# Patent

## Title
Printed circuit board arrangement for supplying antennas via a three-conductor system for exciting different polarizations

## Abstract

The printed-circuit board arrangement is used for the electrical connection of an amplifier unit to at least two antenna elements, whereas the at least two antenna elements are embodied on the printed-circuit board arrangement. The antenna elements are coupled via a three-line system to the amplifier unit, where the three-line system comprises three strip lines mounted on the printed-circuit board arrangement extending parallel to one another.

## Background
The invention relates to a printed-circuit board arrangement with at least one amplifier unit and at least two antenna elements, which are fed via a three-line system and preferably operate in the frequency range of millimeter waves. In particular, the arrangement is suitable for use in antenna arrays with several hundred or thousand antennas, which are capable of radiating different, mutually orthogonal polarisations.
Printed-circuit board arrangements which are used in the named context serve to connect different antenna elements to the corresponding amplifier unit. In this context, the printed-circuit board arrangements should be designed so that the overall system can be constructed to be as compact as possible and the space requirement respectively the associated costs can be reduced to a minimum.
“Dual Aperture-Coupled Microstrip Antenna for Dual or Circular Polarisation”, A. Adrian and D. H. Schaubert, Electronic Letters, 5, Nov. 1987, Volume 23, No. 23, pages 1226-1228 describes a printed-circuit board arrangement on which antenna elements are arranged which excite a patch in order to radiate orthogonal linear polarisations or orthogonal circular polarisations. The disadvantage with the above-named publication is that the two microstriplines feeding the antenna elements are arranged perpendicular to one another in order to achieve a maximum mutual decoupling. This leads to an increased space requirement with the associated costs. In the case of circular polarisations, a configuration of the antenna arrangement with a phase-shifting power splitter, for example, a 90° ring hybrid, which further increases the space requirement and the costs, is additionally required.
The object of the invention is therefore to provide a printed-circuit board arrangement which is constructed in a more compact manner and is therefore more favourable in manufacture and equally suitable for frequencies in the millimeter-wave range. In particular, the invention is suitable for use in antenna arrays with several hundred or thousand antennas, which are capable of transmitting mutually different orthogonal polarisations.
This object is achieved with regard to the printed-circuit board arrangement by the features of claim 1. The dependent claims specify advantageous further developments of the printed-circuit board arrangement according to the invention.
The printed-circuit board arrangement according to the invention is used for the electrical connection of an amplifier unit to at least two antenna elements, where the at least two antenna elements are embodied on the printed-circuit board arrangement. The at least two antenna elements are accordingly coupled to the amplifier unit via a three-line system, where the three-line system comprises three strip lines extending parallel to one another mounted on the printed-circuit board arrangement or introduced into the printed-circuit board arrangement.
It is particularly advantageous that the printed-circuit board arrangement comprises at least two antenna elements, because a horizontal and a vertical polarisation, and also a left-hand or respectively right-hand circular polarisation are possible in this case. Moreover, it is particularly advantageous that the at least two antenna elements are coupled to the amplifier unit by means of a three-line system. In fact, such a three-line system which comprises three strip lines extending parallel to one another and can guide two mutually orthogonal modes allows a very compact structure of the overall printed-circuit board arrangement.
Furthermore, an advantage is achieved with the printed-circuit board arrangement according to the invention if the at least two antenna elements are slot antennas, and if each slot antenna is formed respectively by an aperture on a second metal layer of the printed-circuit board arrangement, and/or if the two apertures continue from the antenna elements in the direction towards the amplifier unit and accordingly separate the three strip lines extending parallel to one another electrically from one another. This allows a very compact structure, whereas the three-line system excites the two antenna elements embodied as slot antennas in an advantageous manner.
Furthermore, an advantage is achieved with the printed-circuit board arrangement according to the invention if the part of the first aperture which forms the first antenna element is preferably arranged orthogonally to the part of the second aperture which forms the second antenna element, so that the first antenna element is orientated orthogonally to the second antenna element, and/or if the first antenna element has the same shape and the same length as the second antenna element. As a result of the fact that the two antenna elements are preferably orientated orthogonally to one another, it is possible to excite them with a horizontal polarisation or a vertical polarisation or a left-hand circular respectively a right-hand circular polarisation.
Additionally, an advantage is achieved with the printed-circuit board arrangement according to the invention, if a plurality of via holes is arranged in a circular ring and encloses the two antenna elements, whereas the circular ring comprising the plurality of via holes provides no via holes in the direction towards the three-line system. In this context, the plurality of via holes ensures that the electromagnetic field transmitted from the two antenna elements is not coupled into other strip lines or components in the printed-circuit board arrangement.
Additionally, an advantage is achieved with the printed-circuit board arrangement according to the invention if a first patch is embodied on a third metal layer which is arranged above the two antenna elements, or if a first patch is embodied on a first metal layer which is arranged below the two antenna elements, whereas the first patch is isolated by apertures within the first metal layer from the latter.
In the context of this application, a patch is understood to mean a metallised area which is limited in its dimensions and which is resonant within the given arrangement for the desired frequency range.
A further advantage of the printed-circuit board arrangement according to the invention is achieved if the first patch has the shape of a rhombus or preferably a square, where a first edge of the first patch extends parallel to a first antenna element and where a second edge of the first patch, which is adjacent to the first edge of the first patch, extends parallel to a second antenna element. This embodiment of the first patch means that the electromagnetic wave can be radiated in an optimum manner.
Furthermore, an advantage is achieved with the printed-circuit board arrangement according to the invention if a second patch is arranged above the first patch which is arranged above the at least two antenna elements, where the two patches are separated respectively from each other and from the at least two antenna elements by a dielectric. The use of a second patch increases the useful bandwidth.
Additionally, an advantage is achieved with the printed-circuit board arrangement according to the invention if an enclosed metal layer which acts as a reflector is present above or below the at least two antenna elements opposite to the patch. As a result, the directivity of the antenna arrangement can be improved.
Moreover, an advantage is achieved with the printed-circuit board arrangement according to the invention if a recess is embodied in the first substrate of the printed-circuit board arrangement which carries the three-line system, and if the amplifier unit is inserted into this recess. In this case, the connections between the amplifier unit and the three-line system can be kept as short as possible, whereby minimising any reflections occurring.
Additionally, an advantage is achieved with the printed-circuit board arrangement according to the invention if the amplifier unit is capable of applying a signal respectively to the two outer lines with the middle line as the common line of the three-line system, in such a manner that the two antenna elements together with the first patch and optionally with the second patch generate an electromagnetic field with a horizontal polarisation or a vertical polarisation or a left-hand circular respectively right-hand circular polarisation.
Finally, an advantage is achieved with the printed-circuit board arrangement according to the invention if the at least two antenna elements are embodied on the printed-circuit board arrangement and orientated orthogonally to one another. In this context, the two antenna elements need not necessarily be orientated exactly orthogonally to one another. Moreover, deviations from a 90°-angle are also permissible.



