Patent Description:
Today, there is an increasing demand for high-throughput satellite communication in portable terminals. However, it is a challenging task to combine high bandwidth communication capacity with coverage in sparsely populated or desolate areas. Providing a truly mobile satellite-based broadband service not only requires compact terminals. It is also necessary that the terminals can be manufactured at a reasonable cost to enable communication services at an attractive price.

The prior art contains some examples of broadband antennas. However, for various reasons, none of these is suitable for mobile applications.

<CIT> shows an antenna, which comprises a ground plane and at least a first and a second antenna element. Here, each antenna element has a feed point, a cavity, a main body, a tip and at least a first tapered portion and a second tapered portion. Each antenna element is arranged on the ground plane, where said first and second tapered portions extend along the antenna element from said tip towards the ground plane of the antenna element, and where each antenna element extends essentially perpendicularly to said ground plane along a center axis of the antenna element. Each antenna element has at least a first leg and a second leg, where said first leg extends from said main body to the first feed point, where said feed point is located between the first leg and the ground plane, and where said second leg extends from said main body to the ground plane, and where said second leg is electrically connected to the ground plane.

<CIT> describes an electrically controlled group antenna, an antenna element suitable for incorporation in such a group antenna and an antenna module including several such antenna elements. The antenna elements include a rotationally symmetrical body tapering towards one end of the body. The rotationally symmetrical body is provided with a metallic casing surface. Several antenna elements are arranged separately on a common earth plane. A broadband group antenna is achieved that has a relatively simple design.

Both the above solutions are suitable for handling broadband signals. However, neither of them has a design appropriate for portable satellite communication equipment. Namely, the antennas are bulky, fragile and/or complex to manufacture.

One object of the present invention is therefore to offer a compact antenna design suitable for handling broadband signals.

Another object of the invention is to offer a solution that enables such an antenna design to be produced at relatively low cost.

Further, it is an object of the invention to provide a comparatively sturdy and robust design of an antenna suitable for handling broadband signals.

According to the invention, these objects are achieved by an antenna array including an array of antenna bodies that are arranged on a planar structure. The planar structure contains a circuit board with a ground plane. The array of antenna bodies is arranged on a top side of the circuit board. Each of the antenna bodies has a dome shaped structure, which is attached to the top side of the circuit board along its base. Each of the antenna bodies is connected to a respective top transmission line that is configured to convey microwave signals to and/or from the antenna bodies. The top transmission lines are further connected to bottom transmission lines via coaxial probes through the ground plane. A resonance cavity is arranged below a bottom side of the circuit board between each of said antenna bodies.

This antenna is advantageous because the circuit-board based design renders the manufacturing process very cost-efficient. It is further straightforward to attain high physical precision when building the antenna around a two-dimensional base in the form of a printed circuit board. Moreover, this type of design results in high overall space efficiency. In other words, the antenna can be made physically thin, especially in comparison to the above-mentioned prior-art solutions. In fact, it is straightforward to include the proposed antenna array in a portable transceiver design compact enough to qualify as carry-on luggage that can be fitted into the overhead compartment of a passenger aircraft.

According to one embodiment of the invention, the antenna bodies are designed to form horns between one another. In particular, a first electrically conductive surface element of a first antenna body is configured to constitute a first portion of an antenna horn, and a second electrically conductive surface element of a second antenna body of said antenna bodies is configured to constitute a second portion of the antenna horn. The first and second antenna bodies adjoin one another in such a manner that the first and second electrically conductive surface elements are located closer to one another than any other surface elements of the first and second antenna bodies.

Preferably, each antenna body is mirror symmetric in exactly two planes that are orthogonal to one another. The antenna bodies are further arranged in the array according to a pattern in which the first and second electrically conductive surface elements of adjoining antenna bodies pairwise form a respective antenna horn in such a manner that the antenna array contains antenna elements configured to transmit and/or receive signals of a first polarization direction via a first subset of said horns and transmit and/or receive signals of a second polarization direction via a second subset of said horns. The first and second polarization directions are here orthogonal to one another and each of the antenna bodies form part of at least one horn included in the first subset and at least one horn included in the second subset. This, is beneficial both in terms of efficiency and design flexibility, since the mutual relationship between the antenna bodies ensures high isolation between signals representing the two polarization directions while enabling the shape of the of the antenna bodies and the distances between them to be optimized to match a particular range of the electromagnetic spectrum.

