Communications: radio wave antennas – Antennas – High frequency type loops
Patent
1987-11-27
1990-05-01
Hille, Rolf
Communications: radio wave antennas
Antennas
High frequency type loops
343867, 340572, H01Q 152, H01Q 700
Patent
active
049222619
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to aerial systems and more particularly to aerial systems operating in the induction communication range and comprising at least one receive and transmit aerial pair. The aerial pair may be used in presence sensing or identification systems employing transponders or tags, such as those described in the following patents: G.B. Pat. Nos. 2017454B, 2077556 and 2102250.
A problem with receive/transmit aerial pairs, especially when the aerials of the pair are relatively closely positioned and operating at similar frequencies, is that mutual interference or interaction occurs.
One solution which has been proposed is to screen the receive aerial from the transmitted field. In certain instances, however, screening is not practical or is ineffective.
Another proposed solution to this problem is to arrange the transmitted aerial so that the electric and magnetic components of the transmitted field are orthogonal with respect to the respective components at the receive aerial. However, this solution cannot be applied where the effective axes of the transmit and receive aerials are constrained. This solution may also be inappropriate where a system comprises two aerial pairs. If two pairs are employed with the aerials within each pair being mutually orthogonal but with the pairs having a random orientation with respect to each other, the range of possible resultant combinations of orientations between the two pairs causes complex problems. In a transponder or tag communication system, for example, the deviation from the optimum value of the signal from the control equipment to the tag may permit activation of the tag without being able to detect its response. Such a system might comprise a small hand-held transponder and control equipment with a fixed reading head comprising a receive and transmit aerial pair. The net effect of such a configuration is to reduce the average range performance of the system.
One particular solution is proposed in U.S. Pat. No. 2,779,908, in which the coupling between the transmitting and receiving coils of an inductive train identification system is reduced by a short-circuited neutralizing coil. However, certain limitations are still imposed on the physical relationship between the coils.
SUMMARY OF THE INVENTION
The present invention seeks to overcome or reduce one or more of the above-mentioned disadvantages.
According to the present invention there is provided an aerial array comprising transmit and receive aerial coil means, a signal transmitted by the transmit aerial coil means being received by the receive aerial coil means, and means for cancelling the effect of the transmitted signal, characterised in that one of the aerial coil means comprises a first part which is relatively close to and closely mutually inductively coupled with the other aerial coil means and a second part which is relatively remote from the other aerial coil means, said first part constituting said cancelling means, whereby the transmitted signal is substantially cancelled by a signal generated by the mutually inductive coupling between said first part and said other aerial means.
An advantage of the above array is that cancellation of the interference signal is achieved whilst still permitting sufficient interaction with a relatively distant transmit/receive system. A further advantage is that by enabling the planes of the receive and transmit aerials to be parallel, rotation of the aerial pair out of its optimal orientation would degrade the performance of the transmit and receive paths by an equal amount. Such an arrangement also permits a compact aerial pair to be provided, since the aerials do not need to be mutually inclined.
The aerials are preferably substantially coplanar and may also be substantially co-axial.
The interaction-cancelling means reduces the interference from the transmit aerial by the introduction into the receive aerial of a second signal which is similar in amplitude but opposite in phase to that which is introduced by th
REFERENCES:
patent: 2597518 (1952-05-01), Parks
patent: 2779908 (1957-01-01), Martin
patent: 4633250 (1986-12-01), Anderson
Cotag International Ltd.
Hille Rolf
Wimer Michael C.
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