Antenna Arrays: A Computational Approach

7 Array Beamforming Networks

An array feed or beamforming network takes the signals at all the elements and combines them to form a receive beam or, conversely, takes a transmitted signal and distributes it to the elements in the array to form a transmit beam. This chapter presents an assortment of analog and digital beamforming networks for creating one or more beams. A corporate feed consists of a series of power splitters/combiners that distribute the signals. One input/output is connected to all the elements. Couplers sample the signals from the elements that are combined to form multiple beams. Examples include the Blass matrix and the Butler matrix. Another approach distributes the signals from one or more antennas to the elements of an array. Bootlace and Rotman lenses are good examples. Finally, the most versatile and advanced beamforming nework is called the digital beamformer. This approach places an RF analog-to-digital converter at each element, so the signal at each element goes directly to the computer.

7.1. TRANSMISSION LINES

Most feed networks are made from (a) transmission lines, such as coaxial cables, stripline, and microstrip, (b) passive devices, such as couplers and power splitters, or (c) active components, such as amplifiers and receivers. Impedance matching is extremely important to ensure efficient power transfer through the feed network. Most devices and transmission lines have a characteristic impedance of 50Ω, so most antennas are designed to have ...