Technical field of the invention

The present invention relates to the technology used to design, integrate and package the radio frequency (RF) part of an antenna system, for use in communication, radar or sensor applications, and e.g. RF components such as waveguide couplers, diplexers, filters, antennas, integrated circuit packages and the like.

Background

There is a need for technologies for fast wireless communication in particular at 60 GHz and above, involving high gain antennas, intended for consumer market, so low-cost manufacturability is a must. The consumer market prefers flat antennas, and these can only be realized as flat planar arrays, and the wide bandwidth of these systems require corporate

distribution network. This is a completely branched network of lines and power dividers that feed each element of the array with the same phase and amplitude to achieve maximum gain. The high gain antennas can also be so- called phased array antennas with distributed amplifiers at each element, in which case it is even possible in the future to mount A D or D/A converters at each element to get full digital control of the beam shaped like in the proposed massive MIMO antenna systems. We will here mainly describe high gain antennas with distributed feed networks, but this is not a limitation of the invention.

A common type of flat antennas is based on a microstrip antenna technology realized on printed circuits boards (PCB). The PCB technology is well suited for mass production of such compact lightweight corporate-fed antenna arrays, in particular because the components of the corporate distribution network can be miniaturized to fit on one PCB layer together with the microstrip antenna elements. However, such microstrip networks suffer from large losses in both the dielectric and conductive materials of the PCB. The dielectric losses do not depend on the miniaturization, but the conductive losses are very high due to the miniaturization of the metal strips (the so- called microstrip lines). Unfortunately, the microstrip lines can only be made wider by increasing substrate thickness, and then the microstrip network starts to radiate, and surface waves starts to propagate, both destroying performance severely.

There is one known PCB-based technology that have low conductive losses and no problems with surface waves and radiation. This is referred to by either of the two names substrate-integrated waveguide (SIW), or post-wall waveguide as in [1 ]. We will herein use the term SIW only. However, the SIW technology still has significant dielectric losses, and low loss dielectric materials are very expensive and soft, and therefore not suitable for low-cost mass production. Therefore, there is a need for better technologies.

Thus, there is a need for a flat antenna for high frequencies, such as at or above 60 GHz, and with reduced dielectric losses and problems with radiation and surface waves. In particular, there is a need for a PCB based technology for realizing corporate distribution networks at 60 GHz or above that do not suffer from dielectric losses and problems with radiation and surface waves.

The gap waveguide technology is based on Prof. Kildal ^' s invention from 2008 & 2009 [2], also described in the introductory paper [3] and validated experimentally in [4]. This patent application as well as the paper [5] describes several types of gap waveguides that can replace microstrip technology, coplanar waveguides, and normal rectangular waveguides in high frequency circuits and antennas.

The gap waveguides are formed between parallel metal plates. The wave propagation is controlled by means of a texture in one or both of the plates. Waves between the parallel plates are prohibited from propagating in directions where the texture is periodic or quasi-periodic (being characterized by a stopband), and it is enhanced in directions where the texture is smooth like along grooves, ridges and metal strips. These grooves, ridges and metal strips form gap waveguides of three different types: groove, ridge and microstrip gap waveguides [6], as described also in the original patent application [2].

The texture can be a periodic or quasi-periodic collection of metal posts or pins on a flat metal surface, or of metal patches on a substrate with metal ized via-holes connecting them to the ground plane, as proposed in [7] and also described in the original patent application [2]. The patches with via- holes are commonly referred to as mushrooms.

A suspended (also called inverted) microstrip gap waveguide was presented in [8] and is also inherent in the descriptions in [6] and [7]. This consists of a metal strip that is etched on and suspended by a PCB substrate resting on top of a surface with a regular texture of metal pins. This substrate has no ground plane. The propagating quasi-TEM wave-mode is formed between the metal strip and the upper smooth metal plate, thereby forming a suspended microstrip gap waveguide.

This waveguide can have low dielectric and conductive losses, but it is not compatible with PCB technology. The textured pin surface could then be realized by mushrooms on a PCB, but this then becomes one of two PCB layers to realize the microstrip network, whereby it would be much more costly to produce than gap waveguides realized only using one PCB layer. Also, there are many problems with this technology: It is difficult to find a good wideband way of connecting transmission lines to it from underneath.

The microstrip gap waveguide with a stopband-texture made of mushrooms were in [9] realized on a single PCB. This PCB-type gap waveguide is called a microstrip-ridge gap waveguide, because the metal strip must have via-holes in the same way as the mushrooms.

A quasi-planar inverted microstrip gap waveguide antenna is described in [10]-[12]. It is expensive both to manufacture the periodic pin array under the microstrip feed network on the substrate located directly upon the pin surface, and the radiating elements which in this case were compact horn antennas.

A small planar array of 4x4 slots were presented in [13]. The antenna was realized as two PCBs, an upper one with the radiating slots realized as an array of 2x2 subarrays, each consisting of 2x2 slots that are backed by an SIW cavity. Each of the 4 SIW cavities was excited by a coupling slot fed by a microstrip-ridge gap waveguide in the surface of a lower PCB located with an air gap below the upper radiating PCB. It was very expensive to realize the PCBs with sufficient tolerances, and in particular to keep the air gap with constant height. The microstrip-ridge gap waveguide also requires an enormous amount of thin metalized via holes that are very expensive to manufacture. In particular, the drilling is expensive because lowloss

substrates are soft.

