What Are Phased Array Antennas?

Phased array antennas are antenna systems composed of multiple radiating elements whose individual feed signals are assigned controlled phase shifts, enabling the composite radiation pattern to be steered electronically without physically moving the antenna structure. By advancing or retarding the phase at each element, the system causes signals from all elements to arrive in phase at the target direction, producing a high-gain beam aimed in that direction, while signals toward other directions cancel through destructive interference. The discipline draws on electromagnetic theory, microwave circuit engineering, and digital signal processing.

Phased arrays contrast with mechanically steered dishes and horn antennas in that the beam direction changes in microseconds rather than the seconds or minutes required to rotate a physical reflector. This speed advantage made phased arrays central to military radar from the 1960s onward, and subsequent integration of phase-shifting and beamforming circuits in semiconductor ICs has brought phased arrays into 5G base stations, satellite terminals, and automotive radar. The related topic of smart antennas encompasses phased arrays as a subset; smart antenna systems add adaptive processing to dynamically shape nulls toward interferers as well as beams toward users.

Array Factor and Beam Steering

The radiation pattern of a phased array is the product of the element pattern and the array factor, a scalar function that depends on element spacing, element count, and the applied phase gradient. For a linear array of N isotropic elements spaced by distance d, the array factor peaks when the progressive phase shift between adjacent elements equals (2 pi d / lambda) sin(theta), where theta is the steering angle from broadside and lambda is the wavelength. Setting the inter-element phase shift to achieve a chosen theta steers the beam to that angle, as explained in detail in Analog Devices' technical series on phased array antenna patterns.

Grating lobes arise when element spacing exceeds lambda/2 at the maximum scan angle, creating parasitic high-gain directions that waste power and create interference. Keeping spacing at or below lambda/2 prevents grating lobes but increases element count and cost for large apertures. Two-dimensional planar arrays extend the principle to azimuth and elevation steering simultaneously.

Active and Passive Array Architectures

Phased arrays divide broadly into passive and active configurations. In a passive phased array, a single transmitter drives all elements through a network of phase shifters and a corporate feed, and a single receiver collects the combined signal. In an active phased array, each element or sub-array has its own transmit/receive (T/R) module containing a power amplifier, low-noise amplifier, phase shifter, and gain control. Active arrays offer graceful degradation when individual T/R modules fail and allow per-element amplitude weighting to control sidelobe levels, at the cost of significantly more complex power and signal distribution.

IEEE publications on beam steering in active phased array antennas describe how advances in GaAs and GaN T/R module technology have driven down cost and power consumption to levels compatible with commercial deployment. Silicon CMOS beamforming ICs now integrate phase shifting, variable gain amplification, and switching for four to sixteen antenna channels on a single chip, enabling dense millimeter-wave array modules for 28 GHz and 39 GHz 5G bands.

Beamforming and Waveform Considerations

Analog beamforming applies phase shifts at RF or IF before analog-to-digital conversion, minimizing the number of data converters required. Digital beamforming performs phase weighting in software after conversion of each element's signal independently, enabling multiple simultaneous beams and adaptive null steering. NASA research on low-cost beam-steering approaches demonstrates hybrid architectures that partition array apertures into sub-arrays, each with analog phase control, while digital combining across sub-arrays retains adaptability.

Applications

Phased array antennas have applications in a wide range of systems, including:

• Air defense, air traffic control, and weather surveillance radar
• 5G millimeter-wave base station and user-terminal links
• Satellite communications Earth terminals with electronic beam pointing
• Automotive collision-avoidance and adaptive cruise control radar
• Medical and industrial phased-array ultrasound imaging