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Improved Method of Alien Radar Suppression

IP.com Disclosure Number: IPCOM000237076D
Publication Date: 2014-May-29
Document File: 3 page(s) / 54K

Publishing Venue

The IP.com Prior Art Database

Abstract

Weather Radars of the same type interfere with each other either directly (antenna to antenna) or indirectly (radiating the same target). There are two standard methods for reducing this problem- Frequency diversity and time diversity. This solution describes an enhanced time diversity system that utilizes GPS Latitude and Longitude information to proactively set epoch timing to insure that Radars within view of each other “walk away” from each other.

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Improved Method of Alien Radar Return Suppression

Abstract:

Weather Radars of the same type interfere with each other either directly (antenna to antenna) or indirectly (radiating the same target). There are two standard methods for reducing this problem- Frequency diversity and time diversity. This solution describes an enhanced time diversity system that utilizes GPS Latitude and Longitude information to proactively set epoch timing to insure that Radars within view of each other "walk away" from each other.

Introduction:

Airborne Weather Radars of the same type interfere with each other either directly (antenna to antenna) or indirectly (radiation of the same target). This paper discusses an improved method for reducing this interference by enhancing the standard methods that have been used for years to address this problem. The ideas and techniques discussed in this paper are applicable to other pulsed transmission systems but this discussion will be limited to Airborne Weather Radar.

Background

There are a few changes that have combined over the years to make the alien interference problem more difficult. The first of these changes is that airports are far more crowded than they used to be with multiple active parallel runways, etc. This change puts many more interfering RADARS in a small area, creating many more "alien" returns that need to be rejected. The second change is that as technology has improved, our RADARS are much more frequency-accurate and stable. This change insures that all the RADARS will be exactly on channel and will not drift from each other due to natural drift of the master oscillators.

Technical Discussion

The removal of "alien" RADAR signals is currently done using two methods.

Frequency diversity is one method used to remove "alien" RADAR signals. This method became widely used with the advent of the programmable digital synthesizer. To enable accurate responses from targets of different sizes and ranges, the typical state of the art RADAR utilizes a standard pulse set that is made up of a mixture of pulses of different lengths. The digital synthesizer can change frequencies almost instantaneously. This is done randomly between pulse lengths and between sets of pulses to provide isolation from other RADARS. The other RADARS are using the same frequency diversity technique which, assuming the frequencies are well isolated statistically provides some level of isolation from alien targets.

Time diversity is another method used to remove "alien" RADAR signals. The set of transmit pulses are randomly delayed relative to an "epoch" signal. The "epoch" signal is the master timing signal that is used to start a new transmit / receive cycle and process received data. The idea is that the other RADARS of the same type will also be dithering this delay and therefore the "alien" return will fall in a slightly different time relative to its transmit signal and will not be persistent. The typical design for this...