Transducer, Mode Splitter/Combiner X-Band OMT Design Review October - - PowerPoint PPT Presentation

Offset Quadruple-Ridge Orthomode Transducer, Mode Splitter/Combiner

X-Band OMT Design Review October 1, 2009

Gordon Coutts

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Introduction

Low-Band EVLA Circular Polarizers

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• Circular to Square

Transition

• Quadruple-Ridge OMT

(separates orthogonal linearly polarized signals)

• Quadrature Hybrid
• Phase-Matched cables

connecting the OMT to the hybrid

Quadrature Hybrid

High-Band EVLA Circular Polarizers

• Circular to Square

Transition

• Sri’s corrugated

waveguide Phase Shifter

• 45 Degree offset mode

splitter

• Bøifot OMT (separates
• rthogonal linearly

polarized signals)

X-Band Design Challenges

• Two options using conventional technology from existing EVLA

receivers: – Cascaded Bøifot OMT/ mode splitter/ phase shifter

• This would scale to an impractically large size at X-band

– Direct scaling of the C-Band Polarizer to work at X-Band

• This would result in very small dimensions (20 mil chamfer, 30mil ridge

gap)

• Manufacturing tolerances would be a significant percentage (of the order
• f 10%) of the scaled dimensions
• Narrow ridge dimensions would not readily accommodate set

screws/coaxial feeds

• Phase matching to an external hybrid would be extremely difficult due to

the required cable length adjustments (1.9mil/degree at 12GHz)

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6

Proposed X-Band OMT Design

Novel X-Band OMT Design

• The new X-Band OMT uses a

45 degree offset quadruple- ridge design

• The novel polarizer design

combines concepts from low- band and high band circular polarizer designs

• The OMT combines the

function of the ‘45 degree twist’ mode splitter and Bøifot OMT used in the high frequency designs

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Novel X-Band OMT Design

• Ridges are offset from the square

waveguide input by 45 degrees

• Square Waveguide Input: 0.947”

x 0.947”

• Detects circularly polarized

signals when used in conjunction with Sri’s waveguide phase shifter

• No external quadrature hybrid or

phased matched cables in this design

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High-Band EVLA Circular Polarizers

• Circular to Square

Transition

• Sri’s corrugated

waveguide Phase Shifter

• 45 Degree offset mode

splitter

• Bøifot OMT (separates
• rthogonal linearly

polarized signals)

Proposed EVLA X-Band Circular Polarizer

• Circular to Square

Transition

• Sri’s corrugated

waveguide Phase Shifter

• 45 Degree offset

quadruple-ridge OMT

Compact Design of X-Band OMT

• Compact design: OMT Length is 6.12”

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X-Band OMT Dimensions

• Chamfer profile similar to C-band

OMT for manufacturability

• 125 mil Ridge Width
• 62 mil Ridge Gap
• 40 mil Chamfer flat section
• Locator block sets ridge gap and

maintains symmetry

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X-Band OMT Dimensions

• The quadruple-ridge waveguide

dimensions: – optimum impedance at low- band edge – Eliminate higher order modes

• 0.047” semi-rigid coaxial feeds
• 62.5mil spaced shorting pins for

impedance matching and TE11 trapped-mode resonance suppression

• One 2-56 set screw for each sorting

pin, with set screws for adjacent pins on opposing ridges

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Theory of Operation

Circularly Polarized Electromagnetic Waves

• LCP (Astronomy Definition)

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• RCP (Astronomy Definition)

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x z

y x

LCP signal

Theory of Operation

y x y x

Apparent motion of electric field vector of circularly polarized electromagnetic waves as viewed from the receiver (astronomy definition).

