Microstrip patch antenna with compact feed to reduce harmonics

In this work, a new method to suppress the harmonic radiation from an square electromagnetically coupled microstrip patch antenna is proposed. The goal of the design is the elimination of the resonances at the 2nd and 3rd harmonic frequencies to reduce spurious radiation due to the corresponding patch modes. The study shows the possibility of controlling the second harmonic resonance matching by varying the lenght of the feeding line. In addition a resonator is placed underneath the antenna¿s feeding line order to suppress the third harmonic. It consists of a printed metallization with a via connected to the ground plane (mushroom type) in a multilayer configuration. This feature could be advantageous in a transmitting active patch antenna to eliminate the harmonic radiation.