An ultra-wideband tightly coupled Vivaldi array with current loops for transient pulse radiation

Abstract A novel ultra-wideband tightly coupled Vivaldi array with current loop is proposed, which exhibits compactness and supports a wide operational bandwidth. The Vivaldi antenna, characterized by its inherent directivity, has been utilized in place of the conventional dipole antenna in tightly coupled arraying. This approach effectively mitigates the short-circuit resonances caused by the metallic reflective ground plane, thereby broadening the radiation bandwidth. To further enhance performance, a short-circuited branch is incorporated between the radiation arm of the Vivaldi antenna and the ground plane to guide the net current, aiming to suppress common-mode resonances and expand the impedance bandwidth. Concurrently, the radiation arm, short-circuited branch and ground plane form a current loop. When combined with the Vivaldi radiation structure, this configuration creates an electromagnetic combined antenna for complementary radiation, further reducing the low cutoff frequency. The element size of the array is 5 cm × 5 cm × 16.5 cm (0.083 λ L × 0.083 λ L × 0.275 λ L ), with a low cutoff frequency of 0.5 GHz and a high cutoff frequency of over 10 GHz. A 4 × 4 UWB pulse array has been fabricated and its time-domain performance has been analyzed. The measured results are in good agreement with the simulated outcomes.