New design of an adjustable compact microstrip lowpass filter using Z‐shaped resonators with low VSWR

Abstract

In this article, an adjustable microstrip lowpass filter(LPF) with the cut‐off frequency (fc) at 1.59 GHz is designed and fabricated. The proposed structure is composed of a Z‐shaped resonator as basic resonator and a combination of modified T‐shaped and Z‐shaped resonators as suppressor units. To describe a theoretical design, the L‐C equivalent circuit of the basic resonator and also its transfer function are calculated precisely; then, the location of the first transmission zero (TZ) is accurately computed. Generating a deep TZ near the cutoff frequency leads to a high roll‐off rate of 195 dB/GH. The LPF also benefits from an extremely wide stopband from 1.72 to 23.67 GHz (15 fc). In passband region, the insertion loss and return loss of the LPF are 0.62 and 22.9 dB, respectively. The experimental results also show that maximum variation of group delay is only 0.53 ns regarding a negligible figure. The electrical size of the LPF is 0.187 × 0.083 λg2 (where λg is the guided wavelength at 1.59 GHz). Finally, the proposed LPF achieves a high figure of merit of 57 860 deemed a great accomplishment.

Design and fabrication of MEMS lowpass filter exploiting space mapping algorithm

“…Planar microstrip LPF has attracted great attention due to its advantages of small size, low‐cost and easy of fabrication. To date, several structures have been reported to obtain high‐performance lowpass filters 1‐14 . In Reference 3, a microstrip low‐pass filter using a stepped impedance hairpin resonator with a pair of coupled stepped impedance resonators (SIRs) inside is presented.…”

“…The LPF with two modified asymmetric hairpin resonators and four open‐circuited stubs has excellent rolling coefficient 9 . By exploiting Z‐shaped resonators, a sophisticated microstrip LPF is designed and fabricated in Reference 10. In Reference 11, a microstrip LPF with sharp roll‐off and wide stopband consisting of radial split ring resonator loaded by folded polygene patches is proposed.…”