Title:
ANTENNA FOR DIRECTION FINDING SYSTEMS
United States Patent 3691561
Abstract:
An antenna arrangement for a shipboard direction finding system is designed to be carried on the ship mast and includes electrically parallel connected, substantially vertically polarized dipole antennas which are uniformly distributed circumferentially in a circle with their radiating elements outwardly inclined from the antenna mast and forming an angle of approximately 30° therewith. A motor controlled rotating differential condenser is connected between the dipole halves and ground to provide means for bringing the dipoles into capacitive symmetry. The antenna arrangement is adapted to be used in proximity to a mast-carried UHF direction finding antenna system through the use of two-terminal networks connected to the dipole elements.


Inventors:
JAGER GERHARD
Application Number:
05/090616
Publication Date:
09/12/1972
Filing Date:
11/18/1970
Assignee:
Licentia, Patent-verwaltungs G. M. B. H. (Frankfurt, DT)
Primary Class:
Other Classes:
343/747, 343/808, 343/890
International Classes:
G01S3/12; H01Q9/28; H01Q21/20; (IPC1-7): H01Q9/28
Field of Search:
343/747,773,774,808,727,890
View Patent Images:
US Patent References:
3521286ORTHOGONAL ARRAY ANTENNA SYSTEM1970-07-21Kuecken
3262121Antenna feed point crossover1966-07-19Holloway
3159838Vertically stacked hollow dipoles conductively supported on a mast1964-12-01Facchine
2968038Multiband tail-cap antenna1961-01-10Hauptschein
2964747Vee antenna1960-12-13Williams
Primary Examiner:
Lieberman, Eli
Claims:
I claim

1. In a short wave antenna arrangement for producing a circular voltage pattern in direction finding systems and composed of a plurality of substantially vertically polarized and electrically parallel connected individual dipole antennas which are mounted on a mast and uniformly distributed around the circumference of a circle, the improvement wherein such individual dipole antennas are bent at their centers in such a manner that their radiating halves are directed away from the mast supporting the antenna arrangement and form an angle of approximately 30° therewith and the centers of said antennas are spaced radially from the mast, whereby said antennas are electrically decoupled from the mast.

2. An antenna arrangement as defined in claim 1 further comprising a rotating differential condenser for balancing the dipoles as regards their capacitance with adjacent structures, including the supporting mast, the stators of said rotary differential condenser being connected with the associated dipole halves and the rotor of said condenser being connected to ground, said condenser being controlled from a remote location by motor means.

3. An antenna arrangement as defined in claim 1 further comprising a UHF antenna carried on the mast, and two-terminal networks connected for electrically subdividing said dipole halves to decouple them from said UHF antenna.

Description:
BACKGROUND OF THE INVENTION

The present invention relates to an antenna for a direction finding (DF) system, particularly one mounted on a ship.

With the present DF systems available for use on shipboard, it is difficult at times to determine from which side of the ship the bearing indication originates. Because of quadrature fields from metallic ship structures, a definite side determination is not possible for some frequencies and in some bearing azimuths when using known DF antennas.

Attempts have been made, therefore, to improve the situation through the use of phase-shifting means designed to receive the output voltage deriving from a circular voltage pattern antenna. The disadvantage to this operation was that a certain phase angle must be selected for each frequency to be used for ranging. Furthermore, there are still some frequency ranges in which, for certain azimuths, it is not possible to determine with certainty the side from which the signal originated.

It was thought that the reason for the lack of success in utilizing phase-shifting means lay in the fact that quadrature fields originating from certain metallic ship structures, such as a crossed-loop antenna, an Adcock antenna, or the like, influenced the DF antenna.

It is also known that, with the use of a simple vertical antenna as the auxiliary antenna, mast currents have an annoying coupling effect on the lead cable. It was therefore proposed to use a dipole arrangement as the auxiliary antenna, particularly for shipboard DF systems, since its lead cable is symmetrical and thus insensitive to interfering influences.

SUMMARY OF THE INVENTION

The present invention is based on applicant's recognition that it is not only the influences of the quadrature fields on the DF antenna and the influences of the mast current on the lead cable which impede the side direction determination, but most of all the influences of the quadrature fields on the mast bearing the antenna arrangement. The effect of the thus influenced mast current on the voltage produced by the circular voltage pattern antenna when the current is coupled with the antenna appears to be a major problem.

The problem resolves itself into a determination of what means can be used to electrically decouple the antenna, which furnishes the circular voltage pattern, from the mast, so that the mast current no longer has any influence on the lateral or side determination.

For this purpose the antenna arrangement for producing a circular voltage pattern, comprising a plurality of substantially vertically polarized and electrically connected dipole antennas which are uniformly distributed around the circumference of a circle, is improved according to the present invention in that the individual dipole antennas are bent at their center so that the radiating elements are directed away from the mast bearing the antennas and form an angle of approximately 30° therewith.

