Amplifiers are one of the most important active devices in microwave and millimeter-wave circuits. Power amplifiers are usually found in the transmitting path of a transceiver in which modulated signals are amplified before being
passed to antennas for radiation. In contrast with low noise amplifiers(LNAs) which are normally found in the receiving path of a transceiver, power amplifiers are more efficient and can handle higher power.
In this lab, we will use AWR Microwave Office to design an LNA to realize the maximum transducer gain. The amplifier will operate at 10 GHz and the transistor used here is the Filtronic LPD200. The LPD200 is an Aluminium Gallium Arsenide/Indium Gallium Arsenide (AlGaAs/InGaAs) Pseudomorphic High Electron Mobility Transistor.
Before starting to work on AWR MWO, let’s see how to design a power amplifier with maximum transducer gain. Recall what we learned in lecture 5. A transistor is an active two-port network whose S-parameters can be written as:
Fig. 3.1 shows the input port of the transistor is connected to a signal source with an internal impedance of 𝑍𝑆 and the output of the port is connected to a load with impedance 𝑍𝐿. There are usually mismatches at both interfaces. The transducer gain 𝐺𝑇 of the transistor is defined as the ratio of the power delivered to the load to the power available from the source:
To maximize the transducer gain, appropriate input and output matching circuits are required as shown in Figure 3.2. Conjugate matching is used here to ensure all power available from the signal source is delivered to the input port of the transistor and all power available at the output of the transistor is delivered to the load.