A proposed device for combining or switching electromagnetic beams would have three ports, would not contain any moving parts, and would be switchable among three operating states: Two of the ports would be for input; the remaining port would be for output. In one operating state, the signals at both input ports would be coupled through to the output port. In each of the other two operating states, the signal at only one input port would be coupled to the output port. The input port would be selected through choice of the operating state

Perez, Raul

NASA Technical Reports Server

NASA Tech Briefs, November 2008 11
Electronics/Computers
Interferometric synthetic aperture
radar (InSAR) has been shown to pro-
vide very sensitive measurements of sur-
face deformation and displacement on
the order of 1 cm. Future systematic
measurements of surface deformation
will require this capability over very
large areas (300 km) from space. To
achieve these required accuracies, these
spaceborne sensors must exhibit low
temporal decorrelation and be tempo-
rally stable systems. An L-band (24-cm-
wavelength) InSAR instrument using an
electronically steerable radar antenna is
suited to meet these needs. In order to
achieve the 1-cm displacement accuracy,
the phased array antenna requires
phase-stable transmit/receive (T/R)
modules. The T/R module operates at
L-band (1.24 GHz) and has less than 1-
deg absolute phase stability and less
than 0.1-dB absolute amplitude stability
over temperature. The T/R module is
also high power (30 W) and power effi-
cient (60-percent overall efficiency).
The design is currently implemented
using discrete components and surface
mount technology. 
The basic T/R module architecture is
augmented with a calibration loop to
compensate for temperature variations,
component variations, and path loss
variations as a function of beam settings.
The calibration circuit consists of an am-
plitude and phase detector, and other
control circuitry, to compare the meas-
ured gain and phase to a reference sig-
nal and uses this signal to control a pre-
cision analog phase shifter and analog
attenuator. An architecture was devel-
oped to allow for the module to be bidi-
rectional, to operate in both transmit
and receive mode. The architecture also
includes a power detector used to main-
tain a transmitter power output constant
within 0.1 dB.
The use of a simple, stable, low-cost,
and high-accuracy gain and phase de-
tector made by Analog Devices
(AD8302), combined with a very-high-
efficiency T/R module, is novel. While
a self-calibrating T/R module capability
has been sought for years, a practical
and cost-effective solution has never
been demonstrated. By adding the cali-
bration loop to an existing high-effi-
ciency T/R module, there is a demon-
strated order-of-magnitude
improvement in the amplitude and
phase stability.
This work was done by Constantine An-
dricos and Wendy Edelstein of Caltech and
Vladimir Krimskiy of Santa Barbara Ap-
plied Research for NASA’s Jet Propulsion
Laboratory. Further information is contained
in a TSP (see page 1).NPO-45147
L-Band Transmit/Receive Module for Phase-Stable Array Antennas
A self-calibrating interferometric synthetic aperture radar instrument uses an electronically
steerable radar antenna to achieve greater accuracy. 
NASA’s Jet Propulsion Laboratory, Pasadena, California 
The photo shows the T/R Module on the front side and the 30-W Power Amp on the reverse side.
Microwave  Power Combiner/Switch Utilizing a Faraday Rotator
Either or both of two input ports could be coupled to one output port.
NASA’s Jet Propulsion Laboratory, Pasadena, California
A proposed device for combining or
switching electromagnetic beams would
have three ports, would not contain any
moving parts, and would be switchable
among three operating states:
• Two of the ports would be for input;
the remaining port would be for out-
put.
• In one operating state, the signals at
both input ports would be coupled
through to the output port.
• In each of the other two operating
states, the signal at only one input port
would be coupled to the output port.
The input port would be selected
through choice of the operating state.
In one potential application, the device
would be used to switch or combine mi-
crowave signals in a quasi-optical transmis-
sion-line assembly that would be part of a
millimeter-wave radar or telecommunica-
tion system. In another potential applica-
tion, a modified version of the device
would be used to switch or combine light
signals in a fiber-optic telecommunication
link.
The two input ports would be config-
ured to accommodate signals having
mutually orthogonal linear polariza-
tions. A polarizer would be positioned to
bisect the right angle formed by the lon-
gitudinal axes of the input ports, and its
polarization would be oriented to so that
it would allow one input signal to pass
through and would reflect the other
input signal. The orientations of the
aforementioned components would be
such that after impinging on the polar-
izer, both input signals would propagate
https://ntrs.nasa.gov/search.jsp?R=20080047192 2019-08-30T05:41:16+00:00Z
12 NASA Tech Briefs, November 2008
