Abstract:
A phased array antenna system formed from an antenna-integrated printed wiring board for performing the functions of a waveguide impedance matching layers, a honeycomb support structure, RF antenna probes, DC logic and RF distribution. The printed wiring board construction of the present invention significantly reduces the number of component parts required to form a phased array antenna assembly, as well as simplifying the manufacturing process of the antenna assembly. The antenna-integrated printed wiring board is formed from an inexpensive, photolithographic process to create a single part (or optionally a two part) structure for performing the above-listed functions.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to phased array antennas, and more particularly to an integrated printed wiring board antenna for forming a phased array antenna system in which the antenna elements and their associated electronics are integrated onto one, or a pair of, printed wiring board assemblies.  
         BACKGROUND OF THE INVENTION  
         [0002]    The assignee of the present application, The Boeing Company, is a leading innovator in the design of high performance, low cost, compact phased array antenna modules. The Boeing antenna module shown in FIGS. 1 a - 1   c  have been used in many military and commercial phased array antennas from X-band to Q-band. These modules are described in U.S. Pat. No. 5,886,671 to Riemer et al and U.S. Pat. No. 5,276,455 to Fitzsimmons et al, both being hereby incorporated by reference.  
           [0003]    The in-line first generation module was used in a brick-style phased-array architecture at K-band and Q-band frequencies. This approach is shown in FIG. 1 a.  This approach requires some complexity for DC power, logic and RF distribution but it provides ample room for electronics. As Boeing phased array antenna module technology has matured, many efforts made in the development of module technology resulted in reduced parts count, reduced complexity and reduced cost of several key components of such modules. Boeing has also enhanced the performance of the phased array antenna with multiple beams, wider instantaneous bandwidths and greater polarization flexibility.  
           [0004]    The second generation module, shown in FIG. 1 b,  represented a significant improvement over the in-line module of FIG. 1 a  in terms of performance, complexity and cost. It is sometimes referred to as the “can and spring” design. This design can provide dual orthogonal polarization in an even more compact, lower-profile package than the in-line module of FIG. 1 a.  The can-and-spring module forms the basis for several dual simultaneous beam phased arrays used in tile-type antenna architectures from X-band to K-band. The can and spring module was later improved even further through the use of chemical etching, metal forming and injection molding technology. The third generation module developed by the assignee, shown in FIG. 1 c,  provides an even lower-cost production design adapted for use in a dual polarization receive phased array antenna.  
           [0005]    Each of the phased-array antenna module architectures shown in FIGS. 1 a - 1   c  require multiple module components and interconnects. In each module, a relatively large plurality of vertical interconnects such as buttons and springs are used to provide DC and RF connectivity between the distribution printed wiring board (PWB), ceramic chip carrier and antenna probes.  
           [0006]    A further step directed to reduce the parts count and assembly complexity of the antenna module as described above is described in pending U.S. patent application Ser. No. 09/915,836, “Antenna Integrated Ceramic Chip Carrier For A Phased Array Antenna”. This application involves forming an antenna integrated ceramic chip carrier (AICC) module which combines the antenna probe (or probes) of the phased array module with the ceramic chip carrier that contains the module electronics into a single integrated ceramic component. The AICC module eliminates vertical interconnects between the ceramic chip carrier and antenna probes and takes advantage of the fine line accuracy and repeatability of multi-layer, co-fired ceramic technology. This metallization accuracy, multi-layer registration produces a more repeatable, stable design over process variations. The use of mature ceramic technology also provides enhanced flexibility, layout and signal routing through the availability of stacked, blind and buried vias between internal layers, with no fundamental limit to the layer count in the ceramic stack-up of the module. The resulting AICC module has fewer independent components for assembly, improved dimensional precision and increased reliability.  
           [0007]    In spite of the foregoing improvements in antenna module design, there is still a need to further combine more functions of a phased array antenna into a single component. This would further reduce the parts count, improve alignment and mechanical tolerances during manufacturing and assembly, improve electrical performance, and reduce assembly time and processes to ultimately reduce phased array antenna system costs. More specifically, it would be highly desirable to eliminate dielectric “pucks” that need to be used in a completed antenna module, as well as to entirely eliminate the use of buttons, button holders, flex members, cans, sleeves, elastomers and springs. If all of these independent parts could be eliminated, then the only issue bearing on the cost of the antenna assembly would be the material and process cost of manufacturing the antenna assembly.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a phased array antenna system which incorporates an antenna integrated printed wiring board (AIPWB) assembly. The AIPWB includes circuitry for DC/logic and RF power distribution as well as the antenna probes. The metal honeycomb waveguide plate used with previous designs of phased array antenna modules is eliminated in favor of a multi-layer printed wiring board which includes vias which form circular waveguides and a plurality of layers (stack-up) for providing a honeycomb waveguide structure and wide angle impedance matching network (WAIM). Thus, the antenna system of the present invention completely eliminates the need for dielectric pucks, which previous designs of phased array antenna modules have heretofore required. The entire phased array antenna system is thus formed from either a single, multi-layer printed wiring board, or two multi-layer printed wiring boards placed adjacent to one another. This construction significantly reduces the independent number of component parts required to produce a phased array antenna system. Each of the two printed wiring boards are produced using an inexpensive, photolithographic process. Forming the entire antenna system essentially into one or two printed wiring boards significantly eases the assembly of the phased array antenna system, as well as significantly reducing its manufacturing cost.  
