Investigation on compact modified wideband interdigital bandpass filter with wide stopband using spurlines and defected ground structures

Abstract

In this paper, a compact modified microstrip interdigital bandpass filter (IBPF) having two pairs of spurlines and a pair of defected ground structures (DGS) containing stepped impedance resonators (SIRs) is described for L–Band receiver applications. A combination of spurlines and SIR‐shaped DGS is used to obtain the proposed compact IBPF with wide stop‐ and pass‐bands. The reduction in size and wide stopband characteristic of the filter result from band notched characteristic of spurline, and harmonic suppression along with miniaturization characteristic of DGS. The equivalent circuit parameters of the spurlines and DGS are also extracted and their values are computed. The proposed compact filter is of size 0.24λg × 0.34λg (0.107λ0 × 0.075λ0), where λg=λ0/εr, λ0 is the free space wavelength at the centre frequency (f0) of 1.47 GHz and εr (=10.2) is the dielectric constant of the substrate. The simulated and measured 3‐dB fractional bandwidths of the proposed filter are 80% (over the frequency range 0.89 −2.05 GHz) and 79% (over the frequency range 0.87–2.01 GHz) respectively. The proposed BPF has stopband attenuation better than 17 dB upto a frequency of approximately six times the centre frequency of the desired passband. For the validation of the simulated results, the prototype of the proposed filter was fabricated and its parameters like S–parameters, group delay and phase responses were measured. The experimental results for the proposed BPF are nearly in agreement with the respective simulation results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2634–2639, 2016