LCP signal RCP signal

Theory of Operation: Phase Shifter

y x

Direction of Propagation

y x

Direction of Propagation

LCP signal RCP signal

Theory of Operation: OMT

Port 1 Port 2 Port 1 Port 2 y y' x x' (mode 1) (mode 2)

Theory of Operation: OMT

Port 2 Port 1

LCP signal

• utput

Port 2 Port 1

RCP signal

• utput

LCP signal RCP signal

y y' x x'

HFSS Simulated OMT Performance

• HFSS simulated modal transmission S-parameter

magnitude from OMT input to the coaxial OMT output ports

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• 5
• 4.5
• 4
• 3.5
• 3
• 2.5
• 2
• 1.5
• 1
• 0.5

8 8.5 9 9.5 10 10.5 11 11.5 12 Transmission Mag. (dB)

• Freq. (GHz)

S{2,TE10'} S{2,TE01'} S{1,TE10'} S{1,TE01'}

HFSS Simulated OMT Performance

• HFSS simulated reflection OMT S-parameters

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• 50
• 45
• 40
• 35
• 30
• 25
• 20
• 15
• 10
• 5

8 8.5 9 9.5 10 10.5 11 11.5 12 Reflection Mag. (dB)

• Freq. (GHz)

S11 S22

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Measured X-Band OMT Performance

Measured OMT Performance

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• 5
• 4.5
• 4
• 3.5
• 3
• 2.5
• 2
• 1.5
• 1
• 0.5

8 9 10 11 12 Transmission Mag. (dB)

• Freq. (GHz)

X-Band OMT Transmission - First Prototype

Mode2 - FP Mode2 - BP Mode1 - FP Mode1 - BP

Measured OMT Performance

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• 35
• 30
• 25
• 20
• 15
• 10
• 5

8 9 10 11 12 Reflection Mag. (dB)

• Freq. (GHz)

X-Band OMT Reflection - First Prototype

Mode2 Mode1 Specification

Measured OMT Performance

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• 70
• 60
• 50
• 40
• 30
• 20
• 10

8 9 10 11 12 Isolation Mag. (dB)

• Freq. (GHz)

X-Band OMT Isolation - First Prototype

Measured OMT Performance

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• 5
• 4.5
• 4
• 3.5
• 3
• 2.5
• 2
• 1.5
• 1
• 0.5

8 9 10 11 12 Transmission Mag. (dB)

• Freq. (GHz)

X-Band OMT Transmission - Second Prototype

Mode2 - FP Mode2 - BP Mode1 - FP Mode1 - BP

Measured OMT Performance

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• 25
• 20
• 15
• 10
• 5

8 9 10 11 12 Reflection Mag. (dB)

• Freq. (GHz)

X-Band OMT Reflection - Second Prototype

Mode2 Mode1 Specification

Measured OMT Performance

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• 60
• 50
• 40
• 30
• 20
• 10

8 9 10 11 12 Isolation Mag. (dB)

• Freq. (GHz)

X-Band OMT Isolation - Second Prototype

Measured Circular Polarization Performance using Machined Prototype Phase Shifters

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Machined Phase Shifters

• Prototype X-Band phase

shifters were fabricated in-house

• Used to evaluate circular

polarization performance

• f the new X-Band OMT
• The X-Band OMT was

connected to the phase shifter and measured using the PNA

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Machined Phase Shifter Measured Performance

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50 60 70 80 90 100 110 8 9 10 11 12 Phase (Degrees)

• Freq. (GHz)

Machined Phase Shifter #1: Measured Relative Phase Shift

Relative Phase Shift Ideal Phase Difference

Measured Axial Ratio Performance

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0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 8 9 10 11 12 Axial Ratio (dB)

• Freq. (GHz)

Axial Ratio - OMT Proto #2 - Machined Phase Shifter #1

FP Out (Meas.) BP Out (Meas.) FP Out (Calc. From Meas. Data) BP Out (Calc. From Meas. Data)

Circular Polarization Performance

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• 7
• 6
• 5
• 4
• 3
• 2
• 1

8 8.2 8.4 8.6 8.8 9 Transmission Mag. (dB)

• Freq. (GHz)

Circular Co-Polarization Response: Septum Polarizer Input, Quad-Ridge OMT Output (P.S.#1, OMT#2)

Meas Co-Pol (NB OMT L - WB Proto FP Out) Meas Co-Pol (NB OMT R - WB Proto BP Out) Co-Pol (CP IN - WB Proto BP Out) - Calc from Meas. Data Co-Pol (CP IN - WB Proto FP Out) - Calc from Meas. Data

