Question

Describe the working of directional coupler with neat diagram. 

Answer 1

Directional couplers are devices that will pass signal across one path while passing a much smaller signal along another path. 

One of the most common uses of the directional coupler is to sample a RF power signal either for controlling transmitter output power level or for measurement. 

Two Hole Directional Couplers:

 

 

i. The principle of operation of a two-hole directional coupler is shown in figure above. It consists of two guides; the main and the auxiliary with two tiny holes common between them as shown.

ii. The two holes are at a distance of  

is the guide wavelength.

iii. The two leakages out of holes 1 and 2 both in phase at position of 2nd hole and hence they add up contributing to Pf . But the two leakages are out of phase by 180° at the position of the 1st hole and therefore they cancel each other making Pb = 0(ideally). iv. The magnitude of power coming out of the two holes depends on the dimension of the holes. v. Although a high degree of directivity can be achieved at a fixed frequency, it is quite difficult over a band of frequencies. The frequency determines the separation of the two holes as a fraction of the wavelength.