Field of the invention

The present invention is related to quasi-planar array antenna, and in particular to a planar parallel-plate array antenna, i.e. an array antenna realized using parallel-plate waveguide technology. The antenna is particular useful for high frequencies, at frequencies exceeding 30 GHz, such as at 60-120 GHz.

Background

The data capacity required for the exchange of data, distribution of high- definition video, and other services on the Internet and wireless communication systems continues to rise each year.

For areas where, for cost or geographic reasons, it is difficult to install physical lines, such as optic cable systems, high-speed wireless systems can often be a preferred alternative. Wireless systems are also useful for setting up temporary connections to handle data transfer loads, e.g. when disaster and special events happen, or when a temporary connection is needed for other reasons.

There are presently three major wireless communication systems under development, aiming to more than 10-Gbps (gigabit per second) data transfer capacity: 1) 60 GHz-band wireless systems; 2) E-band (71-76 and 81-86 GHz bands) wireless systems; and 3) 120-GHz-band wireless systems.

The 60-GHz-band wireless communication systems have gained a lot of attention due to their unique characteristics, such as license-free, wideband (7 GHz), high data-rate communication, oxygen absorption and security advantages.

The E-band wireless systems are permitted for ultra high capacity point-to- point communications. The 10 GHz of spectrum available enables fiber- like Gbps data rates that cannot be achieved at the bandwidth- limited lower microwave frequency bands. E-band propagation characteristics are comparable to those at the widely used microwave bands, and link distances of several kilometers/miles can confidently be realized. The 120 GHz-band wireless link uses the ultrahigh- frequency 120-GHz band to achieve 10 Gbps data transfer. There are still very few devices that operate in the over-lOO-GHz range in particular, so wireless communications technology adapted to this range need to be developed further.

In all these wireless systems, a high-gain, directive beam, low-cost, low- profile antenna is a crucial issue.

Many types of high frequency antennas have been proposed and used.

However, planar or quasi-planar array antennas have many advantages: high gain and low sidelobes, low-profile, low-cost and easy installation. In particular, the SIW (substrate-integrated waveguide) planar or quasi-planar array antennas, hollow waveguide slot array antenna and CTS (continuous transverse stub) planar or quasi- planar array antennas are important examples of such antennas.

Possible realizations of SIW planar array antennas are e.g. discussed in J. Hirokawa and M. Ando, "Single-layer feed waveguide consisting of posts for plane tem wave excitation in parallel plates," IEEE Trans. Antenn. & Propaga., vol. 46, no. 5, pp. 625-630, 1998 and J. Xu, W. Hong, P. Chen, and K. Wu, "Design and implementation of low sidelobe substrate integrated waveguide longitudinal slot array antennas," IET Microwaves, Antennas & Propagation, vol. 3, no. 5, pp. 790-797, 2009.

Hollow waveguide slot array antennas are e.g. discussed in M. Z. J. H. T.

Tomura, Y. Miura and M. Ando, "A 45° linearly polarized ho How- waveguide corporate-feed slot array antenna in the 60-ghz band," IEEE Trans. Antenn. & Propaga., vol. 60, no. 8, pp. 3640-3646, 2012.

CTS planar array antennas are discussed inter alia in US 5 266 961 and US 5 483 248, and also in W. W. Milroy, "The continuous transverse stub (CTS) array: Basic theory, experiment and application," in Proc. Antenna Applications Symp., Allerton Park, ILy, Sept. 25-27, 1991.

The main drawback of the SIW antennas is the dielectric loss, typically about 10 dB/m over 60 GHz band, which often result in a typical 5 dB loss in a planar array antenna. The problem with the hollow waveguide slot array is the narrow bandwidth and the difficulty to manufacture.

The CTS antenna is a type of leaky waveguide antenna, where many transverse stubs are allocated on a waveguide in series. The wave is leaked out from these stubs and radiated into free space. Therefore, the main radiation direction is not in the direction normal to the waveguide plane. Although this phenomenon can be alleviated by a slant wave input to the stubs, this adds to the complexity of the antenna, and also the solution has a very narrow band performance. In general, the CTS antenna is a narrow band antenna.

There is therefore still a need for a high frequency antenna with improved properties, such as higher gain, wider bandwidth, a more directive beam, lower production cost, and/or lower antenna profile.

Summary of the invention It is therefore an object of the present invention to provide a quasi-planar array antenna, and in particular a planar parallel-plate antenna, which alleviates at least some of the above-discussed problems.

This object is obtained by means of a quasi-planar array antenna as defined in the appended claims.

According to the invention, there is provided a quasi-planar array antenna for transmitting or receiving electromagnetic waves comprising:

elements being in the form of slots that extends in H-plane from one side of the array to the other and being limited at both ends by sidewalls, and being located side-by-side to form a planar radiating aperture, wherein the slots are fed in such a way that one or more directive beams are radiating vertically or almost vertically from said planar radiating aperture.

