Omnidirectional antennas are used for example as indoor antennas. They are multiband capable and preferably radiate with a vertical polarisation orientation. For this purpose, they may comprise a base or earth plate (reflector), which may for example be disc-shaped and on which a monopole radiator rises transversely and in particular perpendicularly to the base plate. The entire arrangement is generally covered by a protective housing, i.e. an antenna cover (radome).
The present broadband omnidirectional antenna can not only be used within buildings, but for example also in vehicles, in particular rail vehicles or boats.
A generic omnidirectional antenna is known for example from DE 103 59 605 A1. The monopole radiator known from this document rises vertically above a base plate, from which it is galvanically isolated. The antenna known from this document comprises a vertically polarised monopole radiator. In this case, the vertically polarised radiator is in particular in the shape of a hollow cylinder or hollow cone and extends away from the base plate.
The omnidirectional antenna from DE 103 59 605 A1 is disadvantageous in that the lower limiting frequency is limited by the specified overall height and the specified diameter.
The example non-limiting technology provides a broadband omnidirectional antenna which can be produced so as to be as simple, cost-effective and compact as possible, and which at the same time covers a wider frequency spectrum.
This is achieved by means of a broadband omnidirectional antenna as described herein.
A broadband omnidirectional antenna comprises a first radiator that is arranged on a base plate, which base plate is preferably also used as a reflector, and that has a longitudinal axis which extends at least approximately, predominantly or completely perpendicularly to the base plate. In that case, the first radiator extends from the base plate away therefrom. The first radiator has a first end comprising a foot and/or feed-in point and a second end which is opposite the first end. The first end, i.e. the foot and/or feed-in point, of the first radiator is in this case galvanically isolated from the base plate, but is arranged closer to the base plate than the second end. The first radiator also comprises radiator surfaces which originate in the region of the first end and extend towards the second end. A distance between the radiator surfaces and the longitudinal axis increases at least in portions from the first end towards the second end. This means that the radiator surfaces diverge from one another along the longitudinal axis at least over a partial length. Furthermore, the omnidirectional antenna comprises a second radiator which comprises at least one radiator surface. The second radiator is arranged on the first radiator so as to be galvanically isolated therefrom and can be fed preferably exclusively or predominantly by the first radiator. In one embodiment, the radiator surfaces of the second radiator are arranged in relation to the radiator surfaces of the first radiator such that they can act as a continuation thereof. This means that the second radiator is a continuation of the first radiator. In this case, the radiator surfaces of the second radiator can be inclined at least in portions or can only extend in parallel with the longitudinal axis. They are spaced further apart from the base plate than the radiator surfaces of the first radiator. Alternatively, i.e. in another embodiment, it would also be possible for the at least one radiator surface of the second radiator to be arranged in the region of the second end of the first radiator, in particular between the radiator surfaces of the first radiator, i.e. within said radiator, so as to be in parallel with the base plate or such that one of the components thereof is predominantly parallel to said base plate.
It is particularly advantageous for the second radiator to be fed exclusively or predominantly by the first radiator. In this case, a separate feed line for the second radiator is not required or provided. In this case, it is advantageous for the second radiator to be a continuation of the first radiator, the two radiators being galvanically isolated from one another. This increases the band width that can be produced and keeps the production costs low.
In an advantageous embodiment of the broadband omnidirectional antenna, a feed device is arranged at the foot and/or feed-in point. In this case, the feed device extends towards the base plate and preferably passes therethrough. A connector element, in particular in the form of a socket, is arranged on a bottom side of the base plate, which side is opposite the assembly side comprising the received first and second radiators. A feed cable can be or is connected to said connector element. The feed device preferably extends, at least by its first end, into the connector element, it being possible for electrical contact to be established, or said electrical contact being established, at least indirectly (via an additional conductor) or directly, between the first end of the feed device and an internal conductor of the feed cable. In this case, the feed device is galvanically isolated from the base plate. Depending on the embodiment of the broadband omnidirectional antenna, the feed device is galvanically, but preferably in a solder-free manner, connected to the first radiator at the foot and/or feed-in point. The feed device could also be capacitively coupled to the first radiator at the foot and/or feed-in point, the feed device extending towards the second end of the radiator surfaces of the first radiator at least in part along the longitudinal axis or such that one of its components is predominantly in parallel with the longitudinal axis.
