What is a Phased Array Antenna?

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- everything RF

Jun 27, 2020

Phased Array Antennas are antenna arrays that have the unique ability to change the shape and direction of the radiation pattern without physically moving the antenna. Elements in an antenna array are placed in such a way that the signals transmitted by individual antennas sum up and provide better gain, directivity and performance in a particular direction.

This is achieved by transmitting signals of the same frequency from all the individual elements in the array but with a certain phase difference/shift between each antenna element in the array. The phase shift is calculated to provide constructive interference in the desired direction while destructive interference may 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.