Abstract:
A waveguide interface and a method of manufacturing is disclosed. The interface includes a support block that has a printed circuit board. A communication device is coupled to the circuit board. A launch transducer is positioned adjacent to and coupled to the communication device. The launch transducer includes one or more transmission lines in a first portion and at least one antenna element in a second portion. The antenna element radiates millimeter wave frequency signals. An interface plate coupled to the support block has a rectangular slot having predetermined dimensions. A waveguide component is coupled to the interface plate and has a waveguide opening. The first portion of the launch transducer is positioned within the slot such that the slot prevents energy from the transmission line from emitting toward the circuit board or the waveguide opening but allows energy to pass from the antenna element into the waveguide opening.

Description:
STATEMENT OF RELATED APPLICATIONS 
     The present application is national phase filing under 35 USC 371 of International Application No. PCT/US2010/046028 having an International Filing Date of 19, Aug. 2010 and entitled, “Precision Waveguide Interface”, of which claims the benefit of priority based on U.S. Provisional Patent Application Ser. No. 61/235,245, filed on 19, Aug. 2009, both of the above in the name of inventors Michael G. Pettus and James R. A. Bardeen, all of the above applications commonly owned herewith. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to microwave and millimeter wave radio frequency waveguide interface technologies. 
     BACKGROUND 
     As the semiconductor industry continues to increase circuit complexity and density by reduction of process node geometries, operating signal frequencies continue to increase. It is now possible to obtain semiconductors that operate well into the millimeter wave region of radio spectrum (30 GHz to 300 GHz). Traditionally the types of semiconductors used have been in the category of “III-V” types, indicating that the semiconductor compounds have been derived from period table elements in the third and fifth columns. Examples of these are gallium arsenide (GaAs) and indium phosphide (InP). In recent years, less expensive semiconductor processes that arise from column IV (such as silicon and germanium, Si and Ge) have been produced in silicon CMOS (complementary metal oxide semiconductor) and silicon germanium (SiGe) compounds. The result has been to extend the operating frequency of low-cost silicon well into the 60 to 80 GHz range of frequencies. By having low-cost semiconductor technology available, it has put pressure on the millimeter wave manufactures to bring the overall costs down for the electromechanical support mechanisms that enable these semiconductor devices. 
     Commercial waveguide structures enable low-loss energy transfer at millimeter wave frequencies, with the additional benefit of having been standardized on size and mechanical coupling flange designs. By having standardized sizes and coupling flanges, interoperability between different devices and different manufactures is enabled, providing maximal flexibility for millimeter wave system design. The traditional method for interfacing semiconductor devices within a mechanical waveguide has been to either provide a split-cavity type of assembly with expensive precision machining requirements or to couple energy from an orthogonal planar printed circuit launch probe with associated lossy energy transfer. In addition, with new semiconductor designs providing balanced transmission line outputs, there has been no straightforward electromechanical method for coupling millimeter wave energy from the balanced outputs directly to a waveguide without added circuitry such as a balun transformer which is also exhibits excessive losses as the frequency range of operation increases. 
     The prior art methods for coupling energy into and out of semiconductor devices can be divided into two categories. The first is the use of split-cavity metallic structures that allow the semiconductor chip to be placed into one of the cavities, with the other half of the cavity then brought together with the first half with precision fit. The typical precision required for the internal dimensions of a millimeter wave waveguide is on the order of ±0.001″ (0.025 mm). Holding this precision in the construction of the upper and lower cavity halves through machining, and maintaining registration alignment for assembly is expensive. 
     The second method used is to provide a printed circuit board with a stub or paddle energy launch. The stub or paddle launch is orthogonal to the waveguide cavity, also requiring a split-cavity type of assembly method. 
     In each case a custom, highly precision machining process is required to maintain the internal waveguide dimensional requirements. Some cost reduction can be afforded through a casting process, but secondary machining operations are still necessary to realize the precision needed. 
     The above methods are also designed for single-ended circuit configurations only. It is necessary to provide low-cost and efficient coupling methods for both single-ended and differential circuits. Millimeter wave semiconductor circuit designs often make use of differential amplifier and output stage configurations to enable high gain and power efficiencies. 
