Parallel feed bandpass filter with high selectivity and wide stopband

Abstract

A quasi-elliptic function bandpass filter (BPF) based on parallel feed topology is presented. The parallel feed topology is realised by splitting the input/output port of the filter into two paths through a T-junction to excite a pair of resonators simultaneously. This configuration contributes to further improving the selectivity of the filter by introducing more transmission zeros (TZs) near the passband. In addition, a defected microstrip structure is utilised to enhance the out-band attenuation and spur suppression. In order to verify the proposed topology, a fourth order BPF with cross-coupling is designed, fabricated and measured. The measured frequency responses agree well with simulated ones. Four TZs can be obtained with two TZs on each side of the passband.

Compact X‐band bandpass filter using stub‐loaded T‐shape resonator with source‐load coupling

“…Table shows comparisons between our design and previous X‐band BPFs reported in Refs. . It indicates that our proposed filter has competitive advantages of miniature size, wide passband, fairly low passband IL, and a quite good stopband performance.…”

“…In Lacroix and Papapolymerou, an X‐band BPF based on a triple‐mode ring resonator is presented on a duroid substrate. In He et al, a parallel feed BPF with defected microstrip structures is designed using printed circuit board (PCB) technology. These works possess advantage of easy to be manufactured, but their over 2dB passband insertion losses are a little high.…”

High Selective and Wide-Stopband Bandpass Filter Using Simple Uniform Impedance Resonators

“…However, in these examples, the selectivity of the bandpass filter needs to be improved. The transmission zeros are generated near the passband by dividing the input/output port of the filter into two paths in [7] and by introducing cross-coupling in [8] to improve the selectivity. Few methods mention how to design a filter with both high selectivity and wide stopband.…”

Miniaturised highly selective bandpass filter with very wide stopband using meander coupled lines

“…To achieve these primary requirements recently many works were reported [1][2][3][4][5][6]. In [1], shorted stub-loaded stepped impedance resonator (SIR) and stepped impedance stub-loaded shorted SIR were arranged in a way to attain mixed-and cross-coupling (CC) between the resonators to achieve wide passband with transmission zeros (TZs) around.…”

“…The proposed filter is extremely competitive when compared with reported works as can be seen from Table 1. [2] 2.45/32 1.98 13 3.2f 0 (30 dB) 0.38 × 0.12λ g [3] 3.2/20.6 < 2.2 12.5 2.9f 0 (20 dB) 1.1 × 0.63λ g [4] 8.7/18.4 < 2.4 16.5 2.2f 0 (20 dB) 0.43 × 0.20λ g [5] 2.5/54.4 < 0.9 16 2f 0 (20 dB) 0.35 × 0.35λ g [6] a 3.05/37 < 1.0 17 2.8f 0 (20 dB) 0.61 × 0.55λ g AQ2PW 0.38/48.5 0.43 17.5 8.7f 0 (25 dB) 0.09 × 0.12λ g f 0 = Centre frequency (GHz); FBW = fractional bandwidth (%); IL = minimum insertion loss (dB); RL = maximum return loss (dB); S = selectivity; H.S. = harmonic suppression up to.…”