Design of an ultra-wideband tightly coupled array antenna based on dielectric matching layer impedance gradient

Background Tightly coupled array (TCA) generally employ dielectric matching layers to achieve ultrawideband radiation. Conventional TCA use a single dielectric matching layer, which must be relatively thick to maintain low-frequency impedance matching, thereby increasing the antenna profile and mass.

Purpose This study proposes a lightweight TCA design based on a multilayer graded-impedance dielectric matching structure to reduce the profile and mass while maintaining ultrawideband performance.

Methods Equivalent-circuit and transmission-line models were used to analyze the low-frequency mismatch caused by the abrupt impedance transition at the dielectric-air interface. A graded matching structure was constructed using a Rogers RO4350B substrate and F4B and PTFE layers arranged in descending order of relative permittivity. Several matching-layer thickness combinations were simulated and optimized. Considering both operating bandwidth and engineering feasibility, a six-element prototype with a 0.5 mm + 0.5 mm double-layer configuration was fabricated, and its voltage standing-wave ratio, pulsed-radiation characteristics, effective potential gain, and mass were measured.

Results The double-layer graded-impedance structure effectively improved the impedance matching of the TCA. As the total matching-layer thickness decreased, the lower cutoff frequency increased; when the total thickness was reduced from 1 mm to 0.5 mm, the lower cutoff frequency remained nearly unchanged. The measured active voltage standing-wave ratio was not greater than 3 from 313 MHz to 6.77 GHz, corresponding to a bandwidth ratio of 21.63∶1. The profile was 5.3% of the free-space wavelength at the lower cutoff frequency. Compared with the reference array using a 5 mm single-layer Rogers RO4350B matching structure, the total mass of the prototype was reduced by 41.7%, and the effective potential gain was increased by 40.9%.

Conclusions The proposed graded-impedance dielectric matching structure achieves substantial profile and mass reduction while preserving ultrawideband impedance matching and improving pulsed-radiation performance. It provides a practical basis for the lightweight design of ultrawideband high-power microwave radiation systems.