Search

In this brief, compact multi-channel bandpass filters and diplexers are proposed based on dual-coaxial resonators. One coaxial resonator is embedded into the other to form a dual-mode resonator without increasing the size, where the resonant section of one resonator acts as the shielding cavity of the other one. In this way, the two modes of the dual-coaxial resonator are ideally isolated and can be controlled independently. By properly designing the feeding and coupling structures between resonators, the two modes in one dual-coaxial resonator can be excited and coupled to construct different filter channels without influencing each other. Accordingly, multi-channel filters are realized. For verification, a dual-channel and a triple-channel filters are presented. Moreover, the filter channels in a dual-channel filter can be applied to design the diplexer, resulting in a compact size. Experimental results are presented with good in-band responses and high isolation. [ABSTRACT FROM AUTHOR]

In this article, quarter-mode substrate-integrated waveguide (QMSIW) filters featuring ultrawide stopband and flexibly allocated transmission zeros (TZs) are proposed. Eight higher modes with resonant frequencies up to 4.7 times of the fundamental mode are highly suppressed. It is realized by the combination of three approaches without extra circuit areas. First, a slot is cut in the first and last QMSIW resonators to make their resonant frequencies of higher modes different from those of other resonators. Second, avoid exciting the specific higher modes by setting the feed point in the area where the electric field strength of the higher modes is weak. Third, mismatch the higher modes when matching the passband. It is realized by using a stripline impedance transformer with its main body not exceeding the area of QMSIW resonators. Furthermore, except for the TZs derived by the classical cross-coupling matrix, two more independently controlled TZs are generated. The packaged filter is fabricated by using a benzocyclobutene (BCB)-based microelectromechanical systems (MEMS) process, which is suitable for millimeter-wave 3-D system-on-package (SOP) applications. The fabricated thin-film filter is measured with an insertion loss of 2.96 dB at 29.4 GHz and a fractional bandwidth (BW) of 17%. Higher mode suppressions up to 138.3 GHz are achieved. [ABSTRACT FROM AUTHOR]

In this brief, substrate integrated waveguide (SIW) multi-channel filtering crossovers are proposed for two sets of intersecting signals operating at the same or different frequencies. The number of filtering channels in two directions can be independently extended. Square SIW cavities with TE102 and TE201 modes are used as building blocks. By properly arranging feeding ports and coupling regions, isolation between different channels is achieved and bandpass responses are integrated. The design procedure can be simplified as that of single-channel bandpass filter. For demonstration, a six- and a five-channel filtering crossovers with the same operating frequency in two directions are designed and fabricated. By etching a slot on the square SIW cavity, the TE102 and TE201 modes are split and thus the frequencies can be controlled. A four-channel filtering crossover with different operating frequencies in two directions is implemented for further verification. Compared to other multi-channel crossovers, the proposed designs feature good inter-channel isolation and intra-channel filtering responses with flexibly extended channel number and controllable frequencies. [ABSTRACT FROM AUTHOR]

This paper presents a method for designing low-loss varactor-based tunable bandpass filters (BPFs) with constant absolute bandwidth (CABW) and wide tuning range based on coaxial resonators. The whole structure consists of a metallic cavity and a piece of printed circuit board (PCB). Varactors and their biasing components are mounted on the PCB, which are connected to the coaxial resonators to enable frequency tuning. The coupling control between coaxial resonators and the nonsynchronous tuning of the resonators are utilized to realize the CABW over a wide tuning range. Moreover, transmission zeros are generated near the passband, resulting in high skirt selectivity. For demonstration, a second-order tunable coaxial BPF with a wide tuning range from 698 to 960 MHz (31.5%) is designed and fabricated. Due to the use of high- $Q$ -factor coaxial resonators, the proposed tunable filter realizes low insertion losses ranging from 0.82 to 2.03 dB under a narrowband specification. The 1-dB bandwidth is measured as 35.3 ± 2.7 MHz, showing excellent CABW responses. Moreover, a third-order tunable coaxial BPF is also designed and implemented with enhanced skirt selectivity and out-of-band rejection. Comparison with other reported tunable BPFs is given, where the proposed designs show excellent performance of wide tuning range, CABW, high selectivity, and high tuning speed. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for designing a dual-channel balanced filter and a dual-channel balun filter based on the quad-mode dielectric resonator (DR) for the first time. By sharing one common quad-mode DR, two balanced filters or two balun filters are integrated as one single-cavity configuration, featuring compact size and high integration. A cylindrical DR with two short ends is investigated to construct the quad-mode DR. By properly arranging input and output feeding probes, two modes of the DR are only excited by the feeding probes of one channel and the other two modes are excited by that of the other channel. Accordingly, signals cannot be transmitted between the two channels, resulting in high isolation. Moreover, the required out-of-phase characteristics of the balanced and balun filters can be obtained by the inherent electromagnetic field properties of the DR without adding additional circuits, featuring a simple structure. For demonstration, a dual-channel balanced filter and a dual-channel balun filter are designed and fabricated, showing excellent balanced or balun filter performance of each channel as well as high isolation between the two channels. As compared to the other reported DR balanced and balun filters, the proposed designs exhibit a significant size reduction, which are attractive in wireless systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for designing the narrowband filtering rat-race couplers using the quad-mode dielectric resonator (DR) for the first time. The filtering rat-race couplers are designed in single-cavity configuration with one quad-mode DR and four feeding probes, featuring compact size. Based on the investigation on resonant frequencies of a rectangular DR, a quad-mode DR is first constructed. Electromagnetic (EM) field distributions at two resonant mode pairs are studied for guiding the filtering rat-race DR coupler realization. The desired 0° and 180° phase differences of the rat-race coupler are realized by the inherent in-phase and out-of-phase EM-fields of the DR. By properly arranging the four feeding probes, the single-cavity configuration is designed to fulfill the transmission characteristics of a rat-race coupler topology, such as the magnitude and phase properties. The detailed design method is presented. For demonstration, a filtering rat-race coupler based on the rectangular DR is fabricated and measured, showing excellent performance of filtering responses, amplitude balance, as well as the 0° and 180° phase differences. Moreover, the other filtering rat-race coupler is implemented by using a cylindrical DR with an improved $Q$ -factor. Comparison with other reported filtering couplers indicates that proposed designs exhibit the advantages of compact size, high $Q$ -factor, and good filtering responses. [ABSTRACT FROM AUTHOR]