The antenna of the present invention may be used for either transmission or reception of electromagnetic waves, or both. The description of the principle of operation in the following is limited to the transmitting case. However, it is to be appreciated by the skilled reader that the performance for the receiving case will be the same in terms of all the characterizing parameters such as losses, efficiency, directivity and far field function. Also, the disclosed embodiments are equally useful and useable both for transmission and for reception.

The plane of the radiating elements are referred to as the aperture plane or the xy-plane, and the direction of the main radiation lobe is in vertical z-direction or close to this direction, or several main lobes located around the z-direction. The text below describes only the generation of one such lobe, and then only the one that is the closest to the z-axis. However, it is to be appreciated by the skilled reader that other lobes may easily be provided by the H-plane feeding arrangement. For example, by using several source points that together may create several radiation lobes distributed in H-plane of the antenna.

The description makes use of the terms layer, layers, and multilayer. These terms are needed to describe the function of the antenna, and they may be

representative to how it is manufactured, but it may not always be so. The

manufacturing can also make use of other special characteristics of the geometry, e.g. that mechanical arrangement in all layers except the first layer can be considered to consist of parallel cylinders of different cross sections that are held together e.g. by means of plates acting as bounding sidewalls parallel to the yz-plane.

The antenna is preferably linearly polarized with E-plane parallel with the yz- plane, and H-plane with the xz-plane. The power distribution to the aperture of the antenna may be done in terms of waves propagating in the narrow gap between two conductive surfaces. These waves and waveguides are below described as parallel- plate waves and parallel-plate waveguides, but these terms are to be construed broadly, and includes other realizations than ideal such parallel-plate waves or parallel-plate waveguides. For example, if there are metal sidewalls of the antenna structure, the parallel-plate waveguides may be realized by rather normal rectangular waveguides oversized in the transverse x-direction, therefore having many possible propagating modes. These are the basic TE mode and several higher-order TE modes. There are also ways of creating sidewalls that makes a more uniform field distribution in H-plane as described in some subclaims, representing then gap waveguides as described in WO 2010/003808 "Waveguides and transmission lines in gaps between parallel conducting surfaces". Preferably, at least one of a feeding arrangement and a power distribution arrangement, arranged to provide radiation to or from the slot elements, comprises parallel-plate-type waveguides.

According to the invention, there is preferably provided a quasi-planar array antenna comprising long x-directed slots in the xy-plane being fed in such a way that they all have almost the same phase and that each of the slots have an almost constant phase distribution in x-direction so that the slots together generate a directive main lobe in the z-direction with high directivity and a resulting high aperture efficiency.

The antenna further preferably comprises an H-plane feeding arrangement located in a narrow gap between conductive surfaces transforming a diverging parallel-plate-type wave from a concentrated source to a parallel-plate-type wave that is distributed with constant phase over the extent of the array in H-plane or nearly so. Additionally or alternatively, the antenna may comprise an H-plane feeding arrangement between two closely located parallel conductive plates preferably parallel to the xy-plane, used to distribute the power from one or more concentrated sources to a lateral field distribution in H-plane with constant or almost constant phase along the lateral x-direction, and thereafter preferably a vertical transition to the next layer above combined with a T-shaped power divider.

The antenna further preferably comprises a multilayer E-plane power distribution arrangement distributing the power of a parallel-plate-type wave in the E- plane via a corporate network of vertical transitions in the form of 90 degree E-plane bends and T-shaped power dividers in such a way that each slot element is fed by a constant phase. Additionally or alternatively, the antenna comprises a power distribution arrangement distributing the power of the parallel-plate waves in the E- plane (yz-plane), wherein the power distribution arrangement divide the parallel plate waves from one parallel-plate layer to the next in terms of a combined vertical transition and a T-shaped power divider in such a way that there is one T-shaped power divider from the first to the second parallel-plate layer, two T-shaped power dividers from the second to the third parallel-plate layer and so on until we have typically one or a two wavelengths between each T-shaped power divider.

The radiating elements may preferably be realized as a plurality of parallel radiating slots being feed from the last T-shaped power divider. These may in E-plane be shaped as horn antennas, i.e. have a horn-like shape in the E-plane cross-section, in order to create some E-plane directivity from each slot.

By "planar array" antenna is in this context generally to be understood an array antenna in which the centers of the radiating elements are all in the same plane. However, feeding arrangements, power distribution arrangements and/or other parts of the antenna may optionally be arranged in layer(s) arranged underneath the plane of the radiating elements, but traditionally, such antennas have sometimes not been regarded as planar array antennas. Accordingly, to avoid confusion, this application mostly refers to quasi-planar array antennas, which includes both planar array antennas according to the traditional understanding of the term, and planar array having e.g. feeding arrangements, power distribution arrangements and/or other parts of the antenna arranged in layer(s) arranged underneath the plane of the radiating elements.

