Microwave circuit deals with very high frequency where electrical signals are no more treated as simple low frequency signal but are treated as wave. Wave has the property of reflection and transmission. So in microwave any of the ports which is not in use cannot be kept open circuited or short circuited since this will cause the wave to get reflected from these ports. This reflected signal from the open or short circuited port interfere with incident signal and standing wave is formed. Standing wave causes unwanted loss in the circuit and also reduces the efficiency of the device. To avoid such situation proper termination of microwave system is required.

There are following types of terminations:

i) Taper Termination ii) Step termination

Taper Load: It consists of a taper conical rod of lossy material that is either fixed at one end as shown in figure and is aligned with propagation axis. Total length of the lossy material is l1 +l2. When taper length l1 is greater than a few wavelengths at the lowest operating frequency, reflections are quite small (swr <1.04). The length L2 is chosen so that the combined loss through l1 and l2 is greater than 20 dB. Therefore there will be 20 dB loss in forward direction and 20 dB loss in reverse direction (after reflection) so the total loss of 40 dB will reduce the swr (standing wave ratio) to a great extent.

Step load:

This is designed to overcome the disadvantage of larger length of the taper load. This load contains a block of lossy dielectric material as shown in figure. Wave enters from open end of the load and hits the surface A of the lossy material whose dimension is b1. Since the dimension b1 of the lossy material alters the characteristic impedance of the waveguide some part of the wave is reflected back and the remaining is propagated to hit the surface B. Some part of the wave hitting surface B also gets reflected and moves in reverse direction towards the input of the load. Since the length l1 is λ/4 the total distance travelled by reflected wave from surface B is λ/2 (λ/4 distance from surface A to surface B and λ/4 distance from surface B back to surface A). Due to this the reflected wave from surface B when reaches to surface A undergoes a phase shift of 1800 w.r.t. reflected wave at surface A and the two reflected waves cancel each other. Length l2 is chosen in such a way that the total loss due to the l1 and l2 in one direction is 20dB.