Frequency control of a circularly-polarized ring microstrip antenna fed by an L-probe with four varactor diodes

Authors:
Publisher website
Google Scholar
Abstract
This paper presents basic operation of a frequency-tunable circularly-polarized ring microstrip antenna (MSA) fed by an L-probe with four varactor diodes. In order to develop a frequency-tunable circularly-polarized MSA, four varactor diodes are mounted on the corners of a square ring patch element. An L-shaped probe is arranged under the ring patch to excite the ring patch from a 50Q feeding coaxial cable. When two DC bias voltages applied for two varactor diodes on the adjacent corners of the ring patch are changed, resonant frequencies of two orthogonal modes of the ring patch can be controlled independently. Therefore, by tuning the appropriate combination of the two DC bias voltages, the frequency of circular polarization of the ring MSA can be changed. When the two DC bias voltages are changed within 0V to 8V, respectively, the measured circularly-polarized frequency with an axial ratio less than 3 dB of the ring MSA can be controlled from 3.32 to 3.59 GHz.