How does a phase shifter steer a phased array beam?

A phased array steers its beam by applying a progressive phase shift across its elements. To steer the beam to angle theta from boresight, the phase difference between adjacent elements must be delta_phi = (2 pi d sin theta) / lambda, where d is the element spacing. For a 64-element linear array at 10 GHz with half-wavelength spacing (d = 15 mm), steering to 30 degrees requires delta_phi = pi/2 = 90 degrees per element. The first element gets 0 degrees, the second 90 degrees, the third 180, and so on up to 63 times 90 = 5670 degrees for the last element. Each element's phase shifter must provide 0 to 360 degrees of controllable phase shift with sufficient resolution to maintain the beam shape and sidelobe levels. A 6-bit phase shifter provides 5.625-degree resolution (360/64), which keeps pointing error below 0.1 beamwidth and quantization sidelobes below minus 30 dB.

What is the difference between analog and digital phase shifters?

Analog phase shifters provide continuous phase control using voltage-tunable elements like varactor diodes or current-tunable ferrite materials. A varactor loaded transmission line changes phase by 0 to 360 degrees as the control voltage sweeps from 0 to 15 V. Advantages: infinite resolution, fast tuning (nanoseconds for varactor). Disadvantages: phase shift varies with frequency (not true time delay), amplitude variation across the tuning range, and calibration complexity. Digital phase shifters use switched transmission line sections of fixed lengths to provide discrete phase states. A 6-bit shifter has six sections providing 180, 90, 45, 22.5, 11.25, and 5.625 degrees, switched in or out using PIN diodes or FET switches. Advantages: repeatable, temperature-stable, easy digital control. Disadvantages: quantized resolution, higher insertion loss from multiple switch stages.

Why do wideband systems need true time delay instead of phase shifters?

A phase shifter applies a fixed phase shift in degrees, independent of frequency. But beam steering requires a time delay that is constant across frequency. At 10 GHz, 90 degrees of phase shift corresponds to 25 picoseconds of delay. At 11 GHz, the same 90 degrees corresponds to 22.7 picoseconds. If the system operates over 10 to 11 GHz (10 percent bandwidth), the beam points at different angles at different frequencies: beam squint. For a 64-element array steered to 30 degrees, the beam squints by approximately 3 degrees across 10 percent bandwidth, which is about one full beamwidth. This destroys the beam pattern for wideband signals. True time delay elements provide constant delay in seconds rather than constant phase in degrees, eliminating squint. Technologies include switched transmission line delays, optical delay lines, and trombone adjustable coaxial lines.

Active Components

Phase Shifter

A 5G mmWave base station at 28 GHz uses a 256-element phased array to form and steer beams toward individual users in under 10 microseconds. Behind each element sits a 6-bit digital phase shifter that sets one of 64 phase states (5.625° resolution) with 4 dB insertion loss and 25 dB return loss. The beamforming controller updates all 256 phase shifters simultaneously through a serial digital bus, steering the 6°-wide beam anywhere within a ±60° scan volume. Without phase shifters, the antenna is a fixed-beam panel. With them, it is a software-defined beam that tracks users, nulls interferers, and shapes coverage in real time.

Category: Active Components

Function: Controllable phase at constant amplitude

Key App: Phased array beam steering

Phase Shifter Technologies

Type	IL	Resolution	Speed	Freq. Range	Use Case
Switched-line (PIN)	3 to 6 dB	4 to 6 bit	10 to 100 ns	1 to 40 GHz	Radar, 5G
Switched-line (FET)	4 to 8 dB	4 to 6 bit	1 to 10 ns	1 to 60 GHz	AESA, satcom
Varactor (analog)	2 to 5 dB	Continuous	1 to 10 ns	0.5 to 20 GHz	Agile tuning
Ferrite (Reggia-Spencer)	0.5 to 2 dB	Continuous	1 to 100 μs	1 to 100 GHz	High-power radar
MEMS switched-line	1 to 3 dB	4 to 6 bit	5 to 50 μs	1 to 100 GHz	Satcom, instruments
SiGe/CMOS IC	5 to 10 dB	5 to 7 bit	1 to 5 ns	20 to 80 GHz	5G mmWave RFIC

Progressive phase for beam steering:
Δφ = (2πd·sinθ) / λ
d = element spacing, θ = scan angle
10 GHz, d = λ/2, θ = 30°: Δφ = 90°

Quantization sidelobe level:
SLL ≈ −6N dB (N = number of bits)
6-bit: −36 dB. 4-bit: −24 dB

Beam squint (narrowband phase shifter):
Δθ ≈ Δf/f₀ × tanθ₀ (radians)

Common Questions

Frequently Asked Questions

How does it steer a beam?

Progressive Δφ across elements: Δφ = 2πd·sinθ/λ. 64 elements at 10 GHz, θ = 30°: 90° per element. 6-bit shifter: 5.625° resolution, quantization SLL < −36 dB, pointing error <0.1 beamwidth.

Analog vs. digital?

Analog (varactor/ferrite): continuous, infinite resolution, but phase varies with frequency and amplitude varies with tuning. Digital (switched-line): discrete states, repeatable, temperature-stable, easy control, but quantized resolution and more IL from switch stages.

Why true time delay for wideband?

Phase shifters give constant degrees, but steering needs constant delay. 90° at 10 GHz = 25 ps; at 11 GHz = 22.7 ps. 10% BW causes ~3° beam squint (one full beamwidth for 64 elements). TTD elements provide constant ps delay, eliminating squint.

Related Terms

← Phase Noise PLL →

Array Design

Phase Shifter Resolution Planner

Enter array size, scan angle, and sidelobe requirement. Compute the minimum phase shifter bit resolution and maximum beam squint for your bandwidth.

Plan Phase Shifter