Window Antenna

Abstract

Window antenna is provided in which directional effect is minimized and maximum output secured. The antenna is mounted in conductive lines on a supporting surface such as a window pane, the lines forming a cruciform antenna within a bipolar antenna both of which are attached to a common terminal, the dimensions of the two antenna being complementary and producing an inphase output, the system being without discrete reactances and the arms of the bipolar antenna being spaced from bleeders.

Description

This invention relates to antennae of the type which are composed of conductive lines mounted on a supporting surface. A particularly valuable use of such antennae is in vehicles where they have been mounted on the windows, usually on the windshield, but such antennae have a high directional effect and have not been wholly satisfactory. This invention will be described in its application to a vehicle windshield but it is to be understood that it is equally applicable to the windows of buildings or to any broad surface.

The good operation of a receiver of radio electric waves is notably dependent on the tuning of the antenna to the wave length to be received, to its adaptation to the input impedance of the receiving apparatus, as well as to its position and arrangement.

The influence of the antenna is particularly important for the reception of short wave lengths and it is for this reason that a large number of radiophonic receivers are provided with two distinct antenna contacts or terminals of which one connects to a quarter wave doublet antenna appropriate to the reception of the high frequencies presently employed for frequency modulation broadcasts, and of which the other is connected to an antenna of greater length which is better suited to the reception of lower frequencies such as broadcasts in amplitude modulation.

The problem of adapting such antennae reaches major magnitude in vehicles, especially automobiles, because working conditions are usually bad and the number of technical processes which can be used are few. For example, the arrangements which it is possible to employ are limited and the receivers employed are usually provided with a single antenna contact.

It has been proposed to incorporate such antennae in the windows of vehicles either as wires or lines mounted between the different layers of the laminar type of window, or as printed lines, Such antennae have had the classical form destined to receive metric waves, that is, using variants of doublts or a length near a meter, generally of T shape even though that shape is highly directional. It has also been proposed to introduce modifications calculated to improve reception of broadcasts of longer wave length without too much reducing the reception of the first. It has also been proposed to install two distinct antennae, but that requires switching outside the receiver either by a manual switch or by an automatic electronic filter of complex construction. Neither proposal improves the efficiency of either antenna.

Among the objects of the present invention are to provide antennae of reduced directivity, which are more omnidirectional than those presently known, which are of improved efficiency as receivers or as transmitters, which are of simple construction, free of manual controls and electrical complexity, are readily applied by known techniques, and which provide excellent reception or transmission for a wide band of wave lengths. The present disclosure will assume that the problems are to be solved for an automobile receiver covering both FM and AM broadcasts.

The objects are accomplished, generally speaking, by an antenna comprising a support, a cruciform antenna thereon, a bipolar antenna embracing the cruciform antenna, and a common terminal attached to both antennae, the dimensions of the two antennae being complementary and producing an in-phase output.

According to the invention this result is obtained by an antenna comprising a non-conductive, flattish support, an antenna mounted thereon comprising a plurality if distinct principal branches of different directivity connected to a single terminal, and a cable connecting the terminal to receiver means, one of the branches comprising linear conductor means and another comprising linear conductor means embracing the first branch, the dimensions of the branches being complementary and producing an in-phase output without the use of discrete reactances, the output terminal being connected to a receiver by a cable of complementary length. The antenna has two principal branches of different directivity which directly supply a single terminal located on the windshield which is directly connected to a cable connected to the receiver. One of the antennae is preferably a vertical conductor centrally located in the windshield which is frequently, especially in windshields of small height, of cruciform shape, for instance a T of which the horizontal branch extends along the upper part of the windshield. The second antenna embraces or even encircles the first, follows the windshield frame but at a distance sufficient to prevent bleeding by the metallic parts of the vehicle; a distance of a few centimeters from such bleeders is sufficient to keep the total capacity below about 100 pF, which can be used as a test of adequate spacing. This second antenna may be roughly U-shaped, at least in part, and follows the outline of the frame. In an advantageous form of the invention the horizontal bar of a T-shaped antenna and the arms of the U-antenna constitute a line following the line of the frame, interrupted only by two short, symmetrical gaps at the ends of the crossbar. To provide a desired length each of the two branches may be duplicated or provided with auxiliary conductive lines. The output impedance of such an antenna may be on the order of 150 ohms, which will permit direct connection to the ordinary coaxial cable. The two antennae, or the two branches of the antenna, even in the range of frequency modulation, play equivalent roles, their signals reinforce one another, and each compensates for the directivity of the other.

