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1

National Institute of Information andCommunications Technology

E. Kawai, J. Nakajima, H. Takeuchi, H. Kuboki,and T. Kondo

Kashima Space Research Center, NICT

K. Saito, and M. SuzukiDENSO CORPORATION Research Laboratories

RFI mitigation at a 2GHz band

by using a wide-band high-temperature superconductor filter

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Kashima 34-m antenna

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Contents

RFI situation at Kashima High-Temperature Superconductor

(HTS) filter

Results

Future possibilities

Conclusions

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RFI situation at Kashima

-80

-70

-60-50

-40

-30

-20

-10

0

2100 2200 2300 2400 2500

RX freq. (MHz)

RXou

tput(dBm)

RBW 300KHz VBW 1KHz SWP 4sec

After RFI

Before RFI

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Vicinity of Kashima 34-m antennaand the base stations

34-m antenna

2.6km6.2km

2.4km

B1B2

B3

B4 B5

B6

8.2km 6.1km

1.7km

C1

0.75km

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IMT-2000 frequency assignment and Kashima34-m antenna receiving frequency

Service start: Company B 2nd March 2002, Company C 1st July 2003

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If LNA is not saturated, we can takecountermeasure after LNA.

Maximum LNA output of interferencesignal was -17.6dBm.

We performed to measure LNA linearity.

Is LNA saturated?

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Test block diagram

LNA linearity test

RHCP Coupler LNASpectrumAnalyzer

SG

Dewar

Cable loss-1.5dB

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LNA linearity test

-60

-50

-40

-30

-20

-10

0

-60 -50 -40 -30 -20 -10 0 10

LNA input (uncorrected) (dBm)

LNA

outpu

t(dBm)

1dB compression -6.5dBm

LNA linearity test result

IMT-2000 RFI level-17.6dBm at present

Current margin is 11.1dB.

LNA input (dBm)

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Countermeasure

ToObs. room

HTSFilter

LNA

dewar

subsystem

D/C

Receiver block diagram

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HTS filter

60 mm

From http//www.kreynet.de/asc/ybco.html

Low loss: 0.5dB

Sharp cut-off: 60dB/23MHz

Wide-band: 280 MHz

Small size: 60mm in diameter

The filters were fabricated on superconductorYBCO films on MgO substrates.HTS filter operating temperature is 70 K.

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HTS filter

60 mm

Cryogenic subsystem

LNA output D/C input To observation room

filter unit

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Low loss

Due to low resistance of HTS films inmicrowave frequency, Tsys increasecan be very small even if the filter is

installed before LNA.

HTS filter 0.5dB/32 sections

Conventional filter 1dB/19 sections

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Sharp cut-off

32 sections was possible due to lowresistance of HTS films. 60dB/23MHz

Resulting extension of observablefrequency range than conventional filter.

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Wide-band Wide-band by new filter design.

Bandwidth ratio 1% ->12%(280MHz)

Small size

Miniaturization by new filter design. Diameter 60mm, thickness 14mm

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HTS filter specifications

Frequency (GHz)

Attenuation

(dB) Pass band2193-2473 MHz

Attenuation>60 dB at 2170MHz

Insertion Loss

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Inside of HTS filter subsystemWeight 11.5kg

Width 270 mm

Depth 170 mm

Height 270 mm

A case, a controller,and a power supplyare not included.

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69.97

69.98

69.99

70.00

70.01

70.02

70.03

0 600 1200 1800 2400 3000 3600

Time (S)

Chambertemperature(K)

Temperaturecharacteristicsof cut-off

frequency

100kHz/K(at70K)

100kHz x 0.01K

=1kHz

Chamber temperature (1 hour)

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S-band receiver outputcharacteristics

The frequency of 2193 to 2350MHz became observable.

-90

-80

-70

-60

-50

-40

2100 2200 2300 2400 2500RX freq. (MHz)

RX

output(dBm)

RBW 300kHz VBW 1kHz SWP 4sec

RFI perfectly suppressed

57MHzHTS filter

Coventional filter

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-40

-30

-20

-10

0

0 2 4 6 8 10

Distance from 34-m antenna (km)

LN

A

out

put

(dB

m

)

LN A saturation level -6.5dB m

no traffic

maximum traffic

Base station distance and LNA output

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The countermeasure for LNA saturation

As IMT-2000 is becoming popular, the

interference level will increase. HTS filter can be installed before LNA as a

countermeasure.

The increase of Tsys can be minimized byusing the HTS filter.

Increase in Tsys with a filter

Conventional filter 62KHTS filter 8K

Future possibility

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Conclusions S-band observations became difficult

after IMT-2000 service started.

We succeeded to develop HTS filter tomitigate the RFI in S-band.

Because of its low loss characteristics,the HTS filter can be installed beforeLNA.