What is the difference between an analog beamforming and a digital beamforming phased array?
Beamforming Architectures
Analog beamforming is the traditional phased array approach: a single RF signal is distributed to all elements through a corporate feed network, with a phase shifter (and optionally an attenuator) at each element. The phase shifters create the beam in real-time at RF frequencies. Advantages: simple architecture, low DC power consumption, mature technology. Limitations: single beam, fixed amplitude/phase weighting (no adaptive optimization per snapshot), and the phase shifters add insertion loss (1-3 dB per bit).
Digital beamforming provides maximum flexibility by digitizing the signal at each element. All processing happens in the digital domain: beam steering, adaptive nulling, multiple simultaneous beams, and sophisticated space-time adaptive processing (STAP) for clutter rejection. The cost is N ADCs, N receivers, and enormous digital processing throughput (N × sample rate × bits per sample).
Hybrid beamforming (used in 5G NR) divides the array into sub-arrays of 4-16 elements, each with analog beamforming. The sub-array outputs are then digitized and combined digitally. This provides K simultaneous beams (where K = number of sub-arrays) with reduced hardware complexity. For 5G: a 256-element array with 16 digital sub-arrays provides 16 simultaneous beams for multi-user MIMO.
Frequently Asked Questions
Which architecture for radar?
Military radar: DBF for maximum flexibility (adaptive clutter rejection, multiple simultaneous tracking beams). Commercial radar (weather, marine): analog for cost-effectiveness. Automotive radar: typically analog or hybrid with 4-8 digital channels.
What about power consumption?
Analog BF: 10-50 mW per element (phase shifter + control). Digital BF: 0.5-2W per element (ADC + digital processing). For a 1000-element array: analog = 10-50W, digital = 500-2000W. Hybrid: 100-500W (between analog and digital). The power difference drives the architecture choice for battery-powered and space-constrained systems.
Is full digital practical at mmWave?
Emerging. At 28 GHz: recent 5G systems use hybrid beamforming with 4-8 RF chains. Full digital at mmWave requires very fast ADCs (multi-GHz bandwidth) with acceptable power consumption: current ADCs for mmWave consume 1-3W per channel, making full digital feasible for small arrays (16-64 elements) but not yet practical for 256+ element arrays.