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In this article, a novel coplanar waveguide (CPW) spiral cross resonators (SCRs) is introduced for creating a dual‐band balanced bandpass filter (BPF) with adjustable passbands. The resonant properties of the SCRs in both the differential mode (DM) and common mode (CM) are scrutinized. Furthermore, DM bisection offers two distinct parameters for internal coupling adjustment, enabling independent passband width control. A novel grounding wire feeding arrangement matches the external Q factor of the dual DM passbands. An additional stepped‐impedance short‐circuited conducting stub between resonators prevents excessive coupling while obtaining moderate bandwidths. Inherent CM suppression can be attained by distinguishing CM resonant frequencies distinct from the DM frequencies. To validate the design, a dual‐band balanced BPF designed and fabricated to operate at 2.42 and 5.2 GHz exhibits closely matching measured results compared to the simulated ones. [ABSTRACT FROM AUTHOR]

In this letter, a novel dual‐band bandpass filter (BPF) with independently controllable center frequencies, bandwidths, and transmission zeros (TZs) is presented. The proposed BPF is realized by using eighth‐mode substrate‐integrated circular cavities (EMSICCs) and coplanar waveguide (CPW) resonators. The CPW resonators are embedded in the upper surface of the EMSICCs, allowing for a compact size without additional circuit dimensions. Finally, a dual‐band BPF for WLAN is designed and fabricated with center frequencies of 2.45 and 5.2 GHz. The measured results closely align with the simulated ones, validating the performance of the filter. Multiple TZs are generated by cross‐coupling and source‐load coupling, which results in good out‐of‐band rejection performance. [ABSTRACT FROM AUTHOR]

In this article, a balanced bandpass filter (BPF) is developed by using the improved parallel‐coupled line (IPCL) and the parallel‐coupled‐line‐loaded resonators (PCLLRs). The proposed IPCL, which is realized by loading the short‐circuited or open‐circuited parallel‐coupled line section to the traditional one, behaves the bandpass response or bandstop property. Thus, feeding structure of balanced BPF constructed by IPCL can realize intrinsic common‐mode suppression. Besides, compared with traditional stub‐loaded resonator, PCLLR can provide two transmission zeros (TZs) on both sides of passband when short‐circuited parallel coupled‐line is applied. Moreover, short‐circuited stepped‐impedance stubs are installed at input and output feed lines for TZs to further enhance the selectivity of passband. Finally, a high‐selectivity balanced BPF operated at 2.5 GHz with fractional bandwidth of 11% is designed and fabricated. The measured results agree well with the simulated ones and show a desirable in‐band common‐mode suppression of higher than 44 dB. [ABSTRACT FROM AUTHOR]

A simple tunable bandpass filter (BPF) with constant 3‐dB absolute bandwidth using folded slotline uniform impedance resonators (UIRs) is proposed. The tunable BPF consists of a pair of coupled folded slotline UIR, where the varactor diode elements are loaded to control its center frequency. Measured results show that a wide tuning range from 1.76 to 2.35 GHz with constant 3‐dB absolute bandwidth (ABW) of 310 ± 10 MHz is realized. Meanwhile, a pair of transmission zeros (TZs) are generated aside both sides of the passband due to the coupling between source and load, which improves the selectivity of the passband. [ABSTRACT FROM AUTHOR]

In this paper, a newly composite right-/left-handed (CRLH) resonator is presented and applied to constitute a compact dual-band balanced bandpass filter (BPF). The proposed CRLH resonator contains two spiral coupled line segments. By imposing the differential-mode (DM) and common-mode (CM) excitation, the DM and CM equivalent circuits of the presented resonator and their lumped-element circuit models are built for investigating the resonant property. The CRLH resonator has two DM resonances and are adopted to design two DM passbands. Also, the CM resonances are all far away from DM resonances, achieved intrinsic desirable CM rejection within DM frequency range without any auxiliary elements. Attributing to the mixed electric and magnetic coupling between two coupled resonators and the introduced source-loaded coupling, multiple transmission zeros are obtained and therefore enhance the selectivity and attenuation in stopband. Finally, a well-designed dual-band balanced BPF is fabricated. Verification of the presented structure and design method's validity is evidenced by the measured results, which are in agreement with the simulations. [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]

