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Summary: This paper proposes a wideband quasi‐reflectionless bandpass filter with high‐selectivity based on signal‐interference method. The bandpass filter is composed of a bandpass section and two absorptive sections, which consist of a quarter‐wavelength coupled line and signal‐interfering/resistively loaded path, respectively. The bandpass section mainly performs bandpass filtering characteristics while the absorptive sections are applied to consume the reflected signals. By virtue of rationally setting electric lengths and characteristic impedances of the absorptive section to form signal interference, signal dissipation within a wider frequency range and higher selectivity can be realized. Finally, the quasi‐reflectionless bandpass filter was designed and demonstrated with well‐matched measurement and simulation results. Compared with conventional works, the proposed bandpass filter can simultaneously attain wideband, high‐selectivity, and two‐port quasi‐reflectionless performance within a single‐layer topology and well‐integrated structure owing to the signal‐interference technology. The proposed technique may be extensively applied in the RF front‐end and decreases the effect on the stability of communication systems caused by reflected signal. [ABSTRACT FROM AUTHOR]

Summary: This 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. [ABSTRACT FROM AUTHOR]

In this study, a class of wideband bandstop filters is proposed based on wideband 180° phase shifters. Different from traditional signal–interference-based bandstop filters, they make use of a 180° phase shifting in a wide operating band in principle. After numerical analysis of the phase responses of the two coupling-line paths, the optimal solutions for the largest 180° phase-shifting bandwidth or minimum impedance ratio can be obtained. Then, the wideband bandstop filter based on these two unique coupling lines is intensively analysed to reveal that three transmission zeros are generated in the stopband as the two paths have a 180° phase difference, thus exhibiting its wideband property. Moreover, by enlarging the impedance of the two paths, good out-of-band characteristics of the bandstop filter can be attained, while in-band performances are almost unchanged. Next, two types of bandstop filters with extended bandwidth are proposed by cascading an extra delay line for both paths, and they hold similar filtering characteristics as the aforementioned one. Finally, the design process and demonstration are provided. The measured results of the three fabricated filters show that Type-I, Type-II, and Type-III filters can satisfactorily obtain a 3 dB bandwidth of 108, 122, and 130% with 25, 14.7, and 11.6 dB rejection level, respectively. [ABSTRACT FROM AUTHOR]

In this study, a class of wideband bandstop filters is proposed based on wideband 180° phase shifters. Different from traditional signal–interference‐based bandstop filters, they make use of a 180° phase shifting in a wide operating band in principle. After numerical analysis of the phase responses of the two coupling‐line paths, the optimal solutions for the largest 180° phase‐shifting bandwidth or minimum impedance ratio can be obtained. Then, the wideband bandstop filter based on these two unique coupling lines is intensively analysed to reveal that three transmission zeros are generated in the stopband as the two paths have a 180° phase difference, thus exhibiting its wideband property. Moreover, by enlarging the impedance of the two paths, good out‐of‐band characteristics of the bandstop filter can be attained, while in‐band performances are almost unchanged. Next, two types of bandstop filters with extended bandwidth are proposed by cascading an extra delay line for both paths, and they hold similar filtering characteristics as the aforementioned one. Finally, the design process and demonstration are provided. The measured results of the three fabricated filters show that Type‐I, Type‐II, and Type‐III filters can satisfactorily obtain a 3 dB bandwidth of 108, 122, and 130% with 25, 14.7, and 11.6 dB rejection level, respectively. [ABSTRACT FROM AUTHOR]

In this letter, a pin‐loaded triple‐mode square patch resonator is proposed for bandpass filter (BPF) design. By loading short‐circuited pins underneath the patch, the patch resonator not only enables DC‐blocking, but also brings out one additional resonant mode, thus a triple‐mode patch resonator can be formed up under operation with a pair of degenerate modes. According to the field distributions, these three resonant modes can be tuned by virtue of loaded slots and pins, while these two degenerate modes can be properly split by offset‐positioning the two sets of pins. In final, a pin‐loaded triple‐mode patch BPF is designed, fabricated and measured to validate the predicted results. [ABSTRACT FROM AUTHOR]

ABSTRACT A sharp-rejection dual-band bandstop filter using transversal signal-interaction with three paths, consisting of a transmission line path and two coupled paths, is proposed. By tuning the coupling coefficient and odd-mode impedance of the coupled lines, the center frequency ratio and bandwidth can be controlled, respectively, and the transmission line impedance is used to allocate the transmission poles to sharp the attenuation rate. A compact dual-band bandstop filter prototype is designed and fabricated. The simulation and measurement results agree well. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:657-660, 2015 [ABSTRACT FROM AUTHOR]

Summary: A tunable circularly polarized square patch antenna with parasitic elements is designed for a wide frequency tuning range and high gain characteristics. The proposed antenna is constructed by one main patch and four semi‐elliptic parasitic units. By loading four varactor diodes and adjusting their capacitance values, the tunable feature is performed to reallocate the corresponding working frequency. Moreover, the diagonal corners of the antenna are cut and loaded with varactor diodes, which provide the appropriate perturbation between the two orthogonality modes of the antenna, so as to ensure the circular polarization characteristic in the entire operating tuning band. The experimental results demonstrate that the reflection coefficient and axial ratio are less than −13 dB and 3 dB, respectively. The proposed antenna features a relatively wide continuously tuning range of 24% within 1.9‐2.3 GHz and a stable gain of over 7 dBi with a radiation efficiency of above 85%. [ABSTRACT FROM AUTHOR]