Feed-Connected Fully-Connected PASS Beamforming for Multi-User mmWave Transmission

Abstract

Pinching antenna systems (PASS) place movable radiators on dielectric waveguides, but sub-connected feeds restrict cross-waveguide mixing. This letter studies a feed-connected fully-connected PASS for millimeter-wave downlink, where radio-frequency (RF) signals are mixed at waveguide feeds before guided excitation of pinching antennas (PAs). We derive a closed-form identity tying the feed-level trace surrogate to the achievable sum mean-square error, and a refined tri-hybrid matching-pursuit (TH-MP-R) RF update that restores the RF-column orthonormality this identity presumes, cutting the identity’s relative error from 9.4% to 0.21%. PA positions follow a criterion coupling waveguide attenuation into the gradient itself, advanced by projected adaptive-moment ascent. At 10 dB, under a common position-search budget for all schemes, spectral efficiency improves by 16.7% over projected-gradient alternating optimization and by 28.6–65.1% over sub-connected, random-RF, and fixed-PA baselines, within 1.1% of an evolutionary tri-hybrid search at $2.7\times $ lower runtime.