Work on the development of an improved 183 GHz subharmonic mixer was concentrated in two areas. First, there was an improved performance from current mixer body designs by testing different diodes and varying the whisker lengths. Second, there is the design of a new body structure. The whisker and diode pinsare in the same piece of the mixer that holds the substrate, reducing any motion of the parts that form the ohmic contacts of the diodes circuit. The broadband, low loss, quasi-optical diplexer, which is designed for use with a single ended mixer, has been developed. It uses a Gaussian beam waveguide as its transmission medium. The difference between the diplexer and other diplexers is the use of a Fabry Perot parallel plate filter. One is a multichannel radiometer system. Another approach is a quasi-optical RF polarization diplexer and another receiver. Some of the receivers developed were flown in aircraft and degraded considerably because of an LO failure. A technique for adding a 118 GHz channel to the existing Atmospheric Moisture Microwave Scanner radiometer system, using the RF diplexing scheme, is presented

Forsythe, R. E.

English

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https://ntrs.nasa.gov/search.jsp?R=19840026584 2020-03-20T21:34:29+00:00Z
IGENII-ANNUAL STATUS REPORT
(bA;,A — CL— 'a7 39 o4 )	 ULStAULH 16 81LL1llLTEb	 084 -34E57
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RLSEARCH IN MILLIMETER WAVE TECHNIQUES
NASA GRANT NO. 14SG-5012
GT/EES PROJECT NO. A-1642
R. E. Forsythe
Project Di rector /Pr inc;pal Investigatcr
L. R. Dod
Project Monitor for NASA/GSFC
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Report Period 15 July 1983 — 15 July 1984
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August 1984
GEORGIA►
 INSTITUTE OF TECHNOLOGY
A Unit of the University System of Georgia
Engineering Experiment Station
Atlanta, Georgia 30332
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Semiannual Status Report	 o.
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RESEARCH IN MILLIMETER WAVE TECHNIQUES
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NASA Grant No. NSG-5012
GT/EES Project No. A-1642
Report Period
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July 1983 - July 198'4
Project Director/Principal Investigator
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L. R. Dod
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TABLE OF CONTENTS
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1.0 Introduction 2
3.0 183 GHz Subharmonic Mixer Development 2
3.0 Quasi Optical RF-LO Diplexer 2
4.0 IF Interface Investigation of AMMS 4
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5.0 AMMS RF and IF Measurements 11`
6.0 Addition of a 118 GHz Radiometer to the AMMS 11
7.0 Plans for the Next Period 13 u	 ^
References 16
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LIST OF FIGURES
Figure Pace
1. AMMS IF Configurations Using a Broadband IF Amplifier 5
2. Offset LO Technique for Mixing RF Energy Close to 9
183 GHz (Avoids RFI)
3. Addition of 118 GHz Radiometer to the AMMS Using 12
Quasi Optical Polarization Diplexer
4. Broadband Mixer Approach for Adding a 118 GHz 14
Radiometer to the AMMS
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LIST OF TABLES
Pace
I	 183 GHz RF/LO Diplexer Measured Performance
	 3
II	 Current AMMS IF Noise Figure Contributions
	 6
III Currently Available IF Amplifiers and Noise Figures
	 7
IV Sensitivity Comparisons of Different Receiver
	 10
Configurations
V	 Comparison of 94 and 118 GHz Noise Figures
	 15
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FOREWORD
This is the eighteenth and nineteenth semiannual status
reports on NASA Grant NSG-5012. Due to reduced funding levels
during this period, it has been necessary to combine these two
reports. The grant period is from June 15, 1974 to June 30, 1985
and includes twelve extensions and increases to the scope an;l
funding of the program. The total funding to date is $831,825 t
NASA funds and $35,961 in Georgia Tech cost-sharing funds, for a
total of $867,786. Current grant funding is at a level of
$25,116.
Responsibility for technical effort on this grant lies in
the Electromagnet ics Laboratory, under the general supervision of
R. G. Shackelford, Director. Mr. R. E. Forsythe has been the
Principal Investigator of this program, which has the internal
project number A-1642, since January 1979. Earlier principal
investigators were Mr. J. W. Dees and Dr.. R. W. McMillan: The
program technical effort is divided between the Millimeter Wave
Technology Division, responsible for source and mixer
development, radiometric measurements, quasi-optical techniques,
and analysis, and the Physical Sciences Division, responsible for
mm-wave mixer diode development.
Contributors to the technical efforts and/or this report
during the past six month period include: J. M. Cotton, D. 0.
Gallentine, R. W. McMillan, G. N. Hill, R. G. Shackelford, S. M.
Halpern, D. Swank, R. A. Bohlander, J. J. Gallagher, A. Howard
and Student Assistants: S. Shapiro and M. Leon. The assistance of
G. Lamb at NASA/GSFC is also greatly appreciated.
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1.0 Introduction
During the past twelve month period, the efforts on this
program have been primarily devoted to:;
1) Continued development of a reliable lower noise
subharmonic mixer;
2) Continued development of a 183 GHz broadband, low noise
quasi-optical RF-LO diplexer;
3) Investigations into IF interfaces of the three 183 GHz
channels of the AMMS radiometer; and,
4) Support and evaluation of the AMMS RF and IF
performance before and after data flights.
2.0 183 GHz Subharmonic Mixer Development
Work on the development of improved 183 GHz subharmonic
	
