Abstract:
A dual stacked stripline circulator includes multiple composite ferrite discs, each having an inner portion and an outer portion; a first substrate having an edge with a first composite ferrite disc disposed in the first substrate; a second substrate having an edge with a second composite ferrite disc disposed in the second substrate; a third substrate having an edge with a third composite ferrite disc disposed in the third substrate, the third substrate disposed adjacent the second substrate; a fourth substrate having an edge with a fourth composite ferrite disc disposed in the fourth substrate; a first pattern defining three ports of a first three-port circulator disposed between the first substrate and the second substrate; a second pattern defining three ports of a second three-port circulator disposed between the third substrate and the fourth substrate; and a metal film encircling the edge of the first, second, third and fourth substrate.

Description:
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH 
       [0001]    This invention was made with Government support under Contract No. N00019-10-C-0073 awarded by the Department of the navy. The Government has certain rights in this invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure relates generally to radio frequency (RF) antenna arrays and more particularly to a which can be used in the feed structure for such antenna arrays. 
       BACKGROUND 
       [0003]    As is known in the art, feed structures are used to couple a radar or communication system to an array of antenna elements. One component of a feed structure is a circulator. U.S. Pat. No. 5,374,241 entitled “Dual Junction Back-To-Back Microstrip Four-Port Circulators” describes a back-to-back four port microstrip circulator configured from two three-port single junction circulators whose substrates lay back-to-back and are interconnected with a coaxial feedthrough. The teachings of U.S. Pat. No. 5,374,241 describe the advantages of such a configuration. 
       SUMMARY 
       [0004]    In accordance with the present disclosure, a dual stacked stripline circulator includes: a first composite ferrite disc having an inner portion and an outer portion; a second composite ferrite disc having an inner and an outer portion; a third composite ferrite disc having an inner and an outer portion; a fourth composite ferrite disc having an inner and outer portion; a first substrate having an edge with the first composite ferrite disc disposed in the first substrate; a second substrate having and edge with the second composite ferrite disc disposed in the second substrate; a third substrate having an edge with the third composite ferrite disc disposed in the third substrate, the third substrate disposed adjacent the second substrate; a fourth substrate having and edge with the fourth composite ferrite disc disposed in the fourth substrate; a first pattern defining three ports of a first three-port circulator disposed between the first substrate and the second substrate; a second pattern defining three ports of a second three-port circulator disposed between the third substrate and the fourth substrate; and a metal film encircling the edge of the first, second, third and fourth substrate. With such an arrangement, two circulator devices can be packaged in a tile architecture within an antenna lattice spacing required for an antenna having active elements utilizing circulators fabricated using unique thick film processing techniques. 
         [0005]    In accordance with the present disclosure, a dual stacked stripline circulator includes multiple composite ferrite discs, each having an inner portion and an outer portion; a first substrate having an edge with a first composite ferrite disc disposed in the first substrate; a second substrate having an edge with a second composite ferrite disc disposed in the second substrate; a third substrate having an edge with a third composite ferrite disc disposed in the third substrate, the third substrate disposed adjacent the second substrate; a fourth substrate having and edge with a fourth composite ferrite disc disposed in the fourth substrate; a first pattern defining three ports of a first three-port circulator disposed between the first substrate and the second substrate; a second pattern defining three ports of a second three-port circulator disposed between the third substrate and the fourth substrate; and a metal film encircling the edge of the first, second, third and fourth substrate, With such an arrangement, a dual stacked stiipline circulator is provided suitable for use with a dual polarized active electronically scanned array (AESA) antenna where each radiating element is being actively fed. 
