Solid-state Modular Microwave System

Abstract

A solid-state, modular microwave transmitter-receiver assembly made up of a large number of transmit-receive modules each having an antenna. Each of the modules has functional electronic blocks mounted on both sides of a center mounting plate contained within a hermetically sealed package. The module packages generally conform to the center mounting plate and are elongated, with a greater width than thickness. The antenna extends from the front end of the module and connectors extend from the rear end. The connectors are plugged into a rear support structure and are retained in place by a series of retaining plates fastened by long screws to the rear support structure. The retaining plates also form the ground plane for the antenna array. The antennae are arrayed in horizontal rows and vertical columns, and the module packages are arranged in rows extending diagonally of the antenna rows and columns with the edges of the packages in each row abutting. A cooling fluid duct is formed between each adjacent pair of module rows by the walls of the module packages, the retaining plates and the rear support structure. A manifold and header assembly directs cooling fluid in opposite directions through alternate cooling fluid ducts. The antenna assembly of each module provides a hermetically sealed coupling between the antenna and the interior of the package, supports the dipole elements, and provides impedance and balun transforming. The functional electronic blocks are easily secured on the mounting plate by spot welded brackets and are replaceable. The hermetically sealed antenna assembly and coaxial input and output connections are connected to microstrip lines within the module by spot welded straps of solid ribbon or woven metal wire fabric, as are adjacent microstrip lines on adjacent abutting functional electronic blocks. Connections are made between functional electronic blocks on opposite faces of the mounting plate by a special coaxial structure extending through the mounting plate.

Parent Case Text

This is a divisional application of application Ser. No. 889,780 filed Dec. 15, 1969 now abandoned, which in turn was a divisional application of application Ser. No. 628,140 filed Apr. 3, 1967, now U.S. Pat. No. 3,549,949.

Description

This invention relates generally to microwave transmitting and receiving, and more particularly relates to solid-state microwave antenna arrays.

While the specific embodiment of the invention described herein is an airborne terrain-following radar, this invention is equally applicable to other radar systems, such as those used for ground mapping, search and detection, fire control, tracking and navigation, as well as to microwave transmitting and receiving generally.

Radar systems in general, and airborne radar systems in particular, have long required considerable servicing and have been somewhat unreliable because of the many mechanical parts, such as rotary joints, motors, synchros, gears and other servo components normally essential to scanning the system, and the magnetrons used for transmitting, Kylstrons used for transmitting and local oscillator service, and the high power transmit-receive (TR) protection devices, for example. It is also difficult to achieve high power at higher frequencies and the electronic components mentioned tend to be more unreliable and less practical as the frequency of the transmitted and received energy increases.

In copending U.S. Pat. application Ser. No. 397,519, entitled "Modular Integrated Electronics Radar," filed on behalf of Tom M. Hyltin, Ser. No. 397,472, entitled "Phased Array Radar Antenna Scan Control," filed on behalf of Leo A. Chamberlin, Jr., and Ser. No. 397,491, entitled "Integrated Circuit Modular Radar Antenna," filed on behalf of Harry F. Cooke, et al., all of which were filed on Sept. 18, 1964 and are assigned to the assignee of the present invention, a radar system is described which utilizes a large array of solid-state modules. Each module is substantially a complete microwave transmitter and receiver. Each module includes the necessary circuitry for amplifying relatively low RF carrier energy applied simultaneously to all of the modules, and multiplying the frequency to a higher frequency for transmission from the antenna. Each module also includes circuitry for processing high frequency energy received by the antenna to produce a lower frequency IF signal, which is also preamplified. In addition, each module includes phase shifting means for both the transmitted and the received energy so that the beam from the fixed antenna array can be electronically scanned. Although an X-band module transmitting at 9 GHz (9 .times. 10.sup.9 cycles per second) typically has a transmitting power of only about one watt, when a very large number of the modules transmit simultaneously, the total transmitting power is essentially the sum of the power of all of the modules. Arrays having on the order of thousands of modules are practical.

