Dual mode antenna having simultaneous operating modes

A dual mode broad band antenna especially designed to provide simultaneously high and low angle radiation patterns relative to a horizontal ground plane is disclosed herein. This particular antenna utilizes four wire radiators in the form of an inverted conical log-spiral supported in a vertically extending fashion a predetermined distance above the horizontal ground plane. In order to operate the antenna in its high and low angle modes simultaneously, first and second oppositely phased AC currents are applied to the radiators in two different ways through specifically connected hybrid isolating transformers.

The present invention relates generally to antennas and more particularly 
to a specific improvement in the four wire dual mode spiral antenna 
described in U.S. patent application Ser. No. 454,693 filed Dec. 30, 1982, 
now U.S. Pat. No. 4,498,084 (hereinafter referred to as the "Werner et al 
application"). 
In the Werner et al patent application just recited, a broad band antenna 
taking the form of a four radiator inverted conical log-spiral is 
disclosed. More specifically, means are provided for supporting first, 
second, third and fourth wire radiators in electrically insulated 
relationship to one another around the surface of an imaginary inverted 
cone. The cone is supported vertically on a horizontal ground plane and 
has its apex located a fixed distance above that plane. Moreover, the four 
radiators defining the cone, starting with the first one, are supported so 
as to provide successively interlaced spiral windings beginning at the 
lowermost ends of the radiators adjacent the apex of the cone and ending 
at their uppermost ends adjacent the cone's inverted base. Both the 
lowermost ends and the uppermost ends of these radiators are 
circumferentially spaced 90.degree. from one another about the cone's 
central axis. In addition to these components, the overall antenna 
includes a power feed arrangement which utilizes first and second 
alternating currents having the same amplitude and a given frequency but 
180.degree. out of phase with one another. 
In accordance with one particular aspect of the Werner et al antenna, the 
feed arrangement just recited includes means for simultaneously 
electrically connecting the first alternating current to the lowermost 
ends of the first and second radiators (e.g., one pair of adjacent 
radiators) and the second alternating current to the lowermost ends of the 
third and fourth radiators (e.g., a second pair of adjacent radiators). In 
this way, the four individual radiators are functionally converted to a 
single pair for producing a high angle radiation pattern relative to the 
horizontal ground plane. At the same time, the overall feed arrangement 
includes a simple switch, for example, a vacuum-type of double pole double 
throw relay switch, for alternatively connecting one of the alternating 
currents to the lowermost ends of the first and third radiators (a first 
pair of opposite ones) while the other alternating current is connected to 
the lowermost ends of the second and fourth radiators (a second pair of 
opposite ones). This causes the antenna to operate as a four element 
spiral to produce a low angle radiation pattern relative to the same 
horizontal ground plane. 
The Werner et al antenna is quite satisfactory for its intended purpose, 
that is, as a means for alternatively producing high and low angle 
radiation patterns. However, this antenna (as specifically described in 
the Werner et al patent application) cannot produce the same high and low 
angle radiation patterns simultaneously. This is best exemplified in FIGS. 
1 and 2 which will be discussed in detail hereinafter. 
In view of the foregoing, it is an object of the present invention to 
improve upon the antenna described in the Werner et al patent application 
by providing relatively uncomplicated and reliable means for allowing it 
to produce the disclosed high and low angle radiation patterns 
simulataneously. 
Another object of the present invention is to provide an antenna generally 
which is capable of producing simultaneously a plurality of separate and 
distinct radiation patterns, each being produced as if the others were not 
present. 
As will be described in more detail hereinafter, the antenna disclosed 
herein is one which comprises a plurality of radiators and means for 
supporting the radiators in electrically insulated relationship to one 
another relative to a fixed reference. The antenna also includes a 
radiator energizing arrangment which utilizes first means connected with 
the radiators in a first specific operating mode for energizing these 
radiators in order to produce a first specific radiation pattern relative 
to the fixed reference and second means connected with the radiators in a 
second, different specific operating mode for energizing the radiators in 
order to produce a second, different specific radiation pattern relative 
to the same fixed reference. In accordance with the present invention, the 
first radiator energizing means includes its own signal isolating means 
for preventing connection of the second radiator energizing means with the 
radiators in the second operating mode from affecting the energization of 
the radiators in said first operating mode. At the same time, the second 
radiator energizing means includes its own signal isolating means for 
preventing connection of the first radiator energizing means with the 
radiators in the first operating mode from affecting the energization of 
the radiators in said second operating mode. In this way, the radiators 
can be energized in both the operating modes simultaneously for producing 
both of the radiation patterns simultaneously. 