There is therefore a need for a new waveguide and RF packaging technology that have good performance and in addition is cost-effective to produce.

Summary of the invention

It is therefore an object of the present invention to alleviate the above- discussed problems, and specifically to provide a new waveguide and RF packaging technology, which has good performance and which is cost- effective to produce, in particular for use above 30 GHz, and e.g. for use in an antenna system for use in communication, radar or sensor applications.

According to a first aspect of the invention there is provided a radio frequency (RF) part of an antenna system, e.g. for use in communication, radar or sensor applications, comprising:

a first conducting layer, e.g. being provided on a substrate;

a plurality of monolithic waveguide elements, each having a base and protruding fingers extending up from the base, wherein the waveguide elements are conductively connected with the first conducting layer, and arranged to form a waveguide along the first conducting layer; and

a second conducting layer arranged on top of the first conducting layer, so that a gap is formed between the first and second conducting layers, wherein the waveguide elements are enclosed within said gap, and the protruding fingers of the waveguide elements form a set of periodically or quasi-periodically arranged protruding elements forming a texture to stop wave propagation in a frequency band of operation in other directions than along intended waveguiding paths, even though the fingers may not have any metal contact with the second conducting layer.

The first conducting layer can be arranged as a metal plate or the like, but is preferably arranged as a metal ized layer on a substrate. The

conducting layer is preferably very thin, which is simplified by locating it on a stiff and solid dielectric substrate to improve mechanical performance and lower cost.

Thus, a gap waveguide is formed, having two conducting layers arranged with a gap there between, and a set of periodically or quasi- periodically arranged protruding fingers connected to at least one of said conducting layers. The monolithic waveguide elements and their protruding fingers are preferably all electrically connected to each other via said conducting layer on which they are connected, thereby forming a texture to stop wave propagation - in a frequency band of operation - in other directions than along intended waveguiding paths.

It has been found by the present inventors that smaller monolithic waveguide elements, each having a base and protruding fingers extending up from the base, can be manufactured quite easily and cost-effectively. Further, placement and connection of the waveguide elements on the first conducting layer/substrate can also be accomplished in a relatively simple and cost- effective way, such as by using pick-and-place technology, or other surface mount technology (SMT) component placement systems. In particular, the present invention makes it possible to provide standardized waveguide elements, and to use such standardized components, solely or at least to a relatively large extent, when producing various types of RF parts.

Pick-and-place processes are per se known, and have been used for production of electronic assemblies. Such processes typically involve supply of the elements to be picked and placed, e.g. on paper or plastic tapes, on trays or the like, and pick up of an element at a time from the supply, e.g. by means of pneumatic suction cups. The suction cups may be attached to a plotter-like device, or other arrangements, to place the picked up elements on a conductive layer that may be located on a dielectric substrate thereby forming a PCB. When placed on the conductive layer, such as a metallized substrate, the element(s) is maintained in place by adhesive solder-paste or the like. When all elements have been placed on the substrate/layer, the assembly is heat treated at an elevated temperature, whereby the solder- paste melts and fixes the placed elements to the substrate/layer. This solder connection is very strong after returning to room temperature.

It has been found by the present inventors that the provision of monolithic waveguide elements having a base and protruding fingers extending up from the base makes it possible to pre-produce components of one or several types, and to assemble the elements by pick-and-place methodology. This is made possible for example by making the base of the monolithic waveguide elements large enough to serve as a suction area to be picked up by pneumatic suction cups.

The protruding fingers may have any desired shape, but are preferably made of essentially uniform width, thickness and height, making the fingers essentially rectangular in shape. However, other forms, such as having rounded or angular tops or sides, etc, are also feasible. The fingers can also be round pins, having a circular cross-section.

By RF part is in the context of the present application meant a part of an antenna system used in the radio frequency transmitting and/or receiving sections of the antenna system, sections which are commonly referred to as the front end or RF front end of the antenna system. The RF part may be a separate part/device connected to other components of the antenna system, or may form an integrated part of the antenna system or other parts of the antenna system.

The waveguide and RF packaging technology of the present invention may be realized by mounting monolithic pieces together using PCB technology and pick-and-place machines or similar, and is in particular suitable for realizing a wideband and efficient flat planar array antenna.

However, it may also be used for other parts of the antenna system, such as waveguides, filters, integrated circuit packaging and the like, and in particular for integration and RF packaging of such parts into a complete RF front-end or antenna system. The waveguide elements of the present invention may be provided as standardized components, and can be assembled by surface mount placement technologies, such as by per se known pick-and-place equipment. This makes it possible to provide a large variety of different RF part in a relatively simple, quick and cost-effective manner. Thus, a great flexibility in designing and producing RF parts is obtained. At the same time, the RF parts have low losses, and better EMC properties, compared to microstrip solutions and the like.

The waveguide elements preferably comprise flat base plates for formation of groove gap waveguides. A flat base plate is particularly well suited to be lifted by a pneumatic suction cup. However, alternatively the waveguide elements may comprise bases provided with protruding ridges, for formation of ridge gap waveguides. In such an alternative, the top surface of the ridge or the like may serve as a surface to be lifted by a pneumatic suction cup.

The protruding fingers of all waveguide elements are preferably in conductive/electrical contact with each other via the conductive surface to which they are connected. The waveguide elements preferably comprise conductive surfaces, and wherein the base and all the fingers of each waveguide element are in electric contact with each other. For example, the waveguide elements may be made of metal. Each waveguide element may, e.g., be made of a single sheet of metal, wherein cut-out tongues are bent upwards to form the protruding fingers.

