Novel Horn Antenna for Large Element Spacing Phased Array

This paper presents a novel Linearly Polarized (LP) horn antenna for the planar phased array radar composed of periodic subarrays with large element spacing. The proposed horn antenna is cascaded by a coaxial to waveguide transition and a modified pyramidal horn. To suppress the high-order modes and improve the radiation efficiency, a metal cross and a substrate cover are added to the radiation aperture of the horn. Meanwhile, with the using of metal cross, the field distribution at the aperture changes from the approximate cosine distribution of the conventional horn to the dual cosine distribution, which is more effective to suppress the broadside grating lobes of array factor. Moreover, in order to adjust the parasitic resonance caused by the gaps in-between the elements, a metal frame is added to the sidewall of the horn and the parasitic resonance can be tuned flexibly. The aperture size of the proposed horn antenna is about 1.43 λ × 1.43 λ (λ is the wavelength in the air). The simulated effective bandwidth of scan active voltage standing wave ratio (VSWR) ≤ 2.5 and gain ≥ 12.5 dBi is 24.4%, from 8.42 GHz to 10.76 GHz.