Various exemplary embodiments of the invention are described by way of example below with reference to the drawings. The same subject matters provide the same reference numbers. The corresponding figures in the drawings show in detail:
FIG. 1A an antenna of an exemplary embodiment with two ports, which is excited by an MMIC amplifier unit via a three-line system and radiates an electromagnetic field with a horizontal or vertical polarisation;
FIG. 1B an antenna of an exemplary embodiment with two ports, which is excited by an MMIC amplifier unit via a three-line system and radiates an electromagnetic field with a left-hand circular respectively right-hand circular polarisation;
FIG. 1C a sample exemplary structure of an MMIC amplifier unit for the excitation of an antenna for a horizontal or vertical or left-hand circular respectively right-hand circular polarisation;
FIG. 2A an exemplary embodiment of the printed-circuit board arrangement according to the invention, which comprises two antenna elements which are fed by a three-line system, and a first patch;
FIG. 2B a further exemplary embodiment of the printed-circuit board arrangement according to the invention, which comprises two antenna elements which are fed by a three-line system, and two patches;
FIG. 2C a further exemplary embodiment of the printed-circuit board arrangement according to the invention, which comprises two antenna elements which are fed by a three-line system, and a first patch radiating downwards;
FIG. 3A a plan view of the first and second metal layer of the printed-circuit board arrangement according to the invention;
FIG. 3B a further plan view of the first, second and third metal layer of an exemplary embodiment of the printed-circuit board arrangement according to the invention;
FIG. 3C a further plan view of the first, second, third and fourth metal layer of an exemplary embodiment of the printed-circuit board arrangement according to the invention;
FIG. 4A a further plan view of the first, second, third and fourth metal layer of the printed-circuit board arrangement according to the invention, explaining the functionality of the first patch in the case of a vertical or horizontal polarisation; and
FIG. 4B a further plan view of the first, second, third and fourth metal layer of an exemplary embodiment of the printed-circuit board arrangement according to the invention, explaining the functionality of the patch in the case of a left-hand circular respectively right-hand circular polarisation.