The new quasi-planar array antenna, which may sometimes in the following also be referred to as a Sheet Waveguide Element (SWE) antenna, provides a wideband thin quasi-planar gap-waveguide antenna. The reason is that E-plane power dividers are very wideband compared to H-plane power dividers, and the initial power distribution in H-plane between the two first parallel plates is also very wideband if done by using e.g. a parabolic-shaped reflecting wall in the gap between the two plates. In this way the antenna gets an excellent wideband performance over e.g. the frequency band 50 to 70 GHz in the examples to be discussed in more detail in the following. The antenna also has high gain, and low sidelobes in the 45 deg D- plane between E- and H-planes. Further, the antenna can be made very thin in profile. For example, a 140 ^χ 140 mm ² 60 GHz antenna can be made with a thickness of only 5 mm. Still further, the antenna provides low ohmic loss, because there is no need for dielectric material. Still, foam material may be used of mechanical reasons to separate the parallel-plates, but such foam material will have very low loss compared to solid dielectric material. Further, all the parallel plates form very wide parallel-plate waveguides that are known to have much lower conductive losses than other normal (and thereby narrower) waveguides or microstrip transmission lines. Still further, the new antenna lends itself very well for automated and low-cost manufacture, e.g. by using the method of diffusion bonding of laminated thin metal plates.

Some notable differences between the new SWE antenna and the CTS antennas discussed previously are first that the SWE antenna uses elongate, and preferably overmode/oversized radiating elements, and preferably with a horn-like shape in E-plane cross-section. In CTS antennas, continuous transverse stubs are used. This difference leads inter alia to the SWE antenna being a wideband solution, whereas CTS provides a narrow bandwidth. Further, the feeding mechanism is different. In the SWE antenna, T-shaped power dividers are used in E-plane, and in H-plane the SWE antenna uses a reflector or lens arrangement between two parallel plates to provide a constant phase field distribution in H-plane to be discussed in more detail later. In CTS, some of the stubs are in series and the H-plane makes use of standard waveguide power dividers. In addition, the SWE antenna of this application is readily combined with gap waveguide technology, to be discussed in more detail in the following, which reduces problems with higher order mode generation in the different layers of the whole power distribution arrangement.

Simulations show that the new quasi-planar array antenna (SWE antenna) has a reflection coefficient below -12 dB over 50-70 GHz, a stable directivity between 36.3 and 37.8 dBi over the band and the radiation patterns have low sidelobes satisfying ETSI standard in the 45 deg D-plane.

The parallel plate waveguides are preferably oversized. By waveguides being "oversized" or "overmode" is here to be understood that they are so wide that several cylindrical waveguide modes can propagate in them. Normally waveguides are limited in cross-sectional size so much that only the dominant mode can propagate, because in most practical applications, oversized waveguides are problematic or impossible to use. However, in the context of the present quasi-planar array antenna, it has been found by the present inventors that oversized/overmode waveguides may be used in a very efficient way, and surprisingly with no apparent drawbacks, and, any possible problems of this kind will be effectively solved by using gap waveguide technology.

"Gap waveguide" technology is a technology used to control wave

propagation in the narrow gap between parallel conducting plates, for realizing microwave devices, such as electromagnetic transmission lines, waveguides and circuits of them. The wave propagation is stopped by using periodic elements such as metal posts (also referred to as pins) in one of the parallel conductive surfaces, and it is guided along metal ridges or grooves in preferably the same metal surface, or along metal strips located on a dielectric substrate between the two surfaces. No metal connections between the two parallel conductive surfaces are needed. The fields are mainly present inside the gap, and not in the texture or layer structure itself, so the losses are small. This type of microwave waveguide technology is particularly advantageous for making microwave devices and circuits when the frequency is so high that existing transmission lines and waveguides have too high losses or cannot be manufactured cost-effectively within the tolerances required. This concept has first been developed by P.-S. Kildal, and is e.g. disclosed in WO 2010/003808 and EP 2 390 953. Further documentation of the new gap waveguide technology is found in E. Rajo-Iglesias, A. U. Zaman and P-S. Kildal, "Parallel Plate Cavity Mode Suppression in Microstrip Circuit Packages Using a Lid of Posts", IEEE Microwave and Wireless Components Letters, Vol. 20, No. 1, January 2010; P.-S. Kildal, A. E., A. Valero- Nogueira, and E. Rajo-Iglesias, "Local metamaterial-based waveguides in gaps between parallel metal plates," IEEE Antennas and Wireless Propagation Letters, no. 8, pp. 84-87, 2009; P.-S. Kildal, A. Uz Zaman, E. Rajo, E. Alfonso, and A. Valero Nogueira, "Design and experimental verification of ridge gap waveguide in bed of nails for parallel plate mode suppression," IET Microwave Antennas and Propag., vol. 5, no. 3, pp. 262-270, 2011; and Hasan Raza, Jian Yang, P.-S. Kildal and E. Alfonso, "Resemblance between gap waveguides and hollow waveguides," IET Microwave Antennas and Propag., submitted, 2012.

