What Happens to an Electronically Steered Antenna's Link When Some Array Elements Fail

What Happens to an Electronically Steered Antenna's Link When Some Array Elements Fail

When a few elements in an electronically steered antenna (ESA) fail, the link normally stays up. Each element is one of many parallel transmit/receive channels whose signals add in phase. A failure removes a small slice of gain and raises the sidelobe floor, but it does not cut the connection. Engineers call this graceful degradation. The real risk depends on three things: how elements fail (dead, stuck or noisy), whether the failures cluster, and how much margin the link had to begin with. StarWin designs its electronically steered phased array terminals in-house, through subarray, PCB, calibration and aging test, and has published a white paper on the key technologies of ESA terminals. These failure modes are what its engineers design against.

TL;DR

·       Scattered element failures cost gain gradually. About 10% dead elements costs roughly 0.92 dB of transmit EIRP and roughly 0.46 dB of receive G/T in the idealised case.

·       A stuck or noisy channel can do more damage than a dead one.

·       Clustered failures, such as a lost subarray, distort the beam more than the same number of scattered failures.

·       Rising sidelobes can push a terminal toward its off-axis emission limits before users notice any throughput loss.

·       Users usually see slower throughput, not a dropped link, unless margin was already thin.

About the Author: This article was prepared by StarWin's R&D team in Chengdu. StarWin is a compound solution provider spanning Communication (5G + NTN across GEO, MEO and LEO), Navigation, Remote Sensing and Computing/Measurement. Its Ku and Ka band ESA terminals have been qualified by satellite operators including SES, Hispasat and Arabsat.

Why does a phased array degrade gracefully instead of failing outright?

Graceful degradation is the defining reliability property of a phased array. As individual elements fail, the array loses gain gradually and its sidelobes rise, but it keeps working. The mechanism is coherent summation. Think of a choir singing one note in unison. If three singers out of a hundred go quiet, the note gets slightly softer, but the song carries on. A soloist losing their voice ends the performance.

·       Mechanically steered antennas typically rely on physical actuators and a single transmitter, so a fault in either can take down the whole link.

·       An ESA spreads power across many independent transmit/receive modules, so one failure removes one voice from the choir.

·       A phased array radar report from the US Office of the Federal Coordinator for Meteorology notes that Navy experience shows up to 10 percent of the transmit/receive elements on an array face can fail before performance degrades significantly.

This is not a verdict against reflectors. Fixed earth stations commonly add redundant amplifier chains to cover their single point of failure. The two architectures simply spread risk differently.

How much gain and EIRP does the link lose when elements fail?

Because the array works by summing many channels, the cost of failures follows simple scaling, and transmit pays roughly twice what receive does.

·       Transmit: each element carries its own power amplifier, so a failure removes both radiated power and coherent array gain. EIRP scales with the square of the number of working elements.

·       Receive: signal voltage and uncorrelated channel noise both fall, so G/T scales roughly in proportion to the number of working elements.

These are idealised figures for a uniformly weighted array with randomly placed dead elements and a boresight beam. Real terminals are assessed with statistical Monte Carlo analysis, because pointing error, sidelobes and calibration residue add to them.

Why does the way an element fails matter more than how many fail?

The table assumes failed elements go quiet, which is the most forgiving case. Field failures are not always so tidy:

·       Dead channel: contributes nothing. It costs gain and slightly raises sidelobes.

·       Stuck phase shifter or attenuator: keeps radiating at the wrong phase, sending energy in the wrong direction and nudging beam pointing.

·       Noisy or oscillating receive channel: injects noise into the combined signal and can hurt G/T more than a dead channel.

·       Clustered failure: a beamformer chip or power rail usually serves several elements, so one fault removes a contiguous block. This produces structured sidelobes and pointing error beyond what scattered failures cause.

The practical lesson is that a terminal able to detect a misbehaving channel and switch it off turns a damaging failure into a harmless one.

Can failed elements push a terminal out of compliance before the link drops?

A related but less discussed consequence is regulatory rather than throughput-related. Failures disturb the amplitude taper that keeps sidelobes low, so the average sidelobe floor rises. In GEO operation, terminals must stay inside off-axis emission masks that protect neighbouring satellites. A degraded array can still close its own link comfortably while radiating more energy toward adjacent orbital slots. Our view is that service thresholds should be set against the off-axis pattern as well as Es/No, because the modem cannot see the interference it causes.

How do scan angle and orbit change the impact of failures?

The same failure costs more when the beam is steered far from broadside. Scan loss shrinks the effective aperture as the beam tilts toward the horizon. As a result, a terminal working low-elevation GEO satellites or LEO passes near the horizon already has its thinnest margin there, and failures stack on top. This is one reason hybrid ESA designs combine electronic and mechanical steering: tilting the panel keeps the electronic scan angle smaller. StarWin's hybrid ESA terminals take this combined approach and use beamforming to track and switch among GEO, LEO and MEO networks.

What does the user actually experience when elements fail?

For most users, element failures show up as slower throughput rather than a dropped connection. Modern satellite modems use adaptive coding and modulation. As signal quality falls, they step down to a more robust scheme. A one-decibel loss on a healthy link barely registers. The same loss during heavy rain, at a spot-beam edge or at low elevation can be enough to lose lock. That is why StarWin's broadband ESA terminals can be integrated with its own UHF, L and S band terminals: a narrowband satellite IoT path keeps telemetry and alerts flowing when the broadband link is under stress.

How should operators detect and manage element failures?

1.       Run built-in self-test at channel level and log which elements are disabled.

2.       Compare Es/No and transmit headroom against the commissioning baseline.

3.       Recalibrate after failures. Reweighting the remaining elements can pull sidelobes down, though lost power cannot be recovered.

4.       Set service thresholds on margin and off-axis compliance, not raw failure count.

5.       At procurement, ask how bad channels are detected and isolated, and what margin remains at your lowest operating elevation.

Frequently Asked Questions

Will one failed element drop my ESA link?
No. In a multi-element array, a single dead element costs a small fraction of a decibel. A stuck or noisy element can do more harm.

Does transmit or receive degrade faster?
Transmit. Each failure removes amplifier power and array gain, so EIRP falls roughly twice as fast in decibels as G/T.

Can software fully compensate for failed elements?
Partly. Recalibration can reshape the beam and lower sidelobes, but it cannot restore missing aperture or power.

Do CRPA anti-jamming antennas degrade the same way?
The physics is similar, but the consequence differs. A CRPA with N elements can form at most N-1 independent nulls, so each failed element reduces how many interference sources it can suppress.

Are mechanically steered antennas less reliable than ESAs?
Not inherently. They concentrate risk in fewer components, which can be made redundant. ESAs spread risk across many channels.

About StarWin

StarWin is a Chengdu-headquartered provider of AI-driven compound solutions spanning Communication (5G + NTN across GEO, MEO and LEO), Navigation, Remote Sensing and Computing/Measurement. Its broadband line covers the Flat Panel Terminal Series, including electronically steered phased array models such as the Ka/Ku Full Dimensional ESA Terminal and Mini Ka/Ku ESA30 Terminal, and the VSAT-class Parabolic Antenna Series. Its narrowband satellite IoT terminals include the TQZD-08, TQZD-10 and TZ043. StarWin products hold FCC, CE, RCM and ANATEL approvals and go through per-unit serial-number full inspection, backed by in-house array design and calibration that let StarWin supply the integrated system rather than a single component.

To discuss how array health, link margin and multi-orbit fallback apply to your network, contact the StarWin team at https://starwincom.com.