GB692692A - Improvements in and relating to radio aerials - Google Patents

Abstract

692,692. Aerials; aerial coupling arrangements. HEATHCOTE, C.A.V. Dec. 13, 1948 [Dec. 24, 1947], No. 34137/47. Classes 40 (v) and 40 (vii). Relates to aerial systems comprising an elongated loop aerial element of the folded dipole type and a coupling circuit, the system being tunable over a wide range of frequencies or to a number of spot frequencies or narrower frequency bands within said wide range and the impedance presented to the coupling circuit by the aerial being substantially resistive at the operational frequencies within said wide range. It is stated that when the unfolded length of the aerial element is #f/2 where #f is the wavelength corresponding to a " fundamental " frequency f then the aerial resonates at frequencies f and 2f and is operable at any frequency between f and 3f with a loss not exceeding 3db and that if the loop is open circuited at a point opposite the feed point, Fig. 4, then the aerial is operable within the same limits of efficiency at frequency f and at any frequency between 3f and 5f, the radiation pattern in all cases being similar to that of a conventional #/2 dipole; at frequencies outside these limits the efficiency is reduced and at frequencies higher than 5f a multi-lobe radiation pattern is produced. If a switch 8, Fig. 4, is provided in the gap, the aerial may be operated in either of the above conditions. The lower resonance frequency is decreased by increasing the separation between the two longer sides of the loop but the upper resonance frequency is less critical in this respect. Coupling circuits. One suitable coupling is shown in Fig. 4 in which a rectangular loop 1 is connected by a feeder 4 to a tunable circuit 12, 13 inductively coupled by a loop 14 to the transmitter or receiver, ganged variable condensers 10 and 11 being inserted in the feeder leads; alternatively a variable condenser may be connected between the feeder lines, Fig. 41 (not shown), or a split-stator condenser with an earthed centre plate may be inserted in inductance 13, Fig. 42 (not shown). In a modification, Fig. 5 (not shown), the feeder leads are adjustably tapped into the coil 13 and the ends of the coil may be adjustably shorted. Inductance may also be inserted in series with each feeder lead, e.g. as in Fig. 41 (not shown), or between condensers 10 and 11. For operation at high frequencies the coupling circuit may be simplified by making the feeder 4 adjustable in length. Any of the variable components may be replaced by switched or selectable plug in components for operation at spot frequencies or alternatively a plurality of switched matching stubs may be employed, Fig. 13 (not shown). Aerial elements, Figs. 7-12, 14-17, 27-32, 34-39, 40, 43 and 44 (not shown). The shape of the elongated loop element need not be rectangular, e.g. the ends may be rounded or pointed, Figs. 7 and 8, the spacing between the sides may be greater or less at the ends than at the centre, Figs. 34-36 and Figs. 9-12, the ends may be turned down or folded to conserve space, Figs. 39 and 40, the aerial conductor may be folded to form a plurality of co-planar or spaced parallel loops, Figs. 37-38 and 27-32. The power handling capacity of the aerial element may be increased by increasing the thickness of the aerial conductor and when a tubular conductor is employed the feeder may pass through a portion of the tubing Figs. 14-17. Any of the above forms of aerial elements shown as continuous loops may be gapped and in such cases a gap switch may be provided as in Fig. 4. The lowest operating frequency of the system may be reduced by loading the loop element by inserting a lumped parasitic loop element on either side, each parasitic element, Fig. 25, having an associated stub with a plurality of shorting bars which are selectively rendered operative by relays in accordance with the required frequency of operation; the stub may be replaced by an adjustable circuit. Specifications 528,817 and 588,044 are referred to.