WO2013185807A1

WO2013185807A1 - Packaging of active and passive microwave circuits using a grid of planar conducting elements on a grid of vertically arranged substrates

Info

Publication number: WO2013185807A1
Application number: PCT/EP2012/061150
Authority: WO
Inventors: Per-Simon Kildal; Ahmed Kishk; Eva RAJO-IGLESIAS
Original assignee: Gapwaves Ab
Priority date: 2012-06-13
Filing date: 2012-06-13
Publication date: 2013-12-19

Abstract

The present invention represents a new, way of packaging passive and active microwave circuits, and in particular circuits involving microstrip transmission lines and similar substrate bound transmission lines. The circuits are located between two conducting surfaces, one of these surface may be the ground plane of the microwave circuit, and at least one of these surfaces are provided with conducting elements formed as angular or curved conducting lines arranged on substrates. The conducting lines may e.g. have a zigzag shape. The two surfaces may form the bottom and lid of a cavity with conducting sidewalls. The conducting elements may with advantage be arrange in a periodic grid, and create together with the ground plane of the microwave circuit board or the smooth metal plane below the microwave circuit board a stop band for waves propagating between the lid with conducting elements and the ground plane. Thereby, cavity resonances are avoided or suppressed that otherwise create a big problem associated with the packaging in metal boxes with smooth metal walls.

Description

PACKAGING OF ACTIVE AND PASSIVE MICROWAVE CIRCUITS USING A

GRID OF PLANAR CONDUCTING ELEMENTS ON A GRID OF VERTICALLY

ARRANGED SUBSTRATES

Field of the invention

The present invention represents a new way of packaging passive and active microwave circuits, and in particular circuits involving microstrip transmission lines and similar substrate bound transmission lines, in such a way that the problem associated with cavity mode resonances are avoided.

Background

Electronic circuits are today used in almost all products, and in particular in products related to transfer of information. Such transfer of information can be done along wires and cables at low frequencies (e.g. wire-bound telephony), or wireless through air at higher frequencies using radio waves both for reception of e.g.

broadcasted audio and TV, and for two-way communication such as in mobile telephony. In the latter high frequency cases both high and low frequency

transmission lines and circuits are used to realize the needed hardware. The high frequency components are used to transmit and receive the radio waves, whereas the low frequency circuits are used for modulating the sound or video information on the radio waves, and for the corresponding demodulation. Thus, both low and high frequency circuits are needed.

Electronic circuits below typically 300 MHz (i.e. wavelengths longer than 1 meter) are easily realized in printed circuit boards (PCB) and in integrated circuits using designs based on concentrated circuit elements such as resistors, inductors, capacitors and transistor amplifiers. Such technology may also work at higher frequency, but the performance degrades gradually when the size of the PCB and integrated circuit package become comparable to a wavelength. When this happens, it is better to realize the circuits by connecting together in various ways pieces of transmission lines or waveguides, such as e.g. microstrip lines of coplanar waveguides. This is normally referred to as microwave technology and is commonly in use between 300 MHz and 30 GHz, i.e. the microwave region. The corresponding electronic circuits can therefore be referred to as microwave circuits, and they are often located on a planar dielectric substrate with a metal ground plane. We will herein refer to such microwave circuit on a substrate with a ground plane as a microwave circuit board.

Both passive and active electronics circuits often need to be packaged in a shielded environment such as a closed metal cavity, e.g. a metal box, for mechanical protection, but also to satisfy requirements to electromagnetic compatibility such as radiated emissions and susceptibility. Such requirements are often regulatory (for commercial devices), but can also be user-defined (such as for radio telescopes). Packaging is difficult in the microwave region, because the volume inside the packaging cavity may be large enough to support resonant modes within the frequency range of the microwave circuits, and, if such modal resonances are present, they will completely destroy the operation of the electronic circuit. Such destruction may appear not only at the frequency of the resonance, but even below and above this band due to nonlinearity and saturation effects in the circuits. There is therefore a need for an improved technical solution to this packaging problem.

