Frequency-Reconfigurable Circularly Polarized Low-Profile Dielectric Patch Antenna for Millimeter-Wave Applications

Abstract

This paper presents a low-profile, frequency-reconfigurable circularly polarized (CP) dielectric patch antenna (DPA) for K-/Ka-band millimeter-wave (mmWave) applications. The proposed antenna employs a high-permittivity ceramic dielectric patch (DP) excited through an asymmetric cross-slot aperture, which generates the two orthogonal modes required for CP operation. Frequency agility was realized using a single PIN diode integrated along a microstrip open stub, enabling electronic control of the effective feed-line electrical length. Because the switching element is confined to the feed network and is physically separated from the CP-generating cross-slots, the antenna preserves its polarization characteristics across reconfigurable states. In addition, a coplanar-strip photonic bandgap (CPS-PBG) structure is incorporated into the DC biasing network to suppress RF leakage without employing lumped RF choke components. A prototype was fabricated and validated experimentally. The measured results demonstrate frequency reconfigurability over multiple bands spanning 21.2–28.8 GHz, corresponding to a frequency-agility ratio (FAR) of 25.8 % evaluated between the lowest and highest measured centre resonances. It is emphasized that circular polarization is realized in the lower operating band (centered near 22 GHz, with a measured 3-dB axial-ratio bandwidth of 4.3%) in both switching states, whereas the upper resonances are linearly polarized (LP). The reported reconfigurability therefore refers to the discrete switching of the impedance response, while stable CP is preserved in the lower band across both states, with a peak realized gain of 6.7 dBic and a simulated radiation efficiency of up to approximately 90%. The proposed design therefore offers a low profile of 0.15 mm for the DP, single-switch, PCB-compatible solution for frequency-agile CP mmWave applications such as integrated sensing and communication (ISAC) and Vehicle-to-everything (V2X) communications.