Patent Application
20080291097
The present invention relates to an on-vehicle antenna system for installation in vehicles, electronic apparatus such as radio receivers, television receivers, portable telephone systems, VICS (Vehicle Information and Communication System), etc. The invention relates also to an electronic apparatus mounted with the antenna system.
There are various types of antenna systems mounted on a vehicle nowadays. For example, radio receivers, television receivers, portable telephone systems, GPS (Global Positioning System), ETC (Electronic Toll Collection System), VICS, etc. have their own antenna systems that fit to their specific operation. Since vehicles are mobile substance, it is not easy for them to recognize direction of a certain signal where it is coming from, with these exceptions of GPS, ETC, etc. where recognition of the signal direction is comparatively easy. Based on the general understanding, radiation pattern of antenna for vehicles other than that for GPS, ETC, etc. has been designed to be non-directional with respect to horizontal direction of a vehicle.
Japanese Patent Unexamined Publication No. H8-298406 (hereinafter referred to as Document 1), Utility Model Unexamined Publication No. S58-61509 (Document 2) and Japanese Patent No. 3594224 (Document 3) are some of the known publications of prior arts on the on-vehicle antenna systems.
Document 2 describes an on-vehicle antenna of space diversity antenna system. The antenna aims to make the directional characteristic into a substantially non-directional characteristic through a compensation of dip point of directional characteristic caused by the vehicle body, etc., using a plurality of antennas disposed at the vehicle's side window.
For the purpose of reducing the overall size of antenna system, monopole antennas of imbalanced operation have been employed for receiving television, radio broadcastings. Dipole antennas of balanced operation are not quite popular nowadays because they eventually take a large total size, and some other reasons. Monopole antenna element alone can not operate as an antenna, but it has to make use of metal body of the vehicle and the ground portion of coaxial cable's power supply line, etc. as part of the antenna system.
The antenna described in Document 1 is an imbalanced type antenna, which belongs to the same type as monopole antenna. It makes use of the metal body of vehicle and the ground portion of coaxial cable's power supply line as part of the antenna. Document 3 describes an imbalanced type antenna for use on a vehicle.
So far, on-vehicle antennas for radio, television reception have been designed so as they are non-directional; therefore, those of imbalanced type have been employed. However, as compared with an antenna installed above the roof of a vehicle, the above-described antenna installed at glass portion of vehicle demonstrates the significantly poorer reception characteristics.
Those illustrated in
Reasons why receiving characteristics deteriorate when monopole antenna unit 2 is installed at a window glass on the cabin surface, as compared with a case where it is disposed outside the cabin, had not been made sufficiently clear. The engineers involved in the present proposed technology started a thorough analysis of the causes by carrying out a number of experiments and simulations, and tried to find out a solution for improving the deterioration problem. They found out that the deterioration was caused in part by those reflected/scattered waves generated as the result of reflection/scattering of digital broadcasting waves by the vehicle's metal frame.
As understood from
Judging from the results of experiments and simulations, a monopole antenna disposed at a vehicle's glass portion receives a number of those waves reflected/scattered by the vehicle's metal frame, etc.
The results of simulation analysis shown in
Other deterioration factor with the reception percentage due to reflected/scattered waves in a vehicle cabin is that there is a difference in the Doppler frequency between a signal coming from the front or the behind of a vehicle received direct by on-vehicle antenna system and that received after it is reflected/scattered in the vehicle cabin. When a plurality of signals each having different Doppler frequency undergo a synchronized detection, symbol location of each demodulated signal is displaced along with the lapse of time from a should-be location, because of influence by the Doppler frequency. Especially in the digital television broadcasting which adopts OFDM (Orthogonal Frequency Division Multiplex) modulation, interference is caused at the synchronized detection between the carriers by the reflected/scattered waves in the cabin. Because of these, it turns out to be difficult to enforce the equalization processing on propagation path at a high accuracy level. This invites deterioration in bit error rate (BER) and packet error rate (PER), eventually causing deterioration of the antenna's receiving characteristics. The adverse influence of those waves reflected/scattered in a vehicle cabin reveals significantly when receiving the digital television broadcasting, digital radio broadcasting and portable telephone system which use digital signals. The influence ill-affects the demodulation also with the analog radio broadcasting and analog television broadcasting which use analog signals, and deteriorates the reception characteristics.
