Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

1

EVLA Front-End CDR

Octave Bandwidth OMT Development in the 1-8 GHz Range

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

2

Frequency Ranges

• L: 1- 2 GHz 2:1 (“Octave”)• S: 2 – 4 GHz 2:1 (“Octave”)• C: 4 – 8 GHz 2:1 (“Octave”)• X: 8 – 12 GHz 1.5:1• Ku: 12 – 18 GHz 1.5:1• K: 18 – 26 GHz 1.44:1• Ka: 26 – 40 GHz 1.54:1• Q: 40 – 50 GHz 1.25:1

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

3

Why Quad-Ridge?

• Septum, Boifot types ~ 1.5:1 maximum

• cf. Q-R horns 2-18 GHz

• Low impedance structure

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

4

“Good” Mode

fco = 0.68

“Z” ~ 50 W fco = .74 fco = .91

“Z” ~ 500W

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

5

“Bad Mode”

fco = .69

fco = .88 fco = 1.28

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

6

fco vs. distance

Modes in Square Quad-Ridge GuideModes "sorted"

0.0000

0.5000

1.0000

1.5000

2.0000

2.5000

3.0000

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000

Gap

Fc

o, G

Hz

TE01

TE10

TE11

TM11

TE02

TE20

TE12

TE21

TM12

TM21

TE22

TM22

TE30

TE33

TExx

PAL 021019 sqqrfco.xls

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

7

Quad-Ridge

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

8

OMT Components

Window

Circular-to-Square

thermal gap

Square-to-QR QR-to-coax

mode suppression

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

9

Sliding Load

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

10

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

11

Return Loss

OMT Return Loss

-40.00

-30.00

-20.00

-10.00

0.00

1 1.2 1.4 1.6 1.8 2

GHz

dB EVLA Front

EVLA Rear

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

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vs. ERA OMT

OMT Return Loss

-40.00

-30.00

-20.00

-10.00

0.00

1 1.2 1.4 1.6 1.8 2

GHz

dB

EVLA Front

EVLA Rear

ERA Front

ERA Rear

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

13

Isolation

EVLA OMT Isolation

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

GHz

dB

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

14

90-degree hybrid

2/1

Hybrid

In

Iso.

Coup.

Thru2/j

RCP

Nothing

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

15

Mis-matched90-degree hybrid

2/1

Hybrid

In

Iso.

Coup.

Thru2/j

Less RCP

Some RCP

Gx

Gy

Gr

Gl

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

16

Math

)(

)(

and ))((2

input, RCP pureWith

1 2

YXL

YRL

XYR

BGAGGBA

AGBGGBAj

R

L

BGBGGBAd

jR

kBkSinA

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

17

Axial Ratio (Amplitudes;Voltages)

0575.122.1 ,dB" 1 " for

||

|| where

1

1

R

L

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

18

For a< 1 dB

• (With some assumptions) we can specify that the return losses of a pair of ports must sum to better than ~34 dB

• This sort of tradeoff applies to any polarizer.

• With perfect amplitude & phase, the sum would be ~25 dB.

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

19

Next to do

• Reduce mass of OMT.

• Improve Cooling.

• Better window material.

• Investigate manufacturability.

Paul Lilie EVLA Front-End CDR – OMT DevelopmentApril 24, 2006

20

Conclusions

• Prototypes have been built

• Return loss is acceptable across band

• Isolation is good across band

• “Suck-out” suppression is effective