There are already existing solutions to the packaging problem, such as reducing the size of the cavity volume and loading the cavity with microwave absorbers. However, the size reduction may not always be possible due to the given size of the circuit board. E. g., the enclosing cavity needs to have at least two dimensions (height and width) smaller than typically 0.5 wavelengths in order to be sure to avoid cavity resonances. The requirement may become even stronger if the substrate of the circuit board has high permittivity or is thick. Also, absorbers inside the cavity may cause undesired losses and therefore reduced performance of the microwave circuit. There is therefore a need for an alternative packaging solution that is easy to apply also when the circuit boards and correspondingly the enclosing cavities are wider than 0.5 wavelengths, and which does not require use of any absorbing material.

P.-S. Kildal disclosed in the application WO 2010/003808 a new way of realizing microwave devices, such as electromagnetic transmission lines, waveguides and circuits of them, that is advantageous when the frequency is so high that existing transmission lines and waveguides have too large losses or cannot be manufactured cost-effectively with the tolerances required. The microwave devices are realized by a narrow gap between two parallel surfaces of conducting material, by using a texture or multilayer structure on one of the surfaces. The fields are mainly present inside the gap, and not in the texture or layer structure itself, so the losses are small. The microwave device further comprises one or more conducting elements, such as a metal ridge or a groove in one of the two surfaces, or a metal strip located in a multilayer structure between the two surfaces. The waves propagate along the conducting elements. No metal connections between the two metal surfaces are needed. At least one of the surfaces is provided with means, such as a bed of posts/nails, to prohibit the waves from propagating in other directions between them than along the ridge, groove or strip,

WO 2010/003808 describes how at least one of two parallel metal plates can be provided with means that stop wave propagation in the gap between the two surfaces, which may be used as a packaging solution. In particular, the bed of posts/posts disclosed in WO 2010/003808 has been demonstrated to be very useful, as described 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.

However, when this technique is applied at frequencies typically below 10 GHz, the packaged microwave device becomes large and bulky because the height of the posts needs to be close to a quarter of a wavelength. Therefore, there is a need for a thinner and more compact solution, still providing low loss and a large stopband for cavity resonances.

Kildal describes also in WO 2010/003808 how wave propagation between two parallel metal plates can be stopped by using a multilayer structure on one of the surfaces, where the posts/posts are replaced by an EBG surface in the form of metal patches. These form a periodic pattern in two directions along the lower surface. However, such multilayer surfaces are difficult to realize cost-effectively at low frequencies with large relative bandwidth, and in particular below 10 GHz.

The above-discussed problem was addressed in EP 2 390 953, also by P-S Kildal et al, proposing a solution where a bed of conducting elements in the form of helically curved posts hindered wave propagation inside the gap between the two conducting surfaces. This solution was shown to be highly efficient. However, a drawback with this solution is that its fabrication is relatively complex, and quite costly. Further, it was found that the capacitive effect between the upper end of the helically curved posts and the overlaying conducting surface was quite significant, and contributes to decrease the lower limit of the stop band.

There is therefore a need for a more cost-efficient solution, and/or a solution with improved performance.

Summary of the invention

The object of the present invention is to provide a compact and cost-efficient way of packaging passive and active microwave circuits that efficiently removes or at least strongly reduces problems related to resonances in the cavity inside which the circuit board is located.

This object is achieved by means of a microwave circuit package as defined in the appended claims.

According to a first aspect of the present invention there is provided a passive or active microwave circuit package, comprising:

two conducting surfaces forming a gap there between; and

a microwave circuit located on a microwave substrate with a ground plane and comprising one or more sections of one or more different transmission lines, e.g. microstrip lines or coplanar waveguides,

wherein said microwave circuit is enclosed in the gap between said two conducting surfaces, where one of the surfaces may be formed by the ground plane of the microwave circuit board or an extension of this, and

wherein at least one of the surfaces is provided with a plurality of conducting elements of conducting material rising from and being attached to the conducting surface in such a way that wave propagation inside the gap between the two surfaces is stopped, at least at the frequency of operation, and