FIG. 1A shows an antenna with two ports which is excited by an amplifier unit 1 via a three-line system 2 with a horizontal or vertical polarisation. The amplifier unit 1 is preferably an MMIC amplifier unit 1 (English: Monolithic Microwave Integrated Circuit; German: monolithischer Mikrowellenschaltkreis). The three-line system 2 preferably comprises three parallel lines, whereas voltages, which can differ in modulus and phase, are guided along the two lines 31, 32. In this context, the third line 33 serves as a reference ground and is also referred to as the middle line 33 and is used as a common line for the two lines 31, 32.
FIG. 1A shows that a first line 31 of the three-line system 2 is connected to the connecting port 1 of the antenna 4. A second line 32 connects the amplifier unit to the second connecting port of the antenna 4. The third line 33 is a ground line, which is also guided to the antenna 4. It is also evident that the antenna 4 in FIG. 1A radiates both a horizontal polarisation and also a vertical polarisation. In this context, the drawn-through arrows in FIG. 1A indicate two voltages which in fact have the same amplitude U, but their phase differs by 180°. As will be explained in detail below, with a line definition of this kind, the antenna 4 radiates a vertically polarised electromagnetic field. In the inverse case, which is marked with the dashed arrow, voltages which are identical in their amplitude and also their phase angle are fed to the antenna 4. The antenna 4 then radiates a horizontally polarised electromagnetic field.
However, it must also be stated that the respective polarisation is ultimately obtained exclusively from the arrangement of the excitation structures in the antenna 4 and from the arrangement of the antenna 4 in the reference system itself.
As will be explained in detail below, the structures of the antenna 4 and also the amplifier unit 1 illustrated in FIGS. 1A to 1C are imaged in their entirety on the printed-circuit board arrangement 5 according to the invention.
FIG. 1B shows an antenna 4 with two ports, which is excited by an amplifier unit 1 via a three-line system 2 with a circular polarisation. With regard to the structure, reference is made to the description for FIG. 1A. In FIG. 1B also, a voltage is applied to the first line 31 and the second line 32, which form the two outer lines of the three-line system 2. In this context, the amplitude of these two voltages generated by the amplifier unit 1 is identical. However, the phase of the voltage applied to the first line 31 is shifted by −90° in comparison to the phase of the voltage applied to the second line 32. In this case, the antenna 4 radiates a left-hand circular polarised electromagnetic field. This fact is indicated by the dashed arrows in FIG. 1B.
It is also possible for the voltage on the first line 31 to be shifted by +90° in comparison to the voltage on the second line 32. In this case, the antenna 4 radiates a right-hand circular polarised electromagnetic field. This fact is illustrated in FIG. 1B by the drawn-through arrows. Which phase displacement produces which circular polarisation here also ultimately depends upon the arrangement of the structures within the antenna 4 and the arrangement of the antenna 4 in the reference system itself. However, it must be stated that, with identical amplitude and a phase shift of −90° or a phase shift of +90°, an electromagnetic field which exhibits either a left-hand circular or a right-hand circular polarisation is radiated by the antenna 4.
Furthermore, the application case according to which a difference in the amplitude and also in the phase is present in the voltages on the first line 31 and the second line 32 is not illustrated. In this case, the antenna 4 radiates an electromagnetic field which exhibits either a left-hand or right-hand elliptical polarisation.
As a result of the fact that the amplifier unit 1 can generate voltages which provide a different phase angle and/or a different amplitude, and that these different voltages can be fed to the antenna 4 on the first line 31 and the second line 32 with the line 33 as a reference ground, electromagnetic waves which have a different polarisation are generated. As already explained, it is particularly advantageous if the amplifier unit 1 is constructed according to the MMIC principle, because as a result, the phase adjustment and/or amplitude adjustment can be manufactured via a three-line system 2 with a small space requirement and in a cost favourable manner, for example, in SiGe technology.
FIG. 1C shows an exemplary structure of an amplifier unit 1 for the excitation of an antenna 4 with horizontal or vertical or circular or elliptical polarisation. The amplifier unit 1 provides five connecting ports at the output end, which are embodied as bonding pads (pads) 61, 62, 63, 64, and 65. In this context, the pads 61, 63, and 65 are connected to ground, whereas different voltages are connected to the pads 62 and 64. As illustrated in detail below, the first line 31 is connected by means of a bonding process via bonding wires to the pad 62. The second line 32 is connected to the pad 64. The third line 33 is connected to the pad 63. A high-frequency signal to be amplified is supplied within the amplifier unit 1 to a 3-dB coupler 7. This 3-dB coupler splits the applied input signal into two output signals, which have the same amplitude and the same phasing. The first output signal is amplified via a first high-frequency amplifier 81, whereas a second output signal is amplified via a second high-frequency amplifier 82.
