US2393903A - Radio guiding system - Google Patents

Description

Jan. 29; 1946. J. HEATON-ARMSTRONG 2,393,903

RADIO GUIDING SYSTEM Filed June 24, 1943 2 Sheets -Shet 1 Inventor tau/J Jag //Am// A/msmoue I I" '7 Attorn 29, 1946. L. .LHEATON-ARMSTRONG 2,393,903

RADIO GUIDING SYSTEM Filed (June 24, 1943 2 Sheets-She et 2 I Inventor Lou/s ubmvgefAraw ARMJZ'RDNG Patented Jan. 29, 1946 RADIO GUIDING SYSTEM Louis John Keaton-Armstrong, London, England, assignor to Standard Telephones and Cables Limited, London. England, a British company Application June 24, 1943, Serial No. 492,081 In Great Britain July 30, 1942' 8 Claims. 250-11) The present invention relates. to a. radio beacon for radio guiding systems of the kind in which a field distribution or field strength pattern is commutated so as to produce. complementary sigmale, for example A-N signals to the right and left of the course respectively, and on the course a continuous dash or no-signal.

Hitherto radio beacons for systems of the type specified which have been largely employed comprise a central energised antenna and two reflector antennae laterally disposed with respect to the central antenna. The two reflector antennae are keyed alternately so as to cause the radiation pattern produced by the beacon to oscillate about the course line in a now well known manner. The great advantage of such a beacon is its simplicity. It i very easy to set up on a new frequency and alignment and tuning is not unduly difficult. The aerial spacing. is not changed over the frequency band from 30-40 megacycles per second.

Simplicity is, however, paid for by the following disadvantages:

l. The beam width cannot be made less than 2 whatever the reflector spacing. Modern con ditiogs call for a beam width of the order of .5 to 1.

2. Critically timed keying relays are necessary.

Careful lining u is necessary in order to avoid key clicks.

4. It is difiicult to get both back and front beams free from. key clicks.

5. The field distribution pattern is of such a shape that the likelihood of splits in the. beam due to reflectionsv from the hangars, trees, etc., is considerable.

The present invention. has. for its object to provide a radio guiding system in which all these disadvantages are absent whilst retaining simplicity of the system, and without introducing any further disadvantages.

According to one aspect of this invention. a radio beacon of the type hereinbefore specified comprises three antennae arranged at a distance apart and each fed directly from a source of high frequency currents phased with respect to each other and a single make" or break contact device for commutating the field strength pattern formed by said antennae.

According to another aspect of the present invention a radio beacon for a. radio guiding system of the kind specified hereinhefore. comprises three linear antennae mounted. above the ground and, symmetrically located with respect. to thedesired course, means for feeding the enter antennae with currents in opposite phases, and for feeding the centre antennae with currents of the same frequency and with a phase angle of degrees or less with respect to the current in either of the two outer antennae and means for changing the relative phases of the centre and outer antennae from a phase lead to a phase la or vice versa to produce the commutation of the field strength pattern.

In a preferred embodiment of the invention the radio beacon comprises three vertical dipole antennae mounted approximately one half-wave length above the ground in alignment perpendicular to the desired course, the two outer antennae being at equal distances from the centre antenna which is located on the course line, all the dipoles are centre fed, from the same source of high frequency current, the two outer dipoles being fed in phase opposition and the centre dipole being fed with current having a phase angle of 90 degrees or less with the currents in either of the outer dipoles. Means is provided to change the phase of the current in the centre dipole, for example by 90 or so that with respect to the currents in one of the outer dipoles the current in the centre dipole alternately leads and lags and with respect to the currents in the other outer dipole, the current in the centre dipole alternately lags and leads respectively. The distance between the outer dipoles and the centre dipole and the phase angle between the energising currents is so chosen to give the practical minimum beam width, that is the width of the overlapping portion of the field strength patterns in its two commutated positions. In one particular example, the distance between the outer dipoles and the centre dipole is .475 of the operating wave length and the phases of the currents in the three dipoles are respectively 0, 45 and 180 and alternately due to keying 0, 315 and 180. A single "make or "break contact de vice is employed for eiiecting this commutation of the field strength pattern.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which,

Figure 1 shows diagrammatically a preferred embodiment of the invention;

Figure 2 shows the circuit arrangements used in the embodiment shown in Figure 1;

Figures 3A-D and 4A-D are explanatory diagrams used in the description.