In order to operate at high frequencies, the individual antennae of the array must be spaced about one-half wavelength apart, which for X-band systems means that the antennae are arrayed in horizontal rows and vertical columns with about 0.7 inch spacing between the rows and columns. As a result, the frontal area of each module must be confined to a square about 0.7 inch on a side. Also, it is highly desirable to locate the electronic components as close to the antenna as possible, particularly the circuits operating at the higher frequencies. Merely obtaining sufficient space within the module to mount all the functional hybrid or integrated circuits, even though the circuits are highly microminiaturized, is a serious problem. Since very large numbers of modules are required, it will be appreciated that a very large number of relatively high power devices must be packed into a minimum volume, making it difficult to provide adequate cooling.

Also, there are very real problems associated with supplying high frequency signals to th module, transferring the high frequency signals between the various functional circuits within the module, transferring high frequency energy between the externally mounted radiating element and the internal circuitry, and getting the high frequency signals out of the module while maintaining the module hermetically sealed. Because of the number of components, it is also very desirable to be able to replace malfunctioning components during fabrication, rather than lose the entire module.

This invention is concerned with the structure of the array and individual modules required in order to achieve high component density and adequate cooling, economical fabrication costs, low maintenance requirements, and long service life. This is achieved by orienting the modules in spaced rows to form cooling fluid ducts between each two adjacent rows of modules. The rows of modules are preferably disposed diagonally of the rows and columns of antennae so that each module can have a maximum width, and thus maximum circuit mounting area for a given spacing between the antennae. The mounting area for the circuits is further increased by a package having a mounting plate extending between midpoints of a peripheral wall with the solid-state functional electronic components mounted on both sides of the mounting plate and hermetically sealed by a pair of lids. Support means for securing the modules in position in the array also forms the ground plane for the antenna array, and also two opposite walls of the cooling fluid ducts, and achieves this without obstructions within the cooling fluid ducts.

The invention is further concerned with an antenna assembly which mechanically supports a dipole in the proper position, transfers the RF energy through the wall of the hermetically sealed module package, and provides the necessary impedance and balun transformation between the internal transmission line and the radiating elements.

The invention is also concerned with a means for mounting the functional electronic blocks on the mounting plate of the module package, interconnecting functional electronic blocks mounted on the same side of the mounting plate, interconnecting functional electronic blocks mounted on opposite sides of the mounting plate, and interconnecting the blocks and hermetically sealed conductors extending through the wall of the package.

The novel features believed characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a front perspective view of a microwave antenna array in accordance with the present invention;

FIG. 2 is an enlarged front view of a portion of the antenna array of FIG. 1;

FIG. 3 is an exploded perspective view of the parts missing from the structure illustrated in FIG. 2;

FIG. 4 is a sectional view taken substantially on lines 4--4 of FIG. 2;

FIG. 5 is a sectional view taken substantially on lines 5--5 of FIG. 2;

FIG. 6 is an isometric view of an RF module of the array of FIG. 1;

FIG. 7 is a side view of the module of FIG. 6;

FIG. 8 is a sectional view taken substantially on lines 8--8 of FIG. 7;

FIG. 9 is an edge view of the module of FIG. 6;

FIG. 10 is a front end view of the module of FIG. 6;

FIG. 11 is a rear end view of the module of FIG. 6;

FIG. 12 is a somewhat schematic front view of the antenna array of FIG. 1 with a portion of the structure removed to better illustrate certain aspects of the invention;

FIG. 13 is a side view of the structure shown in FIG. 12;

FIG. 14 is a rear view of the structure shown in FIG. 12;

FIG. 15 is a somewhat schematic layout of the functional integrated and hybrid circuits mounted in one half of the module of FIG. 6;

FIG. 16 is a somewhat schematic layout of the functional integrated and hybrid circuits mounted in the other half of the module of FIG. 6;

FIG. 17 is a sectional view taken substantially on lines 17--17 of FIG. 16;

FIG. 18 is a perspective view of the antenna assembly of the module of FIG. 6;

FIG. 19 is a sectional view taken substantially on lines 19--19 of FIG. 18;

FIG. 20 is an enlarged view of a portion of FIG. 19;

FIG. 21 is a sectional view taken substantially on lines 21--21 of FIG. 20;

FIGS. 22A and 22B are somewhat schematic isometric views illustrating alternative means for mounting the integrated and hybrid circuits within the module of FIG. 6;

FIG. 23 is a somewhat schematic isometric view illustrating how the microwave circuits on adjacent substrates may be interconnected; and

FIG. 24 is a sectional view illustrating the manner in which the microwave circuits formed on substrates mounted in the different compartments of the module of FIG. 6 may be interconnected.

