FI58996C - PAO ELLER I EN FORDONSFOENSTERRUTA ANORDNAD ANTENN - Google Patents

Description

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Patent and Registration Office .... . ,. , _. (44) Date of Nihtlvikilpenofi et al. -

Patent · och registerstyrelsen v 'Anastan utta | d och uti.tkrifun pubikand 30.01.81 (32) (33) (31) «uollwi» * - e ** lrd priori »· * 1I4.01.72

France-France (FR) 7201219 (71) Saint-Gobain Industries, 62, Bd. Victor Hugo, F-92209 Neuilly sur Seine, France-Frankfurt (FR) (72) Gerd Sauer, Broichweiden, Federal Republic of Germany-Förbundsrepubliken lyskland (DE) (7l) Berggren Oy Ab (5l) Antenna fitted to or inside a vehicle window - Pä eller i en fordonsfönsterruta anordnad antenn

The invention relates to an antenna arranged in a vehicle window according to the preamble of claim 1.

These "windshield antennas" have various advantages over conventional antennas, and in particular the advantage that they are cheaper and more durable; however, the shape of the antenna poses somewhat difficult problems to solve, in particular because the available surface area is usually relatively small, which in practice forces, in the case of cars, to use only the windscreen for this purpose. The conductors may be embedded inside the glass if it is laminated glass, but are preferably printed on the inner surface of the glass.

It must be borne in mind that visibility cannot be impaired, which requires the use of conductors which are sufficiently thin for the edge zones or also for the center zone, but which are outside the driver's normal field of vision; otherwise, it is clear that the proximity of the vehicle body is likely to degrade the quality of reception. In addition, the receiver must generally be able to receive both frequency modulated transmissions, i.e., transmitted at short wavelengths, and amplitude modulated, i.e., transmitted at long and medium long wavelengths.

Generally, antennas intended for frequency modulation are symmetrical in shape, T or V-shaped, and have one or more branches and they are tuned to a half-wave length, while the antennas for the amplitude modulation of the windscreen frame shape.

Attempts have been made to connect two different antennas to the same windshield, one suitable for amplitude modulation transmissions and the other for frequency modulation transmissions, and also to give certain branches of one antenna a special function by separating them by impedances so that they operate only on a certain wavelength range. This improves the fit of the antenna; however, these solutions have proved to be incomplete, especially because the directional effect of these antennas is usually too great in the metric wave range. This is a serious drawback in a mobile receiver, such as a vehicle-mounted receiver, because the orientation of the antenna varies with the direction of the transmitter.

In order to examine this directional effect, it must be borne in mind that the characteristics of the antenna conductors fitted to the windscreen of the vehicle are the result of the action of the conductors and the vehicle body and cannot be calculated in the same way as for a separate antenna.

For example, in the reception of horizontally polarized radio waves, which is currently the most common case, there are two minima in the diagram of the horizontal antenna conductor when the vehicle is in a position perpendicular to the direction of the transmitter.

Compared to the previous antenna conductor, the output voltage of an oblique line-adapted antenna conductor, which for convenience is called vertical, has two highly emphasized minima under the same conditions when the vehicle is directed in the direction of the transmitter. The output voltage of the antenna is then only 10% of the voltage when the vehicle is perpendicular to the transmitter.

In addition, it is known that if different horizontal and vertical branches are connected to the antenna, their conductivity properties become combined in a manner which also depends on their respective phases, whereby the minima are at least partially removed.

Thus, the tuned T-shaped antenna retains the same characteristics as a "vertical" conductor, while the tuned U-shaped antenna is combined in its characteristics and has a minimum of 3,5996 detected when the vehicle is parallel to the transmitter, in addition to other minima that occur when the vehicle is perpendicular to the transmitter. in relation to.

Finally, it is known that by varying the location and electrical length of the different branches of the antenna, i.e. the impedance, its essential operating characteristics, the performance and also the radiation diagram can be corrected.

However, the conductors are usually made complex in shape, as the surfaces used are not only inclined but also convex and their dimensions are quite small, so it is usually necessary to bend the conductors along the edges. Under these conditions, it is practically impossible to calculate in advance the essential function of the antenna, such as its radiation, and all adjustments must be made experimentally.

Particularly interesting results have been described above, which are obtained by combining two tuned separate main branches, of which the central branch is T-shaped and the edge branch is U-shaped, which directly feed a cable connecting the antenna to the receiver via a common contact fitted to the glass. Both of these branches operate at all wavelengths entering the receiver, but one is more dominant in frequency modulation and the other in amplitude modulation. In the region of metric waves, where the reception capacity of both of them is combinatorial, they are in the same phase and each promotes reception in a different direction. The contact is preferably located at the bottom of the windshield.

