LHCP
Understanding LHCP
LHCP and RHCP together form a complete orthogonal polarization basis. Any electromagnetic wave can be decomposed into LHCP and RHCP components. Using both simultaneously on the same frequency doubles the capacity of a communication link.
LHCP Applications
- Dual-CP satellite: RHCP and LHCP on the same frequency double capacity.
- Radar clutter rejection: Rain reverses CP sense. Transmitting one sense and receiving the other rejects rain clutter.
- Polarization diversity: Using RHCP and LHCP provides diversity gain in fading channels.
Generating LHCP
- Helical antenna: Left-hand wound helix produces LHCP.
- Crossed dipoles: Quadrature feeding with reversed phase produces LHCP.
- Patch antenna: Sequential rotation array or dual-feed with 90-degree hybrid and reversed ports.
Frequently Asked Questions
What is LHCP?
LHCP is circular polarization with counter-clockwise rotation. It is orthogonal to RHCP, meaning an LHCP antenna cannot receive RHCP signals and vice versa. This orthogonality enables frequency reuse and polarization diversity.
When is LHCP used?
LHCP is used for dual-polarization satellite systems (paired with RHCP), as the cross-pol reference in antenna measurement, and in some radar applications. GPS is exclusively RHCP; LHCP would be used as the cross-pol measurement reference.
Can you convert between RHCP and LHCP?
Yes. An orthomode transducer (OMT) or circular polarizer can separate RHCP and LHCP from a single feed. A reflection reverses the sense (RHCP reflects as LHCP). Rotating a halfwave plate converts between RHCP and LHCP.