need some clarification pl

[jsp]

hi all rf experts

i would like to know the following things

1. what is the difference between
a. 90 deg/quadrature hybrid
b. ring hybrid/ rat race combiner
c. wilkinson combiner
2. which one to use at what condition?

3. waht is the advantage of ring hybrid/rat race?

4.what is the advantage of 90 deg / quadrature hybrid?

thanks in advance expecting reply.

 

[dowjones]

hello jsp,

I give you my vision of these components:
1) differences
a) 90deg hybrid is a 4-port directional coupler. if you enter on port 1, your outputs are port 2 and 3 with the same amplitude and 90deg shifted. port 4 is isolated from port 1. if you enter on port 4, your outputs are 2 and 3 and the shift is -90deg.

b) rat race. is a 180deg 4 port directional coupler. if you enter on port 1, the outputs are 2 and 3 and they are 180 out of phase. port 4 is isolated from 1. If you enter on port 4, port 2 and 3 are the outputs with the same phase. This device is useful to add/substract signals

c) wilkinson. is a 3 port device (with a resistor inside). gives in-phase outputs, i.e., enter on port 1 and ports 2 and 3 are in-phase. since all ports are matched and the outputs are isolated this is a sort of directional coupler wher the 4th port is internal, and connected to the resistor

2) depends on the application you are thinking on. e.g., if you have a 2 port antenna for circular polarization you have to use the 90deg hybrid. If you are designing a mixer with in-phase signal+out of phase local oscillator, you should use the rat race, if you are splitting/combining a signal, you can use the wilkinson,...

3) and 4) there is no advantage of using one or another, it depends what you want to do with the signals.

regards