characterized in that it further comprises a plurality of substrates being arranged within said gap, each having at least one surface extending between said conducting surfaces, and in that said conducting elements are formed as curved or angular conducting lines arranged on said surfaces of the substrates, and wherein a plurality of conducting elements are provided on each substrate. The invention is in particular useable for packaging of microstrip circuits, but it is not limited to this. According to the invention, there is provided a metal cavity with conducting walls, e.g. of metal, that encloses the microwave circuit board, where the ground plane of the microwave circuit board may form at least part of one of the larger walls of the cavity. At least one of the two larger opposing surfaces of the cavity is provided with conducting elements, e.g. of metal, arranged as conducting lines on substrate surfaces, and preferably located in a periodic or nearly-periodic grid over at least part of the surface. The conducting elements are preferably arranged in such a way that there is a narrow or no gap between the ends of the conducting elements and the microwave circuits, and in such a way that the conducting elements do not mechanically touch the conducting parts of the transmission lines on the microwave circuit board. Thus, the conducting elements may be connected only to one of said surfaces each in such a way that the conducting elements on either of the surfaces are facing a smooth part of the opposite conducting surface, and preferably the surface not carrying the transmission line. The other end of the conducting elements may form a gap to the other surface. Alternatively, the other end may be touching a dielectric parts of the microwave circuit board, or be touching the ground plane of the microwave circuit board.

All of the conducting elements are preferably conductive ly connected to the conducting surfaces. Further, each conducting elements is preferably conductively connected only to one of the conducting surfaces, and preferably, all conducting elements are conductively connected to one and the same conducting surface.

However, a realization where some of the conducting elements are conductively connected to one of the conducting surfaces, and other conducting elements are conductively connected to the other conducting surface, is also feasible. The conductive connection is preferably realized as a direct metal connection.

The surfaces of the substrates containing the curved or angular conducting lines are preferably arranged vertically in the gap, so that they extend perpendicularly in relation to the conducting surfaces. Thus, "vertical" is here used to indicate an angular relationship between the substrate surfaces and the conducting surfaces, and not the actual position in the space. Naturally, the microwave circuit can be arranged in any orientation in space, The microwave circuit packaging solution of the present invention provides a very efficient remedy to the above-discussed problem with resonant modes experienced in many prior art packaging solutions. Further, the present invention provides an alternative packaging solution that is easy to apply also when the circuit boards and correspondingly the enclosing cavities are wider than 0.5 wavelengths, and it does not require use of any absorbing material. Still further, the microwave circuit package of the present invention is relatively simple and cost-efficient to realize, and e.g. more cost-efficient than EBG surfaces. The present invention represents a new, way of packaging passive and active microwave circuits, and in particular circuits involving microstrip transmission lines and similar substrate bound transmission lines. The two surfaces may form the bottom and lid of a cavity with conducting sidewalls. The conducting elements, preferably arranged in a periodic grid, creates together with the ground plane of the microwave circuit board, or together with the smooth metal plane below the microwave circuit board, a stopband for waves propagating between the lid of conducting elements and the ground plane. Thereby, cavity resonances are avoided or suppressed that otherwise create a big problem associated with the packaging in metal boxes with smooth metal walls.

The solution of the present invention performs as well as, or even better than, the previously known solution with a bed of helically formed posts presented in EP 2 390 953. In addition, the solution of the present invention is significantly easier and less costly to produce. The substrates may be produced by conventional techniques, such as e.g. the ones being used for production of ordinary PCBs. Further, the substrates are easier to mount on the conducting surface than the helically formed posts, and by the provision of several conducting elements on each substrate, such groups of conducting elements may be mounted much more efficiently than if each conducting element was to be mounted separately.

