EP1842263B1 - Planar multiband antenna - Google Patents

Abstract

The present invention provides a planar multiband antenna having a ground area, a first radiation electrode, a second radiation electrode, a third radiation electrode and a feeder. The feeder is implemented to feed the first radiation electrode. The first radiation electrode is arranged at least partly between the ground area and the second radiation electrode and does not protrude from an external periphery of the third radiation electrode. The third radiation electrode is arranged such that it completely surrounds an external periphery of the second radiation electrode, wherein there is a gap between the second radiation electrode and the third radiation electrode.

Description

The present invention relates generally to a multi-band planar antenna, more particularly to an aperture-coupled circularly polarized planar dual band antenna used in the ISM bands from 2.40 GHz to 2.48 GHz and 5.15 GHz to 5.35 GHz can.

Currently, more and more wireless systems are being developed that need to work in multiple frequency bands. For this purpose, compact antennas are often necessary to keep the volume of the antennas small and to allow use in portable devices.

It is possible to provide a separate antenna for each frequency band to be used. The disadvantage of using separate antennas, however, is that a multiplexer must be used. Furthermore, when using separate antennas, the area required for the antennas increases.

The reception of a plurality of different wireless transmission systems with a single broadband antenna is problematic, since broadband antennas are conventionally not produced in a compact design at low cost. So if you wanted to receive all relevant systems with only a single broadband antenna, so this is not possible with a small low-cost antenna.

For receiving a plurality of frequency bands, a multi-element antenna may be used which has its own radiator for each frequency range. Most known antenna concepts, which are suitable for the reception of two or more frequency bands (dual band concepts or multiband concepts), and which can be used for or in patch antennas, such. As integrated inverted-F antennas (inverted-F antennas, IFA) and planar inverted-F antennas (planar inverted-F antennas, PIFA) have only a linear polarization. Such known antenna forms are described, for example, in the book " Planar Antennas for Wireless Communications "by Kin-Lu Wong (John Wiley & Sons, Inc., Hoboken, New Jersey, 2003 ).

Especially for mobile applications, it is desirable to use a circular polarization, since in this case the alignment of the transmitting and receiving antenna is not critical, while using linear polarization, the orientation of the antennas must be selected appropriately.

While a number of integrable antennas having circular polarization are known, many of the integrable geometries for generating circular polarization have significant disadvantages. For example, almost square patches (planar conductive surfaces) with coaxial feed have a low impedance bandwidth, as for example in the diploma thesis "Investigation and construction of multiband antennas for receiving circularly polarized signals" by U. Wiesman, which in 2002 at the Fraunhofer Institute for Integrated Circuits in Erlangen was made. Another coaxial feed multiband antenna is described in the article "A Dual Band Antenna for WLAN Applications by Double Rectangular Patch with 4 Bridges" by Chang Won Jung and Franco De Flaviis, of the Department of Electrical Engineering and Computer Science, University of California. Irvine, Irvine, CA, 92697, USA and available on the Internet at http://www.ece.uci.edu/rfmems/publications/papers-pdf/C089-APS04.pdf.

One of the design possibilities of a circularly polarized dual-band antenna is the use of the aperture coupling. Such a solution is in the article " A Dual-Band Cirularly Polarized Aperture-Coupled Stacked Microstrip Antenna for Global Positioning Satellite "by DM Pozar and SM Duffy, described in the IEEE Transactions on Antennas and Propagation, Vol. 45, No. 11, November 1997 has been published. However, it is preferably used for broadband antennas with a resonant frequency or for antennas with several resonant frequencies close to each other, but not well suited for use with multiband antennas.

The European patent EP 1 072 065 B1 shows a dual band antenna for GSM and DCS with dual polarization. In this case stacked antenna elements are fed through a cross-shaped opening in the reflector device. Microwave energy is conducted through a coupling surface element and also a cross-shaped opening in a first radiating surface element to a second radiating surface element. The disadvantage of such an antenna arrangement is that for the generation of circular polarization in this antenna two feed channels must be combined by a quadrature hybrid broadband branch line coupler. The European patent also makes no information about the polarization purity and the impedance bandwidth.

In the European patent application EP 1 353 405 A1 For example, there is proposed an antenna for two frequency bands (dual band antenna) suitable for both the GSM 900 band and the GSM 1800 band and UMTS band, and which is based on a single radiator type. The individual antennas have an upwardly open metallic box and a feed through conductor tracks or conductor structures. The individual radiators are further designed so that they have an octahedral opening in the center, and as a result can be placed one above the other. The disadvantage of the described antenna is that it has a complicated and not completely planar structure.

In summary, it can be stated that no technically simple and inexpensive realizable antenna design is known from the cited prior art, which allows for a good efficiency and sufficient bandwidth radiation of a circularly polarized electromagnetic wave in two different frequency bands.

US-A-5 952 971 describes an antenna according to the preamble of claim 1. It is the object of the present invention to provide a dual-band antenna, which allows the most uniform radiation of circularly polarized waves in two frequency bands with an arbitrary frequency difference, without the need to use three-dimensional structures ,

This object is achieved by a planar multi-band antenna according to claim 1.

The present invention provides a multi-band planar antenna having a ground plane, a first radiation electrode, a second radiation electrode, a third radiation electrode, and a feeder configured to feed the first radiation electrode. In this case, the first radiation electrode is at least partially disposed between the ground plane and the second radiation electrode and does not protrude beyond an outer circumference of the third radiation electrode. The third radiation electrode is disposed circumferentially around an outer circumference of the second radiation electrode with a gap therebetween.

In other words, in a parallel projection of the second radiation electrode and the third radiation electrode into an image plane, the image of the third radiation electrode completely encloses the second radiation electrode, with a gap between the image of the third radiation electrode and the image of the second radiation electrode. The first radiation electrode is at least partially interposed between the second radiation electrode and the ground surface, the region between the second radiation electrode and the ground surface being defined by rays normal to the surface of the second radiation electrode from the second radiation electrode to the ground surface passing through the second radiation electrode Range between the second radiation electrode and the ground plane. Thus, the area between the second radiation electrode and the ground plane is an area that would be swept by the second radiation electrode if it were displaced in a direction normal to its surface toward the ground plane.

Thus, the first radiation electrode is within the meaning of the above definition between a surface which is bounded by an outer contour of the third radiation electrode, and the ground surface. That is, the first radiation electrode does not project beyond the outer circumference of the third radiation electrode.

It is the gist of the present invention that a multi-band planar antenna having particularly advantageous characteristics can be obtained by disposing the first radiation electrode between the ground plane and a combination of the second radiation electrode and the third radiation electrode, the third radiation electrode being arranged. that it completely surrounds an outer circumference of the second radiation electrode, with a gap between an outer periphery of the second radiation electrode and an inner circumference of the third radiation electrode. A maximum dimension of the first radiation electrode is thus smaller than a maximum dimension of the third radiation electrode. The first radiation electrode, which is located at least partially between the second radiation electrode and the ground surface, can hereby serve as a radiator for an upper Frequency range serve. In a lower frequency range, for example in a frequency band which has a lower frequency than the upper frequency range, the second radiation electrode and the third radiation electrode, which are farther from the ground surface than the first radiation electrode, can act together as a radiating element. A gap existing between the second radiation electrode and the third radiation electrode completely enclosing the second radiation electrode thereby enables the first radiation electrode to radiate electromagnetic waves into free space when operating in the upper frequency band. In other words, the gap between the outer periphery of the second radiation electrode and the inner periphery of the third radiation electrode prevents the second and third radiation electrodes, which together are larger than the first radiation electrode, from shielding the radiation from the first radiation electrode.

