What is an RF Crossover?

An RF crossover or 0 dB crossover is a 4-port device that consists of two parallel transmission lines connected by multiple perpendicular λ/4 lines as seen in the image above. The input from Port 1 is routed to Port 3 and the Input from Port 4 is routed to Port 2, while keeping the signals reasonably isolated from one another. The name “crossover” comes from the fact that the signal crosses over to alternate paths. This architecture enables the signals in a single layer to cross over in different paths.

If all the ports are matched, power entering port 1 is transferred to port 3 with no change in phase, and good isolation from ports 2 and 4. This will give a result of the coupling value, S31 = 0 dB and the phase of S31 = 0 Degrees. Similarly, power entering port 4 is transferred to port 2.

Therefore, no coupling or division takes place thus the name “0 dB crossover”. 0 dB crossovers are employed in RF networks to transfer the signal among different lines without any coupling or phase change, such as in the case of a Butler matrix. A butler matrix uses hybrid couplers and phase shifters to get different phases and then RF crossovers are used to route the signals to different antenna ports.

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