US2937374A

US2937374A - Two band antenna with different time delay in each band

Info

Publication number: US2937374A
Application number: US537820A
Authority: US
Inventors: Cork Edward Cecil
Original assignee: EMI Ltd
Current assignee: EMI Ltd; Electrical and Musical Industries Ltd
Priority date: 1954-10-06
Filing date: 1955-09-30
Publication date: 1960-05-17
Anticipated expiration: 1977-05-17
Also published as: GB804462A; DE1015868B; FR1138380A

Description

y 7, 1960 E. c. CORK 2,937,374

TWO BAND ANTENNA wrra DIFFERENT TIME DELAY IN EACH BAND Filed Sept. 30, 1955 FIG. 2.

H6. 3. H64 FIG. 5.

FIG. 8. FIG. 9.

United States TWO BAND ANTENNA WITH DIFFERENT TIME DELAY IN EACH BAND' Edward Cecil Cork, Ealing', London, England, assignor to Electric 8: Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application September 30, 1955, Serial No. 537,820

Claims priority, application Great Britain October 6, 19541 4 Claims. (Cl. 343-814) This invention relates to aerials 'such as are employed for the reception of television signals.

A common form of such an aerial is the H-type of aerial comprising a pair of dipole elements, together with a pair of reflectors or directors (comprehensively termed parasitic elements), the'dipole elements and the parasitic elements being spaced apart and arranged in parallel relationship. Another well-known type of aerial is the X-type of aerial in which the dipole elements are arranged in the same plane but sub-tend an angle less than 180 and likewise the parasitic elements are similarly disposed with the apices of the dipole elements and the parasitic elements adjacent one another. Unipole aerials are also known which can be provided with parasitic elements. In these types of aerials the aerial elements and the parasitic elements are usually insulated from one another and the purpose of the latter elements is to reduce the sensitivity of pick-up of the aerial in the rearward direction and to improve the directivity and gain in the forward direction. Such aerials are commonly used for television reception in Great Britain in band'l, is. in a frequency range of 41 to 65 megacycles per second but a band I aerial is not suitable for use in band III, is. 170 to 220 megacycles per second since the gain of such an aerial in band III is insufficient. Such aerials can, however, be converted for use also in band III by attaching units to the elements of the aerial which effectively shorten the length thereof so that they can also effectively operate in the higher frequency band.

The object of the present invention, however, is to provide an improved aerial which can be satisfactorily operated in two frequency bands without the necessity of adding units which effectively shorten the length of the elements and in which the aerial has a higher gain than the aforesaid types of aerials and in which the sensitivity is further reduced in the rearward direction so as to provide a high so-called front to back ratio.

According to the invention there is provided an aerial comprising a pair of spaced conducting elements electrically interconnected through time delay means which affords different time delays in different frequency bands whereby signals picked up by each element in the different bands are additive.

According to the present invention there is also pro vided an aerial comprising a pair of conducting elements and a further pair of conducting elements arranged in substantially the same plane, the two pairs of elements being electrically interconnected through time delay means which affords different time delays in difierent frequency bands, whereby signals picked up by each pair of elements in the different bands are additive.

Further, according to the invention there is provided an aerial comprising a pair of dipole elements disposed at an angle with respect to one another and a further pair of dipole elements also disposed at an angle to one another with the apices of the dipole elements disposed adjacent one another so as to form the shape of across and wherein the pairs of dipole elements are electrically interconnected through time delay means which affords different time delays in different frequency bands whereby signals picked up by each pair of elements in the different bands are additive.

Since the time delay means employed in the invention causes the signals picked up by the elements to be added, the gain and directivity of the aerial are improved.

In order that the said invention maybe clearly understood and readily carried into effect, it'will now be more fully described with reference to the accompanying drawings, in which:

Figure 1 illustrates diagrammtically one example of an aerial in accordance with the invention,

Figures 2, 3, 4 and 5 illustrate polar diagrams of the aerial shown in Figure 1,

Figure 6 illustrates a modified form of the time delay means shown in Figurel,

Figure 7 illustrates'a modification of the aerial shown in Figure 1,

Figure 8 illustrates a perspective view of a practical embodiment of the invention, and

Figure 9 illustrates diagrammaticallythe invention as applied to a unipole aerial.