The engineers involved in the present proposed technology made extensive experiments and simulations, and understood the whole mechanism of deterioration how receiving of digital television broadcasting, etc. was ill-affected by those reflected/delayed waves caused by a metal frame of vehicle, etc. This subject had remained as a drawback whose picture was not clarified yet. Based on the new understandings, the engineers conceived that it was difficult to solve the deterioration issue through the conventional technical philosophy of pursuing an antenna of non-directional characteristics, or using a conventional monopole antenna aiming to reduce the overall size.
The present invention aims, on the basis of new knowledge, to overcome the inconvenience and offers an on-vehicle antenna system which would provide superior reception characteristics.
An on-vehicle antenna system in accordance with the present invention is installed at glass portion of a vehicle, with direction of the greatest radiation pattern directed towards ahead of the vehicle while the smallest radiation pattern towards behind of the vehicle. Or, it is installed at glass portion of a vehicle, with direction of the greatest radiation pattern directed towards outside of the vehicle's cabin in relation to the glass surface while the smallest radiation pattern towards inside of the cabin in relation to the glass surface. Being different from the conventional on-vehicle antenna systems which have non-directional radiation pattern, an on-vehicle antenna system in the present invention employs a certain directional antenna. The antenna system can receive only those waves arriving from outside of the vehicle, with those reflected/scattered waves suppressed. Receiving of the reflected/delayed waves, which being a key deteriorating factor with the antenna reception characteristics, is thus suppressed, and the reception characteristics are improved.
An on-vehicle antenna system proposed in the present invention is based also on the new inconveniences found out as the results of thorough studies carried out by the engineers involved, including the experiments and simulations for analyzing deterioration phenomenon due to those reflected/scattered waves caused by a metal frame of the vehicle. The engineers found out an effective means which significantly improves the reception characteristic of on-vehicle antenna system installed at a vehicle's glass portion by adopting an antenna having a certain directional property; the use of such a directional antenna was hardly thinkable in the conventional technical approach. A proposed antenna system provided at the glass portion of a vehicle, either on the surface at the vehicle's cabin or in the glass pane itself, in accordance with the present invention offers an additional advantage in favor of car designers who have long been afraid that an antenna installed outside of vehicle would injure subtle appearance of vehicle and induce a possible theft, besides an outstanding reception characteristic that is superior to conventional in-cabin antennas.
An electronic apparatus having on-vehicle antenna system, which being another item included in the present invention, is the one which is provided with at least one of a first on-vehicle antenna system installed at glass portion of the vehicle with direction of the smallest radiation pattern directed towards behind of the vehicle and a second on-vehicle antenna installed at glass portion of the vehicle with direction of the smallest radiation pattern directed towards inside of the cabin with respect to the glass surface.
An on-vehicle antenna system in accordance with a first embodiment of the present invention is described with reference to
“Direction of the greatest radiation pattern” means, in an exemplary illustration
“Direction towards ahead of a vehicle” means direction towards ahead of vehicle 14 from boundary plane 10 which contains the location of power supply portion 9 of radiation pattern 11. “Direction towards behind of a vehicle” means direction towards behind of vehicle 15 from boundary plane 10.
Based on the above definitions, that “direction of the greatest radiation pattern is directed towards ahead of a vehicle” means that direction of the greatest radiation pattern 12 of radiation pattern 11 is directed towards somewhere in the region ahead of vehicle 14 from boundary plane 10. That “direction of the smallest radiation pattern is directed towards behind of a vehicle” means that smallest radiation pattern 13 of radiation pattern 11 is directed towards somewhere in the region behind of vehicle 15 from boundary plane 10.
