Antenna system for a jamming transmitter

This invention relates to an antenna system for a jamming transmitter which is intended to protect a remote object which is remote from the jamming transmitter as well as itself or an object in the immediate vicinity of the jamming transmitter. Known jammer antennas for this purpose radiate either a pencil beam which presents considerable problems in the alignment and orientation and tracking in two planes or alternatively such known antennas are designed as omni directional antenna which however have low antenna gain and are easily detected. In the present invention the difficulties of the prior art are eliminated in that a separate antenna is provided for external or foreign protection and a separate antenna for self protection which antennas produced in the first plane a sharply focused pattern and in a plane perpendicular thereto a radiation pattern (7, 8) which is optimized for external or foreign protection or self protection, respectively. The two antennas can be switched and are structurally combined and designed to be jointly rotatable in the first plane. A single antenna can also be provided which can be tilted between two positions one for external or foreign protection and the other position for self protection so as to transmit and radiate instead of two separately optimized patterns a single pattern which is a mean of the two desired patterns.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to an antenna system for a jamming 
transmitter which is intended to protect an object remote from the 
transmitter as well as protect the transmitter itself and/or objects in 
its immediate proximity. 
2. Description of the Prior Art 
A jammer antenna system of this type is intended to radiate jamming or 
interfering radiation from the ground or ship against airplanes flying at 
a constant height or from the airplane against objects on the ground or on 
the water so that independently of the distance the same jamming effect is 
obtained and that the radiated signal serves to protect the transmitting 
location as well as protect external objects. 
So as to achieve an optimum jamming effect at the receiving location 
jamming antennas frequently have a pencil shaped beam, however, 
difficulties arise because of the problem of aligning and tracking in two 
planes for example, in the horizontal and vertical planes of the fine 
beam. An omni directional antenna comprises an antenna with the lowest 
antenna cost but has the disadvantages that the omni directional antenna 
has very low gain and is very easily detected. 
SUMMARY OF THE INVENTION 
The present invention makes it possible to decrease the cost which is 
necessary in the case of a pencil beam antenna on one hand and to avoid 
the disadvantages of an omni directional antenna system on the other hand. 
The antenna system is intended to be capable of simple, small, light 
weight and rapid motion so that it can be universally utilized and can be 
aligned with various objects and in a very rapid manner. 
According to the invention this object is achieved in that for external 
protection and for self protection a separate antenna is provided, 
respectively, such that the two antennas have in a first plane a sharply 
focused radiation pattern and in the second plane which is perpendicular 
to the first plane they exhibit a radiation pattern which is optimized for 
external protection or self protection, respectively, and wherein the two 
antennas between which it is possible to switch the radiating signal are 
structurally combined and designed to be commonly rotatable in the first 
plane. 
Another solution to the problem consists in providing a single antenna for 
external protection and for self protection which in the first plane 
produces a sharply focused beam radiation pattern and in a second plane 
which is perpendicular to the first plane produces a radiation pattern 
which although not optimized for external protection or self protection, 
respectively, has a mean diagram common to the two types of protection. 
Furthermore, the antenna in the second plane is designed so that it can be 
tilted so that its direction of maximum radiation or mean beam direction 
corresponds to the direction which is optimum for external protection 
(which has a small angle of elevation) and in the other instance 
corresponds to the direction which is optimum for self protection (which 
requires larger angles of elevation). The antenna can be designed to be 
rotatable in the first plane and the antenna can be switched for operation 
between external protection and self protection by common control 
coordinated with the sweeping and tilt control. An antenna of this system 
can be designed in a very simple manner and which would be simpler than 
the structure mentioned above which requires two separate antennas. 
An antenna system according to the invention needs only follow up in one 
plane and therefore it can be designed so that it is movable only in the 
one plane and can be directed by means of a tracking system. In the plane 
perpendicular to the first plane the radiation pattern covers a large 
angle of elevation depending upon which of the antennas is connected with 
the external protection or self protection, respectively. With the antenna 
system designed according to the invention, a jamming transmitter can be 
matched so as to meet the prevailing threat situation and it is possible 
to rapidly switch back and forth between several objects which are being 
observed. 
Normally the first plane is the horizontal plane, in other words, the 
azimuth plane and the second plane is the vertical plane or the elevation 
plane. Follow-up is then accomplished in the horizontal plane whereas, by 
contrast, in the elevation plane, the suitable broad shaped radiation 
pattern is employed so that the angle of elevation required is in each 
instance covered for external protection or self-protection. 
