Varactor-Based Frequency-Reconfigurable Dual-Polarized mm-Wave Antenna Array for Mobile Devices

Abstract

In this article, a dual-polarized frequency-reconfigurable mm-wave patch antenna array is described. The design incorporates varactor diodes (VDs) symmetrically loaded onto the four corners of a square patch. Parallel plate series capacitors are constructed to achieve the required low total capacitance by moving the square patch to an inner layer. Additionally, novel dual-function shorting vias are implemented into the structure, which serves as an RF choke for providing dc-bias voltage to the varactors and behave as shunt inductive loadings to improve radiation efficiency. A four-element antenna array is implemented and placed into a $21 \times 4.5$ mm2 cavity. The proposed antenna array can be tuned from 23.2 to 30.2 GHz by adjusting the varactor capacitance from 0.22 to 0.033 pF. The array achieves over 20-dB isolation between the orthogonal-polarized antenna elements and more than 15-dB isolation between the same-polarized antenna elements. Total efficiency exceeds -2.5 dB across the tuning range. Peak gain varies from 8.9 to 10.5 dBi. The proposed dual-polarized antenna array offers notable advantages including a wide frequency-tuning range, high efficiency, compact size, and beam-forming capability.