GB2288914A - Radio antenna - Google Patents

Abstract

A radio antenna comprises a three wire transmission line (1) and a reactive terminating circuit (2), which may comprise an inductor (3) and capacitor (4). The length of the transmission line can be chosen to suit the site. The antenna will radiate with a length as short as 6% of the wave. Phasing unit (5) is used to separate the power into two equal parts and connect each part onto the two active conductors, one path from the split point (6) going via the variable delay line (7) and the other path taking the other part-power via a phase advance circuit which is the capacitor (8). The phase control components are adjustable so that any chosen length of antenna can be operated at a wide range of frequencies. The antenna may alternatively take the form of a balanced radiator with a centre feed or a two wire loop. <IMAGE>

Description

TITLE Radio Antennas This invention relates to antennas for the transmission and reception of radio waves for teledommunications, broadcasting sound and television, data, radio navigation and radar, satellite communications and the like. More particularly this invention relates to an electromagnetic delay line radiator or antenna abbreviated herein to "EMDR".

Antennas usually have a single feeder connected to either a single conductor of approximately half a wavelength, or a quarter wavelength above a ground plane itself half a wavelength or larger in diameter. Other presently known antennas are usually half wavelength dipoles held at the focus of a dish reflector, or supported within a group of parasitic such cqnductors, constituting a Yagi-Uda array. Sometimes by means of added components such as inductors, end-capacitors, resonant traps and suchlike devices, antennas can be constructed with somewhat smaller dimensions that the half wave element. However most presently known antennas which are made physically small, have either been disappointing in efficiency or in bandwidth or both, due to the necessarily increased circulating currents which high Q reactive devices cause. In GB 2215524 there is disclosed a system for synthesis of electromagnetic waves using two separate element systems.

According to this invention there is provided a radio antenna which is both electrically small and also efficient and comparatively wide band, both in instantaneous and total working bandwidth including adjustments. Given that a radio wave is, according to presently accepted theory, an electro-magnetic wave, then this invention enables the user to radiate from a very compact device called the Electromagnetic Delay-line Radiator (EMDR) by generating two separate fields, one a radio frequency electric field, and the other the corresponding RF magnetic field. Half the transmit power is allocated to the creation of the electric field, and half to the magnetic field. The two parts are carefully synchronised and made to cross at right angles when colocated, so that in the small volume of space surrounding the antenna, wave synthesis occurs according to the Poynting Theorem, and the total energy radiates as a radio wave at the velocity of light.

Broadly this invention provides also a radio antenna with a radiator comprising a three wire insulated conductor cable carrying on two independent circuits1 two separate currents of a radio frequency desired to be radiated, phased to fulfil the requirements of the generation of a radiating wave system, using a part of the transmitter power for stimulation of the electric field and the remainder for the magnetic field.

The Poynting Vector theorem states that where geometrically orthogonal electric and magnetic fields are simultaneously applied, energy is developed from the cross product of the two separate fields. When published in 1884 at the Royal Society, Professor George Poynting showed that this theory explained all the then known electrical energy transfer phenomena. His work, possibly, giving additional substantiation to the suggestion made earlier by James Clerk Maxwell that there might be invisible electromagnetic waves of wavelengths much longer than those known at the middle of the nineteenth century, and Poynting's paper no doubt encouraged Helmholtz to set his research student Heinrich Hertz on a quest resulting in the discovery of radio waves in 1887.

Writing the Poynting theorem in vector mathematics, the power density S watts per square metre is calculated as the cross product of the Electric field in volts per metre with the Magnetic field in amp-turns per metre, i.e.

S=EXH The perpendicular geometric relationship and the time synchronism implied by the above formula having been found to be critical to the success of the method as disclosed in GB patent 2,215,524B. As background information it should be noted that in general, any single conductor radio frequency circuit working into a reactance has a 90 degree phase difference between current and voltage.

This is because there are zero degrees difference between current and magnetic field, but by Faraday's Law of Magnetic induction, there must be a 90 degree relationship between magnetic field and the resulting induced EMF.

