RRCoupler (Rat-Race Coupler)

Symbol

Parameters

Name	Description	Unit	Default
Subst	Microstrip substrate name	None	MSub1
F	Center frequency	GHz	1
Zo	Characteristic impedance	Ohm	50
Delta	Length added to ring branches for tuning	mil	0

Notes

1. A rat-race coupler equally divides the power input at port 1 between ports 2 and 3. The signal at the output ports 2 and 3 are in-phase. Port 4 is isolated from port 1. If the signal is driven from port 2, then the power is divided between ports 1 and 4 with port 3 isolated. The signal at ports 1 and 4 are 180 degrees out of phase, and therefore this device is sometimes referred to as a 180-degree hybrid.
2. The design specifies the width and length of the microstrip lines to ensure that the ports are matched to Zo and equal power split is achieved at the design center frequency.
3. The optimization minimizes the value of S11 (referenced to the value of Zo) at the design center frequency by changing the length of the ring.
4. A SmartComponent subnetwork is empty until the Design Assistant is used to generate the design. Refer to Design Assistant.

For a more detailed discussion of this device, see: D. M. Pozar, Microwave Engineering, 2nd Edition, John Wiley & Sons: New York, 1998, pp. 401-407.

Example

A rat-race coupler was designed for a 50 Ohm system impedance at a center frequency of 2 GHz. Tuning using the Optimization Assistant yielded a value of Delta =-2.099 mil.