The stop band has intrinsic fundamental limits. On one hand, the total length of the curved or angular conducting lines provides a lower cutoff frequency. An upper limit for the stop band is provided by a cutoff given by the height of the gap formed between the conducting surfaces. However, in the previous solution of EP 2 390 953, the separation distance between the helically formed posts and the overlying surface has a significant influence on the cutoff frequencies, whereas in the present solution, this gap has no significant effect on the cutoff frequencies. The reason for this is the fact that in this flat structure, there is almost no capacitive effect with the upper overlying surface, whereas for the previously known solution, the capacitive effect is substantial. This is of great advantage, since this enables packing at a distance, without affecting the stop band in any significant way.

The smooth surface of the present invention may together with the conducting lines on the microwave circuit board work as a waveguide or waveguide circuit, similar to embodiments disclosed in WO 2010/003808, said document hereby incorporated by reference. Therefore, the present invention is to be considered as a specific realization of the more general invention described in WO 2010/003808, wherein the present invention provides a new realization which is particularly advantageous at low frequencies, such as in an operation frequency range of 100 MHz to 30 GHz, and preferably within the range 500 MHz to 10 GHz, and most preferably within the range 1-10 GHz.

The curved or angular conducting lines of the present inventions reduces the effective length of the conductive elements at the same time as their electrical function that stops wave propagation between the two plates is maintained.

Therefore, they will also prevent cavity mode resonances. Compared to straight conducting elements, the height of the curved or angular conducting lines can be 3-10 times shorter in effective length, thus resulting in a significantly more compact packaged microwave circuit. The period of the helical configuration can be sub- wavelength.

By curved or angular conducting lines is in the present application meant any curved or angular shape, such as a sinusoidal shape, a zigzag shape or the like, continuously forming a number of straight or curved legs or sections. A zigzag shape with essentially straight legs forming angled connections is preferred. The shape of the curved or angular configuration, the total height, the length of the legs/sections, the thickness of the conducting line, the number of legs/sections, the angle between the legs/sections, the distance between the conducting elements and the opposite surface, etc. are all parameters that may be modified for optimization of the conductive elements for particular use situations. For example, an increased number of legs/sections, corresponding to an increased electrical length, will move the frequency band inside which cavity mode resonances are avoided to lower frequencies. Similarly, a larger "diameter", i.e. the width of the conductive elements in a direction of the conductive surfaces, or a larger height also shifts the stopband down in frequency, corresponding to an increased wire length, and the relative size of the stop band is not much affected. Vice versa, smaller diameter, lower height and a reduced number of legs/sections will all move the stop band up in frequency.

By the arrangement of the conducting elements on substrate surfaces, the conducting elements becomes essentially planar, i.e. extending primarily in two dimensions. However, non-planar substrates or substrate surfaces may also be provided, in which case the conducting element would have a corresponding non- planar disposition. For example, the substrates may be arranged in curved shapes. The plurality of substrates are preferably arranged parallel to each other. Further, the plurality of substrates are preferably arranged periodically, with equal distance between each pair of neighboring substrates. Additionally or alternatively, the conducting elements on each substrate are preferably arranged periodically, with equal distance between each pair of neighboring conducting elements. The periodicity between conducting elements arranged on different substrates and the periodicity between conducting elements arranged on the same substrates may be identical to each other, or alternatively a different periodicity may be used. The conducting elements are thus preferably arranged in a periodic or nearly-period grid over at least part of said surface.

The substrates are preferably formed as thin boards, and wherein the conducting elements are formed by cut on metal or direct printing of the substrates.

Each substrate is preferably attached to one of the conducting surfaces, and wherein a separation distance is formed between the substrate and the opposite conducting surface, whereby the conducting elements are connected only to one of said surfaces, leaving a gap towards the other surface.

The substrates are preferably formed as plates, the plates extending in planes perpendicular to the conducting surfaces within the gap. Most preferably, all conducting elements are arranged in parallel planes which are all perpendicular to at least one, and preferably both of the conducting surfaces.

The conducting elements are preferably connected only to one of said surfaces, and the other end may be touching a dielectric parts of the microwave circuit board. Alternatively, the other end may be touching the ground plane of the microwave circuit board. However, according to a preferred embodiment, a gap is formed between the conducting elements and the overlying conducting surface. In one embodiment, each of the conducting elements are ending in a leg with smaller inclination angle than the rest of the legs, and preferably ends in a leg being essentially parallel to the conducting surface which the conducting element is connected to. In this embodiment the ends of the conducting elements define a more unique spacing to the opposite smooth surface than a pointed conducting element.

