Frequency and polarization tuning of a cross patch antenna using capacitive loading

A novel compact dual frequency reconfigurable microstrip antenna achieving polarization tuning by loading a single chip capacitor is presented. A cross shaped patch antenna with an X-slot constitutes the fundamental structure of the antenna. The tuning of the two resonant frequencies is realized by varying the effective electrical length of the slot with an embedded capacitor at the centre of the X-slot. A high tuning range of 34.48% (672- 952 MHz) and 14.3% (1.5145-1.748 GHz) is achieved for the first and third resonant frequencies respectively while minimizing variations of the second resonant frequency. Measured and simulated results of the antenna indicate that the frequency ratio can assume any value in the range 1.025 ≤ f_R ≤ 1.21 with linear or circularly polarized radiation by changing the capacitor value from 1 pF to 100 pF. Furthermore, the proposed antenna offers moderate gain with low cross-polarized radiation and the radiation patterns of each frequency remain unchanged as the capacitor value is changed.