Patent Description:
Radio frequency ("RF") apparatuses such as transponders usually include a patch antenna. A patch antenna primarily consists of a flat sheet of metal, more simply called a patch, arranged over a larger sheet of metal, called a ground plane. In case of microwave circuits, at least some of the associated circuitry needs to be mounted on a substrate that has suitable properties, such as low loss. Such substrates suitable for microwave applications, or more simply called microwave substrates, are generally expensive. The related feed network and circuitry usually requires a microwave substrate for achieving required performance. Usually the feed network and the related circuitry is placed on the ground plane side of the substrate. Even though the rest of the circuitry, besides the microwave circuitry, might not require a special substrate, or microwave substrate, the complexity and cost of adding yet another low-cost/low-performance substrate for the rest of the circuitry does not necessarily pay off. As a result, the overall cost of the apparatus is increased.

<CIT> teaches a miniaturized circularly polarized SDS patch antenna, but it does not address the requirements related to the related circuitry.

<CIT> describes an antenna arrangement including a patch antenna with corresponding microwave circuitry positioned relative to a ground plane using substrates being positioned directly on top of each other. Similar devices are described in the article <NPL> as well as in <CIT> and <CIT>.

The above-mentioned and other problems inherent to the prior art will be shown solved by the features of the accompanying independent claim.

According to an object of the present teachings a patch antenna arrangement that allows utilization of a low cost substrate for the ground-plane can be provided.

According to further an object of the present teachings an integrated patch antenna can be provided.

The present teachings will now be discussed more in detail using the following drawings illustrating the aspects of the teachings by way of examples. The figures are not necessarily drawn to scale, without affecting the scope of the invention as defined in the claims.

<FIG> shows a perspective view (A) and a side view (B) of a conventional patch antenna arrangement <NUM>. The antenna arrangement <NUM> comprises a patch antenna <NUM> placed upon the top-side <NUM> of a substrate <NUM>. On the bottom-side <NUM> of the substrate <NUM>, a ground plane <NUM> is placed. The patch antenna <NUM> and the ground plane <NUM> are usually realized in metal. The patch <NUM> is designed to electrically resonate at a desired frequency over the ground plane <NUM>. On the bottom-side <NUM> of the substrate <NUM>, circuitry is placed. The circuitry includes microwave circuitry <NUM>, that includes components such as feed network and circuits that require a special substrate, but the circuitry can also include other circuits and components <NUM> that do not require a special, or microwave, substrate. The microwave circuitry is connected through a feedline <NUM>, and thereafter to a probe type feed <NUM> for electrically connecting to the patch antenna <NUM>. The positioning of the feed <NUM> normally defines the impedance. The impedance is typically <NUM> ohm, but it can be designed for other values as well as per requirements. Even though the feedline <NUM> can be realized as a microstrip in the same metal layer as the ground plane (not explicitly shown in the figures), it may not be desirable to alter or disrupt the integrity of the ground plane <NUM>. A person skilled in the art will understand that alternatives to this are possible, for example, isolated bridges, or other kinds of isolated tracks, or another dielectric layer, or even another substrate.

Due to requirements set by the microwave circuitry, the substrate <NUM> is a microwave substrate. Even though the rest of the circuitry <NUM> besides the microwave circuitry <NUM> might not require a special substrate or microwave substrate <NUM> for functioning adequately, the complexity and cost of adding yet another low-cost/low-performance substrate for the rest of the circuitry <NUM> does not necessarily pay off, as a result the other circuitry <NUM> is also sharing and occupying area on the same expensive substrate <NUM>.

In an alternative arrangement (not shown in figures), the patch <NUM> is not in direct contact with the microwave substrate <NUM>. In this case the patch <NUM> may be separated from the microwave substrate <NUM> either by an airgap or by another dielectric substrate (not shown in figures). The ground plane can thus in this case be formed on the top-side <NUM> of the substrate, whilst the microwave circuitry <NUM> and the other circuitry <NUM> can still be placed on the bottom side <NUM> of the substrate <NUM>. An advantage of doing this is that either both <NUM> and <NUM>, or at least the microwave circuitry <NUM> may be placed directly underneath the patch <NUM> with a minimal disturbance or disruption in the integrity of the ground plane, which in this case will be formed in the metal layer on the top-side <NUM> of the microwave substrate <NUM>. However, in this case also, adding an alternative low-cost/low-performance substrate for the rest of the circuitry <NUM> is not necessarily worth. Since the required microwave properties of the substrate <NUM> may mean that low cost, e.g., FR4 type, laminates cannot be used, more expensive microwave substrates have be used not only for the entire circuitry but also for the ground plane <NUM>.

