NASA Technical Reports Server (NTRS) 20110014705: X-Band, 17-Watt Solid-State Power Amplifier

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by  NASA Technical Reports Server (NTRS)

ink that contains the ingredients de- power density of 43 percent. At an ap- In accordance with Public Law 96-517,
scribed for step 2, plus 0.035 g of plied current density of 100 mA/cm2, the contractor has elected to retain title to this
poly(tetrafluoroethylene) particles. the cell voltage for the SOA cell and im- invention. Inquiries concerning rights for its
5. The membrane coated with catalyst proved cell are 0.43 and 0.49, respec- commercial use should be addressed to:
layer is bonded to the gas-diffusion/ tively. The increase in cell voltage be- Innovative Technology Assets Management
current-collecting carbon paper by tween the SOA and improved cell JPL
use of heat and pressure. resulted in an increase in cell efficiency Mail Stop 202-233
The performance of membrane elec- of 8 percent when the effects of crossover 4800 Oak Grove Drive
trode assemblies prepared by the new are included. Pasadena, CA 91109-8099
process is compared with those prepared This work was done by Thomas Valdez and [phone]
by the state-of-art (SOA) process in Fig- Sekharipuram Narayanan of Caltech for E-mail: [email protected]
ure 2. The current density at 0.49 V has NASA’s Jet Propulsion Laboratory. Fur- Refer to NPO-30829, volume and number
been raised from 70 mA/cm2 to 100 ther information is contained in a TSP (see of this NASA Tech Briefs issue, and the
mA/cm2. This results in an increase in page 1). page number.
X-Band, 17-Watt Solid-State Power Amplifier
This is a smaller, lighter, less expensive alternative to prior X-band amplifiers.
NASA’s Jet Propulsion Laboratory, Pasadena, California
An advanced solid-state power ampli- wave-tube X-band amplifiers and to gain of the VGA is voltage-variable over a
fier that can generate an output power prior solid-state X-band power ampli- range of 10 to 24 dB. To provide for tem-
of as much as 17 W at a design operating fiers of equivalent output power. This perature compensation of the overall
frequency of 8.4 GHz has been designed amplifier comprises a monolithic mi- amplifier gain, the gain-control voltage
and constructed as a smaller, lighter, crowave integrated circuit (MMIC) am- is generated by an operational-amplifier
less expensive alternative to traveling- plifier module and a power-converter circuit that includes a resistor/thermis-
module integrated into a compact pack- tor temperature-sensing network. The
age (see Figure 1). driver amplifier provides a gain of 14 dB
The amplifier module contains an to an output power of 27 dBm to drive
input variable-gain amplifier (VGA), an the four parallel output PHEMTs, each
intermediate driver stage, a final power of which is nominally capable of putting
stage, and input and output power mon- out as much as 5 W. The driver output is
itors (see Figure 2). The VGA and the sent to the input terminals of the four
driver amplifier are 0.5-µm GaAs-based parallel PHEMTs through microstrip
metal semiconductor field-effect transis- power dividers; the outputs of these
tors (MESFETs). The final power stage PHEMTs are combined by microstrip
Figure 1. The Complete Amplifier Package has
dimensions of 6.75 by 5.25 by 1.75 in. (about contains four parallel high-efficiency, power combiners (which are similar to
17.1 by 13.3 by 4.4 cm). GaAs-based pseudomorphic high-elec- the microstrip power dividers) to obtain
tron-mobility transistors (PHEMTs). The the final output power of 17 W.
Final Power Stage
PD PC
8.4 GHz at 17 Watts
VGA Driver
Radio-Frequency Input:
1 dBm at 8.4 GHz PD PC
Temperature
Input-Power Compensator
Monitor PD PC Output-Power
Monitor
Secondary Voltages
PD: Microstrip Power Divider
PC: Microstrip Power Combiner Temperature
Monitor
28 VDC Input
Power Converter
Figure 2. This Block Diagramshows only major functional blocks of the amplifier and power-converter modules.
12 NASA Tech Briefs, January 2005
The power-converter module contains sation is provided by an error amplifier and stacked in a manner that provides
a high-efficiency (nominally 90-percent and associated resistors and capacitors the best thermally conductive path for
efficient) DC-to-DC power converter plus within the pulse-width modulator. To dissipating heat generated in the final
analog signal-conditioning circuitry for maximize efficiency, the output voltages power stage. The amplifier can operate
use in remote monitoring (e.g., teleme- are obtained via synchronous rectifiers over a temperature range from –40 to
try) of temperature, and of radio-fre- connected to the secondary winding of +70 °C, from sea-level to Mars’ atmos-
quency input and output power levels. the transformer. The ripple in the outputs phere and even to a vacuum.