As illustrated in FIG. 1C, the gain factor of the first high-frequency amplifier 81 can be freely adjusted. The same applies for the gain factor of the second high-frequency amplifier 82. The amplified output signal of the first high-frequency amplifier 81 is supplied to a first phase shifter 91. The output of the first phase shifter 91 is connected to the second pad 62, which, in turn, is connected to the first line 31. The output signal of the second high-frequency amplifier 82 is applied to the input of a second phase shifter 92. The output of the second phase shifter 92 is connected to the fourth pad 64, which in turn is connected, to the second line 32.
The phase of the high-frequency signal to be amplified can be adjusted arbitrarily via the first phase shifter 91 and the second phase shifter 92. By preference, phase shifts of 0°, −90°, 90° and 180° are adjusted. The first phase shifter 91 and the second phase shifter 92 can be made up, for example, from capacitors and inductances, by means of which the phase shift is adjustable. Accordingly, horizontal and vertical polarisations can be achieved. Similarly, left-hand circular and right-hand circular polarisations can be achieved. An elliptical polarisation can be additionally achieved by varying the amplitude of the signal to be amplified by means of the first high-frequency amplifier 81 and the second high-frequency amplifier 82. The amplitude and the phase of the individual high-frequency signals to be amplified can be accurately adjusted in such a manner that even non-ideal affects which for example can be traced back to asymmetries in the line structure originated during the processing of the multi-layer, can be compensated.
FIG. 2A shows an exemplary embodiment of the printed-circuit board arrangement 5 according to the invention, which provides several antenna elements 41, 42 and a first patch 21 which are fed from the three-line system 2. The printed-circuit board arrangement 5 according to the invention comprises four metal layers 221, 222, 223, 224. The first metal layer 221 and the second metal layer 222 are arranged on the underside or on the upper side of a first substrate 231. The first substrate is a dielectric which electrically separates the first metal layer 221 from the second metal layer 222. The third metal layer 223 and the fourth metal layer 224 are disposed on the underside or on the upper side of a second substrate 232. The first substrate 231 and the second substrate 232 should provide dielectric constants which are suitable for high frequencies in the millimeter-wave range. The first substrate 231, which comprises the first metal layer 221 and the second metal layer 222, is separated from the second substrate 232, which comprises the third metal layer 223 and the fourth metal layer 224, by an interlayer 24. The interlayer is a PREPREG (English: pre impregnated fibres; German: vorimprägnierte Fasern), which provides dielectric properties similar to the first substrate 231 and the second substrate 232, whereas the melting temperature of the PREPREG is lower, so that, with a suitable temperature and a high compressive pressure, the two still solid substrates 231, 232 are glued to one another via the interlayer 24.
Furthermore, a recess 28 in which the amplifier unit 1 is inserted is embodied in the first substrate 231 of the printed-circuit board arrangement 5 according to the invention which carries the three-line system 2. This recess 28 is preferably created via a milling process, whereas the recess 28 should be selected to be so deep that the terminal contacts, that is, the pads 61 to 65 of the amplifier unit 1 are at the same level as the three-line system 2. Accordingly, FIG. 2A shows that the first metal layer 221 is significantly thicker than, for example, the second metal layer 222. The relatively greater thickness can be achieved, for example, by copper plating. This guarantees that the first metal layer 221 is not cut through, even in a milling process, and that the amplifier unit 1 can then be securely arranged in the recess 28. In order to create the recess 28 within the first substrate 231, the second substrate 232 with its two metal layers 223, 224 must preferably also be removed together with the interlayer 24 in the region of the recess 28. This can also be implemented by a punching process before pressing.
The antenna 4 preferably comprises two antenna elements 41, 42, which are coupled via the three-line system 2 to the amplifier unit 1. As will be described in detail below, the at least two antenna elements 41, 42 are slot antennas, whereas each slot antenna 41, 42 is formed respectively by an aperture on the second metal layer 222 of the printed-circuit board arrangement 5. These apertures, which are not illustrated in FIG. 2A, are continued from the antenna elements 41, 42 in direction towards the amplifier unit 1 and accordingly separate the three lines 31, 32, 33 extending parallel to one another, that is, the strip lines 31, 32, 33, electrically from one another. In this context, coupling is understood in that the three-line system 2 is converted into two slot lines, of which respectively one part forms an antenna element 41, 42, which is then a slot antenna 41, 42.
