GB2166000A

GB2166000A - A system for transmission of high-frequency electromagnetic signals

Info

Publication number: GB2166000A
Application number: GB08524925A
Authority: GB
Inventors: Allan Northeved; Knud Chr Claus Fabrin
Original assignee: ELECTRONIC INDENTIFICATION SYS
Current assignee: ELECTRONIC INDENTIFICATION SYS
Priority date: 1984-10-24
Filing date: 1985-10-09
Publication date: 1986-04-23
Also published as: DK507584A; DK507584D0; JPS61116425A; DE3537319A1; SE8504933L; GB8524925D0; SE8504933D0; NL8502903A

Abstract

A system for transmitting high- frequency electromagnetic signals comprises a frame aerial of one or more turns in which one or more capacitors C' are disposed. The capacitors are symmetrically disposed with respect to the feed for the aerial which may include a quarter wave transformer or a balun. <IMAGE>

Description

SPECIFICATION A system for transmitting high-frequency, electromagnetic signals The invention relates to a system for transmitting high-frequency, electromagnetic signals and comprising a frame aerial with one or more windings.

The object of the invention is to show how the distant field from the frame aerial is minimized, and the system according to the invention is characterised by one or more capacitors being inserted on at least one of the windings, said capacitors substantially compensating for phase differencies from one end of the aerial to the opposite end. In this manner the potential voltage from one end to the other end is very low whereby the radiation (pointing vector) is correspondingly reduced.

The capacitor or the capacitors may advantageously be symmetrically situated with respect to the feeding points of the frame aerial in such a manner that the transmission line is symmetrically loaded. As a result the transmission line is not oscillating.

The number of capacitors may advantageously be adapted to the desired band width, as a greater number of capacitors causes a greater band width.

According to a particularly advantageous embodiment where the aerial comprises a square winding of an edge length of about 30 cm, a capacitor has been inserted in the winding, said capacitor being of about 45 pF corresponding to a resonance frequency of about 27 MHz.

The invention will be described more detailed below with reference to the accompanying drawing, in which Figure 1 illustrates a conventional frame aerial for receiving, Figure 2 illustrates a system according to the invention for transmitting high-frequency, electromagnetic signals, Figure 3 a second embodiment of the system, Figure 4 a third embodiment of the system, Figure 5 a quarter-wave adaptor to be inserted between the transmission line and the aerial, and Figure 6 a symmetric device to be placed in front of the aerial.

Fig. 1 illustrates a conventional frame aerial providing a distant field.

The system of Fig. 2 for transmitting highfrequency, electromagnetic waves comprises a square frame aerial 1 with one or more windings. The aerial is intended for a frequency of about 27 MHz and is in the preferred embodiment of an edge length of about 30 cm. According to the invention one or more capacitors have been inserted in the aerial in such a manner that the aerial is inresonance at the desired frequency. The capacitor C provides a positive phase displacement in such a manner that the phase difference from one end to the other end of the aerial is almost zero. In this manner substantially only reactive effect is radiated and no distant field is provided. The capacitors are preferably symmetrically situated relative to the feeding point 3 of the frame aerial so that the transmission line is loaded symmetrically as far as possible.In this manner it is possible to avoid an oscillating transmission line 4 provided the transmission line is symmetrically structured. Then the transmission line is unsymmetrically structured and for instance formed by a coaxial cable it is necessary furthermore to insert a balancing line (a balun), cf. Fig. 6.

A quarter-wave transformer, cf. Fig. 5, may be inserted between the transmission line and the aerial, said transformer providing the necessary impedance matching. The quarterwave transformer may be part of the transmission line, which is of a length of an uneven number of quarter wavelengths.

In the embodiment of Fig. 2 the system is of a radius of action of about 40 cm at a transmission effect of about 25 W. The inductance is of a value of about 800 nH and the capacitor is of a value of about 45 pF. In this manner the aerial is of a Qvalue of about 100 corresponding to an Ohmic resistance of about 1.5Q.

In the embodiment of Fig. 3 the capacitor C of Fig. 2 has been replaced by two symmetrically situated capacitors C', each capacitor C' having the double value, i.e. about 90 pF, whereby the resonance frequency is unchanged.

Fig. 4 illustrates an alternative embodiment with several windings.

The system according to the invention can be used both for transmitting and receiving and may for instance be used in connection with the detection system described in German Offenlegungsschrift No. 32 45 881. This system may for instance be used for providing statistical information on the behaviour of pigs. The system is formed by an electronic communication system, a sensor with a predetermined code number being secured to the ears of each pig. This sensor reacts each time the pig approaches a transmitter/receiver. The transmitter/receiver communicates with a central data processing system registering the signals received. It is possible, if desired, at the same time to register other parameter values such as the temperature of the pig in question.

Each transmitter/receiver comprises a function generator oscillating at a frequency of about 5 kHz and transmitting both a triangular wave signal and a pulse signal. The triangular wave signal is used for phase-modulating a HF-signal transmitted every 10 sec. through a coupling device and an aerial. A binary counter is activated simultaneously with the transmission of signals.

On the receiving side of the sensor the signal received is initially transmitted to an electronic relay in the form of a MOS transistor in turn energy-feeding the remaining circuits of the sensor. Subsequently the remaining circuits transfer the signal both to a second harmonic generator and to a phase detector. The phase detector produces a clock pulse signal corresponding to the triangular wave signal.

The clock pulse signal is transferred to a 12 bit binary counter, the counting being compared with a predetermined counting characteristic of the sensor. In case of identity a gate is opened for the second harmonic signal which is then transmitted through a transmitter aerial.

The signal transmitted by the sensor is received by the transmitter/receiver and transferred to a multiplier multiplying said signal with a second harmonic of the transmitted phase modulating signal generated in the transmitter/receiver. In case of identity the product is relatively high and a relatively high signal is transmitted, at a time corresponding in an unambigously manner to the predetermined counting within the sensor. This signal may for instance be used for stopping a counter activated at the beginning of the transmitting period, the stop counting corresponding to the code number. A particular advantage of this signal-recognizing technique is that it excludes irrelevant signals without complicating the circuit.

According to the invention a transmitting/receiving system of a short range has been provided, and the system makes no unnecessary noise on account of the short range.

The system according to the invention may be varied in many ways without thereby deviating from the scope of the invention. Inductances may optionally also be coupled in the frame aerial.

Claims

1. A system for transmitting or receiving high-frequency, electromagnetic signals and comprising a frame aerial with one or more windings and one or more capacitors in at least one of the windings, said capacitors substantially compensating for phase differences from one end of the aerial to the other end thereof.

2. A system as claimed in claim 1, wherein the capacitors are symmetrically arranged relative to the feeding points of the frame aerial.

3. A system as claimed in claim 1 or claim 2, wherein the number of capacitors is adapted to the desired band width.

4. A system as claimed in any one of claims 1 to 3, wherein the frame aerial comprises only one winding.

5. A system as claimed in claim 4, wherein the winding is square.

6. A system as claimed in claim 5, wherein the square winding has an edge length of about 30 cm.

7. A system as claimed in claim 6, wherein the capacitor has a capacitance of substantially 45 pF corresponding to a resonance frequency of substantially 27 MHz.

8. A system as claimed in any one of the preceding claims, which has a quarter-wave impedance matching between the transmission line and the frame aerial.

9. A system as claimed in any one of the preceding claims, wherein the transmission line is of a length corresponding to an uneven number of quarter wavelengths.

10. A transmission or receiving system and/ or an aerial substantially as described herein and with reference to the accompanying drawing.