Preferably, the number of arms/sections of the curved or angular conducting lines is within the range 2-20, and preferably 3-15 and most preferably 4-10.

Further, the conductive elements preferably have conductive contact only to one of said surfaces, leaving a gap towards the other surface inside which the microwave circuit board is located.

The diameter, i.e. the extension in a direction parallel to the planes of the conducting surfaces, of the legs/sections of the curved or angular conducting lines is preferably within the range 10-50% of the axial height of the conducting elements, and preferably within the range 20-40%.

The gap inside which the microwave circuit board is located is preferably filled with air, gas or vacuum. However, it is also feasible to have the gap filled with a dielectric material. The conducting elements and substrates of the present invention can also be surrounded by dielectric material preferable in the form of a foam.

The two surfaces may be connected together for rigidity by a mechanical structure defining the sidewalls of the cavity. The sidewalls may be arranged on all the sides, thereby entirely enclosing the cavity, or along only some sides, leaving at least one opening on the sides. Alternatively, it is possible to use an open solution without sidewalls.

The two surfaces may be essentially planar. However, it is also feasible that at least part of the two surfaces are curved in the same way so that the gap between them is kept is so small that wave propagation inside the gap is stopped.

The microwave circuit boards enclosed between the two surfaces of the present invention may comprise one or more components such as power amplifiers, low noise amplifiers, ICs, MMICs, filters, matching networks, power dividers and combiners, couplers, antennas and so on.

The basic geometry of a microwave circuit package in accordance with the present invention comprises two parallel conducting surfaces forming the two larger walls of a cavity. 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. One of the surfaces is provided with the conducting elements. The two surfaces can be plane or curved, but they are in both cases separated by a very small distance, a gap, between the end of the conducting elements and the other plate, inside which the microwave circuits are located. The conducting elements prohibit wave propagation inside the gap, in such a way that cavity resonances are avoided.

According to another aspect of the invention there is provided a method of packaging a passive or active microwave circuit, comprising the steps:

enclosing a microwave circuit located on a microwave substrate with a ground plane and comprising one or more sections of one or more different transmission lines, e.g. microstrip lines or coplanar waveguides, in the gap between two conducting surfaces, where one of the surfaces may be formed by the ground plane of the microwave circuit board or an extension of this, and

providing at least one of the surfaces with a plurality of conducting elements of conducting material rising from and being attached to the conducting surface in such a way that wave propagation inside the gap between the two surfaces is stopped, at least at the frequency of operation,

characterized in that there is further provided a plurality of substrates within said gap, each having at least one surface extending between said conducting surfaces, and in that said conducting elements are formed as curved or angular conducting lines arranged on said surfaces of the substrates, and wherein a plurality of conducting elements are provided on each substrate. Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention, wherein:

Figure 1 is a schematic illustration of an example of a microwave circuit according to an embodiment of the invention. The larger upper surface, i.e. the lid comprising the conducting elements, is shown up-side-down as a grid of conducting elements in Figure la, the microstrip circuit board is shown in Figure lc, and the microstrip circuit board is shown upside down as located on top of the grid of conducting elements in Figure lb, thereby together forming a metal cavity where the cavity resonances are avoided by the conducting elements according to the invention.

Figure 2 is a schematic cross-sectional side view illustrating a part of the microwave circuit of Figure 1 in more detail.

Figure 3 is a schematic perspective view illustrating an exemplary

arrangement of the conducting elements in a periodic grid in more detail, and also illustrating an alternative configuration of the conductive elements.

Figure 4shows a cross section of the example in Figure 1 when the microstrip line is a so-called inverted or suspended microstrip line.

Figure 5 illustrates a packaged microwave circuit similar to the ones illustrated in Fig. 4, but with the metal walls of the cavity removed.

