Question

What is the working principle behind using dual resonator for impedance bandwidth?


Reference : Low-Profile, Low-Cost, Broadband Millimeter-Wave Antenna Array for High-Data-Rate WPAN Systems Byungje Lee and Yonghyun Yoon

Answer 1

By increasing the thickness of the radiating patch substrate, the aperture size through which the fields are radiating to the space can be enhanced leading to easier impedance matching of antenna aperture which results in antenna bandwidth enhancement. On the other hand, by decreasing the substrate permittivity (making it closer to the permittivity of outer space), the reflection coefficient at the antenna aperture is reduced making it easier to impedance match which provides wider bandwidth for the antenna.

It should be noted that as the thickness of the substrate is increased and the dielectric constant is reduced, the patch size becomes smaller which provides lower gain. In addition, the radiated power by feed network increases leading to more spurious radiation and higher cross-polarisation level. Furthermore, the surface waves are more excited reducing the antenna radiation efficiency.