The angle of 30° results in an optimum choice on the one hand satisfying the requirement of sufficient decoupling from the mast, which would be a maximum with horizontal arrangements of the dipoles, and, on the other hand, because such inclination of the dipole halves from the vertical does not produce too great a loss of useful voltage. The diameter of the circle on which the dipoles are arranged must not be larger than one quarter of the smallest wavelength to be received, so that the circular voltage pattern becomes almost independent of the azimuth.

It would be sufficient for proper functioning of the antenna system if two oppositely disposed dipoles were provided. It is also possible to utilize more than two dipoles for producing the antenna voltage and this produces an advantage in that the individual dipoles may then be made shorter.

If a crossed-loop antenna is used as the DF antenna, the antenna according to the invention is advisably disposed inside the crossed-loop and four dipoles are used. This solution produces an optimum as regards small space requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of the arrangement and electrical connections of the dipoles and associated rotating differential condenser according to one embodiment of the invention.

FIG. 2 is a perspective view of the dipole antenna system on a mast-mounted box which is designed to house the other elements of the short wave DF system.

FIG. 3 is a perspective view of a support frame extending around the antenna arrangement of FIG. 2 so as to provide a support for a UHF DF antenna arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an antenna composed of two opposed dipoles and illustrates the manner in which the individual dipoles of an antenna according to the invention are electrically connected together. All of the upper dipole halves 1 are connected with one stator 3 of a rotating differential condenser 4 and all the lower dipole halves 2 are connected with the other stator 5 of the rotating differential condenser 4. The rotor 6 of the condenser is connected to ground and the function of this differential condenser will be discussed below. Leads 7 and 8 connect the upper dipole halves 1 and lower dipole halves 2, respectively, to a receiver 9 which can be of any known type.

The capacitive influences of the environment on the antenna system as mounted, for example, on a ship mast are different for the individual dipole halves. Thus, the capacitance of the lower dipole halves with respect to the ship's structures and the mast is greater than that of the upper dipole halves. The dipoles must, therefore, be brought into capacitive symmetry. According to the present invention, the associated dipole halves are connected with the stators of the rotating differential condenser 4 whose rotor 6 is connected to ground and which, in order to avoid capacitive influencing of the antenna by operating personnel, can be operated by remote control, through the use of a motor control during the symmetry tuning.

If it is decided that the voltages from the circular voltage pattern antenna and from the DF antenna should be approximately equal in amplitude, then the indication for the symmetry tuning may be this voltage ratio. The dipole antenna system need only be brought into symmetry once during installation by means of the rotating differential condenser. This is done by tuning the rotating differential condenser until the antenna voltages furnished by the dipole antenna system and the DF antenna are approximately of the same amplitude over the entire frequency range for which the antenna arrangement is to be used.

FIG. 2 shows an embodiment of a complete short wave DF antenna arrangement containing an antenna according to the invention. It includes a box 10 of electrically non-conductive material to which dipole elements 1 and 2 of the antenna are fastened. Box 10, which is carried on the mast 11, contains a ferrite DF antenna and all of the circuit components of the entire antenna arrangement in a weather-tight manner. These are of known design and construction and are not shown in detail because they do not form per se a novel part of the invention.

For shipboard DF antenna arrangements, a UHF DF antenna, is usually disposed above the shortwave DF antenna. Care must then be taken that the antenna according to the invention is sufficiently decoupled from the UHF DF antenna. Accordingly, the circular voltage pattern antenna is electrically subdivided through the use of known two-terminal networks. This type of subdivision becomes effective in the UHF range and in the frequency ranges therebelow it is nullified through the use of the two-terminal networks.

In FIG. 3, a UHF DF antenna 12 is shown disposed above the shortwave DF antenna system. The cable leads of the UHF DF antenna, not shown, are brought down through a cross frame 13 past the shortwave DF antenna arrangement. The antenna 12 is supported by the cross frame and the frame may be given a special configuration to enable it to serve as an additional DF antenna.

In a preferred embodiment of the invention using only two dipole antennas like it is shown in FIG. 1, the dipole halves had a length of about 135 cm and was provided for use in a frequency range from about 250 kHz to 30 MHz. In another embodiment of the invention using four dipole antennas, like it is shown in FIG. 2, the dipole halves had a length of about 96 cm when provided for the same frequency range as described above. In both cases the distance between the basic points of two diametrical dipole antennas was chosen about 84 cm. As to the capacitive influences of the environment of the antenna system, which are, as mentioned above, in some cases, e.g., when mounted on a ship mast, different for the individual dipole halves, it was found, that for the embodiment of the invention using four dipole antennas as mentioned above, a capacity of about 60 pF of the rotating differential condenser 4 was sufficient, to balance said capacitive influences.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.