A 410-495 GHz heterodyne receiver, with an array of two Nb/Al2O3/Nb tunneljunctions as mixing element is described. The noise temperature of this receiver is below 230 K (DSB) over the whole frequency range, and has lowest values of 160 K in the 435-460 GHz range. The calculated DSB mixergain over the whole frequency range varies from -11.9 plus or minus 0.6 dB to -12.6 plus or minus 0.6 dB and the mixer noise is 90 plus or minus 30 K

Degraauw, M. W. M.

Delange, G.

Dierichs, M. M. T. M.

Honingh, C. E.

Klapwijk, T. M.

Panhuyzen, R. A.

Schaeffer, H. H. A.

Vandestadt, H.

English

NASA Technical Reports Server

p 210 Third Int^national Symposium on Space Terahertz Technology
N93-2?? 4 3
A low noise 410-495 heterodyne two tuner mixer,
using submicron Nb/AI203/Nb Tunneljunctions
G. DE LANGE*. C.E. HONINGH', M.M.T.M. DIERICHS*, R.A.
PANHUYZEN*, H.H.A. SCHAEFFER', T.M. KLAPWIJK*, H. VAN DE
STADT*, M.W.M DE GRAAUW*. "University of Groningen. Nijenborgh 4. 9747
AG Groningen; 'Space Research Organisation of the Netherlands. Landleven 12.
9747 AD Groningen.
A 410-495 GHz Heterodyne receiver, with an array of two Nb/Al2O-,/Nb
tunneljunctions as mixing element is described. The noise temperature
of this receiver is below 230 K (DSB) over the whole frequency range,
and has lowest values of 160 K in the 435-460 GHz range.The
! calculated DSB mixergain over the whole frequency range varies from
—77.9 ± 0.6 dB to -12.6 ± 0.6 dB and the mixer noise is 90 ± 30 K.
Introduction
SIS-mixers are currently being used as heterodyne receivers up to submillimeter
wavelengths [1][2]. Two different types of mixers are used to achieve low noise
receivers: quasi-optical mixers, with a fixed tuned broadband planar antenna, and
waveguide mixers, with one or two tuning elements.
In this paper a two tuner waveguide mixer designed for the 400-500 GHz range is
described. The used mixing elements are two different arrays of two Nb/Al2O3/Nb
tunneljunctions. This mixer is the second frequency step towards our goal to make
a THz receiver (350-490-750-1000 GHz). At these high frequencies the dimensions
of a waveguide structure become very small (100-400 jim) and it is unclear how far
losses due to surface irregularities deteriorate the mixer performance.
The laboratory tests of the mixer show that in the 400 to 500 GHz frequency range,
waveguide mixers can still achieve low noise temperatures (as low as 160 K DSB),
and the flat response over the band indicates that the current design can be scaled
up to higher frequencies.
https://ntrs.nasa.gov/search.jsp?R=19930018554 2020-03-17T05:45:16+00:00Z
Third International Symposium on Space Terahertz Technology Page 212
The behaviour of SIS-mixers is well described by theory [3][4]. An extensive
comparison between theory and measurements has been performed at 345 GHz [5]
and this comparison is started in the 410-490 GHz range. First results show a good
agreement between calculated and measured IV-curves, from which the
electromagnetic environment of the junction is deduced.
This paper describes the design of the mixer, the results from ihe two different
arrays of junctions and some preliminary analysis of the mixer performance.
Receiver design
The mixer block design for 400-500 GHz is a scaled version of the 345 GHz mixer
described by Honingh et al.[6].
The mixer system is placed inside an Infrared Laboratories HD 3 cryostat. The
signal and LO-power enter the cryostat via a 1 mm thick HDP window of 3 cm
diameter. On the 77 K radiation shield a 200 /im thick quartz plate serves as heat
filter.
A diagonal horn with an aperture size of 4:5 mm, a length of 12 mm and a flare
angle of 11 degrees is used. Laboratory tests of this horn showed a good gaussian
beam-coupling (side lobes <-15db), equal beamwidth in E-,D- and H- planes and
a low cross-polarisation (<-15 dB). In front of the horn a F=31.4 mm HDP lens is
