The key design issues of the Millimeter Wave/Infrared (MMW/IR) monolithic rectenna have been resolved. The work at Georgia Tech in the last year has focused on increasing the power received by the physically small MMW rectennas in order to increase the rectification efficiency. The solution to this problem is to place a focusing element on the back side of the substrate. The size of the focusing element can be adjusted to help maintain the optimum input power density not only for different power densities called for in various mission scenarios, but also for the nonuniform power density profile of a narrow EM-beam

Gouker, Mark A.

English

NASA Technical Reports Server

N90" 10147 -:_2-_
MILLIMETER-WAVE / INFRARED
RECTENNA DEVELOPMENT AT
GEORGIA TECH
/
Mark A. Gouker
Georgia Tech Research Instituteyj /
Atlanta, Georgia _
SPONSORED BY
NASA under GrantandN_ NAG 3-202
\.
Georgia Tech Research Institute
PREC_OING PAGE BLANK NOT FILMED
127
https://ntrs.nasa.gov/search.jsp?R=19900000831 2020-03-20T00:25:57+00:00Z
ABSTRACT i .....
The key design issues of the M_ monolithic rectenna have
been resolved. The work at Georgia Tech, in the last year, has
focused and has been concentrated on increasing the power re-
ceived by the physically small MMW rectennas in order to increase
the rectification efficiency. The solution to this problem is to
place a focusing element on the back side of the substrate. The
size of the focusing element can be adjusted to help maintain the
optimum input power density not only for different power densi-
ties called for in various mission scenarios, but also for the
nonuniform power density profile of a narrow EM-beam.
@ Underlying Technologies for the MMW Rectenna are in
place.
A key element in the rectenna design is an integrated
focusing element.
Aids in optimizing the rectification efficiency
Can compensate power density variations of different
mission scenarios.
Can compensate for the power density profile of a
narrow EM beam.
128
Why go to higher frequencies?
Reduce the size of the transmit and receive
apertures of point to point beamed power systems.
Take advantage of readily available sources at
higher frequencies.
D/He-3 fusion reactors emit synchrotron radiation that
peaks at about 1000 GHz [1].
Black body radiation from the Earth that peaks wave
lengths in the 10 - 15 _m ranges [2].
1 29
EARLY EXPERIMENTAL WORK
In the early work at Georgia Tech metal-oxide-metal diodes
(MOM) were investigated as a rectifying element for the MMW/IR
rectennas. While MOM diodes have been reported to show diode
behavior up to optical frequencies, they do not appear to be
suitable candidates for the rectenna elements.
Summary of Experimental Work
Metal-Oxide- Metal Diodes
Originally proposed for the infrared rectennas; however,
do not appear to be viable for rectifying element.
• Thin oxide layers are very susceptible to shorts.
I-V characteristics are not suitable for efficient
rectifications.
NI-NIO-NI
40-
30-
2O
10
I I I i I
I/AMPERES
i VOLTS
.1 .2 .3 .4 .5
Ni-NiO-Bi l.I.AMPERES
15
,o5
!
, , , , VOLTS
•5 1.0
130
ANTENNA MEASUREMENTS AT 230 GHz
More recent experimental work includes measurements of
substrate mounted dipole antennas at 230 GHz. The antennas at this
frequency are 400 microns long and i0 microns wide. These antennas
are physically much smaller than the dielectric slab on which they
are mounted. In essence the antenna acts as a miniature field
probe that detects how the EM-wave passes through the dielectric
slab; therefore, the problem can be viewed as optics-like, and a
focusing element can be used to increase the field strength in the
vicinity of the antenna.
MMW Substrate Mounted Antenna Measurements
Measured dipole antenna patterns at 230 GHz.
The measured field pattern shapes are in agreement
with a simple super position model of the antenna
reception.
In essence, the antenna receives the local field at the
surface of the substrate.
E-PLANE H-PLANE
_ A;R SIDE __
Q
OO O O a a a a
\ SUSSTRATESIDS
131
MMW-IR RECTENNA DESIGN
The MMW/IR rectenna will have the same subcomponents as the
2.45 GHz rectenna (antenna, low-pass filters, and rectifying
element); however, the large number of rectennas needed at these
higher frequencies will make it necessary to use monolithic IC
fabrication technics. The appropriate frequency range to begin the
MMW/IR development is 100 GHz to 300 GHz, but the design should be
able to easily scale to higher frequencies when suitable rectifiers
become available.
MMW / Infrared Rectenna Design
An antenna feeding a rectifying element is still the
most efficient conversion scheme.
• Conversion from EM wave to dc power will require a
large number of conversion elements.
• The design should be monolithic using high throughput
IC processing techniques.
Appropriate frequency range to begin development
is 100 - 300 GHz.
• Significant decrease in the size of the transmit and
receive apertures.
• GaAs diode characteristics are known at these
frequencies.
Note: There are some problems with GaAs diodes, but
they are the best viable option at this time.
The rectenna design should scale throughout the
MMW and infrared regions.
Low-pass filters and impedance matching sections are
proportional to wavelength.
I _ _'I ]} ANTENNA
1stLOWPASS FILTER
and IMPEDANCE MATCHING
J
41---- RECTIFIER
132
INTEGRATED CIRCUIT ANTENNAS
Among the antennas that should be considered for the MMW/IR
rectenna are the microstrip and substrate mounted type antennas.