           [0009]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]    [0011]FIGS. 1 a - 1   c  represent prior art module designs of the assignee of the present invention;  
         [0012]    [0012]FIG. 2 is an exploded perspective view of the two major components forming a 64 element phased array antenna system in accordance with a preferred embodiment of the present invention;  
         [0013]    [0013]FIG. 3 is a cross sectional side view through one antenna site taken in accordance with section line  3 - 3  in FIG. 2;  
         [0014]    [0014]FIG. 4 is a cross sectional side view taken in accordance with section line  4 - 4  through the upper printed wiring board shown in FIG. 2 illustrating the vias used for forming a circular waveguide, honeycomb support structure, and the stack-up for the wide angle impedance matching network (WAIM);  
         [0015]    [0015]FIG. 5 is a detailed, side cross sectional view of portion  5  of the probe-integrated printing wiring board of FIG. 3 illustrating in greater detail the electrical interconnections formed within the layers of this printed wiring board assembly;  
         [0016]    [0016]FIG. 6 is a plan view of a portion of the probe-integrated wiring board showing the vias that form the can for each pair of RF radiating elements; and  
         [0017]    [0017]FIG. 7 is a view of an alternative preferred embodiment of the present invention wherein the probe-integrated printed wiring board and the waveguide printed wiring board are formed as a single, integrated, multi-layer printed wiring board. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0019]    Referring to FIG. 2, there is illustrated a pre-assembled view of a 64 element phased array antenna system  10  in accordance with a preferred embodiment of the present invention. It will be appreciated immediately, however, that the present invention is not limited to a 64 element phased array antenna system, but that the principles and teachings set forth herein could be used to produce phased array antenna systems having a greater or lesser plurality of antenna elements. The phased array antenna system  10  incorporates a multi-layer probe-integrated printed wiring board  12  and a multi-layer waveguide printed wiring board  14  which are adapted to be disposed adjacent one another in abutting relationship when fully assembled. Conventional threaded or non-threaded fasteners (not shown) can be used to secure the two wiring boards  12  and  14  in close, secure abutting contact. The probe-integrated printed wiring board  12  includes a plurality of antenna elements or modules  16  arranged in an 8×8 grid. Each antenna element  16  includes a pair of radio frequency (RF) probes  18 , but it will be appreciated again that merely a single probe could be incorporated, if desired, and that greater than two probes could be included just as well to meet the needs of a specific application.  
         [0020]    The waveguide printed wiring board  14  includes a plurality of circular waveguides  20  formed to overlay each of the antenna elements  16 . It will be appreciated that as the operating frequency of the antenna system  10  increases, the thickness of the wiring board  14  will decrease. Conversely, as the operating frequency decreases, the thickness of the board  14  will increase.  
         [0021]    Referring to FIG. 3, the probe-integrated printed wiring board  12  can be seen to include a plurality of 15 independent layers  12   a - 12   o  sandwiched together. Again, it will be appreciated that a greater or lesser plurality of layers could be provided to meet the needs of a specific application. RF vias  22   a  and  22   b  are used to form tho probes  18  while vias  24  are arranged circumferentially around the vias  22   a  and  22   b  to form a “can”  26  for the antenna element  16 . This is illustrated in greater detail in FIG. 6. It will be appreciated that the illustration of 20 vias to form the can  26  is presented for illustrative purposes only, and that a greater or lesser plurality of vias  24  could be employed.  
         [0022]    Referring now to FIG. 4, the waveguide printed wiring board can be seen to also include a plurality of independent layers  14   a - 14   q  which form a wide angle impedance matching network (WAIM). Vias  28  extending through layers  14   c - 14   q,  form the waveguide portion of the wiring board  14 . Again, it will be appreciated that vias  28  are arranged in circular orientations such as shown in FIG. 6. Layers  14   a  and  14   b  form impedance matching layers.  
