Evaluation of Suitable Feed Systemes

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• Review of the Ring Focus Antenna

• Quadridge Horn

• Eleven Feed

• Coaxial Horn and Multiband Corrugated Horn

• Conclusion

Gain of Reflector Antennas

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

εηηηηηηηBXPSI

=

ηλ

π2

=

DGη

λ

π2

4 AG =

G = antenna gain

A = aperture area

D = antenna diameter

λ = wavelength

ηI= illumination efficiency

ηS

= spillover efficiency

ηX

= crosspolarization efficiency

ηB

= blockage efficiency

ηε = surface error efficiency

Optical Design Ring Focus Antenna

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

Dm

fp

ds

Para

bo

la A

xis

2c

SubreflectorEllipsoid-Axis

Ring Focus

Main Reflector

System Focus

Ring Focus Antenna

13.2m Antennas with Gaussian Beam Feeds (-12dB at Subreflector Rim)

Aperture Effenciency

60

65

70

75

80

85

0 2 4 6 8 10 12 14 16 18

Frequency [GHz]

Ap

ert

ure

-Eff

icie

ncy [%

]

Gregory-Antenna

Dualoffset-Antenna

Ringfocus-Antenna

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• no field in the blocked center region

• no reflection back to the feed system

• feed can be located close at the subreflector

• high antenna efficiency

• cost-effective mechanical structure

13.2m R ing Focus Antenna

Aperture Field Distribution, f = 5 GH z

-25

-22.5

-20

-17.5

-15

-12.5

-10

-7.5

-5

-2.5

0

-6.5 -6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2 .5 3 3.5 4 4 .5 5 5.5 6 6.5

rho [m ]

Rela

tive

Am

pli

tud

e [

dB

]

Quadridge Horn

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• quadridge waveguide horn

• wide frequency range (2 to 18 GHz)

• dual linear polarization

• VSWR < 3.5:1 (return loss < -5.5 dB)

Quadridge Horn, 3D Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• elliptical radiation patterns

• frequency dependent radiation characteristic

• moving phase center

2 GHz 8 GHz

16 GHz

Quadridge Horn, Polar Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• compromise for the subreflector illumination angle at center frequency

• high subreflector spillover at lowest frequency (high antenna noise temperature)

• low illumination efficiency at highest frequency

Quadridge Horn, f = 2.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

Quadridge Horn, f = 8.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

Quadridge Horn, f = 16.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

13.2m TTW Atenna Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

13.2m Ring Focus Antenna with Quadridge Horn

f = 16.0 GHz, without VSWR Efficiency and Strut Blockage

0

10

20

30

40

50

60

70

-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m Ring Focus Antenna with Quadridge Horn

f = 8.0 GHz, without VSWR Efficiency and Strut Blockage

0

10

20

30

40

50

60

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m Ring Focus Antenna with Quadridge Horn

f = 2.0 GHz, without VSWR Efficiency and Strut Blockage

-10

-5

0

5

10

15

20

25

30

35

40

45

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m TTW Antenna Efficiency with Quadridge Feed

(without VSWR Efficiency and Strut Blockage)

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14 16 18

Frequency [GHz]

Eff

icie

ncy

[%

]

Eleven Feed

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

Dipol Array

Dielectric

Support

Housing

Eleven Feed, 3D Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

2 GHz 8 GHz

16 GHz• rotationally symmetric radiaiton pattern

• frequency-independent feed gain

• fixed phase center

Eleven Feed, Polar Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

Eleven-Feed, f = 8.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

Eleven-Feed, f = 16.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

Eleven-Feed, f = 2.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

• frequency-independent reflector illumination

• constant efficiency in a reflector antenna

Interaction between Subreflector and Feed Cone

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

insignificant interaction

between subreflector

and feed cone and feed

housing

13.2m TTW Atenna Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

13.2m Ring Focus Antenna with Eleven Feed

f = 16.0 GHz, without VSWR-Efficiency and Strut-Blockage

0

10

20

30

40

50

60

70

-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Angle [deg]

Gain

[d

Bi]