The protruding fingers preferably extend with an angle towards the plane of the base, and preferably extend orthogonally to this plane. However, other directions are also feasible, such as forming an acute or obtuse angle in relation to said plane.

At least one of the waveguide elements preferably comprises a plurality of fingers arranged on two opposite sides of the base. Hereby, the waveguide element may form a part of a waveguide surrounded by fingers at each side along a waveguide channel. However, at least for some types of waveguide elements, provision of fingers only on one side may be sufficient. For example, several waveguide elements may be combined to form a waveguide channel being provided with two or more lines of protruding fingers along both sides. Further, waveguides having a single line of protruding fingers on each side may be sufficient for some applications, in particular if the fingers are in conductive contact both with the first and second conductive layers.

The waveguide elements may comprise a plurality of fingers arranged along two or more parallel but separate lines along at least one of the edges. Gap waveguides should preferably have at least two lines of protruding fingers on each side of the waveguide. Therefore, realizations with two or more lines of protruding fingers on each side of the waveguide are normally more efficient. Thus, realization of the waveguide elements with two or more finger lines arranged along one or several sides enables a more efficient assembly of efficient waveguides on the conducting layer/substrate. However, several waveguide elements may also be combined to form a waveguide channel being provided with protruding fingers in two or more lines along both sides.

Additionally or alternatively, at least one of the waveguide elements may comprise a plurality of fingers arranged along a single line along at least one of the edges.

At least some of the fingers may be bent-up tongues extending from the outer side of the base. The tongues may be extending from the outer perimeter of the base. However, alternatively, at least some of the fingers may be bent-up tongues extending from interior cut-outs within the base.

The waveguide elements are preferably adapted to form waveguides for frequencies exceeding 20 GHz, and preferably exceeding 30 GHz, and most preferably exceeding 60 GHz.

The waveguide elements preferably comprises at least one of a straight waveguide element, a curved or bent waveguide element, a branched waveguide element such as a two-way divider, and a transition waveguide element. The transition waveguide element may e.g. be a transition to connect to a monolithic microwave integrated circuit module (MMIC), or a transition to an antenna element located at a layer above the second conducting layer, and excited by a coupling slot in the upper conducting layer. The waveguide elements are preferably connected to the first conducting layer by means of solder tin. Thus, the first conducting layer may prior to placement of the waveguide elements be provided with a solder-paste or the like, preferably making the layer somewhat adherent, to maintain the placed waveguide elements in place. When placed, the first conducting layer together with the waveguide elements may be heat treated at an elevated temperature, thereby fixedly connecting the waveguide elements to the first conducting layer.

The protruding fingers functions as pins, nails etc, in the same way as in previously known gap waveguides. Many different shapes and geometries of the fingers are feasible. For example, the fingers may have a shape varying over the height, such as being slightly conical, being wider and/or thicker in the middle, e.g. resembling an oval or spherical shape, having a narrower cross-section at the top and/or bottom, etc. However, preferably the fingers have a relatively uniform width and thickness over the entire height. It is further preferred that the protruding height of the fingers is greater than the width and thickness of the fingers, and preferably greater than double the width and thickness. Still further, it is preferred that the width of the fingers is greater than the thickness.

It is further preferred that the protruding fingers have maximum cross- sectional dimensions of less than half a wavelength in air at the operating frequency. Preferably, the maximum dimension is much smaller than this. The maximum cross-sectional dimension is the diameter in case of a circular cross-section, or diagonal in case of a square or rectangular cross-section. Additionally or alternatively, it is preferred that the protruding elements in the texture stopping wave propagation are spaced apart by a spacing being smaller than half a wavelength in air at the operating frequency. This means that the separation between any pair of adjacent protruding elements in the texture is smaller than half a wavelength.

The flat central part of the base plate, when used for forming a waveguide along the base plate, preferably has a width that is greater than the height of the protruding fingers. Preferably, this width is the range of 2-3 times the height of the protruding fingers, such as about 2.5. The first and second conducting layers are preferably fixedly

connected to each other. This fixed connection may be obtained by provision of an extending rim or other types of protruding connection elements to one of the layers, and attaching the other conducting layer to said rim or other connection element. The fixed attachment can then be obtained by adhesion, welding, soldering, bolt connections, or the like.

The protruding fingers forming said texture to stop wave propagation are preferably only in contact with one of the conducting layers. However, in some embodiments, it is also feasible that some or all of the fingers are in conductive or non-conductive contact with also the other conducting layer. Such an arrangement may e.g. provide additional fixation of the conductive layer being, e.g. arranged on top of a substrate, on which the waveguide elements have been placed and fixedly connected. This may also serve the purpose of ensuring that the two conductive layers are maintained parallel to each other.

In embodiments where the protruding fingers are in

conductive/electrical contact with both the conductive layers, the protruding fingers may be arranged to at least partly provide the walls of a tunnel or a cavity connecting said conducting layers across the gap between them, said tunnel thereby functioning as a waveguide or a waveguide cavity. Thus, in this embodiment, a smooth upper plate (conducting layer) can also rest on a grid array provided by said protruding fingers or on some part of it, and the protruding elements/pins that provide the support can e.g. be soldered to the upper smooth metal plate (conducting layer) by baking the construction in an oven. Thereby, it is possible to form post-wall waveguides as described in [1 ], said documents hereby being incorporated in its entirety by reference, but without any substrate inside the waveguide. Thus, SIW waveguides are provided without the substrate so to say. Such realizations is advantageous compared to conventional SIW because it reduces the dielectric losses, since there is no substrate inside the waveguide, and can also be produced more cost-effectively, and since the use of expensive lowloss substrate material may now be reduced or even omitted. If the RF part is used as a gap waveguide, the protruding elements forming said texture to stop wave propagation, are preferably only in contact with one of the conducting layers.

