Secondment Report Form

Transcription

1 Secondment Program FP7-INFSO-ICT Secondment Report Form Secondee Host Organization Research Topic(s) Id: TNO Name: Netherlands Organization for Applied Scientific Research Cross-polarization reduction techniques in phased arras Antenna CAD tools evaluation ACTIVITIES DURING THE SECONDMENT The aim of this section is to describe the main activit developed during m sta at TNO, Netherlands Organization for Applied Scientific Research. The activit can be divided in two sections: Section 1 Scope: stud and evaluate techniques to reduce the field cross-polarization components for an antenna configuration consisting of two orthogonal dipoles set along -ais and -ais (see Fig 1). Section 2 Scope: evaluate the computation time performances of the ADF CAD tool when applied to the analsis of large arra antennas (consisting of connected arra of dipoles larger than 1616 elements with an inter element distance of lambda/2). The scope of the present document is limited to the CARE project. Section 1. Figure 1 shows the antenna configuration studied in order to investigate cross-polarization reduction z techniques. Two orthogonal dipoles are centred in Port2 the origin and assumed to be half-wave long at the frequenc of analsis. The co-polar and cross-polar components are defined as the component of the electric field vector Port1 Figure 1: Crossed Dipoles normal and parallel to a desired vector, respectivel. There are different definitions of Co and Cross, depending on the choice of the desired vector; for phased arras and direct radiating antennas, the Ludwig s third definition is tpicall used, which leads to the following epressions of the co-polar and cross-polar fields radiated b the dipoles: Cross Co Cross φ θ φ φ η le = cos E sin E = j = θ φ sin φ sinφ ) sin φe + cos φe = jη sin φ sin φ + ) φ θ φ φ η = sin E + cos E = j sinφ sinφ) Public Page 1 of 5

2 Co = θ φ cos φe sinφe = jη + sinφ sinφ) In order to reduce the cross-pol associated with the dipole along (-dipole), a weight q(θ,φ) can be multiplied to the amplitude of the dipole along (-dipole), as follow: jkr le 4π r ( ) Co = q( θ, φ) jη cosθ sinφ sinφ + jkr le ( ) Cross = q( θ, φ) jη cosθ sinφ sinφ This weight is a function of the observation angles θ and φ. The basic idea to reduce the crosspolarization of the -dipole is to choose the weight q(θ,φ) so that the following equation is satisfied: q( θ, φ) Co = Cross With this choice of q(θ,φ) the co-pol of the -dipole cancels out with the -pol of the -dipole. Figure 2 shows the co-polar and cross-polar components of the -dipole as a function of θ and for φ=45. Analtical epressions (implemented via Matlab) are compared with simulations from Ansoft Designer. θ=45 ; φ=45 ; q(45,45)=.1716 Co (analtical) Cross (analtical) Gain db theta Figure 2: Cross-pol and co-polar - q(45,45)=.1716 The value q(θ,φ) is calculated for θ=45 and φ=45, and thus the cross component shows a null for the angle (45,45 ). Figure 3 refers to q(7,45 ), so the cross-pol of the -dipole vanishes at θ=7 and φ=45. o θ = 7 o φ = 45 Port2 Port1-1 Gain(db) theta Co (analtical) Cross (analtical) Figure 3: Cross-pol and co-polar - q(7,45)=.1716 Public Page 2 of 5

3 Two orthogonal dipoles with shifted phase centres can also be considered (Figure 4). In this case, in order to eliminate the cross-polar component of the -dipole, the weight q(θ,φ) has to be multiplied for a phase term accounting for the distance between the dipole centers: 2π d 2π j sinθ j d sinθ sinφ λ 2 λ 2 e e Figure 5 shows co and cross components for θ=45 and φ=45. Also in this case the cross polar component has a null at (45,45 ). θ=45 ; φ=45 ; q(45,45)=.1716 d 2 z d 2 Figure 4: Shifted dipoles Co (analtical) Cross (analtical) G ai n( Theta(deg) Figure 5: Cross-pol and co-polar - q(45,45)=.1716 Section 2 I studied and designed a connected arra in free space, constituted b 256 dipoles with an inter element distance of lambda/2. In order of reduce the calculation time with respect to other commercial EM solvers, the Antennas Designer Framework (ADF) can be used. ADF is an antenna workbench, developed b IDS Compan, where the user finds a suite of different modelling tools (multi-methods environment), both general purpose and specialised, able to co-operate in the formation of comple modelling procedures (combined methods procedures). Active Parameters Blue line: real part; Red line: imaginar part) Frequenc(GHz) Figure 6: ADF Active impedance Freq [GHz] Figure 7: HFSS - Active impedance Public Page 3 of 5

4 Comparing the active impedance of a central element of the arra obtained via ADF and Ansoft HFSS (Figures 6 and 7), the same dnamic can be observed. In the ADF case, the simulation time is lower: CPU Time: 37 min for frequenc. These results can be deepened. MAIN RESULTS OF THE STAY Number of Publications: 1 Number of Documents/ Reports: Number of Case Studies & Demonstrators: Other(s): (1) epected at EuCAP211 (TBC)_ (2) (3) * Attach all relevant documentation that specifies our results FORECAST ACTIVITIES In order to improve CARE s secondment program, please fill this short questionnaire. Use the space at the end to epand our answers, if needed. Our aim is to improve the general eperience for secondees in future. Disagree GENERAL HOST ORGANIZATION Agree M objectives were achieved The research topics were relevant to m work I benefited from being part of a wider research culture I am satisfied with the qualit and quantit of supervision I received I had access to adequate resources to support m research SECONDMENT PROGRAM I would recommend this secondment programme to others I believe the skills I have learned will help me to improve m job/research I would appl to another programme similar to CARE In general, how would ou classif the CARE Secondment Programme? Public Page 4 of 5

5 Other questions/comments to be potentiall considered: The secondment eperience resulted ver positive from the technical and the coordination point of view. In particular, the TNO matched the epectation in being a etraordinar technical place where to stud the state-of-the-art techniques in antenna arra design. Finall, I would like to epress m thanks to the entire TNO staff that supported m secondment. SIGNATURES Candidate Claudia Casali Date: (ear/month/da) Signature Public Page 5 of 5