Stretch Processing

Reasons for Using Stretch Processing

The linear FM waveform is popular in radar systems because its large time-bandwidth product can provide good range resolution. However, the large bandwidth of this waveform makes digital matched filtering difficult because it requires expensive, high-quality analog-to-digital converters. Stretch processing, also known as deramping or dechirping, is an alternative to matched filtering. Stretch processing provides pulse compression by looking for the return within a predefined range interval of interest. Stretch processing typically occurs in the analog domain. Unlike matched filtering, stretch processing reduces the bandwidth requirement of subsequent processing.

Support for Stretch Processing

The phased.StretchProcessor System object™ implements stretch processing. You can use this object as part of a simulation that uses phased.LinearFMWaveform or directly with your own data.

Stretch Processing Procedure

The typical procedure for stretch processing is as follows:

1. Choose a range interval of interest, centered on a reference range. Stretch processing focuses on this interval instead of the entire range span that the pulse can cover.

2. Define and configure a stretch processor object. The configuration includes the reference range, length of the range interval of interest, characteristics of the linear FM waveform, and signal propagation speed.

   • If you are using a phased.LinearFMWaveform object to implement the linear FM waveform, use the getStretchProcessor method to define and automatically configure a stretch processor object.

   • Otherwise, create a phased.StretchProcessor object directly, and set its properties as needed.

3. Perform stretch processing by calling the step method on your stretch processor object. You provide your received signal as an input argument. The step method generates a reference signal and correlates it with your received signal.

4. Compute a periodogram of the output from step, and identify the peak frequencies. You can use the following features to help you perform this step:

   • periodogram

   • psd

   • findpeaks

5. Convert each peak frequency to the corresponding range value, using the stretchfreq2rng function.