Incidentally, it should be noted that the second radiation electrode, whose dimensions may be similar to those of the first radiation electrode, still supports the radiation from the first radiation electrode. The coupling of the first radiation electrode and the second radiation electrode can in this case exert a positive influence on the bandwidth of the antenna for radiation in the upper frequency band in which the first radiation electrode acts as a radiating element.

It should be noted that the first radiation electrode which functions as a radiating element in the upper frequency band has a smaller distance to the ground surface than the second and third radiation electrodes. This will result in the generation of surface waves in the upper frequency band which would significantly affect the antenna gain or efficiency compared to arrangements in which a radiation electrode for the upper of two frequency bands is removed is arranged from the ground surface, effectively suppressed or minimized.

Furthermore, it is possible in a favorable manner to couple the antenna according to the invention. It is sufficient to provide a feeder which feeds the first, smaller radiation electrode. When operating in the upper frequency band, the first radiation electrode is in resonance, so that an effective direct coupling of the first radiation electrode is possible. On the other hand, when operating in the lower frequency band, the first radiation electrode is out of resonance and thus transmits the energy supplied to it to the combination of the second radiation electrode and the third radiation electrode acting as a radiating element when operating in the lower frequency band. Thus, a separate supply for the lower frequency band and the upper frequency band can be dispensed with. So it is not necessary duplexer, and the feed can be designed accordingly simple. The excitation of a circularly polarized radiation can also take place in an antenna according to the invention in an advantageous manner and with only a single feed device. When operating in the upper frequency band, the lower, first radiation electrode can be directly excited. When operating in the lower frequency band, the first radiation electrode can be excited, which in turn transmits the electrical energy to the second and third radiation electrodes.

An antenna geometry according to the invention also enables the coupling of the first radiation electrode by an aperture coupling. In comparison with a coaxial feed, an aperture-coupled antenna has a particularly large impedance bandwidth, as a result of which the antenna according to the invention is particularly well suited for broadband applications. In an aperture coupling, energy from a waveguide is first coupled to the first radiation electrode because it is closer to the ground plane than the second and the third radiation electrode. Thus, the first radiation electrode is in a direct and undisturbed electromagnetic coupling with the aperture in the ground plane, so that the polarization of an electromagnetic wave emitted by the first radiation electrode during operation in the upper frequency band is determined particularly effectively by the configuration of the aperture and the excitation can. For example, the radiation of a circularly polarized wave with a high polarization purity is possible. When operating in the lower frequency band, the first radiation electrode acts as a coupling electrode because it is not operated in resonance. It thus transmits the electric power coupled through the aperture of the ground plane to the second radiation electrode and the third radiation electrode, which together in the lower frequency band have a resonance and thus a particularly good radiation. Even with the radiation in the lower frequency band by the second and third radiation electrode, a good purity of a desired polarization can be ensured.

The arrangement of the first radiation electrode and the second and third radiation electrode ensures that surface waves are excited only to a small extent, since in the radiation in the upper frequency band, the relevant distance between the first radiation electrode and the ground plane is less than the distance between the second and third third radiation electrode and the ground plane. Thus, the distance between the respective active radiation electrode and the ground plane is adapted to the wavelength of the radiated radiation (small distance for the upper frequency band, long distance for the lower frequency band), so that an optimal reduction of surface waves is possible.

Moreover, it is pointed out that the antenna according to the invention can be produced very technologically very advantageously, since the entire structure is planar.

Furthermore, it is also noted that the antenna according to the invention clearly differs from all known structures. Conventionally, in planar dual band antennas, a large radiation electrode for a lower frequency band is located closer to the ground plane than a small radiation electrode for an upper frequency band, as long as the two radiating elements overlap. However, an overlap is desirable for reasons of space savings. Namely, according to the conventional view, an arrangement in which a smaller radiator is arranged between a larger radiator and the ground surface, does not make sense, since it is conventionally assumed that the larger radiator then shields a radiation of the smaller radiator. Antenna arrangements according to the prior art thus do not allow the described minimization of surface waves. Furthermore, a common feed of radiators for different frequency bands in conventional antennas is not possible if a high degree of polarization is emphasized. Thus, the achievement of a circular polarization with high polarization purity with a conventional arrangement with only one feed is not possible.

In an antenna according to the invention, the third radiation electrode is thus designed so that in a projection of the second radiation electrode and the third radiation electrode along a direction normal to the second radiation electrode in an image plane an image of the third radiation electrode completely surrounds an image of the second radiation electrode.

It is preferred that the second radiation electrode and the third radiation electrode lie in one plane, wherein the third radiation electrode completely encloses the second radiation electrode in the plane. Such an arrangement is advantageous, since in this case the second radiation electrode and the third radiation electrode together in a particularly advantageous manner can form a radiator, which has a resonance for the lower of two frequency bands. Furthermore, the arrangement described is advantageous in terms of manufacture since the second radiation electrode and the third radiation electrode can be applied and structured on a common substrate. Furthermore, the arrangement described makes it possible to produce connections between the second radiation electrode and the third radiation electrode in a technologically simple manner.

Furthermore, it is preferable that a distance between the third radiation electrode and the second radiation electrode is smaller than a distance between the third radiation electrode and the first radiation electrode. The third radiation electrode thus lies closer to the second radiation electrode than to the first radiation electrode. This ensures that an interaction between the second radiation electrode and the third radiation electrode is greater than an interaction between the first radiation electrode and the third radiation electrode. Thus, it is ensured that the first radiation electrode in the upper frequency band has a resonance which is not significantly influenced by the third radiation electrode. In the lower frequency band, on the other hand, the second radiation electrode and the third radiation electrode can strongly interact, so that the second radiation electrode and the third radiation electrode together can be regarded as a large radiator.

In a further preferred embodiment, the first radiation electrode, the second radiation electrode, the third radiation electrode and the feed device are designed so that the planar multi-band antenna can emit a circularly polarized electromagnetic wave. For this purpose, for example, an outer shape of the first radiation electrode, the second radiation electrode and the third radiation electrode are set so that the first radiation electrode, the second radiation electrode, and the third radiation electrode are nearly square, and there is preferably a slight difference in the dimensions or edge lengths. Furthermore, it is possible that the first radiation electrode, the second radiation electrode and the third radiation electrode are rectangular or almost square and furthermore have at least one bevelled corner. It is likewise possible to provide the first radiation electrode and the second radiation electrode with at least one slot in the middle, which promotes or enables the emission of a circularly polarized wave. Furthermore, it can be ensured by a suitable feed that a circularly polarized wave is emitted. By way of example, the first radiation electrode can be coupled by an aperture in the ground plane to a waveguide, which supplies electric power to the first radiation electrode, ie, feeds it. The aperture may, for example, be a cross-aperture, since this is particularly well suited for achieving a circular polarization. However, it is also possible to feed the first radiation electrode via a coaxial line, wherein a suitable selection of the feed point ensures a circular polarization. Furthermore, the first radiation electrode can be excited via two supply lines arranged at different positions, wherein it is to be ensured that the signals on the supply lines have such a phase offset that a circularly polarized wave is emitted. The generation of a circularly polarized radiation is particularly advantageous since a transmission path can thus be realized in which the received field strength is independent of a rotation of the antenna about an axis connecting a transmitting antenna and a receiving antenna. Moreover, it should be noted that the antenna structure according to the invention is particularly well suited for the radiation of a circularly polarized wave, it being sufficient, only the first To feed radiation electrode. The first radiation electrode acts either as a radiating element in the upper frequency band itself or, in the lower frequency band, passes the electrical power supplied thereto to the second and third radiation electrodes without permanently impairing the polarization properties in the lower frequency band.