Circular Polarization Performance

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• 90
• 80
• 70
• 60
• 50
• 40
• 30
• 20
• 10

8 8.2 8.4 8.6 8.8 9 Transmission Mag. (dB)

• Freq. (GHz)

Circular Co-Polarization Response: Septum Polarizer Input, Quad-Ridge OMT Output (P.S.#1, OMT#2)

Meas X-Pol (NB OMT R - WB Proto FP Out) Meas X-Pol (NB OMT L - WB Proto BP Out) Calc X-Pol (CP IN - WB Proto BP Out) Calc X-Pol (CP IN - WB Proto FP Out)

Measured Circular Polarization Performance using Scaled Ku-Band Phase Shifter Experimental Data

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Scaled Phase Shifter Performance

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50 60 70 80 90 100 110 8 9 10 11 12 Phase (Degrees)

• Freq. (GHz)

Measured Ku-Band Phase Shifter Response Scaled to X-Band

Relative Phase Shift Ideal Phase Difference

Measured Axial Ratio Performance using Scaled Ku-Band Phase Shifter Data

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0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 8 9 10 11 12 Axial Ratio (dB)

• Freq. (GHz)

Axial Ratio - OMT Proto #2 - Scaled Ku Band Phase Shifter

FP Out (Calc. From Meas. Data) BP Out (Calc. From Meas. Data)

Circular Polarization Performance

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• 2
• 1.8
• 1.6
• 1.4
• 1.2
• 1
• 0.8
• 0.6
• 0.4
• 0.2

8 9 10 11 12 Transmisssion Mag. (dB)

• Freq. (GHz)

Circular Co-Polarization Response: Omt Proto. 2 with Scaled Ku-Band Phase Shifter

Co-Pol Transmission Calc. from Measured Data - FP Out Co-Pol Transmission Calc. from Measured Data - BP Out

Circular Polarization Performance

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• 70
• 60
• 50
• 40
• 30
• 20
• 10

8 9 10 11 12 Transmisssion Mag. (dB)

• Freq. (GHz)

Circular Cross-Polarization Response: Omt Proto. 2 with Scaled Ku-Band Phase Shifter

X-Pol Transmission Calc. from Measured Data - FP Out X-Pol Transmission Calc. from Measured Data - BP Out

Circular Polarization Performance using Measured OMT Data and Ideal Phase Shifter

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OMT Contribution to Axial Ratio

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 8 9 10 11 12 Axial Ratio (dB)

• Freq. (GHz)

Axial Ratio - OMT Proto #2 - Ideal Phase Shifter

FP Out (Calc. From Meas. Data) BP Out (Calc. From Meas. Data)

OMT CP Insertion Loss

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• 1
• 0.9
• 0.8
• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

8 9 10 11 12 Transmisssion Mag. (dB)

• Freq. (GHz)

Circular Co-Polarization Response: OMT Proto. 2 with Ideal Phase Shifter (OMT Insertion Loss)

Co-Pol Transmission Calc. from Measured Data - FP Out Co-Pol Transmission Calc. from Measured Data - BP Out

OMT CP Isolation

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• 70
• 60
• 50
• 40
• 30
• 20
• 10

8 9 10 11 12 Transmisssion Mag. (dB)

• Freq. (GHz)

Circular Cross-Polarization Response: Omt Proto. 2 with Ideal Phase Shifter (OMT CP Isolation)

X-Pol Transmission Calc. from Measured Data - FP Out X-Pol Transmission Calc. from Measured Data - BP Out

Conclusions

• A novel 45 degree offset quadruple-ridge

OMT design is proposed for the new EVLA wideband X-Band receivers

• Two prototypes have been fabricated and

tested, and exceed specifications by a wide margin

• The compact design is amenable to cooling

with a Model 22 refrigerator

• Measured results show that the novel design

exhibits good axial ratio and circular polarization performance

• As with the other EVLA quadruple-ridge OMT

designs, the new X-Band design is focused

• n excellent performance, ease of tuning and

manufacturability

• The OMT electromagnetic design is ready for

production

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