With particular regard to the antenna described in the Werner et al patent 
application, the present invention preferably provides an arrangement of 
hybrid transformers connected in circuit with the antennas and two 
balanced current sources for simultaneously energizing the individual 
radiators making up the antenna with alternating current in the two 
different operating modes described in order to simultaneously produce the 
radiator patterns set forth and without fear of electrically shorting or 
otherwise damaging either current source as a result of this dual 
operating capability.

Turning now to the drawings, wherein like components are designated by like 
reference numerals throughout the various figures, attention is first 
directed to FIG. 1 which illustrates an antenna 10 located on a 
horizontally extending ground plane 12 which may actually be ground level 
or it could be a raised support surface such as the roof of a building. 
This antenna, which corresponds to the one specifically disclosed in the 
previously recited Werner et al patent application, may be divided into 
two sections. These sections include a radiating section 14 which, as will 
be seen hereinafter, is in the form of a four element (radiator) inverted 
conical log-spiral and a support section 16 for maintaining the central 
axis of the spiral cone in a vertically extending direction and its apex a 
predetermined distance above the ground plane. 
As described in more detail in the Werner et al patent application, antenna 
10 is designed to operate in two alternate modes, one providing a low 
angle, omni-directional radiation pattern and the other providing a high 
angle, omni-directional radiation pattern. The low angle pattern is best 
illustrated by the low angle lobes in the elevation pattern shown in FIG. 
2 and the high angle pattern is best illsutrated by the high angle lobe 
shown there. It should be especially apparent from FIG. 2 that antenna 10 
is capable of radiating at elevation angles from zenith to its lowest lobe 
within a relatively broad bandwidth of 2 MHz (its low frequency cut-off) 
to 30 MHz (its high frequency cut-off). While the antenna produces nulls 
in its pattern in one mode, the nulls become peaks in the other mode, 
thereby providing complete coverage. 
Referring to FIG. 1A in conjunction with FIG. 1, the radiating section 14 
of antenna 10 is shown including four wire radiators 18A, 18B, 18C and 18D 
(hereinafter merely referred to as raditors A, B, C and D). These 
radiators are supported by arrangement 16 in electrically insulated 
relationship to one another above horizontal ground plane 12 and around 
the surface of an imaginary inverted cone (specifically the hexagonal cone 
shown) having its apex 20 located a fixed distance above the ground plane 
and its central axis 22 extending vertically upward therefrom. The 
radiators A, B, C and D specifically define successively interlaced spiral 
windings beginning at the lowermost ends of the radiators adjacent apex 20 
and ending at their uppermost ends adjacent the inverted base 24 of the 
cone. As described in the Werner et al application, the lowermost ends of 
the radiators are circumfrentially spaced 90.degree. from each other about 
central axis 22. As best seen in FIG. 1A, their uppermost ends are also 
circumferentially spaced 90.degree. from each other about the central 
axis. In actuality, the four radiators are identical or substantially 
identical in spiral configuration and are placed on the outer surface of 
the cone but rotated 90.degree. relative to one another. In a preferred 
embodiment, the radiators 18 define a logarithmic spiral, although an 
Archimedes spiral could be utilized. 
Antenna 10 also includes a power feed arrangement which is generally 
indicated at 26 in FIG. 1. This feed arrangement includes a power station 
28 located for example on ground plane 12 adjacent the apex 20 of 
radiating cone 14. The power station includes suitable means for providing 
first and second alternating currents having the same amplitude and a 
given frequency within the bandwidth recited above, but 180.degree. out of 
phase with one another. As described in the Werner et al patent 
application, the feed arrangement also includes a switch, for example a 
vacuum type of double pole double throw relay switch, which connects the 
lowermost ends of the wire radiators to the two AC currents in alternating 
high angle and low angle modes for selectively producing the previously 
described high angle and low angle radiation patterns. More specifically, 
when the switch is in its high angle position, it connects the lowermost 
ends of one directly adjacent pair of radiators, for example radiators A 
and B, to one of the AC currents and it connects the lowermost ends of the 
other pair of directly adjacent radiators, for example radiators C and D, 
to the other AC current. This functionally results in a two radiator 
spiral antenna (using all four radiators). When the switch is in it slow 
angle position, it connects one of the AC currents to the lowermost ends 
of one pair of opposing radiators, for example radiators A and C, while, 
at the same time, the other AC current is connected to the lowermost ends 
of the other pair of opposing radiators, for example radiators B and D. 
