12.9.7 How Do Smart Antennas and Phased Arrays Work?
- What Is a Phased Array?
- Why Does Changing the Phase Steer the Beam?
- Why Is Electronic Steering Better Than Mechanical Steering?
- What Is Beamforming?
- What Makes an Antenna "Smart"?
- How Do Smart Antennas Reduce Interference?
- Why Are Phased Arrays Ideal for Radar?
- How Are Phased Arrays Used in Satellite Communication?
- Why Are Smart Antennas Important for 5G?
- Can One Antenna Form Several Beams?
- Are Phased Arrays More Expensive?
- Will Mechanical Antennas Disappear?
- Why Are Smart Antennas One of the Most Important Developments in Modern Communications?
- What Should You Remember?
Short Answer
Traditional antennas are pointed by physically rotating them. A phased-array antenna, however, steers its beam electronically by adjusting the phase of the signals supplied to many individual antenna elements. Because no mechanical movement is required, the beam can be redirected almost instantaneously. Modern smart antennas extend this concept by continuously adapting their radiation patterns in response to changing propagation conditions, user locations, and interference. These technologies have become fundamental to radar, satellite communication, radio astronomy, Wi-Fi, and modern cellular systems such as 5G.
What Is a Phased Array?
A phased array consists of many individual antenna elements arranged in a regular pattern.
Each element radiates the same signal. The important difference is that the signal supplied to each element is delayed—or phase shifted—by a carefully controlled amount. These small phase differences cause the individual radio waves to combine differently in space. In one direction they reinforce one another. In other directions they partially cancel.
The result is a highly directional beam whose direction depends entirely on the relative phases of the individual elements.
Why Does Changing the Phase Steer the Beam?
Imagine several people throwing stones into a pond.
Each stone produces circular ripples. Where the ripples meet, they combine to produce regions of larger and smaller waves. Radio waves behave in exactly the same way. Each antenna element produces its own electromagnetic wave. By changing the phase of each signal, engineers control where the waves reinforce one another. The direction of maximum reinforcement becomes the main beam.
Changing the phase shifts this region of reinforcement, causing the beam to rotate electronically without moving the antenna itself.
Why Is Electronic Steering Better Than Mechanical Steering?
Traditional directional antennas require motors, gears, and bearings to point towards the desired target.
Although effective, mechanical systems have limitations. They:
- move relatively slowly;
- require regular maintenance;
- suffer mechanical wear;
- consume additional power; and
- cannot easily track multiple targets simultaneously.
Electronic steering avoids these problems.
Beam direction can be changed in microseconds, allowing the antenna to track rapidly moving objects or communicate with several users almost simultaneously.
What Is Beamforming?
Beamforming is the process of shaping and steering an antenna beam electronically.
Instead of transmitting energy equally in every direction, the antenna concentrates power towards a selected receiver. Beamforming provides several important advantages:
- increased signal strength;
- improved communication range;
- reduced interference;
- greater spectral efficiency;
- improved security; and
- reduced transmitter power requirements.
Modern beamforming algorithms continually optimise the radiation pattern as communication conditions change.
What Makes an Antenna "Smart"?
A smart antenna does more than simply steer its beam.
It continually monitors the radio environment and adapts automatically. For example, it may:
- follow a moving user;
- suppress interference;
- avoid sources of jamming;
- optimise signal quality;
- compensate for fading; or
- form several independent beams simultaneously.
The antenna therefore becomes an active part of the communication system rather than a passive radiating device.
This adaptive capability is one of the defining characteristics of modern wireless communication.
How Do Smart Antennas Reduce Interference?
Suppose two users are located in different directions.
A conventional antenna illuminates both equally. A smart antenna can instead:
- direct one beam towards the desired user;
- reduce radiation towards the unwanted user; and
- place nulls towards sources of interference.
A null is a direction in which very little energy is transmitted or received.
By steering these nulls towards interfering transmitters, communication quality can often be improved dramatically.
