How does a phased array antenna steer its beam electronically without mechanical movement?
Electronic Beam Steering
The phased array principle relies on the superposition of electromagnetic waves. When all elements transmit with the same phase, their signals add constructively directly in front of the array (broadside). By adding a linear phase progression, the constructive interference direction shifts to the angle θ₀ where the path-length differences compensate the applied phase shifts.
Phase shifters are the key component: they must provide 0-360° of continuous or discrete phase shift with low insertion loss and fast switching speed. Technologies: ferrite phase shifters (high power, slow, expensive), PIN diode switched-line (moderate power, fast, moderate cost), MMIC reflective-type (low power, very fast, low cost for mass production), and MEMS (very low loss, moderate speed, emerging technology).
The beam steering speed is limited by the phase shifter switching time and the control circuit update rate: PIN diode phase shifters switch in 10-100 ns, MMIC phase shifters in 1-10 ns, and ferrite phase shifters in 1-10 μs. This allows radar systems to repoint the beam thousands of times per second, enabling simultaneous multi-function operation (tracking multiple targets while searching for new ones).
Frequently Asked Questions
What is the maximum scan angle?
Typically ±60° from broadside for a well-designed phased array. Beyond ±60°: the element pattern gain drops significantly (element pattern factor), the beamwidth broadens, and mutual coupling effects increase. The array gain at 60° scan is approximately 3-4 dB less than at broadside due to projected aperture reduction.
Does the beam shape change when steered?
Yes. The beamwidth broadens as 1/cosθ₀ when scanned off broadside. At 60° scan, the beamwidth is approximately twice the broadside value. This is an inherent geometric effect: the effective aperture projected in the beam direction shrinks as the beam steers away from broadside.
What about digital beamforming?
Digital beamforming replaces the analog phase shifters with ADCs at each element: the phase shifting is done digitally after sampling. This provides ultimate flexibility: multiple simultaneous beams, adaptive nulling, and per-element amplitude/phase control. The cost is N ADCs and N digital receivers, which has become practical with modern RFIC technology.