Referring now to the drawings, a microwave antenna array constructed in accordance with the present invention is indicated generally by the reference numeral 10. The particular antenna array 10 herein described and illustrated is a solid-state, electronically scanned airborne radar system of the type described in the above-referenced U.S. Pat. applications. In such a system, a very large number of very small modules 12, as shown in FIG. 6, are assembled in an array with the antennae of the modules disposed in a common plane. Each of the modules is essentially a separate microwave transmitter-receiver which includes solid-state circuitry for amplifying a relatively low frequency RF carrier signal, which can be more easily handled, then multiplying the frequency of the RF signal several times before it is radiated from the antenna during a transmit cycle. During the receive cycle, the high frequency RF signal is mixed with a local oscillator signal to produce an IF signal which is amplified before leaving the module. In addition, each module contains phase shift circuitry for both the transmit and receive cycles in order to electronically scan the beam from the fixed antenna array. For other applications, however, such as microwave relay applications, the modules may only transmit, or only receive, or may not utilize the phase shift networks for beam steering. This invention is concerned primarily with the structure of the modules rather than the electronic function of the modules.

Each of the modules 12 has a metal package with opposite front and rear end walls 14 and 16 which define a length, opposite edge walls 18 and 20 which define a width, and opposite sidewalls 22 and 24 which define a thickness. The opposite end walls 14 and 16 and opposite edge walls 18 and 20 are integrally formed and are of the same height, the height corresponding essentially to the thickness of the module package. A center mounting plate 26 extends between midpoints of the opposite edge walls 18 and 20 and the opposite end walls 14 and 16 and is preferably integral with the sidewalls to achieve the best possible heat transfer between the mounting plate and the walls. Walls 14, 16, 18 and 20 provide a continuous wall which extends around the periphery of the center mounting plate 26, is normal to the plate 26 and extends beyond both of the opposite surfaces of the plate 26, thus forming an integral body having a pair of oppositely facing, open topped chambers indicated generally by the reference numerals 28 and 30. The chambers 28 and 30 are hermetically sealed by lids 32 and 34 which may be stitch welded or soldered around their entire periphery to the edges of the walls 14, 16, 18 and 20. The two lids 32 and 34 and the four walls 14, 16 18 and 20. The two lids 32 and 34 and the four walls 14, 16, 18 and 20 then form a hermetically sealed package.

An antenna assembly, indicated generally by the reference numeral 40, extends through and projects from the front wall 14 and is hermetically sealed therewith. A pair of hermetically sealed coaxial connectors 42 and 44 extend through and project from the rear end wall 16 to provide high frequency connections to the circuits located within chambers 28 and 30 and are also hermetically sealed. The connectors 42 and 44 are the male halves of a conventional plug-in type connector. Similarly, eight low frequency or D.C. male connectors 46 extend through a ceramic block 48 and provide D.C. connections to the interior of the module. The ceramic block 48 is hermetically sealed to the end wall 16 and is hermetically sealed around each of the connectors 46. It will be noted that one of the coaxial connectors and four of the D.C. connectors extend into each of the chambers 28 and 30. An indexing pin 50 also protrudes from rear end wall 16 to insure that he otherwise symmetrical package is inserted in the proper manner in the female receptacle for the connectors 42, 44 and 46. A pair of essentially semicircular grooves 52 and 54 extend the length of the edge walls 18 and 20, respectively. A forward facing, recessed shoulder 56 is formed around the periphery of the front face 14 by machining for purposes which will hereafter become evident.

Each of the modules 12 is plugged into a femal receptacle carried by a rear support structure indicated generally by the reference number 60 in FIGS. 4 and 5. The rear support structure 60 includes a support plate 62 which is coextensive with the octagonal housing as illustrated in FIG. 12. At each position where a module 12 is to be plugged in, the support structure 60 provides a D.C. socket 64 for the eight low frequency connectors 46, a pair of female coaxial sockets 66 and 68 for the male coaxial connectors 42 and 44, and a bore 70 for the indexing pin 50. The D.C. sockets 64 are mounted on a D.C. wiring board 72 and extend through an opening in support plate 62 to a point essentially flush with the front face of plate 62. The coaxial sockets 66 and 68 are mounted on an RF sub-manifold 74 and extend through the D.C. wiring board 72 and partially through the support plate 62.