According to another embodiment of the invention, the base of the dome shaped structure of each antenna body is octagon shaped. Further, each of the horns formed by the first and second electrically conductive surface elements has a tapered profile towards the top side of the circuit board. Moreover, an aperture between these electrically conductive surface elements is symmetric around a normal to the top side of the circuit board. This design is advantageous because it provides further adjustment possibilities with respect to bandwidth requirements and physical form factors.

According to yet another embodiment of the invention, the ground-plane layer is electrically connected to a first circuit pattern on the bottom side of the circuit board, which first circuit pattern is further electrically connected to a second circuit pattern on the top side of the circuit board by means of a plurality of vias through the circuit board. Thereby, the ground plane extends also to the top side of the circuit board. Thus, the antenna bodies can be connected to external circuitry in a very compact and efficient manner.

According to embodiments the invention, the top transmission line arrangement is implemented in suspended stripline, microstrip or stripline design, and the bottom transmission line is implemented by means of a suspended stripline design, a coaxial cable, stripline design or microstrip design. Consequently, a broad range of design options is provided, both in terms of how to implement the antenna itself and in terms of how the connections thereto are embodied.

According to another embodiment of the invention, antenna bodies are attached to the top side of the circuit board by of soldering and/or mechanical fasteners. This renders the manufacturing procedure uncomplicated and cost-efficient. The resulting antenna also becomes comparatively durable.

According to yet another embodiment of the invention, the antenna includes a shell member of a non-conductive material. The shell member is arranged on the planar structure and contains a plurality of cavities, which each constitutes one of the antenna bodies. An electrically conductive layer covers a respective active surface of each cavity, which active surface faces the top side of the circuit board. Thus, the shell member implements the entire array of antenna bodies in a single piece. Naturally, this renders the production process very time efficient.

Preferably, the shell member has a generally flat exterior surface that faces away from the top side of the circuit board because this gives the antenna a nice-looking and easy to clean exterior surface.

<FIG> shows a planar structure <NUM> with antenna bodies according to one embodiment of the invention. The antenna bodies are arranged in an array on a top side of a circuit board that is included in the planar structure <NUM>. This means that the antenna bodies are organized in a pattern of straight rows and columns. The exact number of antenna bodies is not critical. However, of course, a larger number of antenna bodies is associated with higher efficiency than a ditto lower number. Preferably, although not necessarily, the pattern is equilateral, i.e. the number of rows equals the number of columns, say <NUM> by <NUM> to <NUM> by <NUM>, preferably <NUM> by <NUM> to <NUM> by <NUM>. In <FIG>, first and second exemplifying antenna bodies are designated by reference numerals <NUM> and <NUM> respectively.

The planar structure <NUM> further contains a ground-plane layer that is arranged below a bottom side of the circuit board, i.e. opposite to antenna bodies <NUM> and <NUM>. <FIG> shows an example of such a ground-plane layer <NUM> seen from a top side thereof. The ground-plane layer <NUM> is made of an electrically conductive material, such as a metal, e.g. aluminum.

Each of the antenna bodies <NUM> and <NUM> contains a dome shaped structure, which is attached to the top side of the circuit board <NUM>, for example by means of soldering and/or mechanical fasteners. The antenna bodies <NUM> and <NUM> are attached along a respective base of the dome shaped structure. The mechanical fasteners may be represented by snap in fasteners or an arrangement of compressed springs configured to provide galvanic contact between the antenna bodies <NUM> and <NUM> and a circuit pattern on the top side of the circuit board.

Turning now to <FIG>, we see a cross-section side view, illustrating the structure of the antenna array according to one embodiment of the invention.

