Phased array
An antenna array that steers radio beams electronically without moving parts.
A phased array is a computer-controlled group of antennas that can steer a beam of radio waves in different directions without any physical movement of the antennas. This is achieved by feeding power from the transmitter to each radiating element through devices called phase shifters, which are controlled by a computer. The computer can electronically alter the phase or signal delay of each element, causing the combined radio waves to form a beam that can be pointed in any direction. Because an antenna array must span many wavelengths to achieve the narrow beamwidth and high gain needed for many applications, phased arrays are most practical at higher radio frequencies, such as UHF and microwave bands, where wavelengths are conveniently small.
Originally developed for military radar systems to quickly track fast-moving aircraft and missiles, phased arrays are now common in civilian technology, including 5G MIMO for cell phones. The same principle is also applied in acoustics—for example, in medical ultrasound imaging, oil and gas exploration, and military sonar—as well as in optics with optical phased arrays.
There are several types of phased arrays. A passive electronically scanned array (PESA) connects all antenna elements to a single transmitter and receiver, using one receiver/exciter for the entire array. An active electronically scanned array (AESA) gives each antenna element its own analog transmitter/receiver module, which handles the phase shifting. AESAs are a more advanced, second-generation technology that can radiate multiple beams at different frequencies and in different directions simultaneously, though practical packaging limits them to about three simultaneous beams. A digital beam forming (DBF) array has a digital receiver/exciter at each element, digitizing the signal so that beams can be formed digitally in an FPGA or computer, allowing many simultaneous beams. A hybrid beam forming phased array combines aspects of AESA and DBF: it uses subarrays (each an active phased array of, say, 64, 128, or 256 elements) that are combined to form the full array, with each subarray having its own digital receiver/exciter, enabling clusters of simultaneous beams.
- Common types
- Passive electronically scanned array (PESA), active electronically scanned array (AESA), hybrid beam forming phased array, digital beam forming (DBF) array
- Frequency bands
- UHF and microwave bands
- Original application
- Military radar systems
- Civilian application
- 5G MIMO for cell phones
Lore & Background
Phased arrays were originally conceived for use in military radar systems, to steer a beam of radio waves quickly across the sky to detect planes and missiles. These systems are now widely used and have spread to civilian applications such as 5G MIMO for cell phones. The phased array principle is also used in acoustics, and phased arrays of acoustic transducers are used in medical ultrasound imaging scanners (phased array ultrasonics), oil and gas prospecting (reflection seismology), and military sonar systems.
In a phased array, the power from the transmitter is fed to the radiating elements through devices called phase shifters, controlled by a computer system. The computer can alter the phase or signal delay of each antenna element electronically, resulting in a beam of radio waves that can be dynamically steered to propagate in arbitrary directions. Since the size of an antenna array must extend many wavelengths to achieve the high gain needed for narrow beamwidth, phased arrays are mainly practical at the high frequency end of the radio spectrum, in the UHF and microwave bands, in which the operating wavelengths are conveniently small.
The term 'phased array' is also used to a lesser extent for non steerable array antennas in which the phase of the feed power and thus the radiation pattern of the antenna array is fixed. For example, AM broadcast radio antennas consisting of multiple mast radiators fed so as to create a specific radiation pattern are also called 'phased arrays'.
Reader's Guide
Phased arrays represent a significant advancement in antenna technology by enabling electronic beam steering without mechanical movement, allowing rapid target tracking and multiple simultaneous beams. Their development for military radar systems to detect fast-moving planes and missiles led to widespread adoption in civilian applications such as 5G MIMO for cell phones. The technology has also been adapted for acoustics, including medical ultrasound imaging, oil and gas prospecting, and military sonar systems. The four most common types—passive electronically scanned array (PESA), active electronically scanned array (AESA), hybrid beam forming phased array, and digital beam forming (DBF) array—offer varying capabilities: PESAs use a single transmitter/receiver, AESAs have individual T/R modules at each element allowing multiple simultaneous beams, DBF arrays digitize signals at each element for digital beam forming, and hybrid arrays combine subarrays with their own digital receivers. Conformal antennas mount phased arrays on curved surfaces to reduce aerodynamic drag on aircraft and missiles. Time domain and frequency domain beamformers provide different methods for steering beams, with techniques such as delay-and-sum, Butler matrices, and spatial frequency processing enabling simultaneous multiple beams or frequency-dependent beam directions.
Did You Know?
- The phased array principle is also used in acoustics for applications such as phased array ultrasonics and medical ultrasound imaging.
- A passive electronically scanned array (PESA) uses a single transmitter and/or receiver for the entire array.
- An active electronically scanned array (AESA) can radiate several beams of radio waves at multiple frequencies in different directions simultaneously.
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