When the modules 12 are plugged into the sockets carried by support structure 60, the modules are arrayed as illustrated in FIGS. 2 and 12. It will be noted from FIG. 2 that the antenna assemblies 40 are arrayed in orthogonally disposed horizontal rows and vertical columns with the center-to-center spacing approximately one-half wavelength, which at 9 GHz is approximately 0.7 inch. However, the modules 12 are arrayed in rows extending diagonally of the rows and columns of the antenna assemblies 40, and are disposed in substantially edge abutting relationship as best seen in FIG. 12. Since the width of each module is substantially greater than the thickness, the rows of modules 12 are spaced apart and the sidewalls of the modules in each adjacent pair of rows form the opposite sidewalls of cooling fluid ducts 80a and 80b. The ducts 80a and 80b are identical but are designated by different reference characters for purposes which will hereafter become more evident.

The modules 12 are secured in place in their respective sockets by means of a plurality of H-shaped clamp plates 82, as best shown in FIG. 3. Each plate 82 is formed from metal and has an electrically conductive sealing gasket 84 over its rear face. The total thickness of each plate 82 is equal to the distance the shoulder 56 is recessed from the front surface of the front end wall 14. Each plate 82 has a narrow center section 82a which is adapted to fit over the shoulders 56 at the adjacent ends of two adjacent modules. A relatively long screw 86 passes through each center section 82a and extends back through the passageway formed by the adjacent semicircular grooves 52 and 54 of the two adjacent modules and is threaded into the support plate 62, as shown in FIGS. 4 and 5. The ends 82b of the plates 82 extend over the adjacent ducts 80a and 80b and engage the shoulders 56 of the modules in the two adjacent rows. Thus, a single plate 82 engages and secures four modules in place, and conversely each module is secured in place by four plates and four screws. Edges 82c of the plates extend into engagement with the corresponding edges 82c of the adjacent plates so that the combination of plates 82 provides a complete front wall for the cooling fluid ducts. It will be noted that plates 82 and the support plate 62 form the other two opposite sidewalls of the cooling fluid ducts 80a and 80b. The gasket material 84 prevents excessive leakage of the cooling fluid. In addition, the front surfaces of the plates 82 are coplanar with the front surfaces of the end walls 14 and the combined surface acts as the ground plane for the antenna array. The conductive gasket material 84 insures good electrical contact between the plates and the modules.

Referring once again to FIGS. 12, 13 and 14, a cooling fluid header 88a supplies cooling fluid, typically ambient air, under pressure to ducts 80a through inlet ports 90a, and exhausts cooling fluid from ducts 80b through exhaust ports 92a. Similarly, a header 88b supplies cooling fluid under pressure to ducts 80b through input ports 90b and exhausts the cooling fluid from ducts 80a through exhaust ports 92a. The ports 90a and 92a and 90b and 92b are formed by plates 95a and 95b which extend between the rear support plate 60 and a front plate 94 (see FIG. 13) which is coplanar with the retainer plates 82 (see FIG. 3) and which therefore provides a continuation of the ground plane. Mounting holes 93 are provided in plate 94 to support the device. Plates 97 and 99 may extend around the remaining peripheries of plates 60 and 94. A pair of manifolds 96a and 96b extend around the rear surface of the rear support plate 60. Manifold 96a communicates with inlet ports 90a through openings 98a in plate 60, and manifold 96b communicates with inlet ports 90b through openings 98b in plate 60.

Thus, it will be noted that cooling fluid passes through manifold 96a, openings 98a, input ports 90a, ducts 80a, and exhausts through ports 92a, and passes through manifold 96b, openings 98b, input ports 90b, ducts 80b, and exits through exhaust ports 92b. As a result, the cooling fluid flows in opposite directions in the ducts on either side of any one row of modules 12. The modules 12 adjacent the headers 88a and 88b will therefore have relatively cool fluid flowing by one face and relatively warm fluid flowing by the other face, while the modules generally centered between the headers will have cooling fluid at an intermediate temperature flowing over both faces. As a result, the net cooling effect upon all modules is substantially the same so that all modules are maintained at substantially the same temperature.

