8-5 ACTIVE DEVICE Active devices are key components in microwave systems.
The measurements that are made on active devices are similar to
those made on passive devices.
Active devices come in many shapes and sizes. In most cases we are
going to have to develop a fixture in which to mount the device.
Active devices require bias voltages, and in many cases they are easily
damaged. High gain amplifiers may saturate with input signals of
–50 dBm. With active devices, we have a new set of measurement re-
quirements.
The 373xxE has been designed to help you make these types of mea-
surements. It includes one 70 dB step attenuator (60 dB for 37397E)
used to adjust the Port 1 power level. A second 40 dB step attenuator
is also included (with Option 6) in the forward transmission path to al-
low measurement of high gain devices without sacrificing reverse
transmission and reflection measurements (S12,S
22). Bias tees on each
port are used to bias the device via the test port center conductor. This
approach to bias is useful for testing transistors; however, MMIC’s
usually require bias injection at other points (Figure 8-20).
ACTIVE DEVICE MEASUREMENTS
8-24 37xxxE OM
B i a s T e e s
R F
I N
T E S T
P O R T
V
B I A S
Figure 8-20. Bias Tee