toward a three-state Faraday rotator. The
components of the Faraday rotator
would be a ferrite disk, a solenoidal elec-
tromagnet coil for applying magnetic
bias, and two impedance-matching
plates — one on each side of the ferrite
disk. The output port would be posi-
tioned on the side opposite the input
side of the Faraday rotator and would be
oriented to support polarization at an
angle of 45° relative to both of the input
polarizations.
The operating state would be selected
by adjusting the magnetic bias to select
one of three states of the Faraday rota-
tor. In one state, the magnetic bias
would be set to cause the polarization of
a propagating signal to rotate through
an angle of +45° so as to allow one of the
input signals to propagate to the output
port. In another state, the direction of
the magnetic bias would be set at the re-
verse of that of the first-mentioned state
to obtain a polarization rotation of 45°,
thereby allowing the other input signal
to propagate to the output port.
The third state would be used for com-
bining the powers of two mutually coher-
ent input signals that, in an ideal case,
would be of equal magnitude and would
differ in phase by 90°. In this state, the
magnetic bias (and thus, the Faraday rota-
tion) would be set to zero and the super-
position of the input signals would result
in a 45°-polarized sum signal that would
propagate to the output port. In practice,
because of magnetic hysteresis, this state
could not be obtained by simply abruptly
turning off the current in the electromag-
net: It would be necessary to apply a
damped sinusoidal excitation to the elec-
tromagnet coil to effect degaussing.
This work was done by Raul Perez of Cal-
tech for NASA’s Jet Propulsion Laboratory. 
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: iaoffice@jpl.nasa.gov
Refer to NPO-44316, volume and number
of this NASA Tech Briefs issue, and the
page number.
Compact Low-Loss Planar Magic-T
These wireless communications components are useful for base-station receivers, consumer
electronics, and industrial microwave instrumentation.
Goddard Space Flight Center, Greenbelt, Maryland
This design allows broadband power
combining with high isolation between
the H port and E port, and achieves a
lower insertion loss than any other
broadband planar magic-T. Passive mi-
cro wave/millimeter-wave signal power is
combined both in-phase and out-of-
phase at the ports, with the phase error
being less than ±1°, which is limited by
port impedance.
The in-phase signal combiner consists
of two quarter-wavelength-long transmis-
sion lines combined at the microstrip line
junction. The out-of-phase signal com-
biner consists of two half-wavelength-long
transmission lines combined in series.
Structural symmetry creates a virtual
ground plane at the combining junction,
and the combined signal is converted
from microstrip line to slotline. Optimum
realizable characteristic impedances are
used so that the magic-T provides broad-
band response with low return loss.
The magic-T is used in microwave-
and millimeter-wave frequencies, with
the operating bandwidth being approxi-
mately 100 percent. The minimum isola-
tion obtainable is 32 dB from port E to
port H. The magic-T VSWR is less than
1.1 in the operating band. Operating
temperature is mainly dependent on the
variation in the dielectric constant of the
substrate. Using crystallized substrate,
the invention can operate in an ex-
tremely broad range of temperatures
(from 0 to 400 K). It has a very high reli-
ability because it has no moving parts
and requires no maintenance, though it
is desirable that the magic-T operate in a
low-humidity environment. Fabrication
of this design is very simple, using only
two metallized layers. No bond wires, via
holes, or air bridges are required. Addi-
tionally, this magic-T can operate as an
individual component without auxiliary
components.
This work was done by Kongpop U-yen, Ed-
ward J. Wollack, Terence Doiron, and Samuel
H. Moseley of Goddard Space Flight Center.
Further information is contained in a TSP (see
page 1). GSC-15353-1
Single-event upsets (SEUs) pose great
threats to avionic systems’ state machine
control logic, which are frequently used
to control sequence of events and to qual-
ify protocols. The risks of SEUs manifest
in two ways: (a) the state machine’s state
information is changed, causing the state
machine to unexpectedly transition to
another state; (b) due to the asynchro-
nous nature of SEU, the state machine’s
state registers become metastable, conse-
quently causing any combinational logic
associated with the metastable registers to
malfunction temporarily. Effect (a) can
be mitigated with methods such as triple-
modular redundancy (TMR). However,
effect (b) cannot be eliminated and can
degrade the effectiveness of any mitiga-
tion method of effect (a).
Although there is no way to com-
pletely eliminate the risk of SEU-in-
Using Pipelined XNOR Logic to Reduce SEU Risks in State
Machines
Risk is reduced by use of fast state-machine and error-detection logic.
NASA’s Jet Propulsion Laboratory, Pasadena, California


Microwave Power Combiner/Switch Utilizing a Faraday Rotator

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