US2217413A - Radio direction finding system - Google Patents

Description

` KoscHMlEDER. RADIO DIRECTION FINDING SYSTEM Oct. 8, 1940.

Filed Deo. '7.' 1937 2. sheetssheet 1 Oct. 8. 1940. K, KoscHMlEDER 2,217,413

y I RADIO DIRECTION FINDING SYSTEM l Filed Deo. 7, 1957 2 sheets-sneer'z Attorney Patented Oct. 8, 1940 UNITED STATES rarest ortica 2,217,413 RADIO DIRECTION FINDING SYSTEM Application December 7, 1937, Serial No. 178,666

In Germany December 7, 1936 v L 4 Claims.

The present invention relates to a particular design of direction nding systems known per se, which operate with a plurality of individual radiators or with combined antenna arrangements 5 interconnected at one point in order to compare their respective energies. Experience teaches that a reliable direction finding is not always obtained due to the considerable difficulties with respect to the suppression of the horizontal polarization.

The best known antenna system of the above mentioned type is the so-called Adcock antenna arrangement, which substantially comprises four vertical radiators located at the four corners of a square. These radiators are either tuned with earththe so-called U-Adcock--or elevated radiators separated from groundthe so-called H- Adcock. The invention does not concern the construction of the H-Adcock antenna, but deals with the design of the U-Adcock antenna which involves the advantage of considerably lower structural height as compared with the H-Adcock antenna. However, the suppression of the horizontal polarization presents substantially greater 25 diiiculties in connection with the U-Adcock an tenna arrangement than with H-Adcock antennae. The known arrangements employ shielded lines for connecting the individual radiators to the receiver or to a goniometer associated with the input circuit thereof. The shieldings of said lines are thoroughly grounded. It has been found that horizontal polarization phenomena, that is, reception or transmission of horizontally polarized energy, still occur in spite of such precautions, particularly when the ground is not very moist. Careful investigations have proven that the shielded lines themselves act as receivers or emitters, thereby giving rise to direction nding errors due to improperly polarized waves as a result of insuicient symmetry of the antenna structure.

These disadvantages are obviated according to the present invention which provides the interconnecting lines symmetrically between the radiators and earth so that reradiation from the horizontal lines will be symmetrical with respect to the antenna structure.

The invention will be more readily understood from the following description in conjunction with the attached drawings, in which:

Fig. l shows a diagrammatic sectional elevation of a known antenna arrangement, while the Figs. 2 to 4 each illustrates an embodiment of the invention in similar elevation. Figs. 5 and 6 show two other embodiments.

The known antenna arrangement illustrated in Fig. l by way of an example comprises four individual radiating antennae positioned at the four corners of a square. Only the two antennae A1 and A2 are shown in this sectional representation. These antennae are connected to a counterpoise or earth at E1' and E2 over the coupling transformers L1 and L2, respectively, and coupled to the transmitter or receiver G over the energy lines F1 and F2, respectively. The outer sheath of these lines is grounded.

Possibilities for grounding in an exact sense are not available when poor ground conditions prevail, because the shielded cable line oscillates more or less depending upon these conditions. Potential difference between the earth and shield caused by horizontally polarized components set up oscillations in the shield causing reradiation therefrom. Because of the capacity between the shield and the antenna and the shield and earth currents due to this re-radiation are caused to ilow in the antenna giving rise to direction iinding errors. It is possible to proceed according to the inventive idea disclosed in the Fig. 2, that is to say, to insert such a large condenser C in the connection between-the coupling coil for the energy line and the ground network which can be seen will produce aneutralizing voltage effect and, as to compensate forthe capacity C1 of the antenna conductor to earth, or to the cable line. While such a circuit arrangement gives the desired result, it introduces the disadvantages of frequency dependence of the system and the necessity of individual adjustment to each operating wave-length, a rather unsuitable condition in normal communication. The operation of the aforesaid circuit arrangement is based upon the fact that the currents i1 and i2 representing the current caused by the unbalance to earth through C1 and the effect of condenser C, respectively compensate each other. The current i1 denotes the current which ows from the antenna tothe device G, while i2 represents the current flowing from earth or from the counterpoise to the device G. However, in cases that this compensation fails, the energy lines apply diiferent currents through the capacities C1 and C2.

