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A compact filtering switch with wide-stopband responses is presented in this paper. The resonator is designed using microstrip transmission lines and lumped capacitors. It is utilized to shift up the second harmonic frequency for wide-stopband performance and miniaturize the circuit size. In the ON-state, the circuit is the same as the bandpass filter without signals passing through the p-i-n diode, which avoids additional loss introduced by p-i-n diode. Two transmission zeros are generated near the passband to enhance the skirt selectivity. In the off-state, the signals from port 1 to port 2 passing through different transmission path are cancelled out, resulting in high isolation. For demonstration, a filtering switch operating at 780 MHz is implemented with the compact size of 0.072λg×0.066λg. More than 20-dB suppression levels are measured from 0.89 to 5.3 GHz (6.8 f0), featuring wide-stopband responses.

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]

This paper presents a compact power divider with wide-stopband bandpass responses. In the proposed circuit, two identical quarter-wavelength resonators are symmetrically coupled to a stub-loaded resonator to enable dual functions. Discriminating coupling is employed to suppress the third harmonic. By introducing series-connected two capacitors and one resistor, the isolation is enhanced to more than 20 dB. For demonstration, a filtering power divider operating at 2.4 GHz is designed and fabricated. Good agreement is observed between the measured and simulated results. [ABSTRACT FROM AUTHOR]