Frequency Tunable Differentially Fed Inverted Microstrip Patch Antenna with Low Cross-Polarized Radiation

Abstract

In this article tunable characteristic of differentially fed inverted microstrip patch antenna is presented for C-band operation. Differential feeding is applied through a unilayer integrated coupler feed. Near the operating frequency of the designed antenna the fabricated coupler shows that the amplitude imbalance is 0.3 dB and phase imbalance corresponds to 3.2°. Tuning is achieved by changing the air gap height in the antenna structure from 1 to 4 mm. Proposed concept of tunablity is verified for two different patch geometries (circular and rectangular) and three different patch dimensions through analysis and experiments. Closed form expressions are proposed to predict the tuning frequency. This design offers low cross-polarized radiation in the H-plane and symmetric co-polarized radiation in both principal planes. Fabricated prototype is measured and compared with simulated and theoretical values. The comparison among the simulated values, theoretically computed values and the measured values for different air gap heights of 2, 3, and 4 mm, shows an error less than 1%.