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A modified quarter-wavelength (λ/4) stepped-impedance resonator (SIR) is proposed to design a miniature dual-band bandpass filter (BPF). The proposed λ/4 SIR has two individually controllable resonances for constructing dual passbands. Moreover, two independent geometrical parameters are adopted to realise individual adjustment of the coupling strengths between two adjacent λ/4 SIRs at the dual passbands. As a result, both the centre frequencies and bandwidths of the two passbands of the filter can be individually designed. Furthermore, multiple transmission zeros are created by the introduced source-load coupling, which improves highly the selectivity of both passbands. The dual-band BPF is designed at 2.35 and 5.8 GHz, and its simulated and measured responses are presented and show good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a systematic design procedure of microstrip higher order tunable bandpass filters (BPFs) that can realize a constant absolute frequency bandwidth (ABW) and transmission zeros (TZs) with the minimum number of varactors and a single controlled dc-bias voltage. To this end, intrinsic frequency dependence of interresonator couplings is employed instead of external controls, but the design has faced a difficulty of realizing ideal frequency curves of coupling coefficients at all the coupling regions, including nonadjacent couplings. To overcome such a difficulty, this paper introduces a frequency-curve shape design approach considering upward- or downward-curved convex that is dependent on the types of interresonator coupling. As illustrative examples, fourth- and sixth-order tunable BPFs are proposed and designed, starting from a coupling-matrix synthesis. Their structural parameters can be efficiently designed with the proposed design method. The frequency agility with keeping a constant ABW, acceptable low insertion loss, a good in-band return loss level, and TZs is numerically and experimentally demonstrated for both fourth- and sixth-order tunable BPFs. [ABSTRACT FROM AUTHOR]

A new simple and straightforward parameter-extraction method for a general transversal resonator array filter, which consists of parallel connected resonators in a circuit model, is proposed. Using this method enables one to effectively extract a direct source/load (S/L) coupling, as well as the external quality factor and the resonant frequency of each resonator path only from input reflection phase characteristics of the singly terminated even- and odd-mode networks, without using any complicated optimization techniques and coupling matrix calculations. One of the advantages noted here is that a frequency-dependent S/L coupling in practical physical filter models can be handled with this method. Furthermore, dissipation effects due to unloaded quality factors of the resonator paths is investigated based on a new closed-form formula derived in this paper. The effectiveness of the proposed extraction technique and equations is verified by the comparison with the optimization method results through applications to three planar filter examples. The proposed extraction technique is indispensable for recent advanced filter designs using a transversal array filter synthesis theory for quasi-elliptic function filters having multiple transmission zeros. [ABSTRACT FROM PUBLISHER]

In this article, a compact dual‐band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub‐loaded dual‐mode resonator and a slotline stub‐loaded dual‐mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual‐band BPF. Multiple TZs are generated by introducing a source‐load coupling, thus improving the selectivity of the passbands. Then, the dual‐band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual‐band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45 GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method. [ABSTRACT FROM AUTHOR]