mixers has been concentrated mainly in two areas. The first area 	
a
is in improved performance of the currently available mixer body
designs by assembling and testing various diodes from different
	
sources and varying the whisker lengths. This work consists of
	
a
assembling and reassembling the mixers and recording data until
the best results are obtained. This is an ongoing task as
upgrades in diode quality continue to take place.
The second area has been the completion of the design of a
new improved body structure. This body has been designed so that
the whisker and diode pins are in the same piece of the mixer
that holds the substrate. This design helps reduce any relative
motion of the parts that form the ohmic contacts of the diodes
circuit. The body has not yet been built and tested due to lack
of current funds. This design has been used with great success on
a separate program at 90 and 140 GHz.
3.0 Quad Optical RP-LO Diplexer
The broadband, low-loss, quasi optical RF-LO diplexer for
use with a 183 GHz receiver has been developed and tested. A
summary of its measured performance is given in Table I. This
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TABLE I
183 GHz RF/LO Diplexer
Measured Performance
0.4	 0.4
0.05	 0.1
0.4	 0.4
0.5	 Varies
See Below
TOTAL	 1.35 dB
RF Loss Summary
Total
Frequency (GHz)
	
Loss (dB)
^RF-LO)
	
Including Fabry Perot
	
0.5	 3.9
	
1.0	 1.65
	
4.0	 0.94
	
7.0	 0.904
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diplexer, which has been described in more detail in previous
reports on this program, is designed for use with a very simple
single ended mixer and uses a gaussian beam waveguide as its
transmission medium. (l) The table shows the results of the
individual devices and expected overall performance parameters. A
proper beam waveguide system (horns and lenses), a low noise
single ended mixer and a Gunn multiplier LO are needed to
cor,.plete the development of a complete receiver system. The low
amount of LO loss allows the use of a solid state local
oscillator at 183 GHz. The main difference between this quasi
optical LO-RF diplexer and other quasi optical diplexers is the
use of the Fabry Perot parallel plate filter which reduces the
number of nearby resonances and increases the instantaneous
bandwidth of the receiver.
4.0 IF Interface Investigation of AMMS
The current AMMS IF frequencies and IF noise figure summary
are given in Table II. The major problems that are present in
this current configuration are the triplexer losses caused by the
vendor missing the cutoff frequencies, cable losses due to cable
length, and IF noise figures. A summary of some currently
available IF amplifiers and their noise figures is given in Table
III. Also included in this table is an improvement factor which
indicates the improvement in overall minimum detectable
temperature considering only the noise figure and bandwidth when
compared to the current AMMS IF amplifiers. Simply divide the
current AMMS sensitivity by the improvement factor to obtain the
relative sensitivity (minimum detectable temperature) with these
newer amps. The narrower band amplifiers have the advantage of
reducing constraints on the IF multiplexer as well. This table is
useful for comparing the state of art low noise IF amps for
radiometric purposes.
One other option is to consider a diplexer and a broadband
preamp followed by another diplexer as shown in Figure 1. A
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Source
IF Amp.
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TABLE I 
Current AMMS IF Noise
Figure Contribtitions
Frequency (GHz)
Low Mid High
1.5-3.0 9.0-6.0 7.5-10.0
2.5 dB 3.2 dB 5.2 dB
0.8 dB 1.0 dB 1.9 dB
2.6 dB 2.0 dB 0.5 dB
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TABLE III
Curreri};1y Available IF
Amplifiei: g and Noise Figures
Low Band (from 0.5 to 3.0 GHz)
Mid Band (from 2 to 6 GHz)
High Band (from 6 to 10 GHz)
DAad	 Frequency. _(GHz)
Low Band* 0.7-1.2
0.5-1.0
1.0-1.5
1.0-2.0
0.5-2.0
1.7 -2.4
0.8-2.4
1.5-3.0
1.5-2.0
Mid Band 2.0-4.0
3.0-3.5
3.7-4.2
3.4-4.2
2.0-6.0
4.0-6.0
High Band 7.25-7.75
8.5
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9.0-10.0
Broadband** 4.0- 8.0
0.1- 6.0
2.0- 8.0
4.0-x.2.0
1.0- 4,0
Improvement
Noigp. E i gure .(db)	 Fsctor
1.0 0.81
1.0 0.81
1.0 0.81
1.1 1.13
2.0 1.12
0.9 0.99
2.0 0.91
1.5 1.26
0.8 0.85
2.0 1.32
1.2 0.79
1.06 0.82
1.3 0.98
3.5 1.32
2.0 1.32
1.6 1,02'
2.5 1.23
1.8 1.38
2.5 TBD
4.0 TBD
4.0 TBD
4.5 TBD
3.0 TBD
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**For use with a diplexer as described later; these allow use of
broader IFs without multiplexing problems.
