Pattern Ripples Caused by Finite Ground for Antenna-in-Package

Pattern ripples are almost inevitable for practical Antenna-in-Packages (AiP) where finite large ground planes are commonly used. In this work, the phenomenon of pattern ripples of a patch-type AiP with a finite ground is investigated. The electric fields (E fields) and magnetic fields (H fields) are sampled on a plane which is a few microns above the patch. The sampled E fields and H fields are utilized as sources to calculate the far fields by applying the theory of near-field to far-field transformation. It is found that pattern ripples are mainly caused by the H fields. Furthermore, to investigate the influence of ground size and offset of the patch on the pattern ripples, a new metric of curve fluctuation factor is introduced and evaluated. The results indicate that the pattern ripples can be reduced to a local minimum by adjusting the module size or antenna location.