| 摘要 |
753,098. Radio aerials. TELEFUNKEN GES., [formerly TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE]. July 23, 1954 [July 23, 1953], No. 21494/54. Class 40 (7). A wide-band aerial comprises a loop which is arranged to operate as a travelling-wave aerial in one band of frequencies and as a resonant loop aerial in a lower band of frequencies. The loop, which may be of square, rhombus, circular or, as shown in Fig. 1, elliptical shape, is comprised of two sections each of which consists, respectively, of two (or more) conductors 1, 2, and 3, 4 connected together at their ends 5, 7 and 6, 8 respectively and spaced apart by a distance which progressively increases from each end, as shown, to avoid impedance discontinuities and render the operation of the aerial uniform over a wide range of frequencies when operating as a travelling-wave aerial. The section ends 7 and 8 are connected together via the series arrangement of condensers 12, 13 and resistance 11, the value of the latter being such as to terminate the sections without introducing reflection and the condensers being of such value as to present a very low reactance in the band in which the aerial functions as a travelling-wave aerial and a very high reactance in the lower frequency band in which the aerial is resonant. The terminating impedance is therefore, effectively, directly connected to the sections in the higher frequency band and, effectively, disconnected in the lower frequency band. In an alternative arrangement the terminating resistance is connected directly between the ends of the sections and shunted by an inductance of such value that the resistance is not affected in the higher frequency band but is, effectively, shortcircuited in the lower frequency band. The terminating resistance and the two condensers (or the inductance) may be formed as an integral unit as described with reference to Figs. 3 and 4 (not shown). In a further alternative arrangement the terminating resistance may be switched in and out of use by means of a remotely controlled switch. The loop, which is mounted in a horizontal plane, is connected at points 5, 6 to a twin feeder 16, 17 which is matched to the characteristic impedance of the aerial by means of the taped line matching section 14, 15 and the parallel conductors 9, 10 which are chosen to have the same characteristic impedance as that of the aerial in the travelling wave band of frequencies. Alternatively one (or more) #/4 matching sections 141, 151 may be employed. Since the impedance of the aerial, in general, will be different for the two bands the matching is arranged to be correct for one of the bands if poorer matching is tolerable on the other band. The matching sections may also act as an aerial for signals in a still lower band of frequencies than the lower of the other two bands. The feeders may be connected to receiving apparatus via terminals 19, 20 for signals lying in the two upper bands (travelling wave and resonant frequency band) and via terminals 22, 23 for the lowest (e.g. broadcast band) frequencies. The directivity diagram of the aerial when operated in the travelling-wave band of frequencies is shown in Fig. 2. |
