Transcript
_..
.2’A”
r
. .
T+,
Sensor and Simulation Notes “”
,
326
Note
10 April 199”1
CANONICAL RADIATION
EXAMPLES
OF HIGH-POWER
MICROWAVE
(HPM)
S17STEMS FOR THE CASE OF ONE FEEDING WAVEGUIDE
by D. V. Giri, Ph.D. Pro-Tech,
3708 Mt. Diablo Boulevard,
#l 10, Lafayette,
CA 94549-3610
Abstract ‘-”-”+
In an earlier siderations
note on this subject
for HPM radiation
systems
[1], we had addressed and concluded
antenna system is well suited for broadcasting tive of maximizing out here, based output
the field at a distance,
on certain
from HPM
sources.
assumptions
some canonical
Specifically,
levels,
we consider
HPM beam. example
chosen
of 100 ns and 1 us in each case.
to have values
and nature of the
average power levels of 3 GW by suitable
The radiating
of 20 m2, 40 m2 and 100 m2 from practical
Both single and dual reflector antenna systems in each case.
With the objec-
systems are worked
frequency
and 10 GW at 1 GHz, and 1 GW and 3 GW at 3 GHz, delivered with pulse widths
are considered,
., ;..,”. ..
”..’.,.
.%-----
~L/fl”i”““ )~,ji!i; $7
sources,
aperture
area is
considerations.
with a single feed horn
The subject of an array of feed horns illuminating
treated here and will be the topic of a future note.
con-
that a single or a dual reflector
a directive
of power
some preliminary
the reflector,
is not
PREFACE
This work was performed by Pro-Tech for the Department of Electrical Engineering, University of California at Los Angeles (UCLA), and was sponsored by the U.S. Army.
The author
encouragement
is thankful
to Professor
Y. Rahmat-Samii
and support, and to Dr. Carl Baum of Phillips
of UCLA Laboratory,
for his I&land
AFM, NM for valuable discussions.
Contents Section
1. Introduction
3
2. Rectangular Wave.guides
8
3. Directional Couplers
12
4. Single Horn Feed
16
5. Offset Parabolic Reflector
21
6. Offset Dual Reflector (Cassegrain)
’73
7. Canonical ExampIes
26
8. Summary
33
References
34
-2-
1. Introduction The objective of this note is to consider some canonical radiating systems, in as much detail as feasible, in order to broadcast note [1] discussed investigating
some preliminary
the applicability
A previous
directive HPM radiation.
considerations
for HPM radiating
of several classical radiating systems.
systems,
by
It was concluded
that reflector antennas in general and an offset Cassegrain system in particular are well suited for generating directive HPM beams.
It is observed that the power is extracted
from the source in N number of evacuated rectangular waveguides
(say).
Here N can
be 1 or more depending on the source and power level etc. We have found it ins@uctive to assume N to be 1 to start with, and investigate canonical examples of the HPM radiation systems.
In other words, what level of far fields can one produce given that
all of the HPM power is extracted from a suitable source in a sing-le evacuated rectangular array,
waveguide?
Future notes will consider values of N > 1, requiring
a feed
At this stage the case of N = 1 is of interest and as we see in later sections,
quite instructive. Having chosen the case of a single waveguide carrying the microwave power out of a suitable source (Xauon),
one needs to make certain assumptions
quencies, power levels and pulse widths, before considering tem examples.
These assumptions
ever, whatever
the source may be, a vacuum
the feed and radiation sys-
are discussed in the next section.
interface where the “source” terminates
about the fre-
It is noted how-
flange can be treated as an universal
and the feed elements begin.
To the left of
this vacuum flange is the source and to its right are the elements of the feed system. Figure 1 shows a block schematic of the radiating system from the source to a single
-3-
CD (SF6/ai
r
interface)
polyethylene @
qas
m
u
single
bag
evacuated
evacuated
waveguide
rectangular
\I J.\
run
waveguide
,
//
d
\ \
I
1
\
1 3
\
I
Bidir~tional
HPM
~
:
/
~
Vacuum
Vacuum
I
Coupler
Source
(60-80
SF-6
I
dB)
I
.
f~ a
/ /
atmosphere,
I
“
“~
I
I
\
(Xatron)
+
%
l—
i’
7
\
.-e
‘
-
‘
–
-
‘“”
I
@
vacuum
evacuated
flang
feed
I
horn @ dielectric interface (vacuum/SF6)
Figure
1.
