How do I design an antenna in package for a millimeter wave communication module?

Designing an antenna in package (AiP) for a millimeter-wave communication module integrates the antenna array directly into the semiconductor package, co-located with the RF transceiver and beamforming ICs, eliminating the lossy interconnections between the IC package and an external antenna that would otherwise degrade performance at mmW frequencies. At 28 GHz, 39 GHz, and 60 GHz, the wavelength is short enough (approximately 10 mm, 7.7 mm, and 5 mm in free space) that practical antenna arrays fit within standard package dimensions. The AiP typically uses a patch antenna array (4x4, 8x8, or larger) fabricated on the package substrate (organic laminate, LTCC, or FOWLP RDL layers) with the feed network and beamforming IC connected through the package interconnections. Key design considerations include: antenna element design (rectangular or circular patch on the top layer of the package, with ground plane below; substrate thickness and dielectric constant determine the element bandwidth and efficiency), array feed network (corporate feed using microstrip or stripline power dividers, with phase shifters for beam steering; loss in the feed network must be minimized), beamforming integration (each antenna element connects to a phase shifter and variable gain amplifier on the beamforming IC through short interconnections within the package), and radiation performance (the package mold compound, lid material, and solder ball grid affect the antenna pattern and must be included in the EM simulation).