Патент USA US2502156

Patented Mar. 28, 1950
. UNITED
.
2,502,155
STATES
PATENT OFFICE
2,502,155
'
LOW-‘ANGLE n-AmAT'ioN ANTENNA
Charles L‘. jefi‘ers, San Antonio, Tex.
Application March 2, 1948, Serial No. 12,592
G'Clainls.‘ (Cl. 250—33‘);
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.
,
v2
1
This invention. relates to a radio antenna sys
with each individual station; and a de?nite ver
tem especially useful as a broadcasting antenna‘,
although it is: not limited to thisuse.
tical radiation characteristic is required to
achieve the ideal in each case. p
An object of the invention is to devise an‘ an
tenna system which radiates very little energy
done towards improving the vertical radiation
over a rather wide high-angle range and- at the
same time provides a substantial gain in signal
strength over the usual sing-1e vertical antenna.
Still‘ another object. of the invention» is to de
vise an antenna system in which the angle of
minimum radiated energy can be varied electri~
cally from. 40 to 60° with. respect to' the hori~
zontal, thus permitting adjustment of the fad
characteristics of broadcast antennas, and today
a tower of uniform‘ cross-section and approxi
mately 0.53 wavelength high is generally used
to‘ secure the maximum nonfading range‘. This
antenna is still far from ideal since the distor
tion. zone usually‘ limits the primary service area
at night.- This undesirable limitation is caused
by the radiation of considerable power at the
ing wall for maximum primary service.
The above objects and others are attained by
forming the antenna system of- two vertically
aligned. sections which are excited by in-phase
currents of- predetermined relative magnitudes,
and the dimensions of the two antenna sections
are chosen. to reduce the high-angle radiation
and increase the low-angle radiation.
My invention will be described in. connection
with the accompanying drawing‘in which
higher vertical angles.
Figure I‘ is a diagrammatic representation of
In recent years, considerable work has been
7
My improved antenna system radiates practi
cally all energy at angles below 50 degrees of the
horizontal and extremely little energy above this
elevation. Further, this angle ‘can be varied from
40 to 60 degrees by a simple electrical adjust
ment with, but a small increase in‘ higher angle
radiation. ’ These‘ ‘limits are equivalent to dis
tances of 80 to 160 miles for the ?rst re?ection
skywave signal, ?xing the location of the center
of the fading zone at approximately 100 to 200
miles from‘ the transmitter.
My antenna system broadly‘ consists of two ver
ferent components of the antenna system;
tical elements, one directly above the other as
Figure 4 is a diagrammatic showing of one
shown in Fig. 1. It‘ is apparent that this is a
speci?c form of antenna system according to my
invention:
‘
30 combination- of an antenna I at ground‘ eleva
tion and an antennaZ‘ elevated above the earth.
Figure 5 is‘ a diagrammatic showing of a sec
The vertical radiation characteristics of each of
ond form of the antenna system; and
these antenna types are‘ well known. It is the
Figure 8: shows three radiation curves for di'fé
unique combination of these two antennas into
fe'rent current ratios in the‘ two sections of the
a single radiator that reduces the high angle
antenna.
the‘ antenna system;
Figures 2 and 3 are radiation curves- for the dif
> The primary service area of a broadcast sta
radiation.
tion is important from a service and a commer
cial point of‘ view. The ideal antenna for a high
In Fig‘. I, the section" I at ground elevation has
a length- A; and the‘ elevated section 2 has a
powered broadcast station, providing both a
groundwave and a" skywave service, should‘ have‘
av vertical radiation characteristic such that they
skywave signal does not interfere with the desir
able groundwave service. The nightt'me primary
service area would‘ then be practically as large
as the daytime area, since the fading or distor
tion wall would not be) the limiting factor. It is.
length B‘- with the center of this. section at a
height H above ground. The dimensions A, B
and may‘ be expressed in degrees of the wave
length‘x in free space'as follows:
further desirable that the skywave signal strength
rise rapidly- in order to limit the intense fading
area to a narrow band?‘ around the‘ station.