Referring to Figure l. the transmitter T is connected to an open wire line TD. The radio frequency power splits up at D- and isfed to the three dipoles A, B and C, the distance between AB and BC being .475 the operating wave length. The open wire lines DA and DC have each a length equal to one and a quarter wave lengths and the open wire line DB is three-quarters of a wave length long. Lines DA and DC are deliberately made an odd multiple of quarter wave 7 lengths as the currents then fed to the dipoles.

half or approximately one half the operating wave length.

Referring now to Figure 2. the transmitter feeds into a 500 ohm line TD by means of a transformer TR having tuned primary and secondary winch ings. LIC3 is a circuit for sup ressing arallel currents on the line TD, capacities C I. C2 and C4 and inductances L2, L3 form a network for feeding the o erating current from supply S to the relay REL! along the line, thus eliminating the requirement of a separate cable. ing mechanism is represented as a key K, and connects the source S to the line TD through the inductances L2. L3.

Keying is efiected by shunting a reactance across the centre dipole. Since the line length DB is an odd number of quarter wavelengths. the efiect of the reactance is to change the phase of the current fed to the centre dipole. By using a reactance equal in ma nitude to the antenna resistance, and changing the reactance from capacitive to inductive and vice versa. a hase change of 90 is obtained whilst maintaining a constant current in the antenna. In Figure 2 the keying unit consists of an adjustable inductive-loop L4 of, for example '70 ohms impedance and a capacity C5 of 140 ohm impedance which is placed in series with the inductance. The relay RELI when operated short circuits the condenser C5 by closing the makecntact r! This converts the impedance across-the dipole from 70-ohms capacitive reactance to 70 ohms inductive reactance. C6 is a blocking condenser t prevent the relay short circuiting its operating current, L is a choke coil to keep the radio frequency energy from the relay winding W.

The principle of operation of the beacon according to the invention is as follows, reference being made to Figures 3 and 4.

Consider three antennae A. B and C (Figure3A fed with currents IA. is and I0 having the hases 'shownin Figure 3A. These currents will give,

rise to fields FA Fe Fe at point P at a great distance away. FA and Fe cancel each other since they are in phase opposition. 4

If we move from P to P1 also at a greatdistance away and near the approach path with dipole B- as centre, the field from B will be unchangedin magnitude and phase, while that from A will be retarded andthat from C willbe advanced as compared with the phases at P. The outer dipoles will then form at P1 a resultant field FAG which is always 180 substantially out of phase with FB as shown in Figure 30. As we move round the antenna B the resultantFAo varies.- On moving to the A side. of the antenna B, FAG changes 180 in phase and is .then in phase The 'key- 7 The dipoles. A

with Fe. will be obtained which has a big lobe on one side and a small one on the other as shown in Figure 3D. If for commutation of the field pattern the phase of the current in the centre aerial, or in both outer aerials, is reversed by 180 the diagram will be reversed, the large lobe being replaced by the small one and vice versa, thus pro-' ment or timed change over relays, the latter leading to difficulties due to a third field pattern during the change over just as in the known system utilising reflectors. However, by using a phase shift of less than 180 the problem is greatly simplified. In practice about 90 is used. This solution has only two disadvantages.

1. The beam width is slightly broader than it would be if 180 phase change were used. More power has, therefore, to be fed into the outer. dipoles, in order to get a beam of a given width, than would be necessary with 180 phase change. This means that the on course signal is less than it would be with 180 phase change. However. compared to the keyed reflector system the 3 antenna system with 90 keying is at no disadvantage in this respect. as the greater dipole spacing that is possible with the system according to this invention helps to give a narrower beam. 7

2. The phase change of 90 of the current in the centre dipole is obtained by shunting the latter with a reactance which is changed'from a capacitive to an inductive value with keying. This throws a load back onto the transmitter which varies with keying, so that if the output circuit is badly mistuned it isipossible to change the orientation of. the'beam. If this possibility is realised, and the values of reactance are kept small. the change of orientation may be made a negligible. Field tests show that very bad mistuning of the transmitter gives a maximum change of not more than .4 in orientation. Normal tuning adjustments are not likely to give more change than .1.

Keying with 90 phase change Referring now to Figure 4, A, B and C are 3 dipoles fed with current in relative phase of 0 45 180 as shown in Figure 4A. On keying, as hereinbefore described in relation to Figure 2, the phase of the centre dipole current is changed by 90 giving the relative phases of 0 315 180. At P we therefore have the field fromthe centre aerial alone producing a signal since the fields from the outer dipoles cancel. On moving to P1 we have the field F3 from B, and the-resultant FAG of the fields from A and C as shown in Fig.

