A Series-Fed Circularly Polarized Array with Microbumps for Sub-THz Applications

In this paper, a series-fed right-hand circularly polarized (RHCP) antenna array with microbumps based on high resistivity silicon (HRSi) is proposed for sub-Terahertz (sub-THz) applications. The circularly polarized (CP) unit comprises four circular patches which are integrated with microbumps. These patches are arranged with quarter-wavelength spacing along the microstrip line, establishing a rotational sequential feeding mechanism that generates RHCP radiation gain. The array is constructed by cascading four CP units in a series-fed configuration. Meander lines are specially designed to ensure the in-phase excitation of the CP units. The array achieves a -10 dB impedance bandwidth of 13.2% (235-269 GHz) and a 3-dB AR bandwidth of 8.9% (246-269 GHz). The integration of microbumps onto the patches through flipchip technology significantly enhances gain and radiation performance without necessitating complex fabrication processes or substantial cost increments. Compared with the array without microbumps, the proposed array with microbumps achieves a maximum radiation efficiency improvement from 8.9% to 13% and the maximum peak RHCP-gain improvement from 0.94 dBi to 2.65 dBi.