The power, frequency, and the ground conduc- '
tivity around the individual station, determine
the signal strength at‘ a given location, while the
general noise level ?xes the minimum signal‘ in;
tensity required to‘ provide a satisfactory service.
Thus,v the limit of satisfactory service“ is" unique 55
',
A=360> (ct/X) degrees.
‘5:360’ (b/x) degrees
H=360 (iii/M degrees
where a, 5 and h are the corresponding distances
expressed in the same unit. of length as A.
The antenna sections are excited or driven so
that the loop currents in elements I and 2 are‘
inlvphase. If the magnitude of the loop current
inv I is considered as unity, the currentra'tio can‘
be expressed-as.
‘
2,502,155
3
4
the vertical radiation characteristic for the lower
section I is
KAJ‘(0) =[cos (A sin 6) —cos Al/cos 0
(2)
where 0 is the angle above the horizontal. For
the upper section 2, which for simplicity in cal
culations is considered a half-Wave element, the
vertical characteristic is
KBf<6> =2m cos (so sin 0) cos (H sin 0) /cos a (3)
and for both sections, adding’ (2) and (3), we
have
Kof(9) =[cos (a sin 0) —cos Al/cos 0+
2m cos (90 sin 0) cos (H sin 0) /cos 0 (4)
The form factor, Kc, referred to the current loop
is
1-cos A+2ml
and the vertical radiation characteristic for the
antenna is
(9) =
,
cos (A sin 6) — cos A+2m cos (90 sin 6) cos (Hsin 0)
(l—~cos A+2m) cos 0
(5) ‘
Since the vertical characteristic of a half wave
element in space (cos (90 sin 0)/cos 0), is prac
tically equal to cos 6, Equation 4.- and likewise
5 will hold as an approximation if the upper ele
ment is made less than one half wave long.
The form factor, K0, is a constant for a par
ticular combination of element length, A, and
current ratio, m, and cos 0 affects both elements
similarly; therefore it is convenient to omit the
eifect of the denominator of Equation 5 in de- 1'
veloping the optimum design of an antenna to
give a particular radiation characteristic. This
is done by evaluating separately the ?rst part
of the numerator of (5) for
40
(6)
K0 cos 0f(0)A=cos (A sin 0)-—cos A
and the second part of the numerator for
From Figure 6 it will be seen that the angle of
zero radiation may be shifted from 40 to 60 de
grees simply by changing the current ratio in
the two antenna sections, and this involves only
an electrical adjustment.
It is of interest to note from Figure 6 that for
the design of zero radiation at 50 degrees, the
maximum high-angle radiation occurs at 56 de
grees where it is less than 0.02 of that in the hori
zontal plane.
The theoretical ?eld gain of my antenna, for
an m ratio of 0.69, is 14.5% compared to a 0.53
wavelength antenna, or 41.5% referred to a quar
ter wavelength antenna. These ?eld gains are
equivalent to power gains of 32 and 100 per cent
respectively.
The advantage of my antenna system may be
shown by comparing its performance with that
of a 0.53 wavelength antenna. Both antennas
are assumed to radiate a ?eld of 1770 millivolts
per meter at one mile on a frequency of 1000 kilo
cycles over earth with a conductivity of 10-13
E. M. U. The skywave signal values are for 50%
of the time. For the 0.53 antenna, the center of
the fading zone is at 127 miles where the ground
wave signal has an intensity of 0.6 mv./m. My
antenna has the same distortion point at 164
miles and at a signal intensity of 0.29 mv./m.
The width of the tWo-to-one signal ratio skywave
and groundwave fading zone has been reduced
from 36 miles to 24. miles because of the differ
ence in the angle of the skywave signal rise. In
other words, the distortion zone of bad fading
has been moved from a point of good rural pri
mary service to a point where the groundwave
signal strength is hardly adequate for year round
noise-free reception. If a current ratio, m, of
0.9 is used, the point of maximum fading would
be moved to a distance of 185 miles for a signal
level of 0.2 mv./m.
