A new type of quint-mode square ring resonator is proposed in this paper. Due to the symmetry of the resonator, the classical odd- and even-mode method is used to analyze the characteristics of the proposed resonator ,which shows that it has five resonant modes and three transmission zeros. As an example, a dual-band BPF with central frequencies (CFs) at 1.78/3.04 GHz and 3-dB fractional bandwidths (FBWs) of 10.1/18.1% is designed and fabricated. By tuning the widths of the microstrip sections, we can control the bandwidth of the second passband of the above BPF on a large scale and two single band bandwidth controllable BPFs with FBWs of 19.86% and 15.9% and CFs both at 3.5 GHz are designed and fabricated. In addition, asymmetric interdigital coupled line (AICL) is utilized to general proper couplings in these filters. What’s more, the five TPs can be divided into three groups by the TZs as the lengths of the specific microstrip sections changes. Therefore, we design a dual-band BPF with good band-in-band isolation between first and second passbands, which is better than that with 26.3 dB. All of the BPFs in this paper are fabricated on the Rogers 4003C substrate with h=0.508 mm, εr=3.38 and tanδ=0.0027. The results of the simulation and measurement are in good agreements.
Comments: 18 Pages.
[v1] 2017-04-05 23:15:57
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