What is a Phased Array Antenna?

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Editorial Team - everything RF

Jun 27, 2020

There are various types of antennas that are used in wireless communication. When a group of antennas are placed together the system is called an Antenna Array. Elements in an antenna array are placed in a specific way so that the signals transmitted by each individual antenna sums up so that the overall antenna array can provide better gain, directivity and performance over using a single antenna.

Phased Array Antennas, as the name suggests, can be termed as an antenna array. What makes them unique is their ability to change the shape and direction of the radiation pattern without physically moving the antennas. This is achieved by transmitting signals of equal frequency from all the individual elements in the array but with a certain phase difference/shift between them. This phase shift will introduce interference between the signals transmitted. The phase shift between the signals should be such that there is constructive interference in the desired direction while destructive interference should occur in other directions.

The interference can be either constructive or destructive, depending on the direction and phase shift introduced between the transmitted signals. In phased array antennas, the phase shift between the signals should be such there is constructive interference in the desired direction while destructive interference should occur in other directions.

Determining the phase shift in accordance with the desired direction of beamforming involves complex mathematical calculations and is done by a computer system.

Passive Electronically Steered Array (PESA)

The signal from the transmitter is sent to the antennas via a phase shifter, which is controlled by a computer system (phase controller), that changes the phase electronically thus controlling the direction of the radiation pattern of the antenna array. 

Phased Array Antennas consist of multiple smaller antennas whose number can range anywhere from a few antennas to somewhere in the hundreds or thousands. 

To reduce the overall size, phased array is best to use phased arrays for higher frequency applications as the antenna size is inversely proportional to the operating frequency so the higher the frequency the smaller the antennas. This makes phased array antennas a great choice for mm-Wave 5G Applications and other high frequency applications.

Phased Array Antennas on a PCB

Types of Phased Array Antennas

Phased Array Antennas can be of various types however, there are four commonly used types:

  1. Passive Electronically Steered Array (PESA)
  2. Active Electronically Steered Array (AESA)
  3. Digital Beam Forming (DBF)
  4. Hybrid Beam Forming (HBF)

Passive Electronically Steered Array (PESA)

PESA is a type of Phased Array Antenna that uses a single transmitter for all the antenna elements present, as shown in the image below. In this setup, each antenna element has a phase shifter which phase shifts the signal as required by the antenna to regulate the antenna beam. Passive Electronically Steered Antenna Arrays can be thought of as the first generation of Phased Array Antennas and have been used in various military and commercial applications.

Active Electronically Phased Array

The Active Electronically Steered Array (AESA) is the second generation of Phased Array Antennas. In this, there are separate transmitters for each antenna element all of which are computer controlled. This setup is more advanced than the PESA and can transmit several radio waves of varying frequencies simultaneously in different directions.

AESA Basic Schematic

Digital Beam Forming

Digital Beam Forming (DFB) based phased arrays have digital receivers connected to each antenna element. As the signal is digitized at each of the antenna elements by the receivers, antenna beams can be formed digitally in a Field Programmable Gate Array (FPGA).

Hybrid Beam Forming

Hybrid Beam Forming (HBF) based phased arrays can be thought of as a combination of PESA and AESA. HBF uses subarrays of antenna elements which are connected to separate transmitters. A full array is formed by combining these subarrays. Due to the presence of multiple subarrays, clusters of simultaneous beams can be formed using HBF.

PESA fitted on the tip of a fighter jet

Phased Array Antennas have been used for military applications for years. In fact, they were created to be used in radars systems but their applications have grown over the years. They are now used in broadcasting, space probe communication, weather research, optics, human-machine interfaces, etc. Phased Array Antennas are also being used for new commercial wireless technologies such as 5G and the new Wi-Fi 6.