A proposal for a Ka-Band (32 GHz) Link Experiment (KABLE) with the Mars Observer mission was submitted to NASA. The experiment will rely on the fourth harmonic of the spacecraft X-band transmitter to generate a 33.6 GHz signal. The experiment will rely also on the Deep Space Network (DSN) receiving station equipped to simultaneously receive X- and Ka-band signals. The experiment will accurately measure the spacecraft-to-Earth telecommunication link performance at Ka-band and X-band (8.4 GHz)

Hansen, D. M.

Hartop, R. W.

Mileant, A.

Riley, A. L.

English

NASA Technical Reports Server

N87-17962
TDA Progress Report 42-88 October - December 1986
A Ka-Band (32 GHz) Beacon Link Experiment (KABLE)
With Mars Observer
A. L. Riley
Spacecraft Telecommunications Equipment Section
D. M. Hansen and A. Mileant
Telecommunications Systems Section
R. W. Hartop
Radio Frequency and Microwave Subsystems Section
A proposal for a Ka-Band (32 GHz) Link Experiment (KABLE) with theMars Observer
mission has been submitted to NASA. The experiment will rely on the fourth harmonic
of the spacecraft X-band transmitter to generate a 33.6 GHz signal. The experiment will
rely also on a DSN receiving station equipped to simultaneously receive X- and Ka-band
signals. The experiment will accurately measure the spacecraft-to-Earth telecommunica-
tion link performance at Ka-band and at X-band (8.4 GHz).
I. Introduction
This article describes a proposal to implement the Mars
Observer spacecraft (MO) with a, Ka-band beacon to enable a
Ka-Band Link Experiment (KABLE). The experiment will
measure and document the Ka-band (32 GHz) deep space
communications link advantage with respect to the X-band
(8.4 GHz) link. Implementation of a Ka-band beacon in the
Mars Observer spacecraft and a simultaneous X- and Ka-band
receiving capability in a DSN R&D receiving station is required.
Added benefits of the Ka-band beacon include the ability to
calibrate plasma effects not possible with a single frequency
radio link and the enhancement of gravitational wave experi-
ments, relativistic bending experiments and spacecraft naviga-
tion. Radio science experiments are coordinated with the Mars
Observer radio science team and are not a part of the proposal.
Propagation measurements and analyses show that a signifi-
cant advantage can be achieved by using Ka-band instead of
X-band for deep space communications and navigation. The
performance advantage in the communications link can be as
large as a factor of 10 and needs to be quantified with the
precision required for future mission planning. Previous
measurements of the effects that degrade deep space com-
munications link performance suffered due to significant
errors in the absolute accuracy of the separate evaluations. A
simultaneous relative measurement of Ka-band and X-band
141
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link performance will yield the necessary high accuracy
results.
II. Experiment Objectives
The primary engineering objective of this experiment is to
accurately measure and document the Ka-band spacecraft-to-
Earth telecommunications link (downlink) performance with
respect to the X-band downlink performance.
Parameters of interest include:
(a)
(2)
Effects of ground antenna pointing and efficiency as
a function of elevation angle, wind, irregular atmo-
spheric refraction and thermal gradients experienced
at sunrise, sunset and during a variety of weather
conditions.
Effects of water vapor and water droplets (clouds and
rain) along the propagation path at various ground
antenna elevations.
(3) Effects of solar corona and solar wind.
Documentation of these telecommunications link param-
,_ters will provide accurate inputs for future deep space mis-
sion planning. This will enable future flight projects to maxi-
mize the benefits of using improved telecommunications link
capabilities at Ka-band.
It is expected that this experiment will confirm the predic-
tion that during 90% of the time the Ka-band telemetry link
performance will exceed the X-band telemetry link perfor-
mance by a factor of 6 to 10. The 90% time period is based on
current knowledge of the effects of weather including wind,
clouds, and rain. Recent data obtained during the Voyager
Uranus encounter have added to evidence that shows the DSN
X-band weather model to be overly pessimistic. This experi-
ment will significantly increase knowledge about the effects of
weather and enable the improvement of the DSN weather
models both for X-band and Ka-band.
The frequency and timing stability of the entire link
(Earth based transmitter to spacecraft and back to the Earth
based receiver) will be measured ana is expected to be near
1 part in 10 is. Use of a Ka-band link offers a factor of 16
reduction in the sensitivity to plasma effects over X-band.
Use of simultaneous X- and Ka-band offers the additional
capability to calibrate the plasma and thereby reduce its
effect even more. This can result in a factor of at least 10
improvement in stability and calibration accuracy over exist-
