A WAVEGUIDE AND A METHOD OF MAKING THE SAME

Abstract: When machining waveguides a problem exists because of the flexing of the machining tool, this leading to in­ accuracies in the waveguide. This is especially pronounced for narrow waveguides designed for high frequency opera­ tion since the tool has had to be of correspondingly narrow diameter. In Figure 2 a number of waveguides having a nar­ row dimension W are formed by interdigitated projections (6, 6A) on two piece of material 1 and 2. These intedigitated projections are produced by machining relatively wide paral­ lel grooves in the two pieces of material and this can be done using a relatively large diameter tool which is not appreciably subject to flexing during operation. The result is relatively accurate, narrow waveguides of high surface finish unobtain­ able using conventional techniques.

Description: Europe: PATENT SPECIFICATION TITLE:- A waveguide and a method of making the same. A WAVEGUIDE AND A METHOD OF MATING THE SAME This invention relates to waveguides. It arose in the design and manufacture of a squintless antenna having a plurality of waveguides leading to an array of radiating apertures. A squintless antenna is an antenna in which radiation is fed to an array of radiating positions in such a way that it arrives at each of those positions at the same phase. Squintless antenna for operation in the L and S band of frequencies, have been made in the past by machining grooves in two sheets or plates of conductive material. These sheets are then fitted together, one on top of the other, so that each groove in one sheet co-operates with a corresponding groove in the other sheet to form one of the waveguides. A problem has arisen in machining the grooves since it is necessary that their dimensions be defined within small tolerances. The inventor has found that this problem is accentuated when the antenna is designed to operate at high frequencies, e.g. in the J band. This is because the waveguides need to be correspondingly narrower. They therefore need to be machined using an end mill or other tool of relatively small diameter. The small diameter means that the tool is liable to flex in operation and this leads to inaccuracies in the surfaces of the grooves. It is not just the diameter of the tool which is relevant but the relationship between the diameter and the length, the minimum possible length of the tool being dictated by the depth of the groove required. As an example, rectangular waveguides for J band operation might typically be one millimeter wide and ten millimeters deep. Using the conventional technique described above this would mean machining grooves one millimeter wide and five millimeters deep. This invention provides a method of making a waveguide in which a groove having a base and two sides is formed in one piece of material, a projection is formed on another piece of material and the projection is then fitted into the groove so as to form the waveguide between a side of the projection and a side of the groove. The invention also provides apparatus comprising a waveguide formed between a side of a groove having a base and two sides in one piece of material and a side of a projection having an end face and two sides on another piece of material, the projection fitting in the groove. One way in which the invention may be performed will now be described with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of a squintless antenna constructed in accordance with the invention; and Figure 2 is a perspective view of the antenna shown in Figure 1 viewed from the direction indicated by arrow A on Figure 1. Referring firstly to Figure 1, the antenna is formed from first, second and third. pieces of conductive material, e.g.., brass or aluminium. The first piece 1 of material is machined with a number of grooves 4 of various different lengths and extending generally parallel to each other as shown. Each groove 4 has, at its base, a portion of reduced width forming a slot 5. These slots 5 may be machined before or after machining of the rest of the grooves 4 using a tool of narrower diameter. Alternatively, a specially shaped tool having a narrower diameter at its free end could be used. Between each pair of adjacent grooves 4 a flange 6 is defined. It will be noted that the grooves 4 are not straight. Each has a bend 7 and a bend 8. The second piece 2 of material has features 4A, 5A, 6A, 7A and 8A corresponding to 4,5,6,7 and 8. The flanges 6A form projections which fit snugly into the slots 5. The parts 1 and 2 have respective rebates 9 and 9A and these co-operate with the third piece 3 of material as will now be explained. The piece 3 of material is machined so as to form a channel 10 which tapers from a relatively deep end 11 to a relatively shallow end 12. Rebates 13 form lips 14 which fit into the rebates 9 and 9A of the respective parts 1 and 2. When the parts 1,2 and 3 are assembled, as shown in Figure 2, the taper of the channel 10 serves to distribute microwave energy introduced through the end 11 of the channel 10 evenly into each of the waveguides formed by the parts 1 and 2. Referring now to Figure 2, this shows the parts 1 and 2 fitted together and it can be seen that each side of each projection 6A co-operates with an adjacent side of a flange 6 to form a waveguide of width W. This width W is much smaller than the diameter of the tool needed to machine the various grooves and slots which have been referred to previously. It is thus possible by employing the invention to produce narrow waveguides of great accuracy and high surface finish. It will be apparent that the invention is applicable to non-squintless feeds and to other type of apparatus besides the squintless feed illustrated. It could for example be employed in the manufacture of diverging and/or tapered waveguides as might be used in an organpipe scanner.

Claims: CLAIMS: 1. A method of making a waveguide in which a groove having a base and two sides is formed in one piece of material, and a projection having an end face and two sides is formed on',anc,ther piece of material, characterised in that the project'ion is then fitted into the groove so as to form the waveguide between a side of the projection and a side of the groove. 2. A method according to claim 1 in which two waveguides are formed on opposite sides of the projection between the projection and corresponding sides of the groove. 3. A method according to claim 1 or 2 in which said one piece of material has a plurality of grooves and the other piece of material has a plurality of projections, each projection fitting in a corresponding groove to form a plurality of waveguides. 4. A method according to claim 3 in which a main waveguide is formed by securing to the said two pieces of material, a third piece of material forming a channel which communicates with each of the said plurality of waveguides. 5. A method according to claim 4 of making an antenna having a plurality of radiating apertures in which each of said plurality of waveguides has an open end, opposite to an end communicating with the channel, each said open end constituting one of said radiating apertures. 6. A method according to claim 5 of making a squintless antenna. 7. A method according to any preceding claim in which the waveguide or each waveguide is for operation at J band. 8. Apparatus comprising a waveguide characterised in that the waveguide is formed between a side of a groove having a base and two sides in one piece of material and a surface of a projection having an end face and two sides on another piece of material, the projection fitting in the groove. 9. Apparatus according to claim 8 in which two wave Suides are formed on respective opposite sides of the projection, between the projection and corresponding sides of the groove. 10. Apparatus according to claim 8 or 9 in which said one piece of material has a plurality of grooves and the other piece of material has a plurality of projections, each projection fitting in a corresponding groove to form a plurality of waveguides. 11. Apparatus according to claim 10 comprising a main waveguide formed by a third piece of material defining a channel which communicates with each of said plurality of waveguides. 12. Apparatus according to claim 11 in the form of an antenna having a plurality of radiating apertures, each of said plurality of waveguides having an open end opposite to an end communicating with the channel, and each said open end constituting one of said radiating apertures. 13. A squintless antenna constructed in accordance with claim 12. 14. A waveguide for J band operation and constructed in accordance with any of claims 8 to 13.

Inventors: SUCKLING, HAROLD FREDERICK
Applicants: THE MARCONI COMPANY LIMITED
Application year: 1981
Main classification: H01P11
IPC codes: H01P11