     What is needed is a low-cost and highly efficient coupling technique for semiconductor microwave, millimeter wave and sub-millimeter wave device energy transfer to and from standardized waveguide structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate one or more exemplary embodiments. 
       In the drawings: 
         FIG. 1A  illustrates a side view of a waveguide interface in accordance with an embodiment; 
         FIG. 1B  illustrates a cross sectional side view of the waveguide interface in accordance with an embodiment; 
         FIG. 2A  illustrates a rear view of a waveguide interface in accordance with an embodiment; 
         FIG. 2B  illustrates a detailed rear view of the waveguide interface in accordance with an embodiment; 
         FIG. 3A  illustrates a top view of the waveguide interface in accordance with an embodiment; 
         FIG. 3B  illustrates a cross sectional top view of the waveguide interface in accordance with an embodiment; 
         FIG. 4A  illustrates a waveguide flange in accordance with an embodiment; 
         FIG. 4B  illustrates an interface plate in accordance with an embodiment; 
         FIG. 4C  illustrates the waveguide flange along with the interface plate in accordance with an embodiment; 
         FIG. 5  illustrates a support block in accordance with an embodiment; 
         FIG. 6A  illustrates a transmitter printed circuit board and launch transducer substrate assembly in accordance with an embodiment; 
         FIG. 6B  illustrates a receiver printed circuit board and launch transducer substrate assembly in accordance with an embodiment; 
         FIG. 7A  illustrates a transmitter launch transducer substrate in accordance with an embodiment; 
         FIG. 7B  illustrates a receiver launch transducer substrate in accordance with an embodiment; 
         FIG. 8  illustrates four views of a printed circuit board in accordance with an embodiment; and 
         FIG. 9  illustrates a close up cross sectional side view of the waveguide interface in accordance with an embodiment. 
     
    
    
     SUMMARY 
     In an aspect, a precision waveguide interface is composed of a circular interface plate with a rectangular slot such that the slot length accepts a printed circuit board and launch transducer subassembly. The printed circuit board and launch transducer subassembly form the bottom half of a short waveguide segment within the rectangular slot of said interface plate. Due to the slot width or narrow dimension, the distance from the printed circuit assembly to the slot width upper boundary constrains the waveguide cutoff frequency of the short waveguide segment such that it is greater than the desired overall operational frequency range of the waveguide interface. By constraining the waveguide cutoff frequency of the short waveguide segment within the interface plate to a higher value than the desired operating frequency range of the waveguide interface, electromagnetic radiation transduction does not occur in this region and only electrically conducted energy is allowed to pass through the transmission line section of the launch transducer. 
     In another aspect, the printed circuit board contains thereon a semiconductor chip that functions as a transmitter or source of high frequency microwave, millimeter wave or sub-millimeter wave energy. 
     In another aspect the printed circuit board contains thereon a semiconductor chip that functions as a receiver of high frequency microwave, millimeter wave or sub-millimeter wave energy. 
     In another aspect the launch transducer is composed of a low-loss dielectric material such as quartz or alumina with deposited metallization such as gold, forming a transmission line and a radiating antenna element. 
     Known in the art are the designations for waveguide internal dimensions corresponding to the direction of the electric field vector as the E-field dimension and to the direction of the magnetic field vector as the H-field dimension. 
     In another aspect the interface plate is positioned flush against a standard waveguide flange such that the narrow dimension of the slot within the interface plate is orthogonal to the longer or H-field dimension (known in the art as the “a” waveguide dimension) of the standard waveguide flange. As such, the interface plate slot width constrains the waveguide segment cutoff frequency along the segment formed by the interface plate slot and the printed circuit and launch transducer subassembly until the standard waveguide flange is encountered by the conducted energy. Just beyond the location of the junction between the interface plate and the standard waveguide flange, the energy conducted within the transmission line of the launch transducer in conjunction with the radiating element is allowed to freely transduce into guided electromagnetic radiation within the standard waveguide channel volume. 