Moreover, a first patch 21 is embodied on the third metal layer 223 which is arranged above the two antenna elements 41, 42. This first patch 21, together with the two slot antennas 41, 42, achieves that an electromagnetic field is radiated upwards or respectively downwards, that is, primarily perpendicular to the first patch 21. In order to prevent this electromagnetic field from leaving the printed-circuit board arrangement 5 according to the invention in two directions, the first metal layer 221 in the exemplary embodiment from FIG. 2A is embodied as an enclosed metal layer, which therefore acts as a reflector and reflects the downwards propagating part of the electromagnetic field back upwards again.
Furthermore, in FIG. 2A, a via hole 25 is embodied, which connects the various metal layers 221 to 224 electrically to one another. The via hole 25 also serves to prevent parts of the electromagnetic field which are radiated from the antenna 4 from penetrating the printed-circuit board arrangement 5 laterally and coupling into further strip lines. For example, an antenna which functions as a receiver can also be embodied on the same printed-circuit board arrangement 5. In order to avoid a direct coupling of the feeding antenna 4 into the receiving antenna, the feeding antenna 4 is surrounded by via holes 25 and therefore shielded, as will be explained later.
FIG. 2B shows a further exemplary embodiment of the printed-circuit board arrangement 5 according to the invention which provides several antenna elements 41, 42 and two patches 21, 26, which are fed from a three-line system 2. The printed-circuit board arrangement 5 from FIG. 2B corresponds to the printed-circuit board arrangement 5 from FIG. 2A with the difference that a second patch 26 is embodied above the first patch 21. The two patches 21, 26 are electrically separated from one another by the second substrate 232. Furthermore, the two patches 21, 26 are electrically separated from the two antenna elements 41, 42 by the interlayer 24. The second patch 26 is embodied on the fourth metal layer 224, which is arranged above the two antenna elements 41, 42, whereas the second patch 26 is isolated by apertures within the fourth metal layer 224 from the latter. FIG. 2B also shows the recess 28 into which the amplifier unit 1 is inserted.
FIG. 2C shows a further exemplary embodiment of the printed-circuit board arrangement 5 according to the invention which provides several antenna elements 41, 42 which are fed from a three-line system 2 and provides a first patch 21 radiating downwards. In this exemplary embodiment, the first patch 21 is embodied on the first metal layer 221, which is arranged below the two antenna elements 41, 42, whereas the first patch 21 is isolated by apertures within the first metal layer 221 from the latter. In order to prevent the electromagnetic field which is radiated from the antenna 4, from leaving the printed-circuit board arrangement 5 according to the invention in two directions, the third metal layer 223 is about a completely enclosed metal layer. In the exemplary embodiment from FIG. 2C, the part of the electromagnetic field which leaves the antenna 4 upwards, that is, in the direction towards the third metal layer 223 and the fourth metal layer 224, is reflected back at the third metal layer 223. In this case, the electromagnetic field leaves the printed-circuit board arrangement 5 according to the invention only at its bottom. Accordingly, the direction of radiation can be influenced very simply by changing the arrangement of the first patch 21 and the enclosed metal layer.
FIG. 3A shows a plan view of the first and second metal layer 221, 222 of the printed-circuit board arrangement 5 according to the invention. The amplifier unit 1 of which the pads 62 to 64 developed as terminal contacts are connected via bond wires to the three-line system 2 is clearly evident. Furthermore, the first line 31, the second line 32 and the third line 33 of the three-line system 2, which are embodied on the first metal layer 222, are illustrated. Moreover, it is clearly evident that the first line 31 is separated from the third line 33 by an aperture. Furthermore, the second line 32 is also separated from the third line 33 by a further aperture. In this context, the first line 31, the second line 32 and the third line 33 run parallel to one another.
Furthermore, it is clearly evident that the at least two antenna elements 41, 42 are slot antennas 41, 42, and that each slot antenna 41, 42 is formed respectively by an aperture on the second metal layer 222 of the printed-circuit board arrangement 5 according to the invention. These two apertures continue from the antenna elements 41, 42 in the direction towards the amplifier unit 1, so that the three lines or respectively strip lines 31, 32, 33 extending parallel to one another are electrically separated from one another. Because of the use of a printed-circuit board arrangement 5, the first line 31, the second line 32 and the third line 33 are also strip lines 31, 32, 33.
It is also clearly evident that the two outer lines respectively strip lines 31, 32 of the three-line system 2, which also guide the excitation signals merge into the ground surface 222 in a region in front of the two antenna elements 41, 42, so that the three-line system 2 is converted from three parallel lines of finite width into two parallel slot lines. The ground plane 222 is embodied on the second metal layer 222 and connected to the reference ground. This ground plane 222 is embodied at least in the direction towards the amplifier unit 1 in a circular shape thereby avoiding any undesirable radiation at the transition from the three parallel lines of finite width to the two parallel slot lines. However, it is also possible for the ground plane 222 to be embodied as a whole in a rounded manner, especially as a circular.
