From circuit topology to behavioural model of power amplifier dedicated to radar applications

A new behavioural model of a power amplifier (PA) at system level is presented, dedicated to radar applications. This model, which is able to take into account output loading impedance mismatch, is based on a similar topology to the PA's circuit. The model, implemented in Agilent Advanced Design System (ADS), is validated for different loading impedances, until VSWR ¼ 2 (voltage standing wave ratio), on the PA's bandwidth. This approach permits an extraction, resulting from simple CW measurements or simulations, and easy model implementation. Introduction: In recent years the development of active electronically scanned array (AESA) radar has been significant. This technology will equip most of next generation military radar systems [1]. In the framework of the development of such systems, an accurate 'system' simulation is needed. Indeed, nowadays, cost reduction of such systems is a key issue for the European defence industry (an AESA is two times more expensive than a passive electronically scanned array) and that implies the use of accurate simulation tools to decrease margins taken on component specifications. Such simulations must be able to optimise the design of the whole radar functional chain by enabling design engineers to predict and analyse the impact of microwave components on 'system' performance. Unfortunately, design models of microwave components cannot be used for such a simulation because it would lead to huge computing time. That is why technical solutions have been explored to reduce complexity of simulation accuracy with radar signals. Today, simulation tools dedicated to AESA radar describe RF systems in only a unilateral way and with insufficient accuracy. Nevertheless, design constraints of AESA lead to significant load mismatch (up to VSWR ¼ 2) with varying phase in microwave chains implying the need for a nonlinear bilateral model. It appears that development of a powerful simulation tool requires an accurate model of the power amplifier (PA) in order to quantify its impact on transmission=reception (T=R) modules and then on emitted signal characteristics. Indeed, the PA undergoes many disturbances in AESA radars, particularly output loading impedance mismatch. In fact, impedance presented to the output port of the PA varies because of AESA controls. The difference between this impedance and PA load required in the case of optimal match condition can be huge. PA behavioural models employed in these simulations, simple gain or AM=AM-AM=PM, are insufficient. Recently, more efficient behavioural models were developed [2–5] but their implementation and their extraction are …