90°_Co

0°_Co

45°_Co

45°_Cr

13.2m Ring Focus Antenna with Eleven Feed

f = 8.0 GHz, without VSWR Efficiency and Strut-Blockage

0

10

20

30

40

50

60

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m Ring Focus Antenna with Eleven Feed

f = 8.0 GHz, without VSWR Efficiency and Strut-Blockage

0

10

20

30

40

50

60

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m TTW Antenna Efficiency with Eleven Feed

(without VSWR and Strut Blockage Efficiency)

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16 18

Frequency [GHz]

Eff

icie

ncy

[%

]

Coaxial Horn

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

• adjustable phase center

• more than 30% bandwidth in

the lower frequency band

• more than 40% bandwidth in

the upper frequency band

Coaxial Horn, 3D Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

2 GHz 8 GHz

• very good pattern symmetry

• low crosspolarization

• coincidence phase centers for the two frequency bands

Coaxial Horn, Polar Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

Eleven-Feed, f = 2.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

0 [dBi]

5

-5

-10

-15

phi = 0°

phi = 45°

phi = 90°

Subreflector Rim

Mainreflector Rim

10

Eleven-Feed, f = 8.0 GHz0

30

60

90

120

150

180

-150

-120

-90

-60

-30

• low spillover

• constant illumination efficiency in both frequency bands

13.2m TTW Antenna Radiation Patterns

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

13.2m Ring Focus Antenna with Coaxial Waveguide Feed

f = 2.0 GHz, without VSWR Efficiency and Strut-Blockage

0

5

10

15

20

25

30

35

40

45

50

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

Angle [deg]

Gain

[d

Bi] 90°_Co

0°_Co

45°_Co

45°_Cr

13.2m Ring Focus Antenna with Coaxial Feed

f = 8.0 GHz, without VSWR-Efficiency and Strut-Blockage

0

10

20

30

40

50

60

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

Angle [deg]

Gain

[d

Bi]

90°_Co

0°_Co

45°_Co

45°_Cr

13.2m TTW Antenna Efficiency with Coaxial Horn

(without VSWR and Strut Blockage Efficiency)

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16 18

Frequency [GHz]

Eff

icie

ncy

[%

]

• high efficiency in both frequency bands

• low crosspolarization

Multiband Corrugated Horn

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

Corrugated Horn Gain

Semi Flare Angles 10.0°, 12.5°,15.0°, 17.5° and 20.0°

5

7.5

10

12.5

15

17.5

20

22.5

25

27.5

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Aperture Diameter Wavelength

Ga

in (

dB

i)

10.0°

12.5°

15.0°

17.5°

20.0°

Bandwidths for Allowable Groove Depth

0

5

10

15

20

25

30

35

40

45

50

55

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Frequency (GHz)

All

ow

ab

le G

roo

ve

De

pth

(m

m)

1/4 Lambda

1/2 Lambda

3/4 Lambda

1 Lambda

1 1/4 Lambda

1 1/2Lambda

1 3/4 Lambda

2 Lambda

2 1/4 Lambda

2 1/2 Lambda

2 3/4 Lambda

3 Lambda

Exclusion

Exclusion

Exclusion

Exclusion

Exclusion

Exclusion

• generally, a corrugated horn can

achieve a 2:1 frequency bandwidth

• if the corrugation depth is an odd

multiple of a quarter wavelength, the

horn geometry will work

• when the corrugation depth approaches

half of the wavelength, or multiples of it,

the horn pattern will breakdown

• not every frequency combination is

realizable

Multiband Corrugated Horn

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

The conical or tapered form of a corrugated horn is a natural frequency filter.

The frequency bandwith of a coupling junction is limited to a bandwith of about

10%.

Conclusion

MIRAD Microwave AG Broadband Feedsystems IVS VLBI2010 Workshop March 2009

13.2m TTW Antenna Efficiency Eleven Feed, Quadridge Horn and Coaxial Horn

(without VSWR and Strut Blockage Efficiency)

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10 12 14 16 18

Frequency [GHz]

Eff

icie

nc

y [

%]

Eleven Feed

Coaxial Horn

Quadridge Horn

If the frequency

bandwidth is needed, the

Eleven feed is the best

approach.

With coaxial feeds or

multiband corrugated

horns better antenna

performances is possible

in limited frequency

bands.