Elements
of
single
waveguide
feed
system.
Notes @
any
suitable
HPM
standard
source
vacuum
evacuated
feed
rounded o
::ti::::d~::t;::;:;;;::e’uide
@
magnetic
@
evacuated
coupler
wavegude
run
horn
metallic
(e.g.,
pyramidal)
with
edges
wi” vacuum
wall
flanges
(60 to
to the
80
to
SF6
dielectric
interface
with
dB)
feed
horn
sui table gas
bag
metal to
slats
transition
from
SF6
to
a~r
‘Utside
—.. that
I
fray .
contain
parts
of
the
reflectors
in
it
feed horn.
With reference to this figure, we, see an HPM source with a single rec-
tangular
waveguide
interface
between the source and the feed system.
coupler
(60-dB)
waveguide
power extraction.
again ending
run to a vacuum
in a vacuum
flange.
flange is the universal
Following
this is a bidirectional
We then have a section of a
flange to which the feed horn is connected.
horn, which could be pyramidal vacuum and 1 atmosphere
The leftmost vacuum
The feed
is also evacuated and a dielectric interface between
SF6 is present at the horn aperture.
A polyethylene
tainer may be used for holding the SF6 gas and the container
con-
is then an interface
between the SF6 gas and the outside air. All of these elements going from the source to the feed horn are schematically
shown in figure 1 and described
detail for a particular set of assumptions
about the prescribed
later in greater
KPM source.
ous interfaces starting from hard vacuum to outside air, via 1 atmosphere so deiigned
The vari-
SF6 gas are
that the peak elecrnc field anywhere in the outside air medium does not
exceed 1 MV/m. The field anywhere in the SF6 medium is designed not to exceed 3 .MV/m. These values have adequate safety margins. It is noted that we have not so far shown the reflector antenna system illuminated by the feed horn of figure 1. Two possibilities
[2] are; (1) an offset parabolic reflector
and (2) dual offset reflector system, as illustrated in figures 2 and 3. In both cases, the aperture of the main reflector is shown to be circular as an example.
Practical con-
sideration in specific situations will influence the size and shape of the main reflector, Furthermore,
the extant of the SF6 gas bag and its relationship
to the reflectors (main
and/or sub reflector) is also governed by the peak field levels in this region, as we see in later sections. -5-
shaped main reflector \
\
sub-reflector SF6
Container
\
\_
Figure
2.
A by
single an
reflector
offset
feed
system horn
fed
Figure
3.
A
dual
reflector
SF6
system
Container
In concluding this introductory
section, we note that Sections 2 and 3 deal respec-
tively with the wave.guides and directional couplers, whereas in section 4 the feed horn and the dielectric
interfaces are discussed.
the dual reflector systems.
Sections 5 and 6 consider the single and
Canonical examples of far fields, power and energy densi-
ties are estimated as a function of distance, in Section 7. The note is concluded with a summarizing
Section 8, followed by a list of references.
-7-
.
.
2. Rectangular
Recall that WR-975 propagation optimizing
‘a
Waveguides
at frequencies
and WR-340
were chosen in [1] for dominant
of 1 GHz and 3 GFIz.
the power handling
The choices were governed by
One would like to choose a waveguide
capabilities.
with the largest cross sectional dimensions
H 1,0 mode
and operate it at a frequency below the cut
off value of the first higher order mode (i.e., Iio,l or H 2,0 modes which both have the same cut off value). For the canonical
examples
in this note, we have chosen average power levels
Pava of 3 GW and 10 GW at 1 GHz. The average power levels chosen are 1 GW and a 3 GW at the higher frequency propagating
of 3 GHz.