The invention is applicable to antenna windshields comprising two different receiving branches tuned for frequency modulation, one of which is joined by a branch located at the edge of the windshield.

The invention is characterized in that the second conductor is also tuned to the FM region and that the branches on both sides of the connection point of the second conductor are formed asymmetrically. The asymmetry is achieved, for example, by placing an inductance or capacitance in one of its parts; however, it is particularly advantageous to do so simply by means of a different shape of the antenna branch.

By means of the invention, it has been found that breaking the symmetry has two different effects: on the one hand, it clearly improves the shape of the reception diagram and, on the other hand, provides a convenient means of adapting the impedance of the antenna to the impedance of the connecting cable.

Symmetry was maintained in previously known antennas when adjustments were made because the frequency modulation aimed as much as possible at a circular radiation pattern, i.e., 4 58996, i.e., as regular a radiation pattern as possible. This procedure was logical, but when the antenna was tuned, the impedance of the connection point was low, so that the antenna could not be connected to the receiver's communication cable under optimal conditions and an adapter could have to be used. When moving along a half-wavelength tuned conductor, the impedance coefficient varies greatly from a very weak minimum at the center of the conductor to a very pronounced maximum at both ends of the conductor.

In the antennas of the invention, since the characteristic impedance of a cable is usually about 150 ohms, it is clear that a rather small asymmetry is sufficient to change the shape of the diagram in a way that greatly mitigates the minimums and at the same time advantageously and continuously modifies the output impedance.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a directional antenna conductor and a horizontal antenna conductor in horizontal polarization, Figure 2 shows impedance variation in a conductor of length Λ / 2, Figures 3 ~ 9 show different embodiments of an antenna shows a detail of the embodiment according to Fig. 9, Fig. 11 shows comparative directivity diagrams of a known antenna and an antenna according to the invention.

Fig. 1 schematically shows a directional diagram V of a vertical conductor placed in the middle of the windshield and a directional diagram H of a substantially horizontal antenna conductor of the same length; both of these wires are on the car windshield. The marked angles are the angles between the longitudinal axis of the vehicle and the direction of the transmitter. The transmitter is polarized horizontally; the diagram is made in the frequency modulation band.

Looking at the directivity diagram V of the vertical antenna conductor, it is observed that the antenna voltage remains practically the same value in the 240 ° sector. However, when the vehicle is directed towards the transmitter, the antenna voltage has a very pronounced minimum value and remains low when the vehicle is at an angle of one or 10 ° with the direction of the transmitter.

V 5 58996

The horizontal conductor diagram H is similar in shape to V, but phase shifted by 90 ° with respect to it. In diagram H, the minimum values are observed when the vehicle is in a direction perpendicular to the direction of the transmitter. The maximum values of the antenna voltage present in the diagram H are smaller than those of the vertical conductor, whereas the minimum values of the diagram H are less pronounced than in the diagram V; these special features are due to the effect of the vehicle body.

It will be appreciated that directional diagrams may deviate from these ideal shapes in specific cases and depending on the type of vehicle, without, however, losing this characteristic shape. The differences are mainly due to the effect of the vehicle body.

An antenna windshield with ideal directional properties would comprise a T-shaped antenna with a vertical conductor and a horizontal conductor length of λ / 2. In the vibration in the horizontal direction, the horizontal part initially begins to act on the length λ / 2. In this case, the vertical branch only acts as a connecting conductor connected to the horizontal branch, since its length is suitably adjusted in advance, its own impedance is irrelevant and if the ohmic value of the switching point is small, the same is true for the lower switching point. In vertical oscillation, the length of this antenna is 3Μλ.

However, as mentioned earlier, straight conductors of this length cannot be fitted to a normal passenger car windshield: in this case, neither the ideal shape nor the ideal length of the conductors can be maintained, and this has a significant effect on the directivity of the obtained antennas. With the aid of Figure 2, it can be recalled in which way the value of the impedance of an oscillating conductor without the improvement according to the invention varies from a very high ohmic value at both ends of the conductor to 30 ohms at the center of the conductor.

Of course, these values are real only in the case of resonance. Consider such a conductor operating in resonance; the point where its ohmic value is weakest is usually at its center. If the switching point is moved a certain distance to the right or left of the center, the resistance of the lower part of the antenna is made to vary and thus the impedance can be adjusted.

The invention can be applied to antennas built mainly for receiving metric waves.