In many applications, the area of the ground plane <NUM> needs to be at least twice the area of the patch antenna <NUM>, so this means that a microwave substrate at least as large as the area of the ground plane may be required.

<FIG> shows an arrangement <NUM> according a first aspect of the present teachings. <FIG> illustrates a perspective view (A) and a side view (B) of the antenna arrangement <NUM>. In this case, the patch antenna <NUM> is arranged on the top-side <NUM> of a first substrate <NUM>. On the bottom-side of the first substrate <NUM>, substrate sensitive circuitry or microwave circuitry <NUM> is placed or mounted. The combination of essentially; the patch antenna <NUM>, the first substrate <NUM>, and the microwave circuitry <NUM> is termed herein as a "patch antenna group".

The microwave circuitry <NUM> is operably in electrical coupling with the patch antenna <NUM> through a first feed <NUM> that traverses vertically through, or is a via in, the first substrate <NUM>. Alternatively the first feed <NUM> may also contact the antenna <NUM> from a vertical conductive path placed at a desired location on the periphery or edge of the first substrate <NUM> (alternative case not shown in the figures).

The antenna arrangement <NUM> also comprises a second feed <NUM>. The second feed <NUM> can be used, for example, for feeding low frequency signals such as supply voltages and baseband signals to the patch antenna group. Said signals are preferably fed at a "cold" point or spot of the patch <NUM>. In the shape of the patch antenna <NUM> shown, a location essentially at the center of the patch <NUM> is known to be such a "cold" spot, i.e., it typically displays a minimum microwave signal voltage. The example illustrated in <FIG> however does not show the second feed <NUM> contacting at the center of the patch antenna <NUM>, even though it is usually preferable to place the second feed at a cold spot.

<FIG> further shows a ground plane <NUM> that is arranged on the top-side <NUM> of a second substrate <NUM>. <FIG> also shows some field lines <NUM> between the patch antenna <NUM> and the ground plane <NUM>. The second feed <NUM> is in contact with the same conductive layer (typically a metal layer) that the ground plane <NUM> is realized in, however the second feed <NUM> is electrically isolated from the ground plane. The same metal layer on the top-side <NUM> of the second substrate <NUM> can also be used to pattern and route any additional circuitry, for example <NUM> (not shown in <FIG>).

The second feed may also be acting as a mechanical support for the patch antenna group as shown arranged above the top-side <NUM> of the second substrate <NUM>. This is especially the case if the spacing between the patch antenna group and the ground plane <NUM> as shown in <FIG> is an air-gap. There could also be other mechanical supports for mechanically supporting the patch antenna group. These other mechanical supports may or may not be electrically conductive. In case they are electrically conductive, they may also be used for feeding low-frequency or DC signals between the patch antenna group and the other circuitry, for example, <NUM> (not shown in <FIG>).

The bottom-side <NUM> of the second substrate <NUM> is shown empty or unpatterned in <FIG>, but it may include another metal layer if required. Alternatively, or in addition, the additional circuitry may be mounted and or routed on the bottom-side <NUM> of the second substrate <NUM>. In this case, the bottom side <NUM> will also have a conductive layer, or a metal layer for routing and mounting of the additional circuitry.

As a general note, as commented previously, the figures are not essentially to scale, some features sizes may even be disproportionately enlarged with respect to other parts shown in the figures, for the sake of clarity of some features in the figures. For example, the thickness of metal layers <NUM> and <NUM> will usually be significantly smaller than the thickness of the substrate <NUM> in most cases. The skilled person will further note that even though the patch antenna <NUM> is shown in a circular profile in the figures, other shapes such as, square, triangular, semicircular, sectoral, annular ring shapes, and others shapes also fall within the ambit of the invention. Furthermore, as also commented previously, the patch antenna <NUM> and the ground plane <NUM> are normally realized in metal layers. Such layers are deposited, or formed, by a process such as deposition and/or lithography, or other suitable processes, over the substrate <NUM>. These layers, i.e., the one for the patch antenna <NUM>, and the one for the ground plane <NUM> are often of the same material.