Figures 6 a-g are side views schematically showing different embodiments of the conducting elements in curved and angular configurations according to various embodiments of the invention.

Detailed description of the figures

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

Figure 1 shows a sketch of an example of a microwave circuit that is packaged by using a lid comprising a grid of conducting elements.

There are two metal pieces providing the upper 1 and lower 2 conducting surfaces. The lower surface 2 is preferably essentially smooth, and formed by a ground plane 2 on which a microstrip transmission line 5 is arranged. Connectors 9 are arranged on the side of the plane 2 opposite to said transmission line, and connected to the microstrip transmission line through the plane 2.

The upper surface 1 is provided with a surrounding rim 3 to which the upper surface can be mounted, and comprises a region which is lower than the rim and thereby provides a gap 4 between the upper and lower surfaces when assembled. The gap 4 is air- filled, but it can also be fully or partly filled with dielectric material.

The larger upper surface 1 comprises a grid of conducting elements 6 comprising planar curved or angular conducting lines arranged on a plurality of substrates being arranged within the gap. The conducting elements 6 are preferably equidistantly and evenly distributed over the surface. In Fig. la the lid with conducting elements 6 is shown up-side-down as a grid of conducting elements. The conducting elements 6 provide cut-off conditions for all waves propagating between the lower and upper surfaces except the desired waves along the transmission line 5. The conducting elements work similar to a PMC within the operating frequency band.

The rim 3 is preferably arranged to extend to a height exceeding the height of the conducting elements.

The microstrip circuit board is shown in Figure lc, and the microstrip circuit board is shown upside down as located on top of the grid of conducting elements in Figure lb, thereby together forming a metal cavity where the cavity resonances are avoided by the conducting elements. The upper and lower surfaces may be connected to each other by bolting. To this end, screw holes 8 may be arranged at the boundary of the lower upper metal plane, to be used to fix it to the metal rim 3 of the upper metal piece, and there are matching screw holes 7 in this rim.

The microwave circuit of Fig 1 is a microstrip line with two 90 deg bends, and the ground plane of the circuit is used as the opposing larger wall of the enclosing cavity. This microwave circuit is too simple to have any special electronic function, and it is here shown only to demonstrate the packaging principle. It is actually the same type of microwave circuit 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 here similar properties are obtained in a significantly more compact realization.

This package can be used for packaging many conventional circuits to form microwave device of the type discussed above. The package component may typically have a length of about 10 cm, a width of about 5-6 cm. The conducting elements may typically be arranged in even rows and columns. The distances between each row and between each column are preferably about the same. This distance is typically, from center to center of the adjacent posts, 7.5 mm.

Figure 2 illustrates the conducting elements in more detail. The conducting elements are here illustrated as conducting lines 62, arranged on a plane, i.e. with an essentially two-dimensional extension, on a substrate 61. In the illustrated example, the conducting line is arranged in a zigzag shape, having a number of legs/sections being connected together in acute angles. However, other angles, number of legs, shapes, etc, are feasible, as will be discussed in more detail in the following.

The conducting elements are connected to one of the conducting surfaces, and here the horizontal wall 1 lof the lid. A separation distance/gap is here provided between the end of the conducting elements and the opposite conducting surface 2. The height of this separation distance is g, and the total height of the gap between the conducting surfaces is g+h, where h is the height of the conducting elements. The conducting elements further have a "diameter" D, corresponding to the widest extension in a direction parallel to the conducting surfaces.

The substrates 61 are preferably formed as thin boards, and wherein the conducting elements are formed by cut on metal or direct printing of the substrates. The substrates are further preferably formed as plates, the plates extending in planes perpendicular to the conducting surfaces within the gap. Most preferably, all conducting elements are arranged in parallel planes which are all perpendicular to at least one, and preferably both of the conducting surfaces. Such an arrangement is illustrated in Figure 3.

By the arrangement of the conducting elements on substrate surfaces, the conducting elements becomes essentially planar, i.e. extending primarily in two dimensions. However, non-planar substrates or substrate surfaces may also be provided, in which case the conducting element would have a corresponding non- planar disposition. For example, the substrates may be arranged in curved shapes.