A particularly advantageous feed, which allows a large bandwidth, is given when the feed means an aperture in the ground plane and a waveguide, wherein the first radiation electrode, the second radiation electrode and the third radiation electrode, spaced from the ground surface, on a first side of the Ground surface are arranged, and wherein the waveguide is disposed on a second side of the ground surface. The waveguide and the first radiation electrode are arranged so that energy from the waveguide via the aperture to the first radiation electrode can be coupled to feed the first radiation electrode. The waveguide and the aperture may in this case preferably be designed so as to enable the emission of a circularly polarized electromagnetic wave. It has proved to be particularly advantageous in such an aperture coupling that the aperture has at least one first slot and one second slot, which together form a slot of the shape of a cross.

Furthermore, it is preferred that the first radiation electrode and the second radiation electrode have a same shape. This ensures that an outer circumference of the first radiation electrode is substantially parallel to an outer circumference of the second radiation electrode and to the gap between the second radiation electrode and the third radiation electrode. Thus, the radiation from the first radiation electrode can be delivered to the free space particularly effectively without the second radiation electrode and the third radiation electrode develop a pronounced shielding effect.

Furthermore, in a preferred embodiment, a maximum dimension of the second radiation electrode differs by at most 30% from a maximum dimension of the first radiation electrode. This in turn ensures that the outer circumference of the first radiation electrode is located sufficiently close to the gap between the second radiation electrode and the third radiation electrode. This allows radiation from the first radiation electrode to be released through the gap between the second and third radiation electrodes to the free space.

Incidentally, it is preferable that a maximum dimension of the second radiation electrode differs by at most 10% from a maximum dimension of the first radiation electrode, whereby the resonance frequencies of the first radiation electrode and the second radiation electrode differ only slightly. Thus, a strong coupling between the first radiation electrode and the second radiation electrode arise, whereby the second radiation electrode still supports the radiation of the first radiation electrode. Moreover, the bandwidth of the antenna according to the invention can thus be increased, since two coupled resonant radiators, namely the first radiation electrode and the second radiation electrode, have a higher bandwidth than a single radiator. The use of the same dimensions for the first radiation electrode and the second radiation electrode brings the stated advantages and is thus also preferred.

According to the invention, the third radiation electrode and the second radiation electrode are coupled together via four conductive connections.

Thus, it is ensured that the second radiation electrode and the third radiation electrode are effective in the lower frequency band as a common large radiation electrode. This is true even if a field coupling between the second radiation electrode and the third radiation electrode is not sufficiently strong. The conductive connecting webs may be connected to the second radiation electrode, preferably in the middle of outer edges of the second radiation electrode. However, the conductive connecting webs may also be shifted from the middle of the edges towards the corners. If the second radiation electrode has bevelled corners, it is particularly advantageous to displace the connecting webs towards the bevelled corners. Due to the position of the connecting webs, a resonance frequency and adaptation of the second radiation electrode and the third radiation electrode can be influenced overall. Thus, the position of the connecting webs represents a further degree of freedom in a design of an antenna according to the invention. Four conductive connecting webs are used between the third radiation electrode and the second radiant electrode, since as uniform as possible radiation characteristics of the antenna according to the invention can be achieved.

Furthermore, it is preferable that a plane in which the first radiation electrode is located, a plane in which the second radiation electrode is located, and a plane in which the third radiation electrode is located with the ground plane each have a positive angle of at most 20 Degree inflow. The first radiation electrode, the second radiation electrode and the third radiation electrode are thus substantially parallel to the ground plane. Such a design enables a planar construction, and the emission properties are again uniform.

Preferably, the inventive antenna is designed so that an impedance matching is achieved with a VSWR of less than 2 in at least two frequency bands. Thus, a dual band operation or multi-band operation of the antenna according to the invention is possible, with a good adaptation is achieved. However, a good match allows an effective coupling of energy into the antenna.

The antenna according to the invention may preferably be constructed in several layers. In a preferred embodiment, the inventive antenna comprises a first dielectric layer, a first low dielectric constant layer, a second dielectric layer, a second low dielectric constant layer, and a third dielectric layer. The first dielectric layer carries a waveguide on its first surface and the ground surface on its second surface. The second dielectric layer carries on one side the first radiation electrode. The third dielectric layer carries the second radiation electrode and the third radiation electrode. The first low-dielectric constant layer is disposed between the first dielectric layer and the second dielectric layer. The dielectric constant of the first low dielectric constant layer is less than the dielectric constant of the first dielectric layer, the second dielectric layer, and the third dielectric layer. The second low-dielectric-constant layer is disposed between the second dielectric layer and the third dielectric layer. The dielectric constant of the second low dielectric constant layer is lower than the dielectric constant of the first, second or third dielectric layer.

Such an embodiment of an antenna enables a particularly simple production, wherein through the layers low dielectric constant, the radiation characteristics of the antenna can be improved. A layer with a very low dielectric constant reduces the dielectric losses and also reduces the occurrence of surface waves. Furthermore, the production is very favorable, since only radiation electrodes must be processed, which are supported by dielectric layers. Thus, methods can be used which enable a structuring of planar layers on a carrier material, for example photolithographic methods and etching methods. Such methods are very inexpensive and offer very high precision. Moreover, the dielectric layers carrying the radiation electrodes also ensure good mechanical stability of the antenna. A particularly simple and inexpensive production can be achieved by the first, second and third dielectric layer of FR4 material (conventional printed circuit board material) are produced. The low-dielectric-constant layer may preferably be formed by air. It has been found that an antenna according to the invention can be produced very inexpensively with a corresponding design, wherein the radiation properties are not influenced in a negative manner despite the inexpensive materials used.

Fig. 1

ein Schrägbild einer planaren Antennenstruktur, von der eine erfindungsgemäße Antennenstruktur ableitbar ist;

Fig. 2

ein Schrägbild einer erfindungsgemäßen Strahlergeometrie gemäß einem ersten Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 3

ein Schrägbild einer planaren Antennenstruktur, von der eine erfindungsgemäße Antennenstruktur ableitbar ist;

Fig. 4

ein Schrägbild einer erfindungsgemäßen Antennenstruktur gemäß einem zweiten Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 5

ein Bild eines Prototypen einer planaren Antennenstruktur, aus der eine erfindungsgemäße Antennenstruktur ableitbar ist;

Fig. 6

ein Bild eines Prototypen einer erfindungsgemäßen Antennenstruktur gemäß dem zweiten Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 7

eine grafische Darstellung des Verlaufs des Reflexionskoeffizienten S11 für einen Prototypen einer planaren Antennenstruktur, aus der die erfindungsgemäße Antennenstruktur ableitbar ist;

Fig. 8

eine grafische Darstellung des Verlaufs der Polarisationsentkopplung für einen Prototypen einer planaren Antennenstruktur, aus der die erfindungsgemäße Antennenstruktur herleitbar ist; und

Fig. 9

eine grafische Darstellung des Verlaufs des Reflexionskoeffizienten S11 für einen Prototypen einer erfindungsgemäßen Antenne gemäß dem zweiten Ausführungsbeispiel der vorliegenden Erfindung.