In a gap waveguide, the waves propagate mainly in the air gap between the waveguiding structure and the smooth metal surface. The gap can also be filled fully or partly by dielectric material, of mechanical reasons to keep the gap of constant height. The gap can even have metal elements for mechanically supporting the gap at constant height. These metal elements are then preferably located outside the traces of the waveguiding structure. The periodic or quasi-periodic protruding fingers in the textured surface are preferably provided on both sides of the waveguiding elements, and these are designed to stop waves from propagating between the two metal surfaces, in other directions than along the waveguiding structure. The frequency band of this forbidden propagation is called the stopband, and this defines the maximum available operational bandwidth of the gap waveguide.

The protruding fingers may be arranged to at least partly surround a cavity between said conducting layers, said cavity thereby functioning as a waveguide. The waveguide elements preferably form a gap waveguide comprising at least one groove or ridge along which waves are to propagate. In one embodiment, the base of the waveguide elements, surrounded by the protruding fingers, may function as the groove in a groove gap waveguide. In case of a ridge gap waveguide, the base may be provided with a protruding ridge. In this case, the upper area of the ridge may function as a lifting area for being lifted pneumatically for placement.

The RF part may further comprise at least one integrated circuit module, such as a monolithic microwave integrated circuit module, arranged between said conducting layers, the texture to stop wave propagation thereby also functioning as a means of removing resonances within the package for said integrated circuit module(s).

The RF part is particularly suited for forming a flat array antenna comprising a corporate distribution network realized by RF part(s) as discussed above. Thus, according to another aspect of the invention, there is provided a flat array antenna comprising a corporate distribution network realized by a RF part in accordance with the discussion above.

Hereby, similar embodiments and advantages as discussed above are feasible.

According to another aspect of the invention, there is provided a method for producing an RF part of an antenna system, e.g. for use in communication, radar or sensor applications, comprising:

providing a first conducting layer that, that preferably and with advantage may be very thin and located on a stiff and solid dielectric substrate to improve mechanical performance and lower cost;

providing a plurality of monolithic waveguide elements, each having a base and protruding fingers extending up from the base;

conductively connecting the waveguide elements with the first conducting layer, and arranged to form a waveguide along the first conductive layer; and

arranging a second conducting layer on top of the first conducting layer, so that a gap is formed between the first and second conducting layers, wherein the waveguide elements are enclosed within said gap, and the protruding fingers of the waveguide elements form a set of periodically or quasi-periodically arranged protruding elements forming a texture to stop wave propagation in a frequency band of operation in other directions than along intended waveguiding paths.

Hereby, similar advantages and preferred features as discussed above in relation to the first embodiment are conceivable.

The step of conductively connecting the waveguide elements with the first conducting layer is advantageously made by pick-and-place technology. Hereby, a conventional and per se known pick-and-place equipment can be used. Such equipment is commonly used for placement and production of electronic circuits arranged on PCBs. However, it has now been found that the same or similar equipment can also be used very efficiently for production of gap waveguides and similar RF parts. By use of a base in the waveguide elements and/or a ridge of sufficient dimensions, a lifting area is provided which enables the elements to be lifted pneumatically, and the base further provides sufficient stability of the elements in a placed position, prior to soldering.

The step of conductively connecting the waveguide elements with the first conducting layer preferably comprises the sub-steps of:

picking and placing waveguide elements with a vacuum placement system on said first conducting layer, so that the waveguide elements becomes adhered to the first conducting layer; and

heating the first conducting layer at an elevated temperature, thereby connecting the waveguide elements to the first conducting layer by means of soldering.

As discussed in the foregoing, the groove gap waveguide and the ridge gap waveguide have already been demonstrated to work and have lower loss than conventional microstrip lines and coplanar waveguides. The present inventors have now found that similar or better performance can be obtained in a much more cost-effective way by using waveguide elements which can be arranged on a first conducting layer, such as a metalized substrate by e.g. surface mount placement technology, such as pick-and-place technology. Hereby, it is e.g. possible to realize corporate distribution networks at low manufacturing cost and to sufficient accuracy at 60 GHz and higher frequencies.

The RF part is preferably used to realize a waveguide, and in particular a groove gap waveguide or a ridge gap waveguide component, and may also be used for RF integrated circuits such as low noise amplifiers for receiving RF signals and or power amplifiers for transmitting RF signals, or to integrate and package such components and circuits in one package. The RF part(s) may form a distribution network for an array antenna, and they may even be used to form the radiating elements of the array. Thereby, the complete package may represent a complete antenna system.

In one embodiment, the gap waveguide may form the distribution network of an array antenna. The distribution network is preferably fully or partly corporate containing power dividers and transmission lines, realized fully or partly as a gap waveguide, i.e. formed in the gap between one smooth and one textured surface, including either a ridge gap waveguide or a groove gap waveguide, depending on whether the waveguiding structure in the textured surface is a metal ridge or groove.

