broad bandwidth feeds for reflector antennas
TRANSCRIPT
![Page 1: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/1.jpg)
National Radio Astronomy Observatory
Charlottesville, Virginia
![Page 2: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/2.jpg)
Challenges for FASR:
• Extremely wide bandwidth (100 MHz to 30 GHz)
• Small size of the antenna (diameter of 3 – 5 meters)
• Dual polarization
• “Acceptable” G/T
• Minimize number of moving parts
![Page 3: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/3.jpg)
Gain of Reflector Antennas
ηλ
π2
4 AG =
EBXPSI ηηηηηηη =
EfficiencyError Surface
Efficiency Blockage
Efficiencyization Crosspolar
EfficiencyError Phase
EfficiencySpillover
Efficiencyion Illumincat
E
B
X
P
S
I
=
=
=
=
=
=
η
η
η
η
η
η
![Page 4: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/4.jpg)
Gain of Reflector Antennas
Feed pattern is symmetric (E and H plane patterns are identical ) 1X =η
Common phase center for both planes 1P =η
Illumination and spillover losses are the principal causes of gain degradation.
There is usually a compromise between the illumination and spillover.
sidelobes. increasedin results This
feed. realizable afor low toois then 1, If SI ηη =
Clarricoats, P.J.B. and A.D. Olver, Corrugated Horns for Microwave Antennas, Peter Peregrinus, Ltd., London, UK, 1984, p. 100.
![Page 5: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/5.jpg)
Types of Feeds Presented Here
• Hybrid-Mode
• Dipole Above Ground Plane
• Frequency Independent Structures
![Page 6: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/6.jpg)
Hybrid-Mode Feeds
)ˆ2sinˆ2)(cos(4
ˆ)( 21
2
yxo
xo iiKrJkr
UYXiKrAJE φφ +
−−=
2
1
2
1
1rrat boundary theof admittance and reactance Normalized
+=−=
−=−=
=
o
o
zz
o
o
o
zo E
Hj
Z
ZjY
H
Ej
Z
ZjX
ε
µ
µ
ε φφφ
Clarricoats, P.J.B. and A.D. Olver, Corrugated Horns for Microwave Antennas, Peter Peregrinus, Ltd., London, UK, 1984, p. 7.
The Hybrid-Mode Feed offers a means to approach all of the objectives simultaneously.
![Page 7: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/7.jpg)
Hybrid-Mode Feed – Corrugated Waveguide
integer. oddan is m
when 02
tan
0
=
∆=
=
of
fmY
X
π
Co-polar bandwidth
Pattern symmetry and cross-polar characteristics
Position of the phase center and generation of higher order modes
Impedance matching to the waveguide and mode conversion level Clarricoats, P.J.B. and A.D. Olver, Corrugated Horns for
Microwave Antennas, Peter Peregrinus, Ltd., London, UK, 1984, pp. 99-100.
![Page 8: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/8.jpg)
Hybrid-Mode Feed – Corrugated Waveguide
Large flare angle horn (scalar feed) gives a relatively large bandwidth with nearly constant co-polar radiation characteristics.
Thomas, James, and Greene (1986):
Scalar feed having 2.1:1 bandwidth.
James (1984):
Compact profiled horn having 2.4:1 bandwidth (requires some focus adjustment)
Clarricoats, P.J.B. and A.D. Olver, Corrugated Horns for Microwave Antennas, Peter Peregrinus, Ltd., London, UK, 1984, p. 21.
![Page 9: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/9.jpg)
Hybrid-Mode Feed - Corrugated Waveguide
Absorber Lined Horn
band. over the dB 0.5 wasloss Ohmic launcher.)
deby wavegui limitedfrequency (upper eddemonstrat was
GHz 12-4 fromOperation cone. theofpart upper
thelined 0.56 and 1.4 reflector.horn ain
operation mode HE balancednearly edDemonstrat
(1986) Ostertag and Cheng, Knop,
11
=′′=′ εε
Knop, C.M., Y.B. Cheng, and E.L. Ostertag, “On the Fields in a Conical Horn Having an Arbitrary Wall Impedance,” IEEE Trans. Ant. and Propag., Vol. 34, Sept. 1986, pp. 1092-1098.
![Page 10: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/10.jpg)
Hybrid-Mode Feed – Surface-Wave Antenna
Dielectric Waveguide (rod)
( ) ( )( )
( )nYX
nn
Yn
∆−=−
∆+∆
=∆
=
∆
>>
2)(
Thus,
212
1;
2
1X
thenunity, from n, amount, small aonly by
differsindex refractive theif and 1kr If 1
This condition is frequency independent if the dielectric is free from dispersion over the operational bandwidth.