The expression
for Pavm in a waveguide n
a H ~,. mode is given by [1]
P avg=—
EZab1_X2 — 2Z0 2
where
[[1: ~
1/2 =
(2.1)
Puvg
.EO- peak electric field in the waveguide Z. - characteristic
impedance of free space
a = inside larger dimension of the waveguide 1.
b = inside smaller dimension of the waveguide k = operating wavelength
The power density pavg in the waveguide and the peak power P given by
-8-
peak
are respectively
Pavg = 2Pavg/(a b) = ~
(2.2)
[5’4
(Q.3)
‘peak = 2 ‘avg and the peak electric field in the wave,guide is
“=-
Epeak = EQ
(2.4)
where 2 -1/2
z~,, = z,
1– L
Figure
4 shows
the rectangulm
1]
(2.5)
~ 2a
L
waveguide
where
the inside
dimensions
are
denoted by a and b. The elecrnc or the E-wall and the magnetic or the H-wall are also identified in this figure. the directional frequencies
coupler.
This has relevance in the next section where we discuss
In table 1, we list the relevant waveguide parameters
of 1 and 3 GHz.
at both
Also included in table 1 are the power densities (pa,g )
and the peak elecrnc fields in the waveguide
at the assumed power levels.
ments about these assumed power levels are in order.
Few com-
Firstly, such power levels and
power densities appear to be practically realizable from the I-IPM sources in a single waveguide
[3] by proper choice of waveguide
capabilities. waveguide
which maximizes
the power handling
Secondly, the associated peak elecrnc fields call for hard vacuum in the and are also well below the field levels needed for field emission from the
inside walls of the waveguides into the vacuum.
Field emission occurs in the presence
of electric fields of the order of GV/m, the precise field values being governed by frequency, pulse duration
●
emission
of electrons
and the surface conditions.
Field emission
from the surface of a condensed
-9-
is defined as the
phase into another
phase,
.
, /
Figure4.
Recmngularw aveguideo
f=l
Parameter
Wavelengh
finsided
imensionsaandb.
f=3GHz
GHz
0.3 m
0.1m
Waveguide
WR 975
WR 340
Dimensions
a = 247.65 mm b = 123.83 mm
a = 86.36 mm b =43.18 mm
~c (H 1,0)
0.4953 m
0.1727 m
j c (H
605.69 MHz
1.737 GHz
1.2114 GHz
3.474 GHz
4?3.8
46~.4
ohms ‘avg
f.
X
1,0)
(Ho,I)
=
f.
(H2,0)
Ohms
‘1,0
P
‘avg
‘peak
1?avg
GW/m2
MV/m
GW
3
196
13.63
1
10
652
24.88
avg
GW
I
peak
GW/m2
MV/m
536
22.36
ii
II
E
6
Table 1. Rectangulm waveguide parameters at the two frequencies and the two power levels (assumed).
-1o-
usually a vacuum under the influence of high electrostatic text, we are concerned
with emission
wave guides into the vacuum.
The surface potential configuration
tion etc. so, in practical waveguides,
In the present con-
of electrons from the metallic surfaces of the
dition itself affects the field emission profoundly,
a GV/m.
fields.
and the surface con-
in addition to frequency pulse dura-
the field emission could start at levels Iower than
Field ionization is not a factor, since this phenomenon
above those required for field emission.
Field emission
occurs at fields well
then is the limiting factor in
theory and the peak field numbers we have in table 1 should pose no problem, if suitable vacuum conditions are attained.
—
-11-
.
3.
Directional
Couplers
I is desirable waveguide, accomplished
to monitor
the power
which is being
from the HPM source to the antenna system.
transferred
through
This monitoring
the
should be
by a simple device which employs some means of coupling a fractional
power out of the waveguide.
In addition, it is also useful to monitor
power from ~he antenna back to the HPM source. types have been designed
Bidirectional
and used at low power levels.
the reflected
couplers of various
However,
not all of the
readily available designs apply in the context of HPM application. We may consider the field distribution
of the dominant H 1,0 mode in a rec!angu-
lm waveguide [4] as illustrated in figure 5. The elecrnc field for the dominant mode is given by Ey = ED sin(nx/a)
(3.1)
which is seen to vanish on the magnetic or H-walls at x = O and x = a. Consequently, the H-walls are electric charge free and hence in the context
of HPM applications,
directional couplers that couple through the H-walls are preferable. A bidirectional
coupler suitable for HPM application is illustrated in figure 6. As
seen in this figure, a series of small holes in the H-wall of the main waveguide couples power to the bent wave,guides.