We have discovered that it is possible without notably attenuating the signals furnished by each of the antennae to associate them so that their relative phase displacement is always less than 90.degree. simply by slightly retouching their tuning and preferably by tuning the U-shaped branch so that the resultant signal is always better than that of the T-branch considered alone. To this end the branches mounted on vehicles, considered separately, are each tuned in very short wave lengths and thus supply signals of maximum intensity of which the voltages are comparable; then their characteristics are retouched so that these signals are in-phase at the chosen point of tuning, the correct phase state being coordinated, it is understood, with the length of the connecting cable.

The regulation of the tuning of phase may theoretically be made by discrete electronic components placed on each of the branches but at the same time the essential precision of manufacture is difficult to attain. This invention makes it possible and therefore preferable, especially when the conductors of the antennae are composed of a metallic deposit, to effectuate the regulation simply by modifying the geometry of the conductors, lines or wires of each of the branches. In particular, the phase angle of the output voltages of the two branches of the antenna can be adjusted by modifying the length of the conductors especially with respect to auxiliary lines of the U-shaped antenna.

An advantageous method for establishing the optimum layout of the conductors on the surface of a vehicle window, which are connected to a receiver, consists in depositing on the surface a base circuit comprising a peripheral conductor forming a kind of frame situated at a sufficient distance from bleeders such as the frame and at least partially embracing a central conductor connected to the peripheral. The antenna is regulated in amplitude modulation; the two branches are separated; each is separately tuned, the T-branch being made predominant in frequency modulation by varying its length; again connecting the second branch by correcting the length and tuning of its lines so that they will be inphase with the first branch and thus produce a maximum signal. It will be understood that as soon as the proper lengths have been worked out for one signal the lines can be applied by any method, for example by silk screen, to all windshields of the same type without further tuning.

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.

The figures of the drawing are diagrammatic sketches of windshields with various antennae according to the invention.

FIG. 1 shows a windshield 1 of which the outline may be taken as the inner edge of the frame. This glass carries an antenna which has a T branch having a vertical conductor 2 and a conductive, horizontal crossbar 3. A second branch is in the form of a closed figure which follows the outline of the windshield and completely embraces the T-branch. Both branches are connected to a comman terminal 5 to which the cable is also connected which conducts the output of the antenna to the receiver. The cable and receiver have not been shown. The branch 4 is sufficiently far from the frame, which constitutes a bleeder, so that, taking into consideration the capacity of the cable, the total capacity will not exceed about 100 pF, and it is tuned so that the branches work in resonance taking into consideration the input impedances of the receiver and the characteristics of the connecting cable. For a given vehicular installation one will always use a cable of the same length. The T-branch is then connected to the terminal 5 and tuned by modifying the length of crossbar 3 so as to produce once more a maximum output signal.

FIG. 2 shows on windshield 11 an antenna system having a T-branch and a U-branch of which the crossbar 13 of T 12 is parallel to the edge of the windshield and aligned with the ends of the peripheral branch 14 the ends of which 14a and 14b are separated from the ends of the crossbar by gaps 16a and 16b. The two branches are united at point 17 which is connected to the cable terminal 15. The gaps are of such dimensions that the junction 17 with the peripheral branch 14 is inphase with the T-branch. The optimum size of the gap may be determined by measuring the output voltage of the antenna. The final tuning is obtained by establishing the length of the cable so that a maximum output is delivered to the receiver.