This functionally results in the previously described four radiator 
antenna. 
Overall antenna 10 has only been described above, as it relates to the 
present invention For a more detailed description of this antenna, 
reference is made to previously recited Werner et al patent application 
which is incorporated herein by reference. As described in this 
application and as stated previously, the Werner et al antenna is designed 
to produce alternatively the high and low angle radiation patterns 
illustrated in FIG. 2. The antenna, as described, is not capable of 
providing both patterns simultaneously. This is best exemplified in FIG. 3 
which diagrammatically illustrates the four radiators A, B, C and D in 
combination with two current sources generally indicated at 40 and 42. 
Each current source has two terminals, T.sub.1 and T.sub.2, which provide 
the previously recited first and second alternating currents having the 
same amplitude and a given frequency, but 180.degree. out of phase with 
one another. For purposes of simplicity, one of these AC current will be 
referred to as a positive current and the other will be referred to as a 
negative current. 
The current source 40 is shown connected to the radiators A, B, C and D in 
the low angle operating mode of antenna 10. Specifically, one of the AC 
current, for example the positive one, is connected to radiators B and D 
from terminal T.sub.1 through connected junction J while the other AC 
current, for example the negative one, is connected to the radiators A and 
C from terminal T.sub.2 through another junction J. The current source 42 
is shown connected with the radiators in the high angle operating mode of 
antenna 10. Specifically, the positive AC current is connected to 
radiators A and B from terminal T.sub.1 through a junction J and the 
negative AC current is connected to the terminals C and D from junction 
T.sub.2 through a junction J. With the radiators connected up 
simultaneously to current sources 40 and 42 in this way, it should be 
apparent from FIG. 3 that the terminals T.sub.1 and T.sub.2 of each 
current source would be short circuited. For example, assuming the 
connections are as shown in FIG. 3, it is possible to get from terminal 
T.sub.1 of source 40 to terminal T.sub.2 of the same source without going 
through a load, as indicated by the arrow 43. This is also true for the 
terminals T.sub.1 and T.sub.2 of source 42, although for purposes of 
clarity no arrow has been shown between these latter terminals. In each 
case, the connection between the antenna radiators and each current source 
is responsible for shorting out the terminals of the other current source. 
Thus, it is not possible to operate antenna 10 in both of its operating 
modes without eliminating this problem. As will be seen below, the present 
invention does eliminate the problem by providing a specific radiator 
energizing arrangement which isolates the two modes in a way which allows 
them to operate simultaneously. 
Referring to FIG. 4, the same four radiators A, B, C and D illustrated in 
FIGS. 1, 1A and 3 are shown. In an actual working embodiment, each has an 
effective impedance R to ground of, for example, a nominal value of 300 
ohms, as indicated symbolically. These radiators which are fixedly 
supported relative to one another and to ground plane 12 in the manner 
recited are shown in combination with an overall radiator energizing 
arrangement generally indicated at 44. Arrangement 44 is comprised of the 
two current sources 40 and 42 discussed above with regard to FIG. 3 and 
four hybrid transformers 46AD, 46BC, 46BD and 46AC which are 
interconnected with the current sources and the radiators in the manner to 
be described below. 
In the particular embodiment illustrated in FIG. 4, each current source is 
a 50/300 ohm balun transformer having a nominal input impedance presented 
to its balanced terminals T.sub.1 and T.sub.2 of 300 ohms, with an 
approximate SWr of 1.5:1. The use of this particular source assumes that 
the four radiators are symmetrical and that each presents an impedance to 
ground of 300 ohms, as stated above. Each of the hybrid transformers 
includes a pair of magnetic coils which are interconnected in a 
magnetically subtractive fashion relative to its input terminal T.sub.in. 
