GB2221352A - Antenna on automobile side window glass - Google Patents

Description

ANTENNA ON AUTOMOBILE SIDE WINDOW GLASS . /-, n -/- 2 2 16 52 This

invention relates to an antenna provided in an automobile side window glass for the reception of broad5 cast waves. The main element of the antenna is a cond.uctive strip which extends along the perimeter of the window glass.

In recent automobiles there is a trend to adoption of a so-called wi:,(4ow glash eLntenna for receiving broad- cast waves. In most cases the window glass antenna is provided to the rear window glass and is constructed of conductive strips disposed on the glass surface ina suitable pattern. The antenna is located in a relatively narrow space left above an array of defogging heater strips. Usually the conductive strips used as the antenna elements are electrically independent of the heater strips.

With an automobile window glass antenna of the above described type, it is difficult to receive FM radio broadcast waves and television broadcast waves with sufficiently high gains mainly because of narrowness of the space which the antenna is allowed to occupy. As a countermeasure it is known to make an electrical connection between the antenna strips and the heater strips to utilize the heater strips as auxiliary antenna elements. Howeverg a disadvantage of this measure is that during defogging operation considerable noise intrudes into the received signal.

Also it has been developed to provide the windshield of an antomobile with an antenna using either conductive strips or a transparent and conductive film.

In this case it is possible to receive radio broadcast waves with relatively high gains. However, in this case the antenna is liable to obstruct the driver's view, and when the location of the antenna is restricted so as to secure the field of view the antenna does not always exhibit sufficiently high reception gains.

There is a proposal (e.g., JP-A 61-265903) of providing an antenna to an automobile side window glass in which little restrictions are placed on the location and configuration of the antenna. However, with the side window glass antennas proposed until now it is difficult to receive FM radio broadcast waves and TV broadcast waves with sufficiently high gains in every band.

It is an object of the present invention to provide an automobile side window glass antenna which is capable of receiving FM radio broadcast waves and TV broadcast waves with sufficiently high gains.

The present invention provides an antenna attached to an automobile side window glass having a quadri- lateral shape for receiving broadcast waves, the antenna comprising a feed point disposed in a fore-upper corner i 1 1 region of the window glass and a main antenna element which is a conductive strip disposed in marginal regions of the window glass and comprises an essential part which extends from the feed point along the four edges of the window glass and has an end in the fore-upper corner region of the window glass at a short distance from the feed point.

The main antenna element may further comprise a supplementary part which extends from the end of the essential part along at least a portion of one edge of the window glass.

The direction of extension of the main antenna element from the feed point may be either clockwise or counterclockwise. In the former case the essential part of the main antenna element extends from the feed point first along the upper edge of the window glass, then along the aft edge, and then along the lower edge and fially along the fore edge. In this case the optional and supplementary part of the main antenna element extends along and parallel to a portion of the upper edge of the window glass. In the latter case the essential part of the main antenna element extends from the feed point first along the fore edge of the window glass, then along the lower edge, and then along the aft edge and finally along the upper edge. In this case the optional and supplementary part of the main antenna element extends parallel to the fore edge of the window glass and, preferably, further extends parallel to a portion of the lower edge.

Optionally an antenna according to the invention includes an impedance matching antenna element, which is a conductive strip connected to the essential part of the main antenna element at a point not very distant from the feed point. It is permissible to make connection of the impedance matching antenna element to the main antenna element in the manner of insertion of the former element in the latter element. The "insertion" means making a gap in the main antenna element to thereby divide the main element into two segments, connecting one end of the impedance matching element to one segment of the main element and the other end of the impedance matching element to the other segment of the main element.

Although the antenna according to the invention is provided to an automobile side window glass which has a smaller area than the rear window glass, this antenna serves as a wide-band antenna which exhibits sufficiently high gains in receiving FM radio broadcast waves in both the 76-90 MHz band used in Japan and the 88-108 MHz band used in many other countries and TV broadcast waves in the VHF band. Of course this antenna scarcely affects the driver's field of view.