If an on-vehicle antenna system disposed at front windshield glass of the vehicle is provided with such directional pattern 11 directing towards ahead of the vehicle 14 as shown in
Since an on-vehicle antenna system in the present invention has a directional property whose radiation pattern 11 is directed towards ahead 14, the antenna system can avoid the above-described inconvenience. Thus a deterioration factor pertinent to an antenna system disposed at front windshield glass can be eliminated, and the antenna system would be able to generate superior reception characteristics.
In a case where an on-vehicle antenna system having a radiation pattern the greatest radiation pattern of which is directed towards behind of the vehicle while the smallest radiation pattern towards ahead is installed at rear windshield glass which contains a heater wire, an antenna for receiving television/radio broadcastings or something like that, it may be difficult for the antenna to exhibit the superior reception characteristics. This is because that the signals arriving from behind of the vehicle are reflected/scattered in the cabin and those reflected/scattered waves arriving from the front of the vehicle can be suppressed by the directional property of the antenna system, but those waves reflected/scattered by the heater wire, etc. disposed at the rear windshield glass may be difficult to suppress. Furthermore, since the heater wire and the antenna system make an electromagnetic coupling, it is may not be easy to realize a certain desired directional pattern. As the result, the antenna system receives the reflected/scattered waves more, as compared with a case where it is installed at front windshield glass. This means that the expected improvement of reception characteristics is difficult to realize. Therefore, an on-vehicle antenna system in the present invention may be installed at rear windshield glass only when the glass has no heater wire or the like conductive material.
Now, other example of on-vehicle antenna system in accordance with the first embodiment is described with reference to
Location of power supply portion 9 of radiation pattern shown in
By making radiation pattern 11 of an on-vehicle antenna system disposed at vehicle's glass portion to have a directional property towards outside 17 of vehicle cabin with respect to the glass plane as illustrated in
Shown in
Shown at upper area 22 of front windshield is a rear view mirror RM installed in the cabin, and a steering wheel HA at lower area 23.
Apart from the illustration
In
Apart from the illustration
Like in
In
Apart from the illustration
Like the examples shown in
Those logarithmic period dipole antenna 19 in
Furthermore, the number of antennas forming a diversity antenna is not limited to two, but three or more number of antennas may be used.
Although
Microstrip antenna may be installed at rear windshield glass if there is no heater wire or the like conductor existing at the rear glass; in a case where there is a heater wire or the like conductor in the glass, the antenna may be installed at the outside of cabin. Improved reception characteristics would be generated also in these cases, too.
From the reception percentages given in
There had been a concern whether the reception characteristic significantly deteriorated to those signals coming from the direction of smallest radiation pattern, if an on-vehicle antenna system employed such a directional antenna. However, a wave environment in which the practical reception percentage is prone to deteriorate most is the Rayleigh fading environment, where there is no direct wave existing. In an ideal Rayleigh fading environment, signals are arriving from all the directions with equal probability. Therefore, it is hardly thinkable that signals arrive from the direction of smallest radiation pattern with a deviated probability density; but signals are considered to be arriving also from the direction of the greatest radiation pattern at a certain probability rate.
In the actual field tests, on-vehicle antenna system having a certain directional pattern demonstrated the higher reception percentage as compared with the monopole antenna having a non-directional pattern, as shown in
An on-vehicle antenna system in accordance with a second embodiment of the present invention is described referring to
Taking notice on a direction of wave angle 0 degree-30 degrees, or the angle of high signal arriving probability, dipole antenna 27 may be disposed within a distance of 0.325λ from roof board 1. Then, roof board 1 works as reflector of dipole antenna 27 and the directional gain can be made to be 2 dBi or higher at the wave angle 0 degree-30 degree.
