The invention relates to a method for manu¬ facturing a wave guide section that provides a con¬ tinuous transition between two cross-sections of diffe¬ rent size and/or shape from a semi-rigid, flexible wave-guide of constant cross-section. The invention relates also to a microwave antenna comprising the so-obtained wave-guide section.

In the field of microwave ^' technique there is a large number of applications in which microwave devices are used that include wave-guide sections that have vary¬ ing cross-sections along their lengths- and often not only the cross-section but also the form thereof is varied. Such a device is used generally to provide a connection and a signal transmission between an input and an output cross-section that satisfies predetermined electrical and mechanical criteria. According to their designations such devices can be:

- transitions for providing connection between _, two wave¬ guides of different types; - polarization transducers for converting a linearly po¬ larized wave in a circularly polarized one and vica versa;

- the primary radiators of microwave antennas can also be considered to belong to this category. Such devices generally have strictly predetermined mecha¬ nical dimensions and they are manufactured from a metal mainly from copper or brass by means of a cutting process or by electroforming.

./.

At least one end of such devices is provided with a connector to enable connection towards a wave¬ guide. The manufacture of such devices is generally expensive, they should be provided on one or both ends with two connection facilities towards a wave-guide- or another microwave device. The catalogues of several com¬ panies manufacturing microwave devices include large numbers of various embodiments of such devices.

The German laid open publication 3.130.449 re- lates to a polarization transducer, in which a circular wave-guide is inserted in sleeve-like tool which consists of two halves in which respective rectangular recesses are formed which step-wise decreasing cross section. When the circular wave-guide is pressed between these halves, its shape will be deformed elliptically. The so-obtained flaring elliptical cross-section is stabilized in such a way that the two halves will not be removed from the wave-guide and the two connections are tooled on the two end faces of the rigidly compressed sleeve. Such a design is capable of making a polarizatio transducer in the actual field of application, however, the mounting of the sleeve and the final presence thereof around the wave-guide portion are connected with a number of drawbacks. One of them lies in that the discretely changing rectangular recess profile of the two halves cannot provide strictly predetermined cross-sectional area and forms for the deformed wave-guide section which would be necessary for perfect performance.

Of the various equipments using microwave de- vices microwave antennas have outstanding significance. The German laid open publication 2.939.697 relates to a microwave antenna which is equipped with an internal wave¬ guide made by a semi-rigid, flexible tube of elliptical cross-section which is the same type that used to connect a microwave equipment with the antenna. In the embodiment

illustrated in Fig. 1.of that publication the internal wave-guide is formed in a swan's neck shape and the frontal end portion of this internal wave-guide constit¬ utes the primary radiator of the antenna. In the descrip- tion of this publication reference is made to the possib¬ ility that a separate .primary radiator having a flaring elliptical aperture can be connected to the frontal end of the internal wave-guide. For providing appropriate radiation properties concentrical annular loading rings are arranged behind the aperture of the internal wave-guide The embodiment shown in Fig. 2 of the cited publication uses a similar internal wave-guide but this embodiment shows a Cassegrain type antenna. Such antennas can be operated in single polarization mode due to the elliptical cross-section of the internal wave-guide. If the antenna should be operated in double polarization mode, then a primary radiator must be used which has the same aperture in both directions. In such application a polarization converter and a polarization transducer must be inserted in the path between the primary radiator and the internal wave-guide.

In the cited ^' German publication 2.939.697 an annularly reinforced wave-guide is used and reference is made to the possible use of a semi-rigid, flexible seamless aluminum wave-guide. Such a wave-guide is described in the Hungarian patent 177.317 which has a hyperelliptical cross section.

The suggestion for using a semi-rigid, flexible wave-guide as the internal wave-guide of the microwave antenna which can constitute even the primary radiator as taught by the cited publication 2.939.697 has proved to represent a significant step-forward compared to the pre¬ viously existing prior art. The type and cross-section of the wave-guide connecting the microwave equipment to the antenna referred to as "outer wave-guide" are determined

generally by a number of technical considerations which can be influenced by economic aspects, too. The aperture, electrical parameters and other characteristics of the primary radiator are determined mainly by the intended use including the requirements imposed on the tele- ^* communication link, and based on these conditions the size and/or form of the aperture of the primary radiator has to be different from those of the outer wave-guide. In such applications respective transitions must be pro- vided between the outer and inner wave-guides and between the inner wave-guide and the primary radiator. If the outer and the inner wave-guides are of the same type, then the first transition can be spared, while if the inner wave-guide forms the primary radiator, then there will be no need for using the second transition.