In receiving a broadcast wave the gain of an antenna according to the invention depends on the total length of the main antenna element and maximizes when the total length takes an optimum value. In conventional automobile window glass antennas using conductive strips it is usual that the reception gain of an antenna periodically increases and decreases as the total length of the antenna elements varies. However, in the antenna according to the invention the reception gain becomes maximum only when the main antenna element has an optimum total length and decreases as the total length of the main element is made shorter or longer. The above described supplementary part of the main antenna element serves the purpose of optimumly adjusting the total length of the main element.

An antenna according to the invention is very suitable for application to a side window glass in the rear section of an automobile of a station wagon type.

If desired antennas according to the invention may be provided to side window glasses on the both sides of an automobile body. Furthermore, it is possible and will be advantageous to use a side window glass antenna according to the invention in combination with either another window glass antenna or a conventional pole antenna so as to make diversity reception.

In the accompanying drawings:

Fig. 1 is a schematic side elevational view of an automobile of a station wagon type with an antenna on a side window glass in the rear section; -6 Fig. 2 is an elevational view of an automobile side window glass provided with an antenna as an embodiment of the invention; Fig. 3 is a graph showing the dependence of the gain of an antenna according to the invention in receiving a FM radio broadcast wave on the length of the main element of the antenna; Fig. 4 shows a modification of the antenna of Fig. 2; Fig. 5 is an elevational view of an automobile side window glass provided with an antenna as another embodiment-of the invention; Fig. 6 shows a modification of the antenna of Fig. 5; and Fig. 7 shows another modification of the antenna of Fig. 2.

Figs. 1 and 2 show an embodiment of the invention. In an automobile 10 of a station wagon type, a side window glass 12 in the rear section is provided with an antenna having a main antenna element 14 and a feed point 16. The antenna is disposed on the inboard surface of the window glass 12. The main element 14 of the antenna is a conductive strip formed by printing a conductive paste onto the glass surface and, after drying, baking the glass 12 with the printed paste thereon.

The side window glass 12 has a trapezoidal shape, and the feed point 16 is positioned in the fore-upper corner of the window glass 12. The main element 14 of the antenna extends along the quadrilateral perimeter of the window glass 12. As shwon in Fig. 2 the main element extends parallel to the upper edge 12a of the window glass 12 from the feed point 16 to the aft-upper corner of the window glass 12 and turns downward to extend parallel to the aft edge 12b of the glass 12.

the aft-lower corner of the glass 12 the main element turns forward to extend parallel to the lower edge 12c of the glass to the fore-lower corner of the glass and then turns upward to extend parallel to the fore edge 12d of the glass 12. At a short distance from the feed point 16 the main elment 14 turns aft to extend parallel to the upper edge 12a of the glass and terminates in a mid-upper region of the glass 12. That is, the main element 14 consistis of four consecutive parts 14a, 14b, 14c, 14d which extend along the four edges 12a, 12b, 12c, 12d of the window glass, respectively, and a supplementary part 14e which extends from the end of the part 14d along a portion of the upper edge 12a. In other words, the main element 14 extends along the quadrilateral perimeter of the window glass 12 and further extends parallel to one edge of the glass.

The supplementary part 14e of the main element 14 is provided for adjusting the total length of the In 14 element 14. As mentioned hereinbefore, the gain of an antenna according to the invention in receiving a FM radio broadcast wave or a TV broadcast wave depends on the total length of the main element 14 and maximizes at a certain value of the total length. That is, the dependence of the reception gain of the antenna on the total length of the main element 14 is as represented by the curve in Fig. 3, wherein L m indicates an optimum of the total length of the main element 14. With respect to sample antennas of the configuration shown in Fig. 2, a test of the reception of FM radio broadcast waves in the 76-90 MHz band and the 88-108 MHz band was made by varying the total length of the main element 14 (by varying the length of the part 14e and, according to the need, the part 14d). The window glass 12 was 450 mm in the length of the upper edge 12a, 550 mm in the length of the lower- edge 12c and 370 mm in height, and every part of the main element 14 was at a distance of 30-50 mm from the nearest edge of the window glass. As the result, for almost every broadcast wave in the aformentioned bands the length-gain relationship was as shown in Fig. 3. From the test results it is suitable that the total length of the main element 14 is 15001700 mm, and preferably 1550-1650 mm, which means that the supplementary part 14e is considerably shorter than the upper edge 12a of the window glass.

