Patent Description:
Multiband patch antennas are known and are used for wireless communication devices with no external antennas, i.e. devices in which the antenna is within a housing. However, multiband patch antennas are weakly directional meaning that the emitted electromagnetic radiation is also radiated deeper into the housing of the device. This leads to adverse effects, like interference with the electronic components within the housing.

Multiband patch antennas with highly directional radiation characteristics that do not interfere with the electronic components are usually very thick and thus occupy valuable space within the housing.

<CIT> discloses a dual band stacked patch antenna having two separate patch fields of different patch field types. The patch field are located in different planes spaced apart from one another.

<CIT>, <CIT> and <CIT> also show patch antennas.

<CIT> discloses an antenna having a resonating element, wherein the resonating element includes a cross-shaped patch having arms extending along different axes.

<CIT> discloses an antenna package structure having a plurality of antenna ground planes and an antenna array with active antenna elements and dummy antenna elements.

It is the purpose of the invention to provide a thin multiband patch antenna with a highly directional radiation characteristic.

For this purpose, a multiband patch antenna, in particular a multiband printed circuit board (PCB) antenna according to claim <NUM> is provided.

By overlapping several patch fields with different resonance frequencies, it is possible to achieve a highly directional radiation characteristic of the multiband patch antenna.

Of course, the patch fields emit electromagnetic radiation in conjunction with the ground plane. However, for the sake of simplicity, it is referred to that the patch fields emit the electromagnetic radiation.

A first patch field of a first patch field type with a first resonance frequency, at least one second patch field of a second patch field type with a second resonance frequency and at least one third patch field of a third patch field type with a third resonance frequency are provided, wherein the first patch field partly overlaps with the at least one second patch field and the at least one third patch field, particularly wherein the at least one second patch field and the at least one third patch field do not overlap. This way, the radiation characteristic of each of the resonance frequencies is highly directional.

Preferably, the at least two patch fields are free of cutouts so that the fabrication of the antenna is simplified.

The at least two patch fields may have a rectangular geometry and/or the patch fields of the at least two patch field types may have different sizes. This way, the resonance frequency of the patch fields may be tuned easily.

To this end, the vertical length and/or the horizontal length of the patch fields may depend on the resonance frequency of the respective patch field type.

In an embodiment of the invention, for at least one of the at least two patch field types two patch fields are provided in order to improve radiation performance.

In an aspect, the multiband patch antenna is symmetrical with respect to an axis, particularly wherein the axis extend through the geometric center of the patch fields. This way, the radiation characteristics may be improved further.

The geometric center of the patch fields is, in particular, the geometric center of the antenna area. The antenna area is thus also symmetrical.

For an improved directional radiation characteristics, the ground plane is quadratic and/or has a cutout for each of the at least one feedpoint only, in particular that the ground plane is free of cutouts.

In a further embodiment, the multiband patch antenna comprises a support layer being provided between the at least one patch field and the ground plane, wherein the support layer has a via for each of the at least one feedpoint only, in particular that the support layer is free of vias. This design simplifies fabrication of the multiband patch antenna even further.

For reliable feeding, the at least one feedpoint is provided as a coaxial feed or an insert feed.

For a reliably feed the multiband patch antenna, the at least one feedpoint may be located at the at least one second patch field and/or at the least one third patch field.

In order to improve the radiation characteristics of electromagnetic radiation with the first resonance frequency, the at least one second patch field and at the least one third patch field may be spaced apart by a vertical distance, wherein the sum of the vertical distance, the vertical length of the at least one second patch field and the vertical length of the at least one third patch field is about equal to the horizontal length of the first patch field.

In another embodiment, exactly one first patch field, exactly two second patch fields and exactly two third patch fields are provided, particularly wherein the two second and two third patch fields each overlap with one of the corners of the first patch field.

To improve the radiation characteristics even further, the two third patch fields may be spaced apart by a third horizontal distance, wherein the third horizontal distance is about equal to the horizontal length of the third patch fields and/or the two second patch fields may be spaced apart by a second horizontal distance, wherein either the second horizontal distance is about equal to half of the horizontal length of the second patch fields or the second horizontal distance is about equal to the third horizontal distance.

For a symmetrical radiation characteristic, the geometric center of the first patch field may be the geometric center of the patch fields, in particular the geometric center of the antenna area.

Further features and advantages will be apparent from the following description as well as the accompanying drawings, to which reference is made. In the drawings:.

<FIG> show a multiband patch antenna <NUM>, in the shown embodiment a multiband printed circuit board (PCB) antenna.

The multiband patch antenna <NUM> may be used in devices requiring wireless communication, like routers, access points, weather stations, and mobile devices, like mobile phones, tablets, laptop computers, Internet of Things (IoT) devices and any other device with a communication interface.

The multiband patch antenna <NUM> is for example used for Wi-Fi communication, for example for MU-MIMO WLAN access points.

In such devices, the multiband patch antenna <NUM> may be one of a plurality of similar or identical antennas in an antenna array.

The multiband patch antenna <NUM> comprises a ground plane <NUM>, a support layer <NUM>, a plurality of patch fields <NUM> and a feedpoint <NUM>.