In a distribution network, the waveguiding structure may be formed like a tree to become a branched or corporate distribution network by means of power dividers and lines between them.

At least one of the conducting layers may further be provided with at least one opening, preferably in the form of rectangular slot(s), said

opening(s) allowing radiation to be transmitted to and/or received from the waveguide. Such an opening may be used either as radiating openings in an array antenna, or as a coupling opening to transfer radiation to another layer of the antenna system. The openings may preferably be arranged in the smooth metal surface of the waveguide, i.e. in the conducting layer not being provided with the waveguide elements, and the slots may be arranged to radiate directly from its upper side, in which case the spacing between each slot preferably is smaller than one wavelength in free space.

The antenna system may further comprise horn shaped elements connected to the openings in the metal surface of the waveguide. Such slots are coupling slots that make a coupling to an array of horn-shaped elements which are preferably located side-by-side in an array in the upper metal plate/conducting layer. The diameter of each horn element is preferably larger than one wavelength. An example of such horn array is per se described in [10], said document hereby being incorporated in its entirety by reference.

When several slots are used as radiating elements in the upper plate, the spacing between the slots is preferably smaller than one wavelength in air at the operational frequency.

The slots in the upper plate may also have a spacing larger than one wavelength. Then, the slots are coupling slots, which makes a coupling from the ends of a distribution network arranged in the textured surface to a continuation of this distribution network in a layer above it, that divides the power equally into an array of additional slots that together form a radiating an array of subarray of slots, wherein the spacing between each slot of each subarray preferably is smaller than one wavelength. Hereby, the distribution network may be arranged in several layers, thereby obtaining a very compact assembly. For example, a first RF part may form a waveguide therein, in the aforementioned way, and a second RF part may be arranged on top of this. The second RF part may comprise the coupling slots, each of which make a coupling from each ends of the distribution network on the textured surface to a continuation of this distribution network that divides the power equally into a small array of slots formed in a conducting layer arranged at the upper side of the second RF part, that together form a radiating subarray of the whole array antenna. The spacing between each slot of the subarray is preferably smaller than one wavelength.

The distribution network is at the feed point preferably connected to the rest of the RF front-end containing duplexer filters to separate the transmitting and receiving frequency bands, and thereafter transmitting and receiving amplifiers and other electronics. The latter are also referred to as converter modules for transmiting and receiving. These parts may be located beside the antenna array on the same surface as the texture (the protruding fingers) forming the distribution network, or below it. A transition is preferably provided from the distribution network to the duplexer filter, and this may be realized with a hole in the ground plane of the lower RF part and forming a rectangular waveguide interface on the backside of it. Such waveguide interface can also be used for measurement purposes.

The substrate may be of any material having adequate mechanical and electrical properties, such as substrates today used for printed circuit boards.

These and other features and advantages of the present invention will in the following be further clarified with reference to the embodiments described hereinafter. Notably, the invention is in the foregoing described in terms of a terminology implying a transmitting antenna, but naturally the same antenna may also be used for receiving, or both receiving and transmitting electromagnetic waves. The performance of the part of the antenna system that only contains passive components is the same for both transmission and reception, as a result of reciprocity. Thus, any terms used to describe the antenna above should be construed broadly, allowing electromagnetic radiation to be transferred in any or both directions. E.g., the term distribution network should not be construed solely for use in a transmitting antenna, but may also function as a combination network for use in a receiving antenna.

Brief description of the drawings

For exemplifying purposes, the invention will be described in closer detail in the following with reference to embodiments thereof illustrated in the attached drawings, wherein:

Fig 1 is a perspective side view showing a rectangular waveguide in accordance with one embodiment of the present invention;

Fig 2 is a perspective side view showing a waveguide forming element according to a first embodiment, wherein the right hand figure shows the waveguide forming element, and the left hand figure shows a punched out perform for formation of the waveguide element of the right hand figure;

Fig. 3 is a perspective top view of a partly assembled waveguide, made by the waveguide elements of Fig. 2;

Fig. 4 is a cross-sectional view of the waveguide of Fig. 3;

Figs. 5-8 illustrate waveguide elements of a similar type as in Fig. 2, but having different geometries;

Figs. 9-12 are schematic cross-sectional views illustrating various ways of using waveguide elements to form different types of waveguides;

Figs. 13-14 illustrate different embodiments of waveguide elements having two rows of protruding fingers along each side;

Figs. 15-17 are schematic illustrations of how different waveguide elements may be combined into more complex waveguide parts;

Figs. 18, 19 and 21 are perspective top views illustrating embodiments of waveguide elements having a solid ridge, for forming ridge gap

waveguides;

Fig. 20 is a schematic cross-sectional view of a waveguide elements similar to the one in Fig. 13, but having the base formed into a non-solid ridge;

Fig. 22 is a schematic top-view illustrating use of waveguide elements to connect to an integrated circuit; and Fig. 23 is a schematic top-view illustrating the use of waveguide elements to form a grid of protruding fingers.

Detailed description of preferred embodiments

In the following detailed description, preferred embodiments of the present invention will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. Even though in the following description, numerous specific details are set forth to provide a more thorough understanding of e present invention, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known constructions or functions are not described in detail, so as not to obscure the present invention.

A radio frequency (RF) part of an antenna system can be a whole or a part of a gap waveguide, but also other types of parts, such as dividers, adaptors, transition elements, couplers (such as Ratch Race, branches and the like), etc.

