Dual polarized multi-range antenna

A dual-polarized multiband antenna includes first and second radiating element modules having first and second dipole elements. First dipole elements are positioned at right angles to one another to transmit and/or receive radiation in the first frequency band range with two linear orthogonal polarizations. The dipole elements form a dipole square. The second radiating element module transmits or receives radiation in a second frequency band range higher than the first frequency band range. The second module has dipole elements orthogonally related to one another and aligned parallel or at right angles to the first dipoled elements. The second dipoles are arranged in a cruciform.

BACKGROUND OF THE INVENTION
 The invention relates to a dual-polarized multiband antenna.
 Dual-polarized multiband antennas are used for transmitting (or receiving)
 two linear polarizations which are aligned at right angles to one another
 and may be aligned, for example, vertically and horizontally. However, in
 practice those operational cases in which the polarizations are aligned at
 +45.degree. and -45.degree. to the vertical (or to the horizontal) are
 also of particular importance. In the case of dual-polarized multiband
 antennas, said antennas are operated in at least two frequency bands, as a
 rule with two mid-frequencies which are well apart from one another. In
 this case, the upper mid-frequency should be at least 1.5 times the lower
 mid-frequency.
 With such a large frequency separation, two antenna modules or antenna
 arrays arranged physically separately from one another are normally used,
 namely for transmitting and receiving in the one frequency band range and
 for transmitting and receiving in the other frequency band range
 (frequency band).
 Dual-polarized antennas as such are known. They are used for simultaneously
 transmitting or receiving two orthogonal polarizations. In this case, such
 radiating element arrangements may comprise, for example, a plurality of
 elements in the form of dipoles, slots, planar radiating elements or
 so-called patch radiating elements, as are known, for example, from EP 0
 685 900 A1 or from the prior publication "Antennen [Antennas], Part 2,
 Bibliographical Institute, Mannheim/Vienna/Zurich, 1970, pages 47 to 50".
 Dipoles arranged in a cruciform shape (cruciform dipoles) or double-dipole
 arrangements which have a square structure in plan view (dipole square)
 are preferably used for the dipole arrangements.
 Dual-polarized antennas are furthermore also known, for example, from WO
 98/01923.
 Dual-polarized antennas are likewise known from the publication
 "Dual-Frequency Patch Antennas", IEEE AP Magazine, page 13 et seq. This
 document describes dual-polarized multiband antennas which use different
 patch structures, but have a series of disadvantages. For example
 inadequate decoupling for both polarizations is thus typical. The
 described designs allow only one horizontal/vertical position alignment.
 For example, it is impossible with simple means to produce a multiple
 array arrangement with a +45.degree./-45.degree. alignment.
 Further antenna forms which have become known once again use two antennas
 arranged separately one above the other for the respective frequency
 range.
 Finally, for example, a microstrip antenna is known from DE-A1 362 079,
 which is suitable for transmission in two frequency ranges, but with only
 one polarization. This antenna arrangement not only has a low gain, but it
 has also been found to be disadvantageous that the polar diagrams which
 can be achieved with such an antenna cannot be used for array antennas.
 In contrast, the object of the present invention is to provide a
 dual-polarized multiband antenna, in particular a so-called X-polarized
 multiband antenna, which avoids the disadvantages mentioned above. This
 antenna is thus intended to be operable in at least two frequency ranges,
 which are preferably well apart from one another. Furthermore, it is
 preferably intended to have a high level of decoupling between the two
 polarizations.
 The object is achieved according to the invention in accordance with the
 features specified in
 Claim 1 and Claim 2. Advantageous refinements of the invention are
 specified in the dependent claims.
