A L, S and C-Band Source-Controlled Voltage Variable Attenuator for Beam Control

This paper demonstrates a source-controlled attenuator, where control voltage is given to the source terminal of the main transistor (MT). The current is being attenuated from reaching the output. Conventional attenuators employ voltage divider principle or phase cancellation technique. In this work, at maximum attenuation, gate-to-source voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</inf>) is less than threshold voltage of the main transistor and hence, no current reaches the output. At minimum attenuation, V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</inf> is greater than threshold voltage and hence, entire current is transferred to the output. The attenuator shows good attenuation flatness, wide bandwidth, good linearity, unconditional stability and low noise figure for control voltages ranging from 0.93 V to 1.23 V with a step of 0.01 V. For fixed load, the attenuator has less than 1 dB amplitude error in the required bands (1.1-1.3 GHz, 2.7-2.9 GHz and 5.4-5.8 GHz). The attenuator can be used in T/R module of phased array radar.