Patent Publication Number: US-9887449-B2

Title: Radio frequency coupling structure and a method of manufacturing thereof

Description:
FIELD OF THE INVENTION 
     This invention relates to a radio frequency coupling structure, a printed circuit board, a radio frequency device, a radar sensor and to a method of manufacturing the radio frequency coupling structure. 
     BACKGROUND OF THE INVENTION 
     Radio frequency (RF) coupling structures may be used to couple a RF signal from one side to another side of a RF device. The RF signal may for example be transmitted from a first radiating element to a second radiating element via the RF coupling structure. Alternatively, in a reciprocal path, the RF signal may be received by the second radiating element and transmitted via the RF structure to the first radiating element. The first radiating element and the second radiating element may be for example an antenna, a waveguide, a transmission line coupled to the RF coupling structure. The RF signal may be attenuated during the transfer from the first radiating element to the second radiating element in a way such that the RF signal may not be transmittable with sufficient strength. RF coupling structures may limit attenuations of the RF signal by matching at radio frequencies the first radiating element with the second radiating element. 
     Techniques are described in literature to enhance radio frequency coupling between a first radiating element and a second radiating element. 
     An example of such techniques is disclosed in U.S. Pat. No. 8,169,060 B2. U.S. Pat. No. 8,169,060 B2 discloses an integrated circuit package assembly. The integrated circuit package assembly includes an integrated circuit package and a printed circuit board substrate. The printed circuit board substrate includes a waveguide. The integrated circuit package houses a first antenna that is configured to radiate a first electromagnetic signal. The waveguide generates a waveguide signal based on the first electromagnetic signal, and passes the waveguide signal to a second antenna that is electrically coupled to the waveguide. The second antenna is configured to radiate a second electromagnetic signal received from the waveguide. A conductive layer is formed over an external surface on the integrated circuit package, extends over a top dielectric layer of the integrated circuit package and reflects power radiated from the first antenna towards the waveguide. 
     SUMMARY OF THE INVENTION 
     The present invention provides a radio frequency coupling structure, a printed circuit board, a radio frequency device, a radar sensor and a method of manufacturing a radio frequency coupling structure as described in the accompanying claims. 
     Specific embodiments of the invention are set forth in the dependent claims. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the Figures, elements which correspond to elements already described may have the same reference numerals. 
         FIG. 1  shows a cross section of an example of an embodiment of a radio frequency coupling structure taken along the line I-I. in  FIG. 2 . 
         FIG. 2  shows a planar view of the example shown in  FIG. 1 . 
         FIG. 3  shows a cross section of the example shown in  FIG. 1  and  FIG. 2  taken along the line III-III in  FIG. 2 . 
         FIG. 4  shows a cross section of the example shown in  FIGS. 1-3 . 
         FIG. 5  shows a cross section of a radio frequency device. 
         FIG. 6  shows a planar view of an example of an embodiment of a radiating element. 
         FIG. 7  graphically shows the simulated scattering parameters for the example shown in  FIGS. 5 and 6 . 
         FIG. 8  schematically shows an example of a radar sensor. 
         FIG. 9  schematically shows a flow diagram of an example of a method of manufacturing a radio frequency coupling structure. 
         FIG. 10  schematically shows a flow diagram of an example of a method of manufacturing a radio frequency coupling structure. 
         FIG. 11  schematically shows a flow diagram of an example of a method of manufacturing a radio frequency coupling structure. 
         FIG. 12  schematically shows a flow diagram of an example of a method of manufacturing a radio frequency coupling structure. 
         FIG. 13A-13E  show planar views of intermediate structures obtained in a first example of a method of manufacturing a radio frequency coupling structure. 
         FIG. 14A-14F  show planar views of intermediate structures obtained in a second example of a method of manufacturing a radio frequency coupling structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An example of a radio frequency (RF) transmission structure  10  will be hereinafter described with reference to  FIG. 1  and  FIG. 2 . 
       FIG. 1  shows a cross section of the RF coupling structure  10  taken along the line I-I in  FIG. 2 . 
       FIG. 2  shows a cross section of the RF coupling structure  10  along a plane parallel to a surface  3  of  FIG. 1 . 
