Feed Network
Understanding Feed Networks
The feed network is often the performance-limiting element in an array antenna. Its loss directly reduces system efficiency and increases noise temperature. Its amplitude and phase accuracy across the bandwidth determine the quality of the radiation pattern.
Feed Network Types
- Corporate feed: Binary tree of power dividers. Each element has an independent path from the input. Equal path lengths = wideband. Higher loss.
- Series feed: Elements tapped in series along a transmission line. Compact. Narrowband (beam squints with frequency).
- Space feed: A feed antenna illuminates the array through free space. No RF feed network loss. Used for large arrays.
Feed Network Loss
For a 16-element corporate feed with 4 power divider stages: 4 x 0.3 dB (divider excess loss) + transmission line loss = 1.5-3 dB total. This loss directly reduces EIRP and increases system noise figure.
Frequently Asked Questions
What is a feed network?
A feed network distributes the RF signal to all antenna elements with correct amplitude and phase. It uses power dividers, couplers, and transmission lines. Feed network loss and accuracy directly affect array efficiency and beam quality.
What is the difference between corporate and series feed?
Corporate feed uses a binary tree of dividers (equal path lengths, wideband, higher loss). Series feed taps elements along a single line (compact, narrowband, beam squints with frequency). Corporate is standard for most phased arrays.
Why does feed network loss matter?
Feed network loss reduces the power reaching the antenna elements, directly lowering EIRP. On receive, the feed network loss before the LNA adds directly to the system noise figure. Minimizing feed loss is a primary design goal.