     In another aspect the printed circuit board and launch transducer subassembly are positioned such that the launch transducer radiating element is located within the standard waveguide area adjacent to the short waveguide segment formed by the printed circuit and launch transducer subassembly. The launch substrate transducer is configured to provide maximum energy radiation in the direction of the waveguide axis, known as an end-fire radiation pattern. 
     In an aspect, a waveguide interface includes a support block that has a printed circuit board. A communication device is coupled to the circuit board. A launch transducer is positioned adjacent to the circuit board and is coupled to the communication device. The launch transducer includes one or more transmission lines in a first portion and at least one antenna element in a second portion. The antenna element radiates millimeter wave frequency signals. An interface plate coupled to the support block has a rectangular slot having predetermined dimensions. A waveguide component is coupled to the interface plate and has a waveguide opening. The first portion of the launch transducer is positioned within the slot such that the slot prevents energy from the transmission line from emitting toward the circuit board or the waveguide opening but allows energy to pass from the antenna element into the waveguide opening. 
     In an aspect, a method of forming a precision waveguide interface comprising: selecting a support block including a printed circuit board, the support block oriented along a plane; coupling a communication device to the printed circuit board; coupling a launch transducer to the communication device, wherein the launch transducer is positioned adjacent to the printed circuit board, the launch transducer including one or more transmission lines in a first portion of the launch transducer and at least one antenna element coupled to the one or more transmission lines in a second portion of the launch transducer, wherein the at least one antenna element is configured to radiate millimeter wave frequency signals; coupling a circular interface plate to an end of the support block and oriented perpendicular to the plane, the interface plane having a rectangular slot having predetermined dimensions; and coupling a waveguide component to the interface plate, the waveguide component having a waveguide opening, wherein the first portion of the launch transducer is positioned within the rectangular slot such that the rectangular slot prevents energy from the transmission line from being emitted toward the printed circuit board or the waveguide opening and allows energy to pass from the at least one antenna element into the waveguide opening. 
     In an aspect, the second portion of the launch transducer is positioned within the waveguide opening. The launch transducer is positioned midway between opposing width edges of the support block. The communication device is positioned within a recess in the printed circuit board such that the first portion of the transducer is at a predetermined height within the rectangular slot. The launch substrate transducer is configured to provide maximum energy radiation in the direction of the waveguide axis. 
     DETAILED DESCRIPTION 
     Various example embodiments are described herein in the context of a precision waveguide interface. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to the exemplary implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed descriptions to refer to the same or like parts and may not be described with respect to all drawing figures in which they appear. 
     In an embodiment, the waveguide interface utilizes 60 GHz millimeter wave launch transducer antennas and enabled communication devices, although not limited thereto. As described below, an embodiment of the inventive subject matter will be discussed in relation to various types of launch transducer antennas, whereby each launch transducer antenna is coupled to a respective communication device. Also as described below, an embodiment of the inventive subject matter will be discussed in the contexts of electromagnetic transmission and electromagnetic reception. Those of ordinary skill in the art will realize that both the transmission context and the reception context equally apply due to the Lorentz electromagnetic reciprocity theorem. 
     In general, the following is directed to an interface between a standard waveguide flange structure and an enabled communication device. The lower-frequency electrical signals and power connections to the communication device are made to the waveguide interface through a multi-pin connector on the printed circuit board at the rear of the waveguide interface assembly; the high frequency millimeter wave electromagnetic energy is guided by the standard waveguide structure. 
     In an embodiment, the enabled communication device is a highly integrated millimeter wave radio transmitter that is attached to the printed circuit assembly. In another embodiment the enabled communication device is a highly integrated millimeter wave radio receiver that is attached to the printed circuit assembly. In an embodiment, the communication device is a silicon germanium (SiGe) chip although gallium arsenide (GaAs), complimentary metal oxide semiconductor (CMOS), or other semiconductor chips are contemplated. The details of the workings of the communication device are known in the art and are not discussed herein. 