     With reference to  FIG. 1 , the RF coupling structure  10  couples a RF signal between a first radiating element  100  and a second radiating element  200 . The first radiating element  100  is arranged at a first side  1  of a first dielectric substrate  20 . The second radiating element  200  is arranged at a second side  2  of the first dielectric substrate  20 . The second side  2  is opposite to the first side  1 . The RF coupling structure  10  comprises a hole  25  arranged through the first dielectric substrate  20  and extending from the first side  1  to the second side  2 . The hole  25  is provided in the first dielectric substrate  20 . The RF coupling structure  10  comprises a first electrically conductive layer  30  arranged on a first wall  40  of the hole  25  and a second electrically conductive layer  90  arranged on a second wall  95  of the hole  25 . The second wall  95  is opposite to the first wall  40 . The first electrically conductive layer  30  is arranged to electrically connect a first signal terminal  110  of the first radiating element  100  to a second signal terminal  210  of the second radiating element  200 . The second electrically conductive layer  90  is arranged to electrically connect a first reference terminal  120  of the first radiating element  100  to a second reference terminal  220  of the second radiating element  200 . The first electrically conductive layer  30  is separated from the second electrically conductive layer  90  in the hole  25 . The hole  25  extends beyond the first wall  40  away from the second wall  95 . In other words, the hole  25  extends in a plane parallel to a surface  3  of the first dielectric substrate  20  on both sides of the first electrically conductive layer  30  beyond the first wall  40  away from the second wall  95 . 
     With reference to  FIG. 2 , the hole  25  may for example comprise a first part  26 , a second part  27  and a third part  29 . In  FIG. 2 , the first part  26 , the second part  27  and the third part  29  are indicated with dashed lines. The first electrically conductive layer  30  may be arranged on a first wall  40  of the first part  26 . The second electrically conductive layer  90  may be arranged on a second wall  95  of the first part  26 . The second part  27  and the third part  29  partially overlap the first part  26 . The second part  27  does not overlap the third part  29 . The first electrically conductive layer  30  may be separated from the second electrically conductive layer  90  in the first part  26  of the hole  25 . The hole  25  extends in the plane of  FIG. 2 , i.e. in the plane parallel to the surface  3  of the first dielectric substrate  20 , from both sides  50  and  60  of the first electrically conductive layer  30  beyond the first wall  40  and away from the second wall  95 . The second part  27  and the third part  29  of the hole  25  extend beyond the first wall  40  away from the second wall  95 . 
     The hole  25  may have a first sidewall  55  and a second sidewall  65 . The first sidewall may extend from a first edge  54  of the first sidewall  55  with the first wall  40  away from the first wall  40 . The second sidewall  65  may extend from a second edge  64  of the second sidewall  65  with the first wall  40  away from the first wall  40 . The first electrically conductive layer  30  may extend from the first edge  54  to the second edge  64 . The electrically conductive layer  30  may for example be aligned at both sides  50  and  60  with the first sidewall  55  and the second sidewall  65  of the hole  25 , respectively. 
     The first electrically conductive layer  30  has a first width w 1  and the second electrically conductive layer  90  has a second width w 2 . The second width w 2  may be larger than the first width w 1 . Alternatively, the second width w 2  may be substantially equal to the first width w 1 . 
     The second conductive layer  90  may extend from the second wall  95  onto a third sidewall  57  and a fourth sidewall  67  of the hole  25 . The second conductive layer  90  may extend onto the third sidewall  57  to an interface between the first part  26  and the second part  27 . In addition, the second conductive layer  90  may extend onto the fourth sidewall  67  to an interface between the first part  26  and the third part  29 . 
       FIG. 3  shows a cross section of the RF coupling structure  10  taken along the line III-III in  FIG. 2 .  FIG. 3  shows the first part  26  and the second part  27  of the hole  25  in the cross-section. The first part  26 , the second part  27  and the third part  29  (not shown in  FIG. 3 ) extend through the first dielectric substrate  20  from the first side  1  to the second side  2 . 
     An effect of having the hole  25  extending beyond the first wall  40  away from the second wall  95  will be hereinafter described with reference to  FIG. 4 . 
