TABLE OF CONTENTS As has been seen in previous chapters the gallium arsenide field effect transistor has revolutionized the design of low-noise and power microwave frequency amplifiers as well as providing an excellent device for oscillators, modulators and mixers. The GaAs FET is often used in its unencapsulated or bare chip form in microwave circuits but for many applications it is desirable to package the device or devices in well characterized hermetic enclosures, For high frequency applications these packages need to be as small as possible to minimize the effect of reactances associated with the encapsulation. It is desirable to make the electrical length between the packaged device and the circuit as small as possible to avoid large phase angle changes in the input and output reflection coefficients as the frequency is changed. Such large phase angle differences lead to an inability to match the packaged FET over wide bandwidths. Small packages, however, tend to increase the effect of feedback paths thus increasing the S 12 of the FET and decreasing the frequency range over which the device is stable.
Microwave packaging techniques are only just catching up with the rapid advances of the GaAs FET in its frequency performance and its applications and it is only recently that some fundamental problems encountered with certain packaging techniques have been understood and overcome at frequencies above 15 GHz.
"Pre-matching" the FETs, i.e. including matching circuits within the package so that the influence of the package on device performance is minimized, is...
