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What is Beam Squinting in Phased Arrays?

By RF Wireless Expert Team

Beam squinting in phased array antennas is a spatial distortion phenomenon where a wideband radio frequency (RF) beam unintentionally points in slightly different directions depending on the specific frequency being transmitted. This occurs because traditional phase shifters apply a fixed phase angle to steer the beam; since higher and lower frequencies possess different wavelengths, this fixed angle causes the edges of the frequency band to physically over steer or under steer off the target. To prevent this severe signal degradation in modern high capacity SATCOM and 5G networks, engineers eliminate beam squint by replacing standard phase shifters with Time Delay Units (TDUs) to apply true time delay across the antenna array.

Introduction : In modern wireless communications, antennas are no longer static dishes that physically rotate. Instead, the industry relies on Active Electronically Scanned Arrays (AESAs).

AESAs consist of a grid of dozens, hundreds or even thousands of small, stationary antenna elements. By carefully controlling the exact moment a radio frequency (RF) signal is emitted from each individual element, the waves combine in the air (constructive interference) to form a focused beam pointing in a specific direction.

To control this timing, engineers historically rely on a component called Phase Shifter. These phase shifters introduce a significant physical limitation i.e. Beam Squinting in high bandwidth systems.

What is Beam Squinting?

It is a spatial distortion where an antenna beam accidentally points in slightly different directions depending on the frequency of the signal being transmitted.

To understand why this happens, we have to look at how phase shifters work. A phase shifter steers a beam by altering “phase angle” of the RF wave (e.g. delaying the signal by 90 degrees). The calculations used to set these phase angles are perfectly tuned to the center frequency of the system.

However, modern communication systems don’t just transmit a single frequency; they transmit a “band” of frequencies (bandwidth). Because higher frequencies have shorter wavelengths and lower frequencies have longer wavelengths, applying the exact same fixed phase shift (e.g., 90 degrees) to the entire band causes a physical discrepancy.

  • At center frequency, the beam points exactly where you want it.
  • At higher frequencies of the band, the phase shift isn’t quite enough, causing the beam to under-steer.
  • At lower frequencies of the band, the phase shift is too much, causing the beam to over-steer.

The result is a beam that “spreads” or “squints” across different angles. Visually, it is very similar to how a glass prism splits white light into a rainbow of different colors pointing in slightly different directions.

Why is Beam Squint a Problem?

In narrow band systems, the frequency range is so small that beam squint is negligible. However, in next generation SATCOM and 5G mmWave networks, operators are using massive instantaneous bandwidths to push gigabits of data per second.

If a wideband signal suffers from beam squint, the receiver will only pick up the center frequencies at full strength. The high and low frequencies will physically point away from the target, leading to signal distortion, loss of gain or wastage of bandwidth.

How to Fix Beam Squint

Engineers have developed a few primary methods to eliminate or mitigate beam squint, depending on the system’s budget, size and bandwidth requirements.

  • The most mathematically perfect way to fix beam squint is to stop using phase shifters entirely and replace them with “Time Delay Units (TDUs)”.
  • To balance cost and performance, engineers use Hybrid Architecture consisting of both phase shifters and TDUs. Inexpensive phase shifters are placed at every individual antenna element to handle the fine, localized steering. A TDU is placed behind the entire sub-array to apply a “bulk” true time delay to that specific cluster of elements.

Summary

Beam squinting is an unavoidable physics problem when using phase shifters to steer wideband RF signals. While phase shifters are cheap and ubiquitous, the demand for massive data throughput in modern SATCOM requires a solution. By implementing Time Delay Units (TDUs) either at the element level for flawless wideband performance or at the sub-array level in a cost effective hybrid design; engineers can eliminate squint, keep their beams focused, and unlock the full potential of next-generation satellite networks.

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