A POLARIZER FOR PARALLEL PLATE WAVEGUIDES

Abstract

A polarizing screen for altering a polarization state of a radio frequency waveform radiated from a parallel plate waveguide (PPW) wherein the waveform has a centre frequency and a bandwidth, the polarizing screen comprising a plurality of developable sheets arranged stacked in parallel to each other in direction of a local normal vector of a first sheet at respective inter-sheet spacings, each sheet comprising an electrically conductive pattern forming a one-dimensional periodic structure of unit-cells in an extension direction, wherein the periodic structure is associated with a height measured orthogonally to the extension direction and orthogonally to the local normal vector of the shat, where each cell comprises an aperture configured to transmit the radio frequency waveform at a predetermined polarization state, wherein the height is determined in dependence of the centre frequency and/or the bandwidth of the radio frequency waveform such that the pre-determined polarization state is provided as well as matching between the PPW and a transmission medium of the radio frequency waveform.

Claims

1. A polarizing screen for altering a polarization state of a radio frequency waveform radiated from a parallel plate waveguide; (PPW), wherein the waveform has a center frequency and a bandwidth, the polarizing screen comprising a plurality of developable sheet arranged stacked in parallel to each other in direction of a local normal vector of a first sheet at respective inter-sheet spacings (d1, d2), each sheet comprising an electrically conductive pattern forming a one-dimensional periodic structure of unit-cells in an extension direction, wherein the periodic structure is associated with a height measured orthogonally to the extension direction and orthogonally to the local normal vector of the sheet, where each cell comprises an aperture configured to transmit the radio frequency waveform at a pre determined polarization state, wherein the height is determined in dependence of the center frequency and/or the bandwidth of the radio frequency waveform such that the pre-determined polarization state is provided as well as matching between the PPW and a transmission medium of the radio frequency waveform.

2. The polarizing screen of claim 1, wherein the height is smaller than a wavelength corresponding to the center frequency.

3. The polarizing screen of claim 1, comprising two, three or four sheets.

4. The polarizing screen of claim 1, wherein the electrically conductive patterns of adjacent sheets differ in terms of a rotation of the unit-cells about respective unit-cell center axes parallel to the normal vector.

5. The polarizing screen of claim 1, wherein the unit-cells are formed as complementary split ring resonators, CSRRs, with dimensions (py, px, g, r, R) determined in dependence of the center frequency and/or the bandwidth of the radio frequency waveform where the CSRRs of one sheet are rotated about the center axes at an angle relative to the CSRRs of an adjacent sheet or relative to a reference angle associated with the PPW.

6. The polarizing screen of claim 1, wherein the unit-cells are formed as any of: conformal split square (rectangle) resonators, slots, dual slots, or dog-bone slots, where the unit-cells of one sheet are rotated about a center axes of the respective unit-cell at an angle relative to the unit-cells of an adjacent sheet.

7. The polarizing screen of claim 1, wherein the sheets are metal sheets and where the electrically conductive patterns are formed as apertures in the sheets, where a sheet is between 0.1 mm and 1.0 mm thick.

8. The polarizing screen of claim 1, wherein the polarizing screen has a straight elongated profile where the unit-cells are arranged with equal spacing along a straight line.

9. The polarizing screen of claim 1, wherein the polarizing screen has an arcuate profile and where the unit-cells are arranged with equal spacing along an arcuate line, or the polarizing screen is shaped to match an aperture of the PPW.

10. (canceled)

11. The polarizing screen of claim 1, wherein the electrically conductive sheets are arranged as separate members with first and second opposing edges configured to be received in respective opposing slots of a PPW.

12. (canceled)

13. The polarizing screen claim 1, wherein the electrically conductive sheets are arranged as metallized surfaces on one or more dielectric carrier members, and the one or more dielectric carrier members are made of Polytetrafluoroethylene, PIPE, polymers, such as polyether ether ketone, PEEK, polyimide, Kapton, and polycarbonate, PC.

14. The polarizing screen claim 1, wherein the electrically conductive sheets are arranged as metallized surfaces on one or more dielectric carrier members, and the one or more dielectric carrier members are integrally formed with a part of the PPW.

