Abstract:
The invention relates to a process for the production of a microwave waveguide having a step of determining the zone or zones (z 1 ) of the waveguide (g 1 ) where an electric field concentration occurs. A step of produces at least one enlargement (el 1 ) of the waveguide in the zone or zones thus determined. The invention also relates to a microwave filter in which the stubs are provided with such enlargement. The invention has application in microwave filters.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present Application is based on International Application No. PCT/EP2007/055410, filed on Jun. 1, 2007, which in turn corresponds to French Application No. 06 52011 filed on Jun. 2, 2006, and priority is hereby claimed under 35 USC §119 based on these applications. Each of these applications are hereby incorporated by reference in their entirety into the present application. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a microwave waveguide, to its production process and to its application to a microwave filter, notably a very high-power microwave filter. The invention is applicable more particularly to filters comprising length-adjustable short-circuited transmission lines, called stubs in the art, and used for producing impedances. The invention also relates to a microwave transmit/receive station using the microwave filter applicable notably in the space field. 
       BACKGROUND OF THE INVENTION 
       [0003]    In certain fields of application, there is a need for microwave filters of very high power. This is the case for example in the space field, where the transmit power must be particularly high and where the filters used must be effective at high power levels in order to provide a maximum transmit power. This is the case for example in direct transmission systems by satellite. The satellite must then be able to transmit with a maximum power. However, the invention is applicable in any other field in which high-power operation is required. 
         [0004]    When a waveguide is used in a vacuum (for space applications) and in the case of high-power waveguides, it is possible to initiate an electron avalanche, called a multipactor effect, in certain zones of the waveguide. 
         [0005]    This multipactor effect is caused by a concentration of the electromagnetic field which tears electrons out of the walls of the waveguide. The electrons are then accelerated toward the opposite wall of the waveguide. The impact of these electrons on the latter wall causes in turn electrons to be torn therefrom, and so on. An electron avalanche phenomenon thus occurs, which degrades the electrical performance of the waveguide and may lead to it being destroyed. 
         [0006]    This phenomenon therefore occurs notably in the space field in which the waveguides operate in a vacuum in the absence of air molecules. 
         [0007]    The multipactor power level is the maximum power at which a component can be used without initiating the multipactor effect. This threshold power can be calculated between two parallel plates from the following equation: 
         [0000]        P= (1/VMF 2 )×( V   multi   2 /2 Z   0 ) 
         [0000]    where
       the multipactor threshold voltage (V multi ) is dependent on the type of equipment used to manufacture the waveguide, but this voltage is always proportional to the product of the frequency multiplied by the critical distance between the plates (f×d);   the VMF (voltage magnification factor) is the ratio of the voltage at the point of calculation and the input voltage of the component. This VMF increases with the field concentration between the two plates at the calculation point; and   the impedance (Z 0 ) depends on the standard of waveguide used and on the working frequency (normally fixed by the application).       
 
         [0011]    To reduce this multipactor effect, it is possible either to move the walls of the waveguide further apart in order to increase the V multi  or to reduce the electric field concentration in order to reduce the VMF. 
         [0012]    Both these solutions pose problems. If moving the walls of the waveguide further apart is envisioned, the operating frequency range is reduced and the device will have difficulties matching the waveguide for all frequencies in the operating range. 
         [0013]    To reduce the concentration of the electric field at the critical point, it is necessary to modify the topology of the devices, or even, in the case of filters, to change the type of filter. 
         [0014]    The object of the invention is to solve these problems and to provide a microwave waveguide and microwave filters in which the multipactor power level has been notably increased. 
       SUMMARY OF THE INVENTION 
       [0015]    The invention therefore relates to a process for the production of a microwave waveguide comprising the following steps:
       a step of determining the critical zone or zones of the waveguide where an electric field concentration occurs; and   a step of producing at least one enlargement of the waveguide in the zone or zones thus determined.       
 
         [0018]    This process is applicable to the production of a microwave filter comprising length-adjustable short-circuited transmission lines, such as stubs. This process includes:
       a step of determining, in the stubs, critical zones where electric field concentrations occur; and   a step of producing at least one enlargement of the stubs in the zone or zones thus determined.       
 
