A symmetrical compact microstrip lowpass filter (LPF) with ultra‐wide rejection band and low voltage standing wave ratio (VSWR) using a novel structure of stepped impedance and butterfly‐shaped resonators is presented and fabricated. The LPF has a 3 dB cut‐off frequency at 1.513 GHz. The series structure of the butterfly‐shaped resonators result in a high roll‐off rate of 187.8 dB/GHz. By generating multiple transmission zeros, a wide stopband (with 35 dB rejection degree) is achieved. To reach a small circuit, the bended transmission line is properly utilised. Moreover, 171% relative stopband bandwidth and dimensions of 0.087λg × 0.157λg (λg is the guided wavelength at 1.513 GHz) are other specifications of this LPF. In addition, an acceptable match is obtained between the simulated and measured responses. In the end, the LPF achieves a high figure‐of‐merit of 82288.
Using polygonal resonators and bended lines, a new type of dual-band bandpass filter (BPF) is presented generating a fixed passband centred at 2.70 (f 01) and an independently-electronically tunable passband (f 02) which can be tuned between 3.65 and 6.51 GHz (56% tuning range). The measured results indicate that the return losses of both passbands are >21 dB throughout the tuning range. Furthermore, the use of bended lines leads to extremely small size of 0.136 × 0.098l 2 g , where l g is the guided wavelength at the lowest working frequency (f 01). The proposed BPF also benefits from an ultra-wide upper stopband from 7.03 up to 14.41 GHz (based on 21 dB points), suppressing unwanted signal by more than 21 dB considered as a positive point. The filter prototype is investigated in four design stages with the LC analysis to support the design process theoretically and fabrication results to validate the design practically.
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