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In this article, a new class of high-order balanced dual-band high-temperature superconducting (HTS) bandpass filter (BPF) based on modified multimode stub-loaded resonators (SLRs) is presented. First, a detailed theoretical analysis of the multimode SLRs is provided to obtain insight into their frequency response characteristics under the differential-mode (DM) and common-mode (CM) operations. Specifically, the SLRs under the DM operation are designed to generate their second and third resonant modes in the two specified passbands, and they are sequentially cascaded by alternate $J$ and $K$ inverters for sharp rejection skirts. Following that, the working mechanism of the CM rejection of the resonator is investigated for achieving good CM suppression performance for this filter. Finally, for experimental validation, an eighth-order prototype filter is designed and fabricated on the MgO substrate with double-sided YBa2Cu3Oy (YBCO) thin films. Good agreement between measured and simulated results is obtained, and the filter is at the same time with low insertion loss, flexible frequency ratio, sharp rejection skirts, and good CM suppression level. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of a new class of cross-coupled blocks incorporating frequency-variant couplings, that is, the frequency-variant blocks (FVBs), and their planar implementations based on an analytical approach. The proposed FVBs require fewer coupling elements with regard to traditional blocks, while can realize a quasi-canonical characteristic (i.e., realizing $k$ -1 transmission zeros for a block of $k$ th order). Derivation of the FVBs relies on a uniform synthesis process, where each transformation is mathematically simplified as a non-reciprocal matrix. An $N$ th-order quasi-canonical filter (possessing either symmetric or asymmetric TZs) can thereafter be synthesized by properly cascading the FVBs. Moreover, a unique planar technique is introduced to construct the quasi-canonical filters (with TZs above passband) using parallel-coupled microstrips, where a complete design procedure from synthesis to circuit parameters will be given. Validity of this work is eventually demonstrated by three illustrative examples, whose synthesis, simulation, and test results perform desired responses and are well-matched with each other. [ABSTRACT FROM AUTHOR]

A synthesis theory of ultra-wideband (UWB) bandpass (BP) transformer with short-circuited stubs is proposed in this paper. Based on the short-circuited stub number and their positions, six combination topologies are presented when the transmission line (TL) section is fixed to 4. Although analyzing the characteristic functions of these six combination topologies, the same theoretical Chebyshev transfer function can be summarized. Therefore, by selecting different short-circuited stub number and their positions, we can make a flexible choice of the filtering transformer pattern and keep the Chebyshev response at the same time. Finally, by using the proposed transformer, a UWB BP type Wilkinson power divider can be easily designed. In order to match the numbers and frequencies of output ports reflection zeroes ($S_{22} =0$)/isolation zeroes ($S_{32} = 0$) with those of input port reflection zeroes ($S_{11} =0$), one extra TL and one isolation resistor are newly added in the power divider design. One experimental circuit is fabricated, and its measured frequency response verified well the proposed design theory and method. [ABSTRACT FROM AUTHOR]

In this paper, a fourth-order dual-band high-temperature superconducting (HTS) differential bandpass filter (BPF) with controllable midband frequencies and bandwidths is developed by using modified multimode square ring loaded resonators (SRLRs). The differential-mode (DM) bisection and common-mode (CM) bisection of the modified SRLR are analyzed by using the even- and odd-mode method twice, and the corresponding resonant properties are obtained. With a proper design of the modified SRLR, two lowest DM resonances are chosen to construct two DM passbands with high in-band CM suppression. The DM resonances can be adjusted flexibly after adding tunable patches to the square ring. Meanwhile, the internal coupling between two modified SRLRs can be controlled separately by using two geometrical parameters. Consequently, the proposed dual-band BPF can achieve independent control of both the midband frequencies and the bandwidths of its two passbands. Moreover, a wideband CM suppression is realized by a combined use of an appropriately selected feeding structure and a frequency discrepancy technique. A fourth-order dual-band differential BPF is designed with two passbands operating at 2.325 and 4.900 GHz, respectively. The filter is fabricated using HTS YBCO thin films on a MgO substrate. Good agreement between the simulated and measured frequency responses are observed, verifying well the proposed structure and design method. [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]

In this paper, a novel design theory of two-section two-resistor Wilkinson power divider (WPD) is introduced. By selecting two different physical lengths of two-section transmission lines (TLs), two arbitrary frequency band WPD can be achieved. Compared with the former work, the designable frequency ratio range u can be extremely extended from 1 < u < 3 to 1 < u < \infty , general design equations for characteristic impedances, physical lengths, absorption resistors, and frequency ratio ranges are newly derived and proved from even- and odd-mode analysis. Because of no capacitors or inductors, the proposed WPD can be used for high-frequency applications. Spurious band of appears between two passbands under the condition of two different physical lengths; therefore, a \Pi -type dual-band transformer is newly introduced to replace single TL for spurious band suppression. We proved that \Pi -type structure could effectively suppress spurious band of , maintain two arbitrary frequency passband of S_{21} , and provide an extra isolation band of S_{32}$ at center frequency. Finally, three proposed WPD examples with $\Pi$ -type structure are selected with different frequency ratios, where frequency ratio $u = 4$ in Example A, $u = 6$ in Example B, and $u = 20$ in Example C are designed and fabricated in the experiment. Measured results show good agreement with the theoretical results. [ABSTRACT FROM PUBLISHER]

This paper presents a compact high-temperature superconducting (HTS) diplexer using single-resonance and dual-resonance spiral resonators. The single-resonance spiral resonators (SSRs) are used separately in each individual channel of the diplexer, and the dual-resonance spiral resonators (DSRs) are used as common resonators of both channels. DSRs are designed using a modified stub-loaded resonator, which can produce two resonant frequencies for both the channels of the diplexer. Because the SSRs and the DSRs are dissimilar resonators, their different spurious frequencies result in a wide stopband. Moreover, resonators are connected by a novel coupling diagram to ensure both high performance and compact size. The size of the diplexer can be greatly reduced while the isolation is kept well. Based on the method, a diplexer is designed for 1.8-GHz mobile and 2.4-GHz wireless area networks systems. The diplexer is fabricated on a YBa2Cu3Oy polished MgO substrate wafer, which has a compact size of $0.12~\lambda g \times 0.073~\lambda g$ . The measured frequency responses agree well with the simulated results. The isolations in both channels are larger than 39 dB, and the measured insertion losses of both channels are less than 0.41 dB. [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]

A response from the author of the article "A Parameter-Extraction Method for Microwave Transversal Resonator Array Bandpass Filters with Direct Source-Load Coupling" on network topology, stray couplings and reference-phase equation published in the May 2013 issue of the journal is presented.