Other objects, features, and advantages of the invention will be readily 
apparent from the following description and claims when read in view of 
the drawings in which

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As described above, an antenna follow-up system can be accomplished in only 
one plane; for example, the horizontal plane, and a suitably formed 
broader radiation pattern can be employed in the elevation plane through 
which the angle of elevation allows the range under consideration to be 
covered. The optimum configuration and shaping of the radiation pattern in 
the angle of elevation assuming constant flight altitude or a jamming 
interference effect which is effective up to a specific altitude depends 
upon the objective of the jamming transmitter. 
FIG. 1 illustrates external or foreign protection in which the horizontal 
distance a is plotted on the abscissa and the flight altitude h is plotted 
as the ordinate. If a jammer transmitter 1 is to protect an external or 
foreign object 2, it is important that a target 3 be subjected with a 
specific jamming interference power independently of the distance 
r(.theta.) relative to the jamming transmitter 1. If it is assumed that 
the enemy target 3 lies at a constant altitude H and that it is to be 
jammed from the ground or from a ship, the radiated jamming power G.sub.F 
(.theta.) must increase with the distance r.sup.2 (.theta.) between the 
jamming transmitter 1 and the target 3 so that a constant jamming power 
will arrive at the target location. The following relationship is then 
valid: 
EQU G.sub.F (.theta.)=const..multidot.r.sup.2 (.theta.) (1) 
From the geometry of FIG. 1 it follows: 
EQU sin.theta.=H/r(.theta.) (2) 
Since the flight altitude H is constant, there results 
##EQU1## 
Thus, for external or foreign protection without a vertical follow-up the 
known cosecant-square-law can be utilized. In the coverage diagram shown 
in FIG. 1 which corresponds to a polar field intensity represents due to 
the linear reduction in the field intensity with distance, the line of 
constant flight altitude can be considered as a relative field intensity 
pattern for the jamming or interfering antenna. The law likewise applies 
when the jammer 1 is mounted on board a flying object and is to jam or 
interfere with a target 3 located on the ground. The illustration of FIG. 
1 is such case can then merely be turned upside down to illustrate such a 
situation. In such example, the jamming transmitter 1 will be located at 
the altitude H. The expression in the diagram G.sub.F (.theta.) then 
coincides with ground. 
FIG. 2 illustrates how self protection is accomplished wherein the 
horizontal distance a is plotted on the abscissa and the flight altitude h 
is plotted on the ordinate. For the case in which the jamming transmitter 
4 is protecting itself or an object in its immediate vicinity entirely 
different conditions exist than in the case of external or foreign 
protection illustrated in FIG. 1. The radar on board the target 5 has as 
is assumed detected the system of the jamming transmitter 4 and receives a 
useful power or output N which is dependent upon the radar or backfire 
cross section of the system. This useful power depends upon the distance r 
according to the function. 
##EQU2## 
Effective jamming or interference must function independently of the 
distance r; in other words, the ratio of jamming or interference power S 
to useful power N cannot be permitted to be dependent upon r(.theta.). The 
jamming or interference power arriving at the target results from the 
power or output signal G.sub.E (.theta.) radiated from the jamming or 
interfering transmitter antenna according to the equation 
##EQU3## 
From equations 4 and 5 it follows: 
EQU S/N=G.sub.E (.theta.).multidot.const..multidot.r.sup.2 (.theta.)(6) 
If S/N is to be independent of r(.theta.), then the following relationship 
is valid: 
##EQU4## 
According to equation 2 there results 
EQU G.sub.E (.theta.)=const..multidot.sin.sup.2 (.theta.) (8) 
In the diagram illustrated in FIG. 2 the relative field intensity or 
radiation pattern G.sub.E (.theta.) of the jamming transmitter antenna 4 
results in a semi-circle 6. The angular range in proximity to the zenith 
or nadir, respectively, in the case of an airborne jammer, accordingly, 
requires the greatest proportion of energy. However, due to the short time 
of the fly-over phase and due to the restricted handling capability this 
becomes unimportant at this time. It is therefore desirable to track the 
semicircular shape in the coverage diagram only up to a median angle of 
elevation and to then allow the radiation pattern to break off from the 
semicircle. For ground proximate angles of elevation in the lowest portion 
of the semicircle, by contrast, the diagram signal level should be 
somewhat raised for the purpose of balancing an equalizing ground 
interference effects. 
For the two instances of external protection and self protection the 
optimum radiation pattern for jamming transmitters is illustrated in FIG. 
3. The optimum radiation pattern for external or foreign protection is 
shown by the antenna pattern 7 and the optimum radiation diagram for self 
protection is shown by radiation diagram 8. 
The relationship between the optimum self-protection diagrams and various 
approach altitudes can be observed from considering FIG. 4. In the case of 
a lower approach more jamming power is required. The diagram shape and the 
antenna configuration is not influenced by this fact. The critical angle 
is illustrated by .alpha. and the maximum distance with E. By contrast the 
diagram for external and foreign jamming through the maximum range depends 
upon the flight altitude and is determined by the ratio of detection 
altitude to range. This also influences the shape of the antenna and its 
design. 
