Ahmet ÖZER, Kadir ÖZDEN, Okan Mert YÜCEDAĞ, Hasan KOÇER

Metamalzeme tabanlı geniş bant ışıma emici yapılar kullanılarak radar kesit alanının azaltılması

Metamalzemeler, bilinen doğal malzemelerin aksine farklı elektromanyetik özellikler gösteren yapay malzemelerdir. Son yıllarda keşfedilen özelliklerinden bir tanesi de gelen elektromanyetik dalgaya karşı mükemmel emilim göstermeleridir. Bu özellikleri sayesinde uzaktan algılama sistemlerine karşı mikrodalga bandından optik banda kadar görünmezlik uygulamalarında kullanılabilecekleri değerlendirilmektedir. Buna göre bir platformun metamalzeme ile kaplanması, o platformun radarda görünürlüğünü temsil eden radar kesit alanı (RKA) değerini azaltabilecektir. Bu çalışmada radarların yoğun olarak çalıştığı X bant (8-12 GHz) frekans bölgesinde etkili, geniş bant metamalzeme ışıma emici yapının tasarım, optimizasyon, üretim ve ölçümü incelenmiştir. Geniş bantta emilimi elde edebilmek için öncelikle iki farklı frekansta rezonans gösteren metamalzeme tasarlanmış ve daha sonra bu metamalzemeye ilişkin birim hücrenin ölçeklenebilirlik özelliği kullanılarak X bandında farklı frekanslarda rezonans etki gösteren 16 adet birim hücreden oluşan süper hücre yapısına geçilmiştir. Bu birim hücrelerin, ölçekleme faktörünün ve süper hücre içerisindeki yerleşim yerlerinin optimizasyonu neticesinde 8,7-11,4 GHz frekans aralığında geniş bantta emilim sağlayan metamalzeme tabanlı ışıma emici yapı tasarlanmıştır. Simülasyon ve deney sonuçlarının birbirleri ile uyumlu olduğu gözlemlenmiştir. Tasarımı gerçeklenen metamalzeme emici yapının, aynı boyutlardaki iletken yapıya göre atış kontrol ve keşif gözetleme radarlarının yoğun olarak çalıştığı frekans aralığında, radar kesit alanını en az 10 dB seviyesinde azalttığı nümerik ve deneysel sonuçlarla gösterilmiştir.

Reduction of radar cross section using metamaterial based broadband absorbers

Metamaterials are artificial structures which exhibit different electromagnetic properties contrary to the known materials. One of the features discovered in recent years is performing perfect absorption against the incident electromagnetic wave. Metamaterial absorbers with this property can be used in stealth technology against remote sensing applications over a significant range of electromagnetic spectrum from microwave to optics. According to this, radar cross section of relevant targets representing the visibility in radar can be reduced by coating target with metamaterial absorber. In this paper; design, simulation and measurements of a novel X band metamaterial broadband absorber are investigated. Primarily, a dual band metamaterial absorber is obtained and then, depending on superposition of the different neighboring resonant frequencies of the differently sized unit cells, a super cell of metamaterial absorber has been demonstrated at X band. Due to the optimization of size and location of unit cell, a broadband metamaterial absorber is designed in the frequency range of 8.7 to 11.4 GHz. It is observed that the simulation results are in good agreement with the measurements. At least a 10 dB radar cross section reduction of the metamaterial absorber compared with a fully metallic plate with comparable dimensions is demonstrated both numerically and experimentally in the frequency range of fire control and surveillance radars.

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