Microwave Hybrid Circuits Notes | Study Basic Electronics Engineering for SSC JE (Technical) - Electrical Engineering (EE)

 Microwave Hybrid Circuits

The interconnection of two or more microwave device using waveguides, tees or direction coupler is called as microwave junction. 

• We use traveling waves as a variables to characterize the hybrid parameters because at microwave range:
  (i) It is difficult to mea sure total voltage a nd current at the posrts of network.
  (ii) Short and open circuits are difficult to achieve over a broad band of frequencies.

To overcome these problems, we characterize the new parameters called S-parameters.

Waveguide Tees: 

E-plane Tee (Series Tee): S₁₃ = – S₂₃ For a matched junction S-matrix

S- matrix of E-plane tee is given by

H-plane Tee : S₁₃ = S₂₃

S=matrix

Magic Tee (Hybrid Tee) : Combination of E=plane Tee and H-plane Tee

1. If input at port 1 and port 2 is applied, the output will be zero at port 3 and additive at port 4.
2. If input is appllied at port 4 it is divided equally between port 1 and port 2 and does not appear at port 3.
3. If input is applied at port 3, it will produce an output of equal magnitude and opposite phase at port 1 and port 2 and output at port 4 is zero i.e. S₃₄ = S₄₃ = 0.

Application of Magic Tee: Measurement of impedance, as a mixer, duplexer.
Hybrid rings (Rat-Race circuits):

S-matrix:

If input is at port 1, it will not appear at port 3. If input is at port 2, it will not appear at port 4.

Directional Coupler:

Coupling Factor :

Directivity:

Coupling factor is a measure of percentage of incident power being sampled while directivity is a measure of how well the directional coupler distinguish between the forward and the reverse travelling powers.

Isolation:

S-Matrix:

Circulator: circulator is a four port microwave device in which wave can only flow from nth port to (n+1)th port

Isolator: An isolator is a device which provides very small attenuation in one direction and provides maximum attenuation in the opposite direction. 

• It is uniline device used to improve frequency stability in microwave generators in which the reflection from the load affects the generating frequency.