Tunable balanced BPF with wide tuning range and high selectivity

Abstract

A highly-selective tunable balanced bandpass filter (BPF) with wide tuning range of center frequency is presented. The balanced BPF is designed by using compact varactor-tuned parallel coupled-line resonators with the direct-feed structure. It can realize a wide tuning range with an almost constant fractional bandwidth (CFBW). Three differential-mode (DM) transmission zeros (TZs) close to the tunable passband are obtained by mixed electromagnetic coupling and frequency-variant source-load (S-L) coupling. Meanwhile, the three TZs can almost keep the same relative location of passband to achieve continuous high selectivity and good out-of-band rejection over the whole frequency-tuning range. For verification, a tunable 1.02-3.25 GHz balanced BPF with three selfadaptive TZs is designed, fabricated and measured. And experimental and simulated results are in good agreement.

Compact balanced filter with high common mode suppression using hybrid microstrip and slotline spoof surface plasmon polaritons

“…Furthermore, adopting the high-order modes of the SSPP unit cell is another effective method for achieving bandpass response [21,22]. In recent years, the balanced BPFs show advantage of intrinsic common mode (CM) noise rejection capability [23,24,25]. Hence, a few balanced BPFs implemented by the SSPP structure are reported to broaden its application in balanced components design [26,27,28,29,30,31].…”

Highly‐tunable and wide stopband microstrip bandpass filters

“…Different elements are loaded in the centre of resonators to suppress the common mode without influencing the differential mode response. In, 25 a highly‐selective tunable bandpass filter is reported based on varactor diode‐loaded microstrip resonators. Moreover, a mixed electromagnetic and source‐load coupling scheme is used to generate TZs on either side of the passband.…”