         [0021]    Advantageously, each enlargement is located at a distance λg/4 from the short-circuit zone of the stub, λg being a guided wavelength lying within the operating wavelength range of the filter. 
         [0022]    The invention also relates to a microwave filter produced by this process. Each stub takes the form of a Latin cross in which the horizontal arms perpendicular to the axis of the stub correspond to said enlargements. 
         [0023]    According to one embodiment of the invention, the horizontal arms are of unequal lengths. 
         [0024]    According to another embodiment of the invention, at least one horizontal arm has sections of different dimensions. The section closest to the axis of the stub is larger than the section or sections further away from the axis of the stub. 
         [0025]    According to another embodiment, at least one horizontal arm has sections of different dimensions, the section closest to the axis of the stub being smaller than the section or sections further away from the axis of the stub. 
         [0026]    It is also possible for the end face of each horizontal arm to be inclined to the axis of the stub. 
         [0027]    According to another embodiment of the invention, it is also possible for the end face of each horizontal arm to have a curved shape. 
         [0028]    The invention is also applicable to a microwave transmit/receive station using the microwave filter thus described. This station therefore comprises:
       a first diplexer for horizontally polarized signals and comprising a first receive filter and a first transmit filter as described above;   a second diplexer for vertically polarized signals and comprising a second receive filter and a second transmit filter as described above; and   a polarization mode splitter/combiner having a first port for the horizontally polarized signals, connected to the first diplexer, a second port for the vertically polarized signals, connected to the second diplexer, and a third port connected to a transmit/receive horn.       
 
