A Compact mmWave 1x4 Antenna Array Design with Shorted Parasitic Elements for 5G AiP Applications

In this paper, we introduce a compact 28GHz 1x4 antenna array featuring shorted parasitic elements, designed on a 10(4+2+4) multi-layer organic substrate. This allows for a broad bandwidth in a compact Antenna-in-Package (AiP) module. While Microstrip patch antennas are favored in AiP for their low profile, ease of fabrication, cost-effectiveness, and seamless RF chip integration, they typically exhibit drawbacks like narrow bandwidth and diminished gain. An established solution to counter these limitations involves the use of stacked patch antennas with parasitic elements, which enhance impedance bandwidth and gain. Yet, this comes at the expense of a larger AiP footprint and cost, posing integration challenges in mobile devices and complicating mechanical designs. To address the size constraint, we introduce a novel design: a stacked patch antenna incorporating shorted parasitic elements. This innovative design uses smaller parasitic elements but doesn't compromise on performance. By grounding the parasitic elements appropriately, a short-circuit mirror-image current effect is realized, leading to a reduced component area. Post-optimization, the size is refined from 6.5 x 25 mm
²
to 4.5 x 25 mm
²
, marking a 31% reduction. Performance-wise, simulations reveal a return loss exceeding 10 dB within the 25-30 GHz spectrum, about 5 GHz bandwidth, and a high-gain per element radiation pattern (over ~6 dBi) suitable for 28GHz applications. Further, a 28GHz beamforming array is detailed, incorporating a four-channel transceiver with a 1 x 4 antenna array. For active testing, we designed an integrated socket and load board to support the mmWave module, bridging the Device Under Test (DUT) and the test system. The load board substrate is segmented to manage the IF, LO, and DC distribution networks. There's also a four-channel transmit beamforming array front-end module earmarked for design. The paper culminates by showcasing the 3D beam steering capabilities of the 1x4 antenna array across multi-states at 28 GHz, achieving a peak gain of 11 dBi in the primary beam direction. Our results affirm that by manipulating the signal phase in individual antenna elements, beamforming can be oriented towards a precise direction. The beam steering range spans approximately 75 degrees. This compact antenna design offers both bandwidth and size advantages, making it an attractive solution for 28GHz mmWave bands in mobile devices, specifically for n257, n258, and n261 channels.