GB1561742A - Multiband antenna for window panes - Google Patents

Description

(54) MULTIBAND ANTENNA FOR WINDOW PANES (71) We, SOCIETA ITALLANA VETRO SIV SPA, an Italian Joint Stock Company, of Vasto (Chieti), Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a multiband receiving antenna supported on a windowpane, particularly on the windshield of a motor vehicle, for a radio receiving set.

The term "windowpane" is intended to mean a pane of glass or of plastics material.

The antenna may consist of conductors deposited by the silk screen process on the pane. In the case of an antenna supported on the windshield of a motor vehicle it is preferred where the windshield is formed from tempered glass that the antenna is deposited on that face of the pane which, when fitted in the vehicle, is the internal one, and where the windshield is formed from two glass panes bonded together that the antenna is deposited on one of the faces of the pane which is in contact with another face. Instead of depositing the conductors by the silk screen process, a conducting metal wire may be used.

Obviously, an antenna may be supported on any window of a motor vehicle, although the windshield is the most suitable place.

The present invention further relates to an antenna for receiving radio signals lying in various wave bands, for example, in the long wave band, the medium wave band, the short wave band, the metric or VHF wave band, the decimetric wave band, the UHF wave band, and generally in all the wave bands used for sound and television transmission, including the frequencies reserved for radio amateurs.

It is well known that majority of radio receiving sets for motor vehicles are provided with a single antenna socket in contrast to domestic receivers which has on one input socket for the medium wave band and another input socket for the metric wave band. Therefore, a problem which must be faced with antennas provided on motor vehicle windshields is obtaining good reception, for example, in the medium wave band as well as in the metric wave band with a single antenna socket provided in the radio receiving set.

In the prior art various shapes of antennas incorporated or embedded in windshields have been suggested in an attempt to ensure good reception in all wave bands. For this purpose antennas have been devised having a central vertical monopole or T-shaped element, which affords good reception particularly in the metric wave band, and there have also been devised antennas of greater length which run along the rim of the window pane, which afford good reception in the medium wave band.

However, the problem in these types of antennas with separate receiving elements for the various frequency bands is that the signals received by the individual elements add at the single input socket of the receiving set and thus it is difficult to obtain good reception through all wave bands. For example, an antenna designed to give good reception in the medium wave band generally does not have characteristics which give it good reception in the metric wave band and vice versa. In the prior art there has been suggested a type of antenna which was supported on the wind shield of a motor vehicle in which that part of the antenna which ways suitable for a certain wave band formed an undesirable load when the antenna was operated in a different wave band and, furthermore, in particular in the reception of the metric wave band the efficiency of the known types of antenna varied with the direction of reception.

According to the present invention there is provided a multi-band antenna supported on a window pane comprising an electrically conductive monopole component, an electrically conductive frame-shaped component, and an antenna terminal connected to both components, the frame-shaped component consisting of a single conductor commencing at the antenna terminal, bordering substantially the entire rim of the window, and ending short of the terminal, and the part of the frame-shaped component which borders the lower rim of the window including a succession of flattened S-shaped loops extending perpendicularly to the monopole component, each loop having a length corresponding to an odd multiple of a quarter of the wavelength corresponding to the central frequency of the metric wave band.

In the antenna of the present invention, the monopole component prevalently contributes to the reception of signals in the metric wave band and the frame-shaped component prevalently contributes to the reception of signal in another wave band, for example the medium wave band. Each component also contributes to the order of 10 to 20% to the reception of signals prevalently received by the other component. In this manner, instead of having two antenna components, each of which is active in the reception of signal in one wave band whilst the other component is without utility or even a parasitic load in the reception of this wave band, in the antenna of the present invention both components give an active contribution to the reception of signals.

The antenna of the present invention has the advantage of compensating for the reactive component of the impedance of the monopole component within a wide range of frequencies. The S-shaped loops in the part of the frame-shaped conductor which borders the lower rim of the window also have the function of raising the minima of the directivity curve by actively contributing to signal reception, said contribution being particularly valuable for those directions corresponding to the minima of the directivity curve for the monopole component.

The total impedance of the antenna of the present invention varies within the frequency range from 87.5 to 110 MHz between 100 and 200 ohms. The optimum impedance for matching an aerial to a car radio is 150Ohms, and so the antenna of the present invention tranfers the maximum input signal to an associated car radio.

The principle underlying the configuration of the frame-shaped component is that of obtaining a capacitance of approximately 100 picofarads together with a high loss resistance.

An antenna of the present invention satisfies the requirements of the majority of radio receiving sets presently marketed, which require a very high antenna capacitance of 70 to 100 picofarads (a capacitance value which when added to the capacitance of the co-axial cable and of the connector makes it possible, by means of a trimmer capacitor provided in the receiving set, to obtain the best possible tuning between the antenna and the receiving set with a total capacitance of approximately 150 picofarads) together with a high loss resistance (several lOOkilohms) for the reception of signals in the medium wave band and an antenna impedance of approximately 1500hms, which is prevalently resistive and which has a phase angle lying within + 300 in the metric wave band.

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a first embodiment of the present invention; and Figure 2 shows a second embodiment of the present invention.

Referring now to Figures 1 and 2, there is shown in each Figure an antenna supported on a motor vehicle windshield 1. Each antenna comprises an electrically conductive monopole component 2 extending vertically along the centre line of the windshield 1 and an electrically conductive frame-shaped component bordering substantially the entire rim of the windshield 1. Both components are connected to a common terminal 4 positioned adjacent the lower rim of the windshield for connecting the antenna to a radio receiving set.