In this paper, a dual-channel dielectric resonator (DR) filter is presented for the first time. Two bandpass filters (BPFs) are integrated as one dual-channel filter with two input ports and two output ports. By using a common quad-mode DR shared by two second-order BPFs, only one metallic cavity is needed, which greatly reduces the circuit size. Frequency control of the DR is investigated and electromagnetic field properties at HEH11 and HEE11 resonant pairs are studied for guiding the dual-channel filter realization. By properly arranging the input and output feeding probes, two of the resonant modes are excited for one channel and other two for the other channel. Since the feeding probes of one channel filter do not excite the resonant modes of the other one, isolation between two filters is achieved. Three transmission zeros are generated near the passband, resulting in high selectivity. For verification, the dual-channel filter is implemented, which features good bandpass responses and offers a significant size reduction in comparison with conventional two DR filters. What is more, the dual-channel filter with the impedance transformation function is integrated with a $2 \times 2$ Doherty power amplifier for 5G massive multiple-input multiple-output system application, featuring high efficiency, good filtering responses, and high integration. [ABSTRACT FROM AUTHOR]

In this paper, a low-temperature co-fired ceramic (LTCC) diplexer is presented with compact size and high isolation. By using the common stub-loaded resonator shared by two channel filters, combining and matching networks are eliminated and only three resonators are used to design the two second-order channel filters, resulting in simple structure and miniaturized size. A novel transmission path is utilized to not only realize the higher channel filter but also prevent the signal at the lower frequency band. And a specific coupling region is selected to simultaneously realize the coupling strength required by lower channel filter and a transmission zero at higher-band frequency. In this way, each channel filter can generate a transmission zero at the passband frequency of the other channel filter, resulting in high isolation. Moreover, the bandwidths and center frequencies of the two channel filters can be individually controlled due to the design flexibility of the multilayer LTCC structure. For demonstration, a diplexer operating at 3.5 and 5.5 GHz is fabricated. The core circuit has the compact size of 1.9 mm $\times1.7$ mm \times2$ mm or 0.054~\lambda _{g} \times 0.048 \lambda _{g} \times 0.057~\lambda _{g} . Within the 3-dB passbands of the lower and higher channel filters, the measured isolation levels are better than 40 and 45 dB, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a new method of using electric and magnetic coupling cancellation to extend the stopband of bandpass filters (BPFs). The mechanism is theoretically analyzed based on the lumped-element equivalent circuit. Due to the cancellation of electric and magnetic coupling between two resonators, three transmission zeros (TZs) can be generated and controlled by manipulating the coupling strength. Using the proposed method together with source–load coupling, a low temperature cofire ceramic (LTCC) BPF is designed with four TZs at the passband edges and within the stopband, resulting in high skirt selectivity and harmonic suppression. Due to the LTCC multilayer structure, the filter size is 0.054 \(\lambda _{g}* 0.045 \lambda _{g}*0.013\lambda _{g}\) , or \(2.48~{\rm mm}\times 2.02~ {\rm mm}\times 0.6\) mm. The theoretical, simulated and measured results of the LTCC BPF are presented to validate the proposed design. [ABSTRACT FROM AUTHOR]

This letter presents a novel compact quad-band bandpass filter (BPF) with controllable operating frequencies and bandwidths. The proposed filter utilizes a novel second-order multi-stub-loaded resonator with four modes. Theoretical analysis indicates that the four modes can be controlled individually, resulting in controllable operating frequencies. Meanwhile, by controlling external quality factors and coupling coefficients, the bandwidths can also be adjusted individually. To validate the proposed idea, an experimental filter is implemented. Good agreement between the predicted and measured results demonstrates the proposed idea. [ABSTRACT FROM PUBLISHER]