What is a Phased Array Antenna?

A phased array antenna is a group of elemental antennas arranged into an array that works together like a single antenna, producing electronically steered radio waves pointing in one or more directions without requiring physical movement.

In a process called beamforming, phased array systems send a signal at the same frequency from each antenna element, but the phase and magnitude of each element varies. Doing so causes constructive and destructive interference as the radio waves combine to create a radiation pattern representing a directional, high-gain beam.

Most phased array antennas are planar, consisting of hundreds or even thousands of individual elements in an array arranged linearly, on a single plane, or in three dimensions. Engineers use the physics of high-frequency electromagnetics, driven by simulation, to design the array elements, the overall array configuration, and the radio frequency (RF) hardware and electronic circuitry that drives the antenna. 

Phased array antenna systems are complex systems that use power electronics, RF components, and antenna designs in a single powerful system. To understand how design teams configure phased array antenna systems and which applications are best suited for this technology, engineers should be familiar with the following fundamentals.

Radio Wave Amplitude, Phase, Frequency, and Wavelength

Radio waves are a form of high-frequency electromagnetic radiation that takes the form of a sinusoidal wave oscillating in a bandwidth of around 3 KHz to 3,000 GHz. This figure shows the fundamental characteristics of any wave:

The wavelength is the distance the wave travels in one cycle. The amplitude is the maximum value of the wave, and the phase is the difference, or the time delay, between the peak amplitude of each wave. The frequency is generally constant with only small variations in a phased array antenna, but both the phase and the amplitude can be varied at each antenna.

Antenna Elements

Antenna elements are the individual antennas in an array. Although there are many different types of antenna elements that can be combined to form the array, the antenna elements most commonly used are patch antennas, microstrip patch antennas, waveguide horns, or monopole antennas. The antennas' operating frequency determines the elements' size and spacing.

Antenna Gain

Antenna gain is the strength of the signal (the amplitude) in any given direction compared to a theoretical single isotropic radiator, which would spread the signal equally in all directions.

Phased Array Antenna Beamformer Components

A beamformer consists of electronic and RF circuitry used to convert an input signal into a steerable transmitted signal. For passive phased array systems — the most common type of phased array antenna — a single input signal is converted into a signal pointing in the desired direction using a series of components: a transmitter power amplifier, a beamformer, and the individual antenna elements. The beamformer typically consists of attenuators, phase shifters, or components that provide similar functionality. 

• Transceiver power amplifier (PA): The input signal is amplified to create the desired signal at the needed amplification. This is the signal that the receiver will measure.
• Power divider: A power divider splits the input signal into multiple signals for each antenna element circuit.
• Attenuators: The amplitude for each antenna element is increased or decreased as needed by attenuators. These can be digital or analog devices and can be passive or active. 
• Phase shifters: These digital or analog devices introduce a small delay to the waveform, the key step in steering the beam.
• Antenna elements: Finally, the signal arrives at the antenna element and is transmitted at the desired phase and amplitude.
• Low-noise amplifier (LNA): If the antenna is also used as a receiving antenna, it will include a low-noise amplifier.
• Transmit receive switches: If the antenna is also used to receive signals, a switch will send the incoming signal through the LNA instead of the power amplifier.

The computer controlling the phased array electronically modifies the amplitude and phase of each antenna element, making changes quickly so that the beam direction can rapidly shift.

Beam Direction

The beam direction is the direction pointing from the antenna's origin to the point of maximum signal magnitude after the signal from each antenna element is combined. Antenna designs use two angles to specify the vector. The azimuth is the angle parallel to the horizon, and the elevation is the angle above the horizon.

Beam Width

A plot of signal amplitude vs. steering angle shows the primary beam and other beams generated by the phased array as humps on the graph, called lobes. The beam width is the width of the strongest lobe in degrees.

There are two standards for measuring beam width. The first measurement from null location to null location is called the first null beam width (FNBW). The second method measures at half power down from the peak and is called the half-power beam width (HPBW).

Beam Steering and Scanning

Electronically setting the beam direction is referred to as beam steering. When the beam direction moves in a pattern, this is known as beam scanning. More complex phased array antennas can steer multiple beams in different directions at slightly different frequencies.

Sidelobes

A sidelobe is any local maximum in the radiation pattern that is not the main beam. They waste energy and can cause interference. Array design seeks to minimize the magnitude of sidelobes. 

Phased array antennas can take many forms. Experts use topology and beamformer technology to classify different types of phased array antennas.

Phased Array Topology

One way to distinguish the types of phased array systems is to classify them by the relative position of the antenna elements. Most systems fall into one of the following topological types:

1. Line (1D) arrays: The antenna elements are arranged in a horizontal line to change the azimuth angle of the beam or in a vertical line to control the elevation.
2. Planar (2D) arrays: The antenna elements are arranged on a flat surface (a planar structure) and can be steered in both elevation and azimuth angles to cover the entire space above the antenna.
3. 3D array: The antenna elements are arranged across a volume, allowing the steering of one or more beams in any direction.