These waveguides are then connected to non-reflecting
detector systems to independently
monitor both the forward and the reflected powers.
A 60 to 80 dB coupler is required to monitor the forward power.
Typically, one may
have 2, holes in the H-wall that are separated by &/4 which is efficient at a single frequency.’ A series of holes may be employed
-12-
to provide for some bandwid~h for the
●
● E-wal
\ \
b
Figure
5.
Cross section of a rectangular showing the H 1 ~ mode electric Y
— —
-13-
waveguide field.
1
Vacuum
flange
(Un~ versal a
interface
suitable
HPM
to
source)
f-’-”
vacuum
electric
/
“an”
To source
~
To
a L
non-reflecting detector to
measure
magnetic
—
/
system
non-reflecting
reflected
detector
power
to
system
measure
forward
power
Figure
6.
Magnetic
wall
bidirectional
coupler
(60-80dB)
Notes @
several
@
the
holes
electric
in field
the
magnetic
and
electric
wall
will
ch~rge
.—
provide
some
vanishess
on
—
bandwidth the
magnetic
wall
wall
antenna
bidirectional
coupler.
low power level tests.
The performance
features of these couplers may be optimized at
It may also be noted that directional
only the forward power can also be built if needed. would then consist of providing
couplers for monitoring
The modification
to figure 6
for a matched load in the port carrying the reflected
power and, maybe even avoid the bending of the waveguide that carries a fraction of the reflected power.
-15-
.
4.
●
Single Horn Feed The reflector antenna systems under consideration
here are fed by a single horn,
which is connected to a vacuum flange to the waveguide run starting at the end of the directional
The single feed horn is illustrated
coupler.
elecuomagnetic
horn of figure 7 is for ihs~ative
in figure 7.
purposes only.
The pyramidal
What is of interest
here is to discuss the design aspects of such a horn in the HPM context.
At low
power levels, the theory of design and performance of single horns are well known. In the HP,M application,
where the power
wfaveguide and the horn are evacuated.
levels are in the GW range,
the
sity and the peak electric field at the mouth of the horn enable a transition
from
vacuum to 1 atmosphere SF6 gas. Nominally, this means the peak electric field at the horn aperture be below 3 MV/m to avoid excessive electical down.
If the horn aperture has dimensions
(height) corresponding
stresses causing a break-
a’ (2d2/1)
The values of R
at the assumed frequency of 1 GHz, for the three reflectors are 170 m, 340 m and 850 m. The values of R at the assumed frequency of 3 GHz for the three reflectors are 510 m, 1.02 km and 2,54 km. The far field estimates will be valid at R values .geater than the (2d 2/L) values above. Consider for example, the offset parabolic reflector antenna of figure 8. Let us assume that the criterion of minimum height b‘ of the horn aperture from Table 2 is satisfied as noted below:
,,,,,
-26-
f=l
GHz
Pm8=10GW
b’ = 3.5L
f=3GHz
Ping=
1
b’ = 3.5A
f=3GHz
Ping=
3 GW
GW
b’ = 6L
b’ is the height of the horn aperture and above values satisfy the minimum height cnteria required waveguide
to interface
from vacuum
to SF6.
Knowing
the height
b of the
and b’, it is a simple matter to estimate the peak elecrnc field value at the
horn aperture, to ensure that it is below 3 MV/m to permit vacuurn/SF6 transition. IXText,one can estimate approximately in the waveguide
the field at the reflector by scaling the field
by a factor of waveguide” height to reflector height.
Knowing
the
field at the reflector, the far field parameters may then be estimated using
Epeak(far field) = Epeak(reflector)
.E&k(far
pav~ (far field) = [
[1 1 &
‘ie]d)
2z~
V/~
~~,m J
energy density = u = @avgAt ) J/m2
recalling that we have assumed two values of At to be 100 ns and 1 US. Tables 3 to 6 contain estimates of far field parameters.
The frequency of operation and the average
power Pmg is held fixed on each of these tables.
Three values of A and 2 values of
At are considered for each set. One can see the peak far field (kV/m) as a function of distance R away from the reflector.
The average power density and energy density
(for both values of pulse width At) are also tabulated.
-27-
The reflector antenna aperture
TABLE
3.