Each antenna body <NUM> and <NUM> is connected to a respective top transmission line <NUM>, which is configured to convey microwave signals to and/or from the antenna body <NUM> or <NUM> respectively, i.e. for transmitting and/or receiving electromagnetic energy. Here, the top transmission lines <NUM> are implemented in suspended stripline design. The top transmission lines <NUM> are further connected to bottom transmission lines <NUM> via a respective coaxial probe <NUM> through the circuit board <NUM> and the ground-plane layer <NUM>. The ground-plane layer <NUM> may be a solid piece of metal in which a pattern of cavities and openings have been milled out. In this embodiment, also the bottom transmission line <NUM> is implemented in suspended stripline design. However, as will be discussed below, a number of alternative bottom transmission line designs are also conceivable according to the invention. In fact, the same is true for the top transmission line design. Furthermore, according to the invention, any combination of top and bottom transmission line design is possible. The choice of the designs used is merely a matter of what is most suitable for the specific implementation.

A plurality of vias <NUM> through the circuit board <NUM> connect the ground-plane layer <NUM> to circuitry on the top side of the circuit board <NUM> so that the ground plane effectively extends above the circuit board <NUM> and thus can be further connected to the antenna bodies <NUM> and <NUM>.

A resonance cavity <NUM> is arranged below the bottom side of the circuit board <NUM> between each of said antenna bodies <NUM> and <NUM> respectively. The resonance cavity <NUM> constitutes a stub, i.e. a length of waveguide connected at one end only, which is configured to direct as much as possible of the electromagnetic energy from the top transmission line <NUM> "upwards" towards the antenna bodies <NUM> and <NUM>. Analogously, when the antenna operates in a receiving mode, the resonance cavity <NUM> configured to direct as much as possible of the electromagnetic energy that reaches the antenna bodies <NUM> and <NUM> "downwards" towards the top transmission line <NUM>.

In <FIG>, the resonance cavity is represented by the reference numeral <NUM>. As can be seen here, the resonance cavity <NUM> is, in fact, a continuous milled-out volume between all the antenna elements, which each is mounted on a respective "island" <NUM> and <NUM> respectively where no, or only relatively little, material has been milled out from the solid piece of metal.

According to one embodiment of the invention, each antenna body <NUM> and <NUM> contains electrically conductive surface elements. Specifically, here, a first electrically conductive surface element <NUM> of a first antenna body <NUM> is configured to constitute a first portion of an antenna horn. Analogously, a second electrically conductive surface element <NUM> of a second antenna body <NUM> is configured to constitute a second portion of the antenna horn. The first and second antenna bodies <NUM> and <NUM> adjoin one another in such a manner that the first and second electrically conductive surface elements <NUM> and <NUM> respectively are located closer to one another than any other surface elements of the first and second antenna bodies <NUM> and <NUM>. Thus, together, the first and second electrically conductive surface elements <NUM> and <NUM> form a horn configured to convey electromagnetic waves towards or from the top transmission line <NUM> depending on whether the antenna receives or transmits signals.

Each of the horns formed by the first and second electrically conductive surface elements <NUM> and <NUM> has a tapered profile towards the top side of the circuit board <NUM>, for example as illustrated in <FIG>. An aperture towards the resonance cavity <NUM> between the first and second electrically conductive surface elements <NUM> and <NUM> is symmetric around a normal to the top side of the circuit board <NUM>.

The distance between the first and second electrically conductive surface elements <NUM> and <NUM> along the circuit board <NUM>, the center distance between the first and second antenna bodies <NUM> and <NUM>, the height of the first and second antenna bodies <NUM> and <NUM> above the circuit board <NUM> and the profile of the first and second electrically conductive surface elements <NUM> and <NUM> are different design parameters, which are selected depending on the frequency spectrum, the efficiency required and various physical constraints placed on the implementation.

Preferably, each antenna body <NUM> and <NUM> is mirror symmetric in exactly two planes that are orthogonal to one another. For example, the base of the dome shaped structure of the antenna bodies <NUM> and <NUM> may be octagon shaped, as shown in <FIG>.