By "diffusion bonding" is meant a method of joining metallic or non-metallic materials, which is involves atomic diffusion of elements at the joining interface. The diffusion process comprises the transport of mass in form of atom movement or diffusion through the lattice of a crystalline solid. Diffusion of atoms proceeds by many mechanisms, such as exchange of places between adjacent atoms, motion of interstitial atoms or motion of vacancies in a crystalline lattice structure. To obtain diffusion bonding, the two materials are preferably pressed together at an elevated temperature, usually between 50 and 70% of the melting point, e.g. by being held together under an applied force and heated in a vacuum furnace.

The power distribution arrangement preferably divides the radiation from the feed waveguide with an E-plane power divider into at least one overlaid layer into two or more parallel elongate distributed waveguides. However, preferably, the power distribution arrangement comprises a plurality of distribution layers, each dividing the power in the E-plane of underlying elongate distributed waveguides of an underlying distribution layer into two or more overlaying elongate distributed waveguides of an overlaying distribution layer, the elongate distributed waveguides of the underlying layer(s) being parallel to the elongate distributed waveguides of the overlaying layer(s). Preferably, the E-plane power distribution arrangement is formed by a plurality of distribution layers, each dividing the power in the E-plane of underlying parallel-plate-type waveguides of an underlying distribution layer into two overlaying parallel-plate-type waveguides of an overlaying distribution layer, the parallel-plate-type waveguides of the underlying layer(s) being parallel to the parallel-plate-type waveguides of the overlaying layer(s). Hereby, an efficient division of the input radiation can be obtained, to provide a relatively large aperture area of the planar array.

The feeding arrangement may comprise several sources (input ports), together providing a plurality of parallel beams. For all these sources the feeding arrangement provides a power distribution in H-plane. For example, the feeding arrangement may comprise a parallel-plate waveguide formed in the gap between two planar parallel conductive surfaces, a feed entry to input radiation between said conductive surfaces, and a parabolic-shaped reflecting wall arranged between said conductive surfaces, thereby providing constant phase in the transverse x-direction. Preferably, the H- plane feeding arrangement comprises a parallel-plate-type waveguide formed between two planar parallel conductive surfaces with a gap there between, a feed entry to input a source of diverging electromagnetic wave between said conductive surfaces, and a reflecting wall arranged between said conductive surfaces and having parabolic shape in the horizontal plane, thereby providing a parallel-plate wave distributed with constant phase over the whole extent of the array antenna in H-plane. The parabolic reflecting wall may be realized as a full metallic wall fixed to both of the two metal plates. However, alternatively the parabolic reflector may be provided by a plurality of posts (or other periodic elements as described in WO 2010/003808 and EP 2 390 953) being in metallic contact with only one of the two conducting surfaces, and being arranged along at least one parabolic shaped line. Preferably, the posts are arranged in two or more parallel parabolic shaped lines. Hereby, a feeding arrangement being realized by means of gap waveguide technology is obtained.

Additionally or alternatively, the H-plane distribution arrangement may form a kind of lens antenna realized between two parallel-plates. This lens may be of any kind explained in previous literature, such as Rotman lens, Luneberg lens, or simply a convex or concave dielectric lens, realized by natural or artificial dielectric material. Preferably, the H-plane distribution arrangement has several feed entries and concentrated sources, so that many parallel-plate-type waves are originating from it, one associated with each feed entry, in which case the phase is constant along straight lines that make a small angle with the H-plane of the antenna, thereby creating a multiple of directive beams from the array making different angles with the vertical axis in the H-plane. The H-plane distribution arrangement may also be a normal corporate waveguide distribution system consisting of H-plane power dividers or similar.

At least some, and preferably all, the waveguides of the antenna are oversized/overmode waveguides, guiding a plurality of modes.

The antenna has a planar shape, and preferably the width and length dimension widely exceed the thickness dimension. It is also preferred that the dimensions in E- and H-planes widely exceed the thickness dimension. For example, the width and length dimension and/or the dimensions in E- and H-plane may be at least 5 times the thickness dimension, and preferably at least 10 times the thickness dimension, and most preferably, at least 20 times the thickness dimension.

Further, the antenna is preferably flat, and with an essentially rectangular shape. However, other shapes are also feasible, such as circular, oval are also feasible. The shape may also be in the form of a hexagon, octagon or other polygons.

