Abstract:
A series of tuning brackets are mounted on the microwave waveguide manifold at positions between the input waveguide/filter couplings. These brackets constrain the manifold and are constructed with adjustment screws extending through the brackets and mechanically connected to the manifold. The movement of the adjustment screw will tend to deform the manifold dimensions resulting in a fine adjustment of the wavelength (λ) of the multiplexer.

Description:
BACKGROUND OF THE INVENTION 
     It is now prevalent in satellite microwave communications systems for such systems to process multiple channels. This requires the combination or separation of the channels either for transmission or for processing after acquisition. This function is usually accomplished by means of a multiplexer. 
     The typical multiplexer consists of a series of input waveguides generally including filter elements connected to a waveguide manifold through ports or iris&#39;Each of the filters is tuned and the iris&#39; designed for maximum efficiency of the overall system. The connections of the input waveguides to the manifolds must be accurately positioned according to strict spacing requirements governed by the wavelength (λ) of the transmitted microwave energy. The spacing is measured along the longitudinal axis of the manifold from the shorted end. 
     The spacing requirements are often difficult to meet because of manufacturing tolerances. Prior art systems, however, provide no means by which spacing inaccuracies can be adjusted after the parts of the multiplexer are constructed and assembled. It is a purpose of this invention to provide a means to adjust the manifold spacing. 
     In order to obtain optimum performance of the multiplexer, while minimizing losses, the internal impedance of the various components must be closely matched. This process of tuning the system requires the balancing of hundreds of variables many of which are extremely sensitive because of the high frequency environment. The design of these components has, therefore, become a difficult technological challenge. 
     Although the optimization problem can be diminished through the use of various design techniques, precise construction of the components is made difficult, if not impossible by the inherent limitations of manufacturing tolerances. The design of the these components, therefore, ultimately relies on a trial and error process in which multiplexers are constructed, tested, modified, retested and gradually optimized. There are limits however, to the number of iterations which can be employed with constructive results. 
     It is therefore desirable to provide additional methods of tuning a manifold. It is therefore a purpose of this invention to provide a method of simulating manifold spacing adjustment by deforming the manifold dimensions to change the wavelength and assist in the tuning of the overall system. 
     SUMMARY OF THE INVENTION 
     The manifold of this invention is constructed with a primary manifold section to which the input wave guides, including filters, are connected. One end of the manifold is shorted and the other is open to form an output port. The filter couplings are spaced along the longitudinal axis of the manifold a predetermined distance from the shorted end of the manifold. A series of tuning brackets are mounted on the manifold at positions between the input waveguide/filter couplings. These brackets constrain the manifold and are constructed with adjustment screws extending through the brackets and mechanically connected to the manifold. The screws engage the bracket by means of threads to enable the screw to be adjusted in and out of the bracket. The movement of the adjustment screw will tend to deform the manifold dimensions resulting in a fine adjustment of the guide wavelength (λ) of the multiplexer. In affect this change in the microwave characteristics of the manifold acts as a spatial adjustment of the position of the input wave guides. 
    
    
     DESCRIPTION OF THE DRAWING 
     The invention is described in more detail below with reference to the attached drawing in which: 
     FIG. 1 is a schematic diagram of the multiplexer of this invention; 
     FIG. 2 is a cross sectional view of the tuning bracket of this invention; 
     FIG. 3 is a graph showing the relationship of waveguide wavelength (λ) with waveguide dimensions and frequency; and 
     FIG. 4 is a graph showing the relationship between changes in waveguide wavelength relative to adjustments in waveguide width. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The system of this invention is constructed for use in a satellite communications network in which multiple channels are required. In the process of receiving and transmitting microwave signals, either at a ground station or on board an orbiting satellite, it is necessary to combine or separate the communication channels before further processing. This task is accomplished by means of a multiplexer. For illustration purposes an output multiplexer  1  is described with particular reference to FIG.  1 . In this particular application the channeled output of the multiplexer  1  is fed to an antenna for transmission to a ground station. 
     Since it is intended for use onboard a satellite, the system must be accurately tuned because there is no opportunity for further correction after it is in orbit. The multiplexer  1  is an assembly of several waveguides  2 - 4  with waveguide cavity filters  15 - 17  which are coupled to the manifold  5 , as shown in FIG.  1 . Each of the input waveguides  2 - 4  receive microwave signals through an input port  14  and are coupled to the manifold  5  by an appropriate coupling mechanism  22 , as is known in the art. The waveguides  2 - 4  will generally be coupled through filters  15 ,  16  and  17 . The filters may be provided with tuning screws  10  as used in the prior art. 
     The manifold  5  is constructed having a primary section  7  enclosing a waveguide  6 . The primary section has shorting cap  18  at one end and an output  8  at the other end. The primary section  7  may be constructed of an appropriate lightweight, high strength material having the necessary conductivity characteristics such as silver plated carbon reinforced composite or a temperature stable alloy such as is sold under the trademark INVAR. In addition the waveguide can be constructed from the walled aluminum sheet. In general the manifold is constructed with a rectangular cross section having a broad wall  24  at the top, side walls  25 , and a bottom wall  26 . 
     The input waveguides  2 - 4  are positioned along the longitudinal dimension of the manifold at distances x,y, and z respectively from the short  18 . The wavelength of the waveguide is chosen from the middle of the waveguide band. The general practice is to start by spacing the input waveguides at distances of half wavelengths and then adjust in plus or minus increments. It follows that the distances from the short  18  will be multiples of half wavelengths at least at the start. According to this invention a method and apparatus are provided which effectively adjusts the dimensions X, Y, and Z electrically by small changes in the width (w) of the waveguide. 
     In accordance with this invention, a series of tuning brackets  9 ,  11 , and  12  are mounted on waveguide  7  at predetermined locations, between each of the input waveguides  2 - 4  and between the waveguide  3  and the short  18 . In order to obtain maximum effectiveness of the adjustment the brackets are placed midway between the incoming waveguides as shown in FIG.  1 . Brackets  9 , 11 ,  12  are restrained from movement on the waveguide by means of angle members  19  and  21  held in place by screws  20 . An adjustment screw  13  extends through the bracket and is operatively connected to manifold  7  through a pad  11  fixed to manifold  7 . The screw may be operated to apply a deformation force  22 , either in compression or tension, to the short side  23  of the manifold  7 . This serves to adjust the width (w) at the manifold in small increments on the order of 0.001 inches. 
     The overall system  1  of this invention is tuned to optimize the performance of the multiplexer while minimizing losses. The design is performed taking into consideration the many variables in accordance with the trial and error practices currently in use. In order to tune the multiplexer of the subject invention, the adjustment screw  13  is moved in and out by applying an appropriate torque. This will deform the manifold width (w) sufficiently to change the characteristic wavelength of the manifold. Since the spacing of the input components of the multiplexer  1  is dependent on the wavelength, this adjustment by deformation has the effect of adjusting the spacing between the input components. This adjustment allows a fine tuning of the multiplexer  1  beyond currently available design methods. 
     As shown in FIG. 4, the adjustment of the width of the manifold will change the on/off frequency of the waveguide λ C  which is equal to 2w. The waveguide (λ Y ) will change in accordance with the formula λ Y =λ O / (1−λO 2 /λ O   2 )½. In this manner a simple and reliable mechanism is provided to tune the multiplexer of the assembly.