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A standard substrate integrated waveguide (SIW)-based bandpass filter (BPF) suffers from bulkiness that limits its application in the implementation of compact size low phase noise oscillator. Instead, in this letter, an eighth mode SIW (EMSIW) resonator-based BPF is utilized to realize a miniaturized low phase noise oscillator for $X$ -band applications. Additionally, an equivalent circuit model of EMSIW-BPF is presented. A compact feedback-type oscillator prototype using EMSIW-BPF is designed and fabricated for the first time with a circuit area of just 1092 mm2. The experimental results of the prototype show a phase noise of −126.13 dBc/Hz at 1 MHz offset from 9.97 GHz oscillation frequency with an output power of 3.17 dBm.

Generally, a conventional voltage doubler circuit possesses a large variation of its input impedance over the bandwidth, which results in limited bandwidth and low RF-dc conversion efficiency. A basic aspect for designing wideband voltage doubler rectifiers is the use of complex matching circuits to achieve decade and octave impedance and RF-dc conversion efficiency bandwidths. Still, the reported techniques till now have been accompanied by a large fluctuation of the RF-dc conversion efficiency over the operating bandwidth. In this paper, we propose a novel rectification circuit with minimal inter-stage matching that consists of a single short-circuit stub and a virtual battery, which contributes negligible losses and overcomes these existing problems. Consequently, the proposed rectifier circuit achieves a diode physical-limit-bandwidth efficient rectification. In other words, the rectification bandwidth, as well as the peak efficiency, are controlled by the length of the stub and the physical limitation of the diodes.

This paper presents a C-band low phase noise oscillator using small size low-profile substrate integrated waveguide (SIW) resonator for RF applications. A compact 6 GHz SIW resonator size is possible by introducing λ g /4 resonating slots. A size reduction of 29.87% is achieved while maintaining the quality factor. Also, the impedance of the SIW resonator is controlled by appropriate selection of the location of these introduced slots; which advantages for the conjugate matching between SIW resonator and the active device and removes the need of matching circuit between them. Then, a C-band oscillator prototype utilizing the proposed compact SIW resonator is designed, fabricated and measured. The measured results shows a phase noise of -122.11 dBc/Hz at 1 MHz offset with an output power of -4.2 dBm at 5.96 GHz oscillation frequency.