Preferred embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings. Show it:

Fig. 1

an oblique image of a planar antenna structure, from which an antenna structure according to the invention can be derived;

Fig. 2

an oblique view of a radiator geometry according to the invention according to a first embodiment of the present invention;

Fig. 3

an oblique image of a planar antenna structure, from which an antenna structure according to the invention can be derived;

Fig. 4

an oblique view of an antenna structure according to the invention according to a second embodiment of the present invention;

Fig. 5

an image of a prototype of a planar antenna structure, from which an antenna structure according to the invention can be derived;

Fig. 6

an image of a prototype of an antenna structure according to the invention according to the second embodiment of the present invention;

Fig. 7

a graphical representation of the course of the reflection coefficient S11 for a prototype of a planar antenna structure, from which the antenna structure according to the invention can be derived;

Fig. 8

a graphical representation of the course of the polarization decoupling for a prototype of a planar antenna structure, from which the antenna structure according to the invention can be derived; and

Fig. 9

a graphical representation of the course of the reflection coefficient S11 for a prototype of an antenna according to the invention according to the second embodiment of the present invention.

Fig. 1 shows an oblique image of a planar antenna structure, from which an antenna structure according to the invention can be derived. The antenna structure is designated 100 in its entirety. The antenna structure 100 includes a ground plane 110 having an aperture 120. Furthermore, the antenna structure comprises a radiation electrode 130, which is arranged above the ground surface 110. A feed line 140, shown here as a conductive strip, is disposed below the ground plane 110. The aperture 120 includes a first slot 150, a second slot 152 and a third slot 154. The first, second and third slots 150, 152, 154 each have a rectangular shape and constitute an opening of the ground plane 110. The first slot 150 and the second slot 152 are arranged so as to form a cross. The lengths of the first slot 150 and the second slot 152 are the same in the embodiment shown. The third slot 154 is longer than the first slot 150 and the second slot 152, and intersects the first and second slots 150, 152 in the area where the first and second slots 150, 152 also intersect, that is in the area Center of the cross formed by the first and the second slot. It should also be noted that the third slot 154 is perpendicular to the feed line 140 in a plan view, along a direction indicated by an arrow 170. The aperture 120 also has a high symmetry. The geometric center of the first, second and third slot 150, 152, 154 coincide, apart from manufacturing tolerances together. Further, there is axial symmetry of the aperture with respect to an axis 158 of the third slot 154. Further, the aperture 120 is positioned with respect to the feedline 140 such that in a plan view the feedline 140 passes through the region where the first, second and third Slit 150, 152, 154 intersect.

The radiation electrode 130 is a planar conductive electrode, which may also be referred to as a patch. It is arranged above the aperture 120 in the embodiment shown. The radiation electrode 130 shown is substantially rectangular. The radiation electrode 130 is designed to allow the radiation of a circularly polarized electromagnetic wave. In the embodiment shown, the radiation electrode is nearly square. Likewise, it is possible to have a rectangular one Radiation electrode to use in which at least one corner is beveled or cut off. Also, a radiation electrode having a slit in the center which allows circular polarization can be used. Finally, other geometries can be used as long as it is ensured that they allow a circular polarization. The radiation electrode 130 is arranged so that the aperture 120 is symmetrically located below the radiation electrode 130 in a plan view along a direction indicated by the arrow 170.

It should also be noted that overall, the waveguide and the radiation electrode are arranged so that energy from the waveguide can be coupled via the aperture to the radiation electrode (patch).

The operation of the present antenna structure can be easily described. The aperture 120 forms a resonant cross aperture. The first slot 150 and the second slot 152 form a slot of the shape of a cross. The slots are sized so that no resonance of the cross-shaped slot occurs in an operating frequency range of the antenna. It is thus achieved that a vibration is excited on the radiation electrode, which results in the emission of a circularly polarized electromagnetic wave. The cross-shaped configuration of the first and second slots 150, 152 of the aperture 120 assists in exciting a suitable mixed mode of vibration which enables such circular polarization of the radiated waves. The third slot 154 is operated in the vicinity of its resonance, so that it contributes to the improvement of the adaptation of the described antenna. As shown, the third slot 154 is typically longer than the first and second slots 150, 152, which drives the slot 154 closer to resonance than the first and second slots. It is further noted that it is amazing that the third slot 154 does not interfere with the circular polarization of the radiated electromagnetic wave as would be expected according to conventional theories.

The geometry shown can be changed in a wide range. For example, lengths of the three slots 150, 152, 154 that form the aperture 120 may be changed. For example, the length of the third slot 154 may be increased or decreased. Likewise, it is not necessary that the first slot 150 and the second slot 152 have the same length. Rather, the length of the slots 150, 152, 154 can be changed from each other to allow fine adjustments of the antenna structure. Furthermore, it is possible to deviate from the strict symmetry of the aperture. This may be helpful, for example, even if the radiation electrode 130 does not have complete symmetry. Also with regard to the angle between the slots and between a slot and the feed line changes can be made. Twisting the slots by up to 20 degrees is possible to allow fine tuning of the antenna structure. Thus, the angle between the first slot and the second slot may deviate from a right angle by up to 20 degrees. The same applies to the angle between the third slot and the feed line.

Also, the radiation electrode 130 can be changed in a wide range. This can for example be rectangular or almost rectangular. It is preferable to use a radiation electrode which is almost square, with the dimensions or edge lengths slightly different. Such a radiation electrode allows the radiation of a circularly polarized electromagnetic wave. Likewise, it is preferably possible to use a radiation electrode having a nearly rectangular or square shape, wherein at least one corner is chamfered. It is further preferred in this case for symmetry reasons, two opposite corners chamfer. Finally, a radiation electrode can be used which has a slot in the middle, wherein the slot is designed so that a circularly polarized wave can be radiated. Common extensions are possible, for example, the coupling of additional metallic elements to the radiation electrode 130. Also parasitic elements, for example, capacitive, inductive or resistive nature, can be coupled to the radiation electrode 130. This can be forced to form a desired mode. In addition, the bandwidth of the antenna can be further improved by parasitic elements. Finally, it is possible to cut corners of the radiation electrode 130 or beveled. This results in a coupling of different vibration modes that may exist between the radiation electrode 130 and the ground plane 110. As a result, a proper phase relationship is established between the various modes so that right-handed or left-handed circular polarization can be set. Incidentally, the radiation electrode may be changed in another form, for example, by adding slits to the radiation electrode, suppressing unwanted modes, or providing a proper phase relationship between the desired modes.

The feeding of the antenna structure shown can be done in various ways. The metallic stripline 140 shown here may be replaced by various waveguides. For example, these waveguides may be a microstrip line. A coplanar waveguide can also be used. Furthermore, the supply of electrical energy can be effected by a stripline, a dielectric waveguide or a cavity waveguide.

It should also be noted that the Fig. 1 just a schematic representation of the basic structure of a planar antenna. Features relevant to the antenna are not essential, are not shown here. It is therefore to be noted that the illustrated metallic structures, in particular the ground plane 110, the radiation electrode 130 and the stripline 140 are typically supported by dielectric materials. Namely, it is possible to incorporate into the illustrated antenna structure 100 almost arbitrarily layers or structures of dielectric materials. Such structures may be, for example, layers that run parallel to the ground plane 110. The conductive structures may be deposited on these dielectric layers and patterned by a suitable method, such as an etching process. All that is required here is that the dielectric constant of a dielectric layer is not too large, since this increases the losses occurring in the antenna structure and worsens the radiation. Furthermore, care must be taken when introducing dielectric structures that no surface waves are excited, since these also significantly impair the radiation efficiency of an antenna structure.