When a wave-guide transition is used, a signal pass_tg_ should be provided between the input and output cross-sections that can ensure a sufficient operational • bandwidth, a required mode purity and suitable trans- mission parameters /attenuation and reflexion coefficient/. If a separate transition device is used, respective con¬ nection facilities must be provided at both ends of the device and the means used as connectors have respective limiting transmission characteristics and their presence decreases the compactness and reliability of the whole microwave antenna system. It is a well known objective of all designers to minimize the number of devices used in a microwave antenna system. Similar considerations can be applied regarding polarization converters if the microwave transmission must be designed for multi-polarizational performance.

The design of a transition device that can provide a connection between wave-guides of differring cross-sections with predetermined transmission charac- teristics represents a complicated task even for a skilled

designer. As a result of .several calculations cross- sectional profiles are obtained for the transition that cannot be realized due to limitations in available manu¬ facturing technique. Of such reasons the production of microwave transition devices is often based even nowadays on empirical ov semi-empirical considerations. A manu¬ facturing limitation lies e.g. in providing the required surface-quality which decreases the freedom of design.

> "Major manufacturing companies produce therefore a discrete number of standard types of transition devices and the user has the possibility of choosing one of such types instead of directly designing an optimum transition for the particular task.

In connection with the production of microwave antennas a further manufacturing limitation should be mentioned. The required radiation properties of a primary radiator often necessitate the. use of outer annular load¬ ing rings which should be arranged concentrically around the aperture of the primary radiator. In ^' case of aperture cross-sections which are elliptical or represent a form between a circle and an ellipse, it is rather difficult to ensure the required concentricity between the aperture and the loading rings, since the aperture can be excentric relative to the outer surface of the primary radiator, whereby there might be no usable basis surface for making the annular rings.

The object of the invention is to provide a method which enables the simple and perfect manufacture of a wave guide section that can serve as a transition between cross sections of different size and/or form,

A further object of the invention lies in pro¬ viding a microwave antenna using the wave-guide section manufactured by the aforementioned method.

The invention is based on the recognition that a flexible , semi-ri gi d wave-guide like the one disclosed

in the Hungarian patent 17*7.317 has a sufficient de- formability for being able to take the form of a mandrel tooled to the form of the transition, if such a mandrel is pressed therein. In that case there will be no need for providing a separate connection between the wave-guide and the transition, since this latter forms an integral part and an extension of the wave¬ guide.

According to the invention a method has been suggested for manufacturing a wave-guide section pro¬ viding a continuous transition between two cross-sections of different size and/or form by using a flexible and semi-ridig wave-guide of uniform cross-section, in which a mandrel is provided which has a form corresponding to the required form of the transitional .wave-guide section and made of a material substantially harder than said wave¬ guide, the cross-s.ection of said mandrel is changing along * the length thereof according to a monotonic function, and said mandrel is axially inserted in the end of said wave- guide by applying a sufficient pressure, whereby the end of the wave-guide is deformed to an extent which corres¬ ponds at most to the highest permissible deformation li¬ mit determined for the material thereof.

It is preferable concerning the realization of the method if the wave-guide is made of a material, preferably of aluminum which has a deformability of at least 20%.

In a further preferable embodiment the cross- section of the transition is symmetrical to two mutually perpendicular axes along the whole length thereof.

The method can be carried out in a simple way if the deforming step is performed in a cold state.

The number of possible applications will be increased if respective mandrels are used and both end portions of the wave-guide section are deformed by these

mandrels to obtain a pair of communicating transitions which have a common axis and their inner end faces meet each-other or they are spaced and the spacing is at most as long as three-times the operational wavelength. When using the method according to the inven¬ tion a further preferable property can be utilized, i.e. the mandrel, when being pressed in the end of the wave¬ guide, can be used as a centering support during a cutting step adapted for making an appropriate outer surface either on the wave-guide or on an element attached thereto. By means of this possibility the concentrical manufacturing of the loading rings can be made without difficulties. When the outer surface has been tooled, the mandrel can be pull¬ ed out of the interior of the deformed wave-guide section. It is particularly advantageous if at least one of the two outer cross-sections is hyperelliptical, how¬ ever, still further advantageous features can.be obtained if both of these cross-sections and each transitional cross-section therebetween are also hyperelliptical, and in the mathematical formulae defining the respective cross- sections the power is varied according to a monotonic function.