The power converter contains a trans- of the rectifiers is attenuated by use of in- This work was done by Anthony Mittskus
former in a push-pull, pulse-width-modu- ductance-capacitance filters. and Ernest Stone of Caltech and William
lated buck regulator circuit. Feedback for The output power of 17 W is obtained Boger, David Burgess, Richard Honda, and
regulation of power-converter output volt- with a nominal input radio-frequency Carl Nuckolls of General Dynamics Decision
ages is provided by a transformer winding power of 1 dBm (≈1.3 mW) and an input Systems for NASA’s Jet Propulsion Labora-
that is in addition to the primary and sec- DC power of 59 W. The amplifier and tory. Further information is contained in a
ondary winding. Feedback-loop compen- power-converter modules are configured TSP (see page 1). NPO-30663
Improved Anode for a Direct Methanol Fuel Cell
Electrical resistance is decreased and utilization of catalyst is increased.
NASA’s Jet Propulsion Laboratory, Pasadena, California
A modified chemical composition has Some background information is help- ally deposited onto a polymer-electrolyte
been devised to improve the perfor- ful for understanding the benefit afforded (proton-conducting) membrane and onto
mance of the anode of a direct by the addition of hydrous ruthenium an anode gas-diffusion/current-collector
methanol fuel cell. The main feature of oxide. The anode of a direct methanol fuel sheet that is subsequently bonded to the
the modified composition is the incor- cell sustains the electro-oxidation of proton-conducting membrane by hot
poration of hydrous ruthenium oxide methanol to carbon dioxide in the reac- pressing.
into the anode structure. This modifica- tion CH3OH + H2O →CO2+ 6H++ 6e–. Heretofore, the areal density of
tion can reduce the internal electrical An electrocatalyst is needed to enable this noble-metal catalyst typically needed
resistance of the cell and increase the reaction to occur. The catalyst that offers for high performance has been about
degree of utilization of the anode cata- the highest activity is an alloy of approxi- 8 mg/cm2. However, not all of the cata-
lyst. As a result, a higher anode current mately equal numbers of atoms of the lyst has been utilized in the catalyzed
density can be sustained with a smaller noble metals platinum and ruthenium. electro-oxidation reaction. Increasing
amount of anode catalyst. These im- The anode is made of a composite mater- the degree of utilization of the catalyst
provements can translate into a smaller ial that includes high-surface-area Pt/Ru- would make it possible to improve the
fuel-cell system and higher efficiency of alloy particles and a proton-conducting performance of the cell for a given cata-
conversion. ionomeric material. This composite is usu- lyst loading and/or reduce the catalyst
loading (thereby reducing the cost of
0.6 the cell).
The use of carbon and possibly other
s
Versu 0.5 4 mg/cm2 Pt:Ru + Hydrous RuO2 elalyeecrt rhoansi cb eceonn dpuroctpoorsse di nf otrh ien ccreaataslinysgt
ed) 4 mg/cm2 Pt:Ru the utilization of the catalyst by increas-
Correcte, Volts0.4 8 mg/cm2 Pt:Ru ilnysgt pelaerctitcrliecas.l Hcoonwneevcetri,v tihtye breetlwateievenl yc alotaw-
esistance n Electrod0.3 dlmaeyenetrhsisat ytnh ooaflt ctioam rtbphoeend c era etthsauleyl ttmisc ia nssis tt ehtrsia.c nkAs lcpsaoot,ra ttl hyoseft
Re electrical conductivity of carbon is less
al (Internal mal Hydrog0.2 tmbhroaannre e1, m/t3ah0te0e rthipa loo ilfsy tmaycpeiidrc-iaecll eamcntedrt oamllyso.t seFt ummrtehetemarls--
entiNor are not chemically stable in contact with
ot it. Finally, a material that conducts elec-
P
e 0.1 trons (but not protons) does not con-
d
no tribute to the needed transport of pro-
A
tons produced in the electro-oxidation
0 reaction.
10 100 1000 10,000
Hence, what is needed is an additive
Current Density, mA/cm2
that is stable in contact with the polymer-
electrolyte membrane and that conducts
These Plots of Anode Overpotential Versus Current Densitywere obtained in tests of direct methanol
fuel cells operated at a temperature of 90 °C and a methanol concentration of 1 M. both electrons and protons. Hydrous
NASA Tech Briefs, January 2005 13