15. A parallel plate waveguide (PPW) arrangement comprising at least one polarizing screen of claim 1, wherein the polarizing screen is arranged in a vicinity of a peripheral edge of the PPW to simultaneously alter a polarization state of the radio frequency waveform radiated from the PPW and also provide matching with respect to a transmission medium.

16. The PPW arrangement of claim 15, comprising a tapered section arranged adjacent to and leading up to the at least one polarizing screen.

17. The PPW arrangement of claim 15, comprising first and second opposing slots configured to receive respective opposing edges of an electrically conductive sheet comprised in the polarizing screen.

18. The PPW arrangement of claim 15, further comprising a quasi-optical beamformer; and a plurality of antenna ports arranged along a part of the lens periphery opposite from the polarizing screen and separated tangentially along the lens periphery.

19. (canceled)

20. An antenna system comprising the PPW arrangement of claim 15; and a plurality of lenses stacked along a lens axis.

21. The antenna system of claim 20, arranged as a dual polarized lens antenna comprising a first type of polarizing screen associated with a first polarization and a second type of polarizing screen associated with a second polarization different from the first polarization.

22. (canceled)

23. A method for manufacturing a parallel plate waveguide, PPW arrangement configured to alter a polarization state of a radio frequency waveform having a center frequency and a bandwidth, the method comprising: producing a plurality of developable sheets arranged in parallel to each other in direction of a normal vector of a first sheet at respective inter-sheet spacings, each sheet comprising an electrically conductive pattern forming a one-dimensional periodic structure of unit-cells, where each cell comprises an aperture configured to transmit the radio frequency waveform at a pre-determined polarization state, and integrating the plurality of developable sheet at a peripheral edge of the PPW.

24. The method of claim 23, further comprising: producing the plurality of developable sheets as separate metal sheets with edges configured to be received in slots formed in the PPW; and/or producing the plurality of developable sheets as metallized surfaces on one or more dielectric carrier members.

25. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present disclosure will now be described in more detail with reference to the appended drawings, where:

[0025] FIG. 1 shows aspects of an example communication system;

[0026] FIGS. 2A-B schematically illustrate multiple beam antenna systems comprising a beamforming device;

[0027] FIG. 3 illustrates an example complementary split ring resonator (CSRR) unit-cell;

[0028] FIGS. 4A-B show stacks of unit-cells for polarizing a radio frequency waveform;

[0029] FIG. 5 illustrates a polarizing screen comprising stacked rows of unit-cells;

[0030] FIG. 6 illustrates a tapered transition towards a polarizing screen;

[0031] FIG. 7 shows a Luneburg lens antenna with antenna ports and a polarizing screen;

[0032] FIGS. 8-9 schematically illustrate stacks of Luneburg lenses comprising polarizing screens;

[0033] FIGS. 10A-B shows front and back sides of a metallized dielectric carrier member;

[0034] FIG. 11 is a flow chart illustrating methods;

[0035] FIG. 12 schematically illustrates processing circuitry;

[0036] FIG. 13 shows a computer program product; and

[0037] FIGS. 14A-D schematically illustrate a number of example unit cell geometries.

DETAILED DESCRIPTION

[0038] Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0039] The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0040] FIG. 1 illustrates an example communication system 100 where access points 110, 111 provide wireless network access to wireless devices 140, 150 over a coverage area 130. An access point in a fourth generation (4G) 3GPP network is normally referred to as an evolved node B (eNodeB), while an access point in a fifth generation (5G) 3GPP network is referred to as a next generation node B (gNodeB). The access points 110, 111 are connected to some type of core network 120, such as an evolved packet core network (EPC). The EPC is an example of a network which may comprise wired communication links, such as optical links 121, 122.

[0041] The communication system 100 may also comprise one or more satellite transceivers 160 arranged to establish and to maintain a communication link 165 to the wireless devices 140, 150. The satellite transceiver 160 may also be arranged to establish and to maintain a communication link 166 to a land-based satellite communication transceiver 170, which may be connected 123 to the EPC 120 or to some other wireline communication network.

[0042] The wireless access network 100 supports at least one radio access technology (RAT) for communicating 145, 155 with wireless devices 140, 150, at times referred to as user equipment (UE). It is appreciated that the present disclosure is not limited to any particular type of wireless access network type or standard, nor any particular RAT. The techniques disclosed herein are, however, particularly suitable for use with 3GPP defined wireless access networks.

