GB2062968A

GB2062968A - Improvements in or relating to antennae

Info

Publication number: GB2062968A
Application number: GB7933620A
Authority: GB
Original assignee: SENSONICS Ltd
Current assignee: SENSONICS Ltd
Priority date: 1979-09-27
Filing date: 1979-09-27
Publication date: 1981-05-28

Abstract

A receiving or transmitting antenna is made of individual conductors 10 each of such a length as not to resonate when excited by a signal within a broad band of operating frequencies. In the transmitting mode, each conductor 10 is driven by a respective amplifier 14 receiving a control signal from the centre of the loop antenna. In the receiving mode, each individual conductor drives a respective amplifier, the amplifiers having a common output. <IMAGE>

Description

SPECIFICATION Improvements in or relating to antennae The present invention relates to receiving and transmitting antennae and relates in particular to antenna for the transmission of radio waves in radar and telecommunications.

The invention seeks to provide an antennae which is suitable for transmitting or receiving broad band signals but which is non-resonant at any of the frequencies within its frequency range of transmission or reception.

In accordance with a first aspect of the present invention, there is provided a transmitting antenna which comprises a plurality of conductors each of such a length as not to resonate when excited by a signal of frequency within a predetermined broad band of operating frequencies, and a plurality of amplifiers each drive operative to drive current in a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient transmission of the frequencies within the said broad band. By this it is meant that the radiation resistance should be at least comparable with the reactance of the radiator.

In accordance with a second aspect of the present invention, there is provided a receiving antenna which comprises a plurality of conductors each of such a length as not to resonate when excited by a signal of a frequency within a predetermined broad band of operating frequencies and a plurality of amplifiers providing a common output and each driven by a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient reception of the frequencies within the said broad band.

With the aid of the present invention, the conductor elements may be arranged so as to approximate to an ideal current distribution for efficiency and/or directivity.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a circuit diagram of a transmitting antenna in accordance with the present invention.

The accompanying drawing shows a circular loop transmitting antenna for the transmission of frequencies in the VHF band. The loop antenna consists of thirty-two linear conductors 10 of which, for convenience, only four have been illustrated in the accompanying drawing, it being understood that the interconnections between the conductors as described below being identical for all thirty-two conductors. The clockwise end 12 of each conductor 10 is connected to the drain of a field effect transistor 14which may, for example, bySiliconixVMOStype VN88AFfield effect transistor. The source of the transistor 14 is connected by way of a capacitor 16 to the anti-clockwise end of the next succeeding conductor 10.In this way, a continuous AC current path is formed driven at intervals corresponding to the length of the conductors 10, which may, for exam ple, be 100 mm. Power is fed at approxomately 50 volts from the centre of the circle to the anticlockwise ends of the conductors and 0 volts is applied to the sources of the field effect transistors from the centre of the circle. The currents in the radial conductors serve to maintain the charge on the interconductorcapacitors 16. Signal pulses are also fed from the centre of the loop to the gates of the field effect transistors, thus operating the transistors simultaneously. The result is a pulsed, uniform ring of current containing frequencies up to 300 MHz.

If desired, a set of capacitors may be connected between the positive power feed to each conductor and the zero line to its own FET, as shown in dotted lines by the field effect transistor 18. The transistors 18 would allow small differences between the currents driven by each transistor to avoid possible disturbances. The capacitors 18 should, however, be small compared with the interconductor capacitors 16 since they represent a reverse current and therefore tend to reduce the efficiency of the transmitter.

The current distribution obtained by the antenna described above could not be obtained byfeeding a loop from a single point on its circumference and would be less well controlled if the output power were fed from a single amplifier at the centre of the circle.

1. A transmitting antenna which comprises a plurality of conductors each of such a length as not to resonate when excited by a signal of a frequency within a predetermined broad band of operating frequencies, and a plurality of amplifiers each drive operative to drive current in a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient transmission of the frequencies within the said broad band.

2. A receiving antenna which comprises a plural ity of conductors each of such a length as not to resonate when excited by a signal of a frequency within a predetermined broad band of operating frequencies and a plurality of amplifiers providing a common output and each driven by a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient reception of the frequencies within the said broad band.

3. An antenna constructed and as shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to antennae The present invention relates to receiving and transmitting antennae and relates in particular to antenna for the transmission of radio waves in radar and telecommunications. The invention seeks to provide an antennae which is suitable for transmitting or receiving broad band signals but which is non-resonant at any of the frequencies within its frequency range of transmission or reception. In accordance with a first aspect of the present invention, there is provided a transmitting antenna which comprises a plurality of conductors each of such a length as not to resonate when excited by a signal of frequency within a predetermined broad band of operating frequencies, and a plurality of amplifiers each drive operative to drive current in a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient transmission of the frequencies within the said broad band. By this it is meant that the radiation resistance should be at least comparable with the reactance of the radiator. In accordance with a second aspect of the present invention, there is provided a receiving antenna which comprises a plurality of conductors each of such a length as not to resonate when excited by a signal of a frequency within a predetermined broad band of operating frequencies and a plurality of amplifiers providing a common output and each driven by a respective one of the conductors, the conductors being arranged such that the dimensions of the complete antenna array allow efficient reception of the frequencies within the said broad band. With the aid of the present invention, the conductor elements may be arranged so as to approximate to an ideal current distribution for efficiency and/or directivity. The invention will now be described further, by way of example, with reference to the accompanying drawing which is a circuit diagram of a transmitting antenna in accordance with the present invention. The accompanying drawing shows a circular loop transmitting antenna for the transmission of frequencies in the VHF band. The loop antenna consists of thirty-two linear conductors 10 of which, for convenience, only four have been illustrated in the accompanying drawing, it being understood that the interconnections between the conductors as described below being identical for all thirty-two conductors. The clockwise end 12 of each conductor 10 is connected to the drain of a field effect transistor 14which may, for example, bySiliconixVMOStype VN88AFfield effect transistor. The source of the transistor 14 is connected by way of a capacitor 16 to the anti-clockwise end of the next succeeding conductor 10.In this way, a continuous AC current path is formed driven at intervals corresponding to the length of the conductors 10, which may, for exam ple, be 100 mm. Power is fed at approxomately 50 volts from the centre of the circle to the anticlockwise ends of the conductors and 0 volts is applied to the sources of the field effect transistors from the centre of the circle. The currents in the radial conductors serve to maintain the charge on the interconductorcapacitors 16. Signal pulses are also fed from the centre of the loop to the gates of the field effect transistors, thus operating the transistors simultaneously. The result is a pulsed, uniform ring of current containing frequencies up to 300 MHz. If desired, a set of capacitors may be connected between the positive power feed to each conductor and the zero line to its own FET, as shown in dotted lines by the field effect transistor 18. The transistors 18 would allow small differences between the currents driven by each transistor to avoid possible disturbances. The capacitors 18 should, however, be small compared with the interconductor capacitors 16 since they represent a reverse current and therefore tend to reduce the efficiency of the transmitter. The current distribution obtained by the antenna described above could not be obtained byfeeding a loop from a single point on its circumference and would be less well controlled if the output power were fed from a single amplifier at the centre of the circle. CLAIMS

3. An antenna constructed and as shown in the accompanying drawing.