Thus, with respect to AC currents passing through the coils from terminal 
T.sub.in, the resultant magnetic fields cancel one another which, in turn, 
means that the overall hybrid transformer acts merely as a low or zero 
impedance junction. On the other hand, with respect to AC current passing 
through the coils in the opposite direction, the coils are additive and 
the overall hybrid transformer presents sufficiently high reactance to 
function as an effective open circuit. It is to be understood that both 
these hybrid transformers and the current sources just described are 
readily providable by those with ordinary skill in the art to which the 
present invention pertains. 
As specifically illustrated in FIG. 4, the terminal T.sub.1 of source 40 is 
connected to the radiators B and D through the hybrid transformer 46BD 
from its input terminal T.sub.in. Terminal T.sub.2 of this same current 
source is connected to the radiators A and C through transformer 46AC from 
its terminal T.sub.in. Since the AC currents energizing the antennas from 
source 40 enter transformers 46BD and 46AC from their input terminals 
T.sub.in, the transformers act merely as jucntions, e.g. as if they were 
not there. In this way, the source 40 can energize the four radiators in 
the manner required to produce the low angle radiation pattern illustrated 
in FIG. 2. As will be discussed hereinafter, the fact that current source 
42 is also connected to the radiators in the manner to be described below 
does not prevent source 40 from opeating in this manner. 
As also seen in FIG. 4, terminal T.sub.1 of current source 42 is connected 
to the radiators B and C through the hybrid transformer 46BC through its 
input terminal T.sub.in. At the same time, terminal T.sub.2 of transformer 
42 is connected to radiators A and D through transformer 46 AD from its 
input terminal T.sub.in. Since the AC currents from source 42 enter these 
transformers from their input terminals, the transformers merely function 
as junctions and therefore source 42 energizes the radiators in the manner 
necessary to produce the high angle radiation pattern shown in FIG. 2. As 
will be seen below, the fact that source 40 is also connected to the 
radiators does not prevent source 42 from operating in this manner. 
Still referring to FIG. 4, the reason that the operation of current source 
40 on radiators A, B, C and D is not affected by the simultaneous 
operation of current source 42 on the radiators, and vice versa, is 
because of hybrid transformers 46. For example, current from terminal 
T.sub.1 of source 42 passing through transformer 46BC to radiators B and C 
is effectively blocked from reaching source 40 of its own T.sub.2 terminal 
by the transformers 46BD and 46AC which function as open circuits to this 
current. At the same time, current from terminal T.sub.2 of current source 
42 directed to radiators A and D are blocked from reaching current source 
40 or its own terminal T.sub.1 by the same transformers which, again, act 
as open circuits to this current. Thus, current source 42 functions to 
energize radiators A, B, C and D as if source 40 were not connected to the 
radiators. In the same manner, AC current from terminal T.sub.1 of 
transformer 40 directed to radiators B and D are blocked from reaching 
current source 42 or its own terminal T.sub.2 by hybrid transformers 46BC 
and 46AD which function as open circuits to this current. At the same 
time, current from terminal T.sub.2 of source 40 which is directed to 
radiators A and C is blocked from reaching source 42 or its own terminal 
T.sub.1 by the same transformers which, again, function as open circuits 
to this current. Thus, current source 40 serves to energize radiators A, 
B, C and D as if source 42 were not connected to the radiators. As a 
result, the radiators receive current from each source simultaneously, as 
if the other was not there, and therefore these radiators simultaneously 
produce the high and low angle radiation patterns shown in FIG. 2. 
In view of the foregoing, it should be apparent that radiator energizing 
arrangement 44 in combination with the four radiators A, B, C and D 
forming part of antenna 10 provide a way of simultaneously producing the 
high and low angle radiation patterns shown in FIG. 2. However, it should 
be apparent that arrangement 44 is not limited to the particular 
configuration of radiators illustrated but may be equally applicable with 
regard to other types of radiator combinations. It should also be apparent 
that the present invention is not limited to the particular current 
sources and hybrid transformers shown so long as suitable devices are 
provided to eenrgize the cooperating radiators in a manner which allows 
simultaneous production of different radiation patterns. Also, it is quite 
possible to use a single current source rather than dual sources, as will 
be discussed hereinafter with regard to FIG. 8. Finally, with regard to 
the breadth of the present invention, it should also be apparent that 
hybrid transformers 46 (or equivalent devices) could be used in 
conjunction with the radiators to serve as a dual mode receiving antenna, 
that is, as a means of simultaneously receiving two radiation patterns. 