[0043] The roles and benefits of satellites in 5G have been studied in 3GPP, see, e.g., 3GPP TS 22.261 V18.0.0 (2020-09). Satellite-based communication is foreseen as especially relevant for mission critical and industrial applications where ubiquitous coverage is crucial.

[0044] Herein, satellite communication refers to communication to or via spaceborne vehicles in Low Earth Orbits (LEO), Medium Earth Orbits (MEO), Geostationary Earth Orbit (GEO) or in Highly Elliptical Orbits (HEO). It may also extend to communication to or via so-called pseudo-satellites or atmospheric satellites, such as high altitude platforms (HAPs), drones and atmospheric balloons.

[0045] FIG. 2A illustrates an example polarized communication system 200 where an antenna arrangement 220 generates a plurality of antenna beams of a first polarization 210 for communicating 145 with a wireless device 140.

[0046] FIG. 2B illustrates another polarized communication system 250 based on a dual-polarized antenna arrangement 240, where the beams of the first polarization 210 have been complemented by beams of a second polarization 230. The communication system 250 is generally associated with an increased total capacity compared to the communication system 200 in FIG. 2A.

[0047] The present disclosure relates to a compact PPW structure which provides both wideband matching to free space and also polarization transformation. This kind of structure can be used with advantage for lens antenna applications or other antennas based on quasi-optical beamformers. For instance, the PPW structures and antenna arrangements discussed herein can be used with advantage in the radio transceivers discussed above in connection to FIG. 1.

[0048] At millimeter-wave frequencies, losses are critical and fully metallic EM devices, based for example on waveguide components, are often preferred. However, discrete beam forming networks become complex as the aperture size increases. For such applications, there is an interest in using PPWs, which are mechanically simple and tolerant to manufacturing errors, leading to possible cost savings in mass production. They also provide very wide mono-mode frequency bandwidth, suitable for millimeter-wave wireless communications. A major limitation of PPW devices is that they operate in a single linear polarization state, perpendicular to the waveguide plates. It would be advantageous to have a polarizer altering the polarization state of a PPW without compromising its advantages.

[0049] The designs proposed herein evolve around a polarizer for PPWs with a one-dimensional periodic structure that provides wideband matching to free-space and polarization conversion at the same time. The implementation relies on thin polarizing sheets or metallized surfaces that may be bent to adapt to the curvature of the aperture (e.g. in combination with a Luneburg or geodesic lens). In other words, the polarizing sheets discussed herein are developable. A developable surface is a smooth surface with zero Gaussian curvature. That is, it is a surface that can be flattened onto a plane without distortion (i.e. it can be bent without stretching or compression). Conversely, it is a surface which can be made by transforming a plane (i.e. folding, bending, rolling, cutting and/or gluing). In three dimensions all developable surfaces are ruled surfaces (but not vice versa). The envelop of a single parameter family of planes is called a developable surface.

[0050] The polarizing screens disclosed herein provide linear polarization rotation (45) to enable polarization diversity from a stack of PPW beamformers. The size of the aperture in the dimension perpendicular to the plane of the lens is less than a wavelength (typically around half-a-wavelength), thus enabling beam scanning along the direction orthogonal to the PPW beamformers using a stack of PPW beamformers, which is an advantage. Alternatively, the polarizing screens may be designed to change linear polarization into circular polarization. Polarization diversity is then obtained with a stack of PPW beamformers combining screens altering the linear polarization of the PPW into left hand and right hand circular polarizations.

[0051] Herein, half-a-wavelength is a measure corresponding to approximately half the wavelength of the EM field measured at center frequency. According to some aspects, half-a-wavelength is a range of wavelengths from about 80% of the wavelength at center frequency to 120% of the wavelength at center frequency.

[0052] Aspects of the proposed concept comprise two or three layers of unit-cell elements arranged in parallel to obtain wide band polarization conversion. Usually, when designing such unit-cells, a free-space two-dimensional periodic environment (Floquet's theorem) is considered and not a parallel plate waveguide environment as it is the case here. As described above, the PPW environment results in a highly dispersive behavior, particularly when the height of the PPW aperture is small compared to the wavelength (typically half-a-wavelength). Therefore, it is not obvious and indeed somewhat surprising that wide band performance can be maintained in a design of the type presented herein. In addition, electrically small apertures are known to provide poor matching to free-space. The proposed design combines these two functionalities into a flare structure, namely the functionalities of polarization conversion and matching to free space. In the PPW environment, a counter intuitive property was also discovered, which is that better performances are obtained with a smaller number of layers, typically two or three. It is, however, appreciated that a design with a single thin layer is not theoretically possible.