The angle incident upon dipole antenna 27 of those signals came into cabin from the direction of wave angle 0 degree-30 degree and reflected/scattered by metal substance, etc. in the cabin seems to be concentrating within a range between −150 degree and −180 degree, which being the opposite angle to the wave angle range 0 degree-30 degree. What is important in this occasion is that the directional gain at the angle range between −150 degree and −180 degree is small. If the antenna installation distance S between dipole antenna 27 and edge of roof board 1 is greater than 0.325λ, the directional gain at wave angle −150 degree becomes to be greater than that at wave angle 30 degree; namely, the antenna receives signals with more weight on the reflected/scattered waves which are coming from inside of the cabin.
Therefore, it is essential to install dipole antenna 27 within the antenna installation distance S 0.325λ (wave length) from the edge of roof board 1. Dipole antenna 27 installed at front windshield glass 3 in accordance with the above-described arrangement makes use of roof board 1 as the reflector and demonstrates superior receiving characteristics realizing a certain specific radiation pattern. The monopole antenna conventionally employed for an on-vehicle antenna system utilizes metal frame of the vehicle and the ground portion of a coaxial cable for power supply as part of the antenna. Therefore, the antenna is prone to receive the reflected/scattered waves.
Being different from the monopole antenna, since the dipole antenna performs a balanced operation it is not necessary for dipole antenna to utilize the vehicle's metal frame and the ground portion of power supply coaxial cable as part of the antenna. In this respect, the dipole antenna is not the type of antenna which readily receives the reflected/scattered waves coming from inside of the cabin. This is one of the important points for implementing a superior receiving performance. The same applies also to dipole-based Yagi antennas, logarithmic period dipole antennas and array antennas formed of two or more number of dipole antennas arranged on a straight line.
The method of using roof board 1 as the reflector and generating a higher directional gain in the direction towards ahead of a vehicle and a lower directional gain in the direction towards behind of the vehicle may be applied on Yagi antenna or logarithmic period dipole antenna, for reciting the same effects. If reflector of Yagi antenna is substituted by roof board 1, overall size of the antenna system can be further reduced.
The above-described dipole antenna, Yagi antenna, logarithmic period dipole antenna and array antenna may be provided formed within the glass pane. Or, the antennas may be provided by forming antenna conductor lines using a conductive material on a transparent film of PET (Polyethylene Terephthalate), PEN (Polyethylene Naphthalete), etc. and then affixing the film on the glass surface from inside. Method of forming the conductor lines can be a process of printing a conductor paste on the film, or depositing/sputtering copper or silver on a transparent film and etching it off leaving the area of antenna element. Or, copper or the like conductor lines may be affixed on a transparent film.
In order to provide seated passengers with a good visibility, it is preferred to install the antenna system at the upper area of front windshield glass, to be as close to the edge of roof board; describing more precisely, within 30 mm from the border between metal roof board edge and windshield glass, either contained in the glass pane itself or on the glass surface. When the antenna system is installed as such, the passengers can hardly recognize it, because it is almost hidden by decorative interior stuff disposed in the neighborhood region. This may also be another advantage.
In the cases of Yagi antennas, logarithmic period dipole antennas, array antennas, with which the overall size tends to become bulky, width of antenna elements may be made broader in a region hardly recognizable by the passengers' eyes, while that in other region narrower. By so doing, the radiation efficiency can be raised without substantially damaging the good sight.
The particulars of the second embodiment may be summarized as follows: Average width value of the antenna elements locating in a region within 30 mm from boundary between the metal roof board edge and windshield glass, regardless of either the elements are contained in the glass pane or on the surface of glass pane, is made to be greater than that of those locating out of the above region.