In figures, for example, in <FIG>, the cross-sections of these layers are shown in different shading. This is done primarily for making it easier to correlate layers of similar functionality discussed in various aspects of the present teachings in this disclosure. It will further be appreciated that in this disclosure terms like top, bottom, downwards, are used in a relative sense and in relation to the orientation of the pictures shown in the figures for ease of understanding. Such terms do not limit the functionality or generality of the present teachings. The material of these layers, whether similar or not is not limiting to the scope of the invention as defined in the claims. It can also be mentioned that even though it may be apparent by looking at the figures that the ground plane covers the entire surface of the substrate side where the ground plane is placed, it may not necessarily be the case. It is also possible to place at least the other circuitry besides the ground plane, routed in the same metal layer as the ground plane is realized in. The size or area of the ground plane is usually related to the size and shape of the patch antenna. It is often desired to have the ground plane area extending beyond the footprint of the patch antenna especially for reducing back radiation. In cases where back radiation is actually desired, the ground plane size may be roughly of the same size as the patch antenna aligned over it. Such aspects of antenna design are known in the field.

It can further be mentioned that the spacing between the patch antenna and the ground plane in the present invention is usually arranged between around <NUM>% and around <NUM>% of the diameter of the patch antenna when the patch antenna has a circular shape. In case the patch antenna has another shape or pattern, a similar range with respect to a circle encompassing the periphery of the antenna shape may be used. In typical cases, the spacing is around <NUM>% of the diameter of the patch antenna. Besides, the spacing may also be calculated, for example, based upon bandwidth requirements from the antenna, and may thus even be determined empirically or by experiments.

According to an aspect, in the antenna arrangement, the second substrate <NUM> is used only for providing the conducting ground plane <NUM>. According to another aspect, the second substrate <NUM> is used also for mounting the other circuitry <NUM>.

In either case, the second substrate <NUM> may be a low cost type, for example, a low-cost PCB such as FR4 type or other low-cost glass-reinforced epoxy laminates. As a result, only the first substrate <NUM> substrate of the patch antenna group requires to have microwave properties. Since the area of such a substrate is similar to the and area of the patch antenna <NUM>, the overall cost of the substrate is appreciably reduced. Furthermore, the crucial feed arrangement <NUM> is relatively simplified and routing distance thereof is reduced as the microwave circuitry <NUM> does not utilize the metal layer that the ground plane <NUM> uses. This further means that the footprint of the microwave circuitry <NUM> may be further minimized, which also appreciably reduces the area required by the microwave circuitry <NUM> realized according to the present teachings.

Another advantage of the present teachings is that the patch antenna group may be realized as an independent module and placed at a suitable location on different kind of wireless products without demanding special requirements such a special PCB, or necessity to adapt PCB layout for the microwave circuitry. The requirements for a suitable location in simplest sense will be that it provides a ground plane and area for mounting the patch antenna group. The second substrate may even be a multilayered PCB with at least some of the other circuitry lying within the footprint of the patch antenna group. In this way, overall size of a wireless apparatus, using the antenna arrangement as proposed, may be reduced without significantly affecting the performance of the patch antenna group. In addition, when realized as an independent module, capable of being mounted on different kinds of PCBs and wireless products, the development costs may also be reduced, for example, by being able to reuse the same design of the patch antenna group.

Yet another advantage of the present teachings is that the patch antenna group may be flipped either way. This is shown in <FIG> where a side view of an antenna arrangement <NUM> with a flipped patch antenna group is illustrated. In this case, on the top-side <NUM> of the first substrate <NUM>, microwave circuitry <NUM> is mounted. The first feed <NUM> now traverses downwards from the microwave circuitry <NUM> to make electrical contact with the patch antenna <NUM> which is now arranged on the bottom-side of the patch antenna group. The second feed <NUM> now traverses through the patch antenna <NUM> to make electrical contact with the microwave circuitry <NUM> on the top-side <NUM>. For electrically isolating the second feed <NUM> from the patch antenna <NUM>, an opening <NUM> is provided into the patch antenna for the second feed <NUM> to pass through without contacting the patch antenna <NUM>. The field lines <NUM> are also shown. Rest of the arrangement is essentially similar to that shown in <FIG>.

A flexibility in terms of possibility to flip the patch antenna group means that the arrangement as most suitable in a given application may be selected. As an example, the arrangement of <FIG> may be more suitable in applications where it is desired to have the patch antenna <NUM> least exposed to other components around a package where the antenna arrangement is to be installed. The arrangement of <FIG> may also provide better flexibility in terms of adjusting antenna impedance in terms of adapting the distance between the patch antenna <NUM> and the ground plane <NUM>.

As also described earlier, a skilled person will note that the spacing between the patch antenna group and the top-side <NUM> of the second substrate may either be an air-gap or even be a suitable material of desired dielectric constant. These aspects are flexible according to desired antenna properties and system requirements. The examples in this disclosure are shown in their simplest sense for ease of explanation.