Figure 1 of the drawings illustrates an aerial in accordance with the preferred form of the invention and as shown, the aerial comprises a pair of conducting elements 1 and 2 and a further pair of conducting elements 3 and 4. All of the elements of the aerial are preferably arranged in the same plane but the elements 1 and a 2 are disposed at an angle with respect to one another and likewise the elements 3 and 4 are disposed at an angle to one another with apices of the Vs so formed disposed adjacent to one another as indicated in Figure l. The element 1 is electrically connected to the element 4 by a conductor 5 and the element 2 is electrically connected to the element 3 by a conductor 6 and through time delay means in each of said conductors 5 and 6, as indicated in Figure 1. The time delay means comprises an inductance 7 connecting the adjacent ends of the elements 3 and 4 and the conductors 5 and 6 each a shunt circuit comprising a parallel combination of" an inductance 12 and capacity 13 is employed. The aerial showniri Figure 1 may be designed for operation in bands I and III and the length of the elements 1, 2, 3 and 4 when designed for operation band I may be approximately a quarter of a wavelength long (or an odd multiple thereof). Signals will be picked up by the elements 1 and 2 and the elements 3 and 4 and the time delay means is designed so that the signals picked up by the respective pairs of elements are in additive phase at the feed point of the aerial so that the gain and directivity of the aerial are improved. In band III the aerial elements 1, 2, 3 and 4 will be about three-quarters of a wavelength long. The time delay means is also so designed that at the frequencies encountered in band III the signals picked up by the respective pairs of elements will also be in additive phase at the feed point of the aerial, so that the gain and directivity of the aerial when operating in band III will also be improved.

In a specific example of an aerial according to Figure 1 constructed for operation for the receptionof television signals transmitted respectively on carrier waves of 45 megacycles per second, and 194.75 'megacycles per second, each aerial element 1, 2, 3 and 4 is in the form of an aluminium tube half an inch in external diameter with each element five feet long disposed respectively at an angle of 90 with respect to one another and all mounted in the same plane. The inductance 7 is 0.48 h, the inductances 8 are each 0.06 ah. and the capacities 9 are each 15 pf. The feeder 10 may comprise a feeder having a characteristic impedance of 75 ohms and the inductances 11 of the matching network shown in Figure 1 each have an inductance of 0.1 ,ul1., the inductance 12 is 0.165 pub. and the capacity 13 is 4 pf. The values of the components stated are those when measured at 45 megacycles per second. An aerial constructed in the above manner has a measured gain over a half wavelength dipole in band I of 2.75 dbs and a measured gain in band III of db. The front to back ratio in bands I and III is about :1 signal ratio.

The shape of the polar diagrams with an aerial in accordance with the invention when operating in band I is shown in Figures 2 and 3 and when operating in band III the respective polar diagrams are as shown in Figures 4 and 5. It is assumed that the aerials in accordance with the invention will be mounted in a vertical plane with the elements 3 and 4 facing a source of radiation and Figure 2 of the drawings illustrates the polar diagram of the aerial in the vertical plane and Figure 3 the polar diagram in the horizontal plane and likewise Figure 4 illustrates the polar diagram of the aerial when operating in band III, in the vertical plane, and Figure 5 in the horizontal plane.

It is assumed that signals in the respective frequency bands for which the aerial is designed to operate will be radiated from the same direction but if the signals emanate from slightly different directions, then it may be necessary to vary the lengths of the aerial elements and their angles and the time delay means in order to provide optimum results.

Instead of employing lumped impedances to form the time delay means as shown in Figure 1, said time delay means may comprise a suitable length of transmission line indicated at 14 in Figure 6, the line being coiled as indicated so as to decrease its overall length so as to enable the apices of the conducting elements of the aerial to be arranged close together. In order to enable the line 14 to be effective to introduce the required time delay for both frequency bands, the effective length of the line 14 is required to be shorter for operation in band 111 and in order efiectively to shorten the line for operation in such band, an appropriate length of the line 14 is effectively short-circuited by the provision of shortcircuiting studs 15. These studs may also be coiled for compactness.

If desired the elements 1, 2, 3 and 4 may be combined with additional conductors in order to increase the bandwidth of the aerial and Figure 7 illustrates one example of such an arrangement. In this figure the elements 1 and 2 are connected to similarly disposed conducting elements 1a and 2a, the inner ends of the conductors 1a and 2a being interconnected through a resistance 16. Likewise the elements 3 and 4 are connected to

similar conductors

3a and 4a which are likewise connected together at their inner ends through a resistance 17. The time delay means employed in the invention is indicated by the rectangle 18. The additional conductors employed are arranged parallel with their associated conductors and the

resistances

16 and 17 are chosen so as to be equal to the characteristic impedances of the conducting elements. If desired the

resistances

16 and 17 can be omitted and the additional conductors directly connected together at their inner ends. The omission of the

resistances

16 and 17, however, results in some sacrifice of bandwidth.