The antenna assembly 40 is illustrated in detail in FIGS. 18 and 19. The antenna assembly 40 is comprised of a tubular sleeve 150, a center conductor 152, a ceramic disk 154, and a pair of antenna elements 156 and 158. The ceramic disk 154 is hermetically sealed within the end of the tubular sleeve 150 and also around the end of the center conductor 152 by vacuum-tight hard solder seals. The diameter of the input portion 152a of the center conductor is selected relative to the diameter of the adjacent portion of the tubular sleeve 150 so as to provide a coaxial transmission line having a 50 ohm characteristic impedance. The center conductor has portions 152b and 152c of enlarged diameter for transforming the 50 ohm characteristic impedance to the complex impedance required by the radiating elements 156 and 158 when positioned in the antenna array. The sleeve 150 is split into halves 150a and 150b to provide a balun transformation from the unbalanced coaxial transmission system to the balanced transmission system required to feed energy to the radiating elements 156 and 158. The slits 160 which separate the sleeve 150 into halves are approximately one-quarter wavelength long. Antenna element 156 is secured in one of the sleeve halves 150a by a hard solder connection, and antenna element 158 is simply a continuation of the center conductor 152, but is also connected in a slot 162 by a hard solder connection. The antenna elements 156 and 158 are disposed one-quarter wavelength from the ground plane. Thus, the antenna assembly 40 provides a hermetically sealed coaxial connection through the wall 14 of the module package, provides an impedance transformer for matching the standard 50 ohm characteristic input impedance of the microstrip transmission of the internal circuit to the complex impedance required for the antenna, provides a balun transformer to convert from the unbalanced coaxial input to the balanced dipole antenna, and mechanically supports the radiating elements 156 and 158 aproximately one-quarter wavelength above the surface of the end wall 14, which forms a portion of the ground plane for the antenna array.

The modules 12 may house, for example, the electronic circuitry described in copending U.S. Pat. application Ser. No. 606,427, entitled "Transmit-Receive Module for X-Band Phased Arrray Radar System," filed on behalf of Tom M. Hyltin and assigned to the assignee of the present invention. All of the functional blocks within the module are either hybrid circuits, in which case microstrip transmission lines and discrete semiconductor components are mounted on a ceramic substrate, or monolithic integrated circuits, in which case the active components are formed in a semiconductor substrate which also acts as the dielectric for the microstrip transmission lines. A typical layout for these circuits is shown in FIGS. 15-17.

During the transmit cycle at 2.25 GHz carrier signal is applied through input coaxial connector 44 and is transferred by a strap 109 to a microstrip transmission line (not shown) on interconnector chip 110 and through interconnection strap 112 to an S-band preamplifier 113. The output of the preamplifier 113 is coupled by strap 114 to the input of a duplexer switch 115 which, during the transmit cycle, directs the signal through strap 116 to a transmit phase shifter 117. The output of the transmit phase shifter 117 is connected by strap 118 to a microstrip transmission line 119 on the receive multiplier 120, which in turn is connected by strap 121 to microstrip transmission line 122 on an interconnect chip 123. Line 122 is coupled by feed through connector 124 to a microstrip transmission line 125 on micromodulator 126, and by strap 127 to the input of a power amplifier 128. The output of power amplifier 128 is connected by strap 129 to a transmit multiplier 130, which increases the frequency to 9.0 GHz. The RF frequency signal is then applied by strap 131 to a TR switch 132 which, during the transmit cycle, directs the energy to the center conductor 152 of the antenna assembly 40 by way of a strap connector 133.

During the receive cycle, a 2.125 GHz signal is applied to input coaxial connector 44 and is passed through strap coupling 112 to the S-band preamplifier, strap coupling 114 to the duplexer, and strap coupling 134 to a receive phase shifter 135. The output of the receive phase shifter is applied by strap coupling 136 to the receive multiplier 120 which increases the frequency to 8.5 GHz. The output of multiplier 120 is connected by feed through connection 137 to a mixer 138. Also during the receive cycle, the TR switch connects the antenna to the mixer 138 where the 9.0 GHz energy received by the antenna is mixed with the 8.5 GHz local oscillator signal produced by multiplier 120 to derive a 500 MHz IF signal. The IF signal is applied by way of strap connector 139 to IF preamplifier 140. The output of the IF preamplifier is connected by strap connector 141 to a microstrip transmission line 142 on the micromodulator 126, which in turn is connected by strap connector 143 to a microstrip transmission line 144 on interconnector chip 145. The microstrip transmission line 144 is then connected to the output coaxial connector 42 by strap connector 146.

