**Subject :**Microwave Engineering

**Unit :**Microwave measurements

## Insertion and attenuation loss measurements

When a device or network is inserted in Ihe transmission line, part P_{r} of the input signal power P_{i} is reflected from the input terminal and the remaining part P_{i}-P_{r} which actually enters the network is attenuated due to the non-zero loss of the network. The output signal power P_{o} is therefore less than P_{i}. Therefore, insertion loss is defined by Ihe difference in the power arriving at the terminating load with and without the network in the circuit.

Since ,

..(1)

or

..(2)

Where, by definition

..(3)

..(4)

..(5)

..(6)

For perfect matching , Pr =0 and the insertion loss and the attenuation loss become the same. The experimental setup for insertion and attenuation loss measurements are shown below in figure 1 . The relative power levels are measured by using detectors and a VSWR meter. DC_{1} and DC_{2} are two identical directional couplers .

**Figure 1 : Insertion loss and attenuation loss measurement setup
**