Estimates
Waveguide:
P
Horn
Aperture:
of
a vg
far
field
quantities
(f
=3GW
height
E
b’
=
2A
E
=
UZ
1 GHz)
300J peak peak
=
13.63
z
.2.81
Mv/in
d
= 5.05
E A
peak
P
E
0.2
0.33
111
1
0.07
23
10
0.007
2.3
7.02
50
0.001
0.45
0.28
103
0,(11)07
Q+~~
KV/m
Kld/m2
100
I ns
1.63
16337 702
o.g7
At 1 us 16.3
ns
A
= 40
d
=
) =
M2
7.14 236
m KV/m
T
P
peak
avg
KV/m
KM/m2
+
100
ns
0.5
0.27
63.72
5384
0.54
5.4
1
0.13
30.68
1248
0.12
1.2
10
0.013
3.07
12.5
1 .2 X1 O-3
1.2 X10-2
0.7
7.OX1O-4
7.0X10-3
50
0.003
0.7?
0.67
6.7x10”5
6.7x10-4
2.8x10-5
2.8x~o-4
100
0.0013
0.31
0.13
1.3X10-5
1.3Y10-4
7.0X113-6
7.(3X10-5
200
0.0007
0.16
3.0X10-6
3.0xlo-5
r1 1Km
100m2
source
7. OX1O-2
R
A=
A K
Km
u(J/n12) At
w
the
I
a vg
Km
= 100
m KV/m R
R
At
from
MV/m
.P(refl
) = 335
at
bnerqy
‘3tL)atAt=lps [
A=20mZ
Ep(refl
microwave
A
R
0.03
— I
I E
peak
P
KV/m
KWlm2 3315
1
0.333
50
10
0.033
5
50
0.007
1
0.0’03
0.5
0.0017
0.25
u(J/
a vg
) At
At l-- 100
ns
0.33
1 ps 3.3
d=ll.28m
---1 Ep(refl
) =
150
KV/m
I
●
ZOO
L
500
✌✌
T 33.15
3.3X1O-3
3.3 X1 O-2
1.33
1.3X1O-4
T .3 X10-3
0.33
3.3X10-5
3.3X10-4
0:-08
&:oxl
8.Qx]~-5
0=6
1 .0X10-5
● ✌ ✎
● TABLE
● 4.
Estimates
Wa~uide:
Horn
P
Aperture:
of
a vg
far
=
10
height
field
quantities
(f
GW
b’
=
E 3.5
A
E
=
1 GHz)
u
= 24.88
peak
MV/m
= microwave =(
IKJ
at. At=
Ep(refl)
A
=
20
=
5.05m
A
pea k
P
E KV/m
‘)
u(J/I
At
At
Km
m
KV/m
KkJ/m2
0.2
0.33
202.6
54,428
5.44
54.4
1
0.07
42.1
2,350
0.23
2.3
10
0.007
4.21
23.50
2.3x10-3
2.3x10-2
50
0.001
0.82
0.89
8:9xlo-5
8.9xlo-4
100
0.0007
0.42
0.23
2.3x10-5
2.3xlo-4
200
0.0003
0.20
0.05
100
ns
1 ps
5X1 O-6
5X10-5
R KM
E A w
A
100
mz
d=ll.28m Ep(refl)
=
274
I
KV/m
‘
0.333
1(I
0..033
50
0.007
peak
18,027
1.80
18.0
1
0.13
56.1
4,173
0.42
4.2
10
0.013
5.62
41.8
4.2x10-3
4.2xlo-2
50
0.003
1.30
2.24
2.2X1O-4
2.2X1O-3
100
0.0013
0.57
0.43
4.3X1O-5
4.3X1(-J-4
200
0.0007
0.29
0.11
1.1 X113-5
1.1X1O-4
500
0.0003
0.11
0.02
u(J/
At
100
ns
1 .12X10-3
2.8x10-5
2.8x10-4
500
0.0007
U_
1.11
1.12X10-4
0.46
At
116.6
4.4X1O-3
0.0017
‘)
0.27
4.4X1O-4
200
At
0.5
1.83 0.92
u(J,
avg
KW/m2
1.1X1O-2
0.003
KV/m l__
KV/m
9.15
100
P
431
RA
91.5
+
=
Km
peak
KV/m
(refl)
I =
= IFS
z E
R
avg
A
source
ns
A=40m2
IL w t
the
d=7.14m
I
E
from
MV/m
m2
= 611
100
~11.?KJ stat = 2.93
pea k
, d
energy
I I
0.11
4.OX1O-5
100
ns
2X11)-6
1 us
2X113-5
.
