A harmonic-free microstrip patch antenna with compact mushroom resonators embedded in an antenna substrate

This paper proposes a harmonic-free microstrip patch antenna (MSPA) with two suspended-mushroom resonators embedded in an antenna substrate just beneath the patch. Comparing with a regular MSPA without mushrooms, resonance up to 3f₀ can be perfectly removed except the fundamental resonant frequency f₀. As an embedded mushroom is small enough and it has frequency selectivity, the degradation in the fundamental antenna performance due to the presence of the mushroom is almost negligible, and the frequency shift of f₀ was only 0.3% in the theory before and after the installation of the mushroom. The theoretical predictions agreed well with the experiments.