Compact dual‐mode differential bandpass filter using stepped impedance resonators

Abstract

A compact dual‐mode differential bandpass filter using a pair of identical stepped impedance resonators connected by a short microstrip line is presented in this letter. The proposed filter showcases good differential‐mode (DM) bandpass response centered at 2.5 GHz (f0) while possesses inherent bandstop effect across the differential passband for the common‐mode (CM) signal. In addition, there is a transmission zero for the CM operation located within the DM passband. Accordingly, the loaded lumped element or stub for the CM suppression is not required in this design. In addition, compact size and wide stopband of the differential filter are both achieved, and the DM stopband rejection is more than 30 dB up to 8.0 GHz (3.2 f0). © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2055–2058, 2014

Multilayer circular SIW cavity differential bandpass filter with wide‐stopband characteristics

“…[1][2][3] A number of differential bandpass filters with suppressed CM signal are presented. [3][4][5][6] Due to low cost, low profile, light weight, and ease of integration with planar microwave circuits, substrateintegrated waveguide (SIW) technology is becoming more popular in recent years. 7 Owing to these advantages, several differential or balanced bandpass filters based on SIW have been reported in the literature.…”

“…Microwave differential circuits have gained significant attention in modern communication systems owing to their excellent performance in terms of signal quality, power handling capability, and immunity to common‐mode (CM) noise 1–3 . A number of differential bandpass filters with suppressed CM signal are presented 3–6 . Due to low cost, low profile, light weight, and ease of integration with planar microwave circuits, substrate‐integrated waveguide (SIW) technology is becoming more popular in recent years 7 .…”

Differential bandpass filter on dual‐mode ring resonator with slotline feeding scheme

“…So far, various differential BPFs have been explored [1][2][3][4][5]. In [1,2], the multi-stage branch-line topologies on a single-layer microstrip line were utilised to design a class of wideband differential BPFs, but these filters suffer from a large overall circuit area.…”

“…In [3,4], a slotline MMR was applied to design a class of wideband differential BPFs. In [5], a dual-mode differential BPF using a pair of identically stepped impedance resonators was presented. However, a feeding structure based on the direct connection of the microstrip feeding line and the ring resonator not only causes a poor rejection property in a frequency range below the desired differential-mode (DM) passband, but also makes the common mode (CM) suppression merely more than 20 dB, which is not good enough for most applications.…”

“…Besides the MMR used in [3][4][5], the planar dual-mode ring resonator [7] has been attracting much interest both in the academic and the engineering because of its easy realisation of transmission zeros below and above the passband. However, such a ring resonator suffers from a extremely narrow bandwidth of the desired passband due to the weak coupling strength of a paralleled gap between the feed line and the ring resonator.…”