To obtain the radiation pattern illustrated in FIG. 3 a doubly curved 
reflector can be utilized. The various radiation patterns of FIG. 3 can be 
produced by different antennas or reflectors. If a jamming transmitter has 
only a single of the two objects or functions, that is, satisfying either 
self protection or external or foreign protection then it is sufficient to 
select a matching arrangement. If by contrast the jamming transmitter due 
to the problem must protect itself or another object then this can be 
accomplished by using a combination of two antennas which is possible in a 
compact manner particularly in the frequency range S/Ku-band. The antenna 
arrangements illustrated in FIGS. 5 through 8 can be utilized for 
generating such patterns. 
FIG. 5 illustrates an embodiment wherein a pair of reflectors 11 and 12 are 
mounted for rotation together and such antennas are fed by stationary 
radiators or antennas 9 and 10. The two primary radiators of the antenna 9 
and 10 are in the form of stationary horn type radiators which are 
respectively fed by feed lines 16 and 17 respectively and such radiators 9 
and 10 are stationary and are mounted on opposite sides of the reflectors 
11 and 12 with the radiator 9 feeding the reflector 11 and the radiator 10 
feeding the reflector 12 as shown. The reflectors are mounted back-to-back 
to each other and are supported on a common vertical axis 13. A supporting 
mounting 14 supports the reflectors 11 and 12 and the support mounting 14 
is mounted on a bearing 15 which is centered on the axis between the 
radiators 9 and 10 so that the reflectors 11 and 12 rotate on the 
dash-dotted line between the reflectors 9 and 10. 
The two feed lines 16 and 17 are stationary as are the horn-type radiators 
9 and 10 and the feed line 17 for the upper horn-type radiator 10 extends 
upwardly as shown. Minor shadowings might result from the feed line 17 
however, this does not substantially influence the overall radiation 
pattern. 
The lower antenna 9 and reflector 11 serve as the external or foreign 
protection antenna and the upper antenna 10 and reflector 12 provides self 
protection. The entire antenna is enclosed in a stationary radome 18 which 
can consist of a low-loss polyurethane-integral foam to which the feed 
line 17 for the upper horn radiator 10 is attached. 
So as to avoid directionally dependent polarization for the stationary 
radiators 9 and 10 can be selected to have circular polarization. The 
obvious application of spiral antennas will not be possible in many 
instances due to the restricted efficiency. Therefore, circularly 
polarized horn-type radiators are advantageously employed for which the 
frequency band widths of up to an octave can be obtained. The greater band 
width of the linearly polarized horn-type radiators, which are fed by 
ridge wave guides, would, with a full rotating metal reflector lead to a 
directionally dependent linear polarization. Thus, in FIG. 5 the two 
reflectors 11 and 12 rotate on a common axis supported by bearing 15 and 
the feed antennas 9 and 10 are stationary. 
FIG. 6 illustrates a modification of the embodiment in which only one of 
the primary radiators, particularly the horn-type radiator 19 is 
stationary and the other horn-type radiator 20 together with the two 
reflectors 21 and 22 which are inclined and mounted one above the other 
with a back-to-back relationship are rotatably mounted about a common 
vertical axis. The feed line 23 to the upper horn-type radiator 20 thus 
jointly rotates with the two reflectors 21 and 22 and is connected by way 
of a rotary coupling 24 to the jamming transmitter. In the case of this 
antenna arrangement there is no shadowing by a feeder line and for the 
upper rotating antenna 20 a random polarization for example, a linear 
polarization of 45.degree. can be selected. In the antenna illustrated in 
FIG. 6, the antenna consists of the stationary horn-type radiator 19 and 
rotating reflector 21 which serves the purpose of external protection and 
the upper antenna consisting of the rotating horn-type radiator 20 and the 
rotating reflector 22 serve for self protection. The antenna of FIG. 6 is 
also covered with a radome 25 for protection. 
In the embodiments of FIGS. 5 and 6 the reflectors of the two antennas are 
mounted back-to-back and as a consequence the direction of maximum 
radiation of the two antennas are offset relative to each other by 
180.degree. in azimuth. However, due to the different requirements for the 
two antennas this does not cause any serious problems. 
