GB1153199A - Transponder Array - Google Patents

Abstract

1,153,199. Aerials; acoustic transponder; transponder apparatus. R. BENJAMIN. 13 Sept., 1967 [17 Sept., 1966], No. 41612/66. Headings H4A, H4D and H4L. In a transponder array designed to give directional replies in response to received signals, a number of transponder elements are disposed about a common origin O, Fig. 1b. Each comprises a receiving transducer R, cable L as necessary to equalize in each the total cable length and consequently the line transmission time, an amplifier A, and a retransmitting transducer T. In each transponder element the transducers R and L have the same relative angular relationship with respect to the origin O. When a plane wave from a distant source passes through the array, a plane wave moving in a pre-determined direction, e.g. the opposite direction, is set up, the two waves meeting at the origin O. In order to prevent the reflected wave affecting the receiving transducers, a suitable additional delay is introduced in each transponder element, i.e. to exceed the largest signal duration to be handled, and the repeater action is blockd for a similar period following acceptance and re-transmission of an incoming signal. In an alternative arrangement, in which the two transducers of each transponder element are equally and oppositely spaced from the common echo origin, each transducer has the same limited arc of coverage and is used both for transmission and reception, a hybrid transformer separating the two directions of signal flow in the element. In other embodiments transducers may be uniformly distributed within a sphere (Fig. 2, not shown) or within a spherical shell (Figs. 3a,, 3b, not shown) or within a circular disc (Fig. 4a, not shown). An embodiment is also described in which the receiving transducers R 1 . . . R 5 , Fig. 5, of the transponder elements are disposed along a first line from the origin O and the re-transmitting transducers T 1 . . . T 5 are disposed along a second line from the origin O which is at an angle # to the first line. In this case, the direction of a reply signal from the array is at an angle # to an interrogation signal. The transponder elements may comprise modulation means so that the reply signals are characteristically coded. Means are also described whereby a scanning effect may be obtained by introducing into each transponder element a delay device which is variable by an amount proportional to the distance of the receiving transducer from the origin and then cyclically varying all the delay devices. One array of this kind may be constructed for acoustic waves and another for electromagnetic waves, or an array may be arranged to receive one kind of wave and re-transmit another kind. Possible applications which are indicated include, navigational or indentification beacons, echo-enhancing or identifying transponders, signalling to or from mobile stations, including communications satellites and on-demand directional release of stored messages.