* Question
Brief description of the active array structure.
* Answer
Here’s a concise, engineering‐level overview of an active array (active electronically scanned array, AESA):
What it is
An antenna array in which each radiating element (or small subarray) has its own transmit/receive (T/R) electronics—so gain, phase, and often frequency conversion are distributed rather than centralized. This enables electronic beam steering, agile beam shaping, and graceful degradation.
Core building blocks
Radiating elements: Patches, dipoles, slots, or tiles; often dual-pol.
T/R module per element or subarray:
Tx chain: Driver → phase shifter and attenuator (or vector modulator) → power amplifier (PA).
Rx chain: Low-noise amplifier (LNA) → phase/atten control → protection/limiter.
Switching or duplexing (circulator/TR switch) for T/R isolation.
Optional up/down-conversion (LO/mixer) for IF-digitized architectures.
Beamforming network:
Analog RF (phase/atten at RF), digital (per-element ADC/DAC + DSP), or hybrid (subarray analog + digital combining).
Control & timing: Bias, SPI/I²C control for phase/atten, synchronization and LO distribution, calibration tables.
Power distribution: DC/DC modules per tile, current monitoring, sequencing.
Health & calibration: Embedded detectors, couplers, temperature sensors; cal loops to correct phase/amplitude drift.
Mechanical/thermal: Heat spreaders, cold plates, or vapor chambers; radome; environmental sealing.
Typical signal flow (Tx/Rx)
Tx: Baseband/IF → (DAC) → up-conversion (if used) → per-element phase/amp control → PA → element.
Rx: Element → LNA → phase/amp control → (down-conversion) → (ADC) → digital combining/processing.
Why “active”
Because amplification and phase control are at or near each element, the array achieves:
Fast, wide-angle electronic beam steering (no moving parts).
Multiple beams (with digital or hybrid beamforming).
High reliability (failure of a few modules only slightly reduces performance).
Adaptive calibration to maintain sidelobes, gain, and pointing accuracy.
Variants & notes
Element-level vs. subarray-level T/R modules (cost vs. performance).
Tile architecture: Repeating, factory-calibrated tiles simplify scaling.
Polarization: Dual-pol elements with independent T/R chains per pol.
Frequency: From L/S/C bands to mmWave; integration level increases with frequency.
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