Types of Beamformers

Passive electronically scanned array (PESA): A passive phased array is an antenna with a single transceiver for the entire array. This is the most common type of phased array configuration.

Active electronically scanned array (AESA): An active phased array is an antenna in which each antenna element or subset of elements has an analog transceiver module to produce the phase shift in each element. Military applications tend to use this more advanced approach.

Digital beamforming (DBF) phased array: A DBF array antenna uses a digital transceiver module to vary the phase and amplitude in each antenna element. It can also produce multiple beams and uses a field-programmable gate array (FPGA) chip or an array computer to digitally form the antenna pattern. Digital beamforming arrays can also develop radiation pattern nulls to reduce power sensitivity and receive sensitivity are purposely minimized to mitigate interference to or from known directions.

Hybrid beamforming phased array: The AESA and DBF approaches can be combined to form a hybrid beamforming phased array. This approach includes subarrays. Each subarray uses an analog transceiver, and each array element in the subarrays has its own digital transceiver. This approach can create clusters of simultaneous beams.

Engineers designing communication systems and sensors use phased array antennas to create a spatially selective wireless RF signal source. An antenna array enables a system to take advantage of one or more of the following capabilities:

1. Combine multiple antenna elements to create a large aperture and a stronger signal
2. Use beamforming to create an electronically steerable antenna
3. Use adaptive, hybrid, or digital beamforming to create beams pointing in multiple directions at the same time, and to minimize interference to and from other RF systems

These capabilities deliver some significant advantages over transitional mechanically steered reflector and mast antennas:

• Electronically steered beams can scan much faster or switch beam direction very quickly.
• Compared to a reflector antenna with mechanical steering and a large dish, a phased array antenna usually takes up less space and weighs less. It can fit onto the surface of a vehicle or on a building.
• In most cases, phased array systems also cost less for the same level of performance, especially when integrated circuits (ICs) are used for beamforming or for the antenna elements.
• Reliability. Individual components within a channel may fail without compromising the basic performance of the antenna system overall. In fact, performance degrades gracefully with component failures, in contrast to single point of failure issues with mechanical antenna systems.
• Point the signal in multiple directions with a single device.
• Because the power for each antenna element adds up, they are more power efficient.

These advantages led early RF pioneers to develop phased array radar and radio astronomy arrays that could amplify very weak signals from distant stars. Over time, the number of phased array applications grew to include antennas for other aerospace systems as well as medical, automotive, industrial, and communication systems.

Multidirectional array antenna systems enable:

• Modern 4G and 5G telecommunication networks
• Future 6G telecommunication networks
• The latest WiFi access points
• Radar systems for autonomous automobiles
• Therapeutic medical devices

Designing even small arrays for phased array antennas would be difficult without simulation, and it becomes essential for systems with thousands of antenna elements. Everything from arracy spacing to sidelobe losses is difficult to calculate by hand. Measuring radiation patterns in an anechoic chamber is also expensive and time-consuming. 

An animation of a simulation showing how a phased array antenna’s maximum gain dynamically points at a ground station as it orbits the area 

With simulation, engineers can not only design their arrays and the beamforming components, but they can also optimize their systems for efficiency, cost, and speed. Teams also use simulation to understand the impact of manufacturing tolerances and material variation on the design.

Engineers use simulation tools to design, verify, and optimize antenna arrays, antenna elements, and beamforming components. They can also simulate how their antennas interact with the entire system.

A comprehensive, easy-to-use, and accurate high-frequency electromagnetics finite element tool like Ansys HFSS high-frequency electromagnetic simulation software is ideal for almost every electromagnetic aspect of simulating phased array antennas. With powerful meshing, parallel solvers, and workflows specifically created for arrays, it is the gold standard for component and system-level modeling. HFSS software simulates everything from individual waveguides to signal propagation through the entire assembly, modeling the antenna long before hardware is available.

Shooting and bouncing ray technology found in applications like Ansys Perceive EM radio frequency channel and radar signature simulation software takes simulation to the next level by enabling users to model how their antennas perform across long distances and around obstacles like shelving in a warehouse or buildings in a city. Teams designing for the local installation impact of their antenna systems use the shooting and bouncing rays (SBR) feature inside HFSS software to capture the antenna's self-coupling to the tower, buildings, or vehicle it is mounted on. Engineers can also use simulation to model how their antenna design works in a network with a system-level tool like Ansys RF Channel Modeler high-fidelity wireless channel modeling software.

Once the electromagnetic characteristics are understood and optimized, design teams need to look at the thermal and structural response of the phased array system. They can use tools like Ansys Mechanical structural finite element analysis (FEA) software or Ansys Icepak electronics cooling simulation software, which can interface with their high-frequency electromagnetic solver. And if the antenna is mounted on a vehicle or aircraft, they may need to use a CFD tool such as Ansys Fluent fluid simulation software to understand and design for aerodynamic loading at speed. 

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