[0053] Aspects of the proposed solution relate to fully metallic structures, which use two or three sheets comprising respective one-dimensional periodic designs based on sub-wavelength elements (typically half-a-wavelength), of e.g. twist-symmetric complementary CSRRs. The starting point of the sheet pattern design is a conventional periodic unit-cell approach. This type of unit-cell is applied to rotate the electric field in steps in such a way that vertical polarization is transformed into, e.g., a 45 polarization angle relative to a common reference angle.

[0054] FIG. 3 illustrates an example CSRR unit-cell 300. The CSRR unit-cell comprises an arcuate form aperture 310 with outer and inner radii R and r, respectively, i.e., the CSRR aperture width is R-r. The separation of the arcuate segments of the CSRR is referred to as g. The height of the unit-cell is py and its width is px.

[0055] FIGS. 4A and 4B shows stacks 400a, 400b of unit-cells 410, 420, 430 arranged in parallel with apertures 310 facing in the same direction. The unit-cells of one layer has been rotated about a unit-cell central axis A at an angle 0, 1, 2, measured relative to a rotation angle 0 of the first layer of unit-cells or relative to some other reference angle. The inter-sheet spacings are referred to as d1 and d2 in FIGS. 4A and 4B. The geometry in FIG. 4A provides a first polarization state of the EM field while the geometry in FIG. 4B provides another polarization state of the EM field. The obtained polarization state is a function of, among other things, the sequence of rotation angles 0, 1, 2

[0056] According to an example, the below values provide an example of dimensions for use in polarizing a radio frequency waveform at carrier frequency 28 GHz with a bandwidth of 6 GHz.

TABLE-US-00001 Parameter Value px 5.5 mm py 5.5 mm R 2.6 mm r 1.6 mm d1 2.55 mm d2 2.6 mm 1-0 22 degrees 2-0 45 degrees

[0057] FIG. 5 shows an example polarizing screen 500 arranged to alter a polarization state of a radio frequency waveform, having a centre frequency and a bandwidth, in a PPW environment. In this example the polarizing screen has a straight elongated profile where the unit-cells 300 are arranged with equal spacing along a straight line L extending in extension direction D. The polarizing screen 500 comprises sheets 510, 520, 530 with unit-cells 300 which are integrated within an extended PPW configuration. The height of the polarizing screen 500, py, is determined in dependence of the centre frequency and/or the bandwidth of the radio frequency waveform such that the pre-determined polarization state is provided as well as matching between the PPW and a transmission medium of the radio frequency waveform. Preferably, the height py is smaller than a wavelength corresponding to the centre frequency of the radio frequency waveform, and preferably about half-a-wavelength at centre frequency.

[0058] Each sheet in the plurality of developable sheets 510, 520, 530 is arranged stacked in parallel to the other sheets in direction of a local normal vector V of a first sheet 510 at respective inter-sheet spacings d1, d2. Each sheet 510, 520, 530 comprises an electrically conductive pattern forming a one-dimensional periodic structure of unit-cells 300, 410, 420, 430 in the extension direction D. The height py is measured orthogonally to the extension direction D and also orthogonally to the local normal vector V of the sheet as shown in, e.g., FIG. 5. It is appreciated that each unit-cell comprises an aperture 310 configured to transmit a radio frequency waveform at a pre-determined polarization state.

[0059] As noted above, the polarizing screen preferably comprises two, three or four sheets, and preferably two sheets. As noted above, this is not in agreement with the prior art where the prevailing opinion has been that more sheets provide better performance, not worse performance. However, in this context, more than three or four sheets arranged in parallel will not improve polarization transformation nor matching to free space, because of the dispersive nature of a PPW operated with two modes, the quasi-TEM and the TE01 modes

[0060] The electrically conductive patterns of adjacent sheets differ in terms of a rotation 0, 1, 2 of the unit-cells 300, 410, 420, 430 about respective unit-cell centre axes A parallel to the normal vector V.

