Control of Higher Order Modes and Their Radiation in Microstrip Antenna Using Extremely Compact Defected Ground Structure & Symmetric Stub

Suppression of the radiation from higher order modes requires the elimination of those modes. In this paper, the elimination has been implemented with a novel miniaturized low pass filter (LPF) with high filter selectivity and wide stop band. Here, the fundamental operating frequency of the antenna falls in the pass band of the LPF. The attenuation of other higher order mode occurs since their frequencies fall in the LPF stop band. In this paper suppression has been carried out by using this LPF on antenna feed line. A successful demonstration has been presented to control the occurrence of higher order modes up to the second harmonic of the fundamental resonant frequency in a microstrip antenna. A miniaturized hair pin type defected ground structure (DGS) has been integrated to obtain elimination of higher order modes in the antenna at its microstrip feed level. A rectangular spiral type stub has been added to the feed line in order to improve the rejection characteristics.