         [0006]    In at least one embodiment, each disc includes an inner portion of a high saturation magnetization material and an outer portion of a low saturation magnetization material and the metal film is gold. Furthermore, the inner portion of a high saturation magnetization material is adhered to the outer portion of a low saturation magnetization material using a high temperature adhesive. This construct is commonly used to realize wideband circulators whose ratio of upper operating frequency to lower operating frequency is 3 or greater. Narrower band circulators can be realized using a single ferrite disc of an appropriate saturation magnetization material for the frequency of operation. The methods of this disclosure are applicable to the single ferrite disc as well as the composite ferrite disc, 
         [0007]    A method of providing a dual stacked stripline circulator includes: forming a first substrate with a first composite ferrite disc having an inner portion with a high saturation magnetization material and an outer portion of a low saturation magnetization material; forming a second substrate with a second composite ferrite disc having an inner portion with a high saturation magnetization material and an outer portion of a low saturation magnetization material; forming a third substrate with a third composite ferrite disc having an inner portion with a high saturation magnetization material and an outer portion of a low saturation magnetization material; forming a fourth substrate With a fourth composite ferrite disc having an inner portion with a high saturation magnetization material and an outer portion of a low saturation magnetization material; disposing a first pattern defining three ports of a first three-port circulator on each of the first substrate and the second substrate; disposing a second pattern defining three ports of a second three-port circulator on each of the third substrate and the fourth substrate; stacking the first substrate, the second substrate, the third substrate and the fourth substrate; and encircling a metal film around the first, second, third and fourth substrate. With such a technique, a dual stacked stripline circulator is provided compact in size and suitable for use in a feed arrangement for an antenna feed with active elements. 
         [0008]    The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a top perspective view of a dual stacked stripline circulator according to the disclosure; 
           [0010]      FIG. 1A  is a side cross sectional view of a portion of a dual stacked stripline circulator according to the disclosure; 
           [0011]      FIG. 1B  is a bottom perspective view of a dual stacked stripline circulator according to the disclosure; 
           [0012]      FIG. 2  is a side cross sectional view of a portion of a dual stacked stripline circulator according to the disclosure; 
           [0013]      FIGS. 2A to 2F  are top perspective views of portions of the dual stacked stripline circulator during fabrication according to the disclosure; 
           [0014]      FIG. 3  is a top perspective view of a dual stacked stripline circulator fabricated using the steps shown in  FIGS. 2A-2F  according to the disclosure; 
           [0015]      FIG. 3A  is a side perspective view of a dual stacked stripline circulator fabricated using the steps shown in  FIGS. 2A-2F  according to the disclosure; and 
           [0016]      FIG. 4  is a diagram showing the various steps used to fabricate a dual stacked stripline circulator according to the invention. 
       
    
    
       [0017]    Like reference symbols in the various drawings indicate like elements, 
       DETAILED DESCRIPTION 
       [0018]    It should be appreciated that an active electronically scanned way (AESA) antenna requires a circulator component connected to each radiating element. The circulator duplexes is the signals from the antenna, routing the transmit signal to the radiating element and the receive signal from the radiating element, while providing isolation between the transmit path and the receive path, An array lattice spacing is typically set at ½ the free space wavelength, which determines the space available for packaging a circulator in the plane of the array, in a dual polarized array, two circulator devices are needed to be packaged within the array lattice spacing, further restricting the space available per circulator. Typically, there are two packaging options, circulator resonator and transmission lines parallel (brick) or perpendicular (tile) to the direction of antenna radiation propagation. Since a circulator&#39;s size is much larger in the plane of the resonator and transmission lines, it is easier to package in the brick architecture. However, if the circulators are packaged in the tile architecture, the overall array depth is reduced substantially. This size and weight savings increases as the frequency of operation decreases. This disclosure allows two circulator devices to be packaged in a tile architecture within the antenna lattice spacing utilizing circulators fabricated using unique thick film processing techniques. 
         [0019]    Referring now to  FIGS. 1 ,  1 A,  1 B and  2 , a dual stacked stripline circulator  100  is shown where two stripline circulators are stacked on top of each other for use in the 0.5 to 2.0 GHz band. The dual stacked stripline circulator  100  includes four substrates, substrate  101 , substrate  102 , substrate  103  and substrate  104 . A coldplate  110  is attached to substrate  104 . Each circulator includes two substrates for a total of four substrates stalked together to provide the dual stacked stripline circulator  100 . A magnetic bias is provided by a magnetic pole piece  105  and permanent magnet  107  and magnetic pole piece  106  and permanent magnet  108  positioned, respectively, on the top and the bottom of the stacked substrate assembly. The interconnections between the circulators and the T/R modules (not shown) on the bottom and the circulators and the antenna radiators (not shown) on top are made using coaxial spring probe contacts  111 . The dual stacked stripline circulator  100  has coaxial to stripline vertical transitions formed using vias  44  and metallization  46  as shown in  FIG. 2  within the stack and connected with RF ports  42 . Ground vias provide isolation between the two independent circulators. The four substrates are bonded together, two at a time, using a thick film sealing glass paste  109  ( FIG. 1A ) as to be described further. The vias  44  are formed in each substrate layer individually and then connected together when the stack is bonded using a low shrinkage gold thick film paste fired at 800 C. The circulator stripline circuit layer is printed and pattern etched on both sides of the substrates and then connected together with wet thick film paste and fired at 800 C. Mirrored patterning and wet attachment processes are used to prevent any gaps between the circuit and substrate since any gap could cause a resonance spike in the operating band. Grounds are connected together on the outside of the entire stack using a low temperature (525 C) thick film paste edge wrap process as to be described. The low firing, low shrinkage edge wrap pastes prevents cracks between the substrate interfaces. 