used. The lens is mounted in a holder which can be directly mounted on the
mixerblock. The mixerblock is cut in OFHC. The full height waveguide with
dimensions 0.44*0.22 mm, has a cut off frequency of 340 GHz. The waveguide
system has two moving shorts as tuning elements, each with a quarter wave choke
section to improve the quality of the short. In order to suppress the Josephson
currents in the junction, a coil with 10.000 turns of 0.1 mm Nb wire is placed
around the horn, in front of the mixerblock. The IF-chain consists of a Radiall
R443533 T-bias, a Pamtech LTE 1290 isolator and a Berkshire Technologies L-1.4-
30H IF-amplifier.
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Third International Symposium on Space Terahertz Technology Page 213
SIS-junctions
The fabrication of the used junction arrays, is described elsewhere [7]. Up to now
two different types of arrays have been used. The arrays differ in junction area,
current density, RF-filterstructure and gapvoltage. An overview is given in table 1.
Junction array
A (1 junction) (Mm2)
Ic (A/cm2)
Rn (n)
RF-filter
Gap-voltage (mV)
Q34
0.8
7000
100
Chebychev
2.7
Q35
2
12.000
22
V 4 X
2.4
Table 1. Overview of the 2 different junction arrays.
The lower gapvoltage of junctions Q35 is caused by a higher oxygen background
pressure during sputter deposition of the trilayer.
Measurement set-up
A schematic diagram of the measurement set-up is given in Fig. 1. The use of two
coherent sources, in combination with a spectrum analyser allow to analyse the
mixer performance at the LO and the upper and lower sideband frequencies. In the
measurements the carcinotron acted as LO-source.
The noise temperature of the mixer was measured by using the well known "Y-
factor" method. The measurements were corrected for the loss of the beamsplitter
(15 Mm mylar, 95% transmission).
Results
The DSB noise temperature of the receiver is shown in Fig. 2 for two different
junction arrays. Array Q34 (Rn= 100 n, A=0.8 Mm2, Chebychev RF-filter) has noise
temperatures below 230 K over the whole 410-495 GHz range. The lowest value
measured was 160 K at 445 GHz. Array Q35 (Rn=22 n, 2 Mm2,1/4 A RF-filter) has
noise temperatures between 260 K to 220 K in the frequency range 445-495 GHz.
The noise temperature increases sharply below 445 GHz, due to leakage of the RF-
filter.
Page 214 Third International Symposium on Space Terahertz Technology
800
700
600
500
400
300
200
100
SRON 410-490 GHZ 2-tuner mixer
Q35 Rn-22 Ohms, 1/4 Xfiiter, 2 urn 2
Q34 Rn-100 Ohms, Chebychev filter .8 urn 2
2-junction array
DSB Noise Temperature
junction
a Q35
A 034
A.
J I
400 410 420 430 440 450 460 470 480 490 500
Frequency (GHz)
State University Groningen
SRON Groningen, The Netherlands
Fig. 2
Third International Symposium on Space Terahertz Technology Page 215
1200
1100
1000
900
800
700
600
500
400
300
200
100
SRON 490 GHZ 2-tuner mixer
Tuned and instantaneous bandwidth
Q34 Rn-100 Ohms ,Chebychev-filter
DSB Noise Temperature
D
D a
m ; a
/ m /
400 410 420 430 440 450 460 470 480 490 500
Frequency (GHz)
State University Groningen
SRON Groningen, The Netherlands
Fig. 3
Page 216 Third International Symposium on Space Terahertz Technology
The instantaneous bandwidth of junction Q34 is shown in Fig. 3. Here the frequency
was changed without adjusting the tuners, only the pump power was adjusted for
optimum H/C response.
The unpumped and pumped IV-curves of the two arrays at two different frequencies
are shown in Fig. 4. Array Q34 has a low leakage current, a gap voltage of 2.1 mV
(1 junction) and a well defined photon step above the gap. The gap voltage of array
Q35 is 2.4 mV and it is clearly observed that if the LO-power is radiated on the
junction the gap voltage decreases due to heating. The shape of the photon step
above the gap also indicates heating effects occur in the junction.