The micromodulator 126 produces the high current pulses defining the transmit cycle which are required to operate power amplifier 128 and switch duplexer 115 and TR switch 132. Choke 147 improves the operation of mixer 138. A number of D.C. connections are illustrated on the drawings but will not be discussed in detail because they do not present an interconnection problem and are not an advance in the art. In general, the D.C. connections are made to the D.C. inputs 46 by ball bonded jumper wires, and all connections between strip conductors on the various substrates can also be made by ball bonded jumper wires.

Since all circuits are mounted on the body of the package and interconnected to the antenna assembly of the various connectors before the lids 32 and 34 are sealed in place, the circuit can easily be tested after it is assembled. Because of the large number of functional blocks, it is highly desirable to be able to replace one or more faulty circuits after the entire module is assembled and tested, rather than discarding all of the circuits if any one circuit is bad. By mounting the circuits on the center mounting plate 26 using the bracket indicated generally by the reference numeral 170 in FIG. 22A, rather than by the conventional method of soldering the circuits in place, the faulty modules can be removed and replaced after the entire module has been tested as a unit.

The bracket 170 is comprised of a thin metal plate 172, 0.001 inch thick nickel foil, for example, which is substantially coextensive with the center mounting plate 26. A number of straps 178 are cut from the foil and bent upwardly as shown in dotted outline at 178a. The straps 178 are located at points spaced around the peripheries of the various circuits, represented by circuit 174 in FIG. 22A, to be mounted by the bracket 170. Where it is desirable to place two circuits in closely abutting relationship, the straps 178 may be received in notches cut in the sides of the circuits, or may even extend through holes cut through the circuits. The straps 178 extend upwardly from the plate 172 a distance substantially greater than the thickness of the circuits to be mounted. A large number of tongue-like spring members 175 are also cut from the plate 172 and bent upwardly at an angle of approximately 45.degree. or slightly less. The spring members 175 are disposed generally uniformly over the entire base plate 172. The base plate 172 is resistively spot welded to the mounting plate 26 at a number of points 176 generally spaced uniformly over its entire area.

The circuit 174 is placed in its proper position over the base plate 172 and between the appropriate straps 178, then is forced downwardly to compress the spring members 175 back into the plane of the base plate 172. The straps 178 are then bent over metallized pads 177 on the surface of the circuit. The pads 177 may be very thin vacuum deposited gold films, for example. The straps 178 are then welded to the pads 177 using a split tip or gap resistance welder 179. The resulting weld is adequate to hold the circuit in place, but can be broken to remove a faulty circuit without damaging bracket 170. The faulty circuit can then be replaced in the same manner.

The spring members 175 insure good thermal and electrical contact between the circuits and the mounting plate 26 because the springs bias the base plate against the mounting plate 26 and are themselves biased against the metallized ground plane on the bottom surface of the circuits.

An alternative method for securing the circuit in position on the bracket 170 is illustrated in FIG. 22B. Rather than bending the straps 178 over the edge of the circuit and welding it to the pads 177 as shown in FIG. 22A, a gusset 181 may be welded to each of the straps. The gussets 181 may be formed from the same sheet material as the bracket 170. Each gusset has a first flange portion 181a which engages the top of the circuit and a second flange portion 181b which is disposed at a right angle to the first portion and is spot welded to the respective strap 178 at a point 182 above the top of the circuit. The welds 182 can also be broken to remove a faulty circuit without damaging bracket 170 and the circuit replaced.

The center conductor 152 of the antenna assembly 40 may be connected to the output of the TR switch 132 using the structure illustrated in FIGS. 20 and 21. The center conductor 152 of the antenna assembly extends beyond the inner edge 14a of the front end wall 14 and into a slot 190 formed in the center mounting plate 26. Since the center conductor 152 has a diameter approximately equal to the thickness of the mounting plate 26, the surface of the center conductor 152 is essentially coplanar with the surface of the mounting plate 26. However, the substrate on which the TR switch 132 is formed is almost as thick as the mounting plate 26 and is resting on the bracket 172. Therefore, the microstrip transmission line 192, which is the output of the TR switch and which extends to the edge of the substrate upon which the TR switch is formed, is not only spaced from the end of the center conductor 152, but is also spaced substantially above the plane of the center conductor. Thus, any interconnection between the coaxial transmission line and the microstrip transmission line will tend to create an impedance discontinuity due to the change from a ceramic dielectric to air and back to ceramic and due to the change in planes. Such an impedance discontinuity can reflect an intolerable amount of energy, particularly at 9 GHz.

In accordance with this invention, however, the center conductor 152 can be connected to the microstrip transmission line 192 by a metal strap 133. The metal strap is preferably solid metal ribbon, but can also be woven wire mesh. The solid metal ribbon can be resistively welded to the coaxial center conductor 152 and to the microstrip line 192. In order to compensate for the dielectric and geometric discontinuities of the interconnection, the width of the strap 133 is increased to provide substantially the same characteristic impedance. For example, when connecting the coaxial transmission line from the antenna assembly 40, which has a 50 ohm characteristic impedance, to a microstrip transmission line, also having a 50 ohm characteristic impedance, the strap 133 should be about 0.045 inch wide. This compares with a width of 0.020 inch required for the microstrip transmission line to provide a 50 ohm characteristic impedance when using a ceramic substrate 0.020 inch thick.

The woven wire fabric is not as mechanically stable as the solid metal ribbon, but has the advantage of being easily welded to the center conductor and to the strip transmission line using a heated tool having a very small tip to press the wire fabric against the center conductor and microstrip line.

It will be noted from FIGS. 15 and 16 that the entire surfaces of the mounting plate 26 are substantially covered by functional circuit blocks and interconnector chips, the interconnector chips merely providing the microstrip transmission lines necessary to interconnect the circuits and the coaxial connectors extending through the end wall. The circuit blocks and interconnector chips all have the same thickness and a metallized ground plane on the bottom face. Microstrip transmission lines are formed by strip conductors on the top surface of the substrate and the ground plane. The characteristic impedance of the microstrip transmission lines is determined by the thickness and dielectric properties of the substrate material and the width of the strip conductors, and these variables are customarily selected to produce a transmission line having a 50 ohm characteristic impedance. Since all of the substrates have substantially the same thickness, the microstrip transmission lines carrying the high frequency signals can be interconnected by connector straps as described in connection with FIGS. 15 and 16. For example, connector strap 131 which connects the output of the transmit mutiplier 130 to the TR switch 132 may be formed as shown in FIG. 23. The microstrip transmission line 202 on the duplexer switch 132 extends to the edge of the circuit block. A microstrip transmission line 208 extends to the edge of the multiplier circuit block 130 and is aligned with the microstrip transmission line 202 on the TR switch. A strap of gold wire mesh 131 bridges the gap between the adjacent circuit blocks and extends over the adjacent ends of the microstrip transmission lines 202 and 208. The strap is welded to the transmission lines by using the tip of a heated tool to press the wire mesh against the respective microstrip transmission lines to form localized welds 209. Alternatively, a solid metal ribbon may be substituted for the wire mesh strap and welded using the split tip resistive welder illustrated in FIG. 22A.

The dielectric discontinuity resulting from the change from ceramic to air at the gap which must necessarily exist between the adjacent substrates may be compensated by increasing the width of the strap 131 in order to maintain the same characteristic impedance and thus eliminate impedance discontinuities which would reflect an intolerable amount of high frequency energy. However, for very close spacing between the circuit blocks, the strap may be the same width as the microstrip transmission lines.

In accordance with another aspect of this invention, the feed through connectors 124 and 137 (see FIGS. 15 and 16), for example, may be constructed as shown in detailed sectional view of FIG. 24. A hole 220 is bored through the central mounting plate 26. The bore 220 may be located immediately adjacent the edge of the two substrates to be connected, as illustrated by the relationship of the bore to substrate 222, or may pass through both substrates, as illustrated by the relationship of the bore to substrate 224, or may be a combination of the relationships as actually illustrated in FIG. 24. The substrates 222 and 224 may be mounted on the mounting plate 26 using the brackets 170 as illustrated. The microstrip transmission lines to be interconnected, for example, strip line 226 on substrate 222 and strip line 228 on substrate 224, extend to points immediately adjacent the bore 220.

An insulating sleeve 230, preferably made of quartz, is coated with a metallized film 231 around its midportion, but is not coated adjacent the ends. The sleeve is then inserted in the bore 220. A wire conductor 232 passes through the insulating sleeve 230 and the opposite ends are flattened at 232a and 232b until they are approximately the same width as the strip lines 226 and 228. The flat portions of the conductor 232 are bent over the strip lines and spot welded using an electrip gap welder as previously described.

Using a trial and error procedure, the characteristic impedance of the feed through connector can be adjusted by varying the length of the metallized film 231 on the insulating sleeve 230, or the diameter of wire 232 adjusted, until any impedance discontinuity is reduced to an acceptable level for a given installation.

Although preferred embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

What is claimed is:

1. In a microwave module, the combination of:

a hermetically sealed package having a mounting plate with a sidewall disposed generally normal thereto,

a hermetically sealed transmission line extending through the sidewall having a center conductor terminating within the package,

a functional circuit block mounted on the mounting plate having a microstrip transmission line terminating adjacent the end of the center conductor, and

a metal strap interconnecting the microstrip transmission line and the center conductor, the metal strap having a width selected to substantially match the characteristic impedance of the coaxial transmission line with the characteristic impedance of the microstrip transmission line.

2. The combination defined in claim 1 wherein the package is further characterized by:

a second sidewall disposed generally normal to the mounting plate,

a second hermetically sealed coaxial transmission line extending through the second side wall having a center conductor

terminating within the package,

a second circuit block mounted on the mounting plate having a microstrip transmission line extending to a point adjacent the end of the center conductor of the second coaxial transmission line, and

a second metal strap interconnecting the end of the center conductor of the second coaxial transmission line and the end of the second microstrip transmission line, the width of the metal strap being selected to substantially match the characteristic impedance of the second coaxial transmission line to the impedance of the second microstrip transmission line,

the circuits on the first and second circuit blocks being interconnected by microstrip transmission lines.

3. The combination defined in claim 2 wherein the microstrip transmission line interconnecting the circuits on the first and second circuit blocks includes at least one joint comprising:

a pair of microstrip transmission lines extending to the respective adjacent edges of a pair of circuit blocks and a metal strap spanning the gap between the circuit blocks and connected to each of the microstrip transmission lines, the width of the metal strap being selected to substantially match the characteristic impedance of one of the microstrip transmission lines to the characteristic impedance of the other microstrip transmission line.

4. The combination defined in claim 1 wherein said strap is a solid metal ribbon having a width substantially greater than its thickness.

5. The combination defined in claim 1 wherein said strap is woven wire fabric.

6. In a microwave module, the combination of:

a metal mounting plate,

first and second circuit blocks mounted on the mounting plate in edge-to-edge relationship,

first and second microstrip transmission lines on the first and second circuit blocks, respectively, extending to adjacent points at the edges of the respective circuit blocks, and

a metal strap bridging the gap between the circuit blocks and extending over the first and second microstrip lines, the metal strap being welded to each of the underlying microstrip lines, the width of the metal strap being selected to substantially match the characteristic impedance of the first microstrip transmission line and the characteristic impedance of the second microstrip transmission line.

7. The combination defined in claim 6 wherein:

the metal strap comprises a solid metal ribbon having a width substantially greater than its thickness.

8. The combination defined in claim 6 wherein:

the metal strap comprises a woven wire fabric.

9. In a microwave module, the combination of:

a mounting plate having opposite mounting surfaces,

a circuit block mounted on each of the opposite mounting surfaces,

a bore extending through the mounting plate and disposed adjacent an edge of each of the circuit blocks,

an insulating sleeve disposed in the bore,

a metallic film coating the outer surface of the insulating sleeve, the metallic film terminating before reaching the top surface of either circuit block,

a microstrip transmission line formed on the top surface of each of the circuit blocks and terminating adjacent the bore, and

a conductor extending through the insulating sleeve and over the ends of the microstrip transmission lines and bonded to each to interconnect the microstrip transmission lines, the length of the metallized film on the sleeve, the size of the sleeve, and the size of the conductor being selected to substantially match the characteristic impedance of one of the microstrip transmission lines to the characteristic impedance of the other microstrip transmission line.

10. The combination defined in claim 9 wherein the sleeve is tubular and the conductor is cylindrical.

11. The combination defined in claim 9 wherein the edge of one of the circuit blocks adjacent the bore is formed by a bore through the circuit block.