In this case, it is particularly advantageous for the foot and/or feed-in point of the first radiator to have a sleeve-shaped or hollow cylindrical extension towards the second end of the first radiator. The feed device is arranged in the sleeve-shaped extension at least over a partial length thereof, the feed device and the sleeve-shaped extension being galvanically isolated from one another. The sleeve-shaped extension can extend as far as the second end of the first radiator or beyond the second end of the first radiator. Depending on the use, the first radiator can thus be fed capacitively or inductively.
In a particularly preferred embodiment, the first radiator has, along its longitudinal axis and over its entire length or a partial length thereof, a progression that is in part or predominantly or completely conical or funnel-shaped. The second radiator comprises a predominantly or preferably completely peripheral radiator surface, a diameter or circumference of the peripheral radiator surface of the second radiator at the first end thereof being adapted to a diameter or circumference of the second end of the first radiator.
Adaptation of this kind is preferably achieved by the diameter or circumference at the first end of the second radiator deviating from the diameter or circumference at the second end of the first radiator by less than 20%, 15%, 10%, 8%, 5% or 3%. It is particularly advantageous for the diameter or circumference at the first end of the second radiator to be slightly larger than the diameter or circumference at the second end of the first radiator. “Slightly larger” should be understood to mean larger by a small number of millimeters, in particular by less than 8 mm, 6 mm, 4 mm or 2 mm, but preferably by more than 1 mm, 3 mm, 5 mm, 7 mm or 9 mm.
In the context of another embodiment, the diameter of the second radiator remains constant along the longitudinal axis or decreases in the direction of the longitudinal axis from the first end towards the second end. This is particularly advantageous in that the omnidirectional antenna can be constructed so as to be compact.
In another preferred embodiment of the omnidirectional antenna, the second radiator comprises one or more slots, which extend from the second end thereof, which is opposite the first end, towards said first end and terminate at a distance therefrom. In this case, the width of these slots can be constant or decrease towards the first end. In principle, the first slots could also extend from the first end towards the second end and terminate at a distance from the second end.
So that the first radiator and the second radiator are permanently oriented relative to one another in a precisely defined position, in a particularly preferred embodiment of the omnidirectional antenna, a (dielectric) holding and/or spacing element is used which is arranged at least in part within the first radiator and is non-rotatably fastened thereto. The holding and/or spacing element is preferably also non-rotatably fastened to the second radiator, the holding and/or spacing element being designed such that a gap (along the longitudinal axis) between the first end of the second radiator and the second end of the first radiator has an adjustable width. The first radiator and the second radiator are therefore arranged in relation to one another such that they do not overlap. The holding and/or spacing element therefore performs a number of functions. Firstly, the holding and/or spacing element prevents the first radiator and the second radiator from rotating relative to one another over time. Furthermore, said element ensures that the first radiator and the second radiator are galvanically isolated from one another. The gap, which is adjusted between the first radiator and the second radiator by the holding and/or spacing element, is preferably larger than 0.1 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm, 12 mm, 15 mm, 17 mm, 20 mm, 30 mm, 40 mm or 50 mm, and is preferably smaller than 40 mm, 30 mm, 20 mm, 18 mm, 16 mm, 13 mm, 11 mm, 9 mm, 8 mm, 6 mm, 3 mm or 1 mm.