Pumped IV-curves 410-490 GHz Pumped IV-curves 430-490 GHz
junction Q34 junction Q35
2 4 • • tt 19 U 0 > 4 • •
Baa voltage (mV) Biaa voltage (mV)
Fig. 4 Pumped and unpumped IV-curves of the two junction arrays
Fig. 5 shows the IF power output at two LO-frequencies, when a hot or cold load
are placed in front of the junction. The smooth curves indicate that the Josephson
current is suppressed sufficiently. The structure (at 3 mV) in the IF-output seen at
495 GHz is due to the fact that the second photonstep from the negative bias
voltage range "creeps" into the first photonstep at the positive voltage range.
Third International Symposium on Space Terahertz Technology Page 217
Hot/Cold response 410 GHz Hot/Cold response 495 GHz
IF-output (uW)
60
40
SO
20
10
IF-output (uW)
12 W
Bias voltage (mV) Biaa voltage (mV)
Fig. 5 IF-output with hot and cold signal
Analysis
In the analysis of the noise temperatures, the receiver is divided into three
elements: the RF-input, the mixer and the IF-output. A schematic diagram of the
whole receiver is given in Fig. 6. Each of these elements contributes to the total
receiever noise and gain.
RF-input Mixer IF-output
Fig. 6 Schematic representation of the noise and gain
contributions in the receiver
For the analysis of the contribution of the IF chain (T-bias, isolator, IF-amplifiers),
the shotnoise of an unpumped junction is used. With the known shdtnoise of an
unpumped junction a Y-factor measurement on the IF-chain is performed. The total
power at the end of the IF-chain is given by (1). Here r is the reflection coefficient
between the 50 n line and the junction. P .^..?^ , and PIF are the noise powers
Page 218 Third International Symposium on Space Terahertz Technology
coming from the junction, the isolator load and the IF-amplifier. GIF,Gisol and GT_
bias are the gains from the various components. The noisepower from an unpumped
array of two junctions is given by (2), where B is the bandwidth, Rdyn is the dynamic
resistance of the array and V is the voltage over the entire array.
P — ( P . r j_ P ,c\ r\ j IF \s~i /~i /^ / - I N
•* out — V-* lunc1- T -» isol \L ~~ L I < 7^ ~^ 1^IF^isol^T— bias (ij
1
8 (2)
IF-noise of unpumped junction
IF-output (uW)
T-Bias
Isolator
4 a 8 10 12 M
Bias voltage (mV)
-amplifier
Schematic Diagram of junction and IF-
chain
Fig. 7 Measured and calculated
noisepower output of an unpumped
array of two junctions
Fig. 7 shows the experimental and fitted curves. The values for the gain and noise
contributions of the IF-chain are: G,F=88.4 ±0.1 dB, TjF=4.8 ± 0.2 K.
The gain and noise contributions of the RF input (beamsplitter, HDP-window,
quartz-filter, lens, horn, waveguide and tuners) are difficult to estimate. Several
elements were measured seperately, but reflections at the horn waveguide transition
and losses in the waveguide and thf two tuners are difficult to find. The total gain
and noise at the RF-input are: 0^=0.77 ±0.1 and TRF=56 ± 20 K.
Third International Symposium on Space Terahertz Technology Page 219
The mixer noise and gain are now calculated with (3) and (4), where $Pout is
measured power difference at the IF-frequency and 5Pin is the difference in input
power from the hot and the cold load. T^ is the measured total receiver noise
temperature.
6 Pout
V-7mix ~~ (3)
in
= TrecGRF ~
Tip (4)
'mix
The gain and noise of the mixer are, just as the receiver noise temperature, nearly
constant over the 400-500 GHz band. Typical values for the contributions in the
receiver DSB gain and noise are: Gmix= -12.5 dB ± 0.6 dB and Tmix= 90 ± 30 K.
For a complete calculation of the mixer performance it is necessary to know the
embedding admittances at the LO and the upper and lower sideband frequencies.
These admittances are found by fitting a calculated pumped IV-curve to a measured
pumped IV-curve. An example of the quality of this fit at two different frequencies
