Pulse compression ABP Atoms, Beams & Plasmas Compression of Frequency-Modulated Pulses using Helically Corrugated Waveguide S.V. Samsonov, S.V. Mishakin,

Pulse compression ABP

ABPAtoms, Beams & Plasmas

Compression of Frequency-Modulated Pulses using Helically Corrugated

Waveguide

S.V. Samsonov, S.V. Mishakin, G.G. Denisov, V.L. Bratman and N.G. KolganovInstitute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, 603950, Russia.

M. McStravick, A.W.Cross, W.He, K. Ronald, C.G. Whyte, A.D.R. Phelps,

I.V. Konoplev, G. Burt, P. MacInnes and A.R. Young SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland, U.K.


Compression of frequency-modulated pulses using a helically corrugated waveguide

• Can be used to generate high-peak-power, short- duration microwave pulses

• Does not require additional infrastructure beyond the amplifier’s input source requirements:

• Vacuum pump

• Power supplies

• Increased x-ray shielding


• In a dispersive medium the group velocity is a function of frequency

Sweep-frequency microwave pulse compression in waveguides

axial direction in dispersive medium

tail of pulse

Amplitude of microwave

Lower power microwave

front of pulse

higher power microwave

•If a pulse is modulated from one frequency to a frequency with a higher group velocity, the pulse will compress


Helically corrugated waveguide

Bragg conditions

Dispersion curves of a circular waveguide with a helical corrugation

mA=2, mB=-1

8.0

8.5

9.0

9.5

10.0

10.5

-1.0 -0.5 0.0 0.5 1.0Axial wavenumber(1/cm)

freq

uen

cy (

GH

z)

TE11

TE21

The helical corrugation

• Corrugation couples a counter rotating TE11 wave with a co- rotating TE21 wave on a 3-fold helix.

zkmlrzr cos, 0



Bragg conditions


mA=2, mB=-1

8.0

8.5

9.0

9.5

10.0

10.5


freq

uen

cy (

GH

z)

Operating eigenwave

TE11

TE21


• Corrugation couples a counter rotating TE11wave with a co- rotating TE21 wave on a 3-fold helix.

zkmlrzr cos, 0



Bragg conditions


mA=2, mB=-1

8.0

8.5

9.0

9.5

10.0

10.5


freq

uen

cy (

GH

z)

vg1

vg2

Operating eigenwave

TE11

TE21


• Corrugation couples a counter rotating TE11wave with a co- rotating TE21 wave on a 3-fold helix.

zkmlrzr cos, 0


Advantages of a helically corrugated waveguide as compared to a smooth bore waveguide

•The optimum frequency sweep is from a high frequency to a low frequency Suitable for use with frequency tuneable BWOs

•Helically corrugated waveguide can be designed to have a large change in group velocity as function of frequency;

Shorter lengths of waveguide; Reduced ohmic losses

Results in high energy conversion efficiencies at high powers

•Operates far from cut-off frequency; Less prone to reflection of the input signal Makes it compatible with amplifier technology

TWT Gyro-TWA


CST Microwave Studio

cross-section of a helically corrugated waveguide

-20

-15

-10

-5

0

5

10

15

-20 -10 0 10 20

rcosφ

rsin

φ 3-fold helicallycorrugatedwaveguide

MWS allows dispersion to be calculated without simulating a large number of periods, using periodic boundaries


Dispersion in helically corrugated waveguide

Scalar network analyser Method of perturbations

Microwave studio

8.2

8.4

8.6

8.8

9

9.2

9.4

9.6

9.8

10

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4

axial wavenumber (cm-1)

fre

qu

en

cy

(G

Hz)