Thus transformers have voltage maximum at the moment when the magnetic field is crossing zero. Consequently and in normal single conductor aerials, the voltage maximum and magnetic field maximum occur at different times (90 degrees of phase) in the same place; or in different places on the antenna at the same time. It is a working principle of the Electromagnetic Delay-line Radiator that the said Poynting Vector requirements are achieved by design. The half of the power that is going to be used to initiate the electric field is advanced 45 degrees in phase so that it may correctly interact with the magnetic field deliberately delayed in phase by the same angle.

The electric field arises from the charge maximum stored on the working region of the phase advance conductor, and the magnetic field from the delayed current conductor being at zero with rising gradient. Thus throughout the comparatively short interaction zone there is the best possible situation for the acceleration of the charge, and consequent generation of an electromagnetic wave and power radiation; ref Feynman "Lectures on Physics" Vol II p 21-10. Both circuits carrying the stimulating currents supply energy to the departing waves, and develop a resistive load impedance within. The third conductor is used to pass the resultant net current at some uncertain phase, back to the system earth reference.

This invention is further described and illustrated with reference to the drawings showing embodiments as examples.

Referring to the drawings, Figure 1 shows the construction of a basic EMDR antenna. It consists of a three-wire transmission line (1) made of low-loss materials, and a reactive terminating circuit (2), which can be constructed by a variety of components, but shown here by way of detail as an inductor (3) and capacitor (4). The length of the transmission line can be chosen by the user to suit the restrictions of the site from which it is desired to operate the radio station. The antenna will radiate with the length of the EMDA as short as 6% of the wave, though the shorter the actual length compared with the wavelength to be radiated, the more is the magnitude of the circulating currents and standing wave voltages on the line when working. The phasing unit (5) is used to separate the power into two equal parts and connect each part onto the two active conductors. One path from the split point (6) going to a phase delay circuit via the variable delay line (7) and the other path taking the other part-power via a phase advance circuit which is the capacitor (8). The phase control components are made adjustable so that any chosen length of EMDR can be operated at a wide range of frequencies. When the device is correctly adjusted, the input socket (9) will develop a resistive input impedance which can be made to match the transmitter output impedance, or feeder impedance.

The Electromagnetic Delay-line Radiator may be supported almost anywhere, because the radiation occurs from the whole length. Ideally the antenna could be best used held high up and in the open, but it is a virtue of the device that the working voltages along it are comparatively modest, that is compared with the voltages on conventional wire antennas which require to have standing wave systems of Q typically 10 upon them in order to radiate effectively. How the action takes place may be explained in detail with reference to the Figure 2 which shows an EMDR which is about 1/8 of a wavelength long. The left hand active conductor (10) carries current which is 45 degree phase advanced current, shown for illustrative purposes as arrows along the wire. The right hand active conductor (11) has at this moment a distribution of electric charge which is 45 degrees phase delayed and at the moment shown is at -5V to -3V. The centre conductor (12) acts to return the net current of indeterminate phase back from the other two conductors, and conveys it back to the earthed metallic container of the phasing unit. The circling magnetic field lines (H) stimulated by the current on wire (10) pass the front of the delay line right to left. The negative voltage on the wire (11) causes a widely distributed electric field E curving upwards from the surroundings (and the ground) to the wire (11). There are some other reactive fields (such as between itself and the centre conductor) but these cannot convert to radiated wave energy since they do not have the exact 90 degree phase relationship necessary.

The rising curving electric field lines everywhere cross the circling magnetic field lines, and at every crossing point originate a cross-product S shown at four points by way of illustration here, all directed away from the EMDR and constitute a sheath of radiation which moves away from the whole delay line in all directions taking the power to space as a continuously expanding system of wave fronts with vertical polarisation as in the far field of a conventional vertical quarter wave antenna. The action is sustained by the continuing supply of correctly out of phase energy placed on the two active wires by the phasing unit, and maintained by the reactive termination which stores and returns the unused energy moment by moment throughout the radio frequency cycle so that apart from a small part lost in resistive, dielectric and iron loss, almost the whole power is radiated.