The support layer <NUM> may be a known substrate for printed circuit boards, like a wafer or FR-<NUM>.

The ground plane <NUM> and the patch field <NUM> are located on opposite sides of the support layer <NUM>.

The patch fields <NUM> are created of a conductive material directly onto the support layer <NUM> and all of them have the same thickness.

The ground plane <NUM> is, for example, quadratic. The sides of the quadratic ground plane <NUM> may be <NUM> long. The ground plane <NUM> may be made of a conductive layer created directly on the support layer <NUM>.

The ground plane <NUM> extends in the plane of the support layer <NUM> further than the patch fields <NUM>.

The feedpoint <NUM> is located in one of the patch fields <NUM> and is connected to a signal source <NUM> located on the side of the ground plane <NUM> facing away from the support layer <NUM>.

An electrical connection between the signal source <NUM> and the feedpoint <NUM> is achieved through the support layer <NUM> and the ground plane <NUM>. For this purpose, the ground plane <NUM> and the support layer <NUM> have a cutout and a via, respectively. Apart from the cutout and the via for the feedpoint <NUM>, the ground plane <NUM> and the support layer <NUM> are free of cutouts and vias, respectively.

As can be seen in <FIG>, which shows the multiband patch antenna <NUM> in a top view, the multiband patch antenna <NUM> comprises several patch fields <NUM>.

For illustration purposes, the patch fields <NUM> are drawn distinctly from one another, in reality, however, the patch fields <NUM> define a continuous antenna area <NUM>. In particular, the patch fields <NUM> and thus the antenna area <NUM> are/is free of cutouts.

As can be seen clearly in <FIG>, the multiband patch antenna <NUM> comprises five rectangular patch fields <NUM> being of different patch field types.

In the shown embodiment, the multiband patch antenna <NUM> comprises patch fields <NUM> of three different patch field types, namely a first patch field type A, a second patch field type B and a third patch field type C.

The multiband patch antenna <NUM> comprises exactly one patch field <NUM> of the first patch field type A, called first patch field <NUM> in the following.

Of the second patch field type B, two patch fields <NUM> are provided, called second patch fields <NUM> in the following. Of the third patch field type C also two patch fields <NUM> are provided, called third patch fields <NUM> in the following.

Of course, the number of patch fields <NUM> and patch field types A, B, C are only exemplary. Other numbers of patch fields <NUM> and patch field types are of course conceivable.

In the shown embodiment, all patch fields <NUM>, regardless of the patch field type A, B, C are rectangular, wherein in the patch fields <NUM> of different patch field type A, B, C differ from one another in size.

The first patch field <NUM> is the center of the antenna area <NUM>, i.e. of the multiband patch antenna <NUM> in a top view, and overlaps partly with each of the other patch fields <NUM>, namely the two second patch fields <NUM> and the two third patch fields <NUM>.

Each of the corners of the patch field <NUM> is overlapped with a corner of one of the other patch fields <NUM>. The areas, in which the patch field <NUM> overlap are called overlapping areas O.

For example, with respect to <FIG>, the upper left corner and the upper right corner of the first patch field <NUM> overlap each with a corner of one of the second patch fields <NUM> and the bottom right-hand corner and the bottom left-hand corner of the first patch field <NUM> overlap each with a corner of one of the third patch fields <NUM>, respectively.

In the shown embodiment, the feedpoint <NUM> is provided in the bottom left third patch field <NUM>, in particular outside of the overlapping area O. Of course, the feedpoint <NUM> could also be arranged on any other patch field <NUM>, for example on one of the second patch fields <NUM>.

The feedpoint <NUM> is for example a coaxial feed or an insert feed.

<FIG> shows the patch fields <NUM>, i.e. the antenna area <NUM>, in greater detail.

The different sizes of the patch fields <NUM>, <NUM>, <NUM> of the different patch field types A, B, C become clearer in <FIG>.

For the sake of distinction, the direction of the y-axis of <FIG> is referred to as the vertical direction and the direction of the x-axis is referred as the horizontal direction. This nomenclature is, of course, independent of the mounting position of the multiband patch antenna <NUM>.

The dimensions of each patch field type A, B, C are chosen such that a respective patch field has a predefined resonance frequency. The resonance frequency is the frequency of electromagnetic radiation emitted by the respective patch field <NUM> in conjunction with the ground plane <NUM>, when fed with a feed signal through the feedpoint <NUM>.

First patch fields <NUM> of the first patch field type A have a first resonance frequency f<NUM>, for example <NUM>, the second patch fields <NUM> of the second patch field type B have a second resonance frequency f<NUM>, for example <NUM>, and the third patch fields <NUM> of the third patch field type C have a third resonance frequency f<NUM>, for example <NUM>.

The first resonance frequency f<NUM>, the second resonance frequency f<NUM> and the third resonance frequency f<NUM> differ from one another.

The first patch field <NUM>, the second patch field <NUM> and the third patch field <NUM> together may emit electromagnetic radiation - when fed with a feed signal through feedpoint <NUM> - with a further frequency or one of the resonance frequencies f<NUM>, f<NUM>, f<NUM>.