is shown in Fig. 8.
Pumped IV-curve 410 GHz
G-0.67 B-0.42 (norm, to 1/100 Mho)
DC current (uA)
Pumped IV-curve 490 GHz
G-0.60 B-0.31 (norm, to 1/100 Mho)
DC current (uA)
too - 100
•0
2 4 • • 10
Bias voltage (mV)
2 4 a a 10
Bias voltage (mV)
12
Fig. 8 Measured and calculated IV-curves. The embedding parameters
are shown in the header
Page 220 Third International Symposium on Space Terahertz Technology
It is observed that the quality of the fit is good, except for the discrepancy near the
gap, which is due to heating and difficult to model. The derived embedding
admittances indicate that the tuning elements are able to compensate the junction
capacitance. Unfortunately the sideband admittances are not yet calculated and a
full analysis cannot be performed at the moment. The result of a calculation of the,
mixergain, under the assumption that the sideband admittances are equal to the
LO-admitance, is shown in Fig. 10.
0,14
0.12
0,1
0,01
0,08
0,04
0,02
Calculated Gain 410 GHz
G-0.67 B-0.42 (norm, to 1/100 Mho)
Gain
ou
0,1
0,01
o.oe
0.04
0,02
Calculated gain 490 GHz
G-0.80 8-0.31 (norm, to 1/100 Mho)
Gain
0.8 1 1,8 2
Bias voltage (mV)
2,8 0,8 1 1,8 2
Bias voltage (mV)
2,8
Fig. 10 Measured and calculated mixer gain
In this figure the calculated and measured gain are normalized to each other. One
observes a big discrepancy between the measured and calculated gain, which
indicates that the LO and sideband frequencies differ significantly.
In both the calculated and the measured gain, some fine structure on the first
photonstep region is observed, indicating that the calculation method is working
properly, but the input parameters are wrong.
Summary
Measurements were performed in the 400-500 GHz range with a two tuner
waveguide mixer. The measured (receiver) noise temperatures are amongst the
lowest values measured at these frequencies. The results show that an array of two
Third International Symposium on Space Terahertz Technology Page 221
junctions is suitable in achieving a low noise receiver in the 400-500 GHz range. It
is also found that a qualitatively "bad" junction with a low gap-voltage can still serve
as a low noise mixer element. The preliminary comparisons between theory and
measurement show a good agreement between calculated and measured pumped
IV-curves. Gain calculations indicate that the measured noise temperatures are not
fully DSB measurements. Further analysis is needed to determine the USB and LSB
gain and noise contributions.
Acknowledgements:
This work was supported by ESA under contract No. 7898/88/NL/PB(SC), the
Stichting Technische Wetenschappen and the Stichting voor Fundamenteel
Onderzoek der Materie.
References
1 J.Zmuidzinas, H.G. LeDuc, "Quasi-Optical Slot Antenna SIS Mixer", Proceedings
of the Second International Symposium on THz Technology.
2 CK. Walker, M.Chen, P.L Shafer, H.G. LeDuc, J.E. Carlstrom, T.G. Carlstrom,
T.G. Phillips, "A 492 GHz SIS Waveguid Receiver for Submillimeter Astronomy",
- _ ^
Int J. of IR and Millimeter Waves 1992.
3 J.R. Tucker, M.J. Feldman, "Quantum Detection at Millimeter Wavelengths" Rev.
Mod. Phys 57, 1055 (1985)
4 C.A. Mears, Qing Hu, P.L. Richards, A.H. Worsham, D.E. Prober, A.V. Raisanen,
"Quantum Limited Quasiparticles Mixers at 100 GHz", IEEE Trans. Magn., vol 27,
2, 1991
5 C.E. Honingh, G. de Lange, M.M.T.M Dierichs, H.H.A. Schaeffer, J. Wezelman,
J. v.d. Kuur, Th. de Graauw, T.M. Klapwijk, "Comparison of Measured and
Predicted Performance of a SIS Waveguide Mixer at 345 GHz",.these proceedings
6 C.E. Honingh, unpublished results
7 M.M.T.M. Dierichs, unpublished results


A low noise 410-495 heterodyne two tuner mixer, using submicron Nb/Al2O3/Nb tunneljunctions

A low noise 410-495 heterodyne two tuner mixer, using submicron Nb/Al2O3/Nb tunneljunctions

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