Antenna Arrays

Phased-Array Hardware

Many elements (e.g. a grid of patches) form one aperture
Electronics control how their signals combine
The aperture can remain fixed while the beam moves (vs. gimbals or turning the spacecraft)

Relative phase or delay sets the direction of constructive combination
The elements stay fixed
Transmit and receive use the same principle
Diagram: radiators fed through 0–360° phase shifters from a power distribution network; an equiphase front tilted to the scanned beam direction from broadside
- Element spacing ; progressive phase step between neighbors
Reference: Delos, Broughton, and Kraft, Phased Array Antenna Patterns, Part 1 (Analog Devices)

Eight elements, spacing , uniform amplitudes (calculated linear-array factor)
Changing the phase progression moves the peak: one trace steered to 0°, one steered to 30°
- The 30° beam is visibly broader than the broadside beam
Real scan performance also depends on each element’s own pattern

Common array element signals → separate combining weights → separate receivers
- Weights for beam A → beam A receiver
- Weights for beam B → beam B receiver
Separate combining weights select different directions

Several ground antennas, each with its own receiver, all observe the same spacecraft signal
- Antenna + receiver → delay/phase alignment → signal combiner
Combine aligned voltages or baseband signals
Voyager used ground-antenna arraying (Ludwig and Taylor, Voyager Telecommunications, §§6.3.2–6.3.3)

SNR = signal-to-noise ratio
Four equal 34 m apertures collect like one 68 m aperture if efficiencies match ()
- That does not make their patterns identical
Assumes equal signals/noise, uncorrelated receiver noise, ideal alignment and combining
Example: the Very Large Array (New Mexico) — 27 antennas, 25 m each, signals combined for radio astronomy