 The dual-polarized multiband antenna according to the invention has
 previously unimagined advantages and features. These advantages relate not
 only to the decoupling, the bandwidth and the sensitivity, but also to the
 flexibility of the antenna. The antenna according to the invention is
 distinguished by the fact that it has at least one radiating element
 module in the form of a cruciform dipole and like a dipole square, which
 is located in front of a reflector and which can be operated with dual
 polarization in two alignments positioned at right angles to one another
 which, as a rule, that is to say preferably, assume an alignment of
 +45.degree. and -45.degree. to the vertical or horizontal. This radiating
 element module in the form of a dipole square can be operated in a lower
 frequency range. However, according to the invention, further dipoles are
 now provided for operation in a second upper frequency band with dual
 polarization, with the further dipoles being arranged within the dipole
 square. In addition, the further dipoles are preferably in the form of a
 cruciform dipole. The dipole elements are in this case aligned parallel or
 at right angles to the dipole elements of the dipole square and thus, in
 the case of an X-antenna, likewise have an alignment of +45.degree. and
 -45.degree. to the vertical or horizontal.
 A development of the invention provides that the respective holder for the
 dipoles of the lower frequency range, which at the same time operate as
 so-called balancing, are designed and/or arranged and/or dimensioned such
 that, in consequence, no resonance occurs in the upper frequency range, or
 at least no relevant resonance occurs in the upper frequency range.
 It has furthermore been found to be advantageous if, depending on the
 frequency-dependent wavelength associated with them, the height of the
 dipoles are [sic] arranged such that they are not more than one wavelength
 away from the reflector or the reflector plane. Advantageous values are in
 a range from 1/8 to 1/2 of the respective operating wavelength.
 Above all, it is surprising in the case of the antenna according to the
 invention that, firstly, it has a broad bandwidth and, secondly, at the
 same time has a high level of decoupling between the two polarizations. It
 is also distinguished above all in that, with the antenna according to the
 invention, it is possible to ensure that the horizontal half beamwidths of
 the two radiating element modules are identical or virtually identical,
 that is to say essentially of the same magnitude, in both the lower and
 the upper frequency band ranges.
 The advantages according to the invention can, above all, be achieved even
 when the antenna according to the invention is constructed not only with a
 dipole square and a cruciform dipole arranged in it, but like an antenna
 array with a plurality of such square dipoles, each having further
 internal dipoles, preferably in the form of cruciform dipoles. With this
 embodiment in particular, it is possible to provide a further radiating
 element module for transmission of the upper frequency band between each
 of the two dipole squares for transmitting and receiving the lower
 frequency band.
 However, this further radiating element module is then preferably not in
 the form of a cruciform dipole, but likewise in the form of a dipole
 square.

DETAILED DESCRIPTION OF THE INVENTION
 FIGS. 1 and 2 respectively show a schematic plan view and side view
 parallel to a reflector of a dual-polarized multiband antenna, which
 comprises a first radiating element module 1 for a first frequency range
 and a second radiating element module 3 for a second frequency range.
 The two radiating element modules 1, 3 are arranged in front of a reflector
 5 whose shape is virtually square in the illustrated exemplary embodiment.
 The reflector is conductive. A supply network may be located on the rear
 face of the reflector, via which the first and the second radiating
 element modules are electrically connected, separately. The first
 radiating element module 1 in this case comprises a plurality of dipoles
 1a, namely four dipoles 1a in the illustrated exemplary embodiment, which
 are arranged like a dipole square. The dipoles 1a are mechanically held
 via a so-called balancing device 7 with respect to the reflector or a
 plate located behind it and electrical contact is made with them, that is
 to say they are fed, via the said supply network.
 In the horizontal transmission direction, the reflector plate itself has in
 each case one reflector edge 6, which in the illustrated exemplary
 embodiment projects to a certain height at right angles from the plane of
 reflector plate 5, thus allowing the polar diagram to be influenced in an
 advantageous manner.
 The length of the dipole elements in the first radiating element module is
 matched such that corresponding electromagnetic waves can be transmitted
 or received via it in a lower frequency range. The orthogonal alignment of
 the dipole elements thus results in a dual-polarized antenna in a known
 manner. In the exemplary embodiment, the dipoles 1a are respectively
 aligned at angles of +45.degree. and -45.degree. with respect to the
 vertical (or, equally, with respect to the horizontal), to be precise
 forming an antenna which is also referred to for short as an X-polarized
 antenna.