Figure 3 shows a windscreen 1a with an improved T-shaped antenna 58996 6 according to the invention. The antenna consists of a vertical branch 2 and a horizontal branch 3. The lower end of the vertical conductor 2 has a coupling piece The length of both the vertical and the horizontal conductor is> \ / 2. To calculate the length of the conductors approximately, it must be taken into account that the propagation speed in the glass is obtained by multiplying the corresponding speed in air by a factor of 0.3. But when only part of the electric field is in the glass, the reduction factor is between 1 and 0.39 and at 100 MHz it has been experimentally found that the wavelength is 0.75 times the wavelength calculated in air. The connection point 5 is selected by moving it to the other side so that its impedance is almost the same as the resistance of the lower end of the antenna, for example 150 ohms. This embodiment often gives very good results also with respect to the directivity diagram. If the electrical length of the vertical conductor 2 is too small, it can be stretched, for example, by inductance. The switch cable can also be extended. However, this solution may sometimes result in the total length of the conductor becoming too small to receive an amplitude-modulated transmission.

In the embodiment shown in Fig. 4, the windshield 15 has a vertical conductor 8 of Λ / 4 length, which itself has a horizontal double conductor part 9, by means of which the electrical length of the vertical conductor 8 can be adjusted by slightly changing the capacitive effect due to the length of the horizontal part 9; this conductor part 9 is too short to be truly receptive and therefore cannot actually be considered as a horizontal branch of the antenna. The actual horizontal branch is formed by a conductor 10 parallel to the lower edge of the windscreen and having an overall length λ / 2 and connected to the conductor 8 at a switch 11 located at the lower end of the antenna. The ideal position of this switch point 11 in the conductor 10 is obtained when the minimum values in the directivity diagram have risen as high as possible: this gives the optimal impedance value for the horizontal conductor of the antenna.

Figures 5-8 relate to antennas which are combinations of a T-shaped vertical branch and a U-shaped horizontal branch. The T-shaped and U-shaped arms are each adjusted according to the principles shown in Figures 3 and 4. Solutions for adjusting the impedance of a U-shaped conductor to improve directivity characteristics are as follows:

In the example shown in Fig. 5, the windshield le has a T-shaped central branch 13, 14 and a U-shaped branch with two parts 15a and 15b of the same length. The two conductors are connected to each other at the bottom of the T-conductor near the switch terminal 17. The T and U conductors 7 58996 are symmetrical in shape and the switch point is exactly in the middle. To change the impedance of the U-shaped conductor, the electrical length of the part 15b is shortened by capacitance: for this purpose, a piece of conductor 16 is placed in the glass parallel to the part 15b and connected to the vehicle body by means of conductor 18. Instead of shortening the electrical length of the U-shaped conductor by capacitance, elongation by inductance could have been used.

The antenna windshield Id shown in Fig. 6 is similar in structure to that shown in Fig. 4. The conductors 20, 21 form a T-shaped central branch and the conductors 22a and 22b are part of a U-shaped branch. The common pole of the U- and T-shaped conductors is denoted by reference numeral 23 · The length of the branch 22b is greater than that of the branch 22a. In this way, the switching point is moved to the desired distance from the center of the U-conductor in order to optimize the impedance which strongly dampens the directional action of the antenna windshield.

The embodiment shown in Fig. 7 comprises an antenna windshield le, in which the assembly of T- and U-shaped conductors is made asymmetrical by means of additional parts made in the U-conductor. The T-shaped branch consists of a vertical branch 26 and a horizontal branch 27. Parallel to the lower edge of the windshield is a horizontal conductor, the two parts 28a and 28b of which are of the same length. The antenna windshield further comprises two U-shaped branches 29a and 29b connected to conductors 28a and 28b by bridges 30a and 30b located asymmetrically with respect to the U-axis, so as to obtain the optimal impedance which gives the best directivity characteristics. The common terminal of the U-conductor and the T-conductor is marked with reference number 31 ·

Fig. 8 shows a windshield 1f in which two parts 32a and 32b of a U-shaped branch are bent in a zig-zag shape from parts adjacent to the lower edge of the windshield which are of different lengths. In this way, the same effect as described above is obtained. Here again, the central branch consists of T-shaped conductors 33 and 3 ^ · The coaxial cable connecting the antenna to the receiver is branched at the common connection point 35 of the U-shaped and T-shaped conductors.

Figures 9 and 10 show another particularly effective embodiment.

Here again, the central branch is T-shaped and has a vertical conductor portion 36 and a horizontal conductor portion 37. The lower end of the vertical conductor portion 36 has a coupling terminal 38.