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]

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]

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]

In this letter, a novel compact dual-band filtering power divider (DB-FPD) is proposed. It consists of a U-shaped Wilkinson power divider, two pairs of dual-resonance resonators (DRRs), and a pair of spur lines. With the simultaneous use and appropriate design of the coupled feedlines, mixed electric and magnetic couplings between the DRRs and spur-lines with different lengths, multiple transmission zeros are produced which result in two passbands with desired power division, high-frequency selectivity, good isolation, and an ultrawide stopband. A prototype DB-FPD operating at 2.3 and 3.5 GHz with 3-dB fractional bandwidths of 8% and 6% is designed, fabricated, and measured. The measured responses agree well with the design simulations, exhibiting a stopband up to 13.8 GHz ($6f_{0}$) with 20-dB rejection level. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a quadruple-mode stub-loaded resonator (QM-SLR) is introduced and its four modes are excited using a simple approach, which can provide a dual-band behavior. By changing the length of the loaded stubs, independently tunable transmission characteristics of the proposed quadruple-mode stub-loaded resonator were extensively described for filter design. Moreover, microwave varactors were adopted to represent the length variation of the loaded stubs for the dual-band tunability. The equivalent circuit modeling of the open stub with microwave varactor was given and discussed. Then, adopting the compact quadruple-mode stub-loaded resonator with three varactors, an independently controllable dual-band bandpass filter (BPF) was designed, analyzed, and fabricated. Its separated bandwidths and transmission zeros can be tuned independently by changing the applying voltage of the microwave varactors. A good agreement between simulated and measured results verified the design methodology. The proposed filter possesses compact size, simple structure, and excellent dual-band performances. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:602-608, 2016. [ABSTRACT FROM AUTHOR]

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]

In this paper, a high-temperature superconducting composite right/left-handed (HTS CRLH) resonator is proposed, which is constructed by microstrip spiral coupled lines and step-like microstrip lines. The dispersion characteristics of the CRLH resonator is obtained and analyzed by an equivalent circuit model and a transmission matrix method. To verify this design methodology, the HTS CRLH resonator is designed and fabricated with a compact size of 11.25 mm $\times$ 16 mm on YBa2Cu3O7 films. The power handling capability of the filter is studied. Finally, the measured and simulated results are in good agreement with each other. [ABSTRACT FROM PUBLISHER]

A balanced tri-band bandpass filter (BPF) is proposed based on octo-section stepped-impedance ring resonator (SIRR). The relation and design graphs between the differential-mode (DM) and common-mode (CM) characteristics with different physical parameters are analyzed. It reveals that the proposed SIRR has more degrees of freedom in controlling DM and CM characteristics for tri-band design with excellent out-of-band performances and high CM suppression. Moreover, the SIRR is loaded by open stubs with different lengths to further improve the CM suppression. Finally, a balanced tri-band BPF prototype is fabricated and measured. Good agreement between simulated and experimental results verifies this design method. [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]

A compact quad‐channel high‐temperature superconducting diplexer based on stub‐loaded square ring resonator (S‐LSRR) is proposed. The proposed resonator consists of a square ring with symmetrically loaded two open‐circuited stubs and provides four resonant modes for quad‐channel applications. Even‐ and odd‐mode methods are applied to analyze the S‐LSRR. Analytical study shows that four resonant modes of one S‐LSRR can be designed in two pairs and applied to construct two of four channels of the designed diplexer. A square patch is added to the resonator for providing an additional parameter to tune the resonant modes. Based on the proposed resonator, a quad‐channel diplexer with center frequencies of 2.4, 3.2, 3.9, and 5.6 GHz is designed. For demonstration, the diplexer is fabricated on 2‐in‐diameter 0.5 mm‐thick MgO wafer with double sided YBa2Cu3Oy films and measured at 77 K. Good agreement between the simulation and measurement is obtained. The diplexer has a compact size of 0.25 λg × 0.45 λg, where λg is guided wave length at the center frequency of first channel. [ABSTRACT FROM AUTHOR]

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]