| 摘要 |
804,462. Aerials. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Sept. 19, 1955 [Oct. 6, 1954], No. 28731/54. Class 40 (7). An aerial designed to operate in two frequency bands comprises spaced conductive elements interconnected through time delay means having different time delays in the different bands so that signals from the two elements in both of the frequency bands are added at the feeder. In one embodiment (Fig. 1) four elements 1, 2, 3 and 4 are arranged in double V formation with the apices of the V's adjacent to each other. Elements 1 and 4 and 2 and 3 are connected together through time-delay means comprising inductances'7, 8 and capacitors 9. The feeder 10 is connected to the elements 1, 2, through a matching circuit consisting of units 11, 12, 13. The length of the elements 1, 2, 3, 4 may be a quarter of a wavelength (or an odd multiple thereof) at the lowest frequency. Instead of employing lumped impedances in the delay means a length. of transmission line, provided with short-circuiting stubs as necessary, may be used (Fig. 6, not shown). To increase the bandwidth of the aerial the elements 1, 2, 3 and 4 may be coupled at their outer ends to similarly disposed additional elements la, 2a, 3a and 4a connected together in pairs through resistors 16 and 17 equal to the characteristic impedance of the elements. The resistors may be omitted and replaced by direct connections though this results in some sacrifice in bandwidth. In an aerial consisting of two unipoles 1 and 3 (Fig. 9) the time delay means is inserted between them and artificial earths 23 and 24 of suitable lengths for frequencies in the two bands provided. The coaxial feeder is connected between element 1 and the artificial earths 23, 24. |
