Enabling an On-Demand Frequency Doubling Mechanism Through a Capacitively Loaded Miniaturized Diplexer

This paper presents a diplexer design that generates a pair of fundamental and harmonic frequencies. The diplexer is based on a capacitively loaded resonator that is able to reconfigure its frequency pair with respect to capacitive loading. The system shows a fundamental and harmonic frequency pair of 5 GHz and 10 GHz without any capacitive loading and 2.5 GHz and 5 GHz when loaded with a 1pF/0.5 pF capacitor pair. The complete system is fabricated and tested where good agreement is obtained between the measured and computed results. The testing is performed for the two states of the diplexer, when the diplexer is unloaded and after loading it with the capacitor pairs. For both unloaded and loaded scenarios, the proposed design produces a maximum insertion loss of 0.6 dB with an isolation of at least 35 dB at the corresponding operational frequencies. The structure is also able to provide a minimum return loss of 25 dB at each port. The proposed diplexer is then integrated with a frequency doubler chip and the full system maintains an acceptable efficiency along with a high conversion gain of approximately 15 dB.