The SWR Autotesters and bridges described in this manual are broadband microwave measurement instruments. They are used with other test instruments for making fixed- and swept-frequency return loss (SWR) measurements over a wide range of radio frequencies. Return loss measurements are made to check the performance of systems, subsystems, and microwave components such as Amplifier directional couplers, attenuators Filter plitters, and terminations. The Wiltron SWR Autotesters and bridges offer significant advantages over other microwave measurement devices such as slotted lines and dual- directional couplers. Advantages include using an unmodulated microwave source and providing a greater degree of accuracy over a broader frequency range for both direct and comparison-type measurements.