SNA

MOP

MWS


Group velocity in a helically corrugated waveguide

0.00

0.10

0.20

0.30

0.40

0.50

0.60

9.00 9.10 9.20 9.30 9.40 9.50 9.60 9.70

frequency (GHz)

gro

up

ve

loc

ity

/ c

Method of perturbation

SNA

Scalar network analyser

Method of perturbation

zg dk

dkcv ck


Experimental set-up of helical waveguide compressor - low power

PIN switch

Amplifier

Low and high-pass filters

PIN switch

Low pass filter 8.0 -11.0GHz


Low power experiments with inclusion of amplifier and filters

• Power compression factor of 18

Input pulse Compressed pulse

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

-10.00 0.00 10.00 20.00 30.00 40.00

time (ns)

am

plit

ud

e (

mV

)

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

-20.00 30.00 80.00

time (ns)

am

plit

ud

e (

mV

)


Low power experiments with PIN switch

•Reduced secondary pulses

•Peak power compression factor of 16

‘Chopped’ input pulse Compressed pulse

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

-50.00 0.00 50.00 100.00 150.00 200.00 250.00

time (ns)

am

plit

ud

e (

mV

)

measuredcompressedpulse with crystaldetector KR2

-50

-40

-30

-20

-10

0

10

-50 0 50 100 150 200 250

time (ns)

am

plit

ud

e (

mV

)

input pulsemeasured withcrystal detectorKR2


Arbitrary waveform generator and vector signal generator low power measurements

0

1

2

3

4

5

6

460.00 480.00 500.00 520.00 540.00

time (ns)

po

wer

(m

W)

Measured peak power in input pulse 4mW

Measured peak power incompressed pulse 100mW

Peak power pulse compression factor is 25

Input Pulse Compressed Pulse

0

20

40

60

80

100

120

500.00 505.00 510.00 515.00 520.00 525.00

time (ns)p

ow

er (

mW

)


• Optimum sweep produced by frequency programmable Agilent Arbitrary Waveform Generator

• Feed I/Q output to a 40GHz Agilent Vector Signal Generator

• Used to drive a 7kW X-band TWT amplifier, isolator, directional coupler

• Microwave signal measured on single shot 12GHz DSO

Set-up of compressor experiment using Arbitrary Waveform Generator and Vector Signal Generator with 7kW TWT – high power


High-power TWT results

• Power compression factor 25

• Peak power measurement of 2.73mW

• Attenuation was 63dB• TWT output power into compressor 5.5kW

• Peak power of compressed pulse measured to be 135kW

• Energy losses 25%

High-power compressed pulse

020406080

100120140160

-5.00 5.00 15.00

time (ns)p

ow

er

(kW

)


Future work

Year 2 (Present)

• Construct and assist in the design of a 5-fold helical waveguide

• CST Microwave Studio modelling of propagation of electromagnetic waves through 5-fold helical waveguide

• Perform 5-fold compression experiments using Agilent instrumentation and 7kW TWT amplifier


Future work

Year 3 • Larger diameter 5-fold helical waveguide is needed to

compress MW level frequency swept radiation generated by gyro-TWA – Larger diameter prevent RF breakdown

• Perform frequency swept compression experiments and measure peak power, gain, power and time compression factors and efficiency


Conclusion

• Optimum faster (up to 30MHz/ns) frequency-modulated pulse produced by the Arbitrary Waveform Generator and Vector Signal Generator resulted in a power compression ratio of 25 with energy losses of 25%

• Due to its reflection-less properties a helical compressor can be used effectively at the output of a powerful

amplifier (TWT), (Gyro-TWA)


Acknowledgements

• I would like to thank UK Engineering and Physical Sciences Research Council, MoD JGS scheme, Dave Gamble-Dstl and Doug Clunie-Faraday partnership in high power RF, for supporting this work

• I would like to thank my supervisors; Dr A.W. Cross, Dr W. He and Dr C.G. Whyte and the ABP group

• The loan of a high power 7kW TWT amplifier by TMD Ltd which was used to carry out these experiments is gratefully acknowledged

Documents

Pulse compression ABP Atoms, Beams & Plasmas Compression of Frequency-Modulated Pulses using Helically Corrugated Waveguide S.V. Samsonov, S.V. Mishakin,