         [0020]    To provide wideband circulators with a bandwidth greater than 2:1, composite ferrite substrates are used. These substrates include a center disc of one ferrite material having a high saturation magnetization material and a ring of another ferrite material having a lower saturation magnetization material surrounding the center disc, and a thermally matched dielectric ceramic material surrounding the ferrite materials. It should be noted that the low saturation magnetization material could also be used instead of the thermally matched dielectric ceramic material as a single element. The processes employed in this disclosure are compatible with the usage of the composite ferrite substrates. This disclosure uses thick film post-fired substrate stacking processes applied to ferrite substrates and/or composite ferrite/dielectric substrates for fabrication as to be described further. The unique aspects of the process are: thick film sealing glass for substrate stack bonding; layer to layer and substrate to substrate via interconnects; metallization and patterning across the gaps between. composite materials; and mirrored etched stripline circuit metallization on top and bottom of the substrates and their interconnection. This disclosure uses stacked circulators in a tile architecture to reduce depth and weight for a dual-polarized wideband active array antenna. The overall packaging technique which has two devices per unit cell with shared magnetic bias and utilizing coaxial spring pin vertical interconnects provides a dual stacked stripline circulator  100  satisfactory for use in a dual-polarized wideband active array antenna. 
         [0021]    Referring now to  FIG. 2A , a dual composite disc with dielectric material  20  is shown where the dual composite disc  21  includes an inner central portion  22  of high saturation magnetization material and an outer portion  24  of low saturation magnetization material encircling the central inner portion  22  and a dielectric material  26  encircling the outer portion  24  of the dual composite disc  21  as shown. Also shown is a frame  28  used to support the dielectric substrate material  26  during fabrication, but is disposed of once the dual composite disc with dielectric material  20  is fabricated. It should be noted that instead of using the dielectric material  26 , the low saturation magnetization material could be used alternatively. One technique to fabricate the initial dual composite disc with dielectric material  20  as shown is to start with a block of dielectric material and drill out a hole and fill the hole with a low saturation magnetization material using a high temperature adhesive between the two materials. Once the low saturation magnetization material is bound to the dielectric material, drill out a smaller hole in the low saturation magnetization material and fill the hole with high saturation magnetization material using a high temperature adhesive between the two materials. Once the high saturation magnetization material is bound to the low saturation magnetization material, the block can be sliced to the desired thickness and then ground to the final thickness to provide the dual composite disc with dielectric material  20 . To correct any deficiencies in the thickness of the dielectric material, a thick film dielectric material is printed on the front side and the back side of the dual composite disc with dielectric material  20  to ensure the front side and the back side is planar. The latter will fill in any gaps left on the front or the backside of the composite disc especially at the transitions between the high saturation magnetization material and the low saturation magnetization material and between the low saturation magnetization material and the dielectric material and later allow thick film metallization to be disposed across the surface and then etched to provide a metallization layer as described later. The frame  28  is cut from the dual composite disc with dielectric material  20  using known techniques. 
         [0022]    Referring now to  FIG. 2B , thru-holes are drilled through the dielectric material  26  as required and filled with gold (Au) to provide metalized thru-holes  30  to correspond to the circuitry as described further herein. Alignment holes are also provided in each one of the substrates to facilitate alignment as the substrates are stacked on each other. 
