Conjugate Impedance Matching Method for Wideband and Wide-Angle Impedance Matching Layer With 70° Scanning in the H-Plane

This letter proposes a wideband and wide-angle conjugate impedance matching (WWCIM) method and a WWCIM layer, which are applied to the tightly coupled dipole array (TCDA). The impedance matching problem over an ultrawideband can be well solved by using this method when the scanning angle reaches 70° in the H-plane. At the port position, the impedances of the ultrawideband-phased array change sharply at different frequencies when scanning to large angles in the H-plane. However, we find that the impedances at the upper surface of the array have certain regularity when scanning in the H-plane. The impedances gradually decrease as the scanning angle increases in the H-plane and the reactance parts of the impedances are inductive. Therefore, a new WWCIM layer is proposed. The impedances of the WWCIM layer, seen from down to up, also gradually decrease as the scanning angle increases in the H-plane. But their reactance parts are capacitive. Therefore, in the H-plane, the impedances at the upper surface of the TCDA and the impedances at the lower surface of the WWCIM layer can be well conjugated when scanning to large angles. In the E-plane, because the changes of the port impedances and the WWCIM layer are small within the 70° scanning range, the port impedances can be easily matched. Thus, the impedance matching problem is well solved when scanning at large scanning angles in the H-plane. Finally, a single-polarization array with a bandwidth of 1.02-5.15 GHz (VSWRs <; 2.7) is presented, which can scan up to ±70° in all azimuth planes. The profile of the proposed array is 0.2λ at the lowest working frequency.

I. Introduction

Among wideband-phased arrays, the Vivaldi array [1]–[3] and the tightly coupled dipole array (TCDA) [4] are most popular. The Vivaldi array with ±45° scanning in [1] achieved a 12:1 bandwidth and a profile of 0.3 wavelengths at the lowest frequency. The Vivaldi array in [2] achieved a 7.6:1 bandwidth and ±60° scanning, but the profile reached 0.37 wavelengths at the lowest frequency. In [3], a 10:1 bandwidth and ±60° scanning of the Vivaldi array were achieved, but the profile reached 0.3 wavelengths at the lowest frequency.