Also known as: phased array, electronically scanned array, AESA
A phased-array antenna is an array of many small radiating elements whose beam is aimed electronically — by adjusting the relative phase (and often amplitude) fed to each element — rather than by physically turning the antenna.1 By delaying some elements relative to others, the array makes the wavefronts add up constructively in one chosen direction and cancel elsewhere, so the main lobe can be swept across the sky in microseconds with no moving parts. This ability to steer, and to form multiple beams at once, is what underlies modern radar, 5G base stations, and flat satellite terminals; the underlying signal-processing operation is beamforming.
How it works
Consider a straight row of identical elements spaced a fixed distance apart. If every element radiates in phase, the wavefronts stack up parallel to the array and the beam points straight ahead (broadside). Now add a progressive phase shift — element 2 lags element 1 by Δφ, element 3 by 2Δφ, and so on. The individual wavefronts now line up along a tilted plane, and the beam points off to the side by an angle that depends directly on Δφ. Change Δφ and the beam moves; because Δφ is just a number in a phase shifter or a digital multiply, steering is effectively instantaneous.
Several array facts follow from this:
- More elements, narrower beam and higher gain. A longer array behaves like a larger aperture, so gain rises and beamwidth shrinks with element count — the same aperture logic as a dish, but reconfigurable.
- Scan loss. As the beam steers away from broadside, the array’s projected aperture shrinks, so gain falls and the beam broadens toward the edges of coverage.
- Grating lobes. If the elements are spaced much more than half a wavelength apart, the array forms unwanted extra beams (grating lobes) in other directions. Keeping spacing around λ/2 avoids them.
- Nulls too. The same phase control that builds the main lobe can place deep nulls on interferers — adaptive arrays exploit this to reject jammers.
Variants
- Passive (PESA): one transmitter/receiver drives all elements through phase shifters.
- Active (AESA): every element has its own tiny transmit/receive module. AESAs are more capable and reliable (a few failed modules degrade gracefully) and dominate modern radar.
- Digital / hybrid beamforming: each element or subarray is digitised separately, and the beam is formed in software, allowing many simultaneous independent beams — the architecture behind massive-MIMO 5G.
The elements themselves are often patch antennas on a board, which is how a flat panel can hide a steerable array.
Relevance to SDR
Phased arrays are where antennas and DSP merge, and the SDR world touches them directly through beamforming: with several coherent receivers sampling several antennas, software can steer, null, and estimate directions of arrival exactly as a hardware array would, but entirely in the digital domain. Coherent multi-channel SDRs make small experimental receive arrays practical for direction finding and passive radar. On the infrastructure side, phased arrays are the enabling antenna for 5G NR beam steering, modern radar, and electronically steered flat-panel satellite terminals.
GopherTrunk is a single-channel land-mobile trunking receiver with no array hardware and no beamforming, so it does not implement phased-array steering; the systems it decodes (P25, DMR, NXDN, TETRA) are received on ordinary omnidirectional antennas. This page is included to relate the array world to the broader RF landscape and to explain how electronic beam steering works.
Sources
-
Phased array — Wikipedia, for progressive phase steering, grating lobes, scan loss, and PESA/AESA architectures. ↩