A simple harmonic reduction technique in inset-fed microstrip patch antennas

In this paper a simple technique employing a defected ground structure is presented to eliminate the higher order resonances in inset-fed microstrip antennas. The effects of position of the slot below the feed location and its dimensions are studied. It is shown that a properly placed rectangular slot just below the feed line totally eliminates the higher-order modes without significant effect on the fundamental resonance frequency and the radiation pattern. This technique is validated experimentally and measurement results are in agreement with the simulated results. It is also seen that the mutual coupling in an array environment is significantly reduced at harmonic frequencies.