Compact tunable lowpass filter with sharp roll‐off and low insertion loss

Abstract

A novel continuously tunable lowpass filter (LPF) with compact size, sharp roll‐off and low insertion loss is presented in this paper. The filter employs two varactor diodes, a pair of open‐ended coupled lines and a U‐shape step impedance line (SIL) with an open‐ended stub loaded at the center of the SIL to form a very compact layout. The odd‐ and even‐mode analysis and equivalent circuit model are demonstrated for estimation of the transmission characteristics. Tuning the DC voltage applied on the varactor diodes, the varactor capacitance accordingly changes leading to a varying cutoff frequency fc. The measured results show that the achieved 3‐dB fc tuning range is 60.6% (1.15–2.15 GHz). The measured insertion loss (IL) and roll‐off rate are 0.2‐0.4 dB and 50–73 dB/GHz, respectively. The overall size of the LPF is only 0.005λg2, which shows a competitive advantage comparing with the state‐of‐the‐art work.

A tunable cross‐coupled trisection bandpass filter with constant bandwidth based on dual‐mode resonators

“…Electrical tunable microwave filters are the key components for multiband or reconfigurable wide band radio systems for rejecting the out of band interference . Cross‐coupling topologies with extra transmission zeros (Tzs) beside the passband of microwave bandpass filters (BPFs) are widely used in modern radio systems for improving the frequency selectivity .…”

Design and fabrication of a continuous tunable microstrip lowpass filter with wide stopband and sharp response

“…Reference deals with improvement of LPF parameters and includes all regulations associated with filter design. In recent years, different variables have been used to achieve and improve these parameters . In Reference , a compact LPF with wide stopband using defected ground structures (DGS) is presented.…”

“…Tunable microstrip LPFs with wide stopband, compact size, and wide tuning range are presented in References . A compact tunable LPF with sharp ROF is presented in References . Tuning range of the proposed LPF in Reference is from 1.15 to 2.15 GHz.…”

“…A compact tunable LPF with sharp ROF is presented in References . Tuning range of the proposed LPF in Reference is from 1.15 to 2.15 GHz. In Reference , a tunable LPF is provided with a sharp ROF, and good IL in the passband, however, the stopband is not wide.…”

“…Tuning range of the proposed LPF in Reference is from 1.15 to 2.15 GHz. In Reference , a tunable LPF is provided with a sharp ROF, and good IL in the passband, however, the stopband is not wide. Reference presents a novel compact continuously tunable LPF using varactor‐loaded coupled rhombic stubs.…”