The hyperelliptical design of each cross-section offers the advantage, that a numerically controlled machine tool can be used for making the mandrel, since each cross- section of the transition if defined by a mathematically exact formula, and a further advantage lies in that one can optionally choose the steepness of the change of the power in the formula of definition as it varies along the length of the transition, and this option enhances the freedom of the designer. Such a freedom has not existed in the prior art design methods.

If the transition must be used between cross- sections having a larger difference in size and/or shape than what the maximum permitted deformity of the original

wave-guide would allow, then in a preferable embodiment the transition is made by a number .of parts. Each part is made by a wave-guide section having a uniform cross- section discretely differring from that of the others and respective mandrels with discretely increasing cross- sections are used to deform these parts, and after re¬ moval of the mandrels the flaring parts are connected to each other to provide the transition.

) ^' The wave-guide section made by the method according to the invention can be used as a microwave device in a large number. of applications i.e. as a tran¬ sition, as a polarization transducer and in given cases as the flaring portion of a primary radiator, however, particular significance is attributed to the use of such a wave-guide ^" section in a microwave antenna comprising a primary radiator, an inner transmission line and a connection towards an outer transmission line, in which according to the invention the deformed wave-guide section is provided at least at one end of the inner transmission line having a monotonously expanding cross-section in a direction away from the connection towards the outer trans¬ mission line, and the inner transmission line is made by the flexible, semi-rigid wave-guide used in an end portion for making the transitional wave-guide section. Of course, in such an antenna not only one deformed wave-guide section can be used which is made according to the invention but as many as it is required for providing an optimum per¬ formance for the antenna. It is therefore preferable, if the primary radiator of the antenna is made by a flaring wave-guide section deformed according to the invention.

In case of an antenna designed for bipolar reception and transmission, it is preferable if the primary radiator is coupled to a polarization transducer and this latter to a polarization converter, and the respective polarization gates of the converter are coupled to res-

pective flexible, semi-rigid inner transmission wave¬ guides. In a further preferable design the polarization transducer and the primary radiator of the antenna are made from a single wave-guide section deformed at both ends in such a way the the cross-sections are decreas¬ ing towards the middle of the section.

It is also preferable if the primary radiator of the antenna comprises loading rings tooled by using the mandrel as a centering element when it was pressed in the frontal end of the primary ^' radiator.

The invention will now be described in connectio with preferable embodiments thereof, in which reference will be made to the accompanying drawings. In the draw¬ ing: Fig. ^* 1 is a sketch illustrating the method according to the invention, Fig. 2.is the perspective view of a quarter of the mandrel used for the method hav¬ ing hyperelliptical cross-section, Fig. 3 shows schematically a microwave antenna using the invention, Fig. 4 shows an enlarged detail of the antenna shown in Fig. 3. Fig. 1 shows a flexible, semi-rigid wave-guide 1 made of an aluminum tube. The wave-gβide 1 is designed according to the Hungarian patent 177.317 and it has a hyperelliptical cross-section. A hyperellipse is defined by the formula:

( ^■ *) ^■• W - ^{■ ■} in which x and y designate two mutually perpendicular axes in the cross-sectional plane and m and n are numbers larger than 2. It can be seen from the formula that a and b_ define the two axes of the cross-section along the

directions x and y. If m=n=2 and a=b, then a circle is obtained, if a^ , the formula defines an ellipse, while if m' and n are increasing, the cross-section tends to have less-rounded corners and finally it approaches a rectangle.

A wave-guide section with varying cross-section can be obtained from the wave-guide 1 of uniform cross section by using a mandrel 2 having a form varying along its length according to a required function. The material of the mandrel 2 is substantially harder than the material of the wave-guide 1 e.g. steel. The mandrel 2 comprises a conical introductory section 3, a transitional section 4 with a shape corresponding to the required transition, a shoulder 5 and a shaft 6 which is concentrical with the transitional section and has a circular cross-section.