The antenna bodies <NUM> and <NUM> are further preferably arranged in the array according to a pattern in which the first and second electrically conductive surface elements <NUM> and <NUM> of adjoining antenna bodies pairwise form a respective antenna horn in such a manner that the antenna array contains horns of first and second subsets. The horns of the first subset are configured to transmit and/or receive signals of a first polarization direction, and the horns of the second subset are configured to transmit and/or receive signals of a second polarization direction, which is orthogonal to the first polarization direction. Moreover, each of the antenna bodies <NUM> and <NUM> form part of at least one horn that is included in the first subset and at least one horn that is included in the second subset. In <FIG>, the first subset horns may contain all the electrically conductive surface elements <NUM> and <NUM> extending along a vertical direction, and the second subset horns may contain all the electrically conductive surface elements extending along a horizontal direction in the array of antenna bodies.

An antenna array, wherein the base of the dome shaped structure of each antenna body <NUM> and <NUM> is octagon shaped is advantageous because such geometry provides high isolation between signals representing the two orthogonal polarization directions. At the same time, the octagon shape renders it straightforward to configure the antenna bodies so that their tapered profile and the distances between the antenna bodies is optimized to match a particular range of the electromagnetic spectrum in which the antenna array is to operate. For example, in contrast to a design where the antenna bodies are circularly symmetric, the octagon-shaped base makes it possible to vary a distance along which an opening between the first and second electrically conductive surface elements <NUM> and <NUM> are effectively parallel to one another towards the resonance cavity <NUM> without the need to alter a center-to-center distance between the antenna bodies. From a design point-of-view, this is very beneficial when optimizing the design to a match particular frequency range of operation.

<FIG> shows a cross-section a side view illustrating the structure of the antenna array according to another embodiment of the invention. Here, the top transmission line arrangement is implemented in a microstrip design <NUM>, and the bottom transmission line is implemented by means of a coaxial cable <NUM>.

Analogous to the above, the planar structure <NUM> contains a circuit board <NUM> and a ground-plane layer <NUM>, and the array of antenna bodies <NUM> and <NUM> being arranged on a top side of the circuit board <NUM>, and each antenna body <NUM> and <NUM> contains a dome shaped structure being attached to the top side of the circuit board <NUM> along its base. Each antenna body <NUM> and <NUM> is connected to a respective top transmission line <NUM> configured to convey microwave signals to and/or from the antenna bodies <NUM> and <NUM>. The top transmission lines <NUM> are connected to the bottom transmission lines <NUM> via coaxial probes <NUM> through the ground-plane layer <NUM>. In addition, here a resonance cavity <NUM> is arranged below a bottom side of the circuit board <NUM> between each of the antenna bodies <NUM> and <NUM>. The top transmission line <NUM> together with a slotline in between the antenna bodies <NUM> and <NUM> and the resonance cavity <NUM> constitutes a so-called balun, i.e. a balanced transmission line to an unbalanced transmission line conversion. The balun is configured to convert the signal from being a balanced signal along the top transmission line <NUM> to an unbalanced signal between the antenna bodies <NUM> and <NUM> and the resonance cavity <NUM>.

A first circuit pattern <NUM> on the bottom side of the circuit board is electrically connected to the ground-plane layer <NUM>. The first circuit pattern <NUM>, in turn, is electrically connected to a second circuit pattern on the top side of the circuit board <NUM> by means of a plurality of vias <NUM> through the circuit board <NUM>. Consequently, the ground plane also extends above the circuit board <NUM>.

<FIG> shows the bottom side of the circuit board <NUM> and the first circuit pattern <NUM> according to this embodiment of the invention. Here, the reference numeral <NUM> designates the positions of said plurality of vias through the circuit board <NUM>. The reference numeral <NUM> designates a portion of the first circuit pattern being connected to the coaxial probe <NUM> through the ground-plane layer <NUM>.

<FIG> illustrates, by means of cross-section a side view, the structure of the antenna array according to another embodiment of the invention. Here, the top transmission line arrangement is implemented in a stripline design <NUM>, and the bottom transmission line is implemented by means of a suspended stripline <NUM>.