This is best exemplified in FIG. 8 also, as will be discussed. 
Having described overall radiator energizing arrangement 44 in conjunction 
with the rest of antenna 10 illustrated in FIGS. 1 and 1A, attention is 
now directed to FIGS. 5A and 5B which illustrate an actaul test embodiment 
of arrangement 44 including the two 50/300 ohm balun transformers 40 and 
42 and the four hybrid transformers 46. These latter transformers are 
assembled on a sheet 50 of electrical insulating material. Rather than 
using actual radiators, which would have been impractical for purposes of 
evaluation, 300 ohm resistors were used in their place. These resistors 
were connected from terminals on the sheet 50, which terminals 
respresented the antenna radiators, to a copper ground plane 52 (see FIG. 
5B) about 1.5 inches below the insulation sheet. The radiator terminals 
were connected to the balun transformers and the hybrid transformers in 
the same manner shown in FIG. 4. Preliminary measurements of impedance 
looking into the "low angle" 50 ohm port showed an input SWR versus 
frequency as in FIG. 6, curve A. An improved result was obtained with 
compensating networks, as illustrated by curve B. While not shown, these 
compensating networks comprised inductances and capacitors. With or 
without these compensating networks, no change in the input impedance to 
one mode could be observed when the input to the other mode was opened, 
short circuited or connected to 50 ohms. 
Referring now to FIG. 7A, a modified radiator energizing arrangement 44' is 
illustrated in conjunction with the same radiators A, B, C and D. In this 
arrangement, three current sources 54 which may be identical to current 
sources 40 and 42 are used along with six hybrid transformers 56 (as 
represented by rectangles) which may be identical to the transformers 46. 
In FIG. 7A, the input terminal T.sub.in of each hybrid transformer is 
diagrammatically represented by the center terminal in the rectangle and 
the outputs are represented by the two outer terminals. With this in mind, 
it should be apparent that the current source 54A energizes the radiators 
in the same manner as current souce 40 in order to provide the low angle 
radiation pattern and that the current source 54C energizes the radiators 
in the same manner as current source 42 in order to produce a 
corresponding high angle radiation pattern. In addition, current source 
54B energizes the radiators A and B from its terminal T.sub.2 and C and D 
from its terminal T.sub.1 in order to provide a second type of high angle 
radiation pattern. In other words, the overall arrangement 44' differs 
from arrangement 44 in that it provides three radiations patterns 
simultaneously. Each current source 54 is isolated from the others by 
means of the hybrid transformers in the manner described previously. 
FIG. 7B illustrates a radiator arrangement 44" which includes high angle 
transmission through source 54C, without current sources 54a or 54B. In 
other words, arrangement 44" energizes the four radiators A, B, C and D in 
one high angle mode. However, a low power, high speed transmit/receive 
switch 60 and a receiver 62 are coupled to a balun transformer 54B to the 
four radiators in the manner shown through isolation transformer 56 in 
order to operate the overall arrangement as a transmit/receive station. 
While it is not possible to simultaneously transmit and receive with 
overall arrangement 44", because of the isolation between the transmit and 
receive modes, the switch 60 can be a low power switch and the receiver 62 
does not need to be electronically insulated to any significant degree 
from the high voltage which develops across transformer 54C during the 
transmission mode. 
Referring to FIG. 8, a radiator arrangement 44"' is shown including the 
same radiators A, B, C and D and isolation transformers 46 forming part of 
arrangement 44. 
However, all of the radiators and the isolation transformers of arrangement 
46"' are ultimately connected to a single pair of terminals T.sub.1, 
T.sub.2 so that a single current source (not shown) can be used to 
energize the radiators to provide simultaneous high and low angle modes of 
operation rather than two such sources (40 and 42) as in arrangement 44. 
Also, by connecting a suitable transformer to the two terminals rather 
than a current source such as the one shown by dotted lines in FIG. 8, 
arrangement 44"' could be used to receive high and low angle radiation 
patterns simultaneously. 
FIG. 9 shows an arrangement 44"" which functions in the same manner as 
arrangement 44', without the low angle mode and thus uses only four 
isolation transformers 56. FIG. 10 shows an arrangement 44""' which also 
functions in the same manner as arrangement 44', except that a double pole 
double throw switch 70 is used to alternate between the low angle mode and 
one of the high angle modes using a single current source.