For example, a dielectric layer may be present between ground plane 110 and stripline 140 to form a microstrip line. Such a microstrip line is particularly advantageous for the coupling of a described antenna structure. Moreover, a microstrip line can also be combined particularly well with active and passive circuit structures.

In addition to planar dielectric structures, differently shaped dielectric structures are also possible. For example, the radiation electrode 130 may be supported by a spacer made of a dielectric material. Such a design improves the mechanical stability of the antenna and enables a cost-effective production.

The combination of dielectric layers and layers with very low dielectric constant, such as air layers, is also possible. Air layers reduce the electrical losses and may possibly reduce the excitation of surface waves.

Fig. 2 shows an oblique view of a radiator geometry according to the invention according to a second embodiment of the present invention. The radiator geometry is designated in its entirety by 200. It should be noted that in the Fig. 1 and 2 as well as in the other figures, like reference numerals designate like devices. Shown here is a ground plane 110 having an aperture 120. Details of the aperture are not shown for reasons of clarity, but the aperture corresponds to the basis of the Fig. 1 shown and described. Furthermore, the radiator geometry 200 according to the invention comprises a first radiation electrode 130. The aperture 120 represents an opening in the ground plane 110 which lies below the first radiation electrode 130 in a plan view along a direction which is indicated by the arrow 210. Above the first radiation electrode is a second radiation electrode 220. This is surrounded by the third radiation electrode 230, wherein between the second radiation electrode 220 and the third radiation electrode 230, a gap 240 is made. The second radiation electrode 220 is connected to the third radiation electrode 230 via four conductive bars 250, 252, 254, 256. In the embodiment shown, these webs are arranged approximately in the middle of the edges of the second radiation electrode 220. The second radiation electrode 220 is thus arranged such that the first radiation electrode 130 lies between the second radiation electrode 220 and the ground surface 110. Furthermore, in the embodiment shown, the second radiation electrode 220 and the third radiation electrode 230 lie in a common plane. Furthermore, the dimensions of the second radiation electrode 220 only differ from the dimensions of the first radiation electrode 130 slightly off. Preferably, the deviation is less than 20%.

Based on the structural description, the operation of a radiator geometry according to the invention will be described in more detail below. It should be noted that such a geometry enables the construction of circularly polarized dual or multi-band antennas. The individual layers can be carried by different boards. For example, a first board made of a dielectric material may carry the ground plane 110, while a second board carries the first radiation electrode 130 and a third board carries the second radiation electrode 220 and the third radiation electrode 230. The boards are not shown here for the sake of clarity but can be arranged so that the respective radiation electrodes are supported by any surface of the board. At the bottom of a printed circuit board, which carries the ground plane 110, there may be a microstrip line, from which power is transmitted via the aperture 120 in the ground plane only to a smaller patch formed by the first radiation electrode 130. The smaller patch formed by the first radiation electrode 130 is designed for the upper frequency band of two frequency bands. The power coupled through the aperture may subsequently be overcoupled to a larger patch designed for the lower of two frequency bands. The larger patch effectively consists of two patches, which in the embodiment shown are formed by the second radiation electrode 220 and the third radiation electrode 230. The larger patch can be interpreted as two nested patches with short circuits. The inner minor patch formed by the second radiation electrode 220 is approximately the same size as the lower minor patch formed by the first radiation electrode 130. Conductive connecting webs 250, 252, 254, 256 connect the second radiation electrode 220 and the third radiation electrode 230. The connecting webs 250, 252, 254, 256 act on the second radiation electrode and the third radiation electrode depending on their position as a capacitive or inductive load or coupling, thereby influencing the resonance frequency of the upper radiator is formed by the second radiation electrode 220 and the third radiation electrode 230. A change in the position of a connecting web 250, 252, 254, 256 (with respect to the second and third radiation electrodes 220, 230 and with respect to the remaining connecting webs) can thus be used for a fine tuning of the antenna structure. For example, it is possible to move the connecting webs 250, 252, 254, 256 away from the center of the edges of the second radiation electrode 220 toward the corners of the second radiation electrode 220. In the case where two corners of the second radiation electrode 220 are chamfered, it has been found advantageous to move the connecting webs 250, 252, 254, 256 towards these chamfered corners. For the rest, it should be noted that the connecting webs need not be arranged in a strictly symmetrical manner. Rather, it is expedient to arrange the connecting webs 250, 252, 254, 256 slightly offset at opposite edges of the second radiation electrode so that a connecting line between two opposite connecting webs 250, 252, 254, 256 does not run parallel to an edge of the second radiation electrode. Such an asymmetrical arrangement results in a particularly large freedom in the fine tuning of the upper radiator. Finally, it should also be pointed out that the connecting webs can also be omitted if there is sufficient near-field coupling between the second radiation electrode 220 and the third radiation electrode 230.

The structure according to the invention thus effectively comprises two radiation-capable structures, namely a so-called lower patch, which is formed by the first radiation electrode 130 which is effective at higher frequencies and an upper, larger patch formed by the second radiation electrode 220 and the third radiation electrode 230.

It should further be noted that the distance between the small patch formed by the first radiation electrode 130 and the ground surface is smaller than the distance between the second larger patch formed by the second radiation electrode 220 and the third radiation electrode 230 and the ground plane 110.

A structure according to the invention offers significant advantages over known structures, whereby a circularly polarized radiation in two frequency bands can be achieved without substantially influencing the purity of the polarization or by exciting surface waves to a greater extent.

It should be noted that in general an increase in an electrical substrate thickness leads to the formation of higher-order surface waves. If such surface waves occur, the antenna gain is greatly reduced. In order to avoid or minimize the formation of surface waves, the two antenna structures, which are contained in a geometry according to the invention, have different effective substrate thicknesses for different frequency ranges. At low frequencies, the upper major patch formed by second radiation electrode 220 and third radiation electrode 230 is effective. The effective substrate thickness is equal to the distance of the second and third radiation electrodes from the ground plane 110. This distance is denoted by D here. At higher frequencies, on the other hand, the lower small patch formed by the first radiation electrode 130 is effective. The effective substrate thickness is is equal to the distance between the first radiation electrode 130 and the ground plane 110, which is designated here by d.

Thus, it can be seen that the effective substrate thickness for low frequencies, denoted by D, is greater than the effective substrate thickness for high frequencies, denoted by d. This corresponds to the requirement that antennas for different frequencies must have different substrate thicknesses. Thus, by having the radiators operating at different frequencies at different planes and at different distances from the ground plane 110, the generation of surface waves can be effectively reduced. In fact, it is precisely the requirement that the effective substrate thickness should be lower for high frequencies than for low frequencies.

Likewise, the geometry according to the invention satisfies the requirement that the antenna for the upper frequency band (formed by the first radiation electrode 130) must be closer to the ground plane 110 and to the aperture 120 than the antenna for the lower frequency band (formed by the second Radiation electrode 220 and third radiation electrode 230). If the larger patch were at the bottom (i.e., near the aperture) and the smaller patch at the top (i.e., away from the aperture), this would result in poor polarization characteristics in the upper frequency range because the aperture would be shielded by the larger patch. In such a case, an effective coupling of the small patch over the aperture would no longer be possible. Similarly, a smaller patch that would be separated from the aperture by a larger patch could not radiate a circularly polarized wave with a small amount of orthogonal polarization.

