Passively Balanced Tunable Metasurface Feed for Analog Beamforming Free of Complex Digital Control Circuitry and Active Compensation

The millimetre-wave (mmWave) and terahertz (THz) spectra offer far wider bandwidths than the congested sub- 6 GHz microwave regime, enabling unprecedented data rates for beyond-5G communications and sensing. However, the increased free-space path loss and atmospheric absorption (e.g., from oxygen and water vapour) necessitate directional beamforming, traditionally achieved through phased arrays and, more recently, metasurfaces. This paper explores the underexploited advantages of liquid crystal (LC)-based feeding networks for passive phasecompensated tunable metasurfaces, enabling beamforming without complex digital control circuitry or active amplitude compensation. Across 54 to 66 GHz, the differential true-timedelay (TTD) reports a standard deviation between 0.72 fs and 3.58 fs among various designs (impedance matched at diverse LC-tuned states). Meanwhile, the maximum deviation in insertion loss is within 0.1 dB, evidencing a passively balanced dispersion-free operation for high-fidelity spatial multiplexing.