GB893833A - Improvements in or relating to equipment for testing or monitoring radio apparatus - Google Patents

Abstract

893,833. Aerials; testing radio apparatus. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 8, 1958 [July 18, 1957], No. 22855/57. Classes 40(5) and 40(7). In order to test or monitor radio apparatus connected to an aerial a screen is constructed and placed so as to effectively enclose the said aerial and means are provided within the screen for coupling the aerial to test apparatus. Fig. 2 shows a unipole aerial 3 mounted on a conductive surface 4 and connected by a coaxial line 2-5 to radio equipment 1. The test apparatus 9 is coupled to the aerial through an impedance matching transformer 8 and a screen 6 enclosing the aerial and having within it a coupling element 10. The screen 6 may have choke flanges 7 spaced a suitable distance from the surface 4 as shown or it may be directly coupled thereto. The coupling element 10 may be directly connected to the aerial or may be capacity coupled with it. As shown in the Figure it consists of one or more wires close to and parallel to aerial 3 which are coupled to it electromagnetically. This coupling forms a band-pass filter and transformer which can be used in place of or in addition to transformer 8. The length of the transformer is preferably a quarter wavelength but where it is not possible to achieve this length a capacitor 12 may be used to effectively lengthen it. In the constructional embodiment shown in Fig. 3 the unipole aerial 3 is surrounded by a sleeve connector 10 which has spring elements 19 making contact with the aerial at its root end. The screen 6 is temporarily attached to the aerial supporting structure by screws 17 and is conductively connected to it 14 by shaped conductive ring 15. The screen and connector are made in two parts held together by nut 18 and carry a coaxial socket 20 for the test apparatus. Capacity loading rings 21, 22 may be provided. Where the aerial is a slot aerial 23 in a conductive surface the coupling means may consist of a line 27 across the slot. If the line and the screening cavity 26 are half a wavelength long they may be coupled at the far end of the line as shown. An alternative form of slot coupling consists of an open circuit line lying parallel to and within the local field of the slot. In this case connection is made to the centre of the line. The screen may be made to fit any shape of aerial surrounding and a screen containing a coupling of the general type shown in Fig. 4 for use with a "Notch" aerial is described with reference to Figs. 6 and 7 (both not shown).