The antenna is preferably adapted for use at high frequencies. In particular, it is preferred that it is adapted for use at a frequency/wave region of operation at frequencies above 300 MHz, and preferably above 30 GHz. In one embodiment, the antenna is adapted to radiate at frequencies exceeding 40 GHz, and preferably exceeding 50 GHz, and most preferably exceeding 60 GHz.

The antenna is preferably adapted to wideband radiation and/or wideband applications.

The waveguides of the antenna may be filled with a dielectric material, such as dielectric foam, for mechanical reasons. However, preferably at least some, and preferably all, the waveguides are filled with air, and free from dielectric material.

The antenna may be formed by lamination of a plurality of thin sheets. The sheets may be provided with openings for forming the waveguides and radiation elements. The openings are preferably formed by etching, but other ways of forming openings are also feasible, such as milling. The sheets are preferably connected by means of diffusion bonding.

The parallel plate waveguides of the antenna may advantageously be realized by means of gap waveguide technology, in order to avoid generation of higher order modes, and to avoid any radiation leakage from open sidewalls, to make it less sensitive to tolerances, to make the waveguides operable for high frequencies, etc. Thus, it is preferred that at least one of the layers of parallel plate waveguides comprises posts arranged at the ends and connected to only one of the surfaces. The posts or other periodic elements can also be used to achieve a uniform field distribution of the basic parallel-plate mode. Then, the metal posts should preferably be submerged into the plates, creating effectively a magnetic surface in the continuation of the smooth conducting surface. This magnetic surface create together with the above-located (or below-located) smooth conductive surface a stopband for parallel-plate waves so that they together work as an invisible magnetic wall inside the parallel-plate waveguide. A parallel-plate waveguide between conductive plates with magnetic sidewalls will support a fundamental TEM wave with a uniform field distribution between the two parallel magnetic walls.

In realization of gap waveguides, the means that stops wave propagation in undesired directions inside the gap may also comprise a multilayer structure that contains conductive elements that are arranged in such a way that they stop wave propagation in other directions inside the gap than along said transmission lines or waveguides, at least at the frequency of operation. Alternatively, the means that stops wave propagation in undesired directions inside the gap may comprise a texture that is designed in such a way that it stops wave propagation in other directions inside the gap than along said transmission lines or waveguides, at least at the frequency of operation. The texture may preferably be provided in the form of closely located posts of conducting material rising from an otherwise smooth conducting surface.

Alternatively, the texture may be provided in the form of one or more grooves, ridges or corrugations that are designed to stop wave propagation very strongly in certain directions, at least at the frequency of operation.

Preferably, the means for prohibiting wave propagation is provided on only one of the surfaces, leaving the other one of the conducting surfaces smooth.

In a gap waveguide, no metal connections between the two metal surfaces are needed for transmission purposes. The metal surfaces may be two parallel conducting surfaces. These surfaces can be the surfaces of two metal bulks, but they can also be made of other types of materials having a metalized surface. They can also be made of other materials with good electric conductivity. The two surfaces can be plane or curved, but they are in both cases separated by a very small distance, a gap, and the transmission line / waveguide being formed inside this gap between the two surfaces. The gap is typically filled with air, but it can also be fully or partly dielectric- filled, and the gap between the surfaces is typically smaller than 0.25 wavelengths, effectively.

The two conductive surfaces are preferably not in touch with each other, or at least not in touch with each other over a stop zone around the waveguide or transmission line joint. However, the two opposing surfaces according to the invention can have metal connection to each other at some distance from the gap waveguide itself without affecting its performance.

Further advantages and features of the present invention will become apparent from the following detailed description of specific embodiments.

Drawings

The invention will now be discussed in more detail by means of embodiments, and with reference to the enclosed drawings, on which:

Fig. 1 is a schematic view of a first embodiment of a quasi-planar array antenna according to the present invention;

Fig. 2 is an enlarged view of the radiating element of the top surface in the antenna in Fig. 1;

Fig. 3 is cross-sectional view of the antenna of Fig. 1 in E-plane, taken along line III-III;

Fig. 4 is a detailed view of an embodiment of an H-plane feeding arrangement to be used in the antenna of Fig. 1;

Fig. 5 is a detailed view of another embodiment of an H-plane feeding arrangement to be used in the antenna of Fig. 1;

Figs. 6 a and b are schematic cross-sectional views of a first gap waveguide implementation within a waveguide in a quasi-planar array antenna of the present invention;

Fig. 7a is a schematic top view of a second gap waveguide implementation within a waveguide in a quasi-planar array antenna of the present invention;

Fig. 7b is a cross-sectional view of the gap waveguide implementation of Fig.