In a sample of the window glass antenna of Fig. 2, the window glass 12 was 450 mm in the length of upper edge 12a, 550 mm in the length of lower edge 12c and 370 mm in height, and the feed point 16 was at a distance of 40 mm from the upper edge 12a and at a distance of 20 mm from the fore edge 12d. As to the main element 14: the part 14a was 400 mm in length, the part 14b was 310 mm long and at a distance of 40 mm from the edge 12b, the part 14c was 440 mm long and at a distance of 50 mm from the edge 12c, the part 14d was 260 mm long and at a distance of 40 mm from the edge 12d, and the part 14e was 200 mm long and at a distance of 20 mm from the upper part 14a.

Gains of this sample antenna in receiving FM radio broadcast waves and TV broadcast waves were measured and compared with gains of a standard dipole antenna. That is, for any frequency the gain of the dipole antenna was taken as the basis, 0 dB, and the gain of the sample antenna was marked on this basis. As the result, gain of the sample antenna was -21.9 dB on an average in the Japanese domestic FM radio broadcasting band of 76-90 MHz, -20.8 dB on an average in the foreign FM radio broadcasting band of 88-108 MHz and -20.4 dB on an average of the seven channels in the VHF TV broadcasting band of 90-222 MHz. For comparison, by the same testing a good example of conventional automobile rear window glass antennas in practical use exhibited an average gain (vs. dipole antenna) of -20 to 22 dB in any of the aforementioned three bands. Therefore, the antenna of Fig. 2 is judged to be a good antenna.

Fig. 4 shows a modification of the window glass antenna of Fig. 2. In addition to the main element 14 described with respect to Fig. 2, the antenna has an impedance matching antenna element 18 which connects to the main element 14 at a location near the feed point 16 and extends above the part 14a of the main element and parallel to the upper edge 12a of the window glass 12.

The impedance matching antenna element 18 serves the function of adjusting the impedance of the antenna close to'the impedance of the feeder connected to the antenna to thereby reduce a drop in the reception gain attributed to mismatching loss and to consequently realize wide-band reception of broadcast waves.

When the impedance Z a of an antenna and the impedance Z f of the feeder are mismatched, the amount of mismatching loss cS is given by the following equation: 5 = 11(1 - 1r, 12) where[" = (Z a - Z f)l(za + Zf).

Usually a coaxial cable is used as the feeder, and the resistance component, Rf, of the impedance Zf of the coaxial cable is 75 Assuming that the reactance component of Z f is zero, i.e., Z f = R f = 75SI, and that the impedance Z a of the antenna includes a reactance component X a besides a resistance component R a 9 ice., Z a = R a + iX a, of course it is desirable that the z reactance component X a of the antenna be very close to 0 n. Though the amount of mismatching loss J increases a s the absolute value of X a increases, the amount of the loss S is in a tolerable range insofar as the deviation of X from 0 ú)-is less than about j150 n. As to the resistance component R a it is desirable that R a be equal to or close to 75SI. Actually, however, some difference of R from 75 Slis inevitable. When the a value of R a is smaller than 75 n the difference, (75 - R a a, brings about a great increase in mismatching loss J even though the difference in relatively small. When the value of R a is larger than 75.1rLthe amount of increase in mismatching loss S attributed to the difference, (R a - 75) n, is relatively small. In the present invention the impedance matching antenna element is arranged so as to render the resistance component R a of the antenna impedance close to and greater than 75 S1to thereby decrease the amount of mismatching loss(.

