Integration of Radar Pulses
Integration may be accomplished in the radar receiver used to improve detection. The following section describes the Integration of Radar pulses.
RADAR Pulses Integration:
Many pulses are usually returned from any particular target on each radar scan and can be used to improve detection. The number of pulses nB returned from a point target as the radar antenna scans through its beam width is:
- Typical parameters for a ground-based search radar might be pulse repetition frequency 300 Hz, 1.5˚ beam width, and antenna scan rate 5 rpm (30˚/s). These parameters result in 15 hits from a point target on each scan.
- The process of summing all the radar echo pulses for the purpose of improving detection is called integration.
- Many techniques might be employed for accomplishing integration. All practical integration techniques employ some sort of storage device.
- Perhaps the most common radar integration method is the cathode-ray-tube display combined with the integrating properties of the eye and brain of the radar operator.
- Integration may be accomplished in the radar receiver either before the second detector (in the IF) or after the second detector (in the video).
- A definite distinction must be made between these two cases. Integration before the detector is called pedetection, or coherent, integration, while integration after the detector is called post detection, or no coherent, integration.
- Predetection integration requires that the phase of the echo signal be preserved if full benefit is to be obtained from the summing process.
- On the other hand, phase information is destroyed by the second detector; hence post detection integration is not concerned with preserving RF phase. For this convenience, post detection integration is not as efficient as predetection integration.
- If n pulses, all of the same signal-to-noise ratio, were integrated by an ideal predetection integrator, the resultant, or integrated, signal-to-noise (power) ratio would be exactly n times that of a single pulse.
- If the same n pulses were integrated by an ideal post detection device, the resultant signal-to-noise ratio would be less than n times that of a single pulse. This loss in integration efficiency is caused by the nonlinear action of the second detector, which converts some of the signal energy to noise energy in the rectification process.
- The comparison of predetection and post detection integration may be briefly summarized by stating that although post detection integration is not as efficient as predetection integration, it is easier to implement in most applications. Post detection integration is therefore preferred, even though the integrated signal-to-noise ratio may not be as great. An alert, trained operator viewing a properly designed cathode-ray tube display is a close approximation to the theoretical post detection integrator.
- The efficiency of post detection integration relative to ideal predetection integration has been computed by Marcum when all pulses are of equal amplitude. The integration efficiency may be defined as follows: