Transponders
First Claim
1. A transponder comprising an array of antennas interconnected in pairs by means of transmission lines arranged in a connection pattern in which each of the pairs comprises two antennas positioned symmetrically with respect to the centre point of the array so as to render the array retro-reflective in two dimensions at least some of said transmission lines being of a different length to the remainder and wherein all of the transmission lines pass from one antenna of a pair to the other antenna of the pair without crossing over any other of said transmission lines.
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Accused Products
Abstract
A transponder comprises a retro-reflective antenna array in which the length of the transmission lines is given by I=±A nλ where: A is an arbitrary length; n is zero, or an integer, λ is the wavelength of the retro-reflected signal. The array is fabricated on a board (71) of insulating material, using microstrip techniques. Rectangular patches (not shown) form the individual antennae and these are interconnected by transmission lines (75 to 82), each of which pass through a respective modulation device (43) whereby the retro-reflected signal is modulated. A positioning/tracking system incorporating one or more modulated transponders is also disclosed.
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Citations
30 Claims
- 1. A transponder comprising an array of antennas interconnected in pairs by means of transmission lines arranged in a connection pattern in which each of the pairs comprises two antennas positioned symmetrically with respect to the centre point of the array so as to render the array retro-reflective in two dimensions at least some of said transmission lines being of a different length to the remainder and wherein all of the transmission lines pass from one antenna of a pair to the other antenna of the pair without crossing over any other of said transmission lines.
- 23. A positioning/tracking system for fixed or movable objects, said system comprising at least one modulated transponder, a transmitter for transmitting a signal to illuminate the or each transponder, a receiver for receiving the retro-reflected signal from the transponder or transponders and discriminator means within the receiver for demodulating the modulated signal from the transponder or transponders to enable a wanted reflected signal to be identified, wherein the transmitter includes means for sweeping its transmitted output frequency.
Specification