$Ka$ -Band Multiple Feed per Beam Focal Array Using Interleaved Couplers

In this paper, an original focal array for multibeam antenna is presented. It is based on multiple feed per beam (MFB) geometry. Each beam is produced by a cluster of feed horns illuminating a parabolic reflector. Three adjacent clusters of the focal array overlap for enhancing the illumination performance within the size-constrained array lattice. The beam-forming network is the key component and drives the overall performances of the radiating structure. It is composed of tri-dimensional interleaved couplers made of circular waveguides and interconnected by thin radial rectangular waveguides. The design, manufacturing, and measurement of a Ka-band MFB focal array are reported. It is composed of 31 feed horns displayed in seven clusters, for a global size of about 6λ_d, where λ_d denotes the free-space wavelength at the lowest operating frequency. The realized gain is higher by 1 dB than the gain provided by the single feed per beam focal array having analogous size.