The first antenna element 41 is preferably orientated orthogonally to the second antenna element 42. It is particularly advantageous that the first antenna element 41 has the same shape and the same length as the second antenna element 42.
It is also clearly evident in FIG. 3A that a plurality of through-contacts 25 are arranged in a rounded, especially circular ring and that these enclose the at least two antenna elements 41, 42. The circular ring comprising the plurality of through-contacts 25 provides no through-contacts 25 in direction towards the three-line system 2. As a result of this circular ring with the plurality of through-contacts 25, it is ensured that no electromagnetic field is radiated laterally from the two antenna elements 41, 42 and disturbs receiving antennas, which may optionally be arranged, for example, on the printed-circuit board arrangement 5 according to the invention.
Furthermore, it is clearly evident that the first metal layer 221 is arranged below the first antenna element 41 and the second antenna element 42 and is embodied as a completely enclosed metal layer which acts as a reflector. In this context, the first metal layer 221 which acts as a reflector is separated from the second metal layer 221 only by the first substrate 231.
FIG. 3B shows a further plan view of the first, second and third metal layer 221, 222, 223 of the printed-circuit board arrangement 5 according to the invention. It is evident that a first patch 21 is embodied on a third metal layer 223 which is arranged above the two antenna elements 41, 42. In this context, the third metal layer 223 is separated from the second metal layer 222 by the interlayer 24.
In the illustration, the first patch 21 has the shape of a square, whereas the shape of a rhombus is also possible. By preference, a first edge of the first patch 21 is arranged parallel to the first antenna element 41, and a second edge of the first patch 21, which is adjacent to the first edge of the first patch 21, extends parallel to the second antenna element 42. In this context, adjacent is understood in that the two edges touch at one point. This ensures that almost all points of the first edge of the first patch are at the same distance from the first antenna element 41 and also that almost all points of the second edge of the first patch 21 are at the same distance from the second antenna element 42. The same also applies for almost all points of the first edge and of the second edge relative to one another, which are always at approximately the same distance from the respective antenna element 41, 42.
By preference, the first antenna element 41 and the second antenna element 42 are arranged under the first patch 21. In the drawings, the antenna elements 41, 42 are also arranged with a horizontal and vertical spacing to the first and second edges of the first patch 21 in order to improve visual clarity. The same also applies if the first patch 21 is embodied on the first metal layer 221, as illustrated in FIG. 2C. In this case, the first antenna element 41 and the second antenna element 42 are preferably arranged directly above the first patch 21.
FIG. 3C shows a further plan view of the first, second, third and fourth metal layer 221, 222, 223, 224 of the printed-circuit board arrangement 5 according to the invention. It is clearly evident that a second patch 26 is arranged above the first patch 21 which is arranged above the at least two antenna elements 41, 42, whereas the two patches 21, 26 are separated from one another by a dielectric 232. In this context, the metal layer 224 on which the second patch 26 is embodied, is provided with a recess, so that the second patch 26 is isolated from the remainder of the metal layer 224. The remainder of the metal layer 224 which does not form the second patch 26 is accordingly connected, inter alia, by the via hole 25 to the reference ground. The second patch 26 is separated from the first patch 21 by the second substrate 232. By preference, the second patch 26 is arranged in such a manner above the first patch 21 that the mid-point of the second patch 26 is arranged directly, that is, perpendicularly above the mid-point of the first patch 21. By preference, the second patch 26 provides the shape of a square or a rhombus and accordingly preferably has the same shape as the first patch 21.
In this context, the edges of the second patch 26 have the same length, which is preferably shorter than or the same as the length of the edges of the first patch 21. As already described, the second patch 26 is arranged respectively orientated above the first patch 21 in such a manner that the edges of the second patch 26 extend as parallel as possible to the edges of the first patch 21.
The second patch 26 is spaced from the first patch 21 by a length such that the directional effect of the antenna arrangement with the patch 21 and the two antenna elements 41, 42 is increased. By preference, the length varies within the order of magnitude of λ/4, where the wavelength should be set in the material of the printed-circuit board arrangement. The aperture on the fourth metal layer 224 which isolates the second patch 26 from the remainder of the metal layer 224 is preferably selected in such a manner that the aperture extends from the second patch 26 up to the via holes 25, which are arranged in the shape of a ring. The outer contour of this recess is preferably embodied in a circular manner, so that it matches the via holes 25 arranged in the shape of a ring as closely as possible.
