Patent GB-567876-A (GB)
Title: Improvements in direction-indicating radio transmitting apparatus
IPC: G01S1/02
Filed: 1941-12-24
Abstract: 567,876. Wireless aerial systems. PHILIPS LAMPS, Ltd. (Naamlooze Vennootschap Philips' Gloeilampenfabrieken). Dec. 24, 1941, No. 16647. [Class 40 (v)] Antenna systems producing two fields having a constant ratio of intensities in an inclined plane, which may indicate an aircraft landing path, are designed in accordance with conditions established by a mathematical investigation given in the Specification, so that the angle of inclination of the plane thus indicated does not vary with variation of the reflective power of the soil. It is shown that two infinitesimal dipole elements at respective heights h1 and h2 will, together with their earth images, define a plane making an angle # with the vertical which does not vary with soil conditions when h2 - h1 = n#/2 cos #, where n is an integer and A the wave-length of the transmission, and that for planes at a small angle to the horizontal, substantially the same result is obtained if h2 + h1 = q#/2 cos #, q being an integer. The invention therefore comprises means for producing two dissimilar highfrequency radiation fields having a constant intensity ratio in a plane making an angle # with the vertical, in which the fields are generated by radiations of the same wavelength but different modulation from two radiator systems so formed and arranged that they can be regarded as constituted by a large number of dipole elements of small size in relation to the wave-length, each element in one system at a height h1 having a corresponding element in the other at a height h2, the ratio of the current intensities in the two elements of all such pairs being constant, and h1 and h2 being for all pairs such that either Figure 3 shows a system formed by two equal dipoles Z2 and Z1 at heights h2 and h1 (together with their earth images Z21 and Z<1>1) which may be regarded as formed of small dipole elements corresponding to one another in the above way, the difference in heights of the two elements forming each pair being h2 - h1. The heights h2 and h1 are chosen to give the desired angle # to the vertical of the plane indicated by the constant ratio (or equality) of the intensities of the fields due to the two aerials and their earth images. Alternatively, the dipoles may be at heights given by the equation h2 + h1 = q#/2 cos #, giving a system of less overall height. This equation defines a system in which corresponding elements in the two radiators are symmetrically situated above and below a horizontal plane at height #/4 cos #. Fig. 9 shows a system of this form, consisting of identical loops Z1, Z2 symmetrically situated above and below a plane S at height #/4 cos #, and fed at symmetrically-located points B, C. Fig. 10 shows a modification of this type in which each aerial consists of three mutually perpendicular radiators a, b, c and a<1>, b<1>, c<1>, the image of one reflected in the vertical plane containing the course line being symmetrical with regard to the other in relation to the plane S. In all the foregoing systems the two radiators may be displaced over a few wavelengths, one to each side of the course line. If n = o in the equation h2 - h1 = n #/2 cos #, the heights h2 and h1 become equal, but since two equal dipole elements at the same height give equal field intensities at all points no particular plane is defined. They may, however, in this case be replaced by elements, such as the loops a, a<1> shown in Fig. 11 of different shape in the two radiators, having different field patterns in a vertical plane. Each radiator comprises the same number of elements, identical in each, but differing in the two, the elements being of small dimensions compared with the wavelength, arranged at different levels and similarly oriented. Corresponding elements in the two systems are at the same height and at a constant distance apart, and the ratio of the currents fed to them is constant. Another system is described in which, in addition to n being equal to zero, all elements in each radiator are at the same height, the radiators consisting of unequal numbers of horizontal aerials all parallel to one another.