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summary of suggested IF frequencies for these configurations is
also given.
The desired IF frequencies for the 183 GHz portion of the
AMSU radiometer are 0.75-1.25, 2.5-3.5 and 64 - 8.0 GHz. The AMSU
is a multichannel radiometer system that will be flown in a
satellite at a later date. The lowest channel is difficult, but
not impossible, to realize in an aircraft environment because of
transmitters-such as IFF and TACAN at about 1.O9 GHz. Careful
shielding and filtering are required to eliminate interference.
Another approach is to use a quasi-optical RF polarization
diplexer and another receiver as shown in Figure 2. In the
receiver used for mixing down the channel close to 183 GHz, the
LO is offset so that higher IFs can be usd to mix down the
desired frequencies. A high pass filter is also required to
suppress the reception of the lower sideband in this receiver.
The polarization splitter acts as a diplexer by allowing one
linear polarization to pass while reflecting the other. This
results in a very low loss RF multiplexer since only one
polar izat ^_ n is received by each receiver :anyway. Less than 0.05
dB 1,1es ^n both R? paths (reflected and transmitted) has been
measured using this quasi optical device. It consists of a set of
fine metallic lines photolithographically etched on a very thin
mylar sheet.
Any recommended approach of the choice of IF
multiplexing/amplification depends on the tradeoff between
overall sensitivity, costp and desired similarities to the
eventual AMSU IF and RF frequencies. Enough information has been
gathered in this report to allow suitable recommendations to be
made. Any changes in the AMMS IF system should also be
accompanied with a relocation of the IF preamps to the RF
baseplate to reduce IF cable losses. A sum mF-y of expected
minimum detectable temperatures for some of the candidate
receiver configurations described earlier are given in Table IV.
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Sensitivity Comparisons of Different
Receiver Configurations*
Minimum Detectable Temperature(K)
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Receiver Type Low Mid, High
Figure 1(a) 2.0-8.0 GHz Mp 0.73 0.61 0.61
Figure 1(a) 4.0-8.0 GHz Amp 0.73 0.53 0.53
Figure 1(b) 0.1-6.0 GHz Amp 1.11 0.53 0.64
Figure 1(b) 1.0-4.0 GHz Amp 0.84 0.69 0.53
Figure 2 1.23 0.73 0.58
Triplexer w/0.5-1.0, 3.4-4.2, 0.79 0.67 0.56
and 6-8 GHz IF Channels
Current AMMS with TripllexeV 1.19 1.1 1.37
and Cable Loss
*Assumes TA = 290K, FRF = 7 dB, 0.50 dB IF Diplexer loss,
0.75 dB High Pass Filter Loss(see Fig. 2). 0.4 dB,
Lens loss(see Fig. 2), 0.75 dB Triplexer loss, and
Integration Time of 60 msec.
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From this table it can be seen that the best radiometer
system can be realized using the system described earlier in
Figure 1(a). 0.5-1.0 GHz, 4-6 GHz and 6-8 GHz T_Fs are used to
obtain the best sensitivities. A diplexer separates the 0.5-1.0
and 4 -8 GHz IF energy and this is followed by a broadband 4 -8 GHz
amplifier. This is also one of the easiest to realize in the
current system.
The estimated relative performance of the system described
from Figure 2 (shown earlier) is not as good and much more
difficult to realize but has the advantage of being more closely
related to the expected AMSU channels without the IF interference
problems.
5.0 AMMS RF and IF Measurements
During this period some of the receivers developed on this
program flew in the AMMS as part of a set of data flights in both
the Convair 990 and ERII aircraft. The measured sensitivities of
the 183 GHz channels were 2 F
 3, and 4K for the low, mid, and high
bands respectively at a 0.06 second integration time. The LO
frequency was measured to be one half of 183.3 or 91.65 GHz prior
to these flights. After the flights the system had degraded
considerably due to an LO failure. The frequency of the LO had
shifted to 89 GHz and the output power had dropped. The LO is
being evaluated to determine the problem.
6.0 Addition of a 118 GHz Radiometer to the AMMS
A te:-hnique for adding a 118 GHz channel to the existing
AMMS radiometer system is shown in Figure 3. It uses the same
polarization RF diplexing scheme as described earlier. The
diplexer is broadband and operates anywhere from 30-300 GHz with
low loss. Up to four RF front ends can be combined into the same
lens using a super chopper and this diplexing approach. This
diplexing approach is also ideal for diplexing two RF front ends
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in place of the super chopper if do coupled total power
rad:.ometers are desired.(2)
	