[0061] According to an example, with reference to FIGS. 4A and 4B, the unit-cells 300, 410, 420, 430 are formed as complementary split ring resonators (CSRRs) where the CSRRs of one sheet is rotated about the centre axes A at an angle 0, 1, 2 relative to the CSRRs of an adjacent sheet. However, with reference to FIGS. 14A-D, the unit-cells may also be formed as any of: conformal split square rectangle resonators 1440, slots 1410, dual slots 1420, or dog-bone slots 1430, where the unit-cells of one sheet are rotated about a centre axes A of the respective unit-cell at an angle relative to the unit-cells of an adjacent sheet. Such elements are generally known and will therefore not be discussed in more detail herein.

[0062] FIG. 6 illustrates details of an example PPW 600 with an integrated polarizing screen integrated in vicinity of the PPW aperture or edge 630. A tapered section 620 or tapered transition is arranged adjacent to and leading up to the at least one polarizing screen sheet 510, 520. The tapered transition from the lens to the polarizer is implemented in order to reduce the reflections between the two components. In this example, electrically conductive sheets are arranged as separate members with first and second opposing edges configured to be received in respective opposing slots 610 of the PPW. It is noted that this edge and slot configuration can be applied both to straight sheets as well as to arcuate sheets which are configured conformal to a bent aperture of, e.g., a geodesic lens antenna arrangement.

[0063] The sheets 510, 520 making up the polarizing screen can be constructed as metal sheets and the electrically conductive patterns can be formed as apertures cut or otherwise machined in the sheets. A sheet can be anywhere from about 0.1 mm to 1.0 mm thick, and preferably about 0.3 mm thick. This thickness allows bending of the sheet to conform to, e.g., arcuate shapes and the like.

[0064] FIG. 7 illustrates an example PPW shaped as a Luneburg lens. This type of PPW geodesic lens can be based on parallel curves to realize a low-profile beamformer with a wide angular scanning range, and has been shown to yield a high performing yet compact antenna. PPWs such as this was described in The water drop lens: a modulated geodesic lens antenna based on parallel curves, by Nelson J. G. Fonseca, Qingbi Liao and Oscar Quevedo-Teruel, published in the proceedings of the 2018 international symposium on antennas and propagation (ISAP 2018), Oct. 23-26, 2018.

[0065] The PPW arrangement 700 exemplified in FIG. 7 comprises at least one polarizing screen 720 arranged in a vicinity of a peripheral edge of the PPW to provide simultaneous alteration of the polarization state of a radio frequency waveform and matching with respect to a transmission medium 730 such as air. In this case the polarizing screen 720 has an arcuate profile where the unit-cells 300 are arranged with equal spacing along an arcuate line. However, the polarizing screens disclosed herein may be conformally shaped to match any aperture of a PPW which can be flattened onto a plane without distortion, which is an advantage. Thus, the PPW arrangements discussed herein may also be generally formed as a quasi-optical beamformer, preferably a lens such as a Luneburg lens formed as a geodesic lens, a metasurface lens, or a gradient-index dielectric lens.

[0066] The PPW arrangement 700 in FIG. 7 comprises a plurality of antenna ports P1-P11 arranged along a part of the lens periphery opposite from the polarizing screen 720 and separated tangentially along the lens periphery as illustrated schematically in FIG. 7. Each port generates an antenna beam with a respective pointing direction, similar to the example discussed in connection to FIG. 2A above. It is appreciated that a single Luneburg lens such as that shown in FIG. 7 is associated with a single polarization. In The water drop lens: a modulated geodesic lens antenna based on parallel curves, by Nelson J. G. Fonseca, Qingbi Liao and Oscar Quevedo-Teruel, published in the proceedings of the 2018 international symposium on antennas and propagation (ISAP 2018), Oct. 23-26, 2018, more details of this type of antenna arrangement is given.

[0067] FIG. 8 shows an example of an antenna system 800 arranged as a dual polarized lens antenna comprising a first type of polarizing screen 810 associated with a first polarization POL 1 and a second type of polarizing screen 820 associated with a second polarization POL 2 different from the first polarization. By stacking PPWs on top of each other in this manner along a lens axis Z, a dual polarization antenna system can be created which has low profile.

