A compact circularly polarized monopulse slotted waveguide array for airborne applications

Abstract

In modern radar and communication systems, high gain, high power capability and low-profile antenna systems are frequently utilized. In airborne and space borne applications, slotted waveguide antenna array is widely used due to its rigid structure, low-loss and high power handling capability. In this thesis, a compact, lightweight, high reection bandwidth, high gain and circularly polarzied slotted waveguide array antenna with monopulse capability operating in Ku-band is presented. Target application of this antenna is radio links on airborne platforms with built-in tracking capability . This thesis is divided into two parts: 1) Design of compact standing wave slotted array; 2) Design of a low-cost linear polarization (LP) to circular polarzition (CP) converter. In the first part of thesis, an antenna system is presented that has two key components: monopulse comparator/feed network and antenna section. The antenna is designed at 15 GHz and simulated using ANSYS HFSS. It is a planar array of 6x8 radiating slots with a gain greater than 22:5 dB at 15 GHz , side-lobe level (SLL) 13 dB , reection bandwidth of 1200 MHz. Monopulse comparator network is Magic Tee based waveguide structure. The antenna has maximum dimension of 10:8 cm * 10:7 cm 4 cm that makes it easy to house on an aircraft. In the second part of thesis, a LP to CP polarizer is presented. The proposed polarizer is a multi-layer metasurface based structure that converts incident linearly polarized wave into circularly polarized wave. The polarizer presented in this thesis is based on meander line and strip line hybrid concept. Each substrate layer is rotated 45 with respect to previous layer and is seperated by low permittivity material called spacer. The unit cell of the polarizer is square in shape with dimensions of 5:1mm 5:1 mm. Its axial ratio bandwidth is 2 GHz i.e: axial ratio is less than 3-dB from 14-16 GHz . It is also low-cost as compared to the available literature because thick substrates are used instead of high cost thin substrate and also one substrate layer is based on FR-4 laminate.Modern radar ve ileti sim sistemlerinde, yuksek kazan c, yuksek gu c kapasitesi ve du suk pro lli anten sistemleri s kl kla kullan lmaktad r. Havadan ve yere dayal uygulamalarda, rijit yap s , duuk kayb ve yuksek gu kullanma kabiliyeti nedeniyle oluklu dalga k lavuzu anten dizisi yayg n olarak kullan lmaktad r. Bu tez cal mas nda, Ku-band nda cal an monopuls yetene gine sahip kompakt, ha f, yuksek yans ma bant genili gi, yuksek kazan ve dairesel polarize oluklu dalgal dalga dizisi anten sunulmaktad r. Bu antenin hedef uygulamas , yerleik izleme ozelli gine sahip havadaki platformlardaki radyo ba glant lar d r. Bu tez iki bolume ayr lm st r: 1) Kompakt dura gan dalga oluklu dizisinin tasar m ; 2) Duuk maliyetli bir dourusal polarizasyon (LP) ile dairesel polarizasyon (CP) donuturucusunun ta sar m . Tezin ilk bolumunde, iki ana bile sene sahip bir anten sistemi sunulmu stur: monopuls kar s lat r c besleme a g ve anten bolumu. Anten 15 GHz'de tasarlanm s ve ANSYS HFSS kullan larak simule edilmi stir.15 GHz, yan lob seviyesi (SLL) 13 dB'de 22.5 dB' den daha fazla kazanc olan 6x8 yay lan oluklar n duzlemsel bir dizisidir.,1200 MHz yans tma bant geni sli gi. Monopuls kar s la st r c a g , Magic Tee tabanl dalga k lavuzu yap s d r. Anten, u cakta yerletirmeyi kolaylat ran maksimum 10.8 x 10.7 x 4 cm boyutuna sahiptir. Tezin ikinci bolumunde, bir LP-CP polarizoru sunulmu stur. Onerilen polarizer, olay do grusal polarize dalgay dairesel polarize dalgas na donu sturen cok katmanl bir metasurface bazl yap d r. Bu tezde sunulan polarizer, k vr ml ve duz cizgi hibrid konseptine dayanmaktad r. Her bir substrat katman onceki katmana gore 45 dondurulur ve aralay c ad verilen duuk geirgenlik materyali ile ayr l r. Polarizorun birim hucresi, 5.1 mm x 5.1 mm boyutlar nda kare eklindedir. Eksenel oran bant genili gi 2 GHz'dir, yani eksenel oran 14-16 GHz'den 3-dB'den azd r. Ayn zamanda, mevcut literature k yasla du suk maliyetlidir, cunku yuksek maliyetli ince substrat yerine kal n substratlar kullanlr ve ayrca bir substrat tabakas FR-4 laminat esasl d r.