In contrast, a conventional feeder does not radiate because it only has two conductors, and so the currents cannot be adjusted to lie upon it out of phase.

Figure 3 shows a group of possible termination circuits. The Figure 3a shows a transformer (13) used to provide the capacitor with a reduced, or increased, antiphase termination voltage coupled from the other active conductor. The Figure 3b shows the transformer modified to be an auto transformer 114). The figure 3c shows the use of a capacitive auto-transformer, capacitors (15) and (16), and the replacement of the other reactive component by an inductor (17). This selection is not necessarily complete but merely representative.

Figure 4 shows a balanced form of Electromagnetic Delay-line Radiator. It consists of a central insulated conductor wire (18), within a tube (19), fed through a hole at the centre by a transformer (20), having a secondary winding (21), and primary (22), the whole being placed at the centre of two long conducting cylinders (23) and (24), themselves insulated and fed at the inner ends by transformer (25) which has a centre tap so that the voltage occurring at the delayed terminal (26) of the phasing unit (27) is presented equally as a plus and a minus voltage on the said long cylinders. There are two terminating circuits (28) and (29), which are made with two or three reactive components each and are here shown with a pair of differing forms, corresponding to Figures 3b and 3c.

Figure 5 shows a fully developed manually operated Phasing Unit, with an input transformer (30) which allows the user to select the optimum ratio of voltage applied to either the advance circuit or the delay circuit. The advance is as before shown, a variable capacitor (31) but the delay is a tapped delay line, or inductor, (32) which if constructed on a 16, 8, 4, 2, 1. 2 41, metres basis, gives a sufficiently fine selection for operation at any frequency on the HF band.

Figure 6b shows a form of delay-line antenna which is reduced to be just a two wire loop since the return current is taken to earth by separate or combined returns.

The advanced current source 34 feeds the anticlockwise conductor 35 which is terminated in the inductor 36. The delayed current source 37 feeds the clockwise conductor 38 which lies parallel to the said conductor 35 but insulated from it, and terminates in a capacitor 39. The close presence of the two current carrying conductors constitutes an interaction zone all around the loop from which radio waves radiate by Poynting Vector synthesis.

The size of the loop can be smaller than 1% of a wavelength in diameter and vigorous radiation will be produced when the sources are adjusted to the correct phase relationship and magnitude of a general crossed field antenna. The earth return paths can be short connections if te loop and its phasing unit are close, or separate coaxial Cables back to a more distant phase adjuster placed down near the transmitter.

Figure 6a shows a form of double trombone adjustable delay line which would be suitable for an EMDR to be operated at VHF or UHF.

Figure 7 shows in outline, an automatic system for setting the correct phase. The block SWR is a directional power meter, and PSD is a Phase Sensitive Detector, and FF is a microprocessor which is programmed to drive the controlling motors M which drive the adjustable compcnents.

To summarise: the operation of the EMDR is based on the principle of Poynting Vector Synthesis, by which a radio wave is created in a very compact delay-line carrying two currents of differing phase stimulating two different fields which cross each other at right angles in the close environment which constitutes an interaction zone and form a freely expanding radio wave and by that process causing the sources to experience lowered resistive impedances and draw considerable power from the transmitting source.

By contrast, a single wire antenna is unable to generate radio waves close to itself because the electric and magnetic fields follow one another at a quarter of a cycle time difference and the two fields are never colocated and in synchronism. The fields which are stimulated are induction fields which remain trapped and merely stimulate and return their energy to the wire quarter cycle by quarter cycle.

Experiments at MF, HF and VHF have been performed on prototypes. For example in one practical system an EMDR of 8.5 metres length hung at less than 6 metres height was fed from a 100 watt transceiver which covered the whole of the HF band, and resistive load impedance was created at 1.8, 3.6, 7.0, 10.1, 14.1, 18.1, 21.1, 24.9 and 28.5 MHz.

