Microwave pulse spectrum control

Abstract

Generally, pulsed radar transmitters of the solid-state variety generate rectangularly shaped RF envelope pulses having discontinuities in the rise and fall edges thereof. It has been identified that, while maximizing power radiation efficiency, these sharp rise and fall times additionally provide for excessive energy in the spectral sidelobes about the transmission frequency of the radar signal. This excessive spectral sidelobe energy has been found to degrade the performance of closely operating pulsed radars through mutual interference. The present invention provides for pulse shaping control in a solidstate transmitter of a pulsed radar for reducing the spectral sidelobe energy being transmitted. The control is directed to modulating the shape of the rectangular RF envelope pulses to have substantially continuously rising and falling edges. In the preferred embodiment, a bipolar microwave transistor is coupled, in a common base configuration, cascadedly between low and high power amplification stages of the radar transmitter. A rectangularly pulsed RF power signal conducted through the transistor is modulated in accordance with a preshaped pulsed power supply signal supplied to the transistor coincidently therewith to render a corresponding power output RF pulse envelope substantially free of discontinuities in the rise and fall edges thereof.