         [0032]    Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious aspects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The present invention is illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein: 
           [0034]      FIG. 1   a , a representation of a waveguide for explaining the subject of the invention; 
           [0035]      FIG. 1   b , an exemplary embodiment of a waveguide according to the invention; 
           [0036]      FIG. 2 , an exemplary embodiment of a filter according to the invention; 
           [0037]      FIG. 3 , a microwave filter comprising stubs with a low multipactor power level which carries the risk of initiating the multipactor effect; 
           [0038]      FIGS. 4   a  and  4   b , exemplary embodiments of a microwave filter having stubs according to the invention; 
           [0039]      FIGS. 5   a  to  5   e , various embodiments of the stubs of a microwave filter; 
           [0040]      FIGS. 6   a  to  6   c  and  7   a  to  7   c , alternative embodiments of stubs according to the invention; and 
           [0041]      FIG. 8 , an example of the invention applied to a microwave transmitter/receiver. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]      FIG. 1   a  shows a waveguide g 1  for propagating a microwave. As is known, variations in electromagnetic energy levels can be detected in the waveguide. Variations in energy levels are illustrated in  FIG. 1   a . Energy concentrations appear: notably, in the zone z 1  of the waveguide, a maximum c 1  may be the cause of a multipactor effect, as described above. The zone z 1  of the waveguide may then be damaged. 
         [0043]    To remedy this, the invention therefore provides a way of identifying and locating the zones, such as Z 1 , in which there may be energy concentrations, and of enlarging the waveguide in these zones. 
         [0044]      FIG. 1   b  therefore shows an example of a waveguide according to the invention in which the walls of the waveguide g 1  have an enlargement el 1 . This enlargement is produced in such a way that the energy concentration in the zone z 1  cannot give rise to a multipacter effect. 
         [0045]    The invention is also applicable to the production of microwave filters. 
         [0046]      FIG. 2  shows a portion of a filter that includes coupled impedance-matching elements as shunts on the main waveguide and terminating in short circuits. Such elements are called stubs in the art and will therefore be referred to by this term in the rest of the description. 
         [0047]    It has been found that the stubs of the filters are the site of electromagnetic energy concentrations. To avoid the creation of multipacter effects in the stubs, an enlargement is therefore provided in the energy concentration zones. 
         [0048]    In a stub, such as st 1  in  FIG. 2 , the maximum energy concentration, for a given wavelength λg, occurs at a distance λg/4 from the short-circuit face cc 1  of the stub. The invention therefore provides, at this distance cc 1 , enlargements el 2  and el 3  on the two guiding walls of the stub. The stub therefore takes the form of a Latin cross, the horizontal arms of which are perpendicular to the axis X of the stub sd 1  and form the enlargements el 2  and el 3 . 
         [0049]    An example of the invention applied to a microwave filter having stubs will now be described with reference to  FIGS. 3 ,  4   a  and  4   b.    
         [0050]      FIG. 3  shows a filter g 3  of known type, having six stubs st 2  to st 7 . An energy maximum liable to create a multipactor effect is found in the zone z 3  in the stubs st 4  and st 5 . 
         [0051]    The invention makes it possible to avoid this multipactor effect. To do this, as shown in  FIG. 4   a , the stubs st 4  and st 5  have enlargements e 4  and e 5  in the zone z 3 . These enlargements were positioned as described above. 
         [0052]    However, in certain cases the distance between stubs may not allow these enlargements to be provided in a filter of the type shown in  FIG. 3 . The stubs may then be distributed on either side of the main axis of the filter. What is therefore obtained is a configuration as shown in  FIG. 4   b . In addition, this configuration provides enlargements f 2  to f 7  on all the stubs st′ 2  to st′ 7 . Since the maximum energy concentration is highest in the stubs st′ 4  and st′ 5 , the enlargements f 4  and f 5  of these stubs will be larger than the enlargements f 3  and f 6  of the stubs st′ 3  and st′ 6  and much larger than the enlargements f 2  and f 7  of the stubs st′ 2  and st′ 7 . 
         [0053]    The enlargements may take different forms. 
         [0054]      FIGS. 5   b  to  7   c  give various examples of these forms. 
         [0055]    The aim is to avoid creating a multipactor effect in a stub su 1  shown in  FIG. 5   a  and in which, without enlargement according to the invention, a multipactor effect would be created. 
         [0056]      FIGS. 5   b  and  5   c  show stubs su 1  having enlargements eu 1  and eu 2  as described above. The enlargement eu 2  is larger than the enlargement eu 1  and is provided for a higher initial energy concentration in the stub of  FIG. 5   c  than in the stub of  FIG. 5   b.    
         [0057]    The stub of  FIG. 5   d  possesses enlargements having different sections. A first enlargement eu 3  is of relatively large size, and this enlargement has a second enlargement eu′ 3  of smaller size. 
         [0058]    The enlargements eu 4  and eu′ 4  of  FIG. 5   e  are of the same type as those of  FIG. 5   d , but are of smaller dimensions so as to be effective at different energy levels. 
         [0059]    In these stubs, the enlargements are symmetrical with respect to the axis X of the stubs. 
         [0060]      FIG. 6   a  shows a stub having an enlargement eu 5 , which itself has an enlargement eu′ 5  of larger size. The enlargements are symmetrical with respect to the axis X of the stub and the enlargement eu′ 5  is symmetrical with respect to the axis Y of the enlargement eu 5 . 
         [0061]      FIG. 6   b  shows a stub of the same type as that in  FIG. 6   a , but in which the enlargement eu′ 6  is not symmetrical with respect to the axis Y of the enlargement eu 6 . 
         [0062]      FIG. 6   c  shows a stub that has an enlargement e″ 7  on one side of the axis X of the stub and it has, on the other side of the axis X, an enlargement eu 7  which itself has an enlargement eu′ 7  of larger size. 
         [0063]    Provision is therefore made for producing enlargements that are not symmetrical with respect to the axes X of the stubs. 
         [0064]    Moreover, provision may be made for the faces of the ends of the enlargements furthest away from the axis X of the stub not to be parallel to the axis X. This is shown in  FIGS. 7   a  and  7   b  by the faces fa 9  and fa 10 , which are inclined to the axis X. 
         [0065]    There may also be provision for the walls of the enlargements to have curved surfaces, as shown in  FIG. 7   b.    
         [0066]    According to another embodiment shown in  FIG. 7   c , the end faces fall of the enlargements eu 11  may be of curved shape. 
         [0067]    The various enlargement shapes described above, preventing the multipactor effect, were described within the context of an application to stubs of a filter, but they could be applied to any microwave waveguide. 
         [0068]    By providing stubs as described in the invention, the power level of the filter may be very greatly increased. 
         [0069]    Moreover, the stubs as described in the invention have a volume larger than a stub without an enlargement, as shown in  FIG. 5   a . This increase in volume results in a significant reduction in ohmic losses. It is therefore possible to use this invention to reduce the ohmic losses of a waveguide and more especially in a filter. 
         [0070]    An example of such a filter applied in a transmit/receive unit on board a satellite will now be described with reference to  FIG. 8 . 
         [0071]    Such a unit must be able to transmit and receive signals at different energy levels. It must transmit at a maximum energy level and it must receive relatively attenuated signals. 
         [0072]    The unit shown in  FIG. 8  has a single, common horn CO for both transmitting and receiving. 
         [0073]    Diplexer filters DXH and DXV, for horizontal polarization and vertical polarization respectively, are connected to the ports e 1  and e 2  of a polarization mode splitter/combiner OMT, which is connected via its port e 3  to the transmit/receive horn CO. 
         [0074]    The receive filters FiRxH and FiRxV may be of relatively low operating power. In contrast, the transmit filters FiTxH and FiTxV must be able to operate at high power levels. 
         [0075]    The transmit filters FiTxH and FiTxV are designed according to the invention to allow high power levels. It is then possible to produce a unit as shown in  FIG. 8  with a single horn CO, for both transmitting and receiving. 
         [0076]    The invention therefore makes it possible to obtain, in a waveguide and more particularly in a filter:
       a large increase in the power capability, avoiding the multipactor effects;   a reduction in ohmic losses;   a structure completely compatible with the methods currently used to manufacture filters with “stubs” that guarantee low passive intermodulation products (PIMPs)l; and   a potential saving of one antenna on a satellite. It is possible to combine the transmit (Tx) and receive (Rx) functions into a single antenna even if the Tx power levels are high.       
 
         [0081]    It will be readily seen by one of ordinary skill in the art that the present invention fulfils all of the objects set forth above. After reading the foregoing specification, one of ordinary skill in the art will be able to affect various changes, substitutions of equivalents and various aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by definition contained in the appended claims and equivalents thereof.