Chapter 9 Microwave Attenuators Abstract This chapter presents design and analysis of diode- and transistor-based microwave attenuator circuits including their applications, performance variation and compensation with operating temperature. Complete design details of series-, shunt-, π -, TEE- and hybrid-configured attenuators with their merits and demerits are given. Detailed design and analysis of driver circuits based on equiresistance curves of p-i-n diodes for achieving temperature-insensitive attenuation of the attenuator circuits is also presented. 9.1 Introduction An attenuator provides known amount of attenuation when it is connected in a signal path having known source and load impedances. These are used to control signal level in the signal path. It may provide a fixed or variable/adjustable attenuation depend- ing upon control voltage or current. Fixed attenuators are realized using combina- tion of RF-resistive elements with fixed values, whereas voltage/current-controlled attenuators are realized using combination of voltage/current-dependent resistors. At RF/microwave frequency range, forward-biased p-i-n diodes, BJTs or FETs are used as voltage/current-dependent RF resistors [1–13]. Voltage-variable p-i-n diode attenuators are used to control signal level of communication systems by controlling gain of the system [1–7]. In case of satellite transponders, p-i-n diode or FET-based attenuators are used for on-board gain control of a communication transponder by issuing command from ground or automatically by sensing RF power level. Important performance parameters of a microwave attenuator are operating fre- quency, attenuation range, insertion loss, port return losses, power handling capability and DC power requirements. RF switches discussed in the previous section are also attenuators with maximum attenuation at its OFF state and minimum attenuation at its ON state. OFF-state reflective switch offers maximum attenuation by reflecting the signal which is undesirable as function of attenuator. Variable attenuator provides stepwise or continuous attenuation from its minimum to maximum attenuation range. Known amount of attenuation and port matching over its entire attenuation range are © Springer Nature Singapore Pte Ltd. 2019 S. C. Bera, Microwave Active Devices and Circuits for Communication, Lecture Notes in Electrical Engineering 533, https://doi.org/10.1007/978-981-13-3004-9_9 235