Photonic doping of epsilon-near-zero waveguide cavities for high-gain millimeter-wave antenna arrays

We investigate high-gain millimeter-wave (mm-wave) radiation from epsilon-near-zero (ENZ) rectangular cavities, leveraging the structural dispersion of their fundamental transverse electric TE10 mode near cutoff and photonic doping to achieve impedance-matched aperture excitation. In the ENZ regime, the effective permittivity of a rectangular waveguide approaches zero, leading to wavelength expansion, phase uniformity, and geometry-independent radiation characteristics. Photonic doping is introduced via electrically small rectangular dielectric inclusions, which tune the effective permeability to match the cavity impedance to free space without perturbing the uniform phase distribution. These principles are implemented in a waveguide-fed, slotted cavity-backed antenna array, where broadside radiation is enabled by strategically placed slots in the cavity wall. A four-element prototype, incorporating symmetrical reflectors, was fabricated and experimentally characterized, demonstrating a measured gain of 22.04 dBi and aperture efficiency exceeding 60%, in close agreement with full-wave simulations. The results establish a robust physics-based design framework in which ENZ rectangular waveguide dispersion and photonic doping enable compact, high-performance radiators for integrated mm-wave systems.