       FIG. 4  shows a cross-section of the RF coupling structure  10  similar to the cross-section of  FIG. 2 . The cross-section shown in  FIG. 4  shows the distribution of the electric field (E-field) lines  15  in the RF coupling structure  10 . The E-field lines  15  originated from the first electrically conductive layer  30  may be pointing towards the second electrically conductive layer  90 . The distribution of the electric field lines  15  may depend upon the frequency of RF signal crossing the RF coupling structure  10 , a dielectric constant of the first dielectric substrate  20 , thickness of the first dielectric substrate  40  and geometry of the hole  25  (e.g. distance between the first electrically conductive layer  30  and the second electrically conductive layer  90 , size of the second part  27  and the third part  29  of the hole  25 ). The RF coupling structure  10  may behave as a microstrip line wherein the first electrically conductive layer  30  is a top signal conductor and the second electrically conductive layer  90  is a bottom ground conductor. A space inside the hole  25  between the first electrically conductive layer  30  and the second electrically conductive layer  90  may be filled with air so that most of the E-field lines  15  are distributed inside the hole  25  filled with air. Since most of the E-filed lines  15  of the RF coupling structure  10  are distributed in the hole  25 , e.g. filled with air, less E-field lines  15  propagate inside the first dielectric substrate  20  from an interface hole-first dielectric substrate  20 . E-field lines  15  are bent upwards in proximity of the first edge  54  and the second edge  64  at both sides  50  and  60  of the first electrically conductive layer  30 . An extension of the hole  25  beyond the first wall  40  away from the second wall  95  helps to maintain the E-field lines  15  in proximity of both sides  50  and  60  inside the hole  25 . 
     When the second electrically conductive layer  90  extends onto the sidewalls  57  and  67  of the hole  25 , E-filed lines  15  in proximity of both sides  50  and  60  may propagate from the first electrically conductive layer  30  directly to the second electrically conductive layer  90  without penetrating the first dielectric substrate  20 . 
     Propagation of the E-field lines from the first electrically conductive layer  30  to the second electrically conductive layer  90  through the first dielectric substrate  20 , with e.g. a relatively high dielectric constant, is a narrow-band process. By maintaining most of the E-field lines inside the hole  25 , e.g. in the air filling the hole  25 , a wideband frequency response of the RF coupling structure  10  may be obtained. 
     The hole  25  may be filled with any suitable dielectric material different than air. For example, the hole  25  may be filled with a second dielectric material having a second dielectric constant larger or smaller than a first dielectric constant of the first dielectric substrate  20 . For example, the first dielectric constant may be in a first range of 1.0 to 5.0 while the second dielectric constant may be in a second range of 1.0 to 12.0. Alternatively, the first dielectric constant may be larger than 5.0 and the second dielectric constant larger than 12.0. 
     The first dielectric substrate  20  may be any type of suitable dielectric substrate. For example, a low cost printed circuit board dielectric substrate material may be used, such for example FR4 dielectric substrate material, ceramic dielectric substrate material. 
     The first electrically conductive layer  30  and the second electrically conductive  90  may be arranged parallel to each other as in the examples shown in the  FIGS. 1-4 . However, the first electrically conductive layer  30  and the second electrically conductive  90  may be arranged not in parallel, e.g. if the hole  25  has a rounded shape. 
     The hole  25  may have any shape suitable for the specific implementation. For example, as shown in  FIG. 2 , the hole  25  has substantially a C cross-section, where the longer external side of the C is flat and parallel to the shorter internal side of the C. The first part  26 , the second part  27  and the third part  29  of the hole  25  may have any suitable shape. For example, with reference to  FIG. 2  the first part  26 , the second part  27  and the third part  29  may have a square or rectangular shape. The second part  27  and the third part  29  of the hole  25  may have a suitable shape such that the second part  27  and the third part  29  of the hole  25  extend beyond the first wall  40  away from the second wall  95  by at least two microns. For example, the hole  25  may extend beyond the first wall  40  away from the second wall  95  by at least two microns to 100 millimeters. Size of the first part  26  with respect to the second part  27  and the third part  29 , distance of the first electrically conductive layer  30  to the second electrically conductive layer  95  are selected geometrical parameters of the hole  25  which may be chosen by design to suit a particular application. The selected geometrical parameters of the hole  25  depend upon the radio frequency of operation of the RF coupling structure  10  and will be tuned to provide a desired E-field and magnetic field (H-field) distribution pattern in the RF coupling structure  10  to enhance RF losses and improve matching. 
     For example, referring to  FIG. 2 , for a radio frequency of operation of 70 GHz to 90 GHz, the second part  27  and the third part  29  of the hole  25  may have substantially an equal area. The first part  26  of the hole  25  may have an area substantially equal to the area of the second part  27  or the third part  29 . A distance between the first electrically conductive layer  30  and the second electrically conductive layer  90  may be a few tenth of millimeters or larger, for example in a range between 0.2 to 1 mm. The total area of the hole  25  may be in a range of a few tenth square millimeters or larger, e.g. larger than 0.1 mm 2 . 