The resonance frequency of a patch field can be determined by the so-called cavity model, which is known in the art, that yields the horizontal and vertical length of the patch field for a desired resonance frequency and a desired mode.

For example, the horizontal length a<NUM> and the vertical length a<NUM> of the first patch field <NUM> of the first patch field type A, the horizontal length b<NUM> and vertical length b<NUM> of the second patch fields <NUM> of the second patch field type B and the horizontal length c<NUM> and vertical length c<NUM> of the third patch fields <NUM> of the third patch field type C may be determined as shown in the following table, wherein c<NUM> is the speed of light in vacuum, and εreff is the effective permittivity at the specified frequency. The calculations are carried out for the dominant TM<NUM> mode.

In the shown embodiment, the arrangement of the patch fields <NUM>, and thus the antenna area <NUM>, is symmetrical with respect to an axis S that runs vertically, i.e. parallel to the y-axis, and through the geometric center D of the patch fields <NUM>, i.e. antenna area <NUM>, which is in the shown embodiment also the geometric center of the first patch field <NUM>.

This geometric center of the antenna area <NUM> is regarded as the origin of the coordinate system of <FIG>.

The second patch fields <NUM> are spaced apart by a distance d<NUM> and the third patch fields <NUM> are spaced apart by a distance d<NUM>.

In the shown embodiment, distance d<NUM> and distance d<NUM> are about, in particular exactly equal to one another and correspond to the horizontal length c<NUM> of the third patch fields <NUM>. Because of the symmetry, the distance of the second patch fields <NUM> and the third patch fields <NUM> from the vertical axis S (y-axis) amounts to half of distance d<NUM>, half of distance d<NUM>, respectively.

It is of course conceivable, that the distances d<NUM>, d<NUM> are different from one another. In this case, distances d<NUM>, d<NUM> may be about or particularly exactly equal to the horizontal length b<NUM>, c<NUM> of the second and third patch fields <NUM>, respectively.

The left-hand side second patch field <NUM> and third patch field <NUM> are spaced apart by a vertical distance e. The right-hand side second patch field <NUM> and third patch field <NUM> are also spaced apart by the same vertical distance e.

The vertical distance e may be chosen such that the sum of the vertical distance e, the vertical length b<NUM> and the vertical length c<NUM> is about or exactly equal the horizontal length a<NUM> so that the vertical length of the whole antenna area <NUM> is the horizontal length a<NUM> and thus half a wavelength of electromagnetic radiation with a frequency f<NUM>.

With respect to the geometric center D, in the shown embodiment, the location of the feedpoint <NUM> is <NUM> in the horizontal direction and <NUM> in the vertical direction on one of the third patch fields <NUM>.

For example, the described parameters may take the following values f<NUM> = <NUM>, f<NUM> = <NUM>, f<NUM> = <NUM>, a<NUM> = <NUM>, a<NUM> = <NUM>, b<NUM> = <NUM>, b<NUM> = <NUM>, c<NUM> = <NUM>, c<NUM> = <NUM>, d<NUM> = d<NUM> = <NUM> and e = <NUM>. The feedpoint <NUM> lies at x = <NUM> and y = -<NUM>. The thickness of the ground plane <NUM> and support layers <NUM> is <NUM> and the thickness of the support layer <NUM> is <NUM>.

The deviations from the seemingly exact relations above are due to a numeric optimization. The values are still to be regarded as about equal to the relations given in the equations above.

Claim 1:
Multiband patch antenna, preferably a multiband PCB antenna, comprises a ground plane (<NUM>), at least one feedpoint (<NUM>), and at least two different patch fields (<NUM>; <NUM>, <NUM>, <NUM>) defining a continuous antenna area and being of at least two different patch field types (A, B, C),
wherein each patch field type (A, B, C) is designed for a different predefined resonance frequency (f<NUM>, f<NUM>, f<NUM>),
wherein at least two of the patch fields (<NUM>; <NUM>, <NUM>, <NUM>) have overlapping areas (O), and
wherein the feedpoint (<NUM>) is positioned in a way that, when a feed signal is fed to the feedpoint (<NUM>), each of the at least two patch fields (<NUM>; <NUM>, <NUM>, <NUM>) emits electromagnetic radiation having the frequency of the predefined resonance frequency (f<NUM>, f<NUM>, f<NUM>) of the respective patch field (<NUM>; <NUM>, <NUM>, <NUM>) and/or a combination of two or more of the at least two patch fields (<NUM>; <NUM>, <NUM>, <NUM>) emits electromagnetic radiation having a frequency of one of the resonance frequencies (f<NUM>, f<NUM>, f<NUM>),
characterized in that the multiband patch antenna comprises a first patch field (<NUM>) of a first patch field type (A) with a first resonance frequency (f<NUM>), at least one second patch field (<NUM>) of a second patch field type (B) with a second resonance frequency (f<NUM>) and at least one third patch field (<NUM>) of a third patch field type (C) with a third resonance frequency (f<NUM>), wherein the first patch field (<NUM>) partly overlaps with the at least one second patch field (<NUM>) and the at least one third patch field (<NUM>).