The use of a second patch 26, which is optional, also means that the useful bandwidth of the antenna 4 with the two antenna elements 41, 42 is increased. As already explained, the via holes 25 serve to shield the antenna 4 with the two antenna elements 41, 42, whereas these via holes 25 extend through the metal layers 221, 222 and 224, so that the antenna 4 is framed by this circular edging. Only in the region of the two slot lines of the three-line system 2, which merge into the two antenna elements 41 and 42, this shielding is interrupted. In this manner, the antenna 4 with the two antenna elements 41, 42 radiates perpendicular to the metal layers 221 to 224.
FIG. 4A shows a further plan view of the first, second, third and fourth metal layer 221 to 224 of the printed-circuit board arrangement 5 according to the invention, where the functionality of the first patch 21 is explained for a vertical and/or horizontal polarisation. It is evident that the three-line system 2 is supplied on the one hand with a common-mode excitation and on the other hand with a differential-mode excitation. In the case of a common-mode excitation, the two supply voltages on the first line 31 and the second line 32 are identical in modulus and phase with reference to the third line 33. This fact is illustrated by the dashed arrows in FIG. 4A.
In the case of the differential-mode excitation, the supply voltages on the first line 31 and the second line 32 in fact are identical in amplitude with reference to the third line 33, but their phases differ by 180°. This fact is illustrated in FIG. 4A by the drawn-through arrows. Because of the fact that the first line 31 and the second line 32 on which the supply voltages are provided, merge into the ground surface 222, the common-mode excitation for example leads to a horizontal polarisation of the radiated field, via the slot antennas 41, 42 arranged orthogonally in the proximity of the patch. It is evident, for example, that the field lines extend from the third line 33 towards the second line 32 or towards the first line 31. Via the slot antennas, this leads to the vertical component being cancelled, because the amplitudes are identical in magnitude, so that only a horizontal component is preserved. This leads to a horizontal polarisation of the radiated field, as illustrated by the dashed arrow over the first patch 21.
The functionality when the three-line system is supplied with a differential-mode excitation can be explained by analogy. In this context, reference is made to the drawn-through arrows. Because of the phase difference of 180°, the horizontal components of the electromagnetic fields propagating via the two slot antennas 41, 42 are cancelled, so that the radiated electromagnetic field exhibits only a vertical polarisation. By switching between the two supply modes (common-mode supply, differential-mode supply) in the amplifier unit 1, it is therefore possible to switch directly between the two linear polarisations.
FIG. 4B shows a further plan view of the first, second, third and fourth metal layer 221 to 224 of the printed-circuit board arrangement 5 according to the invention, where the functionality of the first patch is explained in the case of a circular polarisation. As already explained, the supply voltages on the first line 31 and the second line 32 of the three-line system 2 differ in their phase, where the amplitude of these two supply voltages is identical. The dashed arrow explains the case that the phase of the individual supply voltages differs by −90°, whereas the drawn-through arrow describes the case that the phase of the two supply voltages differs by +90°. In this case, the respective horizontal or vertical components of the electrical fields are no longer completely cancelled via the first slot antenna 41 and the second slot antenna 42.
An excitation by means of these supply voltages leads, via the slot antennas 41, 42 arranged orthogonally in the proximity of the patch, to a left-hand circular polarisation or a right-hand circular polarisation of the radiated electromagnetic field. Accordingly, by switching between these two supply modes in the amplifier unit 1, it is possible to switch directly between the two circular polarisations. For the printed-circuit board arrangement 5 according to the invention as described, with a phase displacement of 0° between the two supply voltages on the first line 31 and the second line 32, a linear, horizontally polarised electromagnetic field is radiated, whereas, with a phase displacement of 180°, a linear vertically polarised electromagnetic field is radiated. If the phase shift in the arrangement described is −90°, a left-hand circular polarised electromagnetic field is radiated whereas, with a phase shift of +90°, a right-hand circular polarised field is radiated.
By changing the amplitude within the amplifier unit 1, it is possible to switch to an elliptical polarisation. However, the principle described can also be used, in general, for non-planar antennas and line structures.
Within the framework of the invention, all of the features described and/or illustrated can be combined with one another as required.

