An active electronically scanned array (AESA) amplifies and phase shifts the transmit and receive signals by placing active components at the elements. Figure 6.1 is a diagram of a typical T/R (transmit/receive) module. It may operate in half- or full-duplex mode (sequential or simultaneous transmit and receive), depending on the application. The transmit and receive channels must be isolated, and the transmit amplifier must be protected from reflections due to the changes in impedance during beam scanning. Types of isolating devices include circulators and/or switches (Fig. 6.1 has one of each). In order to reduce components, the transmit and receive signals often share the attenuator and phase shifter that weight the amplitude and phase of the signals. The low-noise amplifier (LNA) establishes a low-noise figure while amplifying the receive signal. A limiter caps the signal amplitude in order to protect the sensitive LNA from large input signals. Power amplifiers (PAs) in the transmit channel compensate for the losses in the feed network. However, increasing the power amplifier output power too much has the negative effect of increasing the heat production which could lead to an expensive and complex cooling requirement.
This chapter introduces T/R modules and associated technology, performance ...
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