       FIGS. 1A ,  2 A, and  3 A show a side, rear and top view, respectively, of the waveguide interface in accordance with an embodiment. As shown in  FIGS. 1A ,  2 A, and  3 A, the waveguide interface includes a printed circuit assembly  21  ( FIGS. 1A ,  3 A), a support block  31  ( FIGS. 1A ,  2 A), an interface plate  32  ( FIGS. 1A ,  2 A), and a standard waveguide flange structure  33  ( FIGS. 1A ,  3 A). The support block  31  and the interface plate  32  are coupled to the waveguide flange  33  by use of machine screws  37  and  37 A ( FIG. 2A ) and/or other types of fasteners, which may be received through holes  32 C ( FIG. 4B ) in the interface plate  32  prior to entry into the waveguide flange  33 . Low frequency electrical signal and power connections are made to a communication device  22  ( FIG. 1B ) via the printed circuit board through the connector  38 . The communication device  22  is preferably protected from the environment by a protective cover or encapsulant  39  as shown in  FIGS. 1A and 3A . Waveguide flange pins  33 A, as shown in  FIGS. 1A ,  2 A,  2 B,  4 A, and  4 C, facilitate precise alignment of interface plate  32  with standard waveguide flange  33 . 
       FIG. 1B  shows a cross sectional side view of the waveguide interface in an embodiment. As shown in  FIG. 1B , the waveguide interface  30  includes a printed circuit assembly  21  having a connector  38  thereon, as well as a communication device  22 , and a launch transducer  26 . As shown in  FIG. 1B , the waveguide interface includes a waveguide opening  33 B in a waveguide flange  33 .  FIG. 1B  also shows a short waveguide segment  32 B defined by the printed circuit assembly  21  and the interface plate slot  32 A. Fasteners  37  and  37 A couple the support block  31  and the interface plate  32  to the waveguide flange  33 , wherein the interface plate  32  is positioned between the support block  31  and the waveguide flange  33 . Support block  31  also contains guide pins  31 B that provide precision alignment of the mechanical interfaces between the support block  31  and the interface plate.  FIG. 2B  illustrates a rear view of the waveguide interface in an embodiment. 
       FIG. 3B  illustrates a cross section top view of the waveguide interface in an embodiment. Low frequency signal and power electrical interconnection between the communication device  22  and the printed circuit assembly  21  is provided by a plurality of wire bond connections  23 , although other appropriate electrical connection means are contemplated. The printed circuit assembly  21  also carries copper plating  25  in an interface region  25 A to provide an electrical ground plane in the local interface region  25 A of the interface plate  32  and waveguide flange assembly  33 . 
       FIG. 4A  illustrates a schematic of the waveguide flange  33  in accordance with an embodiment.  FIG. 4B  illustrates a schematic of the interface plate  32  in accordance with an embodiment.  FIG. 4C  illustrates a schematic of the waveguide flange  33  coupled to the interface plate  32  in accordance with an embodiment, wherein the interface plate  32  is aligned to the waveguide flange assembly  33  with interface plate slot  32 A overlapping with the waveguide flange opening  33 B. The interface plate slot  32 A prevents energy from the transmission line from being emitted toward the printed circuit assembly  21  (as shown in  FIGS. 1A and 3A ) or the waveguide opening  33 B and allows energy to pass from the antenna elements  267 ,  268  (as shown in  FIG. 7A ) into the waveguide opening  33 B. 
     As shown in  FIG. 4A , the waveguide flange  33  includes a waveguide opening  33 B positioned substantially in the center of the circular waveguide flange  33 . In particular, the waveguide opening  33 B is rectangular having an “a” dimension representing the H-field and a “b” dimension representing the E-field for a rectangular waveguide. In an embodiment, the waveguide opening  33 B dimensions are such to be utilized for the frequency range of 50 to 75 GHz, whereby the dimensions are defined by what is known categorized in the art as WR-15 or in military standard MIL-DTL-85/3C as M85/3-018. For the 50 to 75 GHz standard waveguide frequency range, also known as V-band, the “a” dimension is approximately 3.76 mm and the “b” dimension is approximately 1.88 mm. It should be noted that other “a” and “b” dimensions are contemplated for the type of application and/or the frequency range desired and thus are not limited to the values specified above. Precise alignment of interface plate  32  with standard waveguide flange  33  is facilitated by the standard waveguide flange guide pins  33 A inserted into guide pin holes  32 B contained within interface plate  32 , as discussed above. As shown in  FIG. 4B , interface plate includes interface plate machine screw holes  32 C and interface plate guide pin holes  32 , which are configured to receive machine screws  37  ( FIG. 2B ) and guide pins  31 B ( FIG. 1B ), respectively. 
       FIG. 5  shows support block  31  in an embodiment. The support block  31  includes a counter-bored hole  31 A which allows the fastener  37 A ( FIG. 1B ) to be inserted therein to couple the support block  31  to the waveguide flange and interface plate assembly  32 ,  33  as shown in  FIG. 1A . In addition, the support block  31  includes one or more guide pins  31 B which are aligned with the interface plate guide pin holes  32 D ( FIG. 4B ) of the interface plate  32 . The support block  31  provides support for the printed circuit assembly  21  when the waveguide interface operates as a transmitter ( FIG. 1B ). The support block  31  provides support for the printed circuit assembly  11  when the waveguide interface operates as a receiver ( FIG. 6A ). Support block  31  also provides for precise alignment of transmitter printed circuit assembly  21  and the receiver printed circuit assembly  11  with the interface plate  32  and the standard waveguide flange  33 . 
       FIG. 6A  shows a top view detail of the transmitter printed circuit assembly  21  in an embodiment. As shown in  FIG. 6A , the communication device  22  is affixed within a cut out area  28  of the printed circuit assembly  21  and is positioned to abut the cut out area edge  29  adjacent to the launch transducer  26 . As shown by the shaded area, the cut out area  28  and the top area  25  are copper and gold plated to maintain a continuous electrical ground plane. Low-frequency signal and power connections are supplied to the communication device  22  via a plurality of wire bonds  23  from corresponding wire bond pads  24 , although other interconnection technologies besides wire bond pads  24  are contemplated. High-frequency millimeter wave connections are provided between the communication device  22  and the adjacently positioned launch transducer  26  with low-inductance wire or ribbon bonds  27 , although other connection technologies are contemplated. The communication device  22  is configured to have a balanced connection at the high-frequency millimeter wave output terminals. Additionally, the launch transducer  26  is implemented with matching balanced transmission line terminals to efficiently accept high-frequency energy from the communication device  22 . Launch transducer  26  is located precisely at the midpoint between printed circuit assembly  21  width edges  21 A and  21 B. Additionally, the launch transducer  26  has a width dimension Y t  that is precisely matched to the standard waveguide flange opening&#39;s  33 B “b” dimension, as described above with respect to  FIG. 4C . 
       FIG. 6B  shows a top view detail of the receiver printed circuit assembly  11  in an embodiment. The communication device  12  is affixed within the printed circuit assembly  11  cut out area  18  and located to abut the cut out area edge  29  adjacent to the launch transducer  16 . Printed circuit assembly  11  cut out area  18  and top area  15  are copper and gold plated to maintain a continuous electrical ground plane. Low-frequency signal and power connections from the printed circuit assembly  11  are provided to the communication device  12  via a plurality of wire bonds  13  from corresponding wire bond pads  14 , although other interconnection technologies are contemplated. High-frequency millimeter wave connections are communicated between the communication device  12  and the launch transducer  16  with low-inductance wire or ribbon bonds  17 , although other connection technologies are contemplated. Communication device  12  has an unbalanced connection at the high-frequency input terminals. Launch transducer  16  is implemented with matching unbalanced transmission line terminals to efficiently deliver high-frequency energy to the communication device  12 . Launch transducer  16  is located precisely at the midpoint between printed circuit assembly  11  width edges  11 A and  11 B. Launch transducer  16  with is precisely matched to the “b” dimension of the waveguide flange opening  33 B, as described above with respect to  FIG. 4C . 
