GROUND MOVING TARGET INDICATION BY AIRBORNE PASSIVE RADAR
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2021-02-05
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info:eu-repo/semantics/openAccess
Özet
Monostatik radarların aksine, bistatik radarların alıcı ve verici sistemleri farklı konumlara yerleştirilmiştir. Bistatik radar çeşidi olan pasif radarlar, kendilerine ait verici sistemleri olmadığı için halihazırda yeryüzünde bulunan vericileri kullanarak hedef tespiti yaparlar. Bu sayede fark edilmeden operasyonlarını yürütebilirler. Bu avantajı sayesinde popülerlik kazanmış ve birçok çalışma yapılmıştır. Pasif radarın uçan bir platforma yerleştirilerek yeryüzündeki hareketli hedeflerin tespitinde kullanılması ise son yıllarda ilgi çeken bir çalışma alanı olmuştur. Pasif radarın hareketli bir platforma yerleştirilmesi beraberinde bazı dezavantajlar getirmektedir. Platformun hareketinden dolayı bina gibi hareketsiz olan nesnelerin platforma göre bağıl hızları oluşacaktır. Bu durum, binaların da birer hareketli hedef olarak algılanmasına sebep olup menzil/Doppler haritasında kargaşa yayılımı oluşturur ve bu kargaşa yayılımı hedef tespitini sınırlar. Kargaşa, faz merkezi kaydırılan anten (DPCA: Displaced Phase Center Antenna) yöntemi ile yok edilerek sorun çözülür. Fakat DPCA’nın performanslı bir şekilde çalışabilmesi için iletilen sinyalin zamanla değişmeyen bir yapıda olması gerekmektedir. Aktif radarlarda verici sistem radar sistemine dahil olduğu için iletilen sinyalin kontrol edilebilir ve zamanla değişmeyen yapıda sinyaller gönderilerek DPCA’nın tam performanslı çalışması sağlanabilir. Pasif radarlar ise iletilen sinyal kontrol edilemez. Darbe sıkıştırma aşamasında geleneksel filtre kullanmak zamanla değişen yapıda sinyaller üreteceği için DPCA ile etkili bir kargaşa yok etme sağlamaz. Bu sorun geleneksel filtre yerine zamanla değişmeyen yapıda sinyaller üreten karşıt filtre kullanılarak çözülmüştür ve DPCA’nın tam performanslı olarak çalışmasını sağlamıştır. Ayrıca pasif radarın performansını etkileyen içsel kargaşa hareketi (ICM: Internal Clutter Motion), alıcı kanallar arası hatalar ve iletilen sinyalin farklı dalga formuna sahip olması faktörleri incelenmiştir.
Unlike monostatic radars, bistatic radars' receiver and transmitter systems are placed in different locations. Hence passive radars, which are bistatic radar types, do not have their own transmitter systems, the target detection is performed by using transmitters which are already on the ground. In this way, the target detection operations are performed covertly. Thanks to this phenomenon, passive radar has gained popularity and lots of studies have been carried out. But, the use of airborne passive radar for ground moving target indication has been an interesting field of study only in recent years. Placing the passive radar on a mobile platform brings some disadvantages. The stationary objects such as buildings will have relative velocity due to the movement of the platform. This causes buildings to be perceived as moving targets and generates clutter spread, which limits target detection, in the range/Doppler. The problem can be solved by removing the clutter with the DPCA method. However, the transmitted signal waveform must be time-invariant in order for DPCA to operate effectively. Since the transmitter system is dedicated to the radar system in active radar, the transmitted signal can be controlled and the DPCA can be achieved effectively by transmitting signals that have time-invariant waveform. On the contrary, in passive radars, the transmitted signal cannot be controlled. Using a conventional filter in the pulse compression stage does not provide effective clutter cancellation with DPCA, as it will generate signals with a time-varying waveform. In this research, the problem has been solved by using a reciprocal filter, that produces signals that have time-invariant waveform, instead of the conventional filter. The resiprocal filter provides DPCA to operate effectively. In addition, the factors affecting the performance of passive radar such as ICM, inter-channel errors and the transmitted signal having different waveforms were analysed."
Unlike monostatic radars, bistatic radars' receiver and transmitter systems are placed in different locations. Hence passive radars, which are bistatic radar types, do not have their own transmitter systems, the target detection is performed by using transmitters which are already on the ground. In this way, the target detection operations are performed covertly. Thanks to this phenomenon, passive radar has gained popularity and lots of studies have been carried out. But, the use of airborne passive radar for ground moving target indication has been an interesting field of study only in recent years. Placing the passive radar on a mobile platform brings some disadvantages. The stationary objects such as buildings will have relative velocity due to the movement of the platform. This causes buildings to be perceived as moving targets and generates clutter spread, which limits target detection, in the range/Doppler. The problem can be solved by removing the clutter with the DPCA method. However, the transmitted signal waveform must be time-invariant in order for DPCA to operate effectively. Since the transmitter system is dedicated to the radar system in active radar, the transmitted signal can be controlled and the DPCA can be achieved effectively by transmitting signals that have time-invariant waveform. On the contrary, in passive radars, the transmitted signal cannot be controlled. Using a conventional filter in the pulse compression stage does not provide effective clutter cancellation with DPCA, as it will generate signals with a time-varying waveform. In this research, the problem has been solved by using a reciprocal filter, that produces signals that have time-invariant waveform, instead of the conventional filter. The resiprocal filter provides DPCA to operate effectively. In addition, the factors affecting the performance of passive radar such as ICM, inter-channel errors and the transmitted signal having different waveforms were analysed."
Açıklama
Anahtar Kelimeler
Pasif radar, kargaşa yok etme, karşıt filtre, DPCA, FM, GMTI., Passive radar, clutter cancellation, resiprocal filter, DPCA, FM, GMTI.