58996 8 The U-shaped branch 39a, 39b has three parallel conductors 40a-40b, 4la-4lb, 42a-42b in the part parallel to the lower edge of the windshield.

On the other hand, the three conductors 40b, 4lb, 42b are branched in parallel. Before entering the vertical center conductor 36, they terminate in a conductor 43 which rotates the switch terminal 38.

The conductors 40a and 4la form branched conductors with free ends, while the conductor 42a is connected at 47 to the central conductor 36. The appearance of this structure is symmetrical.

The embodiment according to Figures 9 and 10 is similar to the previous two. However, the adjustment of the loop 44, 45 to provide tuning is more reliable, since then only the bridge, i.e. the connecting conductor between the conductors 44 and 45, only needs to be moved. In contrast, in the embodiment of Figure 8, the optimum is obtained only by successively varying the lengths of the compensating conductors 32c and 32d.

In general, when using a T-U combination (Figures 5-10), the connection of two parts of the antenna by means of a side circuit gives easier results than, for example, the connection by means of branches (Fig. 7) or by using additional capacitance on the other side (Fig. 5).

The reason for this is that using exclusively capacitive elements for phase correction, as is the case in the examples shown in Figures 5 and 7, phase equilibrium is obtained only in the narrow band due to the relatively high value of their reactance with respect to their ohmic resistance.

Even a small change in the distance that separates the conductors from the edge of the windshield frame can cause irregularity with these systems and lead to a deterioration in reception capacity.

In contrast, if a relatively large ohmic resistor deviation (about 20 ohms) is used to connect different parts of the antenna, as is the case with the embodiments of Figures 8-10, phase tuning is achieved over a much wider frequency range. These embodiments are thus much more sensitive to variations in the distance between the conductors and the frame.

Of course, in the embodiments according to Figures 9 and 10, it is not absolutely necessary to arrange the three conductors parallel to the lower edge of the windscreen. The principle, which specifically includes rotating the switch terminal and thus connecting the U-shaped second conductor branch to the side of the second branch, can of course also be implemented with only one or two conductors.

Figure 11 illustrates the result obtained with the antenna 9 58996 according to the invention. The measurements have been made with a transmitter with a frequency of 101 MHz and with the horizontal polarization of the transmitter. Diagram T corresponds to the symmetrical pattern of the T-shaped conductor. Diagram I corresponds to the antenna according to Fig. 4, in which an asymmetrical horizontal conductor is added to the T-conductor parallel to the lower edge of the windscreen.

The minimum value corresponding to the position of the vehicle directly towards the transmitter has almost completely disappeared. The minimum corresponding to the vehicle turning to the back transmitter is still left, but its value has increased by 8 dB. This latter minimum value is very difficult to remove because in this position the vehicle body acts as an attenuator between the antenna and the transmitter. This diagram shows that the average level of the antenna voltage in the antenna according to the invention has increased by about 3 dB.

With the exception of the example shown in Fig. 5, in other embodiments, conductor portions are used in all parts of the conductors to improve the directivity effect. From Figure 5, however, it should be noted that small reactances can be used to achieve dysymmetry and that the same effect is obtained by varying the inductance or capacitance; The essential object of the invention is that the vertical branches of the antenna are able to receive the electromagnetic field entering the zone of the windscreen, forming an antenna with good directional properties due to the adjustment of the impedances of the branches.

Claims (10)

1. An antenna for radio reception in the AM and FM area arranged on or in a vehicle window pane, comprising an antenna arranged at the center of the pane, a line tuned to the FM area with substantially vertical parts and a peripheral arranged along the frame, not closed conduit with predominantly horizontal portions, which are directly connected to the first conduit at a junction, characterized in that the second conduit is also tuned to the FM region and that the two sides of the junction point are located on the opposite branches of the second conduit the leads are designed asymmetrical. An antenna according to claim 1, characterized in that the asymmetric configuration is obtained by an inductive or capacitive acting extension of one of the two branches of the other antenna line. Antenna according to claim 1, characterized in that the two branches of the second antenna line are different in length. Antenna according to any of claims 1-3, characterized in that the two branches of the second antenna line are geometrically different. Antenna according to any one of claims 1-4, characterized in that the first antenna line is a vertical line (8) arranged at the center of the box, possibly provided at the upper end with a horizontal part (9) for more accurate tuning, and the second conduit (10) is arranged along the bottom edge of the box. An antenna according to any one of claims 1-4, characterized in that the first antenna line is a substantially vertical T-shaped line (13,14; 20,21) arranged at the center of the box and the second antenna line is arranged along the edges of the box. -shaped conduit (15a, 15b; 22a, 22b). Antenna according to claim 6, characterized in