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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]

In this paper, a wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) is presented using slitted stepped-impedance resonators (slitted-SIRs). The use of SIR is essential in widening the filter stopband. Besides, it is found that introduced slits in SIRs provide additional freedoms to control resonance modes when compared with a conventional SIR. Hence, four types of slitted-SIRs are arranged at same fundamental mode f 0 and different higher order modes by adjusting the slits. The coupling of higher order modes is reduced and wide stopband is achieved. In addition, a composite spurline structure is employed to generate two independently controllable transmission zeros, which further improves the stopband performance. Finally, a cascade quadruplet HTS BPF is designed and fabricated on an MgO wafer with double-sided YBCO films. Measurement shows the passband of the BPF is operated at 2.35 GHz and its minimum insertion loss is less than 0.15 dB. The rejection level is better than 21.9 dB in the stopband up to 13.26 GHz (about 5.64 f0). The designed HTS filter tends to the potential application for the desired wide stopband and the high selectivity performance. [ABSTRACT FROM AUTHOR]

In this paper, a compact dual-mode hairpin ring resonator (HRR) with two controllable resonances is proposed to design high-order dual-band high-temperature superconducting (HTS) bandpass filters. Its noncoupled dual-mode resonant characteristics and the mechanism for inherent transmission zero (TZ) production are studied. Moreover, a general dual-path coupling scheme is introduced for high-order coupling realization and applied to the third-order and eighth-order dual-band filter design. Also, two coupling structures for the adjacent HRRs with different orientations are proposed to excite TZs between the passbands for high selectivity. Besides, dual-parallel input–output feeding structure is adopted to tune the external quality factors of the dual-mode HRR individually so that the two passband are realized easily using high-order structure. For demonstration, an eighth-order dual-band HTS filter both operating at 1.9 and 2.6 GHz for mobile communications application are designed and analyzed. Compared with the third-order one, the selectivity of the eighth-order filter has at least 4.2 times improvement and five TZs are produced for high band-edge selectivity. Finally, the eighth-order dual-band filter is fabricated on MgO substrate with YBCO thin films. Measured results agree well with the simulations and show the excellent performance with 0.12-dB minimum insertion loss and better than −75-dB rejection level up to 5 GHz. In addition, the nonlinear characteristics of the fabricated HTS filter is observed by experiment, which shows the temperature dependence of filter center frequency performance and microwave insertion loss. [ABSTRACT FROM PUBLISHER]

This paper presents a miniaturized high-temperature superconducting (HTS) diplexer for mobile (1.8 GHz) and wireless local area network (2.4 GHz). A stub-loaded spiral resonator is used as a signal splitter and a common resonator for both channels. A cross coupling between the common port and fourth resonator of the lower channel is introduced via a transmission line, transmission zeros have been realized in the transition band of the channel, improving the selectivity of the channel band. Meanwhile, the other transmission line is used to introduce a cross coupling between the common resonator and fourth resonator of the higher channel of the diplexer. The diplexer is fabricated on a YBa2Cu3Oy (YBCO) polished MgO substrate wafer, which has a compact size of 11.1 mm × 8.43 mm. Isolation in both channels is greater than 40 dB, maximum insertion loss in both channels is less than 0.05 dB, and minimum return loss in both channels is greater than 18.5 dB. [ABSTRACT FROM PUBLISHER]

This paper presents a compact wideband bandpass filter (BPF) integrating with two narrow-band notch resonators, for preventing the wideband communication system from interfering. The wideband filter adopts an asymmetric stub-loaded multimode resonator to obtain a bandwidth of 66.7%, with excellent passband fluctuation. In addition, two multiloop resonators are used to implement a 0.56% narrow-band. To illustrate its usefulness, a high-temperature superconducting wideband BPF with built-in narrow-band notch resonators is designed. It is fabricated on 20.8 mm × 16.15 mm YBCO films deposited on a 0.5-mm-thick MgO substrate with a relative permittivity ϵr of 9.78. The proposed wideband filter works at L-band, i.e., 1–2 GHz, and the return loss is greater than 19 dB. The notch-band resonator centered at 1.805 GHz provides more than 25 dB maximum attenuation for avoiding interferences from the global system for mobile communication. Finally, the circuit is measured, and the results agree well with the simulations. [ABSTRACT FROM PUBLISHER]

A triple-band high-temperature superconducting filter with wide stopband properties is obtained by using a multimode stepped-impedance split-ring resonator. Its properties and equivalent circuit models are also investigated by even- and odd-mode analysis. Moreover, it is fabricated and measured with a compact size and low insertion losses. [ABSTRACT FROM AUTHOR]

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]

This paper presents a wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF). The filter is implemented by the asymmetric stepped-impedance resonators (SIRs) with only one step discontinuity, which leads to low loss and compact size. With varied characteristic impedance ratios and length ratios, the diversity of asymmetric SIR has been studied, and the spurious resonant-mode responses are discussed. Adopting different asymmetric SIR units operated at the same fundamental frequency f0 (2.4 GHz), its wide upper stopband can be realized by dispersing the higher order spurious resonant modes of these resonators. Furthermore, a modified input/output (I/O) feedline structure has been utilized to enhance the stopband performance. Finally, a fourth-order HTS BPF for wireless application is designed and fabricated on a MgO wafer with double-sided YBCO films. The filter measurement shows excellent performance with 0.05-dB minimum insertion loss and better than −20-dB rejection level in the stopband up to 10.46 GHz (about 4.4 f0). In addition, the size of the HTS filter is 12.45 mm $\times$ 23 mm (i.e., 0.256 $\lambda_g$ by 0.472 $\lambda_g$, where $\lambda_g$ is the guided wavelength at the center frequency). [ABSTRACT FROM PUBLISHER]

A dual-band high-temperature superconducting (HTS) bandpass filter (BPF) using a quadruple-mode resonator is realized in this paper. The resonator consists of a half-wavelength uniform impedance resonator, an open stub in a symmetrical plane, and two spiral open stubs at the two sides of the symmetrical plane. Distinct characteristics of the quadruple-mode resonator are investigated by using even/odd mode theory, and the design graphs are given to analyze the dual-band filter. A dual-band HTS BPF with central frequencies of 1.8 GHz for GSM applications and 2.4 GHz for wireless local area network applications is designed using the proposed quadruple-mode resonator, which is fabricated by depositing YBCO films on a 0.5-mm-thick MgO substrate. Its size occupies only 13 mm \times 17 mm. Measured results demonstrate that an insertion loss within the passbands is less than 0.25 dB. In addition, a transmission zero is achieved in-between two passbands, and two transmission zeros are realized in the upper stopband of the higher passband, which improve the skirt selectivity and stopband characteristics of the filter. [ABSTRACT FROM PUBLISHER]