Single-Ended and Balanced Bandpass Filters Using Multiple Pairs of Coupled Lines and Stepped-Impedance Stubs

Abstract

Two different types of three pairs of coupled lines (TPCL) structures with bandpass and all-stop filtering (ASF) characteristics, respectively, are proposed and analyzed through impedance matrix deduction and input admittance calculation. Combined with the stepped-impedance stubs, high-selectivity single-ended and balanced filters using TPCL structures have been presented. Five transmission poles (TPs) within the passband and six deep transmission zeros (TZs) from 0 to 2f 0 (f 0 : passband center frequency) can be realized in both of single-ended and balanced filters. For demonstration, two sharp roll-off singleended and balanced filter prototypes with good in-band characteristics (insertion losses and return losses) and high common-mode suppression are designed, whose measured 3-dB fractional bandwidths are of 35% and 34.4% (differential mode), respectively. Good agreement between the simulations and measurements validates the design concept. INDEX TERMS Bandpass filter, balanced filter, parallel coupled lines, transmission pole (TP), transmission zero (TZ).

A high‐selectivity wideband bandpass filter with multiple transmission poles and zeros

“…A high‐selectivity single‐ended filter based on the TPCL structure had been presented. Nevertheless, the bandwidths of the BPFs in References 13 and 14 were narrow. A coupled‐line BPF with T‐shaped stub structure was presented in Reference 15.…”

“…In recent years, wideband BPFs have drawn much attention, which can meet the requirements of large capacity and high speed in communication system. In order to design high performance wideband BPFs, a variety of structures and techniques have been proposed, such as ring resonators, 2‐3 multiple‐mode resonators, 4‐5 short circuited resonators loaded different stubs, 6‐8 microstrip/coplanar waveguide, 9‐10 transversal signal‐interference technique, 11 and coupled line structures 12‐16 …”

“…The BPF in Reference 13 composing of only three pairs of coupled lines achieved multiple transmission zeros (TZs) to enable excellent out‐of‐band suppression and roll‐off rates. Reference 14 introduced a three pairs of coupled lines (TPCL) structure. A high‐selectivity single‐ended filter based on the TPCL structure had been presented.…”

Dual‐band bandpass filter using two simple coupled microstrip rings

“…Due to the essential frequency selective functions, the parallel coupled lines are also widely applied in the design of filters 12‐15 . In this paper, we will present a dual‐band BPF using two simple coupled microstrip rings with sharp roll‐off skirts and high return losses.…”

Novel planar balanced bandpass filter with wideband common‐mode suppression and in‐band common‐mode noise absorption

“…The balanced filters are essentially designed to transmit differential mode (DM) signal over a certain passband with all‐stop or band‐stop common mode (CM) noise transmission suppression. Different approaches have been applied to improve the performance of balanced filters as reported in References 4–11. Transversal signal‐interference concept, 4 180° phase shifters 6 and short−/open‐ended parallel coupled lines 7 are applied to achieve a wide DM passband for ultra wideband (UWB) application.…”