A relatively simple straight gap waveguide part is schematically illustrated in Fig. 1 . The waveguide comprises a first conducting layer 1 , and a second conducting layer 2 (here made semi-transparent, for increased visibility). The conducting layers are arranged at a constant distance h from each other, thereby forming a gap there between.

This waveguide resembles a conventional SIW with metallized via holes in a PCB with metal layer (ground) on both sides, upper (top) and lower (bottom) ground plane. However, here there is no dielectric substrate between the conducting layers, and the metalized via holes are replaced with protruding fingers 3 extending from, and fixedly connected to, the first conducting layer, in a way to be discussed more thoroughly in the following. The second conducting layer 2 may rest on the protruding fingers 3, and be also connected to these, e.g. by means of soldering. However, it is also possible to have a gap or a dielectric material between the protruding fingers and the second conducting layer. Hereby, there may be no physical contact and/or no electric/conductive contact between the second conducting layer and the protruding fingers.

Further, the first and second conductive layers may be attached to each other by means of a rim 5, extending around the periphery of one of the conducting layers. The rim is here made semi-transparent, for increased visibility.

Similar to a SIW waveguide and known gap waveguides, a waveguide is here formed between the conducting elements, here extending between the first and second ports 4.

In this example, a very simple, straight waveguide is illustrated.

However, more complicated paths may be realized in the same way, including curves, branches, etc.

The protruding fingers 3 are provided in the form of monolithic waveguide elements 6, and these elements will now be discussed more thoroughly.

Each waveguide element comprises a base 61 , and fingers 3 protruding from the base, preferably in an essentially orthogonal direction. An example of such a waveguide element is illustrated in the right-hand figure of Fig. 2. Here, the base 61 has an elongate, rectangular form, and protruding fingers are provided at both longitudinal sides. This waveguide element can be produced by punching out a blank in the form of the rectangular centre and tongues extending out from the longitudinal sides, as illustrated in the left- hand figure of Fig. 2. The tongues can then be bent upwards, e.g. by press forming, to the erect position of the right hand figure of Fig. 2.

These waveguide elements can then be picked and placed on the substrate having a conducting layer, as is schematically illustrated in Fig. 3, where six elements of the type discussed in relation to Fig. 2 have been arranged along a T-path. Picking and placing of such elements can be made by a per se known pick-and-place equipment. Preferably, the waveguide elements are provided on tapes, on trays or the like, and are picked by a pickup arrangement, e.g. using pneumatic suction cups. The waveguide elements are then placed on the substrate. The substrate preferably has an adherent surface, to maintain the placed waveguide elements in place during assembly. When all waveguide elements have been properly placed, the connection between the waveguide elements and the substrate is fixated. For example, a soldering paste could be arranged on the substrate prior to placement, which is adherent to maintain the placed elements in the right position during assembly, and which fixates the element when the substrate is subsequently heat treated at an elevated temperature, e.g. by applying infrared heating to the substrate, or by treatment in an oven.

The waveguide elements are preferably made of metal, but may also be made of e.g. plastic materials or the like, which are provided with metal ized surfaces.

Fig. 4 schematically illustrates a waveguide formed in this way, in a schematic cross-sectional view. The waveguide comprises a lower substrate, in this example comprising a lower substrate layer 1 1 , an optional conductive metal layer 12 on top of said lower substrate layer and a solder or solder paste layer 13. A waveguide element 6 is arranged on top of the solder or solder paste layer 13, and consequently the waveguide element is in electric and conductive contact with the conductive layer of the substrate, and fixated to the substrate by means of soldering. The lower substrate layer can be made of metal, whereby it will in itself serve as a conductive layer. In this case, the conductive layer 12 can be omitted. On top of the waveguide element, the second conductive layer 4 is arranged, as discussed in the foregoing, in such a way that a gap is formed between the two conductive layers, enclosing the protruding fingers of the waveguide elements there between.

The waveguide element of Fig. 2 is arranged to provide a straight waveguide section. However, more complex geometries can be provided in essentially the same way. Some examples of such alternative geometries are illustrated in Figs. 5-8.

Fig. 5 illustrate a curved waveguide section, in which the base plate forms a curve, and with protruding fingers being provided along the sides.

Fig. 6 is a straight waveguide section similar to the one of Fig. 2, but having fewer protruding fingers along the longitudinal sides. Fig. 7 illustrates even shorter waveguide elements. Such short waveguide elements may comprise four, six or eight protruding fingers each, with 2-4 fingers on each longitudinal side. Such short waveguide elements may be combined in various ways to provide waveguides in the centre, or be arranged along the sides of waveguides, etc. Some examples of this is provided in the following.

Fig. 8 illustrates a more complex geometry, providing a divider, where one incoming waveguide is split into two outgoing waveguides, or vice versa.

Forming waveguides by use of such waveguide elements can be made in various ways, and some examples are provided in the following, with reference to Figs. 9-12.

In Fig. 9, a waveguide element forms the waveguide along the base plate, with the protruding fingers being arranged on the sides of this waveguide. The waves hereby propagate along the base, and only a single row of protruding fingers is provided at each side. Such embodiments work for some embodiments, in particular if the protruding fingers are in conductive contact with both the first and second conductive layer, but often it is preferred to provide two or more rows of protruding fingers along each side.

In Fig. 10, two waveguide forming elements are placed parallel to each other, and with a separation distance there between. In this embodiment, the waves propagate along the separation distance, and the waveguide elements forming double rows of protruding fingers along each side.