. 4C. These add up vectorially and produce a field pattern as shown in Figure 4D in full line. On changing the phase of the centre aerial current by the pattern is reversed, as shown in Figure-4D dotted line. p

The advantages of the beacon according to the present invention are:

1. The beam width can be set up to any required value.

2. A single contact relay is used for keying, thus eliminating timed relays and the possibility of key clicks. Good back and front beams will always be obtained. 3. The field radiated is concentrated in the dijrectionoif the .beam rather than .to the sides.

If a polar diagram is plotted a pattern.

This reduces the likelihood of split beams as they are usually caused by reflections from objects situated on either side of the course.

4. The antenna system is very simple both in construction and operation and does not require highly skilled personnel to maintain it. 1 The system can be easily set up on a new operating frequency from written instructions.

What is claimed is:

l. A radio beacon for radio guiding systems of the kind in which a field distribution or field strength pattern is commutated so as to produce complementary signals to the right and left of the course respectively, and on the course a continuous dash or no signal, comprising three linear antennae mountedabove theground and symmetrically located with respect to the desired course, means for feeding the outer antennae with currents in opposite phases and for feeding the centre antenna with currents of the same frequency and with a phase angle of 90 degrees-or less with respect to the currents in either of the two outer antennae, and means for changing the relative phases of the centre and outer antennae from a phase lead to a phase lag or vice versa to produce the commutation of the field strength pattern.

2. A radio beacon for radio guiding systems of the kind in which a field distribution or field strength pattern is commutated so as to produce complementary signals to the right and left of the course respectively and on the course a continuous dash or no signal, comprising three antennae arranged at a distance apart and each fed directly from a source of high frequency currents phased with respect to each other, a network associated with one of said antennae for effecting a phase lag or a phase lead of approximately 90 in the excitation of said one antenna withrespect to the other antenna, and a single "make or "break contact device for changing the said network to control the said lead or lag excitations and thereby for commutating the field strength pattern formed by said antennae.

3. A radio beacon for radio guiding systems of the kind in which a field distribution or field strength pattern is commutated so as to produce complementary signals to the right and left of the course respectively and on the course a continuous dash or no signal, comprising three dipole antennae mounted above the ground in alignment perpendicular to the desired course, the two outer antennae being at equal distances from the course line and the centre antenna being on the course line, means for feeding the two outer dipoles with currents in phase opposition and for feeding said centre dipole with currents of the same frequency and having a phase angle with respect to the currents in either of the outer dipoles of 90 or less, and means for changing the phase relationships of the currents in the outer and centre dipoles from a phase lead to a phase lag and vice versa.

4. A radio beacon as claimed in claim 3 Wherein the phase angle of the current in the centre dipole is at with respect to the currents in the outer dipoles and means are provided for reversing said phase angle alternately to produce the commutation.

5. A radio beacon as claimed in claim 3 wherein the phase angle of the current in the centre dipole is at 45 with respect to the current in one of said outer dipoles and means is provided for changing said phase angle by 90 to change said phase angle from a lead to a lag and vice versa.

6. A radio beacon as claimed in claim 3 wherein the phase angle of the current in the center dipoleis at 45 with respect to the current in one of said outer dipoles, including a capacity of the same impedance magnitude as the resistance of the center dipole, means for connecting said capacity in shunt across said center dipole, and further means for periodically short circuiting said capacity so as to render said dipole alternately capacitive and inductive, whereby phase lag and phase lead are produced in said center dipole.

7. A radio beacon as claimed in claim 3 wherein the phase angle of the current in the center dipole is at 45 with respect to the current in one of said outer dipoles, including a capacity of the same impedance magnitude as the resistance of the center dipole means for connecting said capacity in shunt across said center dipole, and further means for periodically short circuiting said capacity so as to render said dipole alternately capacitive and inductive, said further means comprising a single pole make and break contact device, the make contact producing phase lag and the break contact producing phase lead.

8. A radio beacon for radio guiding systems of the kind in which a field strength pattern is commutated so as to produce complementary signals to the right and the left of the course respectively and on the course a continuous dash or no signal, including three antennae arranged at a distance apart and each fed directly from a source of high frequency currents difierentially phased with respect to each other, and a single make or break contact device for commutating the field strength pattern formed by said antennae, said contact device comprising an electromagnetic phase shifting relay located adjacent to one antenna, keying means located adjacent said source of high frequency currents, and means for transmitting relay energizing current over the same line by which said center dipole is fed.

LOUIS JOHN HEATON-ARMSTRONG.

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