       FIG. 5  shows a radio frequency device  350 . The RF device  350  comprises a printed circuit board (PCB)  300  and an integrated circuit package  310 . 
     The PCB  300  comprises the RF coupling structure  10  as described with reference to  FIGS. 1-4 . 
     The PCB  300  may comprise a first board electrically conductive layer  35 , a second board electrically conductive layer  93 , a third board electrically conductive layer  97 , a fourth board electrically conductive layer  99 , a first board dielectric substrate  28  and a second board dielectric substrate  98 . The first board electrically conductive layer  35  is arranged on first board dielectric substrate  28  which is arranged on the second board electrically conductive layer  93 . The second board electrically conductive layer  93  may be arranged on the third board electrically conductive layer  97 . The third board electrically conductive layer  97  may be arranged on the second board dielectric substrate  98 . The second board dielectric substrate  98  may be arranged on the fourth board electrically conductive layer  99 . 
     The first board dielectric substrate  28  is formed as the first dielectric substrate  20  shown in the  FIGS. 1-4 . The hole  25  is arranged through the first board dielectric substrate  28  and extends from the first side  1  to the second side  2  of the first board dielectric substrate  28 . The RF coupling structure  10  of  FIG. 5  is equivalent to the one described with reference to the  FIGS. 1-4 . 
     The first board electrically conductive layer  35  comprises the first signal terminal  110  and the first reference terminal  120  of the first radiating element  100 . For example, the first board electrically conductive layer  35  may be patterned in a first signal path and in a first reference path. The first signal path may be electrically connected to the first signal terminal  110  while the first reference path may be electrically connected to the first reference terminal  120 . 
     Similarly, the second board electrically conductive layer  93  comprises the second signal terminal  210  and the second reference terminal  220 . The second board electrically conductive layer  93  may be patterned in a second signal path and in a second reference path. The second signal path may be electrically connected to the second signal terminal  210  while the second reference path may be electrically connected to the second reference terminal  220 . 
     The PCB  300  comprises the second radiating element  200  which is partly formed in the fourth board electrically conductive layer  99  and contacted to the second signal terminal  210  via a via hole  92  which extends through the second board dielectric substrate  98 . 
     The first radiating element  100  is partially integrated in the RF circuit package  310 . The integrated circuit package  310  comprises an integrated circuit die  250 . The integrated circuit die  250  may be arranged to generate the RF signal for transmitting the RF signal via the first radiating element  100 . Alternatively or additionally, the integrated circuit die  250  may be arranged to receive the RF signal as received via the first radiating element  100 . 
     The integrated circuit die  250  may comprise any circuit suitable for the specific implementation. For example, the circuit integrated die  250  may comprise a circuit of the group of circuits consisting of: a transmitter, a receiver, and a transceiver. The circuit may be electrically coupled to the first radiating element  100 . 
     The integrated circuit package  310  may comprise a package dielectric substrate  101  on which the integrated circuit die  250  is placed, e.g. soldered or mounted on the package dielectric substrate  101 . The integrated circuit die  250  may be electrically connected to the radiating element  100  via e.g. a via hole  104  extending through the package dielectric substrate  101  or via solder balls, or otherwise. The integrated circuit die  250  may be encapsulated by for example a plastic moulding compound  320 . The first signal terminal  110  may be contacted to the first signal path of the first radiating element  100  via one or more solder-balls  122 . The first reference terminal  120  may be contacted to the first reference path of the first radiating element  100  via one or more solder-balls  123 . 
     The first radiating element  100  and the second radiating element  200  may be any type of radiating element suitable for the specific implementation. For example, the first radiating element  100  and the second radiating element  200  may be one of the group of radiating elements comprising: a single-ended microstrip antenna, a differential microstrip antenna, a rectangular patched single-ended antenna, a rectangular patched differential antenna, a square patched single-ended antenna, a square patched differential antenna, a waveguide, and a slotline. 
     The first radiating element  100  and the second radiating element  200  may be arranged to be planar radiating elements. Alternatively, the first radiating element  100  and the second radiating element  200  may be not planar and e.g. be arranged on multiple layers. 
     For example, the first radiating element  100  may comprise a co-planar waveguide  102 . 
