This paper presents a novel method to enhance the quality factor of a simple square resonator designed using Substrate Integrated Waveguide (SIW) technology, while maintaining cost-efficiency and compactness. Our approach leverages parallelized microwave cavities suitable for high-frequency, low phase noise Voltage-Controlled Oscillators (VCOs) used in fifth generation (5G) and Global Navigation Satellite System (GNSS) applications. Modern communication and navigation systems demand precise frequency and timing systems featuring low phase noise performance, compact size, and cost-efficiency. To reduce the need for high manufacturing precision, we incorporated tuning capability into our microwave resonator without compromising performance characteristics. The proposed resonator achieves a competitive loaded quality factor of approximately 150 at 6.8 GHz, with an insertion loss of about 5.5 dB. Its occupied area is about , which is an appealing feature for high-frequency applications. Our method enables improved quality factor through increasing the number of resonating microwave layers within the same occupied area. The central resonance frequency can be adjusted via a DC-biasing circuit that controls a varactor capacitor, providing a tuning range of 250 MHz.

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