Furthermore, by the geometry according to the invention, in which the larger patch is composed of two parts, namely the second radiation electrode 220 and the third Radiation electrode 230, avoided that the radiation of the underlying smaller patch is too much shielded by the larger patch above. Namely, if the antenna for the upper frequency band is closer to the ground plane 110 than the antenna for the lower frequency band, the strong shielding of the small radiator with the large one is to be avoided.

Reduced shielding of the radiation of the lower patch 130 by the overhead patch 220, 230 is achieved by the gap 140 between the second radiation electrode 220 and the third radiation electrode 230.

The radiator geometry 200 according to the invention can also be substantially changed. Thus, all the previously described changes can be applied to the individual radiation electrodes 130, 220, 230. For example, it is advantageous to trim the corners of the corresponding radiation electrodes. As a result, several modes required for circular emission can be coupled, while undesired modes can be suppressed.

Fig. 3 shows an oblique image of a planar antenna structure, from which an antenna structure according to the invention can be derived. The antenna structure is designated in its entirety by 300. It essentially corresponds to the basis of Fig. 1 shown antenna structure 100, so that the same facilities and geometry features are provided here with the same reference numerals. Unchanged features will not be described separately here. It should be noted, however, that in the antenna arrangement 300, a first corner 310 and a second corner 320 of the first radiation electrode 130 are cut off or bevelled. This geometric change helps to radiate a circularly polarized electromagnetic wave. Furthermore, the antenna arrangement 300 has a stub 330, which is attached to the strip line 140. This stub 330 is used a further impedance matching of the present antenna structure. The dimensioning of such a stub for adaptation is well known to a person skilled in the art.

Furthermore, the shows Fig. 3 an enclosing box 340 that encloses the entire antenna structure. Such an enclosing cuboid can be used, for example, to limit a simulation area in an electromagnetic simulation of an antenna structure.

The Fig. 4 shows an oblique view of an antenna structure according to the invention according to a second embodiment of the present invention. The antenna structure is designated 400 in its entirety. The antenna structure 400 comprises a feed line 140, a ground plane 110 with an aperture 120 and a first radiation electrode 130, a second radiation electrode 220 and a third radiation electrode 230. The geometry of the first radiation electrode 130 corresponds substantially to the geometry of FIG Fig. 3 The second and the third radiation electrode 220, 230 are arranged substantially the same as described with reference to FIG Fig. 2 is described. However, in the antenna structure 400, two opposite corners 410, 420 of the second radiation electrode 220 are chamfered. The third radiation electrode 230 in turn encloses the second radiation electrode 220, wherein between the second radiation electrode 220 and the third radiation electrode 230, a slot or gap 240 is present. It should also be noted that the third radiation electrode 230 is adapted in shape to the second radiation electrode 220. That is, the third radiation electrode 230 is fitted to the chamfered corners 410, 420 of the second radiation electrode 220 such that the gap 240 between the second radiation electrode 220 and the third radiation electrode 230 substantially coincides also in the region of the chamfered corners 410, 420 remains constant width. The inner edges of the third Radiation electrode 230 thus extend substantially parallel to the outer edges of the second radiation electrode 220. Also, the third radiation electrode 230 has two outer chamfered corners 430, 440 adjacent to the chamfered corners 410, 420 of the second radiation electrode 220. Thus, each of the first, second, and third radiation electrodes 130, 220, 230 has beveled corners 310, 320, 410, 420, 430, 440, with each of the adjacent corners of the various radiation electrodes being chamfered. The second and third radiation electrodes 220, 230 are coupled via connecting webs 250, 252, 254, 256, wherein the connecting webs 250, 252, 254, 256 approximately in the middle of edges of a rectangle, the second radiation electrode 220, apart from the bevelled Corners, describes, are arranged.

It should also be noted that the size of the second radiation electrode 220 is equal to the size of the first radiation electrode 130, except for a deviation of at most 20%. Also, in shape, the first and second radiation electrodes 130, 220 do not differ significantly. They are therefore almost parallel electrodes of almost the same shape and with almost the same dimensions.

It is also referred to here again explicitly on the layer order. The feed line 140 forms the lowermost conductive layer. In addition, a ground plane 110 is arranged, which has an aperture 120. Once again, the first radiation electrode 130 lies in one plane. In a further, further above, plane, the second radiation electrode 220 and the third radiation electrode 230 are arranged. The respective metallizations, ie the feed line 140, the ground plane 110 and the first, second and third radiation electrodes 130, 220, 230 are each supported by dielectric layers.

It should also be noted here that the width of the feed line 140 is changed for adaptation purposes. Remote from the aperture, the feedline 140 has a wide section 450 while the feedline 140 is narrower near the aperture. A narrow feed line is advantageous because it causes a greater concentration of the electric field. This allows a stronger coupling of the radiation electrodes to the feed line through the aperture 120. Incidentally, the change in the width of the feed line also serves to match the impedance, and the adaptation can be influenced by a suitable choice of the length of the thin piece 460.

In addition, an enclosing rectangle 470 is shown, which delimits a simulation area in which the antenna structure is simulated. The enclosing rectangle also indicates the thickness of the respective layers.

Fig. 5 shows an image of a prototype of a planar antenna structure, from which an antenna structure according to the invention can be derived. Shown here is a constructed mono-band antenna, which is designed for the frequency range from 2.40 GHz to 2.48 GHz. The antenna is designated 500 in its entirety. It has a first plate 510 of a dielectric material and a second plate 520 of a dielectric material. The two plates are separated or fixed by four spacers 530 made of a dielectric material. The first dielectric plate 510 carries a first radiation electrode 130. The second dielectric plate 520 carries on a top surface the ground plane 110 having an aperture 120. The lower side of the dielectric plate 530 carries a feed line through which electrical power is supplied to the antenna from an SMA jack 550.

The antenna assembly 500 has a first dimension 570, which can be considered as a width, of 75 mm. A second dimension 572, which is also considered as a length is also 75 mm. Finally, a third dimension 574, which can be understood as height, is 10 mm. Only for size comparison here is a one-euro coin 576 shown.

Fig. 6 shows an image of a prototype of an antenna structure according to the invention according to the second embodiment of the present invention. The antenna structure is designated in its entirety by 600. It comprises a first dielectric layer 610, a second dielectric layer 620 and a third dielectric layer 630.

The 3 dielectric layers or plates 610, 620, 630 are held by dielectric spacers 640. The first dielectric plate 610 in this case carries a second radiation electrode 220 and a third radiation electrode 230. The second dielectric plate carries a first radiation electrode 130. The third dielectric plate 630 carries on one side a ground plane 110 and on the other side a feed line 140. The feed line Incidentally, it is led out to an SMA socket 650. The entire antenna structure 600 forms a dual band antenna.

The antenna 600 has a first dimension 670, which may also be considered as a length. This first dimension is 75 mm. Furthermore, the antenna 600 has a second dimension 672, which can be considered as a width, and which is also 75 mm. A third dimension 674 of the antenna 600 may be considered as a height. This height is 10.5 mm.