The plurality of substrates are preferably arranged parallel to each other. Further, the plurality of substrates are preferably arranged periodically, with equal distance between each pair of neighboring substrates. In Figure 3, the periodicity of the substrates is denominated Px. Additionally or alternatively, the conducting elements on each substrate may be arranged periodically, with equal distance between each pair of neighboring conducting elements. In Figures 2 and 3, the periodicity of the conducting elements on each substrate is denominated Pz. These periodicities, Px and Pz, may be identical to each other, or be different. The conducting elements are thus preferably arranged in a periodic or nearly-period grid over at least part of said surface.

In an illustrative example, a set of 3-20 substrates 61 may be used, such as e.g.

5. Further, 5-20 conducting elements may be provided on each substrate, such as 10. Further, the conducting elements may comprise a number of legs/sections N being in the range 2-20, and preferably 3-10, and most preferably 3-5, such as 3 or 5. The periodicities Px and Pz may be in the range 2-50 mm, and preferably 5-20 mm, such as 10 mm. The diameter D may be in the range 2-30mm, and preferably 3-10 mm, such as 7 mm. The diameter is preferably smaller than the periodicities. The separation distance/gap g is preferably in the range 0.1 -5mm, and preferably 1-3 mm, such as 2 mm. However, many other dimensions are also feasible, and may be considered for optimization of the microwave circuit package for various

applications.

Figures 4 and 5 show cross sections of the example similar to the one in Figure 1, where the microstrip line 5 forms a so-called inverted or suspended microstrip line. The transmission line is here supported by a thin substrate layer 10 located on the top of the conducting elements 6. The space 11 between the substrates may e.g. be air-filled, or filled with a dielectric, such as a foam. Such lines have the transmission line fields in an air gap, instead of in the dielectric substrate, and the substrate is only used to mechanically support the microstrip line 5 at distance from the conducting elements 6, and at distance from the other smooth metal surface acting as a ground plane 2 for the microstrip line. Figure 5 is used to illustrate that the metal walls 3 of the cavity actually can be removed. The conducting elements 6 will still stop waves from propagating between the two plates according to the invention.

Figures 6 a-g show different embodiments of the conducting lines forming the conducting elements according to various embodiments of the invention.

Fig. 6a illustrates a conducting line being similarly shaped as in the

embodiment shown in Fig. 2, but with five legs instead of four. Naturally, many other number of legs may be considered.

Fig. 6b illustrate an embodiment where the last leg, i.e. the leg being opposite to the connection to the conducting surface to which the conducting element is connected, is formed with a different angle, and here being arranged essentially parallel to the conductive surfaces.

Fig. 6c illustrate another angular shape, in which the angles between the legs are formed in two steps, with a conducting transition element being arranged between the legs.

Figs. 6d and 6e schematically illustrate that the legs need not necessarily have the same inclination relative to the conducting surfaces. In Fig. 6d, the legs being closest to the connection to the conducting surface are less inclined than the legs being farther away, whereas Fig. 6e illustrates an opposite arrangement.

Still further, the legs need not necessarily be entirely straight, but curved legs are also feasible, Further, the angled connections need not be formed as sharp elbows, but more rounded transitions are also feasible. Thus, the shape of the conducting lines may e.g. be of sinusoidal or serpent shapes, as is schematically illustrated in Fig. 6f.

Fig. 6g illustrates still another possible configuration of the conducting elements. Here, the legs are arranged essentially parallel to each other, and parallel to the conducting surfaces, and with conducting transition elements extending between the legs, and in a direction essentially perpendicular to the legs. Thus, the shape of the conducting lines in this embodiment essentially corresponds to a square wave.

The shape of the curved or angular configuration, the total height, the length of the legs/sections, the thickness of the conducting line, the number of legs/sections, the angle between the legs/sections, the distance between the conducting elements and the opposite surface, etc. are all parameters that may be modified for optimization of the conductive elements for particular use situations.