According to the invention, therefore, the connecting lines F1 and F2 from the device G are applied directly to the coupling transformers L1 and L2, respectively, as shown in Fig. 3, and are not underground. The energy line is located in eld symmetry, that is to say, the radiation iield between ground and the energy line is the same as the radiation eld between the antenna and the energy line (compare Fig. 3), whereby the phase difference between the above mentioned currents i1 land 112 is eliminated regardless of the wave length and a symmetric structure of the entire system is attained. Ihe energyv lines are then located Within a eld zone which is the same above andbelow the lines. It has been proven by tests that no horizontal effect exists.

Generally, an adjustment of balance of the arrangement is possible only when the energy line emits radiation. To effect the adjustment a potential which is produced by the local auxiliary transmitter S is applied to the energy line in any known manner. This additional and locally produced potential must develop an equivalent, but opposing effect relative to the horizontal eect set up due to incident oscillations. In order to secure this eect, a coil T is provided about the energy line, said coil being supplied from small high frequency oscillators, the frequency of which corresponds to the operating wave-length of the direction finding system. The condenser C is to be varied until no high frequency component occurs in the device G. Since the oscillations introduced by s correspond toI those which will be induced by the received waves under operating conditions, adjustments to balance out these introduced oscillations will be correct'for compensating those induced by the received waves. It will also be possible to determine the magnitude of the condenser C by a capacity measurement of the antenna arrangement, but this gives approximate values only. On the other hand, atmospheric and like influences under normal operating conditions give rise to capacity changes which are not computable, but which may easily be taken into consideration by a further adjustment of the auxiliary transmitter.

The inventiveidea is by no means limited to antenna systems employing radiators which consist of one single conductor, but is applicable also to such antenna systems which utilize tubular radiators or an antenna assembly comprising a number of separate radiators arranged in a circle, or similar structures. Such antenna systems have the advantage that they are capable of picking up a larger voltage amplitude than other systems, since it is an aperiodic antenna system which employs a larger condenser. From this follows that the voltage drop across the condenser becomes lower.

It is not necessary to provide a shielded twoconductor line as the energy line as shown in the iigures. Also an unshielded line can be employed as placed in field symmetry.

Fig. A5 represents a modification in which the individual wires of which the antenna A is composed are arranged in a circle. The antenna is connected with ground through coupling coil L and a variable condenser C, and through the coupling coil it is connected with the transmission line F.

In the arrangement shown in Fig. 6, the antenna A is in the form of a tube having a large capacity.

What is claimed is:

1. A direction antenna system responsive substantially to vertically polarized energy only comprising earthed vertical antennae, a high frequency device, horizontally disposed lines interconnecting said antennae and said device, a shield arranged `about said lines, said shield inherently tending to reradiate in response to oscillations induced by horizontally polarized energy to produce a radiation eld effective between said shield and said antennae and said shield and earth, and means for substantially eliminating the effect of said reradiation of energy on said high frequency device comprising means supporting said shield and said lines in spaced relation with respect to said earth substantially symmetrically within said produced radiation eld with respect to said antennae and said earth.

2. A system according to claim 1, having coupling means inserted in the antennae for coupling to said line, and a condenser disposed between said coupling means and said earth, said antennae each comprising individual conductors arranged in a circle.

3. A system according to claim l, having coupling means inserted in the antennae for coupling to said line, and a condenser disposed between said coupling means and said earth, said antennae being tubes with large capacity.

4. A direction finding system according to claim 1, and counterpoises associated with said antennae.

KURT KOSCHMIEDER.

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