         [0023]    Referring now to  FIG. 2C , a metallization layer  40  is shown where a gold conductor paste using thick film metallization process techniques was spread on the front and backside of the dual composite disc with dielectric material  20  and then dried at 150 degrees C. and then fired at 850 degrees C. A photo resist is applied, developed and etched on the front and hack side to provide the desired metallization pattern as shown in  FIG. 2C  It should be noted the backside of the dual composite disc with dielectric material  20  is primarily a ground plane with openings disposed to accommodate the gold filled thin-holes  30 . The latter is performed for each of the substrates  101 ,  102 ,  103  and  104  where the desired metallization pattern is etched on one side of the dual composite disc with, dielectric material  20  and a ground plane with openings disposed to accommodate the gold filled thru-holes  30  on the other side of the dual composite disc with dielectric material  20 . It should be appreciated desired metallization pattern is a mirror image of each other for substrates  101  and  102  and the desired metallization pattern is a mirror image of each other for substrates  103  and  104 . The requisite metallization pattern needed to fabricate each of the circulators is well known in the art and will depend on the frequency and bandwidth requirements of the application. The technique used to fabricate the dual stacked stripline circulator  100  is not dependent on any specific metallization pattern and any known metallization pattern used for y-junction circulators may be used. 
         [0024]    Referring now to  FIG. 2D , the substrate  103  is bonded to the substrate  104  and in a similar manner the substrate  101  is bonded to substrate  102 . In preparation, a thick film sealing glass is printed on a surface of the substrates  101  and  103  and dried at 150 degrees C. and a thick film gold via fill is printed on substrates  101  and  103  and dried at 150 degrees C. In a similar manner, a thick film gold via fill is printed on substrates  102  and  104  and substrate  103  is mounted with substrate  104  and substrate  101  is mounted with substrate  102  and dried at 150 degrees C. The stacked substrates  103  and  104  and the stacked substrates  101  and  102  are then fired at 750 degrees C. This generates a first pair of stacked substrates and a second pair of stacked substrates ready for further processing. Also shown in  FIG. 2D  is an RF port  42  which extends through the substrate and is connected to metallization pattern  40  to provide a signal path. 
         [0025]    Referring now to  FIG. 2E , the stacked substrates  101  and  102  are bonded to the stacked substrates  103  and  104 . In preparation, thick film gold via fill is printed on the back side of the stacked substrates  103  and  104  which are then mounted with the stacked substrates  101  and  102  to provide a stacked substrate assembly  112  and dried at 150 degrees C. The stacked substrate assembly  112  Which includes the combined stacked substrates  101 ,  102 ,  103  and  104  is then fired at 750 degrees C. Also shown in  FIG. 2E  are vent holes  44  to allow gasses to vent when the stacked substrates are mounted together and cured. 
         [0026]    Referring now to  FIG. 2F , to finalize the circulator stack, an edge wrap sealing glass  50  is disposed on the stacked substrate assembly  112  and then an edge wrap gold thick paste  60  is disposed on the edge of the stacked substrate assembly  112 . The latter is then dried at 150 degrees C. and then fired at 550 degrees C. 
         [0027]    Referring now to  FIGS. 3 and 3A , completing the dual stacked stripline circulator  100 , a pole piece  105  and a pole piece  106  are disposed on the top and the bottom, respectively, of the stacked substrate assembly  112  and then a permanent magnet  107  is disposed on the pole piece  105  and a permanent magnet  108  is disposed on the pole piece  106 . Referring again to  FIG. 1B , the stacked substrate assembly  112  is mounted to the cold plate  110  to dissipate heat to mitigate overheating. 
         [0028]    Referring again to  FIG. 1A , it can be seen that the dual stacked stripline circulator  100  includes the four ferrite substrates,  101 ,  102   103  and  104 , in the illustrated example each typically having a thickness of 0.1 inches separated by a glass/via filled layer  109  typically having a thickness of 0.0015 inches. A pole piece  105  typically having a thickness of 0.015 inches is mounted with substrate  101  with a layer  113  between the pole piece  105  and the substrate  101  typically having a thickness of 0.002 inches. A permanent magnet  107  typically having a thickness of 0.030 inches is mounted with pole piece  105  with a bonding layer  114  typically having a thickness of 0.002 inches. A pole piece  106  typically having a thickness of 0.050 inches is mounted with substrate  104  with a layer  115  between the pole piece  105  and the substrate  101  typically having a thickness of 0.002 inches. A permanent magnet  108  typically having a thickness of 0.030 inches is mounted with pole piece  106  with a bonding layer  116  typically having a thickness of 0.002 inches. The latter provides a dual stacked stripline circulator  100  having a thickness typically of 0.5025 inches. It should be appreciated the latter thickness may vary depending on the tolerances maintained for each of the individual layers, but provides the preferred dimensions for a multi junction circulator operating in the 0.5 to 2.0 GHz band. It should be appreciated by one skilled in the art the dimensions would vary accordingly if a different operating band is utilized. 