TABLE
5.
Estimates
Wave~uide:
P
Horn
height
Aperture:
of
avg
=
far
field
quantities
(f = E
1 GW
b’
=
3.5
E
k
3GHz)
pea k peak
=
22.36
=
2.76
U MV/m
~
microwave
.
100J at [ lKJatdt=lps
energy
dt
from
= 100
I
.
E
u(J
A K
h
1
R
‘Y!l__
&
U(JI peak
ns
1
E$refl)=l
‘0 R
source
MV/nl
r“Tzzl I
th~
‘avg
KV/m
KW/m2
10~tns
A
At
Km
m
1 )JS
1
0.4
2
0.2
28
5
0.08
11.2 5.6
0.5
0.40
76
7,659
0.77
7.7
1
0.20
38
1,914
0.19
1.9
5
0.04
7.6
76.6
10
0.02
3.8
50
0.004
100
0.002
: ,
100
7.6x10-3
7.6xlo-2
10
0.04
1.91
1 ,9X10-4
1.9 X10-3
50
0.008
1.12
0.76
0.76
7.6x10-5
7.6x10-4
100
0.004
0.56
0.38
0.19
1.9X10-5
1 .9X1 O-4
200
0.002
I I
1,040
ns
0.42
4.2
0.1
1.04
166.3
1.6x10-2
41.6
4.lX1’-3
4,1X1’-2
0.16
I
1.66
1.fjx10-4
1.15x~0-3
I
0.41
4. IX1O-5
4.lX1’-4
1.OX1O-5
1 .’X1’-4
-.. E A Km
m
peak
‘avg
u(J/m2) At
At
Kv]m
KW/m2
0.4
36
1,718
0.17
1.7
0.2
18
430
0.04
0.4
0.1
9
107
1.0X10-2
0.1
50
0.02
1.8
4.3
4.3X1’-4
4.3X1’-3
ioo”
0.01
0.9
‘0:82
500
0. 00?
o.
0.04
100
ns
1 11s
I
u A=100#
25
d=ll.28m
Ep(refl)
●
=
90
5 KV/m
10
L
-s:2Ga-54%1 0-6
8.-ZX10-4 4X1 0-5
.
o
T
6.
Estimates
of
Waveguide:
P
=
—Horn
far
field
quantities
(f
=
●
3 e
Aperture:
a vg
height
3 GW
b’
A
=
d
=
Ep(refl
) =
E
= 6
1
E
peak peak
=
38.73
=
2.79
MV/m
U
=
microwave 300J
MV/m
i3
KJ
energy
from
at
At
=
100
at
at
=
1 US
the
source
ns
20m2 5.05 331
II]
KV/m I
R Km
CL +
E A m
0.5
0.4
1
peak
KV/m
P
u(J
avg
At
KW/m2
100
EO(refl
?-L_
) =
234
KV/m
I
At ns
E
1 \ls
‘avg
peak
R
A
Km
R~
KV/m
Kwl m2
100
1
0.4
93.6
11,617
1.16
11.6
2
0.2
46.8
2,904
0.29
2.9
5
0.08
18.7
464
0.04
0.4
1.0
Atu(Jfi ns
132.4
23,244
2.32
23.2
0.2
66.2
5,811
0.58
5.8
2
0.1
33.1
1,453
0.14
1.4
5
0.04
13.2
231
0.02
0.2
10
0.02
6.62
58
5.8x10-3
5.8xlo-2
10
0.04
9.36
116
0.01
50
0.004
1.32
2.31
2.3x10-4
2.3 X1 O-3
50
0.008
1.87
4.6
4.6x10-4
4.6xlo-3
100
0.002
0.66
0.58
5.8x10-5
5.8x10-4
100
0.004
0.93
1.14
1.14X10-4
1 .14X10-3
200
0.001
0.33
0.14
1.4X1O-5
1.4X11)-4
500
0.001
0.18
0.04
4.0X10-6
4.OX1O-5
I
A
R KM
A
‘peak
P
Ep(refl)
100m2
d=
11.28m
= 148
KV/m
At
At
RA
KV/m
KW/m2
2.5
0.4
59.2
4647
0.46
4.6
5
0.2
29.6
1161
0.11
1.1
10
0.1
14.8
290
0.03
0.3
50
0.02
2.’36
11.6
1.1:?10-3
1.1X1O-2
100
0.01
1.48
2.9
2.9 Y10-4
2.9X10-3
500
0.002
0.29
0.11
1.1 X1 O-5
1.lXIO-4
— A=
u(J/m2)
avg
100
ns
1 ~ls
,
.
