No abstract

Novel compact microstrip quint‐mode multi‐stub‐loaded resonator has been investigated. Meanwhile, its applications to the dual‐band bandpass filter (BPF) and quad‐channel diplexer have also been proposed. The proposed dual‐band BPF is constructed by a single quint‐mode resonator, leading to a very small circuit size. Herein, the first three resonant modes are used to form the first passband, while the other two are used to form the second passband. Besides, the proposed quad‐channel diplexer is constructed by two different quint‐mode resonators, which also occupies a very small circuit size. In this diplexer design, one of the quint‐mode resonator is used to realise the passbands for channels 1 and 3, and the other one is used to realise the passbands for channels 2 and 4. For demonstration, a dual‐band BPF operating at 0.9 and 2.2 GHz with a size of 0.17λg × 0.23λg and a quad‐channel diplexer operating at 0.9, 1.45, 2.1, and 2.7 GHz with a size of 0.28λg × 0.23λg have been designed, fabricated, and measured. The electromagnetic simulated and measured results are in good agreement.

Microstrip dual-and triple-band bandpass filters (BPFs) exhibiting an ultracompact size and high frequency selectivity are proposed in this study. A common resonator feeding technique is proposed and was applied to design the multiband BPFs. In the design, the first and last resonators are realised using stepped-impedance resonators and are used to form a passband that has lower operating frequencies than the passband(s) of other resonator(s). Moreover, the first and last resonators serve as the input-output feeding structure and provide a source-load coupling for the passband(s) operating at higher frequencies. Thus, finite transmission zeros can be formed over the stopband. Hence, size miniaturisation and high frequency selectivity can be achieved simultaneously. The higher operating passband(s) is (are) formed by the dual-mode stub-loaded resonator(s) to reduce the number of resonators and the overall size of a filter. To verify the design approach, a dual-band BPF centred at 1.3 and 2.58 GHz with an ultracompact circuit size of 0.048 λ g × 0.088 λ g (λ g : guided wavelength at the central frequency of the lower passband) and a triple-band BPF centred at 1.24, 2.5, and 3.5 GHz with an ultracompact circuit size of 0.15 λ g × 0.12 λ g were designed and fabricated. The measurement and electromagnetic simulation results were in good agreement.

The design of filtering 180 • hybrids with arbitrary power division and filtering response (filter order) is proposed in this paper. By integrating a 180 • hybrid and bandpass filters into a single component, the overall circuit size can be reduced. The design theory based on the coupled resonator technique was detailed and validated experimentally through the fabrication of the third-order filtering 180 • hybrid with a 0-dB power-dividing ratio and the second-order filtering 180 • hybrid with a 6-dB power-dividing ratio. The power-dividing ratio can be arbitrarily determined through proper design of the coupling coefficients between the resonators. In addition, net-type resonators were selected to ensure compactness of the filtering 180 • hybrids. The prototype sizes of the two example circuits were only approximately 0.25λ g × 0.12λ g and 0.12λ g × 0.12λ g , demonstrating highly compact circuit sizes. Moreover, isolations better than 30 and 21 dB within the operating passbands for the two circuits were achieved. INDEX TERMS 180-degree hybrids, arbitrary power division, bandpass filters (BPFs), microstrip.

A compact eight‐channel multiplexer with independently switchable passbands has been presented and investigated. The use of the dual‐mode stub‐loaded resonators can lead to significant size reduction for the multiplexer, this is because the required resonator number is reduced. In addition, the multiplexer is designed based on the distributed coupling technique, so that each passband can be designed individually due to the loading effect is small. Moreover, the complicated nine‐port matching network at the input is not required. Besides, since the p‐i‐n diodes are connected to the output resonators for each channel, all passbands of the multiplexer can be independently switched on and off when the diode is in the reverse‐biased and forward‐biased states, respectively. Therefore, the proposed multiplexer can arbitrarily transfer to a single‐band bandpass filter, a diplexer, a triplexer, a quadruplexer, a quinqueplexer, a sexaplexer, a septiplexer, and an octoplexer. For a demonstration, an eight‐channel multiplexer with the second‐order bandpass response have been designed and fabricated with microstrip in printed circuit board. The measured results are in good agreement with the full‐wave simulation results.