     Referring to  FIG. 6 , the co-planar waveguide  102  comprises a signal path  106  and a return signal path  108 . The signal path  106  is electrically connected via the via hole  104  to the integrated circuit die  250  and electrically coupled via the one or more solder balls  122 , shown in  FIG. 5 , to the first signal terminal  110 . The return signal path  108  may be connected to the integrated circuit die  250  via one or more electrically conductive vias through the package dielectric substrate  101  shown in  FIG. 5  and via the one or more solder balls  123  to the first reference terminal  120 . The return signal path  108  may be directly connected to a reference potential, e.g. ground, inside the integrated circuit package  310 . Alternatively, the return signal path  108  may connected to the reference potential outside the integrated circuit package  310 , e.g. in the PCB  300  via the first board electrically conductive layer  35 . 
     Referring to  FIG. 5 , the RF device  350  provides a relatively simple transition from the co-planar waveguide  102  integrated in the integrated circuit package  310  to the second radiating element  200 . When the RF signal is transferred from the first radiating element  100  to the second radiating element  200  via the RF coupling structure  10 , the RF signal may undergo several electromagnetic conversion modes. For example, if the second radiating element  200  comprises a microstrip line formed in the fourth electrically conductive layer  99 , the transition is from the co-planar waveguide  102  to the microstrip line via the RF coupling structure  10 . In this example, the RF signal undergoes from a co-planar waveguide electromagnetic mode to a microstrip line electromagnetic mode of the RF coupling structure  10  to another microstrip line electromagnetic mode. Such electromagnetic mode of a microstrip line is known in the art as a quasi-transverse-electromagnetic mode (quasi-TEM mode). The electromagnetic mode of a co-planar waveguide is similar to the electromagnetic mode of a mircrostrip line, i.e. also a quasi-TEM. As a consequence, the RF device  350  may provide an electromagnetic conversion from a quasi-TEM mode of the co-planar waveguide  102  via a quasi-TEM mode of the RF coupling structure  10  to a quasi-TEM mode of the microstrip line formed in the fourth electrically conductive layer  99 . Since the electromagnetic modes in the conversion are of the same types, mismatch losses in the RF device  350  in the transition may be reduced so that insertion losses of the transition can be reduced. Insertion losses of the transition in the example described above are reduced compared to for example a transition in which the RF coupling structure  10  is replaced by a waveguide, as for example in the above mentioned U.S. Pat. No. 8,169,060 B2. 
       FIG. 7  shows a graph schematically indicating the simulated scattering parameters (S-parameters) characteristics for the transition described in the example above of a co-planar waveguide  102  to RF coupling structure  102  to microstrip line. The graph shows simulated insertion loss  355  between an input terminal at the integrated circuit die  250  side of the co-planar waveguide  102  and an output terminal of the microstrip line (not shown) formed in the fourth board electrically conductive layer  99 . The graph further shows simulated return loss  360  at the input terminal. The graph shows that the insertion loss  355  of the transition is within −3 dB in a frequency range of 0 to 90 GHz while the return loss  360  is maintained below −10 dB in the same frequency range. 
     The RF coupling structures  10  and RF devices  350  may be used in RF communications systems of one of the group of RF communications system comprising: a wireless LAN, an E-band backhaul, a radar system. For example, the RF devices  350  may be a radar sensor working at any frequency range suitable for the specific radar system. For example, in a short detection range radar system, e.g. within 5 to 10 meters detection range, the radar sensors may be working at a frequency range of 24-25 GHz, for an intermediate and long detection range radar system, e.g. within 100 meters detection range and beyond, the radar sensors may be working at a frequency range of 76-81 GHz. 
       FIG. 8  schematically shows an example of a radar sensor  400 . The radar sensor  400  comprises the RF device  350  as described in the example shown in  FIG. 5 , and an antenna  1000 . The antenna  1000  may be electrically coupled to second radiating element  200 , e.g. via a coaxial cable, an RF connector soldered or screwed in the printed circuit board  310  (not shown in  FIG. 8 ). The antenna  1000  may be electrically coupled to the second radiating element  200  to transmit and/or receive the RF signal through a frequency channel. The radar sensor  400  may be used to detect a set of targets  2000  in a field of view of e.g. an automotive vehicle within a predetermined detection range. The RF signal may be transmitted from a transceiver in the RF device  350  via the RF coupling structure  10 , and via the antenna  1000  to the targets  2000 . The RF signal may be reflected back from the set of targets  2000  to the antenna  1000 . A circuit, e.g. of the integrated circuit die  250  shown in  FIG. 5  may receive the RF signal reflected back from the set of targets  2000 . 