Another technique would be to use WR-7 waveguide components
	 +;
and a single WR-7 wideband mixer. The cutoff frequency for WR-7
waveguide is about 91 GHz. Figure 4 shows a block diagram and
frequency diagram for this receiver. The WR-7 waveguide is an
	
effective high pass filter that allows single sideband reception
	 `;
of the 118 GHz energy. The appropriate RF channels are separated
later in the IF to get data about this absorption line. This
figure shows the frequency choices of the different LO,, RF and IF
frequencies that would be used in this receiver. The ad,,rantages
of this receiver over the one previously described is primarily
size and simplicity while noise figure would be much higher dua
to the broadband mixer and the hi<;h IF frequencies. A third
technique would be to use a waveguide RF diplexer and narrowband
receivers. A summary of the estimated noise figures for these
approaches is given in Table V.
7.0 Plans for the Next Period
	The plans for the next period are to continue the 183 GHz
	
`{{
	subharmonic :mixer development, the 183 GHz quasi-optical receiver 	 I
development, and begin work on a 183 GHz solid state local
oscillator.
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TABLE V
Comparison of 94 and 118 GHz
Noise Figures
Technique	 Frequency
94S 	 118
Quasi Optical	 6.0 dB	 8.0 dB
Diplexer Approach Noise Figure
Broadband Mixer Approach	 10.0 dB	 14.0 dB
Noise Figure
Waveguide Diplexer Approach	 7.1^ dB	 9.5 dB
15
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References
1. "Research in Millimeter Wave Techniques", Semi-Annual
Report, NASA/GSFC Contract NSG-5012, July 1983.
2. "A 140/220 GHz Radiometer for Airborne Imaging," IEEE
International Symposium on IR and MM-Waves, Miami, December
1983.
 
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Research in millimeter wave techniques

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