Each of the frame-shaped components consists of a single conductor 3. This conductor forms a right lower leg bordering the right half of the lower rim of the windshield, a right lateral leg bordering the right lateral rim of the windshield, an upper leg bordering the upper rim of the windshield up to where, in the vicinity of the left rim of the windshield, it bends downward to form a left lateral leg and, in the vicinity of the lower rim of the windshield, bends inward to form a left lower leg bordering the left lower half of the windshield rim to the end short of the antenna terminal 4.

In the example shown in Figure 1, the conductor bends at the position short of the antenna terminal 4 to form an extension which runs parallel to the previous 3 conductor legs to end short of the right lower leg.

In both examples, the impedance value of the -monopole component 2 is matched by a succession of flattened S-shaped loops formed in the part of the frame-shaped components which borders the lower rim of the window. The S-shaped loops extend perpendicularly to the monopole components 2. In the example shown in Figure 1, there are two S-shaped loops 7 facing in opposite directions formed in the right lower leg of the frame-shaped component 3. In the example shown in Figure 2, there are two S-shaped loops 7' formed in the right lower leg of the frame component, and two S-shaped loops 7 formed in the left lower leg of the frame-shaped components, all the loops facing in the same direction. In the example shown in Figure 1, the impedance of the left lower leg is increased by the edition of a straight conductor 8 which runs parallel to that part of the extension which runs parallel to the left lower leg.

It has been found experimentally that the signal pickup capability of these examples may be improved if the level of the S-shaped loops is higher or at least at the same level at the terminal 4. If the S-shaped loops are positioned at a lower level, they will provide unsatisfactory compensation for the reactive component of the monopole conductor 2 for reception of signals in the metric wave band.

The choice of the spacing of the conductors of the frame-shaped component from the rim of the windshield is determined by the desired capacitance of the antenna and also by the size of the windshield. Since experience proves that the pick up efficiency is improved when the conductors are spaced further from the rim of the windshield, a correct balance should be obtained between a good capacitance value for the antenna and good pick up efficiency.

It has been found that in receiving signals in the medium wave band, with antenna configurations as shown in Figures 1 and 2, a good capacitance is obtained when the spacing of the conductors of the frame-shaped component from the windshield rim is approximately 7cm. When the size of the windshield permits it and the visibility through the windshield is not impaired, it is advantageous to increase this spacing to approximately 9 to locum. In the case of the example shown in Figure 1, the antenna capacitance is increased by the extension.

WHAT WE CLAIM IS: 1. A multi-band antenna supported on a window pane comprising an electrically conductive monopole component, an electrically conductive frame-shaped component, and an antenna terminal connected to both components, the frame-shaped components consisting of a single conductor commencing at the antenna terminal, bordering substantially the entire rim of the window, and ending short of the terminal, and the part of the frame-shaped component which borders the lower rim of the window including a succession of flattened S-shaped loops extending perpendicularly to the monopole component, each loop having a length corresponding to an odd multiple of a quarter of the wavelength corresponding to the central frequency of the metric wave band.

2. A multi-band antenna supported on a window pane substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. S-shaped loops 7 facing in opposite directions formed in the right lower leg of the frame-shaped component 3. In the example shown in Figure 2, there are two S-shaped loops 7' formed in the right lower leg of the frame component, and two S-shaped loops 7 formed in the left lower leg of the frame-shaped components, all the loops facing in the same direction. In the example shown in Figure 1, the impedance of the left lower leg is increased by the edition of a straight conductor 8 which runs parallel to that part of the extension which runs parallel to the left lower leg. It has been found experimentally that the signal pickup capability of these examples may be improved if the level of the S-shaped loops is higher or at least at the same level at the terminal 4. If the S-shaped loops are positioned at a lower level, they will provide unsatisfactory compensation for the reactive component of the monopole conductor 2 for reception of signals in the metric wave band. The choice of the spacing of the conductors of the frame-shaped component from the rim of the windshield is determined by the desired capacitance of the antenna and also by the size of the windshield. Since experience proves that the pick up efficiency is improved when the conductors are spaced further from the rim of the windshield, a correct balance should be obtained between a good capacitance value for the antenna and good pick up efficiency. It has been found that in receiving signals in the medium wave band, with antenna configurations as shown in Figures 1 and 2, a good capacitance is obtained when the spacing of the conductors of the frame-shaped component from the windshield rim is approximately 7cm. When the size of the windshield permits it and the visibility through the windshield is not impaired, it is advantageous to increase this spacing to approximately 9 to locum. In the case of the example shown in Figure 1, the antenna capacitance is increased by the extension. WHAT WE CLAIM IS:

1. A multi-band antenna supported on a window pane comprising an electrically conductive monopole component, an electrically conductive frame-shaped component, and an antenna terminal connected to both components, the frame-shaped components consisting of a single conductor commencing at the antenna terminal, bordering substantially the entire rim of the window, and ending short of the terminal, and the part of the frame-shaped component which borders the lower rim of the window including a succession of flattened S-shaped loops extending perpendicularly to the monopole component, each loop having a length corresponding to an odd multiple of a quarter of the wavelength corresponding to the central frequency of the metric wave band.

2. A multi-band antenna supported on a window pane substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.