Antenna For Direction Finders With Mast Isolation

Abstract

An antenna device for direction finders wherein a sense determining vertical antenna is provided at the center of two loop antennas arranged so as to rectangularly intersect with each other and a primary winding in a transformer for taking a sense determining output out of its secondary side is connected on both sides respectively with the lower central point of said loop antenna or its shield and the lower end of the vertical antenna without earthing said loop antenna or its shield.

Description

This invention relates to antenna devices for direction finders.

As a sense determining vertical antenna for direction finders, there has been already utilized a loop antenna itself having a directivity or a vertical antenna erected at the center of a loop antenna, connected with a feeder line and having had it shield earthed.

However, in case such antenna device is fitted to the upper end of a supporting pole, when the supporting pole or the feeder line perfectly or substantially tuned with incident waves, a voltage induced by the tuned current will be generated in the sensing antenna and the sense determination will be obstructed. If the sensing antenna is set in a position separated from the upper end of the supporting pole, needless to say, such difficulty will not be produced but it will be impossible to fit the antenna.

An object of the present invention is to provide an antenna device wherein a sense determining vertical antenna is set in a position substantially separate from the upper end of a supporting pole by utilizing loop antennas to prevent the above described troubles.

In the drawings:

FIG. 1 is a side view of a device according to the present invention;

FIG. 2 is a sectioned view on line A--A in FIG. 1;

FIG. 3 is a view showing a wiring in an embodiment of the device according to the present invention;

FIG. 4 is a view showing a wiring in another embodiment;

FIG. 5 is a voltage distribution diagram for explaining the operation of the present invention.

In FIGS. 1 to 3, two loop antennas 3 and 4 fitted respectively with tubular shields 1 and 2 are arranged so as to rectangularly intersect with each other and a sense determining vertical antenna 5 is provided at their center. A hollow antenna base 7 formed of an insulator is provided at the upper end of a supporting pole 6 to fit the above mentioned antennas and shields at the lower ends and to contain transformers 8 and 9 as in FIGS. 3 and 4 within it. By the way, in FIG. 3, the loop antenna 4 and its shield 2 are omitted and only the loop antenna 3 and its shield 2 are shown. However, these loop antennas are connected at the lower ends with the primary of the transformers 8. The secondary winding of the transformer 8 is connected at both ends with feeder line terminals 10, the primary winding of said transformer 9 is connected at both ends respectively with the lower central point of the shield and the lower end of the vertical antenna 5 and the secondary winding of said transformer 9 is connected at both ends with feeder line terminals 11 and none of the loop antennas and their shields is earthed.

Further, in FIG. 4, the primary winding of the transformer 9 is connected at both ends respectively with the neutral point of the primary winding of the transformer 8 connected with the loop antenna 3 at the lower end and with the lower end of the vertical antenna 5. In this drawing, too, the same as in FIG. 3, the loop antenna 2 is omitted. However, the primary winding of the transformer inserted between both ends of the loop antenna is connected at the neutral point with the neutral point of the primary winding of the above mentioned transformer 8.

As in the above described embodiment, in the present invention, the primary winding of the transformer 9 for obtaining a sense determining antenna output is inserted between the lower end of the sense determining vertical antenna prlvided at the center of the loop antenna or its shield and the lower central point of the above mentioned loop antenna or its shield without earthing the loop antenna itself or its shield.

Therefore, if the effective height of the vertical antenna is h.sub.1, the effective height of the loop antenna or its shield as a vertical antenna is h.sub.2 and the electrostatic capacitance between the vertical antenna 5 and the shields 1 and 2 or the loop antennas 3 and 4 is C, the electric current flowing through the primary winding of the transformer 9 will be proportional to 2C (h.sub.1 -h.sub.2). Therefore, the output of the above described vertical antenna 5 will be equal to the output of a vertical antenna of an effective height of (h.sub.1 -h.sub.2). That is to say, the voltage induced by incident waves in the part enclosed with the loop antennas in the vertical antenna 5 will be canceled with the voltage induced in said loop antennas or their shields. Therefore, only the part projecting above the loop antennas will operate effectively. Thus, substantially the same effect as in the case of setting only the vertical antenna of the part projecting above the loop antennas as separated from the upper end of the supporting pole 6 will be obtained and the influence of tuning of said pole will be reduced. That is to say, FIG. 5 shows this operation with a voltage distribution diagram. FIG. 5A is a side view of an antenna device of the present invention. In such device, when the supporting pole 6 tunes with incident waves, the distribution of the voltage induced in said supporting pole will be shown by the broken line 12 in FIG. 5B. Therefore, the equipotential lines by said voltage will be of such forms as of the broken lines 13 and the density will reduce with the deviation from the point 14 corresponding to the upper end of the supporting pole.

As described above, the present invention is a simple structure wherein a transformer for taking out a sensing antenna output is only inserted between the lower central point of a loop antenna or its shield and the lower end of a vertical antenna without earthing the loop antenna or its shield so that the vertical antenna may be effectively separated from the upper end of the supporting pole. Therefore, even in case the supporting pole or feeder line tunes with incident waves, the influence of the induced voltage will be reduced and the sense will be able to be accurately determined.

Claims

What is claimed is:

1. An antenna device for direction finders comprising a loop means formed of two loop antennas arranged so as to rectangularly intersect with each other and shields fitted respectively with said antennas, a sense determining vertical antenna provided at the center of said loop means, a hollow insulated base fitted with said loop means at the lower end and a transformer provided within said base so as to take a sense determining output out of its secondary side, the primary winding in said transformer being connected on both sides respectively with the lower central point of said loop means and the lower side of said vertical antenna, all the above mentioned composing members being not earthed.