 GHz. In the desired 3-dB passband, group delay is better than 2.8 ns. The proposed BPF is suitable for the application of satellite navigation like global positioning system carriers which are in the L band, centered at 1176.45 MHz (L5), 1227.60 MHz (L2), 1381.05 MHz (L3), and 1575.42 MHz (L1) frequencies, amateur radio and digital audio broadcasting.