 The second radiating element module 3 is now located within the first
 radiating element module 1, which is in the form of a dipole square. This
 second radiating element module 3 is not in the form of a dipole square,
 but in the form of a cruciform dipole, in the illustrated exemplary
 embodiment. The two dipoles 3a, which are positioned at right angles to
 one another, are likewise once again mechanically supported with respect
 to the reflector or a plate located behind it, and are electrically fed,
 via the balancing network 9 associated with them.
 This second radiating element module 3 is operated in an upper frequency
 range, with the upper mid-frequency in the illustrated exemplary
 embodiment being approximately twice the lower mid-frequency of the first
 radiating element module 1. This arrangement allows horizontal
 half-beamwidths of about 60.degree. to be produced in the two frequency
 ranges, with high decoupling levels between the different .+-.45.degree.
 polarizations being achieved at the same time. However, a comparable
 arrangement is likewise conceivable which, rather than an X-shaped
 alignment, has a vertical/horizontal alignment, in which the one set of
 dipole elements 1a and 3a are aligned horizontally, and the dipole
 elements which are at right angles are aligned vertically with respect to
 them.
 As is evident from the illustration from the side shown in FIG. 2, it can
 be seen that both the first and the second radiating element modules 1, 3
 are arranged at a distance in front of the reflector 5, to be precise at
 different distances. The height of the dipoles above the reflector should
 be not more than the operating wavelength for the associated operating
 frequency, and preferably not more than half the associated operating
 wavelength. However, the distance is preferably more than 1/16, in
 particular more than 1/8 of the associated operating wavelength.
 Surprisingly, despite the mutually interleaved arrangement of the radiating
 element modules, with the first radiating element module comprising a
 dipole square and the second radiating element module 3 preferably
 comprising a cruciform dipole, the antenna formed in such a way has
 characteristic properties which are outstanding in this way. The fact that
 a similar polar diagram, which would not intrinsically be expected, is
 obtained for the two radiating element modules in the two frequency ranges
 may, possibly, be explained, inter alia, by the dipole elements 1a of the
 first radiating element module acting as reflectors for the second
 radiating element module 3.
 An upgraded dual-polarized multiband antenna is shown in FIG. 4, which
 illustrates an embodiment for higher antenna gain levels.
 To achieve this, a plurality of dipole arrangements, as explained with
 reference to FIGS. 1 to 3, have to be cascaded appropriately. In the
 illustrated exemplary embodiment, the dual-polarized multiband antenna
 formed in this way comprises two antenna arrangements as explained with
 reference to FIGS. 1 to 3, in which the radiating element modules are once
 again aligned in the .+-.45.degree. direction with respect to one another,
 and the fitting directions of the two antenna arrangements shown
 individually in FIG. 1 are arranged one above the other in the vertical
 direction. In the same way, the antenna modules may alternatively be
 assembled to form an antenna array in the horizontal fitting direction.
 Finally, a number of antenna modules may also be cascaded laterally
 alongside one another and one above the other in a number of rows and
 columns.
 The intermediate spaces produced in this way between the respective first
 radiating element modules 1 for the lower frequency range are filled by
 corresponding radiating element arrangements for the upper frequency
 range, that is to say with additional second radiating element modules 3'.
 In other words, in the illustrated exemplary embodiment, two radiating
 element modules 1 and one second radiating element module 3 with dipole
 elements 3b are arranged in front of a reflector plate. The antenna
 produced in this way has a high vertical gain, with the same horizontal
 half-beamwidth of about 60.degree. being achievable for both radiating
 element modules.
 Finally, the exemplary embodiment in FIG. 5 shows that the radiating
 element modules 3 arranged in the first radiating element modules 1 may
 differ from the second radiating element modules 3' which are arranged in
 the spaces 15 between the first dipole squares 1. This is because, as can
 be seen from FIGS. 4 and 5, the additional radiating element module 3
 arranged between two radiating element modules 1 in FIG. 4 comprises a
 cruciform dipole, that is to say a cruciform dipole arrangement, and in
 the embodiment shown in FIG. 5 it comprises a dipole square, that is to
 say, in general, a dipole arrangement 3" similar to a dipole square and
 having dipole elements 3b. This fine adaptation and matching allows the
 half-beamwidths of the radiating element arrangement for the upper and
 lower frequency ranges to be equalized better.