In a sample of the window glass antenna of Fig. 4 the impedance matching element 18 had a length of 280 mm. The dimensions of the window glass 12 and the main element 14 of the antenna were as described with respect to the sample of the antenna of Fig. 2. To examine the effects of the impedance matching element 18, reception gains (vs. dipole antenna) of this sample antenna and the above described sample antenna of Fig. 2 were measured for FM radio broadcast waves ranging from 76 to 105 MHz. Impedance values of each sample antenna were also measured. The results are shown in the following table. The results indicate that by the inclusion of the impedance matching element 18 the resistance component R a of the antenna shifts toward the + (plus) side while the reactance component Xa is maintained within:t120 91, and that the reception gains of the antenna further increase by the addition of the impedance matching element 18. By a supplementary test the sample antenna of Fig. 4 exhibited an average gain of -18.9 dB (vs. dipole antenna) in receiving TV broadcast waves in the VHF band, which means an improvement on the antenna of Fig. 2.

Frequency Without Impedance With Impedance Matching Element Matching Element (MHz) (Antenna of Fig. 2) (Antenna of Fig. 4) R X Gain R X Gain a a a a (91) (.Cl) (dB) (rl) (S1) (dB) 76 28.3 -121.8 -25.8 40.6 -97.3 -22.6 0 80 41.2 -68.4 -23.1 64.7 -54.1 -21.8 84 68.1 -31.1 -17.5 77.2 -38.6 -17.8 88 107.3 +28.7 -21.1 112.6 +17.6 -20.9 145.7 +65.2 -21.8 151.1 +58.2 -21.5 163.4 +98.5 -20.5 187.3 +71.4 -20.1 100 123.6 +106.4 -19.3 120.5 +111.2 -18.8 117.4 +143.3 -21.2 96.4 +108.9 -20.4 average - - -21.3 - -20.5 I Fig. 5 shows another embodiment of the invention on the side window glass 12 of the station wagon 10 of Fig. 1. In this antenna the position of the feed point 16 is the same as in the antenna of Fig. 2. The main element 14 of the antenna extends from the feed point 16 first horizontally aftward over a very short distance and then parallel to the fore edge 12d of the window glass 12 to the fore-lower corner of the window glass 12, turns aft to extend parallel to the lower edge 12c of the glass to the aft-lower corner of the glass, turns upward to extend parallel to the aft edge 12b of the glass and then turns foreward to extend parallel to the upper edge 12a of the glass. At a short distance from the feed point 16, the main element 14 further turns downward to extend parallel to the fore edge 12d and, at a short distance from the part extending parallel to the lower edge 12c, turns aft to terminate at some distance from the fore edge 12d of the glass. That is, the main element 14 consists of four consecutive parts 14d, 14c, 14b, 14a which extend along the four edges 12d, 12c, 12b, 12a of the window glass 12, respectively, and a supplementary part (14e + 14f) which extends from the terminal of the part 14a along one edge of the glass and further along a portion of another edge of the glass.

With respect to sample antennas of the configura tion shown in Fig. 5, a test of the reception of FM radio broadcast waves in the 76-90 MHz band and the 88-108 MHz band was made by varying the total length of the main element 14 (by varying the length of the parts 14e and 14f). The dimensions of the window glass 12 were as described hereinbefore, and every part of the main element 14 was at a distance of 30-50 mm from the nearest edge of the window glass. As the result, at almost every frequency in the aformentioned bands the length-gain relationship was as shown in Fig. 3. From the test results it is suitable that the total length of the main element 14 of the antenna of Fig. 5 is 1650- 1850 mm, and preferably 1700-1800 mm, which means that the supplementary bart (14e + 14f) extends along one edge of the window glass and further extends along a portion of the adjacent edge of the glass.

In a sample of the window glass antenna of Fig. 5 the dimensions of the window glass 12 were as described hereinbefore, and the feed point 16 was at a distance of 20 mm from the fore edge 12d of the window glass and at a distance of 40 mm from the upper edge 12a. As to the main element 14: the part 14d was at a distance of 40 mm from the fore edge 12d of the window glass and had a total length of 300 mm including a horizontal length of 20 mm extending from the feed point 16, the part 14c was 440 mm long and at a distance of 50 mm from the lower edge 12c of the glass, the part 14b was 310 mm long and at a distance of 40 mm from the aft edge 12b, the part 14a was 360 mm. long and at a distance of 40 mm from the 1 j upper edge 12a, the part 14e was 260 mm long and at a distance of 20 mm from the part 14d, and the part 14f was 50 mm long and at a distance of 20 mm, from the part 14c. This sample antenna proved to be nearly equivalent to the antenna of Fig. 2 in gains in receiving FM radio broadcast waves and TV broadcast waves (VHF).