ing systems and may lead the way to new discoveries through
an improved radio science capability.
III. Experiment Description
The proposed experiment requires the use of the fourth
harmonic of the spacecraft X-band down]ink signal thereby
providing a Ka-band down]ink to a DSN R&D Earth station.
In order to minimize cost and spacecraft impact, several design
approaches will be investigated. Selection of the specific
approach to be implemented will be made by the Mars Ob-
server Project office. Design approaches include:
(l)
(2)
(3)
Traveling-Wave Tube Amplifier (TWTA) Generation
of the fourth harmonic. This approach utilizes the
fourth harmonic of the X-band downlink signal as
generated by the TWTA; it is believed to be the least
expensive and least intrusive to the spacecraft. Analysis
is extremely difficult because the Ka-band signal must
propagate through the X-band waveguide and com-
ponents which are overmoded at Ka-band. Usefulness
of this approach will be investigated for comparison
with the other, better understood approaches in
consideration of its possible use.
Dual-Frequency Feed with Varactor Diode Quadrupler.
This approach uses a dual-frequency feed at the pri-
mary focal point of the antenna with a varactor diode
assembly to produce the fourth harmonic of the
X-band downlink signal. The details of the multiplier
scheme are covered in the third approach. The multi-
plier package is attached to the focal point feed assem-
bly, adds no additional X-band waveguide or compo-
nents, uses the same amount of the X-band downlink
power, and may add less mass and cost less than the
third approach. A better understanding of the space-
craft antenna feed system is needed in order to evalu-
ate this approach accurately.
Separate Cassegrain Ka-Band Feed with Varactor
Diode Quadrupler. This approach is best understood
and is being used here for scheduling and budgeting
purposes; a detailed description follows.
The Ka-band beacon will consist of a passive frequency
multiplier driven by an X-band signal coupled from the power
amplifier output. The multiplier will produce a signal at the
fourth harmonic (approximately 33.6 GHz) of the X-band
downlink. This Ka-band signal will then be fed to the MO
high-gain antenna for transmission to Earth. The Ka-band
signal will be coherent with the X-band downlink signal and,
when the X-band signal is phase modulated, will provide a
modulated signal with four times the modulation index of the
X-band signal. This will impact the resultant Ka-band carrier
suppression and the effect on the experimental link perfor-
mance. The Ka-band carrier signal-power-to-noise-spectral-
density ratio (Pc/No) versus time for 20 mW transmitter power
142
is shown in Fig. 1 for a DSN 34 meter high-efficiency antenna
during clear, dry weather. The time scale in these figures
begins at Mars orbit insertion (August 1991). Typical link
parameters are given in Table 1.
IV. Flight Hardware
The RCA Mars Observer spacecraft is shown in Fig. 2 with
the high-gain antenna located on an extended boom. The
antenna is mounted to the boom through a two-axis gimbal
containing X-band waveguide rotary joints. The reflector is
1.0 meter in diameter, and the spacecraft transmitter produces
40 W of X-band power at the TWTA output. Figures 3 and 4
show a concept of the Ka-band experiment hardware mounted
to the high-gain antenna. A block diagram is shown in Fig. 5.
The multiplier drive is obtained from a crossguide coupler
which couples approximately 200 mW of X-band signal to the
multiplier assembly, reducing the transmitted X-band signal
by 1%. X-band to Ka-band conversion efficiency of 25% or
more is theoretically possible but to keep the design simple
and cost low a minimum conversion efficiency of 10% will
be considered to produce a minimum output power of 20 mW
at Ka-band. The quadrupler will consist of a cascade of two
frequency doublers. Each doubler will consist of a varactor
diode with an input low-pass matching network and output
band-pass matching network. The varactors will be self-biased
such that bias current is generated by rectification of the RF
signal by the varactor. Thus, no bias supply voltage is required
from the spacecraft.
The Ka-band signal is fed from the multiplier through the
back of the high-gain antenna reflector to a Ka-band feed. The
signal from the feed is reflected from a dichroic Cassegrain
subreflector to illuminate the main reflector. The X-band
signal is transmitted through the subreflector. The mass of the
additional hardware is estimated to be about 1 kilogram.
Thus, the RCA proposed antenna design is modified to
provide the following interfaces with the Ka-band experiment:
(1) An X-band 20 dB crossguide coupler to provide mul-
tiplier input signal.
(2) A mounting bracket on the back of the reflector for
the frequency multiplier.
(3) A port through the back of reflector for Ka-band
feed.
(4) A mounting bracket for the dichroic subreflector.
A number of issues require further investigation. These
include an understanding of the mass handling margin of the