The microstrip type antenna has metalization on both sides of the
substrate while the substrate mounted type antennas have
metalization only on one side of the substrate.
A. MICROSTRIP PATCH
METAL
ANTENNA
SUBSTRATE
GROUND
PLANE
B. SUBSTRATE MOUNTED COPLANAR STRIPS DIPOLE
....._i_i_I!_i!i!i!i_iii!iiii!i!!iii!!ii_i_i_iii_iiii!ii;i!iii!_i;_i!_ii!!i_ii_i;iii_!iiiii;!i!i!!iiiiiiiii!!iiii;iiiiiii_iiii!!i;iii!i!_!iiiii}iii_ii!!iii_i!!i_i!iiiiiiii_i!iiii_iiiii;:_iii....
..,dli!ili@iiiii iiiiiiiiiiiiiiiiijiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii!iiiiiiiiiiiiiiii_iiiiiiif!_iiiiiiifiiii!iiiiiiiii_ii_i_{_ii!_iiJ_i!i_?....
_!iiiii;iiiiiiiilliiiiii !i :;::::: SUBSTRATI=
C. SUBSTRATE MOUNTED SLOT DIPOLE
GROUND
"PLANE
SUBSTRATE
133
RADIATION EFFICIENCY
Microstrip antennas become inefficient in the millimeter wave
region. At 300 GHz with a 2 mil GaAs substrate (thinnest practical
substrate height for mechanical stability), the radiation
efficiency is only 40%. These surface wave losses can be reduced
in the substrate mounted antennas by placing a focusing element on
the back side of the substrate.
Microstrip antennas become inefficient in the MMW
region [3].
£ra12.8
---.-- 14&L F-WAVE DIPOLE
MiCROSTmP PATCH
_ FULL'W&VE DIPQLE
. - .,-- 1SURFACE"'I-- 2 SURFACE-.--1.,- 3 SU_r-_CE---.-: -------
k w*VE : WAVfS ; W, VE,
! I
ea I I
i ;
U ° M. I I 1_
_ tl I I.I
%'../_, I II/ i
"_ I /!/:_
1%. I 1" _
" i _,_. ; _/.,/ _,_
, "_._o_o,_,_ ,,
0 : III i I i i
0 .01 .I .!i .l .Ill
1 34
A substrate mounted (coplanar type) antenna can be
designed to maintain high radiation efficiency.
No ground plane on the back side of the substrate
A focusing element can be placed on the back side of
the substrate:
discourage the propagation of the surface
waves
adjust the power received by each antenna
Integrated Focusing Element - A Method to
Optimize the Efficiency
Incoming
EM Wave
Rectenna
//_ Element
Integrated
Focusing
Element
The integrated focusing element will reduce the loss
to surface waves
The surface wave modes will be discouraged by the
irregular boundary condition of the focusing element
The focusing of the incoming wave will make it more
difficult for surface waves to be launched
The integrated focusing element can be used to
adjust the power received by the antenna.
Resonant antennas at MMW or IR frequencies have
small physical size and thus small effective height.
The focusing element can control the voltage levels
developed at the terminals of the antenna.
The voltage levels across the rectifier can be selected
for the most efficient conversion.
Rectenna performance can be optimized independent of
the EM wave power density.
Integrated focusing element serves as an adjustable
interface between different power densities called for in
various mission scenarios and the optimized power input
to the rectenna element.
1 35
Various size focusing elements can be used to
handle the changing power density of a beamed
EM wave.
It
The focusing elements in the center of the rectenna
array are smaller.
Integrated focusing elements take advantage of
higher frequency instead of fighting it.
Efficiency
The EM capture efficiency should be very high with
the integrated focusing elements
Transmission Line Loss [4]:
1
ot_,_,,,o, _ .f'(o, geometry)
I
C%h.,.,,,.= f(e, lOSStangent)_
Filtersize scaleswithwave-length,transmissionline losses
shouldremainreasonable - well intothe
submillimeter/far-infraredregions.
Rectification efficiency should remain high in the
MMW region with GaAs diodes. Above these
frequencies advances in semiconductor devices or
new rectification technologies are needed.
Time Scale for Implementation of MMW
Rectennas
A program to develop a monolithic, 100 GHz
rectenna array could be accomplished within 3 years.
1= year Develop hybrid rectenna elements with
integrated focusing elements,
2= year Develop hybrid rectenna arrays.
3 '_year Develop monolithic rectenna arrays.
136
SUMMARY
MMW/IR rectenna elements will be made from monolithic
construction of antenna and rectifier. An integrated focusing
element increases the efficiency of the beamed power conversion,
maintains voltage levels for optimum rectenna performance and
adjusts for EM beam power density profile and for different
mission scenarios•
Efficiency should remain high throughout the MMW region, and
if higher frequency rectifiers are developed, well into the far-
infrared region.
A monolithic, i00 GHz rectenna array could be realized
within three years•
ACKNOWLEDGMENTS
Georgia Tech started working on MMW/IR rectennas with a
grant from NASA Lewis Research Center. For the past several
years this work has been supported by internal grants from the
Georgia Tech Research Institute.
REFERENCES
• J. F. Santarius, "Strategy for D/He-3 Fusion Development,"
Proceedings of the Lunar He-3 Fusion Power Workshop,
Sponsored by NASA Lewis Research Center, Cleveland, Ohio,
April 25-26, 1988.
2. M. A. Gouker, D. P. Campbell and J. J. Gallagher, "Technology
for Satellite Power Conversion," Final Technical Report, NASA
Grant No. NAG3-282, June 1987.
• D. M. Pozar, "Considerations for Millimeter Wave Printed
Antennas, "IEEE Trans, vol. AP-31, pp. 740-747, 1983.
• K. C. Gupta, R. Garg and I. J. Bahl, Microstrip Lines and
Slot Lines, Chapter 7, Artech house, Inc., Norwood, MA, 1979•
137


Millimeter-wave/infrared rectenna development at Georgia Tech

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