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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.