Suppression of Higher Order Modes of a Two Element Microstrip Array Using Open-Ended Stubs

Abstract

In this paper suppression of higher order modes of a microstrip antenna array is investigated. The array consists of two radiating elements which are fed by a corporate type microstrip feeding network. The array provides resonance at 5.2 GHz frequency for its fundamental mode (TM 10 mode). Beside this fundamental mode, two harmonics at 10.4 GHz (1st harmonic) and 15.05 GHz (2nd harmonic) and a few sub-harmonics at 7.8 GHz (TM 01), 8.8 GHz (TM 11), and 13.3 GHz (TM 12) are excited. In order to suppress the 1st harmonics, a pair of half wavelength open ended stubs whereas for 2nd harmonic a pair of quarter wavelength open ended stubs are employed. From the simulated results it has been noticed that the 1st and 2nd harmonics are successfully suppressed, and the sub-harmonics are also suppressed. Prototypes of the antenna arrays are fabricated and measured. Measured results have good agreement with simulated ones.