Analogous to the above, the planar structure <NUM> contains a circuit board <NUM> and a ground-plane layer <NUM>, and the array of antenna bodies <NUM> and <NUM> being arranged on a top side of the circuit board <NUM>, and each antenna body <NUM> and <NUM> contains a dome shaped structure being attached to the top side of the circuit board <NUM> along its base. Each antenna body <NUM> and <NUM> is connected to a respective top transmission line <NUM> configured to convey microwave signals to and/or from the antenna bodies <NUM> and <NUM>, and the top transmission lines <NUM> are further connected to the bottom transmission lines <NUM> via coaxial probes <NUM> through the ground-plane layer <NUM>. In addition, here a resonance cavity <NUM> is arranged below a bottom side of the circuit board <NUM> between each of the antenna bodies <NUM> and <NUM>.

The ground-plane layer <NUM> is electrically connected to a first circuit pattern on the bottom side of the circuit board <NUM>, which first circuit pattern is further electrically connected to a second circuit pattern on the top side of the circuit board <NUM> by means of a plurality of vias <NUM> through the circuit board <NUM> so as to extend a ground plane represented by the ground-plane layer <NUM> to the top side of the circuit board <NUM>.

<FIG> illustrates, by means of cross-section a side view, the structure of the antenna array according to another embodiment of the invention. Here, the top transmission line arrangement is implemented in a suspended stripline design <NUM>, and the bottom transmission line is implemented by means of a coaxial cable <NUM>.

<FIG> illustrates, by means of cross-section a side view, the structure of the antenna array according to another embodiment of the invention. Here, the top transmission line arrangement is implemented in a stripline design <NUM>, and the bottom transmission line <NUM> is likewise implemented by means of a stripline design.

<FIG> illustrates, by means of cross-section a side view, the structure of the antenna array according to one embodiment of the invention. Here, the top transmission line arrangement is implemented in a stripline design <NUM>, and the bottom transmission line <NUM> is implemented by means of a microstrip design.

<FIG> shows a cross-section side view of a shell member <NUM> implementing the antenna bodies according to an embodiment of the invention that is combinable with any of the above-described embodiments.

The shell member <NUM> is made of a non-conductive material, and the shell member <NUM> is arranged on the planar structure <NUM> instead of the antenna bodies <NUM> and <NUM>.

The shell member <NUM> contains a plurality of cavities Cn1, Cn2, Cn3,. , Cnm each of replaces one of the antenna bodies <NUM> and <NUM> by means of an electrically conductive layer <NUM> that covers a respective active surface of each cavity of said plurality of cavities Cn1, Cn2, Cn3,. The active surface faces the top side of the circuit board <NUM>, thus representing a circuit element equivalent to the outer surface an antenna body <NUM> or <NUM>. Preferably, the shell member <NUM> has a generally flat exterior surface <NUM> facing away from the top side of the circuit board <NUM>, since thereby the antenna obtains a nice-looking and easy to clean exterior surface.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

Claim 1:
An antenna array comprising an array of antenna bodies (<NUM>, <NUM>) arranged on a planar structure (<NUM>),
the planar structure (<NUM>) comprising a circuit board (<NUM>) and a ground-plane layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>),
the array of antenna bodies (<NUM>, <NUM>) being arranged on a top side of the circuit board (<NUM>),
each of said antenna bodies (<NUM>, <NUM>) comprising a dome shaped structure which is attached to said top side of the circuit board (<NUM>) along a base of the dome shaped structure,
each of said antenna bodies (<NUM>, <NUM>) being connected to a respective top transmission line (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to convey microwave signals to and/or from said antenna bodies (<NUM>, <NUM>),
the top transmission lines (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being further connected to bottom transmission lines (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) via coaxial probes (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) through said ground-plane layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), and
a resonance cavity (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being arranged below a bottom side of the circuit board (<NUM>) between each of said antenna bodies (<NUM>, <NUM>).