It is sometimes desirable to tune the antenna to the length of the cable. In FIG. 3 a windshield 21 has a central T partly embraced by branches 24a, 24b, tuning having been accomplished by shortening the ends of the peripheral branch, which allows one in the first place to tune the branch 22, 23 to the cable which is to be used. The branches 24a, 24b are subsequently connected at 27 to conductor 22 and are shortened until their output voltage is inphase with the output voltage of 22, 23. The cable connecting the antenna to the receiver is connected to a terminal 25 to which the common point of two branches is also connected.

FIG. 4 gives another solution for coupling the two branches inphase. The windshield 31 has T-branch 32, 33 composed of, for example, a fused silver frit, which has been tuned as described for FIG. 3. The arms 34a, 34b are connected at 37 to the foot of the T and both are connected to the cable terminal 35. The correction of the phases of conductors 34a and 34b is carried out by extending them with replications 38a, 38b. Compared to FIG. 3 this offers a greater length of antenna circuit and provides better reception of the amplitude modulation branch.

FIG. 5 shows an antenna in which phase correction is similarly achieved. The T-branch is as described but the U-branch is double in its lower part and includes two additional conductive lines 48a, 48b, approximately parallel and connected at 47 to T 42, 43. The principal lines 44a, 44b of the U-branch are connected to 49a, 49b to the lines 48a, 48b. The free lengths of the leader, as well as the positions of the branches 49a, 49b may be changed to vary the unit of induction H so that the two branches of the antenna may be inphase at their common point 47 and at the terminal 45.

FIG. 6 represents another form of antenna in which the upright of the T-branch is associated with other uprights. This with its upright 52 and its horizontal 53 are the parts of the invention which predominate for frequency modulation broadcasts. The U-branch 54a, 54b is connected to the foot of the T. The auxiliaries 58a, 58b may be lengthened or shortened and their points of attachment 59a, 59b to conductors 54a, 54b may be chosen so that the several branches will be inphase. By placing several conductors in the most active part of the windshield one improves the qualities of the antenna for reception of amplitude modulation signals but the solution is less happy from the point of view of visibility.

These antennae, it should be understood, are equally valuable for broadcasting as for reception and they are employable with the same success in other fields, for example in television and for the reception of telephone signals.

The invention is a universal antenna which may be used in AM and FM, all elements being equally active in all these wave lengths.

EXAMPLE

The windshield was mounted in a 1969 Open-Capitan and was of the shape of FIG. 5. In order to conduct the measurements the two branches were separated but in use the two branches were connected to the same terminal. The test was carried out on an FM wave polarized horizontally. The two branches were put inphase at the point 47 by adjusting the length of the T-crossbar and by adjusting the position of bridges 49a and 49b, the impedance being thus set at about 150.OMEGA.. The voltage of the T branch (U.sub.1) and the voltage of the U-branch (U.sub.2) were measured while the vehicle was turned toward the sending station, and thereafter as the vehicle was rotated through 360.degree.. The results are charted in db in FIG. 8, the angle of the vehicle entered as abscissa, 0.degree. being when the station was in front. The outputs of the two branches are charted as .alpha. B on the ordinate. This shows that the voltage output of the U-branch (curve U.sub.2) is generally stronger than the output of the T-branch (curve U.sub.1), and that the T-branch is highly directional with a sharp minimum at 200.degree.. The U-shaped branch has less directional effect and is complementary in effect, the combination of the two antennae considerably diminishing the directional effect of the T. It is also noted that the angle of phases is always between +90.degree. and -90.degree. and are nearly symmetrical with regard to 0.degree.. Thus, the vectoral combination of voltages U.sub.1 and U.sub.2 is always formed by addition and not by subtraction, voltage U.sub.2 always reinforcing voltage U.sub.1.