7a;

Fig. 8 is a schematic top view of a second gap waveguide implementation within a waveguide in a quasi-planar array antenna of the present invention; Fig. 9 is a perspective view of an antenna according to another embodiment of the quasi-planar array antenna of the present invention;

Fig. 10 is a detailed view of a corner of the upper part of the antenna in Fig. 9;

Figs. 11-14 are illustrations of some thin sheets that may be used in the formation of the antenna of Fig. 9; and

Figs. 15-17 are simulated radiation patterns for the antenna of Figs. 9 in the D- plane, E-plane and H-plane, respectively, at 60 GHz.

Detailed description of the figures

Detailed embodiments of the quasi-planar array antenna will now be discussed with reference to the drawings.

A first embodiment of the quasi-planar array antenna, as illustrated in Fig. 1 and Fig. 2, generally comprises one surface 10 comprising output slots 11 forming an array of radiating elements 12 in the form of two-dimensional horns (E-plane horns). On an opposite side, there is provided an H-plane feeding arrangement 20. Between the feeding arrangement and the radiating elements, there is provided an E-plane power distribution arrangement 30. The H-plane feeding arrangement is arranged in a first lower layer and the radiation arrangement in a last upper layer of the quasi-planar array antenna. The power distribution is arranged in one or several intermediate layers, being arranged between said first layer and last layer.

The H-plane feeding arrangement 20 is arranged to distribute the field with constant phase in H-plane. This parallel-plate wave feeds the multilayer parallel-plate waveguide E-plane distribution network via the first vertical parallel-plate waveguide transition 21 and T-shaped power divider 31 with reference to Fig. 3. The H-plane power distribution can be made with H-plane power dividers in gap waveguide technology. However, preferably it is provided by reflecting wall arrangement, and preferably by means of a parabolic-shaped reflecting wall, as will now be discussed with reference to Fig. 4. It can also be provided by a planar lens located between the two parallel conducting plates.

The parabolic-shaped reflecting wall is located in the gap between two parallel conducting 22, 23 (see Fig 3) surfaces, such as metal plates. A feed entry 24 to input radiation between the conductive surfaces is arranged at one side, and provides a fan shaped beam distribution between the conductive surfaces. Arranged opposite to the feed entry 24, there is the reflecting wall 25 with a parabolic curved shape arranged between the conductive surfaces, which reflects the fan shaped beams into a wave directed with constant phase in x-direction and feeding the parallel-plate E-plane distribution network at its first vertical transition 21.

The reflecting wall 25 may be realized as a metallic wall arranged in a parabolic shape with metal contact to both plates, as illustrated in Fig. 4. However, alternatively a reflecting wall of parabolic-shape may be provided in the form of a plurality of posts or the like, being in metallic contact with only one of the two conducting surfaces, and being arranged side-by-side along at least one parabolic shaped line. Preferably, the posts are arranged in two or more parallel parabolic shaped lines. Such an embodiment is illustrated in Fig. 5. Hereby, a parabolic-shaped feeding-wall arrangement realized by means of gap waveguide technology is obtained.

From the H-plane feeding arrangement, there is a vertical transition 21 and a T-shaped power divider into the second parallel-plate layer which is the first layer of the E-plane power distribution arrangement 30.

The E-plane power distribution arrangement distributes the power in the E- plane, using vertical transitions combined with E-plane T-shaped power divider(s) in multiple layers to the final radiating slots in the aperture of the quasi-planar array antenna.

In the exemplary embodiment, as best seen in Fig. 3, the power distribution arrangement 30 comprises a first E-plane T-shaped power divider 31, separating the radiation power coming from the vertical transition 21 into a first pair of parallel- plate waveguides 32a, 32b, arranged in a first intermediate layer. The power in the parallel-plate waveguides 32a, 32b are then forwarded up to an overlaying layer, via two new vertical transitions and two second T-shaped E-plane power dividers 33, splitting the power coming from each of the parallel-plate waveguide pieces 32a, 32b into new pairs of parallel-plate waveguides 34a, 34b, arranged in a second

intermediate layer. The power of the parallel-plate wave from the parallel-plate waveguides 34a, 34b are then forwarded up to an overlaying layer, via third vertical transitions and third E-plane power dividers 35, separating the power coming of the waves from each of the parallel-plate waveguides 34a, 34b into vertical transitions, T- shaped E-plane power dividers and pairs of parallel-plate waveguides 36a, 36b, arranged in a third intermediate layer. The power of the propagating parallel-plate waves from the waveguides 36a, 36b are then forwarded up to an overlaying layer, via fourth vertical transitions and E-plane power dividers 37, splitting the radiation power coming from each of the waveguides 36a, 36b into pairs of parallel-plate waveguides 38a, 38b, arranged in a fourth intermediate layer. Finally, the power of the waves from the waveguides 38a, 38b are forwarded up to an overlaying layer, via fifth E-plane T-shaped power dividers 39, splitting the power coming from each of the waveguides 38a, 38b into vertical transitions and pairs of radiation slots 12, as will be discussed in more detail in the following, arranged in an overlaying layer.