## Claims

1. A printed-circuit board arrangement comprising:
a printed-circuit board including a first metal layer, a second metal layer, and a third metal layer, the second metal layer being arranged below the third metal layer and arranged above the first metal layer,
an amplifier unit; and
at least two slot antennas formed respectively by apertures in the second metallic layer and coupled to the amplifier unit via a three-line system,
wherein the three-line system includes three strip lines mounted on the printed-circuit board or introduced into the printed-circuit board extending parallel to one another,
wherein voltages, which differ in modulus and phase, are guided along a first strip line and a second strip line of the three-line system,
wherein a third strip line of the three-line system serves as a common ground line for the first strip line and the second strip line,
wherein a first patch is embodied in the third metal layer, the first patch being excited from the three-line system, and
wherein the apertures continue from the at least two slot antennas in a direction towards the amplifier unit and separate the three strip lines extending parallel to one another.

2. The printed-circuit board arrangement according to claim 1, wherein two outer strip lines of the three-line system merge in a region in front of the at least two slot antennas into a ground plane, where the three-line system is converted into two parallel slot lines.

3. The printed-circuit board arrangement according to claim 2, wherein the ground plane is arranged on the second metallic layer, and
wherein the ground plane is embodied in a rounded manner at least in a direction towards the amplifier unit, thereby avoiding any undesirable radiation at a transition from the three strip lines of finite width extending parallel to one another to the two parallel slot lines.

4. The printed-circuit board arrangement according to claim 1, wherein a part of a first aperture which forms a first slot antenna is orthogonal to a part of a second aperture which forms a second slot antenna, and
wherein the first slot antenna has a same shape and a same length as the second slot antenna.

5. The printed-circuit board arrangement according to claim 1, wherein a plurality of via holes are arranged on a ring and enclose the at least two slot antennas, and
wherein the ring provides no via hole in a direction towards the three-line system.

6. The printed-circuit board arrangement according to claim 1,
wherein the first patch has a shape of a square or a rhombus,
wherein a first edge of the first patch extends parallel to a first slot antenna, and
wherein a second edge of the first patch which is adjacent to the first edge of the first patch extends parallel to a second slot antenna.

7. The printed-circuit board arrangement according to claim 6,
wherein the first edge of the first patch and the second edge of the first patch have at least approximately a same length as a first slot antenna and a second slot antenna of the at least two slot antennas, and
wherein the first slot antenna is arranged below the first patch, and the second slot antenna is arranged below the first patch.

8. The printed-circuit board arrangement according to claim 1, wherein a second patch is arranged above the first patch which is arranged above the at least two slot antennas, and
wherein the first and second patches are separated from one another by a dielectric.

9. The printed-circuit board arrangement according to claim 8, wherein a mid-point of the second patch is disposed directly above a mid-point of the first patch,
wherein the second patch has a shape of a square or a rhombus,
wherein edges of the second patch have at least approximately the same length as or are smaller than edges of the first patch,
wherein the second patch is orientated above the first patch in such a manner that edges of the second patch extend parallel to the edges of the first patch, and
wherein the second patch is spaced from the first patch by a vertical length, whereby directivity and a usable bandwidth of the at least two slot antennas are improved.

10. The printed-circuit board arrangement according to claim 1, wherein an enclosed metal layer which acts as a reflector is arranged above or below the at least two slot antennas, opposite to the first patch.

11. The printed-circuit board arrangement according to claim 1, wherein a recess is embodied in a first substrate of the printed-circuit board arrangement, which carries the three-line system, and
wherein the amplifier unit is inserted into the recess.

12. The printed-circuit board arrangement according to claim 1, wherein the amplifier unit is a monolithic microwave integrated circuit of which terminal contacts are connected via bonding wires to the three-line system on the printed-circuit board arrangement, and
wherein the terminal contacts are at least approximately at the same height as the three-line system.

13. The printed-circuit board arrangement according to claim 8, wherein the amplifier unit is embodied to apply respectively a signal to two outer lines with a middle line as a common line of the three-line system, so that the at least two slot antennas together with the first patch or together with the first patch and with the second patch radiate an electromagnetic field with at least one of a horizontal polarisation, a vertical polarisation, a left-hand circular polarisation, or a right-hand circular polarisation.

14. The printed-circuit board arrangement according to claim 1, wherein the at least two slot antennas are orientated orthogonally relative to one another.