Both branches are shown to be active in FM and there is no preponderance of the T-branch, so that the disadvantages of directivity are much reduced, which would not be the case if the T-branch were used alone in FM.

This invention combines a T-unipole antenna with a frame or U-shaped dipole antenna which at least partly embraces the unipole, the phasing of the antennae elements and the adjustment of impedance being accomplished by modifying the length of the T-crossbar and by positioning the bridges 49a and 49b to achieve optimum output. Discrete reactances are not used for this balancing.

The new antenna is particularly adapted to deposition on the surface of the windshield itself but it is also adapted to be applied to a separate sheet, for instance of transparent plastic permitting application to a pane already mounted in a vehicle.

When mounted in the window of a building the directional effect of stations in different geographical positions is also minimized.

All the forms of the invention are applicable to single sheets of glass or plastic as well as to laminar panes such as those which have one or several sheets of glass or of plastic or mixed, interconnected by layers of thermoadhesive such as polyvinyl butyral. In such cases the conductive fine lines of the antenna can be applied either to an outer face or to an interlayer or by incorporation in the glass itself. Deposition is conveniently carried out with silver frit by the silk screen technique. When only a single sheet of glass is used the antenna can be deposed on one of its faces, preferably the inner. The fine lines of the conductors are conveniently between 0.1 and 2 mm., between 0.2 and 0.8 mm. having advantages but their thickness does not have primary importance. Conductive frits can be purchased on the market, for instance "Leitsilber." This can be deposited by silk screen or any other appropriate method, and made permanent by heating to about 600.degree.C. When the panes are bent the heating may be carried out during the bending operation the temperature of which is adequate, and when the glass is to be tempered the temperature attained prior to blowing is adequate.

When laminar panes are being made the conductors can be placed in the plastic sheet which joins the outer lamina in the form of wires impressed in the plastic or lines printed on it; or, of course, it can be applied to an exterior face of the pane.

In order to fix the disposition of the conductors having known type of receiver one may proceed as follows with excellent results:

First one places on the windshield a base circuit composed of a peripheral conductor which follows the shape of the window frame and, centrally, a vertical conductor which is connected at its upper and lower ends to the peripheral conductor. The vertical conductor should be as narrow as possible to avoid obstructing vision, preferably being not wider than 0.4 mm. While the peripheral conductors may be thicker, the lines should be far enough from the bleeders to prevent the capacity of the antenna and the cable from exceeding 100 pF. Some attention should be paid to locating the conductive lines so that they are neither bled by the metal parts of the automobile nor obstruct the vision.

The parts being assembled in the vehicle the performance of the base antenna at a number of frequencies in AM are tested, for instance less than 30 MHz, and one proceeds thence according to the results desired to an eventual retouching of this circuit. The efficiency of the antenna in AM will not be substantially altered by the changes made subsequently so long as one does not remove large parts of the conductive lines. Measurements are then carried out to tune the antenna for FM, rotating it while receiving a frequency between 80 and 100 MHz. In order to do this one disconnects the peripheral conductors from the T at two points near its base and at a certain distance from the crossbar of the T, one of the branches is then tuned, preferably the T, and to this end the length of its crossbar is adjusted by progressively changing the position of the upper gaps, the windshield being implaced in the vehicle and connected to the receiver by its cable. Thereafter, the lower gaps are filled in order to introduce the complementary branch and tests are again made to tune the FM perfectly by changing the length of the lines of the complementary branch. Once the optimum shape of the antenna has been determined that shape can be transferred to a silk screen and used to apply the conductive lines as long as that particular windshield is to be made.

FIG. 7 gives the specific dimensions which were worked for the windshield of FIG. 5 described hereinabove and FIG. 8 gives the results of the tests described above.