FIG. 7 illustrates a further embodiment of the invention for both external 
protection and self protection. In this example, two reflectors 26 and 27 
are mounted at about the same level with a back-to-back relationship to 
each other. Both of the reflectors 26 and 27 together with the two primary 
radiators 28 and 29 which may be of a horn type and are associated 
respectively with the reflectors are rotatably mounted about a common 
vertical axis. A rotating coupling joint 30 is provided for the purpose of 
electrical connection to the rotatably mounted horn type radiators 28 and 
29. A switch 31 for switching over between external and self protection is 
mounted between the rotating coupling joint 30 which can be designed to be 
in the form of a single channel and the feeder lines 32 and 33 which feed 
the two horn type radiators 28 and 29. The rotary base of the entire 
antenna is indicated by numeral 34. The polarization can be randomly 
selected for the two adjacently arranged antennas however preferably it is 
linear at 45.degree.. All the arrangement requires a greater overall 
diameter than the arrangements illustrated in FIGS. 5 and 6. The 
arrangement of FIG. 7 is lower than such embodiments. Also this antenna is 
covered with a radiation transmissive radome 36. 
FIG. 8 illustrates an embodiment wherein common azimuth direction or 
primary radiation of the two antennas is achieved with the antennas 
mounted above each other. The two reflectors 36 and 37 are mounted one 
above the other on a common support mounting 38 and receive radiation from 
two horn-type radiators 39 and 40, respectively. Both of the reflectors 36 
and 37 together with the two horn-type radiators 39 and 40 associated with 
them are rotatably mounted about a common vertical axis. For electrical 
connection to the rotatably mounted horn-type radiators 39 and 40 a rotary 
coupling joint 41 is provided. A switch 42 allows switching over between 
external and self protection and is mounted between the rotary coupling 
joint 41 designed as a single channel and the feeder lines 43 and 44 to 
the two primary radiators 39 and 40. The polarization of both of the 
antennas can be randomly selected however it is preferable to make them 
linear and to select 45.degree.. The arrangement shown in FIG. 8 is higher 
than that illustrated in FIG. 7, however, it requires a smaller diameter. 
The antenna of FIG. 8 is also surrounded by a radiation transmissive 
radome 45. 
The various embodiments illustrated in FIGS. 7 and 8 can be basically 
expanded by adding additional radiators at both sides of the horn-type 
radiators so that they produce radar operation with monopulse reception 
for azimuth follow-up. However, the frequency band width must be narrowed 
down and the antenna dimension possibly enlarged. 
A less costly antenna embodiment can be obtained when only the coarse 
diagram shape is required. In this case the embodiment illustrated in FIG. 
9 which has only a single antenna which consists of a reflector 46 and a 
primary radiator 47 and which can be tilted by way of a joint 48. The 
vertical diagrams for the external or foreign protection and the self 
protection 49 and 50 respectively do not have different shapes as 
illustrated in FIG. 3 but a common mean diagram shape results. The two 
different directions of primary radiation of the antenna are adjusted and 
set by the angles to which they are tilted. The motor driven tilting 
installation 51 is connected with a coupling linkage 57 to the reflector 
46 supporting mounting 58 so that the linkage 57 and gear 59 which engages 
a rack on the linkage 57 causes the reflector 46 to move upwardly and 
downwardly about a horizontal axis 48 as the motor is actuated. The 
optimum range over the entire angle of elevation range is not obtained in 
this embodiment. The motor driven tilting installation 51 is moved by 
closing switch 52 which energizes the motor of the tilting mechanism 51 
from one tilted position for external or foreign protection or to the 
other position for self protection as desired. The entire antenna is 
mounted with its base on a rotary table 53 which rotates about a vertical 
axis and which is supported on a rotary bearing 54. The coupling of the 
feed wave guide 55 for the primary radiator 47 passes through a rotary 
coupling or joint 56. 
For use of the jammer antenna combination according to the invention, it is 
assumed that a radar apparatus or reconnaissance or search apparatus is 
present which determines the azimuth angle of the object which is to be 
jammed. Since these apparatus in most instances effect only target 
locating in azimuth, a jamming antenna combination which follow-up only an 
azimuth operates with such systems in an optimum fashion. The direction or 
guidance and target tracking of the jammer antenna is thus controlled by 
the radar apparatus or reconnaissance apparatus. For the purpose of 
jamming several objects the jamming antenna can be adjusted by means of a 
rapid rotary movement from one object to the next so that it successively 
jams. 
Due to a minimum antenna size, light weight construction of the reflectors 
of metallized foam material and the use of a radome which withstands wind 
forces the very high rotational speeds up to 300 revolutions per minute 
and the high accelerations necessary for this purpose are possible. If the 
threat by various objects is different, in other words, if external 
protection or self protection must be furnished then switching over from 
one to the other antenna can be effected during the direction and guidance 
changes. By the use of a rapid pivotal or swingable antenna combinations 
constructed according to the invention can provide effective jamming of 
several objects so as to provide external or foreign protection as well as 
self protection. 
Although the invention has been described with respect to preferred 
embodiments it is not to be so limited as changes, and modifications can 
be made which are within the full intended scope as defined by the 
appended claims.