A Beamforming Approach for Multiport Antennas [Antenna Applications Corner]

This article presents an approach for the systematic construction of a unitary multibeam transformation for a general multiport antenna. The resulting beamforming transformation produces up to N beams for an antenna with N terminal pairs. The beams are formed sequentially, each with maximum realized gain for the available degrees of freedom (DFs). The construction may be used for sidelobe control by sequentially placing nulls in the pattern, with each null requiring minimal additional incident power. The procedure provides insight into the effects of null placement on array efficiency and gain pattern. The average element pattern is invariant to unitary transformations of the incident waves, and this fact is used to derive a closed-form expression for the multiple signal classification (MUSIC) function P
_MU
(Ω) for the case of two closely separated emitters symmetrically located about the broadside direction of an array of N ideal noninteracting elements with half-wavelength spacing.