Reconfigurable superdirective beamshaping using a PTX-synthesis metasurface

Parity-time-reciprocal scaling (PTX)-symmetry has been recently proposed to tailor the resonance linewidth and gain threshold of non-Hermitian systems with new exhilarating applications, such as coherent perfect absorber-laser (CPAL) and exceptional point (EP)-based devices. Here, we put forward a nearly-lossless, low-index metachannel formed by PTX-symmetric metasurfaces operating at the CPAL point, supporting the undamped weakly-guided fast wave (leaky mode) and thus achieving ultradirective leaky-wave radiation. Moreover, this structure allows for a reconfigurable and tunable radiation angle as well as beamwidth determined by the reciprocally scaled gain-loss parameter. We envision that the proposed PTX-symmetric metasurfaces will shed light on the design of antennas and emitters with ultrahigh directionality, as well as emerging applications enabled by extreme material properties, such as epsilon-near-zero (ENZ) and beyond.