Two physical embodiments of my improved
antenna system are diagrammatically illustrated
in Figures 4 and 5.
K0 cos 0,f(0)B/m=2 cos (90 sin 0) cos (H sin 0) (7)
In Figure 4 the lower antenna section I is
Fig. 2 is a plot of Equation 6, K0 cos 0 times the A ' formed of a vertical metallic tube I2 in which is
positioned a coaxial cable l3 containing a center
vertical radiation characteristics of the lower sec
conductor 14 and being grounded at its lower end.
tion I for various lengths A, while Fig. 3 is a
The upper end of tube [2 is connected to cable
similar plot of Equation '7 for the upper section
l3 at II, and the tube [2 is also connected to the
2 for certain center heights II.
cable H3 at the point l8 located one-quarter
In Fig. 2 curves 6, l and 8 show the character
wavelength above the lower end of tube l2 which
istics for three different lengths of lower sec
is insulated from the cable it by insulator 9.
tion I, that is, for A values of 140°, 120° and 100°,
respectively. On Fig. 3 curves 3, 4 and 5 show the
The upper antenna section is formed of two
aligned tubular sections l0 and H positioned
characteristics for three different heights of the
above the lower section I. Tubular section H]
section 2, that is, for H values of 190°, 210° and '
230°, respectively.
is supported on section II by an insulator 9a,
and the lower end of this section is connected
An examination of Fig. 3 shows, for the values
to the center conductor of the coaxial cable 13
of H considered, that the field from the elevated
element goes through a phase reversal around 25
at l5. The upper end of middle tubular section
degrees, and above this point will be 180 degrees
II is connected to the outer conductor of cable
out of phase with the high angle ?eld from the
l3 as shown at 56, and the lower end of this
lower element. If the parameters A and H are
section is supported on the cable l3 by the in
sulator 9b.
correctly selected and if the loop current in the
elevated element is made less than the current
The two sections of the antenna are excited
in the lower element by the proper amount, the
with energy from a transmission line 22 through
?elds of the two elements can be made nearly
a suitable phasing and power dividing network
equal and will cancel for angles deviating con
2|, the lower section I being excited through
siderably from the vertical.
connection 19 to the lower end of tube l2, and
Figure 6 shows the radiation characteristic of
the upper section being excited by connection
the combined radiation from both vertical sec- A 20 to the lower end of the center conductor M
tions of the antenna system, for three diiferent
of the coaxial cable 1 3,
current ratios. For curve 40, the current ratio
In the arrangement shown in Figure 5 the lower
m is 0.9, for curve 50 the ratio is 0.69, and for
section l of the antenna is formed of a vertical
curve 60 the ratio is 0.6. These curves are for
tubular portion 24 which is insulated from the
dimensions of A=120°, B=1y80° and H=210°.
ground and is excited by a connection 25 from
2,502,155
5
the phasing network 2'! connected to transmis
ial cable arranged within said tubular sections
and having its lower end grounded, a connection
from the center conductor of said cable to the
lower end of the upper section, connections from
the outer conductor of said cable to the upper
sion line 28. The upper section 2 of the antenna
system is formed of a linear conductor 23, which
may be in the form of a conducting tube or a
tower, supported on insulator 9d and extending
upwardly through the tube 24 and beyond the
upper end of this tube to the distance B. The
ends of the middle and lower tubular sections, a
connection between the outer conductor of said
tube 24 is supported on the antenna part 23 by
cable and the lower tubular section at a point
one-quarter wavelength above ground, and ex
insulators 9 and 9c. Antenna section 2 is ex
cited by a connection 26 to the lower end of 10 citing connections to the lower end of said lower
part 23 from the phasing network 21.
section and to thelower end of the center con
It will be understood that by suitable adjust
duct-or of said cable.