The skilled person will also appreciate that the aspects and embodiments explained in this disclosure can be combined with each other to realize an antenna arrangement according to specific requirements. Discussion of an embodiment separately does not mean that an aspect of the teachings cannot be used with the rest of the examples or other embodiments presented herein.

To summarize, the present teachings relate to an antenna arrangement comprising, a patch antenna, a ground plane, at least some microwave circuitry, and a first substrate. The first substrate comprises a first surface and a second surface. The first surface and the second surface are opposite sides of the first substrate. The first surface and the second surface are essentially parallel to each another, with a separation essentially equal to the thickness of the first substrate. In other words, it can be said that the first surface and the second surface are the surfaces having the largest area in the first substrate. The patch antenna is realized in a first electrically conductive material attached to the first surface. The first electrical material is preferably a metal or it comprises at least partially a metal. The patch antenna is arranged with respect to the ground plane so as to form a resonant antenna. The term resonant antenna is well-known in the relevant technical field. Preferably the patch antenna is essentially parallel to the ground plane. Also preferably, the surface of the ground plane is centered with respect to the patch antenna surface. The microwave circuitry is mounted on the second surface. The microwave circuitry is operably connected to the patch antenna through a first feed. The surface area of the ground plane is preferably, but not essentially, greater than the surface area of the patch antenna. The antenna arrangement further comprises a second substrate. The second substrate comprises a third surface and a fourth surface. The third surface and the fourth surface are opposite sides of the second substrate. The third surface and the fourth surface are essentially parallel to each another, with a separation essentially equal to the thickness of the second substrate. The ground plane is realized in a second electrically conductive material attached to the third surface. The second electrical material is preferably a metal or it comprises at least partially a metal.

When referring to the surfaces or areas, especially of the conductive layers such as metal, a person skilled in the art understands which area and surface is meant when referring to such areas or surfaces. Since thickness of such layers is usually significantly smaller than the dimensions of the other exposed area when deposited on a surface, by saying the surface area, it is usually meant, the surface area essentially parallel to the essentially parallel surfaces of the substrate. With reference to the figures, the first surface corresponds for example, with the top-side <NUM> of the first substrate <NUM> shown in <FIG>. The second surface corresponds to the surface on the other side, i.e., the surface where the microwave circuitry110 is shown mounted.

In one embodiment, the surface area of the ground plane is at least <NUM> times the surface area of the patch antenna. In a preferred embodiment, the surface area of the ground plane is essentially <NUM> times the surface area of the patch antenna.

Preferably, the first substrate is a microwave substrate.

Also preferably, the second substrate is a low-cost PCB such as FR4 type or other low-cost glass-reinforced epoxy laminate.

In one embodiment, the first surface is arranged to directly face the ground plane surface. Alternatively, the first surface is arranged to face away from the ground plane surface.

According to the invention the antenna arrangement also comprises a second feed. The second feed is operably electrically connected to at least the microwave circuitry or the patch antenna. Preferably, the second feed is used for feeding low frequency signals such as supply voltages and/or baseband signals to the microwave circuitry. The second feed is also be used for mechanically supporting and retaining the first substrate at least resiliently fixed with respect to the second substrate.

Claim 1:
An antenna arrangement comprising,
a patch antenna (<NUM>);
a ground plane (<NUM>);
microwave circuitry (<NUM>); and
a first substrate (<NUM>) comprising a first surface and a second surface, the first surface and the second surface being opposite sides of the first substrate (<NUM>), being essentially parallel,
the patch antenna being realized in a first electrically conductive material attached to the first surface, and the patch antenna being arranged with respect to the ground plane so as to form a resonant antenna;
the microwave circuitry (<NUM>) being mounted on the second surface of the first substrate (<NUM>), and the microwave circuitry being operably connected to the patch antenna through a first feed (<NUM>), wherein
the antenna arrangement further comprises a second substrate (<NUM>), said second substrate comprising a third surface and a fourth surface, the third surface being essentially parallel to the patch antenna (<NUM>), the third surface and the fourth surface being opposite sides of the second substrate (<NUM>), and the ground plane (<NUM>) being realized in a second electrically conductive material attached to the third surface (<NUM>) and the surface area of the ground plane being at least <NUM> times the surface area of the patch antenna, and wherein
the antenna arrangement comprises a second feed (<NUM>) connected the microwave circuitry (<NUM>) or the patch antenna (<NUM>), the second feed (<NUM>) also being in contact with the same conductive layer that the ground plane (<NUM>) is realized in and being electrically isolated from the ground plane, and
wherein the second feed (<NUM>) is also configured for mechanically supporting and retaining the first substrate (<NUM>) with respect to the second substrate (<NUM>).