Two way communication was established with radio stations around Europe and into Asia and America depending upon the propagation conditions. The received signals were low in noise, although in comparison to the magnitudes of signals that might have been expected on half wave antennas at the lower frequency bands, so that with a low noise modern receiver, good two-way communication could be obtained.

The voltages measured on the outside of the EMDR were low in comparison to those that would have been present on a conventional wire antenna radiating such powers, and therefore the EMDR has additional advantages in terms of safety and immunity to disturbance by the proximity of non-conducting or conducting structures. Considering that the EMDR occupies such a small space, there was a considerable saving in site area.

A loop delay line of the type shown in Figure 6 constructed in a 0.5 square metre was used to transmit and receive at 1.8 to 30MHz i.e. wavelengths from 160 to 10 metres. Supported horizontally the EMDR loop radiates horizontally polarised signals in all azimuthal directions with nulls above and below.

An application for which the EMDR might be ideal is in the testing of equipment for EMC resistance. Under the European Community, rules have been drafted to improve the electromagnetic compatibility (EMC) of electrical and electronic equipment. In particular the test of equipment's resistance to swamping by electromagnetic waves has been difficult to perform. It is impossible to simulate within a practical test chamber of reasonable size and cost, the effect of real EM waves, since conventional aerials are so large. Placing equipment under test close to conventional antennas or, even worse, reduced dimension conventional antennas, will subject the said equipment to high intensity fields (separately electric and magnetic or one or the other) but not genuine radio waves. Certainly it is likely that the screening arrangements of a receiver are much more likely to be passed by a high density induction field plus unknown radiation field such as that coming from a high Q loop, or high voltage plate, than that from a real radio wave containing the two components in proper unity and proportion. It is possible that equipment may be condemned or time wasted over engineering precautions when tested by such crude methods. An EMDR could easily be made for operation over a wide band of frequencies small enough to fit inside such a chamber and to provide a realistic simulation of RF swamping and the equipment's resistance thereto.

Claims (35)

1. A radiator comprising a three wire insulated conductor cable carrying on two independent circuits, two separate currents of a radio frequency desired to be radiated, phased to fulfil the requirements of the generation of a radiating wave system, using a part of the transmitter power for stimulation of the electric field and the remainder for the magnetic field.

2. A radiator according to Claim 1, including a phase adjustment circuit within which the power to be radiated by the cable can be divided into two parts and these parts separately advanced and delayed under manual control.

3. A radiator according to Claim 1, including a phase adjustment circuit which will divide the power to be radiated by the cable into two parts separately advanced and delayed under automatic control.

4. A radiator according to Claim 1, including a phase delay and advance circuit that is preset so that a user is able to operate the delay line radiator at a fixed frequency.

5. A radiator according to any preceding claim, including a termination circuit comprising a capacitor and an inductor to terminate the delay line radiator so that the said separate currents are maintained out of phase whilst being added together and returned to earth.

6. A radiator according to Claim 5, including a termination circuit comprising a capacitor and a transformer to terminate the delay line radiator.

7. A radiator according to Claim 5 including a termination circuit comprising a resistor and capacitor and resistor and inductor with which to terminate the delay line.

8. A radiator according to Claim 5 including a termination circuit comprising a resistor in circuit with a transformer with which to terminate the delay line radiator.

9. A balanced delay line radiator in which the fields are applied to oppositely directed triple conductors fed from a pair of phase splitter transformers so that oppositely directed separately phased currents may be adjusted to cause balanced radiation from an antenna.

10. A balanced delay line radiator as claimed in Claim 9 in which the triple conductors are a pair of tubes, and a wire conductor.

11. A balanced delay line radiator as claimed in Claim 9 in which the triple conductors are a pair of wires and a single tube.

12. A three wire delay line radiator in which the conductors are widely spaced so that the effective inductance per metre is increased and the physical length reduced below 5% of a wave.