ment of the phasing networks 2| and 21, the loop
5. An antenna system comprising a vertical
currents in the two antenna sections are ad
conductor supported in insulated relation with
justed to in-phase relation, and the amplitudes
respect to ground and having a length of sub
of the currents are also adjusted to the desired
stantially 3000 ‘of the operating wavelength, a
values as explained above.
tubular conductor surrounding the lower section
It will be further understood that top loading
of said ?rst conductor for a ‘distance of sub
of the top part of the elevated section 2 would
‘stantially 120° of the operating wavelength and
still preserve the required electrical length yet 20 being insulated therefrom, and exciting connec
reduce the physical length substantially.
tions to the lower ends of said conductors for
I claim:
I
exciting in-phase currents in the tubular con
1. An antenna system comprising a vertical
ductor and in the upper section of the ?rst con
antenna section extending above ground a dis
ductor.
tance of substantially 120 degrees of the operat~ 26
6. A two-part vertical antenna comprising a
ing wavelength, a second vertical antenna sec
lower radiating section insulated from ground
tion arranged immediately above said ?rst section
and extending from ground to a point above
and in alignment therewith, said second section
ground a distance of substantially 129 degrees
having a radiating length of not more than one—
of the operating Wavelength, an upper radiat
half wavelength, and the center of the radiat 30 ing section arranged immediately above said low
ing part of said second section being positioned
or section and in alignment therewith, said up
above ground a distance of substantially 210 de
per section extending above said lower section a
grees of the operating wavelength, and means for
distance of not more than one-halal? wavelength,
exciting said sections by in-phase currents, the
and the center of the radiating part of said up
loop current in the upper section having an am
per section being positioned above ground a dis-
plitude of substantially 0.7 of the amplitude of
the loop current in the lower section.
tance of substantially 210 degrees of the operat
ing wavelength, and feed connections to the
lower ends of said radiating sections for exciting
2. An antenna system comprising a vertical
antenna section extending above ground a dis
in-phase currents therein, the loop current in
tance of between 100 to 140 degrees of the op .40 the upper section having an amplitude of sub
erating wavelength, a second vertical antenna
stantially 0.7 of the amplitude of the loop cur
section arranged immediately above said ?rst
section and in alignment therewith, said second
rent in the lower section.
I
'
‘CHARLES L. JEFFERS.
‘ section having a length of not more than one
half wavelength, and the center of said section lik ill
REFERENCES CITED
The following references are of record in the
tween 190 to 230 degrees of the operating wave
?le of this patent:
length, and means for exciting said sections by
UNITED STATES PATENTS
in-phase currents.
3. An antenna system according to claim 2 50 Number
Name
Date
wherein the ratio of the loop current in the upper
2,066,874
Bohm _____________ __ Jan. 5, 1937
section to the loop current in the lower section
2,113,136
Hansel] ___________ 1. Apr. 5, 1938
is within the range of 0.5 to 0.9.
2,118,429 ‘ Duttera __________ __ May 24, 1938
4. An antenna system comprising three verti
2,171,256
Moullin _________ __ Aug. '29, 1939
‘ being positioned above ground a distance of be
cally aligned tubular sections supported in in
sulated relation, the lower section having a length
of substantially 120° of the operating wave
length, and the two upper sections having lengths
of substantially one-quarter wavelength, a coax
55
2,196,187
2,201,857
2,234,234
2,321,454
Blair ______________ __ Apr. 9, 1940
Dome ___________ __ May 21, 1940
Cork ____________ __. Mar. 11, 1941
Brown __________ __ June 8, 1943
v .
Certi?cate of Correction
Patent No. 2,502,155
March 28, 1950
CHARLES L. JEFFERS
_ It is hereby certi?ed that error appears in the‘printed speci?cation of the above
numbered patent requiringcorreotion as follows:
Column 3, line 22, for “(6):” readf(6)=;
and that the said Letters Patent should be read with this correction therein that the
same may conform to the record of the case in the Patent Of?ce.
Signed and sealed this 8th day of August, A. D. 1950.
[SEAL]
THOMAS F. MURPHY,
Assistant Commissioner of Patents.