       FIG. 7A  shows top and bottom views of transmitter launch transducer  26  in an embodiment. As shown in  FIG. 7A , the launch transducer  26  is composed of low-loss substrate  263  which has a top metallization pattern and bottom metallization pattern. In an aspect, the substrate  263  is composed of fused silica (silicon dioxide) and is 254 micrometers (μm) thick, although other low-loss substrate materials and other material thickness values are anticipated. The metallization pattern is substantially composed of vacuum deposited gold metal from vacuum deposition techniques or other appropriate methods. 
     The top metallization pattern of the transmitter launch transducer  26  is composed of two transmission line sections  261 ,  262 . The transmission line sections  261 ,  262  are preferably implemented over a ground plane  264  on the bottom side of substrate  263 . The transmission line sections  261 ,  262  couples energy from the communication device  22  via bond wires  27  ( FIG. 6A ) or other means to the transmission line sections  265 ,  266 . Transmission line sections  261 ,  262  are implemented to match the output impedance of the communication device  22  and the bond wires  27  in a balanced configuration. Transmission line sections  265 ,  266  are located over a clear substrate section (with no ground plane on the bottom side of substrate  263  in this section) and provides energy from the transmission lines  261 ,  262  to a pair of corresponding antenna elements  267 ,  268 . Transmission line sections  265 ,  266  are implemented to match the input impedance of the antenna elements  267 ,  268 . Antenna elements  267 ,  268  are configured to provide substantial radiation energy in a direction parallel to the substrate  263  and away from transmission line sections  265 ,  266 , thereby forming an end-fire radiation pattern into waveguide flange opening  33 B. Launch transducer  26  width dimension, Yt, is matched to be inserted into the standard waveguide flange opening  33 B having the “b” dimension described above. In an embodiment, the value of Yt is 1.80 mm and the value of Xt is 2.87 mm, although other values are contemplated. 
       FIG. 7B  shows top and bottom views of a receiver launch transducer  16  in an embodiment. Launch transducer  16  is composed of a low-loss substrate  163  which has a top metallization pattern and bottom metallization pattern. In an embodiment substrate  163  is composed of alumina (aluminum oxide) and is 127 micrometers (μm) thick. Other low-loss substrate materials and other material thickness values are anticipated. The metallization pattern is substantially composed of vacuum deposited gold metal using vacuum deposition techniques or other appropriate methods. 
     In an embodiment, the top metallization pattern is composed of an unbalanced transmission line section coupled to a set of antenna elements. Transmission line center conductor  164  traverses a length over ground plane  167  which is on the bottom side of substrate  163 . Beyond the position of ground plane  167 , the transmission line  164  continues and is positioned over a bottom side transmission line  170 . Transmission lines  164  and  170  together couple to antenna elements  168 ,  169  and  171 ,  172 . Antenna elements  168 ,  169  and  171 ,  172  form a dual element dipole and are configured to provide a directional radiation pattern in a direction parallel to substrate  163  and away from transmission lines  164 ,  170 , thereby forming an end-fire radiation pattern into waveguide flange opening  33 B, as shown in  FIGS. 1B and 3B . 
     The unbalanced input circuit configuration is composed of a ground connection  162  and a center conductor  164 . Ground connection  162  is electrically connected through the substrate  163  and facilitated by metalized plated through holes (also known as vias)  165  and  166 , thereby forming a low-inductance connection to ground plane  167  on the bottom side of substrate  163 . In an embodiment, the diameter of via holes  165 ,  166  is 127 micrometers (μm) with gold metallization formed on the inner walls, although other dimensions and material selections are contemplated. Launch transducer  16  width dimension, Yr, is matched to be inserted into the standard waveguide flange opening&#39;s  33 B “b” dimension. In an embodiment, the value of Yr is 1.80 mm and the value of Xr is 3.58 mm, although other dimensions are contemplated. 
     The antenna elements  267 ,  268  of the transmitter launch transducer  26  and antenna elements  168 ,  169 ,  171 ,  172  of the receiver launch transducer  16  are configured to exhibit radio frequency operational bandwidth to be approximately 15% referenced to the center operating frequency range. This operational bandwidth provides for an operating frequency range, whereby the S parameter loss value (known in the art as S 21 ) is to be less than 2 decibels (dB). In an embodiment, launch transducers  26 ,  16  have an operating frequency range of 57 to 66 GHz, although other frequency ranges of operation and bandwidths are contemplated. 
