What causes beam squint?

Phase shifters in a phased array set a constant phase difference between elements, independent of frequency. But the phase needed for steering is frequency-dependent: the required inter-element phase is phi = (2*pi*f/c) * d * sin(theta). At the design frequency f0, the beam points at the intended angle theta_0. At a different frequency f, the same phase difference steers the beam to a different angle: sin(theta_f) = (f0/f) * sin(theta_0). The beam squints toward broadside as frequency increases and away from broadside as frequency decreases. The squint angle increases with the scan angle and with the fractional bandwidth.

How is beam squint prevented?

True Time Delay (TTD) eliminates beam squint by applying a constant time delay (not constant phase) between elements. The required delay is: tau = d * sin(theta) / c. Time delay inherently provides the correct phase at all frequencies: phi(f) = 2*pi*f*tau. TTD can be implemented with switched transmission line lengths, MEMS delay lines, photonic delay lines, or digital delays in the baseband. Sub-array TTD is a hybrid approach: TTD between sub-arrays and phase shifters within each sub-array, which limits squint for moderate bandwidths while reducing the number of expensive TTD elements.

How much beam squint is acceptable?

The typical criterion is that the beam squint should not exceed one-quarter of the half-power beamwidth across the signal bandwidth. Beyond this, the gain at the edges of the band drops by more than 1 dB, causing significant pattern distortion. For a 64-element array steered to 45 degrees with 10% bandwidth: beam squint = approximately 0.7 degrees, while HPBW = approximately 1.6 degrees. The squint is 44% of the HPBW, which exceeds the quarter-beamwidth criterion. This array would need TTD for wideband operation. Narrowband systems (less than 2-3% bandwidth) can generally tolerate the squint from phase-only steering.

Phased Array Design

Beam Squint

/beem skwint/

Beam Squint is the undesired shift in beam pointing direction as a function of frequency in a phased array using constant-phase (not time-delay) steering. The beam squints toward broadside at higher frequencies and away at lower frequencies, with the effect proportional to scan angle and fractional bandwidth. True Time Delay (TTD) is the fundamental solution.

Category: Phased Array Design

Cause: Phase-only steering

Solution: True Time Delay (TTD)

Understanding Beam Squint

In a narrowband phased array, you set a constant phase shift between elements to steer the beam. This works perfectly at one frequency. But if the signal has significant bandwidth (like a wideband radar pulse or a 5G mmWave carrier), the beam points in slightly different directions at the upper and lower band edges. For large arrays steered to wide angles, this can split the beam or cause significant gain loss at the band edges. This is why wideband radar and 5G systems increasingly require True Time Delay.

Beam Squint Formulas

Beam Squint:
Beam Squint is the undesired shift in beam pointing direction as a function of frequency in a phased array using constant-phase (not time-delay) steering. The...

Key specifications:
10 % | -5 % | -30 % | 0 dB | 1 mW | 30 dB

Gain: G = η_ap×4πA/λ²

Beam Squint Mitigation Methods

Method	Squint Reduction	Bandwidth	Complexity	Application
Phase shifters only	None	2-5% (narrowband)	Low	Narrowband radar, comm
Sub-array TTD	Moderate	10-30%	Medium	Wideband radar, 5G
Full element TTD	Complete	Octave+	High	SIGINT, EW
Photonic TTD	Complete	Multi-octave	Very high	Ultra-wideband arrays
Digital TTD (baseband)	Complete	Unlimited	High (digital BF)	Digital arrays, MIMO

Key Equations

Decibel conversion:
Power: dB = 10log(P₂/P₁)
Voltage: dB = 20log(V₂/V₁)

dBm to watts:
P(W) = 10^{(dBm−30)/10}
0 dBm = 1 mW, +30 dBm = 1 W

Wavelength:
λ = c/f = 300/f(MHz) meters

Comparison

Aspect	Beam Squint Spec	Typical Range	Impact	Design Note
Primary function	Beam Squint is the undesired shift in be...	Application-dep.	Critical	Verify in sim
Operating range	The beam squints toward broadside at hig...	Application-dep.	Critical	Verify in sim
Performance	True Time Delay (TTD) is the fundamental...	Application-dep.	Critical	Verify in sim
Integration	Understanding Beam Squint In a narrowban...	Application-dep.	Critical	Verify in sim
Trade-off	This works perfectly at one frequency...	Application-dep.	Critical	Verify in sim

Common Questions

Frequently Asked Questions

What causes it?

Phase shifters apply constant phase, but steering requires frequency-dependent phase (phi = 2*pi*f/c * d * sin(theta)). At non-center frequencies, the same phase steers the beam to a different angle. Squint increases with scan angle and bandwidth.

How to prevent it?

True Time Delay (TTD): constant time delay (not phase) between elements. Provides correct phase at all frequencies (phi(f) = 2*pi*f*tau). Implemented as switched line lengths, MEMS, photonic, or digital delays. Sub-array TTD is a practical hybrid approach.

How much is acceptable?

Standard criterion: squint less than HPBW/4 across signal bandwidth. Beyond this, band-edge gain drops >1 dB. Narrowband systems (less than 2-3% BW) tolerate phase-only steering. Wideband (>10% BW) at wide scan angles needs TTD.

Related Terms

← Beamforming Beam Steering →