In the frontal zone of the transitional section

4 the cross-section of the mandrel 2 is the same as that of the wave-guide 1. During the method the mandrel 2 is pressed /beaten/ in the open end of• the wave-guide 1, whereby its shape is deformed to correspond to that of the transitional section 4.*This step can be performed in such a way that the outer surface of the mandrel 2 is wetted by a liquid that can provide a suitable lubric¬ ation effect and the wave-guide 1 is supported from outside, then the mandrel 2 is introduced in the wave¬ guide 1 by means of a number of smaller axial impacts. The impacting force can be applied by means of a falling weight guided by the shaft 6 which impinges the shoulder

5 or by means of a pneumatic hammer. For the sake of undisturbed axial removal of the mandrel 2 from the wave-guide 1, the transitional section 4 must have a monotonously expanding cross-section towards the shoulder 5. The material of the wave-guide has a relative deformability which lies between ^' 20% and 30%, In order to prevent deformations larger than permitted,

- li ¬

the largest perimeter of the transitional section 4 cannot exceed 1,3 times the perimeter of the wave-guide 1. The monotonous character does not mean that the cross-section of the wave-guide cannot have any size that slightly decreases in a portion along the transition. This limitation means that the general shape of the mandrel 2 is monotonously increasing, whereby it can be pulled out of the wave-guide section without causing a further deformation. When the cross-section of the frontal part of the ^' transitional section 4 of the mandrel 2 is smaller than the cross-section of the wave-guide 1, then there will be parts of the wall which under the effect of the denting forces will shrink and close against the mandrel 2. If the required deformation is as high as to exceed the maximum limit determined for .the wall-material, the transition must be made in a few number of steps. *To this end a further semi-rigid wave-guide is required which has a cross-section substantially equal to the maximally ^' deformed cross-section of the starting wave-guide section

1 and a further mandrel must be used to deform this further wave-guide. When the deformed part of the second wave-guide is separated and provided with an appropriate connection, the smaller end thereof will be connectable to the deform- ed end of the first wave-guide, whereby the transitional sections will represent the extensions of one-another.

Fig. 2 shows a quarter of the shape of a tran¬ sition in a perspective view. It can be seen that along the axis z_ the corner will be more and more rounded i.e. both powers in the definition formula of the hyperellip¬ tical function are monotonously decreasing. Also, the value of a is increasing, while the value of b_ is decreas¬ ing and approaches that of a. In this way starting ellip¬ tical cross-section changes over to a circular form. While the use of a hyperelliptical cross-section

has certain advantages /definitive form, easier design/, the shape of the mandrel 2 does not have to be always hyperelliptical. Elliptical or elliptic-like cross-sections can well be used just as any other conventional forms used for constituting a transitional section. The only requirement which should be kept lies in that the form must ensure that the mandrel can be pulled out after de¬ forming the wave-guide.

The circular shaft 6 arranged at the rear end of the mandrel 2, which is coaxial with the transitional section 4, provides an additional possibility according to which loading rings concentrical with the inner cross- section of the wave-guide can be tooled on a metal fitted to the outer surface of the wave-guide 1 by using the shaft 6 in a cutting machine as a centering means when being inserted in the wave-guide. _ . '

Owing to the manufacturing technology used in the method according to the invention the transitional section forms the direct extension of the wave-guide 1, and from this fact it follows that compared to conven¬ tional discrete transition devices /in other term: tapers/ one of the mechanical connections thereof has been spared /including the mechanical and electrical limitations re¬ sulting from such a connection/. Depending on its shape and design the transition can be used as an interconnect¬ ing member between two wave-guides of different size and/ or cross-section, ^* as a polarization transducer referred also to as a polarizer, as a primary radiator /called also as primary feed/ or as any other microwave device in which a wave-guide section with varying cross-section is required.

In a preferable embodiment the wave-guide 1 can be deformed by respective mandrels introduced in the two ends thereof, whereby two communicating deformed sections are obtained, in which the cross-sectional area

is decreasing from the end faces towards the middle regions. In such use the wave-guide 1 must have an app¬ ropriate length. Such a double transitional configuration can be used as a polarization transducer. It can be en- sured that the two opposing transitional sections have a common axis by providing a common shaft 6 for the two mandrels which can be guided in fitting axial bores tool¬ ed in the mandrels instead of forming integral part thereof. In such an embodiment the deforming step can be carried out by simultaneously pressing the two mandrels in the wave-guide section from opposing directions.