Thus, with this power distribution arrangement, the power provided through the feed waveguide is divided into 32 radiating slot elements, by means of four consecutive layers of power dividers. However, the choice of four power divider layers is only provided as an example. Naturally, it is also possible to use fewer layers, such as 1 , 2 or 3 power divider layers, or to use more than four power divider layers. A larger number of power divider layers makes it possible to use more radiating slot elements, and a larger aperture area is enabled. A more limited number of power divider layers makes it possible to make the antenna thinner, with fewer intermediate layers. However, the radiating slots should preferably be many enough and directive enough to suppress grating lobes in the radiation pattern. Full suppression is achieved when the spacing between the centers of each slot element is smaller than one wavelength. For larger slot elements the directivity of them in E- plane should preferably be large in order to suppress grating lobes. This requires that their horn shaped cross-sections are long in the vertical direction, which makes the array much thicker than if more and closer slot elements are used.

The radiating elements 12, as best seen in Figs. 2 and 3, comprise parallel radiating slot elements being fed by the power distribution arrangement. The parallel slot elements are arranged at the ends of a vertical parallel-plate waveguide transition. Towards the radiating output end 11 , the radiating elements have a width increasing in the vertical direction, thereby providing a horn-shaped E-plane cross-section.

The antenna can be made very thin in profile. For example, the antenna illustrated in Figs. 1-5 can have an aperture size of 140 ^χ 140 mm ² corresponding to 28x28 wavelengths at 60 GHz antenna, and having a thickness of less than 50 mm, such as 29 mm. At least some, and preferably all, the parallel-plate waveguides of the antenna are oversized/overmode waveguides, guiding a plurality of modes. The waveguides may be filled with a dielectric material, such as dielectric foam. However, preferably at least some, and preferably all, the waveguides are filled with air, and are free from dielectric material.

The antenna as discussed above may be manufactured in separate layers, being assembled together. For example, the layers for manufacturing may be the ones schematically illustrated in Fig. 3. The openings in the layers may be formed by etching, milling, or the like.

The surfaces of the waveguides, radiating elements and T-shaped power dividers may have smooth metallic, reflecting surfaces. However, it is also possible, and highly advantageous, to realize at least some of these parts by gap waveguide technology in order to control the propagating modes in the parallel-plate

waveguides. Some examples of such realizations will be discussed in the following.

In a first exemplary realization shown in Fig. 6, gaps between overlaying conducting surfaces are arranged, forming layers of parallel-plate waveguides 61 with waves propagating mainly in y-direction (or z-direction where there are vertical transitions). Further, H-plane sidewalls are arranged, covering and holding together all layers of the multilayer power division structure. These sidewalls stop the waves from radiating sideways out of the parallel-plate waveguides. These can be smooth metal plates, but they can also have metal posts pointing inwards into each gap as shown. The posts can also be located inside each parallel-plate waveguide plate, as shown in Figure 6b. Both pin locations create vertical magnetic walls at each side, located at the top of the posts in Fig. 6a, and at the location of the first pin row in Figure 6b. The posts in Fig 6b create a stopband together with the smooth upper metal plate, in the same way as the stopband is created and used to form magnetic sidewalls in a gap waveguide. The posts have two effects: they create a magnetic wall that stops radiation from leaking out sideways, and, they allow for a basic mode in the parallel- plate waveguide that has a uniform field distribution in H-plane with a high value at these H-plane magnetic walls. This will provide higher aperture efficiency of the array antenna.

The posts in Figures 6a and 6b are of the same type and dimensions in terms of wavelengths that was used to demonstrate packaging by a lid of straight posts/nails in "Parallel Plate Cavity Mode Suppression in Microstrip Circuit Packages Using a Lid of Posts", by E. Rajo-Iglesias, A. U. Zaman and P-S. Kildal, IEEE Microwave and Wireless Components Letters, Vol. 20, No. 1, January 2010 and other papers by Kildal and his research group. However, other types of texture and the like having similar properties may be used. For example, any of the textures as described in WO 2010/003808 can be used. This realization of a gap waveguide, with means that stops wave propagation inside the gap in other directions than along the waveguide and in particular stops waves from leaking out of the sidewalls of the array, may be used in any of the waveguides in the quasi-planar array antenna as discussed above, and hereby a very uniform field distribution and very losses are obtained within the waveguides.