13. A two wire loop radiator in which the advanced and delayed currents flow past each other in opposite directions with the termination components necessary to maintain the phase difference located close to the double current feed point of a loop arrangement to reduce the dimensions.

14. A two wire loop radiator according to Claim 13, in which contra-flowing currents complete more than one revolution of the loop.

15. A two wire loop radiator according to Claim 13 in which contra-flowing currents are arranged so that one of the wires completes an odd number of turns, and the other wire completes an even number of turns.

16. A loop according to Claims 13 or 14 or 15 having an even number of wires in which one or more switches are used to change the number of revolutions travelled by one or both of the phase separate currents.

17. A two wire loop according to Claim 13 carrying currents in contra-rotation and which is constructed of coaxial cable.

18. A contra-wound two wire loop according to Claims 13 to 17 which has three feed conductors from a phasing adjustment device extending for a considerable length and comprising either a three wire low loss feeder, or a pair of separate coaxial cables.

19. A delay line radiator or loop in accordance with Claims 1 to 18 in which the advance and delay is obtained by using feeder cables of either the triple wire type or the coaxial cable type in which the advance and delay is arranged by means of a fixed capacitor and a cut length of feeder.

20. A delay line radiator or loop in accordance with any one of Claims 1 to 19 in which the feed device is a hybrid transformer with appropriate capacitors to cause the opposite exit ports to take on approximately orthogonal phase relationships required for the said radiators to achieve wave synthesis.

21. A delay line radiator in accordance with any one of Claims 1 to 19 in which some or all of the feed phase requirement is achieved by using a balanced transformer.

22. A delay line radiator or loop in accordance with any one of Claims 1 to 19 in which the construction consists of etched copper conductors on single or double sided printed circuit board.

23. A delay line radiator or loop in accordance with any one of Claims 1 to 22 in which a second such device of any kind is also fed with energy from the transmitter in order to provide radiation of mixed polarisation.

24. A delay line radiator or loop in accordance with any one of Claims 1 to 17 in which a second or third or any number of additional antenna devices of any kind are fed with radio frequency power at the original frequency in order to cause a particular radiation pattern or enhancement of directionality.

25. A delay line radiator or loop in accordance with any preceding claim fed with RF power and placed in close proximity with other such devices so that currents are induced thereinto for the purpose of forming a particular pattern of resultant radiation.

26. A delay line radiator or loop in accordance with any preceding claim with currents flowing in differing amounts of proximity in different parts of their circulation so that they produce enhanced directivity in some directions.

27. A delay line radiator or loop in accordance with any preceding claim with switches so that the loop can be configured either to have a single or double or more pairs of contra flowing conductor.

28. A delay line radiator or loop in accordance with any preceding claim with switches to change the directivity of the resultant radiation by causing out of phase currents to interact at differing parts of the line or loop.

29. A delay line radiator or loop in accordance with any preceding claim with arrangements for mechanically moving conductors with flexible connections so that the mutually affecting currents can cause synthesis to occur in differing directions of radiation.

30. A delay line radiator or loop according to any preceding Claim 1 to 22 with lines or coils wound upon material of increased permeability such as iron dust cores or ferrite so that the length of the said radiating device may be reduced in size to a thousandth or ten thousandth part of a wavelength.

31. A delay line radiator in accordance with any preceding Claim 1 to 30 placed at the focus of a parabolic dish or other shaped reflector to improve the directivity of the said radiation.

32. A delay line radiator in accordance with any preceding claim used to radiate into media other than air or space.

33. A delay line radiator in accordance wit any preceding claim used to receive radio waves.

34. A radio antenna using Poynting Vector Synthesis, by which a radio wave is created in a very compact delay-line carrying two currents of differing phase stimulating two different fields which cross each other at right angles in the close environment which constitutes an interaction zone and form a freely expanding radio wave and by that process causing the sources to experience lowered resistive impedances and draw considerable power from the transmitting source.

35. A radio antenna system constructed and arranged to function as described herein and exemplified with particular reference to the drawings.