Reference is made now to Fig. 3 which shows schematically a microwave antenna comprising a few num¬ ber of wave-guide sections made by the method according to the invention. The. enlarged view of Fig. 4 shows the primary radiator of the antenna shown in Fig. 3 and the devices connected thereto. In the illustrated embodiment the antenna is capable of receiving and transmitting cir¬ cularly polarized waves including both right and left senses of rotation. The antenna comprises a parabolic mirror- 7, a primary radiator 8 arranged in the focal zone of the mirror 7 , a polarization transducer 9 coupled to the primary radiator 8, a polar selector 10 with two polarization gates and coupled to the output of the trans- ducer 9, an internal transmission line 13 with an end deformed to comprise a transition as suggested by the pre¬ sent invention, this end is coupled to a first polariz¬ ation gate 11 of the polar selector 10, and an other in¬ ternal transmission line 14 connected to a second polariz- ation gate 12 of the polar selector 10. The internal transmission lines 13 and 14 are coupled through separate connector terminals arranged behind the mirror 7 to res¬ pective outer transmission lines 15 and 16.

Owing to the circular polarization mode both axes of the primary radiator 8 have the same length and

the primary radiator 8 is made by a horn manufactured according to the present invention. It can be seen in Fig. 4 that the primary radiator 8 and the polariza¬ tion transducer 9 arranged behind the radiator 8 are made by the deformation of the two ends ^" of one and the same wave-guide section. By such a technology the two devices will be automatically connected to each other. The out¬ put of the polarization transducer 9 provides a pair of linearly polarized waves in which the planes of polarizatio are normal to each other. The outer periphery of the pri¬ mary radiator 8 is encircled by a number of corrugated ring chokes 17 that exert an influence on the radiation pattern of the antenna.

The vertically extending polarization gate 12 of the polar selector 10 passes one of the linearly polariz¬ ed waves to the internal transmission line 14 designed to have a ratio of the two axes of the cross-section equal- .to ^' 1:2. The cross-section of the inner transmission line 14 is equal to that of the outer transmission lines 15, 16, therefore there is no need for a transition between the line 14 and the line 16. The ratio of the axes of the cross-section in the polarization gate 11 of the polar selector 10 is about 1:1, therefore the connection towards the internal transmission line 13 which has axes with a ratio of 1:2 must be solved by using an appropriate taper. This taper or wave-guide transition can be provided if the end section of the inner transmission line 13 is de¬ formed by a mandrel formed to ensure an optimum transition between these two cross-sections. All wave-guides and wave-guide sections used in the antenna shown in Figs, 3 and 4 have hyperelliptical cross-section.

If the antenna of Fig. 3 were constructed by conventional elements and accessories then the following devices or elements would be necessary:

- a separate connection between the inner transmission line 13 and the transition;

- a transition providing connection between the cross- sections of the inner transmission line and of the polarization transducer;

- a separate polarization transducer;

- a primary radiator;

- a connection between the polarization transducer and the primary radiator. These elements can all be spared by using the antenna sys¬ tem shown in the above example, thus the manufacturing costs of the system have been reduced substantially, an increased reliability has been attained and the electrical performance of the antenna has been improved. Of course, according to the invention less • complex antennas than that shown in Figs. 3 and 4 can al¬ so be made e.g. an antenna which can receive and transmit linearly polarized signals only, in which only a single inner transmission line is used which .has a cross-section identical with that of the outer transmission line. In such an antenna the primary radiator Can be made by the horn-like deformation of the frontal end of the inner transmission line. In that case there is no need of using a separate primary radiator and ^* of a connector associated therewith, and the electrical performance of the antenna is improved, since the limitations that would be caused by the spared accessories will not exist.

Those skilled in the art can appreciate that between the rather complex antenna shown in Figs. 3 and 4 and the last described simplified embodiment a number of more or less complex embodiments of the antenna can be devised which all use in one or other form the transitional section according to the invention and such use is always connected with respective advantages.