         [0029]    Referring now to  FIG. 4 , a fabrication process  200  is shown to fabricate the dual stacked stripline circulator  100 . First, a laser machined composite substrate is received where the substrate includes a dual composite disc fabricated within the substrate as shown by step  202 . As described earlier in connection with  FIG. 2A , a composite disc with dielectric material  20  includes an inner central portion  22  of high saturation magnetization material and an outer portion  24  of low saturation magnetization material encircling the central inner portion  22  and a dielectric material  26  encircling the outer portion  24  of the dual composite disc  21 . Next, as shown in step  204 , a thick film dielectric gap fill is printed on the front side and the back side of the composite disc with dielectric material  20  (also sometimes referred to as a composite ring) and dried at 150 degrees C. and then fired at 850 degree C. Next, as shown in step  206 , the thru-holes are metalized, the holes are plugged in the substrate, and dried at 150 degrees C. and then fired at 850 degrees C. and repeated as necessary. 
         [0030]    Next, as shown is step  208 , gold conductor paste is screen printed on the front and back side of the substrate, dried at 150 degrees C. and fired at 850 degrees C. Next, as shown in step  210 , photo resist is applied, developed, and the front side and hack side of each of the substrates  101 ,  102 ,  103  and  104  are etched. Next, as shown in step  212 , a thick film sealing glass is printed on the front side and back side of each of the substrates  101 ,  102 ,  103  and  104  and dried and then a thick film via fill is printed on the front side and back side of each of the substrates  101  and  103  and dried at 150 degrees C. Next, as shown in step  214 , a thick film gold via fill is printed on substrates  102  and  104  and substrate  102  is mounted with substrate  101  and substrate  104  is mounted with substrate  103  and dried at 150 degrees C. and then fired at 750 degrees C. Next, as shown in step  216 , thick film sealing glass is printed on the substrates and dried and then thick film gold via fill is printed on the backside of the substrate stack with substrate  101  and  102  and dried at 150 degrees C. 
         [0031]    Next, as shown in step  218 , thick film gold via. fill is printed on back side of the substrate stack with substrates  103  and  104  and substrates  103  and  104  are mounted with the substrate stack with substrates  101  and  102  and dried at 150 degrees C., The stacked substrate assembly  112  is then fired at 750 degrees C. Next, as shown in step  220 , sealing glass  50  is edge wrapped or encircled around the stacked substrate assembly  112 , and then gold thick film paste is edged wrapped or encircled around the stacked substrate assembly  112  and dried at 150 degrees C. and then tired at 550 degrees C. 
         [0032]    To complete the dual stacked stripline circulator  100 , pole pieces are placed on universal tape ring frame boats (not shown) and an adhesive is printed on each pole piece, A magnet is placed on the adhesive and the magnet assembly is cured in an oven. Next, the circulator stacks are placed on universal tape ring frame boats and an adhesive is applied to each circulator stack. A magnet assembly (pole piece and magnet) is placed on each circulator stack and cured in an oven. Then the process is repeated to place a magnet assembly on the back side of each circulator stack. The latter steps provide a dual stacked stripline circulator  100  as shown in  FIG. 3A  according to the disclosure. 
         [0033]    It should now be appreciated that with such an arrangement, the dual stacked stripline circulator  100  is preferable for tile packaging used to minimize array depth, works well for X band and below, for example, 0.5 to 2.0 GHz, with a thickness of approximately 0.50 inches vs 4.0 inches for brick packaging. With dual polarization, each unit cell of the array requires two circulators which are accomplished by the disclosure and the circulators share a magnetic bias circuit. The following features are taught by the disclosure; a circulator constructed using thick film post-fired substrate stacking to include: thick film sealing glass for substrate stack bonding, layer to layer and substrate to substrate via interconnects, metallization and patterning across the gaps between composite materials, mirrored etched stripline circuit metallization on top and bottom of the substrates and their interconnection, and the disclosure uses stacked circulators in a tile architecture to reduce depth and weight for a dual-polarized wideband active array antenna. The overall packaging technique which has two devices per unit cell with shared magnetic bias and utilizing coaxial spring pin vertical interconnects provides a compact feed structure for a the array. 
         [0034]    A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.