Dual-polarized dipole antenna

Details Dual-polarized dipole antenna Dual-polarized dipole antenna

2000-08-23

2001-11-06

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Balanced doublet - centerfed

C343S816000

Reexamination Certificate

active

06313809

ABSTRACT:

The invention relates to a dual-polarized dipole radiator according to the preamble of claim
1
.
It is known that two orthogonal polarizations can be emitted or received by means of dual-polarized antennas. If the two systems are connected up appropriately, they can also be used to emit or receive any other desired combinations of the linear orthogonal polarizations such as, for example, a circular polarization.
Dual polarized antennas normally have dipole radiators, patch radiators or slot radiators as primary radiators. With dipole radiators, it is essentially the dipole square, comprising four individual dipoles, and a turnstile dipole arrangement which are included as structures. The said radiators can thereby be operated both horizontally and vertically, as well as with a polarization alignment at an angle of ±45°. In this case, one also speaks, for example, of an X-polarized antenna, as is known in principle from DE 1296 27 015.
There are problems with such types of dual-polarized antennas when, for example, the aim is to implement half-widths of less than approximately 75° in conjunction with a compact antenna design. In this case, it is possible to implement dual-polarized antennas virtually only by means of dipole squares and/or by using very wide reflectors. This is associated with a not inconsiderable wiring outlay. Thus, for example four cables have to be used for feeding the dipoles. The large antenna dimensions are also disadvantageous, however, particularly owing to the wide reflectors which are required.
A further disadvantage consists, in particular in the case of ±45°-polarized dipole antennas, in that there is a relatively high coupling in the case of an array arrangement comprising dipole squares. This relatively high coupling has a disturbing effect, particularly in the case of antennas with a tunable phase relationship of the dipoles (adjustable electric downtilt).
A further embodiment of dual-polarized radiators has been disclosed, for example, in EP 0 685 900 A1. This is a slot radiator which can be appropriately excited. However, the limiting dimensioning of the slot/feed coupling required in this case renders it possible to implement small half-widths only by means of correspondingly large reflectors even in the case of this known prior art.
Starting from the prior art mentioned at the beginning, it is therefore the object of the present invention to create a dual-polarized dipole radiator which is of simple design and, in particular, has an improved decoupling even in the case of an array design when use is made of a plurality of dual-polarized radiator modules.
The dual-polarized dipole radiators according to the invention are of simpler design by comparison with conventional solutions, with the result that the dipole radiators according to the invention can be produced more cost-effectively, for one thing.
However, they also exhibit a completely surprisingly structure which differs from conventional solutions which yield improved values for decoupling, chiefly in the implementation of an antenna array.
What is surprising is that the dual-polarized dipole radiators according to the invention act electrically like a turnstile dipole, but more resemble a dipole square in terms of mechanical design.
It is furthermore surprising that, given dipole components which are aligned horizontally and vertically, the antenna module which more resembles a dipole square in terms of its spatial design results electrically in an X-polarized antenna module, in other words an antenna radiating electrically at ±45°.
If, by contrast, the antenna is to radiate or receive in a polarized fashion in the horizontal and/or vertical direction, that is to say the turnstile dipole is to be aligned electrically with its electric dipole axes in the horizontal and vertical directions, it would be necessary for the module, which more resembles a dipole square in terms of design, to be aligned with the individual dipole components in a ±45° direction.
The invention provides for this purpose that each of the four dipoles is fed by a symmetrical line, and that owing to the special type of interconnection the mutually orthogonal adjacent dipole halves of two adjacent dipoles are respectively excited in phase. These symmetrical or at least essentially or approximately symmetrical feed lines comprise two line halves which, viewed individually, constitute an asymmetric line with respect to a fictitious zero potential. The interconnection of the asymmetric line halves is performed according to the invention in such a way that the two line halves leading to two adjacent dipole halves aligned in a mutually orthogonal fashion are electrically interconnected in each case. The feeding of the resulting overall radiator is performed in this case in a crosswise fashion. That is to say, the two connected line halves, respectively mentioned above, of two mutually perpendicular dipole halves are respectively electrically interconnected in a crosswise fashion with the two line halves of the diametrically opposite adjacent and mutually orthogonal dipole halves, preferably in a crosswise fashion. The overall radiator therefore acts electrically rather like a turnstile dipole, the lines proceeding from the middle not also radiating, or doing so only negligibly owing to their special design. It is possible to this extent to interpret the respectively mutually orthogonal adjacent dipole halves, which are excited in phase, after all, as part of a resulting turnstile dipole. For this reason, the radiator designed according to the invention is also designated as a resulting turnstile dipole. It is not completely surprising that a wideband high decoupling is achieved between the feed points in the first polarization and in the second polarization, which is orthogonal thereto.
The abovementioned symmetrical feed lines connected to the respective dipole halves are preferably of symmetrical design, resulting in the preferred symmetrical line arrangement since, as mentioned, the associated line halves are arranged per se asymmetrically relative to one another with respect to a zero potential and are fed in antiphase. The advantages according to the invention are, of course, still achieved in this case whenever the symmetrical feed line is not 100% symmetrical, but deviates therefrom, the degree of decoupling decreasing with increasingly stronger deviation from the symmetrical design of the feed lines.
In a preferred embodiment of the invention, the respective line half, leading to the dipole, of the symmetrical feed line is constructed as a mechanical holder of the dipole halves, and said holder is situated or terminates preferably at the same distance above the reflector at which the dipole itself is fitted above the reflector. This line can therefore also be interpreted as part of the resulting turnstile dipole, but owing to the antiphase currents on the line halves said line does not radiate, or does so only slightly. This results, therefore, in the desired elimination of the radiation activity and thus in a better focusing of the dipoles. Consequently, it is completely surprising that the corresponding connecting-up in a crosswise fashion at the feed point then results, on the one hand, in emission of the polarization lying in a ±45° plane and, on the other hand, in a wideband high decoupling.
The symmetrical feed lines are preferably arranged with their in each case two asymmetric line halves such that in a top view of a radiator arrangement said line halves proceed from a balun situated approximately in the middle and lead to the respective two connecting points of two dipole halves situated in an axial extension with respect to one another. These feed lines can, however, also be arranged in a fashion running completely differently. For example, it is also possible to lead these line halves of the symmetrical feed line from the rear side of a reflector plate through the latter, the line halves leading, for example, approximately perpendicular to the plane of the reflector

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