Operating limits for distortion reduction by the augmentation technique in nonlinear transistor amplifiers

In airborne military phased array radar systems, detection capability is influenced as much by receiver linearity as it is by system noise performance. The extremely wide dynamic range of the target returns in such systems leads to challenging receiver design compromises between amplifiers exhibiting low distortion or low thermal noise. Conventional methods that are used to improve linearity, such as increasing device size, bias current or supply voltage, inevitably result in enhanced thermal noise, higher power consumption and heat dissipation. In military aircraft, where weight and space are at a premium, these effects are difficult to accommodate. Consequently a method of amplifier linearisation is required that has minimal impact on the power consumption, size and noise figure of the receiver system. A possible solution to this problem, that has recently been advocated, relies on a process termed 'augmentation'. This solution is explored for application to weakly nonlinear receiver amplifiers and easy-to-use relationships are presented to enable designers to assess the frequency limits of the technique for particular devices and processes. © IEE, 2004.