Scalable D-Band Antenna With Coplanar and Stacked Parasitic Elements for Low-Cost Antenna-in-Package

The unquenchable thirst for bandwidth to support next-generation wireless systems is increasingly bringing D-band into the spotlight. This work proposes a scalable D-band patch antenna that features both coplanar and stacked parasitic patch structures. By leveraging inter-patch coupling, different coplanar parasitic elements are excited across different frequency bands, enabling multi-mode operation and thus a wideband response. To mitigate gain fluctuations caused by modal discontinuities, stacked parasitic patches are added and progressively shifted inward to improve the continuity and consistency of modal patterns by suppressing the undesired currents and hence aligning the modal patterns. The resulting antenna element achieves a flat gain of up to 10 dBi over a 28% impedance bandwidth in simulation. To demonstrate the scalability of the design, a 2 times 2 array with a hybrid feed network was fabricated with a high-density interconnect (HDI) PCB process featuring one buildup layer on each side of a two-layer core. The array prototype yields an impedance bandwidth of 29%, a peak gain of 12.3 dB, and a gain bandwidth of 17.8%. These results highlight the strong potential of low-cost HDI-based antenna fabrication for D-band applications.