In a second exemplary realization as shown in Figs 7 and 8, a gap between two conducting surfaces is again arranged for waves propagating in y-direction, or in z-direction in vertical parts, forming a parallel-plate waveguide 71. Further, means that stops wave propagation inside the gap in other directions than along the waveguide, i.e. in x-direction) is arranged between the plates. These means comprises a surface texture, such as a periodic texture of metal posts as discussed above. As seen in Fig. 7a and b, the surface texture, such as posts, may here be arranged within grooves, so that the texture/posts do not exceed the waveguide surface of the conducting plane on which the texture/posts are arranged. Such waveguides may e.g. be manufactured by etching, sawing or milling. The post region will together with a smooth upper plate create a stopband so that no waves can pass the groove with posts.

It is also possible to combine the embodiments explained above, and arrange means that stops wave propagation both at the ends and the sides of the parallel-plate waveguides a shown in Fig. 8. Further, realization of the radiating elements may be provided by means of gap waveguide technology in a corresponding way, then with rows of posts in the vertical direction along the horn-type radiating elements.

This realization of a gap waveguide, with means that stops wave propagation inside the gap in other directions than along the waveguide arranged between adjacent waveguides, may be used in any of the waveguides in the quasi-planar array antenna as discussed above, and hereby very low losses and a very uniform field distribution are obtained within the waveguides. As discussed above, the quasi-planar array antenna may be manufactured by producing a set of different layers which are assembled together. Typically, such layers may have a thickness, which is greater than the height of the waveguides. In the embodiment shown in Fig. 3, about 10 separate layers are assembled to produce the antenna. However, fewer or more layers may naturally be used. It is also possible to produce the antenna in other ways.

In another embodiment now to be discussed, the antenna is manufactured by thin sheets of metal. The sheets may e.g. have a thickness in the range 0.01-2.0 mm, and preferably in the range 0.05-1.0 mm, and more preferably 0.1-0.5 mm, and most preferably 0.2-0.3 mm. Hereby, it is possible to produce extremely thin quasi-planar array antennas, still having similar properties as the antenna discussed above in relation to the first embodiment.

In the illustrative example to be discussed in the following, the antenna has the same general structure as in the first disclosed embodiment. However, whereas the antenna of the first embodiment, when realized as a 140 ^x 140 mm ² 60 GHz antenna, would have a thickness of about 29 mm, an antenna of the same width and length, and for the same frequency range, may have a thickness of e.g. about 6 mm, when using 0.3 mm sheets.

An antenna produced by thin sheets is illustrated in Fig. 9. In Fig. 10, a detailed view of an upper part of the antenna is shown. It is here illustrated how the outputs of the radiating elements may be formed by thin sheets. The sheets are provided with openings, and the openings of the upper layer are slightly larger than the openings of the adjacent lower layer, etc, to form the "horn" output.

Each sheets is preferably formed with rectangular openings, to form the waveguides and radiation elements of the antenna. The openings may be formed by milling or the like. However, in a preferred embodiment, the openings are formed by etching, which enables a very cost-effective manufacture. As examples, some of the sheets that may be used to form an antenna of a similar structure as in the first discussed embodiment will now be discussed, for illustrative purposes. Fig. 11 illustrates a sheet with 64 openings, which may form the radiation outputs of a corresponding number of radiation elements. Fig. 12 illustrates a sheet having 32 openings, which may form the 32 waveguides previous to a final power division, or form the radiation outputs, in case 32 radiation openings should be used (as in the first embodiment). Fig. 13 illustrates a sheet with two openings, forming two elongate waveguides, as to be used after the first power division step. Fig 14 illustrates a sheet with two narrow openings, which may be used as a power divider.

In this way, the antenna may be formed by lamination of a plurality of thin sheets, having openings for forming the waveguides and radiation elements. The sheets are preferably connected by means of diffusion bonding.

The quasi-planar array antenna may also be covered with a thin dielectric layer in order to protect water and dust from penetrating into the radiating slots.

Simulations show that the new quasi-planar array antenna (SWE antenna) has a reflection coefficient below -12 dB over 50-70 GHz, a stable directivity between 36.3 and 37.8 dBi over the band and the radiation patterns have low sidelobes satisfying ETSI standard. In Fig. 15 the radiation pattern in the D-plane of the quasi- planar array antenna of the embodiment discussed above in relation to Fig. 9 is illustrated at 60 GHz, and Figs. 16 and 17 illustrates the corresponding radiation patterns for the E-plane and H-plane, respectively.

The invention is not limited to the embodiments shown here. In particular, the quasi-planar array antenna may be a small antenna, comprising a limited number of radiation elements, or a large antenna comprising a multitude of radiation elements. Further, gap waveguide technology may be used in realization of an H-plane power divider of a feeding arrangement, in realization of the waveguides of the power distributing arrangement, and/or in realization of the radiation elements. Further, even if the above-discussed examples illustrate a quasi-planar array antenna arranged in a flat plane and with a rectangular configuration, the quasi-planar array antenna may also be provided in a curved plane, and/or with non-rectangular shapes, such as in a circular shape, or in the form of different types of polygons.