Radomes-The Rocky Road to Transparency

Transcription

1 Radomes-The Rocky Road to Transparency by Reuven Shavit Electrical and Computer Engineering Department Ben-Gurion University of the Negev 1

2 The word radome, is an acronym of two words "radar" and "dome" and is a structural, weatherproof enclosure that protects the enclosed radar or communication antenna. Main reasons to use radomes: The main objective of the radome is to be fully transparent to the electromagnetic energy transmitted/received by the enclosed antenna. Radomes protect the antenna surfaces from weather and conceal the antenna electronic equipment from the outside radome observer. It enables to use low power antenna rotating systems and weaker antenna mechanical design followed by a significant price reduction. 2

3 Outline Introduction Sandwich Radomes Frequency Selective Surface Radomes Airborne Radomes Ground Based Radomes Concluding Remarks 3

4 Typical radomes Introduction on ships on airplanes 4

5 Typical radomes Introduction Solid laminate radome Inflatable radome Multipanel sandwich radome Metal space frame radome and on the ground Dielectric space frame radome

6 Introduction Radomes are enclosures for antennas. Most radomes are hollow dielectric shells although some contain perforated metallic layers or metallic reinforcing structures. Radomes are used with large antennas on the earth s surface to reduce wind loading and to prevent accumulation of ice or snow. These radomes usually have but not necessarily spherical contours. The radomes affect : Radiation pattern (sidelobe level) Crosspol pattern Power transmittance (transmission loss) Antenna noise temperature Boresight error Boresight error slope 6

7 Sandwich Radomes 7

8 Sandwich Radomes Sandwich A Sandwich B Sandwich C 8

9 Frequency Selective Surfaces (FSS) (a) (b) (c) (d) (e) (f) (g) (h) Airborne radome Some FSS unit cell geometries (a) Square patch. (b) Dipole. (c) Circular patch. (d) Cross dipole. (e) Jerusalem cross. (f) Square loop. (g) Circular loop. (h) Square aperture. 9

10 Frequency Selective Surfaces (FSS) a L x L y b FSS is positioned in the center of the dielectric λ g /2 radome panel 10

11 Airborne Radomes x D x c 2a antenn a (x',z') (x 0,z 0 ) θ' Ώ z c z L The cross section of an airborne radome based on super-spheroids geometry profile. Comparison of radiation patterns of MoM solution, hybrid PO-MoM and antenna without radome for an antenna aperture tilted The length of the radome is 10λ and 5λ in diameter. The antenna is circular with 4λ in diameter. The radome thickness is 0.2 λ and its dielectric constant ε r =4

12 Airborne Radomes Comparison of the normalized radiation of a dipole array in the presence of three types of radome shapes: ogive shape (dash line), conical shape (dotted line), hemisphere shape (solid line) and radiation of the dipole array in free space (dash-dot line).

13 Ground Based Radomes F θ, φ = F θ, φ + F s θ, φ

14 Ground Based Radomes The total scattered field from the beams: M F s θ, φ = g m I m θ, φ θ m 0, φ m 0 f m x m, y m, z m m=1 g m = g cos 2 δ m + g sin 2 δ m in which g, g - are the parallel and perpendicular IFR of the m th beam I m θ, φ θ 0 m, φ 0 m -the scattering pattern from the m th beam f m x m, y m, z m -the excitation of the m th beam

15 Ground Based Radomes Electromagnetic Design Considerations Panel optimization to reduce the transmission losses Computation of the scattering levels due to the seams Reduction of a single seam scattering (IFR) Optimization of the radome geometry to reduce its total scattering effect

16 Ground Based Radomes Single seam scattering Seam scattering reduction options: material shape tuning techniques

17 Ground Based Radomes Single seam scattering IFR vs. shape

18 Ground Based Radomes Single seam scattering IFR vs. frequency (tuned/untuned)

19 Ground Based Radomes Single seam scattering amplitude (db) phase (deg.) (a) untuned dielectric beam amplitude (db) phase (deg.) (b) tuned dielectric beam Scattering pattern of a single seam (tuned/untuned)

20 Seam tuning importance Ground Based Radomes

21 Seam geometry importance Ground Based Radomes

22 Blockage uniformity Ground Based Radomes

23 Ground Based Radomes Tuned sandwich radomes

24 Concluding Remarks Design principles of multilayered radomes have been presented Various radome types and their performance have been discussed Scattering analysis for space frame radomes have been presented 24