       FIG. 8  shows four views of the transmitter printed circuit board  21  in an embodiment. Even though the transmitter printed circuit board  21  is being discussed, the implementation details, as well as all mechanical and electrical characteristics are substantially the same for both transmitter printed circuit board  21  and receiver printed circuit board  11 . The cut out area  28  receives the communication device  22  (as shown in  FIGS. 6A and 6B ), whereby the communication device  22  (as shown in  FIGS. 6A and 6B ) sits within the recessed cut out bottom surface  28 A using a conductive epoxy adhesive. Various conductive epoxy adhesives are known in the art and are not discussed herein. Cutout bottom surface  28 A and sides  28 B are metallized using standard printed circuit plating techniques. In an aspect, the top ground plane area  25 , the side surfaces  25 A, the front surface  25 B, and the bottom ground plane area  25 C are electrically contiguous. Also, the top surface  25  is electrically contiguous with the cutout side surfaces  28 B and the bottom surface  28 A. 
       FIG. 9  shows a detailed cross sectional view of the transmitter waveguide interface in an embodiment. It should be noted that the detailed description of the transmitter waveguide interface operation applies equally to the receiver waveguide interface with the direction of the millimeter wave transduction and energy reversed. Those of ordinary skill in the art will realize that both the transmission context and the reception context equally apply due to the Lorentz electromagnetic reciprocity theorem. Critical to the high efficiency and operation of the waveguide interface is to facilitate radiation of millimeter wave energy into standard waveguide flange opening  33 B and also restrict radiated energy losses as the conducted electrical energy moves from the communications device  22  through the high frequency wire bonds  27  to the transmission lines  261 ,  262 . The short waveguide segment  32 B is defined between the upper edge  32 A of interface plate  32  and the upper ground plane surface  25  of the printed circuit board assembly  21 . Printed circuit board assembly  21  also has contiguous copper plating at surfaces  25 A and  25 B, forming the lower portion of the short waveguide segment  32 B. 
     Waveguide cutoff frequency is the frequency at which all frequencies below the cutoff frequency are substantially attenuated. Equation [1], derived from the Helmholtz equation for electromagnetic waves, provides the waveguide cutoff frequency for rectangular waveguide with internal H-field “a” dimension and internal E-field “b” dimension. 
     
       
         
           
             
               
                 
                   
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     In equation [1], ωc is radian frequency, c is the speed of light, a is the H-field rectangular waveguide dimension, b is the E-field rectangular waveguide dimension, and n and m represent the waveguide mode numbers. The dominant waveguide mode is used to determine waveguide cutoff and is known in the art as transverse electric mode (TE 1,0 ) where n=1 and m=0. With n=1 and m=0, the only variable remaining is the waveguide H-field “a” dimension. For standard waveguide flange  33 , the “a” dimension is 3.76 mm which yields a cutoff frequency of 39.9 GHz, well below the intended operating frequency range of standard waveguide flange  33 , which is 50 to 75 GHz. However it is desired to substantially attenuate the transduction of energy into radiation over the operating frequency range of the waveguide interface in the short waveguide segment  32 B. 
     The H-field dimension of short waveguide segment  32 B is shown as the “a′” dimension in  FIG. 9 . In an embodiment, the “a′” dimension is approximately 0.98 mm (980 μm). Setting a in equation [1] to 0.98 mm with dominant mode (n=1 and m=0) yields a cutoff frequency of 153 GHz, well above the intended operating range of the waveguide interface. There will be slight variations of the cutoff frequency as the dimension “a′” varies as a function of the printed circuit board thickness and the effective dimension “a′” varies due to the dielectric loading properties and thickness variation of launch transducer  22  and launch transducer  12 . However, with all variations taken into account, the minimum waveguide cutoff frequency for either the transmitter waveguide interface or the receiver waveguide interface is greater than 120 GHz. By establishing short segment waveguide  32 B cutoff frequency well above the operating frequency range of the waveguide interface, maximum energy is provided to the standard waveguide opening  33 B.