[0068] FIG. 9 shows an antenna system 900 comprising a PPW arrangement with a plurality of lenses 710 stacked along the lens axis Z. By providing separate feed networks for each polarization, the elevation properties of the antenna beams can be improved. Also, active beam steering at least in the elevation domain can be realized if the transceiver 910 is configured to control the feed networks 920, 930 to control the phases of the transmitted signals on the different ports and lenses.

[0069] FIG. 10 exemplifies yet another method of realizing the polarization screen 1000. Here, the electrically conductive sheets are arranged as metallized surfaces 1010, 1020 on one or more dielectric carrier members 1030. The front side of a part of one such dielectric carrier member 1030 is illustrated in FIG. 10A while the back side of the same dielectric carrier member 1030 is shown in FIG. 10B. According to aspects, the one or more dielectric carrier members are made of Polytetrafluoroethylene, PTFE, or from polymers, such as polyether ether ketone, PEEK, polyimide, Kapton, and polycarbonate, PC.

[0070] In case a larger separating distance is required between adjacent sheets, the sheets may be realized as metallized surfaces on separate carrier members. I.e., for a two-sheet design, two separate thinner dielectric carrier members can be used, each with a single metallized surface. This has the additional advantage of requiring less dielectric material, resulting in lower losses. This way one or more dielectric carrier members can be integrally formed with a part of the PPW, and the metallization can be applied to generate the unit-cell apertures in a cost efficient and robust manner.

[0071] FIG. 11 shows a flow chart illustrating a method for manufacturing a PPW arrangement configured to alter a polarization state of a radio frequency waveform 145, 155, 165, 166 having a centre frequency and a bandwidth, i.e., a PPW according to the above discussion. The method comprises producing S1 a plurality of developable sheets 510, 520, 530 arranged in parallel to each other in direction of a normal vector V of a first sheet 510 at respective inter-sheet spacings d1, d2. Each sheet 510, 520, 530 comprises an electrically conductive pattern forming a one-dimensional periodic structure of unit-cells 300, 410, 420, 430, where each cell comprises an aperture 310 configured to transmit the radio frequency waveform at a pre-determined polarization state, and integrating S2 the plurality of developable sheets 510, 520, 530 at a peripheral edge of the PPW.

[0072] According to one example, discussed above in connection to, e.g., FIG. 6, the method comprises producing S11 the plurality of developable sheets as separate metal sheets 510, 520 with edges configured to be received in slots 610 formed in the PPW.

[0073] According to another example, discussed above in connection to, e.g., FIGS. 10A and 10B, the method comprises producing S12 the plurality of developable sheets as metallized surfaces 1010, 1020 on one or more dielectric carrier members 1030.

[0074] FIG. 12 schematically illustrates, in terms of a number of functional units, the general components of a network node 110, 111, 120, 140, 150, 160, 170 according to embodiments of the discussions herein. Processing circuitry 1210 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium 1230. The processing circuitry 1210 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

[0075] Particularly, the processing circuitry 1210 is configured to cause the device 110, 120 to perform a set of operations, or steps, such as the methods discussed in connection to FIG. 8 and the discussions above. For example, the storage medium 1230 may store the set of operations, and the processing circuitry 1210 may be configured to retrieve the set of operations from the storage medium 1230 to cause the device to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 1210 is thereby arranged to execute methods as herein disclosed. In other words, there is shown a network node 110, 111, 120, 140, 150, 160, comprising processing circuitry 1210, a network interface 1220 coupled to the processing circuitry 1210 and a memory 1230 coupled to the processing circuitry 1210, wherein the memory comprises machine readable computer program instructions that, when executed by the processing circuitry, causes the network node to transmit and to receive a radio frequency waveform 145, 155, 165, 166.

[0076] The storage medium 1230 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0077] The device 110, 111, 120, 140, 150, 160 may further comprise an interface 1220 for communications with at least one external device. As such the interface 1220 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.

[0078] The processing circuitry 1210 controls the general operation of the device 110, 111, 120, 140, 150, 160, e.g., by sending data and control signals to the interface 1220 and the storage medium 1230, by receiving data and reports from the interface 1220, and by retrieving data and instructions from the storage medium 1230. Other components, as well as the related functionality, of the control node are omitted in order not to obscure the concepts presented herein.

[0079] FIG. 13 illustrates a computer readable medium 1310 carrying a computer program comprising program code means 1320 for performing the methods illustrated in, e.g., FIG. 11, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 1300.