In Fig. 1 1 , a waveguide forming element having protruding fingers along each longitudinal side is used as a waveguide, in a similar way as in the embodiment of Fig. 9. However, in addition, additional waveguide elements having protruding fingers only at one side are arranged parallel with the center waveguide element, thereby providing double rows of protruding fingers along the waveguide. The additional waveguide elements may also have protruding fingers on each side, thereby providing three rows of protruding fingers along each side of the waveguide, as is illustrated in Fig. 12. However, the waveguide elements may also comprise two or more rows of protruding fingers. Some examples of such waveguide elements are discussed in the following, in relation to Figs. 13 and 14.

In the embodiment of Fig. 13, a waveguide similar to the one discussed in relation to Fig. 2 is provided, with tongues being formed at the edge of the base. However, in this embodiment, the tongues are bent upwards along two different folding lines at each side, so that every other tongue is situated farther away from the centre line of the waveguide element. Hereby, two rows of staggered protruding fingers are obtained.

In the embodiments of Fig. 14, the tongues are instead punched out within the perimeter of the base plate, whereby two or more rows of protruding fingers can be obtained in a staggered or non-staggered

disposition. In the illustrative examples of Fig. 14, two rows of protruding fingers are provided along each longitudinal side, and in a non-staggered disposition. In the embodiment of Figs. 14 a and b, the base area between the protruding fingers may serve as a lifting area when using pick-and-place assembling. However, for some applications, the base area between the fingers may be insufficient. For example, the base area may have too limited dimensions for certain pick-and-place equipment, the wave guide element may need a more stable base, etc. To this end, the base area may extend past one or both the rows of protruding fingers, to form an additional base area. Such an embodiment, where the base extends past the rows of protruding fingers are one side, is illustrated in Figs. 14c and d.

Such additional base areas on one or several sides may naturally be used on any of type of wave guide element, and this concept is not limited to the particular wave guide element of Fig. 14.

The waveguide elements discussed so far have protruding fingers distributed relatively evenly along the sides. However, other configurations are also feasible. For example, the protruding fingers may be arranged only at the ends of the waveguide element, as in the embodiment illustrated schematically in Fig. 15. However, many other configurations are also feasible. Further, the waveguide elements may comprise a combination of protruding fingers being provided as tongues extending from the edges, and tongues being punched out within the base plate. Further, small waveguide elements, each having a relatively simple configuration, may be assembled together to form more complex geometries.

As an example, Fig. 16 is an illustration of a T power divider having three ports, wherein each port is formed by a waveguide element of the type discussed in relation to Fig. 15, and a centre waveguide element is formed by a combination of internal and external protruding fingers.

As another example, Fig. 17 is an illustration of a right angle corner, having two ports, each formed by a waveguide element of the type discussed in relation to Fig. 15, and a centre waveguide element formed by a

combination of internal and external protruding fingers.

The above two embodiments are merely examples, and other and even more complex geometries can be obtained in the same way. For example, special antenna exciter components to be located below coupling slots can be obtained in the same way.

So far, various examples of waveguide elements primarily intended for groove gap waveguides have been discussed. However, by placing such waveguide elements around a ridge, or by providing a ridge on the base of these elements, most of these waveguide elements can also be used for forming ridge gap waveguides. Further, many other examples of waveguide elements for forming ridge gap waveguides are feasible, some of which will be briefly discussed in the following.

In Fig. 18, a simple waveguide forming element for forming a straight section of a ridge waveguide is illustrated. The waveguide element comprises a base 61 and protruding fingers 3, such as pins, pillars or the like. Further, a ridge 7 is provided, along which waves can propagate. The ridge is here a solid ridge. Elements such as this can e.g. be produced by etching, spark erosion, molding, such as injection molding, and the like. The waveguide element can either be made of metal, or be provided with a metalized, conducting surface. This type of ridge elements can be picked and placed in a similar way as discussed above, by using e.g. the upper surface of the ridge as a lifting surface for picking the elements, e.g. by means of pneumatic suction cups.

However, the ridge need not be solid. An example of such a waveguide element, resembling the element of Fig. 18, is illustrated schematically in the cross-sectional view of Fig. 19. Here, the waveguide element is formed in a similar way as the embodiments of Fig. 13, with double rows of protruding fingers, formed as bent up tongues, along each longitudinal side. However, contrary to the embodiment of Fig. 13, the base is here formed in a bent shape, to form a rectangular shaped ridge along the centre of the base. The ridge hereby is provided with solid side walls and upper surface, but is unfilled in the middle.

The embodiment of Fig. 20 is similar to the embodiment of Fig. 18, but comprises a somewhat more complex form, having a central ridge extending from one side and into an opening, functioning as a coupling port, in the substrate. The ridge is here preferably provided with a non-uniform width, thereby forming a transition towards the coupling opening. This element may be used as an input or output port of a ridge gap waveguide

The embodiment of Fig. 21 is a branched distribution network formed in ridge gap waveguide technology in accordance with [13]. The ridge structure forms a branched so-called corporate distribution network from one input port to four output ports. The distribution network may be much larger than this with many more output ports to feed a larger array. In contrast to the antenna of [13], the stopping texture is here formed as protruding

elements/fingers. The ridge is preferably a solid ridge such as shown in the ridge gap waveguides in e.g. [4].