Unless delta-n is sufficiently large it is impossible to effectively launch the dominant mode of the dielectric waveguide – loose energy in the launcher.
Corrugated waveguide: Lower cross-pol over 2.5:1 bandwidth.
Dielectric waveguide: higher cross-pol over a much wider band.
Clarricoats, P.J.B. and A.D. Olver, Corrugated Horns for Microwave Antennas, Peter Peregrinus, Ltd., London, UK, 1984, p. 9.
Johnson, R. C. Antenna Engineering Handbook,, 3rd
ed., McGraw-Hill, New York, 1993, p. (12-21).
BW= 4:1
![Page 11: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/11.jpg)
Hybrid-Mode Feeds
Disadvantages for FASR:
• Big and bulky (corrugated)
• High machining cost (corrugated)
• Bandwidth not large enough
• Polarizer bandwidth about 2.5:1
• Loss associated with dielectric material
![Page 12: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/12.jpg)
Dipole Above a Ground PlaneConventional half-wave dipole
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (4-12).
![Page 13: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/13.jpg)
Dipole Above a Ground PlaneConventional half-wave dipole
Stutzman, W. and G. Thiele, Antenna Theory and Design, Wiley, New York, 1981, pp. 199-200. BW=1.09:1
![Page 14: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/14.jpg)
Dipole Above a Ground Plane
Fat Dipole
Stutzman, W. and G. Thiele, Antenna Theory and Design, Wiley, New York, 1981, p. 203. BW= 1.18:1
![Page 15: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/15.jpg)
Dipole Above a Ground Plane
Sleeve Dipole
BW= 1.67:1Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (4-21).
![Page 16: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/16.jpg)
Dipole Above a Ground Plane
Folded, Fat Dipole
BW= 1.53:1
![Page 17: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/17.jpg)
Dipole Above a Ground Plane
Short Backfire Antenna
BW= 1.35:1
Ehrenspeck, H.W. “The Short Backfire Antenna,” Proc. of the IEEE, v. 53, Aug. 1965, pp.1138-1140.
Srikanth, S. and G. Behrens, “A New Short Backfore Antenna as a Prome Focus Feed for the GBT”, GBT Memo. #187, May 13, 1998.
![Page 18: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/18.jpg)
Disadvantages for FASR:
• Bulky
• Narrow bandwidth
• Large spillover
Dipole Above a Ground Plane
![Page 19: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/19.jpg)
Frequency Independent Antennas
Provided the antenna is made of practically perfect conductors and dielectrics, the impedance, polarization, pattern, etc. are invariant to a change in scalethat is in proportion to the change in wavelength.
If the shape of the antenna is determined entirely by angles (invariant to scale), the performance would have to be independent of frequency.
Truncation of the shape from that of infinite extent should also give goodperformance (current should decrease with distance from the terminals).
Operational bandwidth:
• lowest frequency limited by the maximum dimension
• upper frequency limited by the input terminal region
• bandwidths can be 10:1 or greater.
Ω===⇒ 5.1882
Designary Complement-Selfη
METALAIR ZZ
![Page 20: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/20.jpg)
Frequency Independent Antennas
Log Periodic
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-30).
![Page 21: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/21.jpg)
Frequency Independent Antennas
Spirals
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-25).
Stutzman, W. and G. Thiele, Antenna Theory and Design, Wiley, New York, 1981, p. 284.
![Page 22: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/22.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-18).
Absorber Loaded Cavity
![Page 23: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/23.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-33).
Conical Log-Spiral
![Page 24: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/24.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-56).
Sinuous
![Page 25: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/25.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-60).
Sinuous
![Page 26: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/26.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-61).
Sinuous
![Page 27: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/27.jpg)
Frequency Independent Antennas
Johnson, R. C. Antenna Engineering Handbook,, 3rd ed., McGraw-Hill, New York, 1993, p. (14-61).
Sinuous Antenna on a Cone
![Page 28: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/28.jpg)
Frequency Independent Antennas
Disadvantages for FASR:
• Integration of feed, LNA and balun
• Could be lossy (affect G/T)
• Dual-polarization
• Gain varies with frequency for fixed position conical
![Page 29: Broad Bandwidth Feeds for Reflector Antennas](https://reader030.vdocuments.pub/reader030/viewer/2022021508/589d7b1e1a28ab444a8b9f3c/html5/thumbnails/29.jpg)
Conclusions
• Frequency independent antennas are the only practical option to cover FASR frequency range.
• Use a cavity backed structure for wide instantaneous bandwidth.
• Accept gain reduction associated with fixed position cone.
• Consider sinuous version of frequency independent structures.
• Integration of feed terminals with LNAs and balun.
• Prototyping highly recommended!
For FASR: