Filtering Crossover Research Articles

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter with all common mode suppression

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter (BPF) is proposed and demonstrated in this paper. The reflectionless balanced BPF is comprised of two hybrid couplers and a filtering crossover. The filtering crossover is composed by a dual-mode ring resonator coupled with four short-circuited open-loop resonators, which is used to replace the traditional two BPFs for reduction of interference. Hybrid couplers are used for absorbing the reflected interference to the input and output ports. In order to achieve common-mode (CM) suppression, a double-layer structure with the same microstrip configuration on the upper and lower surfaces is adopted. The absorption characteristics of the differential mode (DM) and CM signals are optimized by hybrid couplers with improved ground. A third-order quasi-reflectionless balanced BPF with central frequency of 2.3 GHz and fractional bandwidth of 14 % is designed, fabricated, and measured. The final measured results demonstrate great consistency with the simulated ones.

Third‐order filtering crossover using dual‐mode resonator for high‐isolated channels

SummaryThis paper proposes a high‐selective crossover with a third‐order filtering characteristic, high passband isolation, and multiple controllable transmission zeros based on a coupled topology using single‐ and dual‐mode resonators. By virtue of the odd‐ and even‐mode feature of the stub‐loaded dual‐mode ring resonator, not only can the two resonant modes for different passbands be relatively independently controlled, but also better isolation can be achieved. With a single‐mode resonator and stub‐loaded dual‐mode resonant coupling topology, the resultant crossover can perform third‐order filtering performance in two distinct passbands/channels and generate several transmission zeros outside the desired bands to improve the isolation between the passbands. Experimental results demonstrate that, compared with conventional works, the filtering order of the proposed crossover is promoted and its passband isolation can be significantly improved by about 8 dB. The proposed work may facilitate its widespread applications in high‐performance multichannel integrated microwave systems for avoiding interference between multiple intersecting signal paths.

A Novel 1.7–2.85-GHz Filtering Crossover With Independently Tuned Channel Passbands and Reconfigurable Filtering Power-Dividing Function

In this article, a novel filtering crossover with independently tuned channel passbands and reconfigurable filtering power divider (PD) function based on evanescent-mode cavity (EVA) is proposed for the first time. It consists of four substrate-integrated-waveguide (SIW) EVA resonators loaded with piezoelectric actuators for frequency tuning. Four sets of varactors are used between adjacent resonators for control of interstage coupling, whereas four sets of varactors are inserted between ports and resonators for input-output matching. By controlling resonant frequencies of the EVA resonators and coupling coefficients between adjacent resonators, the passbands of the two orthogonal channels in the filtering crossover can be independently tuned in either synchronous or asynchronous fashion within the frequency range of 1.7-2.81 GHz. Meanwhile, by detuning the resonant frequency of one resonator in the crossover, the proposed structure can be reconfigured to become a three-port filtering PD with continuous frequency tuning covering 1.7-2.85 GHz. Moreover, with the independently tuned feature, a filter with reconfigurable filtering PD and diplexer functions can be easily achieved by attaching the proposed crossover to an external matching junction. Several prototypes were given to demonstrate the proposed techniques. Good agreement is obtained between simulated and measured results.

Compact-Balanced BPF and Filtering Crossover With Intrinsic Common-Mode Suppression Using Single-Layered SIW Cavity

In this letter, compact-balanced bandpass filter (BPF) and filtering crossover are proposed with intrinsic common-mode (CM) suppression by using a single-layered substrate-integrated waveguide (SIW) cavity. The SIW cavity with low profile is TEn0m mode resonator, which has only one nonzero electric field component. Hence, it is also a natural frequency selection device of the differential signal. Meanwhile, the CM signal cannot excite the cavity due to the characteristics of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). For the design of the balanced SIW BPF, the differential-mode (DM) equivalent half circuit is a single-ended SIW filter with height halved. Furthermore, the microstrip differential transition structure is designed to excite the SIW cavity and has little conversion between DM and CM. On this basis, a compact SIW-balanced filtering crossover is proposed using the degenerate modes TE102 and TE201. Finally, compact third-order SIW-balanced BPF and filtering crossover are designed and fabricated, and the measured results show good agreement with the simulated ones.

Approach for filtering crossover design using mixed electric and magnetic coupling

A new approach for the filtering crossover design is proposed in this Letter. This approach is based on the mixed electric and magnetic coupling. A compact filtering crossover constructed by the short stub loaded resonator is presented according to the proposed approach. By using a short stub loaded resonator the filtering response is achieved and by using the cancelling effect between the electric coupling and magnetic coupling, the isolation between two signal paths is achieved. A filtering crossover is fabricated for demonstration. The measured result presents good agreement with the simulated result.

Novel Substrate Integrated Waveguide Filtering Crossover Using Orthogonal Degenerate Modes

A novel substrate integrated waveguide (SIW) filtering crossover is presented based on the orthogonal degenerate TE201 and TE102 modes in SIW square cavities. By arranging the feeding ports and coupling windows at the cavity center, excellent transmission and isolation responses can be achieved successfully. In addition, the bandwidth of the crossover can be easily controlled using the well-established coupling matrix synthesis method, and the maximum bandwidth is determined by the acceptable isolation levels. A prototype operating at 20 GHz was designed and fabricated to verify this concept, and the measured results are in excellent agreement with the simulation results.

Patch crossover with bandpass filtering function

ABSTRACTFiltering patch crossovers with single‐ and dual‐band operation are implemented for the first time. For the single‐band filtering crossover, it is composed of four inset fed input/output ports and a circular patch. The dual‐band property can be easily realized with high flexibility by loading four open stubs. To verify the design concept, three filtering crossovers are implemented. The measured results agree well with the simulation, exhibiting crossover characteristics throughout the specific passband and high rejection level within the suppression band. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:301–304, 2016