In another preferred embodiment, the first radiator comprises n radiator surfaces, where n≥2. In this case, the n radiator surfaces are galvanically interconnected or formed in one piece with one another at the first end of the first radiator, the radiator surfaces being arranged around the longitudinal axis of the first radiator so as to be offset from one another, thus forming slots between adjacent radiator surfaces, and the slots beginning at a distance from the first end of the first radiator and extending as far as the second end of the first radiator. In this case, at least part of the at least one radiator surface of the second radiator is arranged at the second end of the first radiator, between the radiator surfaces of the first radiator, so as to be in parallel with the base plate or such that one of the components thereof is predominantly in parallel with said plate. What is particularly advantageous here is that a radiator arrangement of this kind can be produced in a very simple manner, for example from sheet metal parts. An omnidirectional antenna of this kind has a very low overall height, but still operates at a wide range of frequencies.
In another embodiment, the radiator surfaces of the first radiator comprise a plurality of radiator partial surfaces which are oriented at an angle to one another. The same can also apply to the at least one radiator surface of the second radiator.
In this case, the radiator surfaces of the first radiator and second radiator are preferably free of curves (except for the bending edge) and are each arranged in a separate plane. In this case, the first radiator and/or the second radiator can be produced from a metal sheet in a cutting, stamping and/or bending process.
In a particularly preferred embodiment of the omnidirectional antenna, said antenna comprises a coupling device. The coupling device is used in order for it to be possible for the lower limiting frequency at which the omnidirectional antenna can be operated to be reduced further. For this purpose, the coupling device comprises one or more coupling projections, a first end of the coupling projection or coupling projections being galvanically connected to the radiator surface of the second radiator and extending towards the base plate. The coupling projection or coupling projections is/are spaced further apart from the longitudinal axis than the radiator surfaces of the first radiator and second radiator. This means that the coupling projection or coupling projections extend towards the base plate outside of the first radiator and second radiator. At least one coupling surface is formed or integrally formed on a second end of the coupling projection or coupling projections that is opposite the first end and is therefore arranged closer to the base plate than said first end, which coupling surface is galvanically connected to the relevant coupling projection. The at least one coupling surface extends in parallel with the base plate or such that one of the components thereof is (predominantly) in parallel with said plate. Owing to coupling of this kind that is relative to the base plate, the lower limiting frequency can be reduced further. In this case, it is possible for the omnidirectional antenna to be operated in a frequency range of 600 MHz to 6 GHz. Said antenna is preferably operated in a frequency range of 650 MHz or 698 MHz to 6 GHz. Depending on the size and dimensions of the feed point, inter alia, it is also possible for the frequency range to be widened at the upper and/or lower limit.
In another embodiment of the omnidirectional antenna, the at least one coupling surface is galvanically connected to the base plate or is arranged at a distance therefrom such that the at least one coupling surface is capacitively coupled to the base plate. The distance between the coupling surface and the base plate and the size of the coupling surface can be varied as desired, depending on the use. The coupling surface can be arranged so as to be in parallel with the base plate. It can also be arranged obliquely or designed so as to be uneven (e.g. undulating).
In this case, an additional dielectric can be arranged between the at least one coupling surface and the base plate, for example, on which dielectric the at least one coupling surface rests or is supported. As a result, the coupling can again be adjusted more accurately and the stability of the omnidirectional antenna as a whole can be increased.
In another preferred embodiment, the plurality of coupling projections are galvanically connected to a common coupling surface by means of the second end thereof, the coupling surface being in the form of a common coupling frame which defines a receiving space in which part of the first radiator is arranged. In principle, the common coupling frame can be of any shape. In particular, the cross section thereof may be rectangular, square, circular or oval.
In order to further increase the stability of the omnidirectional antenna and further increase weather resistance, in another embodiment, said antenna comprises a covering hood. Preferably, one single covering hood is used, which is connected to the base plate in an interlocking and/or frictional and optionally moisture-tight manner, and surrounds the first radiator and second radiator. In this case, the covering hood is preferably arranged such that it is not in contact with the first radiator and the second radiator.