TABLE OF CONTENTS A solid-state module may be connected to every radiating element or to every subarray of a phased array antenna, forming what is sometimes called an active aperture. Applications range from ultrahigh frequency (UHF) for surveillance to X band and above for airborne systems. Chapter 5 discusses the solid-state transmitter, but this section highlights some aspects specifically related to phased array radar.
A typical module is shown in simple schematic in Fig. 7.44. It consists of a transmitter amplifier chain, a preamplifier for receiving, a shared phase shifter with driver, and circulators and/or switches to separate the transmit and receive paths (the gain around the loop must be less than unity to avoid oscillations).
Power amplifiers for transmitting at the element level would typically have a gain of 30 dB or more to compensate for the loss of power dividing in the beamformer. Transistors are capable of generating high average power but only relatively low peak power. High-duty-cycle waveforms (10 to 20 percent) aretherefore required to transmit enough energy efficiently. This lack in high peak power is the main disadvantage of the solid-state modules in phased array radars. To a great extent, it can be compensated for by using more pulse compression in the receiver and extra-wide bandwidth to counteract jamming, but at the cost of increased signal processing. An important advantage of transistors is their potential for wide bandwidth.
The receiver requires a gain of typically 10 to 20 dB...