The dual-band antenna 600 shown is based on the monoband antenna 500, whereby the monoband antenna has been improved into a dual-band antenna. The antenna 600, the in its basic structure of the in Fig. 4 shown antenna 400 is constructed of several layers, which will be explained in more detail below. The lowest position of the The antenna is formed by a structured conductive layer, for example a metallization layer, which as a whole forms a microstrip line. This microstrip line is deposited on the underside of a first FR4 type substrate, with the first substrate having a thickness of 0.5 mm. The first substrate corresponds to the third dielectric layer 630. On top of the first substrate is applied a ground plane having a total extension of 75 mm x 75 mm. The ground plane further includes an aperture 120. Above the ground plane is a layer that is not filled with a dielectric material. Accordingly, the antenna thus comprises an air layer having a thickness of 5 mm. Above this layer of air is another conductive layer on which the first radiation electrode is formed as a patch. The further conductive layer is supported by a second dielectric layer of FR4, again having a thickness of 0.5 mm. The second dielectric FR4 layer is the same as in FIG Fig. 6 Again, above the second dielectric FR4 layer is a layer in which there is no solid dielectric. This creates a second layer of air whose thickness is 4 mm. Again above it is a third dielectric FR4 layer having a thickness of 0.5 mm. The third FR4 dielectric layer carries another conductive layer on which the second radiation electrode and the third radiation electrode are formed in the form of patches by structuring. Conductive connecting webs between the second radiation electrode and the third radiation electrode have a width of 1 mm. The entire antenna structure thus comprises the following layers in the order shown: microstrip line; FR4 (0.5 mm); Ground area (75 mm x 75 mm, with aperture); Air (5 mm); Patch 1 (first radiation electrode); FR4 (0.5 mm); Air (4 mm); FR4 (0.5 mm) and patch 2 (second radiation electrode and third radiation electrode). All layers and dimensions can order vary up to 30%. However, it is preferred that the deviation from the preferred dimensions is not more than 15%.

Fig. 7 shows a graphical representation of the course of the reflection coefficient S11 for a prototype 500 of a planar antenna, from which the antenna structure according to the invention is derivable. The graphical representation is designated in its entirety by 700. The input reflection factor S11 was measured for a patch antenna designed for a frequency range of 2.40 to 2.48 GHz. A photograph of such an antenna 500 is shown in FIG Fig. 5 shown.

The abscissa 710 has the frequency of 2.15 GHz to 2.85 GHz. The ordinate 712 shows in logarithm form the amount of the input reflection factor S11. Here, the input reflection factor is plotted in a range of -50 dB to 0 dB. A first curve 720 shows a simulated input reflection factor. A second curve 730 shows the measured value for the input reflection factor. According to the measurement, the input reflection factor is below -10 dB in the entire frequency range shown from 2.15 GHz to 2.85 GHz. The simulation also shows a similar broadband characteristic of the antenna.

Fig. 8 shows a graphical representation of the polarization decoupling for a prototype 500 of a planar antenna structure, from which the antenna structure according to the invention can be derived. The graphical representation is designated in its entirety by 800. At abscissa 810, the frequency is plotted in a range of 2.3 GHz to 2.55 GHz. The ordinate 812 shows the polarization decoupling in decibels in a range between 0 and 25 dB. A first curve 820 shows a simulated history of polarization decoupling, while a second curve 830 represents measured values. In the required bandwidth from 2.40 GHz to 2.48 GHz, cross-polarization becomes sufficient Adjustment factor suppressed by more than 15.5 dB.

Fig. 9 FIG. 12 is a graph showing the course of the reflection coefficient S11 for a prototype 600 of an antenna according to the present invention according to the second embodiment of the present invention. The graph is designated 900 in its entirety. Shown here are measurement results for the reflection coefficient of a dual-band antenna according to the invention, as described on the basis of FIG Fig. 4 and 6 has been described. The abscissa 910 shows the frequency range between 2 GHz and 6 GHz. At the ordinate 912, the amount of the input reflection factor S11 is plotted in logarithmic form from -40 dB to + 40 dB. A curve 920 shows the variation of the input reflection factor versus frequency. Also shown are a first marker 930, a second marker 932, a third marker 934 and a fourth marker 936. The first marker indicates that the input reflection factor at 2.40 GHz is -13.618 dB. The second marker shows an input reflection factor of -16.147 dB at 2.48 GHz. The third marker shows an input reflection factor of -9.457 dB at 5.15 GHz, and the fourth marker shows an input reflection factor of -10.011 dB at 5.35 GHz. Finally, the fifth marker shows an input reflection factor of -0.748 dB at 4.0008 GHz.

Thus, it can be seen that the input reflection factor in the ISM band between 2.40 GHz and 2.48 GHz is less than -13 dB, and that the input reflection factor in the ISM band between 5.15 GHz and 5.35 GHz is less than -13 dB -9.4 dB.

In addition to the input reflection factor, the radiation characteristics of the dual-band antenna were also measured. In the ISM band between 2.40 GHz and 2.48 GHz, the antenna gain of a prototype dual band antenna is between 7.9 dBic and 8.3 dBic. The half width is here 70 °, and the polarization decoupling is between 11 dB and 22 dB.

In the ISM band between 5.15 GHz and 5.35 GHz, the antenna gain is between 5.9 dBic and 7.3 dBic. The half width is 35 °, the polarization decoupling between 5 dB and 7 dB.

The required matching properties and radiation properties can thus be achieved with a dual-band antenna according to the invention. It should also be noted that the polarization purity for the upper frequency range can still be optimized. For this example, geometric details can be changed.

For example, a resonant fork-shaped cross aperture can be used. According to a simulation in the ISM band between 2.40 GHz and 2.48 GHz, an antenna gain of up to 7.5 dBic, a half-value width of 70 ° and a polarization decoupling of up to 30 dB result for such an aperture. In the ISM band between 5.15 GHz and 5.35 GHz, according to a simulation, an antenna gain up to 7dBic, a half width of 35 ° and a polarization decoupling up to 17 dB can be achieved.

In summary, therefore, the present invention provides a planar circularly polarized antenna that can be used in the ISM bands from 2.40 GHz to 2.48 GHz and 5.15 GHz to 5.35 GHz. The proposed shape of the slot for an aperture-coupled patch antenna allows the emission of almost purely circularly polarized waves at a relatively large bandwidth of the reflection coefficient S11. This is also possible for multiband antennas. With an antenna according to the invention, a radio link can be achieved in which the strength of the signal received by an antenna according to the invention in a linear polarization of a transmitter is independent of the installation position of the receiving antenna. In other words, by a circularly polarized antenna, a linearly polarized signal can be received regardless of the orientation of the antenna.

The antenna according to the invention was developed in several steps. A first sub-task was to develop an aperture-coupled antenna for a frequency range of 2.40 to 2.48 GHz with right-handed circular polarization (RHCP). In the simulation, particular care was taken to achieve a strong suppression of the orthogonal polarization within the required bandwidth. It has been found that when a patch is fed via a non-resonant cross-aperture, the cross-polarization is very strongly suppressed. However, in such a non-resonant cross-aperture, the bandwidth of the reflection coefficient is narrow. A resonant rectangular aperture (so-called SSFIP principle) has a larger bandwidth, but the polarization decoupling is weaker. Finally, an earlier unknown combination of the two slot geometries has proven to be advantageous, which is referred to here as a resonant cross aperture. A corresponding antenna geometry was in the Fig. 1 . 3 and 5 shown.

Furthermore, it has been shown that a shown geometry of the aperture or the slot also allows the construction of circularly polarized dual or multi-band antennas. For this purpose, the concept described below can be used. In the case of two bands, the antenna consists of three boards. Corresponding arrangements are for example in the Fig. 4 and 6 shown. On the underside of the lower circuit board is a microstrip line whose power is coupled via an aperture in the ground plane first to a small patch (for the upper frequency band) and then to a larger patch (for the two frequency bands), consisting of two patches. The larger patch can be interpreted as "two nested patches with short circuits". The inside smaller Patch is preferably the same size as the bottom patch.

By such a structure or such a dual-band concept, a number of problems that occur in conventional antennas can be solved.

