In the field of array antennas, beamforming, also known as spatial filtering, is a signal processing technique used to transmit and receive wireless radio waves or sound waves in a directional manner. Beamforming is commonly used in radar and sonar systems, wireless communications, acoustics, and biomedical equipment. Typically, beamforming and beam scanning are accomplished by setting the phase relationship between the feed and each element of the antenna array so that all elements transmit or receive signals in phase in a specific direction. During transmission, the beamformer controls the phase and relative amplitude of each transmitter's signal to create constructive and destructive interference patterns on the wavefront. During reception, the sensor array configuration prioritizes reception of the desired radiation pattern.
Beamforming Technology
Beamforming is a technique used to steer a beam radiation pattern to a desired direction with a fixed response. Beamforming and beam scanning of an antenna array can be achieved by a phase shift system or a time delay system.
Phase Shift
In narrowband systems, time delay is also called phase shift. At radio frequency (RF) or intermediate frequency (IF), beamforming can be achieved by phase shifting with ferrite phase shifters. At baseband, phase shifting can be achieved by digital signal processing. In wideband operation, time-delay beamforming is preferred because of the need to make the direction of the main beam invariant with frequency.
RM-PA17731
RM-PA10145-30(10-14.5GHz)
Time lag
Time delay can be introduced by changing the length of the transmission line. As with phase shift, time delay can be introduced at radio frequency (RF) or intermediate frequency (IF), and the time delay introduced in this way works well over a wide frequency range. However, the bandwidth of the time-scanned array is limited by the bandwidth of the dipoles and the electrical spacing between the dipoles. When the operating frequency increases, the electrical spacing between the dipoles increases, resulting in a certain degree of narrowing of the beam width at high frequencies. When the frequency increases further, it will eventually lead to grating lobes. In a phased array, grating lobes will occur when the beamforming direction exceeds the maximum value of the main beam. This phenomenon causes errors in the distribution of the main beam. Therefore, in order to avoid grating lobes, the antenna dipoles must have appropriate spacing.
Weights
The weight vector is a complex vector whose amplitude component determines the sidelobe level and main beam width, while the phase component determines the main beam angle and null position. The phase weights for narrowband arrays are applied by phase shifters.
RM-PA7087-43(71-86GHz)
RM-PA1075145-32(10.75-14.5GHz)
Beamforming Design
Antennas that can adapt to the RF environment by changing their radiation pattern are called active phased array antennas. Beamforming designs can include Butler matrix, Blass matrix, and Wullenweber antenna arrays.
Butler Matrix
The Butler Matrix combines a 90° bridge with a phase shifter to achieve a coverage sector as wide as 360° if the oscillator design and directivity pattern are appropriate. Each beam can be used by a dedicated transmitter or receiver, or by a single transmitter or receiver controlled by an RF switch. In this way, the Butler Matrix can be used to steer the beam of a circular array.
Brahs Matrix
The Burras matrix uses transmission lines and directional couplers to implement time-delay beamforming for broadband operation. The Burras matrix can be designed as a broadside beamformer, but due to the use of resistive terminations, it has higher losses.
Woollenweber antenna array
The Woollenweber antenna array is a circular array used for direction finding applications in the high frequency (HF) band. This type of antenna array can use either omnidirectional or directional elements, and the number of elements is generally 30 to 100, of which one-third are dedicated to sequentially forming highly directional beams. Each element is connected to a radio device that can control the amplitude weighting of the antenna array pattern through a goniometer that can scan 360° with almost no change in the antenna pattern characteristics. In addition, the antenna array forms a beam radiating outward from the antenna array through time delay, thereby achieving broadband operation.
To learn more about antennas, please visit:
Post time: Jun-07-2024