       FIG. 9  shows a flow diagram of a method of manufacturing a radio frequency coupling structure as described with reference to the  FIGS. 1-4 . 
     The method comprises: providing  600  a first dielectric substrate, providing  610  an hole extending through the first dielectric substrate from a first side of the first dielectric substrate to a second side of the first dielectric substrate. The first side is opposite to the second side. The method further comprises providing  650  a first electrically conductive layer and a second electrically conductive layer. 
     The first electrically conductive layer is arranged on a first wall of the hole. The second electrically conductive layer is arranged on a second wall of the hole opposite to the first wall. The first electrically conductive layer is separated from the second electrically conductive layer. The hole extends beyond the first wall away from the second wall. 
     The method will be hereinafter described with reference to three different examples. A first example is hereinafter described with reference to the flow diagram shown in  FIG. 10  and through the  FIGS. 13A-13E .  FIGS. 13A-13E  show planar views of intermediate structures  5  to  9  obtained in a first example of a method of manufacturing the RF coupling structure  10 . 
       FIG. 13A  shows a planar view of a first intermediate structure  5  comprising the first dielectric substrate  20 . 
       FIG. 13B  shows a planar view of a second intermediate structure  6  obtained after providing  600  the first dielectric substrate  20 . After providing  600  the first dielectric substrate  20 , a first hole  36  is provided, e.g. drilled though the first dielectric substrate  20 . The first hole  36  extends through the first dielectric substrate  20  from the first side to the second side (not shown in the planar view of  FIG. 13B ). 
       FIG. 13C  shows a planar view of a third intermediate structure  7  obtained after plating  613  the first hole  36  with an electrically conductive layer  31 . Sidewalls of the first hole  36  are covered with the electrically conductive layer  31 . 
       FIG. 13D  shows a planar view of a fourth intermediate structure  8  obtained after providing  614  the first dielectric substrate  20  with a second hole  37  partially overlapping the first hole  36 . The second hole  37  extends through the first dielectric substrate  20  from the first side to the second side. 
       FIG. 13E  shows a planar view of the complete RF coupling structure  9  after providing  616  the first dielectric substrate  20  with a third hole  39 . The third hole  39  partially overlaps the first hole  36 . The third hole  39  extends through the first dielectric substrate  20  from the first side to the second side. 
     According to this first example, referring to the flow diagram shown in  FIG. 10 , providing  610  the hole  35  comprises providing  602  the first dielectric substrate  20  with the first hole  36 , providing  614  the first dielectric substrate  20  with the second hole  37  and providing  616  the first dielectric substrate  20  with the third hole  39 . The first hole  36 , the second hole  36  and the third hole  39  form the hole  36  e.g. with a desired shape. 
     Providing  614  the first dielectric substrate  20  with the second hole  37  after plating  613  the first hole  36  cuts away a layer part of the electrically conductive layer  31 . 
     Providing  616  the first dielectric substrate  20  with the third hole  39  after plating  613  the first hole  36  and after e.g. providing  614  the first dielectric substrate  20  with the second hole  37 , cuts away a further layer part of the electrically conductive layer  31 . 
     Eventually, after cutting away a layer part with the second hole  37  and after cutting away a further layer part with the third hole  39 , the first electrically conductive layer  32  and the second electrically conductive layer  33  are formed, with the first electrically conductive layer  32  separated from the second electrically conductive layer  33 . 
     The first hole  36  corresponds to the first part  26  of the hole  25  shown in  FIG. 2 . The second hole  37  corresponds to the second part  27  of the hole  25  shown in  FIG. 2 . The third hole  39  corresponds to the third part  29  of the hole  25  shown in  FIG. 2 . The first electrically conductive layer  32  of  FIG. 13E  corresponds to the first electrically conductive layer  30  shown in  FIG. 2 . The second electrically conductive layer  33  of  FIG. 13E  corresponds to the second electrically conductive layer  90  shown in  FIG. 2 .
     A second example of a method of manufacturing a radio frequency coupling structure is described with reference to the  FIGS. 14A-14Ca  and to the flow diagram of  FIG. 11 .   

       FIG. 14A  shows a planar view of a first intermediate structure  11  comprising the first dielectric substrate  20 . 