Figure 8 of the drawings illustrates diagrammatically a practical embodiment of the aerial shown in Figure 1. As shown in this figure, the conducting elements 1 and 2 and the elements 3 and 4 are mechanically interconnected by means of a junction box 19 formed of insulating material which is provided with a removable cover plate 20 by means of which access can be had to the ends of the conductors 1, 2, 3 and 4 which are suitably secured in position in the box 19. The various circuit elements not only of the time delay means but also of the feeder matching means may be formed on a plate mounted in the junction box 19 by printed circuit or similar technique.

Figure 9 of the drawings illustrates diagrammatically the application of the invention to a unipole aerial. In this case the reference numerals 1 and 3 indicate a pair of spaced conducting elements which are disposed at an angle to one another, say and may each be about a quarter of a wavelength long in band I and the adjacent ends of the conductors are connected together through a time delay network comprising inductances 7 and a parallel combination of an inductance 8 and capacity 9 as shown. The feeder for the aerial comprises a concentric line the inner conductor 21 of which is connected to the conductor 1 as shown, whilst the outer conductor 22 of the line is connected to an artificial earth indicated at 23. This artificial earth is composed in known manner of a length of conductor half a wavelength long in band I, the first point of which constitutes the earth point, and is combined with a further artificial earth 24 comprising a conductor which is a half wavelength long in band 111. If desired, of course, the artificial earth may each comprise a conductor a quarter of a wavelength long in the respective bands. Both of the

conductors

23 and 24 may be coiled in known manner in order to reduce their overall length. The ends of the inductances 7 opposite to those connected to the conductors 1 and 3 are also connected to the artificial earth.

If desired, a plurality of aerials as above described may be employed, the aerials being arranged about a common point.

The invention is, of course, not limited to particular angles between the aerial elements referred to above since these may be varied depending on practical considerations and the site of the aerial in relation to the transmitter. Likewise the time delay means may also require variation for similar reasons and depending on the length of the aerial elements.

What I claim is:

1. An aerial comprising a pair of dipole elements disposed at an angle with respect to one another and a further pair of dipole elements also disposed at an angle to one another with the apices of said dipole elements disposed adjacent to one another so as to form the shape of a cross, a feed point for said aerial, time delay means electrically interconnecting said pairs of dipole elements to said feed point, said time delay means including elements chosen to afford different time delays in difierent frequency bands so that signals picked up by said pairs of elements in different frequency bands are in additive phase at said feed point.

2. An aerial comprising a pair of dipole elements disposed at an angle with respect to one another and a further pair of dipole elements also disposed at an angle to one another with the apices of said dipole elements disposed adjacent to one another so as to form the shape of a cross, a feed point for said aerial, time delay means electrically interconnecting said pairs of dipole elements to said feed point, said time delay means including elements chosen to afiord different time delays in different frequency bands so that signals picked up by said pairs of elements in different frequency bands are in additive phase at said feed point, and said dipole elements are combined with additional conductors aranged substantially parallel to said dipole elements the ends of said additional conductors adjacent the apices of the dipole elements being connected together through resistances which are substantially equal to the characteristic impedance of the dipole elements.

3. An aerial comprising a pair of dipole elements dis spam" posed at an angle with respect to one another and a further pair of dipole elements also disposed at an angle with respect to one another with the apices of the dipole elements disposed adjacent one another so as to form the shape of a cross and arranged in the same plane, one element of one pair being cross-connected to an element of the other pair and the other element of the first pair being cross-connected to the other element of the second pair, a feed point for said elements, time delay means electrically interconnecting said elements to said feed point, said time delay means including elements chosen to afford diiferent time delays in different frequency bands so that signals picked up by said pairs of elements in different frequency bands are in additive phase at said feed point.

4. An aerial comprising a pair of dipole elements disposed at an angle with respect to one another and a further pair of dipole elements also disposed at an angle with respect to one another with the apices of the dipole elements disposed adjacent one another so as to form the shape of a cross and arrangedin the same plane, one element of one pair being cross-connected to an element of the other pair and the other element of the first pair being cross-connected to the other element of the second pair, a. feed point for said elements, timedelay means electrically interconnecting said elements to,

said feed point, said time delay means including elements chosen to afiord different time delays in different frequency bands so that signals picked up by said pairs of elements in difierent frequency bands are in additive phase at said feed point, and wherein said dipole elements are combined with additional conductors arranged substantially parallel to said dipole elements, the ends of said additional conductors adjacent the apices of the dipole elements being connected together through resistances which are substantially equal to the characteristic impedances of the dipole elements.

References Cited in the file of this patent