In order to achieve the widest possible bandwidth, radiators that are to be considered independently of one another must have relatively thick substrates with low permittivity for both frequency ranges.

However, increasing the electrical substrate thickness conventionally results in the formation of higher order surface waves, which greatly reduces antenna gain, as will be explained below. Conventionally, two patches for different frequency bands can be placed inside each other on a common substrate. The thickness of the substrate may be determined as a maximum of calculated substrate thicknesses of separate antennas with which the separate antennas have the required bandwidth. However, if the higher frequency band is separated from the lower frequency band by about one octave, and the minimum substrate thickness for the larger patch is so thick in use in the upper frequency range that this results in a high level of higher order surface waves, the surface waves will reduce very strong the antenna gain for the upper frequency range. Therefore, the two antennas must have different substrate thicknesses for different frequency ranges. The antennas for different frequency ranges must therefore be in different levels. This can be achieved with an antenna geometry according to the invention.

A conventional variant with a larger patch at the bottom and a smaller patch at the top has poor polarization properties because the aperture is shielded with the larger patch. The antenna for the upper frequency band must therefore be closer to ground than the antenna for the lower frequency band, which can be achieved with a geometry according to the invention.

Since the antenna for the upper frequency band must therefore be closer to the ground plane than the antenna for the lower frequency band, a strong shielding of the small radiator for the upper frequency band by the large radiator for the lower frequency band is to be avoided. This can be achieved by forming the radiator for the lower frequency band by two radiation electrodes between which there is a gap.

The adaptation of an antenna according to the invention can be done by a transformer or by a stub.

An antenna according to the invention has a number of advantages over conventional antennas. The proposed dual-band concept allows the construction of completely planar antennas that are easy to produce in mass production and therefore cost-effective. At the same time, high polarization purity and a large impedance bandwidth can be achieved. It is also possible to construct planar circularly polarized multiband antennas. In this case, the area requirement of the entire antenna is determined only by the size of the antenna element for the lowest frequency. In comparison to broadband antennas, an antenna according to the invention furthermore offers a better prefiltering.

Claims (15)

1. A planar multiband antenna (400; 600), comprising:

   a ground area (110);

   a first radiation electrode (130), a second radiation electrode (220) and a third radiation electrode (230); and

   feeding means (120, 140) which is implemented to feed the first radiation electrode (130),

   wherein the first radiation electrode (130) is arranged at least partly between the ground area (110) and the second radiation electrode (220) and does not protrude from an external periphery of the third radiation electrode (230);
   wherein the third radiation electrode (230) is arranged to completely surround an external periphery of the second radiation electrode (220) with a gap (240) therebetween; and
   wherein the third radiation electrode is arranged on that side of the first radiation electrode facing away from the ground electrode; characterized in that
   the third radiation electrode (230) and the second radiation electrode (220) are connected to each other via four conductive connection lands.
2. The planar multiband antenna (400; 600) according to claim 1, wherein the third radiation electrode (230) is implemented such that, in a projection of the second radiation electrode (220) and the third radiation electrode (230) along a direction normal to the second radiation electrode (220) in an image plane, an image of the third radiation electrode (230) completely encloses an image of the second radiation electrode (220).
3. The planar multiband antenna (400; 600) according to claim 1 or 2, wherein the second radiation electrode (220) and the third radiation electrode (230) are in one plane, wherein the third radiation electrode (230) completely encloses the second radiation electrode (220) in the plane.
4. The planar multiband antenna (400; 600) according to one of claims 1 to 3, wherein a distance between the third radiation electrode (230) and the second radiation electrode (220) is smaller than a distance between the third radiation electrode (230) and the first radiation electrode (130).
5. The planar multiband antenna (400; 600) according to one of claims 1 to 4, wherein the first radiation electrode (130), the second radiation electrode (220), the third radiation electrode (230) and the feeding means (120, 140) are implemented such that the planar multiband antenna (400, 600) is able to radiate a circularly polarized electromagnetic wave.
6. The planar multiband antenna (400; 600) according to one of claims 1 to 5, wherein the feeding means (120, 140) includes an aperture (120) in the ground area (110) and a wave guide (140), wherein the first radiation electrode (130), the second radiation electrode (220) and the third radiation electrode (230) are arranged spaced apart from the ground area (110) on a first side of the ground area (110), and
   wherein the wave guide (140) is arranged on a second side of the ground area (110); and
   wherein the wave guide (140) and the first radiation electrode (130) are arranged such that energy from the wave guide (140) can be coupled through the aperture (120) to the first radiation electrode (130) to feed the first radiation electrode (130).
7. The planar multiband antenna (400; 600) according to claim 6, wherein the wave guide (140) and the aperture (120) are implemented to allow radiation of a circularly polarized electromagnetic wave.
8. The planar multiband antenna (400; 600) according to claim 7, wherein the aperture (120) comprises at least a first slot (150) and a second slot (152) which together form a slot in the shape of a cross.
9. The planar multiband antenna (400; 600) according to one of claims 1 to 8, wherein the first radiation electrode (130) and the second radiation electrode (220) comprise equal shapes.
10. The planar multiband antenna (400; 600) according to one of claims 1 to 9, wherein a maximum dimension of the second radiation electrode (220) differs by at most 30% from a maximum dimension of the first radiation electrode (130).
11. The planar multiband antenna (400; 600) according to one of claims 1 to 10, wherein a plane in which the first radiation electrode (130) is arranged forms a positive angle of at most 20 degrees with the ground area (110), wherein a plane in which the second radiation electrode (220) is arranged forms a positive angle of at most 20 degrees with the ground area (110), and wherein a plane in which the third radiation electrode (230) is arranged forms a positive angle of at most 20 degrees with the ground area.
12. The planar multiband antenna (400; 600) according to one of claims 1 to 11, which is implemented such that impedance matching of a standing wave ratio of less than 2 is achieved in at least two frequency bands.
13. The planar multiband antenna (400; 600) according to one of claims 1 to 12, comprising a first dielectric layer, a first layer of low dielectric constant, a second dielectric layer, a second layer of low dielectric constant, and a third dielectric layer, wherein the first dielectric layer supports the wave guide (140) on its first surface and supports the ground area (110) on its second surface,
    wherein the second dielectric layer supports the first radiation electrode (130) on a surface;
    wherein the third dielectric layer supports the second radiation electrode and the third radiation electrode;
    wherein the first layer of low dielectric constant is arranged between the first dielectric layer and the second dielectric layer;
    wherein the second layer of low dielectric constant is arranged between the second dielectric layer and the third dielectric layer;
    wherein a dielectric constant of the first layer of low dielectric constant is smaller than a dielectric constant of the first dielectric layer, wherein the dielectric constant of the first layer of low dielectric constant is smaller than a dielectric constant of the second dielectric layer, and wherein the dielectric constant of the first layer of low dielectric constant is smaller than a dielectric constant of the third dielectric layer; and
    wherein a dielectric constant of the second layer of low dielectric constant is smaller than the dielectric constant of the first dielectric layer, wherein the dielectric constant of the second layer of low dielectric constant is smaller than the dielectric constant of the second dielectric layer, and wherein the dielectric constant of the second layer of low dielectric constant is smaller than the dielectric constant of the third dielectric layer.
14. The planar multiband antenna (400; 600) according to claim 13, wherein the first, second or third dielectric layer consists of FR4 material.
15. The planar multiband antenna (400; 600) according to claim 13 or 14, wherein the first layer of low dielectric constant or the second layer of low dielectric constant is an air layer.

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