The invention is not limited to the embodiments shown here. In particular, the invention can be located inside the package of an IC or in the multiple layers on an IC chip. Also, at least one of the conducting surfaces may be provided with penetrating probes, apertures, slots or similar elements through which waves are radiated or being coupled to exterior circuits. Further, the shape and configuration of the conducting elements may be arranged in many different ways, as discussed above. Further, the conducting elements may be arranged on either one of the two surfaces, or even on both surfaces. Further, the two surfaces may be connected in various ways, and the cavity need not be closed, but may be open at one or several sides.

Claims

1. A passive or active microwave circuit package, comprising:

two conducting surfaces forming a gap therebetween; and

characterized in that it further comprises a plurality of substrates being arranged within said gap, each having at least one surface extending between said conducting surfaces, and in that said conducting elements are formed as curved or angular conducting lines arranged on said surfaces of the substrates, and wherein a plurality of conducting elements are provided on each substrate.

2. The microwave circuit of claim 1, wherein the each conducting element is conductively connected to one of said conducting surfaces.

3. The microwave circuit of claim 1 or 2, wherein the surfaces of the substrates on which the curved or angular conducting lines are arranged vertically in the gap, so that they extend perpendicularly in relation to the conducting surfaces.

4. The microwave circuit package of any one of the preceding claims, wherein said plurality of substrates are arranged parallel to each other.

5. The microwave circuit package of claim 4, wherein said plurality of substrates are arranged periodically, with equal distance between each pair of neighboring substrates.

6. The microwave circuit package of any one of the preceding claims, wherein the conducting elements on each substrate are arranged periodically, with equal distance between each pair of neighboring conducting elements.

7. The microwave circuit package of any one of the preceding claims, wherein the conducting elements are formed as angular lines, forming a zigzag shape.

8. The microwave circuit package of any one of the preceding claims, wherein the substrates are formed as thin boards, and wherein the conducting elements are formed by cut on metal or direct printing of the substrates.

9. The microwave circuit package of any one of the preceding claims, wherein each substrate is attached vertically to one of the conducting surfaces, and wherein a separation distance is formed between the substrate and the opposite conducting surface, whereby the conducting elements are connected only to one of said surfaces, leaving a gap towards the other surface.

10. The microwave circuit package of any one of the preceding claims, wherein the substrates are formed as plates, the plates extending in planes

perpendicular to the conducting surfaces within the gap.

11. The microwave circuit package according to any one of the preceding claims, wherein the two surfaces are connected to each other by vertical walls so that a shielded cavity is formed inside which the microwave circuits are located.

12. The microwave circuit package according to any of the previous claims, wherein the gap is filled with air, gas or vacuum.

13. The microwave circuit package according to any of the previous claims, wherein each of the conducting elements are ending in a leg with smaller inclination angle than the rest of the legs, and preferably ends in a leg being essentially parallel to the conducting surface which the conducting element is connected to.

14. The microwave circuit package according to any of the previous claims, wherein the conducting elements are conductively connected only to one of said surfaces, and the other end is touching a dielectric parts of the microwave circuit board.

15. The microwave circuit package according to any of the previous claims, wherein the conducting elements are conductively connected only to one of said surfaces, and the other end is touching the ground plane of the microwave circuit board.

16. The microwave circuit package according to any one of the preceding claims, wherein the conducting elements are arranged in a periodic or nearly-period grid over at least part of said surface.

17. The microwave circuit package according to any one of the preceding claims, wherein the microwave circuit has a frequency of operation within the range 100 MHz - 30 GHz, and preferably within the range 500 MHz to 10 GHz, and most preferably within the range 1 - 10 GHz.

18. A method of packaging a passive or active microwave circuit, comprising the steps:

characterized in that there is further provided a plurality of vertically arranged substrates within said gap, each having at least one surface extending between said conducting surfaces, and in that said conducting elements are formed as curved or angular conducting lines arranged on said surfaces of the substrates, and wherein a plurality of conducting elements are provided on each substrate.