high-gain antenna gimbal and boom system, and the impact of
the high-gain antenna thermal environment upon the frequency
multiplier operation.
The equipment will be designed to enable verification of
proper multiplier operation through the use of a bias voltage
test point located on the multiplier assembly. Measurement of
this bias voltage will be done manually; this measurement is
not required after launch.
V. Ground Support Equipment
A new 34-meter antenna for Research and Development at
the Venus Site, Goldstone, California, is planned for comple-
tion in 1990. The DSN Advanced Systems Program supports
a number of ongoing development efforts (RTOPs) that will
equip this antenna to simultaneously receive 8.4 GHz (X-band)
and 33.6 GHz (Ka-band) signals. This ground station will
provide high-aperture efficiency and ultra-low-noise receiving
systems with frequency stability of approximately one part in
1015. The station will include a multifrequency beam wave-
guide feed system, X- and Ka-band ultra-low-noise amplifiers
(cryogenically cooled masers and high-electron mobility
transistors), hydrogen maser frequency standards, fiber optic
distribution systems, an ultra-stable 100 kW X-band (7.145-
7.190 GHz) transmitter, receivers, a spectrum analyzer with
-180 dBm sensitivity and one hertz resolution, and other
advanced signal, and data processing and recording equipment.
This experiment complements and enhances efforts within
the DSN Advanced Systems Program to develop and demon-
strate Ka-band station technology. The Ka-band link experi-
ment will be closely coordinated with the DSN Advanced
Systems Program so that no additional resources will be
needed to develop, install, use, and maintain the ground sup-
port equipment.
VI. Mission Operations
The objectives of this experiment can be accomplished
without causing any change to the Mars Observer Project mis-
sion plan. Tracking functions at the R&D Venus station will be
coordinated with the Mars Observer mission manager. Sched-
uling of the Venus station will be accomplished and supported
by the DSN Advanced Systems Program as has been and
continues to be the approach used for other research activi-
ties in the DSN.
VII. Analysis and Report
The analysis of data acquired at the R&D Venus site in sup-
port of this experiment will quantify the following parameters:
143
(1) The Ka-band downlink performance with respect to
the X-band downlink performance.
(2) Ground antenna pointing and efficiency as a function
of elevation, wind, irregular atmospheric refraction and
thermal gradients.
(3) Effects of water vapor and water droplets along the
propagation path at various ground antenna elevations.
(4) Effects of solar corona and solar wind.
(5) Total system "turn-around" frequency stability.
VIII. Conclusions
The proposed experiment can provide an initial comparison
of Ka- and X-band link performance using an actual deep space
communication channel at a relatively modest cost. It is one
of the important steps in the continuing evolution of Ka-band
capability for deep space communications.
144
Table 1. Typical Mars Observer Ka-band link parameters
Spacecraft
Output power 20.0 mW
Frequency 33.6 GHz
Antenna diameter 0.5 meter (effective illuminated area)
Antenna efficiency 60.0%
Antenna gain 42.7 dB
Pointing loss 2.71 dB (0.5 degree pointing error)
Carrier Suppression 3 dB at Ka-band
Ground Station
Antenna diameter 34 meters
Antenna gain 79.7 dB
Antenna elevation 30 degrees
Pointing error 0.001 degree
System temperature 29.1 K
Weather Clear and dry, no wind
Link Reliability
To achieve 90% or 95% reliability, additional margins are required to
account for weather and link tolerances. This experiment will record
adequate data over a several year time period to define the margins
needed for 90% or 95% link reliability.
Carrier Signal-Power-to-Noise-Spectral-Density-Ratio (Pc/No)
The objectives of this experiment can be met when the received Pc No
ratio exceeds 10 riB. Figure 1 showsPc/N o ratios ranging from 60
(18 riB) to 1000 (30 riB); these higher ratios enable increased measure-
ment precision.
145
m 
b 
U 
z 
n 
. 
35 I I I 
OPPOSITION 
30 
20 5ii"\_i 
15 c SUPERIOR CONJUNCTION 
I -POSSIBLE EXTENDED MISSION 
0 12 24 36 48 
TIME, months 
Fig. 1. Ka-band carrier signal-power-to-noise-spectral-density 
ratio versus versus time expected for 20 mW Mars Observer beacon 
(see Table 1) 
/ WAVEGUIDE TO Ka-BAND 
FREQUENCY 
QUADRUPLER 
FEED% 
n 
Lx-BAND POWER 
COUPLER 
Fig. 3. Mars Obsewer Ka-Band Link Experiment (KABLE) 
hardware, back view 
Fig. 4. Mars Observer Ka-Band Link Experiment (KABLE) 
hardware concept, front view 
Fig. 2. Mars Observer spacecraft 
146 
20 dB CROSS
GUIDE COUPLER
COAX LINE
D
DICHROIC
SUBREFLECTOR
X-BAND
FEED (EXISTING) Ka-BAND
FEED
MAIN REFLECTOR
(EXISTING)
FREQUENCY
_. MULTIPLIER
ASSEMBLY
r- _7----
E
E
20 mW "
, _1 .... _1
Fig. 5. Mars Observer Ka-Band Link Experiment (KABLE) block diagram
147


A Ka-band (32 GHz) beacon link experiment (KABLE) with Mars Observer

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