Beamforming

R2026b

Beamforming is the process of generating a directional beam from an antenna array. Each element in the array has an excitation defined by an amplitude and a phase. By adjusting these parameters across the array, you shape and steer the radiated beam. Achieve beamforming by weighting individual elements by using side lobe control or beam scanning.

Side Lobe Control

Side lobes are undesired and lead to reception or transmission of energy in unwanted directions. Side lobe control in an array is achieved using amplitude taper or amplitude weighting. Amplitude tapering changes the excitation amplitude of each element in the array. Side lobe levels are controlled using an amplitude taper that decreases from the center of the array toward the edges. Smoother amplitude tapering gives lower side lobe levels and wider half-power beamwidth. These arrays are non-uniformly excited arrays.

Consider a linear array of 21 elements. Without amplitude tapering, the array contains unwanted side lobes in the desired direction:

Directivity pattern at 70 MHz showing a main lobe peaking at 16.9 dBi near 90° and multiple smaller side lobes with decreasing amplitude on either side.

By using amplitude tapering on the linear array, you control the side lobes and achieve a better main beam in the desired direction:

Directivity pattern at 70 MHz with amplitude tapering applied, showing a narrower main lobe peaking at 15.9 dBi near 90° and reduced sidelobe levels compared to the untapered pattern.

Beam Scanning

Beam scanning is the movement of a radiation pattern in space. You can achieve beam scanning by controlling the progressive phase difference between the elements to direct the beam in any desired direction. The phase shift changes the phase of the excitation currents of each element in an array. You can achieve this phase shift using phase shifter devices, a time delay, frequency scanning, beam switching, or digital beamforming.

Consider a linear array of 21 elements where peak directivity is shown without beam scanning:

Directivity plot at 70 MHz showing an unsteered beam with a main lobe at 90° reaching 15.9 dBi and symmetric sidelobes extending to about −25 dBi.

To scan the beam at a specific angle, use phase shift on the linear array:

Directivity plot at 70 MHz showing a beam steered to about 110°, with a 15.1 dBi main lobe and sidelobes down to approximately −27 dBi.

References

[1] Stutzman, W.L. Thiele, G.A. Antenna Theory and Design, 3rd Edition. New York: Wiley, 2013, p. 307.