areas (A = 20 m2, 40 m2 and 100 m2) are also used in determining the reflector (5.05 m, 7.14 m and 11.28 m). lated for illustrative
purposes.
reflector need to be determined reflector.
the diameter of
Once again, these parameters
are tabu-
Acmal sizes and shapes of the feed horn and the with due regard to the proper illumination
of the
The pmameters in the tables 3-6, help in setting a framework for the actual
design of the radiating systems.
The tables merely” point out the practical constraints
on sizes and estimate what is achievable in the fm fieId.
-32-
8. Summary In this note, we have considered some canonical examples of HPM radiation systems,
under
the assumption
of a single
evacuated
employed to extract the power from the source. are considered,
rectangular
waveguide
being
Two frequencies (1 GHz and 3 GHz)
as well as two power levels at each frequency.
Two values of pulse
widths (At = 100 ns and 1 US) and three values of the radiating aperture area (A = 20 2 m,
40 m2 and 100 m2) are also considered,
configurations,
fa_rfield parameters
For each of these source/antenna
such as peak elecrnc field, average power densities
and energy densities are estimated.
These estimates are obtained to set a framework
and ranges of parametric values for future designs of specific antenna systems. An important leading
aspect of the radiation
to best illuminate
system, namely the horn feed optimization
the reflector is not considered
yet.
Given the range of
parametric values of such quantities as Pavg, A, f, At etc., specific designs can now be addressed in future reports. Important future work needed may be listed as follows 1)
measurement
on allowable
fields in vacuum
including
surface conditions
and
pulse widths 2)
horn feed pattern optimization
3)
rectangular/elliptical
(shaping) leading to best filling of the reflector(s)
reflectors versus square or circular to obtain both polariza-
tions.
—
-33-
..-)
1
s
●
Reference
[1]
D. V. Giri, “preliminary ating
Considerations
Circuit
Systems,”
and
for High-Power Microwave (FIPM) Radi-
Elec~omagnetic
System
Design
Note
40,
28
December 1990. D. W. Duan
and Y. Rahmat-Samii,
Applications--Part
for High-Power
1,” UCLA Report No. ENG-90-21,
DAAL02-89-K-0129, [3]
“Antennas
Microwave
US Army Research Grant
September 10, 1990.
V, L. Grantslein and I. Alexeff, Editors, High-Power
Microwave Sources, Artech
House, Norwood, MA, 1987, Chapter 10, pp. 351-395. [4]
N. Marcuvitz, editor, Waveguide Handbook, Dover 1965.
[5]
C. E. Baurn, “Some
Features of Waveguide/Hom
Design,”
Sensor and Simula-
tion Note 314, 18 November 1988. [6]
C. E. Baum, ‘‘Focussed Aperture Antennas, ” Sensor and Simulation
Note 306,
19 May 1987. [7]
J. I-Iuang, Y. Rahmat-Samii
-,
and K. Woo, “A GTD Study of Pyramidal Horns for
Offset Reflector Antenna Applications,”
IEEE Trans. on Antennas
and Propaga-
tion, Vol. AP-31, No. 2, March 1983, pp. 305-309. [8]
Y,
Rahmat-Samii,
Cassegrain
‘‘Subreflector
Antennas--GTD/PO
Extension
Analysis,”
for
Improved
Efficiencies
in
IEEE Trans. on Anrennas and Propa-
gation, Vol. AP-34, No. 10, C)ctober 1986, pp. 1266-1269.
I
● I
-34-
“
