MULTI-FREQUENCY AND ULTRA-WIDEBAND ANTENNA RADOMES

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MULTI-FREQUENCY AND ULTRA-WIDEBAND ANTENNA RADOMES

• Dr. D .J. Kozakoff
• Marietta, GA, USA

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Radome

• A dielectric (RF transparent) cover placed over
  an antenna in order to protect it from the
  environment
• A technology spin off of WWII

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Reasons for its Development

• The maximum speed of an aircraft is limited to
  the speed at which external antennas are able to
  survive.
• In WWII a plastic cover over a B18 bombers radar
  antenna was the first known application
• Today, in what applications are radomes used?

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Maritime Applications

• Ocean Liners

• Small Craft

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Telecon Applications

• Parabolic Reflector Antennas

• Hog Horn Antennas

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Radar and SATCOM Applications

• Air Traffic Control

• SATCOM

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Aircraft and Missile Applications
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Vehicular Applications
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Cell Telephone Tower Antennas
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As a Structure to Conceal an Enclosed Microwave
Communications Antenna

• Antenna Within Structure

• External view

Concealfab Corp.
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As a Structure to Conceal an Enclosed SATCOM
Antenna
Concealfab Corp.
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Revise the last Question

• Are there applications where radomes not used?
• Not many!!!

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Bottlenecks to Consider

• Within a radome, the system bandwidth is limited
  by the radomes bandwidth.
• The noise floor (system noise temperature) cannot
  be less than radome noise temperature
• (in the order of 10o K for every 0.1 dB
  loss.)
• The radome depolarization limits the dynamic
  range in a frequency reuse application.

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Reciprocity
What a Radome does in the transmitting mode, it
does exactly the same thing in the receiving mode
(For instance, if a radome had 1 dB of
transmission signal loss, it would also attenuate
the received signal by 1 dB.
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Parameters that Impact Broadband Performance

• Wall thickness (thin is generally better)
• Wall design number of layers, thickness,
• and permittivity of each layer (more layers
• is better.)
• Shape (flatness is desirable)
• Selection of low loss materials (small loss
• tangent is required).

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Definition of Walls Types
e1
e1
e2
e1
e1
e1
e2
e2
Monolithic
A or B
C
B-Sandwich e1 lt
A-Sandwich e1 gt e2
C-Sandwich e1 gt e2
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Radome Wall Details
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Multifrequency or Ultrabroadband Approaches in
Current Use Thin Wall Radomes
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Monolithic Walls

• Walls that are any multiple of a half wave must
  be precluded because these are narrow band.
• Any wall that is thin in terms of wavelength is
  ultrabroadband but
• - generally has poor mechanical strength.
• - has a loss almost entirely due to
  reflection (loss tangent value is of little
  importance)

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Approximate loss versus thickness
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Inflatable Thin Wall Radome Example
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Multifrequency or Ultrabroadband Approaches in
Current Use Computer OptimizedMultilayer Wall
Designs
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Computer optimization of multi-wall radomes
considerations

• Iterate all possible layer thicknesses in half
  ply
• (6 mil) increments
• Coarse search followed by a fine search and use
• of convergence algorithms was important when
• computers were slow (4 MHz)
• Brute force search through all combinations is
• feasible with todays high speed PC computers
• (2 GHz )
• Optimized solutions are not unique, that is
  various
• combinations of wall thicknesses may suffice

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Multilayer Computer Optimization Procedure

• Describe wall type and max and min thicknesses of
  each layer
• Input layer dielectric constants and loss
  tangents
• Define performance desired in each frequency
  range
• Iterate radome transmission calculations until
  acceptable performance is achieved.

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Multifrequency or Ultrabroadband Approaches in
Research or Development
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Approach 1 Matched Materials Wave Impedance of
a Radome Material

• Where
• Relative permeability
• Relative permittivity

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Approach 1 Matched Materials

• If the relative permittivity of a radome
  material is equal to its relative permeability
  then the intrinsic impedance is the same as the
  intrinsic impedance of free space and there is no
  radome reflection loss.
• Materials with a relative permeability greater
  than one do not yet exist above about 1 GHz
• (above 1 GHz the only practical matched
  material approach is a radome material both
  relative permittivity and relative permeability
  close to 1).

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Approach 1 Structual Foam SATCOM Radome Example
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Summary for Matched Materials Approach

• Materials development needed to find a material
  with a relative permeability greater than 1 above
  1 GHz. (This could be incorporated with a
  standard dielectric using dielectric mix formulas
  in order to achieve a matched material).

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Approach 2 Metamaterials

• Metamaterials are periodic structures that
• Exhibit a negative refractive index
• Microwave metamaterials are usually
• constructed as arrays of electrically conductive
• elements which have suitable reactance
• characteristics.
• Passive circuits.
• (Note metamaterial core
• could replace standard
• Honeycomb core in an A
• Sandwich radome.)

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Metamaterial Radome Features

• A dielectric layer and adjacent to a suitable
• metamaterial used as a radome.
• The structure may be non-reciprocal for
• incoming and outgoing waves.
• Metamaterial radomes can improved power
• Transmission over a broad range of antenna
• scan angles.

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Metamaterial Radome Features

• Metamaterial radomes can enhance out of
• band signal rejection.
• Commercial metamaterial radomes are not
• yet state-of-the-art.
• Metamaterials are useful for multi-band
• Radomes.
• Metamaterials ultra wideband radomes (TBD).

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Metamaterial References

• Use of conjugate dielectric and metamaterial
  slabs as
• radomes, Microwaves, Antennas Propagation
• IET, ISSN 1751-8725, pp.1751-8725, Feb 2007
• Oraizi, H. and M.Afsahi, Design of Metamaterial
• Multilayer Structures as Frequency Selective
• Surfaces, Progress in Electromagnetics Research
  C,
• Vol.6, pp.115-126, 2009
• Wu, C., H. Lin and J.Chen, A novel low profile
  dual
• Polarization metamaterial antenna radome design
  for
• 2.6 GHz WiMAX, 3rd International Congress on
  Advanced
• EM Materials and Optics, 2009

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Approach 3 Pyramidal inner walls

• Bandwidth of 101 or greater potential.
• Performance demonstrated in lab tests over 0 to
  60 deg angle of incidence.
• Excellent circular pol. characteristics.
• This approach has not yet known to have been used
  in any commercial application.

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Pyramidal inner walls reference
Bassett,H. L., D.G.Bodnar, G.K.Huddleston and
J.M.Newton, Broadband Radome Techniques,
AD0920772, Engineering Experiment Station,
Georgia Institute of Technology, Atlanta, GA, 1974
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Approach 4 Active Radomes

• Reconfigurable frequency pass bands and frequency
  reject bands.
• Lightweight and low loss.
• An outgrowth of meta-materials technology.

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Summary

• Current technology thin wall radomes meet
  electrical requirements for ultra wideband
  transmission, but not necessarily meet mechanical
  requirements.
• Current technology computer optimized multi-wall
  radomes using state of the art materials are
  realizable but very expensive.
• Matched material (Approach 1) requires material
  development break thru to use above 1 Ghz.

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Summary (continued)

• Approach 2 (Pyramidal surface matching) has been
  demonstrated in the lab but not yet been
  commercialized.
• Approach 3 (Meta-materials radomes) are passive
  and are in current research.
• Active radomes (Approach 4) are envisioned as a
  future development offering enhanced features and
  capabilities.

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Thank you for your time in listening to this
presentation. Have a good day.
D.J.Kozakoff dr.kozakoff_at_usdigicomm.com