Wideband varactor‐tuned balanced bandpass filter with stable passband selectivity

Abstract

This article presents a wideband tunable balanced bandpass filter (BPF) with stable passband selectivity using optimized varactor‐loaded half‐guided wavelength stepped impedance resonator (SIR). By overall investigation, it can be found that the frequency‐tuning range of the varactor‐loaded SIR is not only controlled by the variation range of the loaded capacitor, but it can be widened by optimizing the SIR. The coupling region between the two coupled SIRs in the proposed BPF is studied for achieving the constant absolute bandwidth (ABW) during the frequency‐tuning process. Meanwhile, the frequency‐dependent source‐to‐load coupling is introduced to realize two self‐adaptive transmission zeros (TZs) on both sides of the tunable differential‐mode (DM) passband so that the proposed filter can keep high selectivity. Benefiting from the constant ABW and two self‐adaptive TZs, the stable DM passband selectivity of the balanced tunable filter can be obtained. For demonstration, a balanced tunable BPF based on the optimized varactor‐loaded SIRs is designed, fabricated and measured. The simulated and measured results, showing good agreement, exhibit a tuning range from 0.542 GHz to 0.926 GHz with 3‐dB constant ABW of around 105 MHz and in‐band insertion loss of 1.5‐2.56 dB.

Fully tunable filter with cross coupling and reconfigurable transmission zero

“…Tunable/reconfigurable microwave filters have become a hot research topic due to the development of high performance multi-band /software-defined/cognitive radio. [1][2][3] Recently, for the purpose of multifunction integration, central frequency and bandwidth tunable filters, called fully tunable filters, are investigated. Some fully tunable filters employ multimode resonators, [4][5][6][7][8] the bandwidth can be tuned by adjusting the frequency splitting of resonant modes.…”

“…Microwave filters are utilized in the radio frequency front‐end (RFFE) for building the frequency channel. Tunable/reconfigurable microwave filters have become a hot research topic due to the development of high performance multi‐band /software‐defined/cognitive radio 1‐3 . Recently, for the purpose of multifunction integration, central frequency and bandwidth tunable filters, called fully tunable filters, are investigated.…”

Compact differential dual‐band bandpass filter using single quad‐mode metal‐loaded dielectric resonator

“…Differential topology is widely applied in constructing microwave circuits and systems because of its high immunity to noise and crosstalk. Corresponding to this trend, many devices have been designed in differential configuration, such as power dividers, phase shifters, antennas, and filters . In earlier works, the differential bandpass filters (BPFs) have been extensively developed by using various technologies, such as the printed circuit board, the low temperature co‐fired ceramic, and the substrate integrated waveguide .…”

“…Corresponding to this trend, many devices have been designed in differential configuration, such as power dividers, 1,2 phase shifters, 3,4 antennas, [5][6][7] and filters. [8][9][10][11][12][13] In earlier works, the differential bandpass filters (BPFs) have been extensively developed by using various technologies, such as the printed circuit board, [8][9][10][11] the low temperature co-fired ceramic, 12 and the substrate integrated waveguide. 13 However, their performance such as passband loss and selectivity could not be acceptable in many applications.…”

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

“…Under these circumstances, the balanced circuit topology has been widely used for its excellent anti‐common‐mode (CM) interference capability. Considering this trend, many scholars and researchers are committed to balanced device researches . Recently, as multiband operation is a commonplace for wireless communication systems, balanced multiband bandpass filter (BPFs) are highly desired.…”