Radomes-The Rocky Road to Transparency

by

Reuven Shavit

Electrical and Computer Engineering Department

Ben-Gurion University of the Negev

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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.

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.

Outline

Introduction

Sandwich Radomes

Frequency Selective Surface Radomes

Airborne Radomes

Ground Based Radomes

Concluding Remarks

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Introduction

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on ships

Typical radomes

on airplanes

Introduction

Typical radomes

and on the ground

Solid laminate radome Inflatable radome Multipanel sandwich radome

Metal space frame radome Dielectric space frame radome

Introduction

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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

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Sandwich Radomes

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Sandwich Radomes

Sandwich A Sandwich B Sandwich C

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Frequency Selective Surfaces (FSS)

Airborne radome

(c)

(f) (g)

(a)

(e)

(b) (d)

(h)

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.

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Frequency Selective Surfaces (FSS)

a Lx

Ly

b

FSS is positioned in the center of

the dielectric λg/2 radome panel

Airborne Radomes

z

Ώ

x

xc zc

L

D

antenn

a

2a

(x0,z0)

θ'

(x',z')

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 100. 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 εr=4

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).

Ground Based Radomes

𝐹′ 𝜃, 𝜙 = 𝐹 𝜃, 𝜙 + 𝐹𝑠 𝜃, 𝜙

Ground Based Radomes

The total scattered field from the beams:

in which

𝑔||, 𝑔⊥- are the parallel and perpendicular

IFR of the mth beam

𝐼𝑚 𝜃, 𝜙 𝜃0𝑚 , 𝜙0

𝑚 -the scattering pattern

from the mth beam

𝑓𝑚 𝑥𝑚, 𝑦𝑚 , 𝑧𝑚 -the excitation of the mth

beam

𝐹𝑠 𝜃, 𝜙 = 𝑔𝑚𝐼𝑚 𝜃, 𝜙 𝜃0𝑚 , 𝜙0

𝑚 𝑓𝑚 𝑥𝑚, 𝑦𝑚 , 𝑧𝑚

𝑀

𝑚=1

𝑔𝑚 = 𝑔||cos2𝛿𝑚 + 𝑔⊥sin

2𝛿𝑚

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

Ground Based Radomes

Single seam scattering

Seam scattering reduction options:

• material

• shape

• tuning techniques

Ground Based Radomes

Single seam scattering

IFR vs. shape

Ground Based Radomes

Single seam scattering

IFR vs. frequency (tuned/untuned)

Ground Based Radomes

Single seam scattering

Scattering pattern of a single seam (tuned/untuned)

amplitude (dB) phase (deg.)

(a) untuned dielectric beam

amplitude (dB) phase (deg.)

(b) tuned dielectric beam

Ground Based Radomes

Seam tuning importance

Ground Based Radomes

Seam geometry importance

Ground Based Radomes

Blockage uniformity

Ground Based Radomes

Tuned sandwich radomes

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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