       FIG. 14B  shows a planar view of a second intermediate structure  12 . The second intermediate structure  12  comprises the hole  35 . The hole  35  is provided through the first dielectric layer  20 . The second intermediate structure  12  may for example be obtained as described with reference to the  FIGS. 13D-13E , e.g. by drilling a first hole, a second hole and a third hole. Alternatively, the second intermediate structure  12  may be obtained by directly drilling the hole  35 , e.g. by using a drilling tip with a desired shape.
     After providing  610  the hole  35 , the hole  35  may be plated  620  with an electrically conductive layer  31  as shown in the planar view of a third intermediate structure  13  of  FIG. 14C . Sidewalls of the hole  35  are covered with the electrically conductive layer  31 .   

     With reference to the intermediate structure  14  of  FIG. 14D , after plating  620  the hole  35  with the electrically conductive layer  31 , a photo-resist layer  31   a  may e.g. be deposited  652  on a first part and a second part of the electrically conductive layer  31 . Depositing  652  the photo-resist layer may be selectively performed along desired walls or desired parts of the walls of the hole  25  by for example paint-like tools. The first part corresponds to the first electrically conductive layer. The second part corresponds to the second electrically conductive layer. The photo-resist layer  31   a  may protect the first and second parts from subsequent etching. 
     With reference to the intermediate structure  16  of  FIG. 14E , parts of the electrically conductive layer  31  non covered by the photo-resist layer may be etched  654  away in an etch process such that the first part and the second part of the electrically conductive layer  31  are maintained. 
     With reference to the intermediate structure  18  of  FIG. 14F , equivalent to that of  FIG. 13E , the photo-resist layer  31   a  may be removed  656  to leave unexposed the first part and the second part of the electrically conductive layer  31 . 
     Referring to the flow diagram shown in  FIG. 12  of a third example of a method of manufacturing a RF coupling structure, providing  650  the first electrically conductive layer  32  may comprise placing  660  one or more first metal staples in the hole  35  to form the first electrically conductive layer  32 . Similarly providing  650  the second electrically conductive layer  33  may comprise placing  662  one or more first metal staples in the hole  35  to form the second electrically conductive layer  33 . In this third example, the first and the second electrically conductive layers  32  and  33  may be provided directly after the hole  35  is formed without additional metal plating and/or metal etching processes, or in combination therewith. 
     Providing  610  the first dielectric substrate  20  with the hole  35  may comprise providing the hole  35  with a first sidewall  56  extending from a first edge  53  of the first sidewall  56  with the first wall  41  away from the first wall  41 . 
     Providing  610  the first dielectric substrate  20  with the hole  35  may comprise providing the hole  35  with a second sidewall  66  extending from a second edge  63  of the second sidewall  66  with the first wall  41  away from the first wall  41 . 
     The first electrically conductive layer  32  may for example extend between the first edge  53  and the second edge  63 . 
     Further, after providing  650  the first and the second electrically conductive layers  32  and  33 , additional holes may be provided, e.g. drilled through the first dielectric substrate  20 , to cut further the second electrically conductive layer  33  such that the second width w 2  of the second electrically conductive  33  is reduced. For example, the second electrically conductive layer  33  may be cut such that the second width w 2  is larger than the first width w 1  of the first electrically conductive layer  32 . Alternatively, the further holes may be provided to cut the second electrically conductive layer  33  such that the second with w 2  is substantially equal to the first width w 1 . 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the scope of the invention as set forth in the appended claims. For example, the electrical connections may be any type of electrical connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise the connections may for example be direct connections or indirect connections. 
     Also, devices functionally forming separate devices may be integrated in a single physical device. For example, as shown through  FIG. 5 , a single integrated circuit die  250  may integrate a transmitter and a receiver. However, the transmitter and the receiver may be integrated in separate integrated circuit dies both electrically coupled to the first radiating element  100 . 
     Although the invention has been described with respect to specific conductivity types or polarity of potentials, skilled artisans appreciated that conductivity types and polarities of potentials may be reversed. For example in the  FIG. 4  the electric field lines have been schematically shown without a specific orientation. However, since the RF signal is a time-dependent signal and varies periodically its sign, the electric field lines may be oriented in a direction going from the first electrically conductive layer  30  to the second electrically conductive layer  90  or in an opposite direction going from the second electrically conductive layer  90  to the first electrically conductive layer  30 . 
     However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.