Simultaneous signal transmission improves Doppler shift and radar accuracy

Accurate measurements of the range and Doppler shift of a target are used to identify the position and speed of that target relative to a source. Many waveform signals can be used in radar processes and the selection of a given waveform is determined by the effectiveness in producing the desired measurement.

Previous approaches for determining the range and Doppler shift of a target include the use of a narrowband signal (continuous wave (CW) waveform signal), a broadband signal (frequency modulated (FM) waveform signal), or a hybrid of these signals — for example, a frequency-hopped (FH) waveform signal. A CW waveform performs well in resolving Doppler shifts but has poor performance in resolving ranges. FM waveform signals exhibit good performance in resolving target ranges but due to their larger bandwidth exhibit poor performance in resolving Doppler shifts.

As a hybrid of CW and FM waveform signals, the FH waveform signal comprises numerous short signals that have varying frequencies within the overall bandwidth yet, each short signal is narrowband in nature. The use of FH waveform signals maintains the FM-type range resolution while improving the Doppler resolution resulting from the CW-type Doppler shift. However, the improvement in Doppler shift resolution is less than what is achieved with a CW signal alone.

Addressing the above, Navy scientists and engineers have developed a system which transmits narrowband signals simultaneously (in parallel) with broadband and other signals (even with other narrowband signals). Transmitting a narrowband signal with a broadband signal leads to a comparatively-small penalty in decreased bandwidth, but great improvement in Doppler resolution. This is because the narrowband signal can be filtered from the other signals and processed as if it was sent alone.