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2 years ago in Electrical Engineering , RF & Antenna Design By Amy
I need to generate orthogonal circular polarization (LHCP & RHCP) from a single aperture. What are the most reliable and bandwidth-friendly feed network configurations?
I'm working on a satellite communications terminal that requires polarization diversity. The radiating element itself (likely a patch or crossed dipole) can support both senses, but the feed network is the challenge. I'm evaluating a dual-port design using a 90° hybrid coupler (branch-line or Lange) versus a more complex orthomode transducer (OMT). For wider bandwidth, is it better to use a corporate feed with separate 90° phase shift lines for each port, or is there a more elegant integrated solution that minimizes loss and maintains port isolation >25 dB across a 10-15% bandwidth?
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By Aamir Answered 1 year ago
For your application, the choice hinges on bandwidth and integration level. For a printed antenna (patch) with 10-15% bandwidth, the most reliable design I've used is a dual feed with a wideband quadrature hybrid coupler (like a Lange coupler in microstrip) off-board. This gives excellent port isolation (>30 dB) and axial ratio across the band. For a horn or reflector feed requiring ultra-wideband/multi-octave performance, an Orthomode Transducer (OMT) is the professional standard, offering near-perfect isolation and very low loss, but it's bulky and expensive. A corporate feed with separate 90° lines is simpler but suffers from poor isolation and sensitive axial ratio if amplitudes aren't perfectly balanced. My recommendation: for a compact terminal, design your crossed-dipole or patch for dual-linear ports, then connect to a commercial surface-mount 90° hybrid; it's the best balance of performance and integration.
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