Fig. 6 shows a modification of the window glass antenna of Fig. 5. In addition to the main element 14 described with respect to Fig. 5, the antenna has an impedance matching antenna element 18 which connects to the main element 14 at or near the feed point 16 and extends parallel to the fore edge 12d of the window glass 12 between the edge 12d and the part 14d of the main element 14.

In a sample of the window glass antenna of Fig. 6 the impedance matching element 18 had a length of 220 mm.

The dimensions of the window glass 12 and the main element 14 of the antenna were as described with respect to the sample of the antenna of Fig. 5. This sample antenna proved to be nearly equivalent to the antenna of Fig. 5 in gains in receiving FM radio broadcast waves and TV broadcast waves (VHF).

In the present invention the impedance matching element 18 is an optional element used mainly for adjusting the resistance component of the antenna impedance rather than the reactance component, as explained hereinbefore. Therefore, the impedance matching element 18 does not need to be a straight linear element as in the above described embodiments. For example, an L-shaped element or a zigzag element may be employed as the impedance matching element. Fig. 7 shows the addition of an impedance matching element 18A in a zigzag shape to the antenna of Fig. 2. As shown in Fig. 7 it is possible to insert the impedance matching element in the main element 14.

In any case the impedance matching element is connected to the main element at a position not very distant from the feed point. The distance of the connecting point from the feed point is chosen according to the intended amount of adjustment of impedance, though it is preferable that the distance does not exceed 200 mm.

k z

Claims (14)

1. An antenna attached to an automobile side window glass having a quadrilateral shape for receiving broadcast waves, the antenna comprising: a feed point disposed in a fore-upper corner region of the window glass; and a main antenna element which is a conductive strip disposed in margi,%nl regions of the windnw glass and comprises an essential part which extends from said feed point along the four edges of the window glass and has an end in said fore-upper corner region at a short distance from said feed point.

2. An antenna according to Claim 11 wherein said main antenna element further comprises a supplementary part which extends from said end of said essential part along at least a portion of one edge of the window glass.

3. An antenna according to Claim 1.or 2, wherein said essential part of said main antenna element extends from said feed point.first along the upper edge of the window glass.

4. An antenna according to Claim 1, 2 or 3, wherein the total length of said essential part and said supplementary part of said main antenna element is in the range from 1500 to 1700 mm.

5. An antenna according to Claim 1 or 2, wherein said essential part of said main antenna element extends from said feed point first along the fore edge of the window glass.

6. An antenna according to Claim 5, wherein the total length of said essential part and said supplementary part of said main antenna element is in the range from 1650 to 1850 mm.

7. An antenna according to any one of the preceding claims, further comprising an impedance matching antenna element which is a conductive strip connected to said essential part of said main antenna element at a short distance from said feed point.

8. An antenna according to Claim 7, wherein said short distance of the connection of said impedance matching antenna element is not longer than 200 mm.

9. An antenna according to Claim 7 or 8, wherein said impedance matching antenna element is a straight element which extends parallel to one edge of the window glass.

10. An antenna according to Claim 7 or 8, wherein said impedance matching antenna element has a zigzag shape.

M X

11. An antenna according to Claim 10, wherein said impedance matching antenna element is connected to said essential part of said main antenna element by making a gap in said essential part and inserting the impedance matching antenna element in said gap.

12. An antenna according to any one of the preceding claims, wherein the side window glass is in a rear section of the automobile.

13. An antenna according to Claim 12, wherein the automobile is of a station wagon type.

14. An automobile side window glass antenna, constructed and arranged substantially as hereinbefore described with reference to Fig. 1 and any of Fig. 2 and Figs. 4 to 7 of the accompanying drawings.

Published 1990 at The Patent Office. State House. 66 71 High Holborn, London WC1R4TP.Purther copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD Printed by Multiplex techniques ltd. St Mary Cray. Kent, Con. l,'87