The windshield antenna is quite superior for the reasons which have been detailed hereinabove and has the additional advantage that no reactances, for instance inductances, are employed in the conductive lines.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

Claims

1. An AM-FM radio antenna for a radio receiver mounted in a vehicle having an opening defined by a metallic frame for a window, such as a windshield, comprising a window mounted in said frame, fine wire conductors applied to the window as a T-shaped branch and a generally U-shaped branch, and an output terminal for said branches and the feedline to the radio receiver centrally disposed on the window a short distance from such frame at the bottom edge of the window, the base of said T-shaped branch being connected to said terminal and the crossbar thereof being generally parallel to and spaced a short distance from said frame along the upper edge of the window and said U-shaped branch being connected at the center point thereof to said terminal and extending from said terminal in a path

2. An antenna as defined in claim 1 wherein the U-shaped branch completely

3. An antenna as defined in claim 1 wherein the free ends of the U-shaped

4. An antenna as defined by claim 1 wherein the effective length of each half of the U-shaped branch is effected by replication in the vicinity of

5. An antenna as defined by claim 1 wherein each half of the U-shaped branch is severed, the severed end lapped, and connected by a bridging

6. An antenna as defined by claim 1 comprising conductors applied to the window adjacent and parallel to the upright leg of the T-shaped branch and

7. An AM-FM radio antenna for a radio receiver mounted in a vehicle having an opening defined by a metallic frame for a window, such as a windshield, comprising a window mounted in said frame, and fine wire conductors applied to the window as a T-shaped branch and a generally U-shaped branch, the conductor constituting said U-shaped branch being spaced a short distance from said frame and said T-shaped branch including a first conductor connected at one end to a central point of the U-shaped branch and extending transversely across the window and a second conductor connected centrally thereof to the other end of said first conductor and extending generally parallel to the frame at a short distance therefrom.

8. An antenna as defined in claim 7 wherein the feedline for the radio

9. An antenna as defined by claim 8 wherein said branches are separately phase-tuned for FM band frequency signals at the point of connection of

10. An antenna as defined by claim 7 comprising a terminal on the window

11. An antenna as defined by claim 7 which is phase tuned for reception by

12. An antenna as defined by claim 7 wherein the difference in the phase angles of the voltages of the FM band frequency signals induced in said branches from a given signal source at any selected angle of rotation of the window relative to said source about a vertical axis is less than 90.degree., whereby said voltages are additive at said central point in

13. An AM-FM windshield antenna comprising a transparent window, a T-shaped conductor applied to the window with the vertical bar thereof adjacent the middle of the window and the horizontal bar thereof adjacent the upper edge of the window, a U-shaped conductor applied to the window, said U-shaped conductor extending adjacent the lower edge of the window and at least part-way up the side edges of the window adjacent those side edges, and conductive means connecting the vertical bar of the T-shaped conductor near its lower end and the U-shaped conductor together to a common

14. A method for determining the layout of an AM-FM broadband radio antenna comprising fine wire conductors applied to the window of a vehicle for use with a radio and feedline therefor mounted on the vehicle which comprises applying to the window conductors forming a U-shaped branch following the peripheral shape of and spaced a short distance from a metallic frame embracing the periphery of the window and a T-shaped branch within the U-shaped branch, the base of said T-shaped branch being connected at a common terminal to the center of the U-shaped branch and said feedline, and the crossbar of the T-shaped branch being generally parallel to and spaced a short distance from an adjacent part of said frame, varying the length of said conductors to phase tune the connected branches for reception of an AM band frequency signal, thereafter varying the length of the conductors to phase tune each said branch separately for reception of an FM band frequency signal, and finally further varying the length of the conductors to phase tune the connected branches to phase tune the same for

15. The method as defined in claim 14 wherein the T-shaped branch is separately phase tuned to supply a signal which exceeds that supplied by

16. The method as defined in claim 14 wherein the final tuning of the connected branches is such that the signal output of the combined branches has more uniform directivity than the signal developed separately by the T-shaped branch.