         [0023]    Each of the printed wiring boards  12  and  14  are formed through an inexpensive, photolithographic process such that each wiring board  12  and  14  is formed as a multi-layer part. The probe-integrated printed wiring board  12  includes the antenna probes  18  and DC/logic and RF distribution circuitry. On this component, the discrete electronic components (i.e., MMICs, ASICs, capacitors, resistors, etc) can be placed and enclosed by a suitable lid or cover (not shown). Accordingly, the multiple electrical and mechanical functions of radiation, RF distribution, DC power and logic are all taken care of by the probe-integrated printed wiring board  12 .  
         [0024]    Referring now to FIG. 5, the probe-integrated printed wiring board  12  is shown in further detail. Layer  12   a  comprises a ground pad  30  on an outer surface thereof. Ground pad  30  is electrically coupled to a ground pad  32  on an outer surface of layer  12   o  by a conductive via  34  extending through each of the layers  12   a - 12   o.  Via  34  is also electrically coupled to an RF ground circuit trace  36 . Layers  12   a - 12   i  are separated by ground layers  38 . The ground layers help to reduce the inductance of the vias formed in the board  12 .  
         [0025]    With further reference to FIG. 5, via  39  and pads  39   a  and  39   b  provide electrical coupling to layer  12   o,  which forms a stripline for distributing RF energy between the RF probes  18  and the vias  39 . It will be appreciated that for a 64 element phased array antenna, there will be 64 of the vias  39 , with each via  39  associated with one of the 64 antenna elements.  
         [0026]    Referring further to FIG. 5, pad  40  on layer  12   a  and pad  42  on layer  12   o  are electrically coupled by a conductive via  44 . Pad  46  on layer  12   a  and pad  48  on layer  12   o  are electrically coupled by conductive via  50 . Pad  52  on layer  12   a  and pad  54  on layer  12   o  are electrically coupled by conductive via  56 , while pad  58  on layer  12   a  and pad  60  on layer  12   o  are electrically coupled by conductive via  62 . Via  44  extends completely through all of the layers  12   a - 12   o  and is also electrically coupled to a clock circuit trace  64 . Via  50  extends through all of the layers  12   a - 12   o  and is electrically coupled to a data circuit trace  66 , Via  56  extends through all of layers  12   a - 12   o  and is electrically coupled to a DC source (−5V) circuit trace  68 . Via  62  likewise extends through all of layers  12   a - 12   o  and is electrically coupled to another DC power (+5V) circuit trace  70 .  
         [0027]    One via  24  is shown which helps to form the can  26  (FIG. 6). Via  24  is essentially a conductive column of material that extends through each of layers  12   a - 12   o.  Finally, one of the RF vias  18  is illustrated. Via  18  extends through each of layers  12   a - 12   o  and includes a perpendicularly extending leg  74  formed on an outer surface of layer  12   a.    
         [0028]    Again, however, it will be appreciated that the drawing of FIG. 5 represents only a very small cross sectional portion of the probe-integrated printed wiring board  12 . In practice, a large plurality of RF probe vias  18 , and a large plurality of vias  24  for forming the can  26 , will be implemented. For the phased array antenna system  10  shown in FIG. 2, 128 RF probe vias  18  are formed in the probe-integrated printed wiring board  12 , together with a much larger plurality of vias  24 . Also, it will be appreciated that the various electronic components used with the antenna system  10 , although not shown, will be secured adjacent layer  12 P in FIG. 5.  
         [0029]    It will also be appreciated that the probe-integrated printed wiring board  12  and the waveguide printed wiring board  14  could just as easily be formed as one integrally formed, multi-layer printed wiring board to form an antenna system  10  in accordance with an alternative preferred embodiment of the present invention. Such an implementation is illustrated in the cross sectional drawing of FIG. 7, wherein reference numeral  78  denotes the single multi-layer printed wiring board which includes a probe-integrated printed wiring board portion  80  and a waveguide printed wiring board portion  82 . RF vias  84  extend through both boards  80  and  82  together with a plurality of vias  86  forming the can.  
         [0030]    The preferred embodiments disclosed herein thus provide a means for forming a phased array antenna from a significantly fewer number of component parts, and in a manner which significantly eases the assembly of a phased array antenna system. The preferred embodiments are capable of being formed from an inexpensive, photolithographic process to create a single part, or two parts, which perform the functions of the WAIM, honeycomb structure, dielectric pucks, antenna probes, DC logic current and RF distribution circuit of a phased array antenna.  
         [0031]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.