Some examples of waveguide elements have now been discussed. However, it should be acknowledged by the skilled addressee that many other embodiments and variations are feasible. Hereby, a range of

standardized waveguide elements can be provided, and used for formation of whole or parts of essentially any type of waveguide or RF part. Since standardized elements may be used, and picked and placed by e.g. ordinary pick and place equipment, waveguides and RF parts can hereby be manufactured very cost-effectively, both in small and large series. The RF parts can even be custom made in a quick and cost-effective way.

Some examples of RF parts have been discussed in the following. However, many other types of per se known RF parts can be produced by using waveguide elements in the above-discussed way. For example, a circular cavity of a rectangular waveguide can be formed in this way, e.g. using curved waveguide elements, so that the protruding fingers/elements are arranged along a circular path, enclosing a circular cavity. Further, in such an embodiment, a feeding arrangement may be provided within the cavity, as well as a radiating opening, such as a X-shaped radiating slot opening.

It is also possible to produce RF parts to form flat array antennas with this technology. For example, antennas structurally and functionally resembling the antenna disclosed in [12] and/or the antenna discussed in [13] can be cost-effectively produced in this way, said documents hereby being incorporated in its entirety by reference. One or several of the waveguide layers of such an antenna may be made as a waveguide as discussed in the foregoing, without any substrate between the two metal ground planes, and with protruding fingers/elements extending between the two conducting layers, formed by waveguide elements with bases attached to the substrate. Then, the conventional via holes, as discussed in [13], will instead be fingers, such as metal pins or the like, forming a waveguide cavity between the two metal plates, within each unit cell of the whole antenna array.

The RF part may also be a gap waveguide filter, structurally and functionally similar to the one disclosed in [14], said document hereby being incorporated in its entirety by reference. However, contrary to the waveguide filter disclosed in this document, the protruding fingers/elements are now then arranged on a lower conducting layer by use of the above-discussed waveguide elements. Another example of a waveguide filter producible in this way is the filter disclosed in [15], said document hereby being incorporated in its entirety by reference.

The RF part may also be used to form a connection to and from an integrated circuit, and in particular MMICs, such as MMIC amplifier modules. Such an embodiment is illustrated schematically in Fig. 22. Here, an integrated circuit is arranged on a substrate, such as a PCB. Waveguide elements, as discussed in the foregoing, may then be placed to form waveguides leading to/from the integrated circuit, and to form a transition between the waveguide and the integrated circuit. In the illustrative example, a MMIC 81 is connected to waveguide elements 82 by a transition element 83. A lid may be arranged on top of the substrate, to form the upper conductive surface of the waveguides.

Further, grids of protruding fingers may also be provided by waveguide elements of the general type discussed above, for use e.g. for packaging. Such grids may e.g. be formed by providing waveguide elements having one, two or more rows of protruding fingers side-by-side on a substrate. Such an embodiment is illustrated schematically in Fig 23. In case the rows of the grid are so closely arranged that there is not sufficient space left for pneumatically lifting the waveguide elements, an extension of the base plate may extend out on one of the sides, to function as a lifting area, as schematically illustrated in Fig. 23.

Figs. 24 a and b illustrate two different perspective views of a passive network comprising a branched waveguide, and provide an example of how various types of waveguide elements can be combined to produce more complex realizations. In the illustrative example of Fig. 24, the waveguide network comprises a branched waveguide element similar to the one of Fig. 8, followed by straight waveguide elements, similar to the one of Fig. 6, and subsequently followed by curved waveguide elements, similar to the one of Fig. 5. In addition, a plurality of smaller waveguide elements, similar to the ones of Fig. 7 are arranged around the perimeter of the waveguide, to provide additional protruding fingers outside the first row of protruding fingers provided by the above-discussed waveguide elements. Hereby, each waveguide section is provided with two or more rows of protruding fingers at each side at all, or at least most, positions.

Figs. 25 a and b illustrate an example of an active component, similar to the embodiment of Fig. 22, but illustrated in greater detail. In this

embodiment, two active components 81 ', such as MMICs, are provided. The active components 81 ' are at the input/output ports connected to a plurality of input/output lines, such as microst p lines 84 for providing bias voltages to the MMIC. Further, some RF input/output ports are connected to gap waveguide transmission lines, via transition elements 83'. The gap

waveguides are here illustrated as straight waveguides, being formed e.g. by elements similar to the one discussed in relation to Figs. 2 and 6. However, more complex waveguide transmission lines or networks may also be used. Further, a plurality of smaller waveguide elements, here of the type illustrated in Fig. 7, are provided around both the gap waveguides and the active components, to improve the performance of the gap waveguides and provide shielding between the components. In addition, further elements, such as passive components 86 and the like may be provided.

Both the passive network illustrated in Fig. 24 and the active

component network of Fig. 25 are merely examples, and the skilled reader will appreciate that other realizations are also feasible in a similar way, to obtain the same or other functionality.

The invention has now been described with reference to specific embodiments. However, several variations of the technology of the

waveguide and RF packaging in the antenna system are feasible. For example, a multitude of different waveguide elements useable to form various types of waveguides and other RF parts are feasible, either for use as standardized elements, or for dedicated purposes or even being customized for certain uses and applications. Further, even though assembly by means of pick-and-place equipment is preferred, other types of surface mount technology placement may also be used, and the waveguide elements may also be assembled in other ways.

Such and other obvious modifications must be considered to be within the scope of the present invention, as it is defined by the appended claims. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, a single unit may perform the functions of several means recited in the claims.

References

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