Why Are Phased Arrays Ideal for Radar?
Radar systems must often track many rapidly moving targets.
A mechanically rotated antenna may require several seconds to scan the sky. A phased array can redirect its beam almost instantaneously. This allows modern radar systems to:
- track aircraft continuously;
- monitor multiple targets simultaneously;
- perform surveillance while tracking;
- adapt to changing threats; and
- maintain very high reliability.
Many military, civilian aviation, and weather radars now employ phased-array technology.
How Are Phased Arrays Used in Satellite Communication?
Traditional satellite earth stations employ mechanically pointed reflector antennas.
Increasingly, however, flat-panel phased arrays are replacing these dishes. Electronic steering allows the antenna to:
- track moving satellites;
- switch rapidly between satellites;
- eliminate mechanical motors;
- reduce maintenance; and
- provide lower-profile installations.
These advantages are particularly valuable for:
- aircraft;
- ships;
- trains;
- motor vehicles; and
- low-Earth-orbit (LEO) satellite constellations.
Flat electronically steerable antennas are expected to become increasingly common as satellite communication continues to expand.
Why Are Smart Antennas Important for 5G?
Modern cellular networks must support enormous numbers of users.
Instead of broadcasting uniformly across an entire cell, 5G base stations employ beamforming to create narrow beams directed towards individual users. This approach provides:
- higher received signal levels;
- reduced interference between users;
- greater spectral efficiency;
- improved battery life for mobile devices; and
- much higher overall network capacity.
Without beamforming, many of the performance targets of modern cellular systems would be difficult to achieve.
Can One Antenna Form Several Beams?
Yes.
One of the greatest advantages of digital phased arrays is that they can produce several independent beams simultaneously. For example, a single antenna may:
- communicate with several users;
- track multiple satellites;
- perform radar surveillance while tracking targets; or
- support communication and sensing simultaneously.
This capability greatly increases system flexibility and makes much more efficient use of the available spectrum.
Are Phased Arrays More Expensive?
Historically they were.
Early phased arrays required hundreds or thousands of expensive phase shifters and transmitters. Recent advances in:
- semiconductor technology;
- microwave integrated circuits;
- digital signal processing;
- software-defined radio; and
- mass production
have reduced costs dramatically.
Although phased arrays remain more complex than simple antennas, they are becoming increasingly affordable and are now found in many commercial products.
Will Mechanical Antennas Disappear?
Probably not.
Mechanical antennas remain attractive whenever:
- only occasional pointing adjustments are required;
- maximum efficiency is important;
- very high transmitter power is used; or
- cost must be minimised.
Large satellite earth stations and radio telescopes, for example, will continue to employ mechanically steered reflector antennas for many years.
Nevertheless, electronically steerable arrays are steadily replacing mechanical systems wherever rapid beam steering provides significant operational advantages.
Why Are Smart Antennas One of the Most Important Developments in Modern Communications?
Smart antennas represent a fundamental shift in antenna design.
Instead of radiating fixed patterns, modern antennas increasingly:
- adapt automatically;
- optimise communication continuously;
- suppress interference;
- track users dynamically; and
- exploit advanced digital signal processing.
This transformation has enabled many technologies that are now taken for granted, including high-capacity mobile networks, electronically scanned radar, broadband satellite communication, and adaptive wireless systems.
As communication networks continue to evolve, smart antennas are expected to become even more capable and more widespread.
What Should You Remember?
- A phased array steers its beam electronically by adjusting the relative phase of signals supplied to many antenna elements.
- Electronic beam steering eliminates the need for mechanical antenna movement.
- Beamforming concentrates energy towards desired users while reducing interference.
- Smart antennas continually adapt their radiation patterns in response to changing propagation conditions.
- Phased arrays are widely used in radar, satellite communication, radio astronomy, Wi-Fi, and modern cellular systems.
- Many phased arrays can form multiple independent beams simultaneously.
- Smart antennas are transforming wireless communication by making antennas adaptive rather than passive components of the communication system.