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. They array provides resonance at 5.2 GHz frequency for its fundamental mode (TM10 mode). Beside this fundamental mode, two harmonics at 10.4 GHz (1st harmonic) and 15.05 GHz (2nd harmonic) and few sub-harmonics at 7.8 GHz (TM12), 8.8 GHz (TM22), and 13.3 GHz (TM32) are excited. In order to suppress 1st harmonic, a pair of half wavelength open ended stubs (pair of stub-A) whereas for 2nd harmonic a pair of quarter wavelength open ended stubs (pair of stub-B) are employed. From the simulated results it is 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.
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