Waveform generator

A waveform generator is an essential component of a coherent radar device . The waveform generator in the radar transmitter generates the transmission signal at the intermediate frequency. This can be an IF oscillation limited by the envelope of a square pulse , or (when using the pulse compression method ) a non-linearly modulated IF pulse generated in a complicated way. Since this pulse is also the reference for the received signal, the highest demands are placed on frequency constancy.

The entire modulation course of the transmission pulse is composed of 2048 individual voltage steps, the voltage and phase angle values ​​of which are stored in programmable memory components ( PROMs ). In practice, the process that takes place in an I&Q phase detector is operated backwards. This form of the waveform generator has the advantage that the content of the memory modules is also known to the evaluation program, which thus has a tabular description of the transmission pulse. In this way, the pulse compression on the receive path can also be carried out by the signal processor .

Block diagram of a waveform generator for a non-linearly modulated pulse

The bistable multivibrator (FF) controls the 11-bit counter. The counter is enabled after the start pulse at the input. The counter counts the addresses for the memory circuits from the 25 MHz clock frequency. After a complete cycle of all counting levels, the multivibrator is reset by the carry pulse and the counter is blocked.

There are two memory circuits programmed with the digital description of the desired pulse shape. The output data of these memories are converted into an analog signal with a digital to analog converter. These signals are modulated with the nominal frequency of the IF and can be measured at the two test points. They are then combined in a hybrid mixer to form the final transmission signal. This signal then has to be mixed up to the transmission frequency in the modulator .