A Frequency-Reconfigurable Microstrip Antenna with Constant Dipole-Like Radiation Patterns Using Single Bias, Triple Varactor Tuning with Reduced Complexity

This work proposes a novel frequency-reconfigurable circular patch antenna incorporated with a rectangular slot and a narrow slot capable of producing constant dipole-like radiation patterns. The antenna compactness is achieved with the integration of the rectangular slot defected ground structure (DGS) on the ground. The proposed antenna is able to perform continuous frequency tuning between 1.91 and 2.77 GHz with a frequency ratio of 1.5:1, in addition to stable dipole-like radiation patterns. The resonant frequency of the antenna is controlled by tuning a simple DC biasing network that consists of three RF varactor diodes located on the narrow slot DGS. Implementing the DC biasing network at the narrow slot DGS while maintaining the large slot DGS helps the antenna miniaturization and maintains the constant dipole-like radiation pattern over all frequency tuning range. The results are validated via simulations and experimental validations in terms of reflection coefficients and the radiation patterns. Measurements indicated that an impedance bandwidth of 85 MHz is featured for each tuned frequency band, with dipole-like patterns and an average gain of 1.57 dBi.