Although
There is difference in the Doppler frequency between the signal, either coming from ahead of a vehicle or behind of a vehicle, received direct by an on-vehicle antenna system and that received after it was reflected/scattered in the vehicle cabin. This is one of the deterioration factors with respect to the receiving performance. Doppler frequency is produced because the vehicle is proceeding ahead, or behind; in other words, it is not produced with respect to the waves arriving from the direction perpendicular to the vehicle's moving direction. So, the generation of Doppler frequency may be suppressed by introducing an on-vehicle antenna system having a directional pattern, whose greatest radiation pattern is directed perpendicular to the vehicle's direction of proceeding forward-behind while the smallest radiation pattern towards ahead, or behind, of the vehicle.
After making a thorough study with focus on the generation of Doppler frequency, which being one of the deterioration factors, the engineers involved came to propose a concept which uses a diversity antenna, which would solve the problem under discussion.
An on-vehicle antenna system in accordance with a fourth embodiment of the present invention is described with reference to
Other example of the fourth embodiment is described with reference to
Specific band of frequency used for the surface wave television broadcasting is as broad as 50% in UHF, 84% in VHF. It is not an easy task to realize such a broad specific band with a balanced type antenna. An on-vehicle antenna system in the fifth embodiment is the one which accomplished the task.
First conductor 102 has first right-angled vertex 104, first power supply vertex 105 connected with power supply section 101, and first acute angle vertex 106 other than those first right-angled vertex 104 and first power supply vertex 105. First conductor 102 includes first parallel side 107 connecting first power supply vertex 105 and first right-angled vertex 104 straight, first triangle base 108 connecting first right-angled vertex 104 and first acute angle vertex 106 straight, and first oblique side 109 connecting first acute angle vertex 106 and first power supply vertex 105 straight.
Second conductor 103 has second right-angled vertex 110, second power supply vertex 111 connected with power supply section 101, and second acute angle vertex 112 other than those second right-angled vertex 110 and second power supply vertex 111. Second conductor 103 includes second parallel side 113 connecting second power supply vertex 111 and second right-angled vertex 110 straight, second triangle base 114 connecting second right-angled vertex 110 and second acute angle vertex 112 straight, and second oblique side 115 connecting second acute angle vertex 112 and second power supply vertex 111 straight. First conductor 102's first parallel side 107 and second conductor 103's second parallel side 113 are disposed substantially parallel to each other.
The antenna system is disposed so as, for example, first triangle base 108 and second triangle base 114 are substantially parallel to conductive base 116. Further, the antenna system is disposed so as power supply section 101 is closest to base 116. The antenna system is disposed, for example, at front windshield glass so that first triangle base 108 and second triangle base 114 are substantially parallel to the boundary line formed between base 116, or the roof board of vehicle, and the front windshield glass.
Now, in the following, the operation how an antenna system in the fifth embodiment receives signal is described referring to
First conductor 102 is supplied from power supply section 101, and reception current i 108 which contributes to the signal reception flows in first oblique side 109, first parallel side 107 and first triangle base 108, respectively. Likewise, second conductor 103 is supplied from power supply section 101, and reception current i 114 which contributes to the signal reception flows in second oblique side 115, second parallel side 113 and second triangle base 114, respectively.
Reception current i 109 in first oblique side 109 flows from first acute angle vertex 106 towards first power supply vertex 105. Reception current i 115 in second oblique side 115 flows from second power supply vertex 111 towards second acute angle vertex 112. The antenna system resonates at a certain specific resonance frequency f1 because of reception currents i 109 and i 115 in first oblique side 109 and second oblique side 115. On the other hand, reception current i 108 in first triangle base 108 flows from first acute angle vertex 106 towards first right-angled vertex 104. Reception current i 114 in second triangle base 114 flows from second right-angled vertex 110 towards second acute angle vertex 112. The antenna system resonates at a certain specific resonance frequency f2 because of reception currents i 108 and i 114 in first triangle base 108 and second triangle base 114.
The flow direction of reception current i 107 in first parallel side 107 and that of reception current i 113 in second parallel side 113 is opposite to each other, as shown in
Specific band of an antenna system becomes broader because of these two different resonance frequencies f1 and f2 in the antenna system. As already described earlier, specific band is the measure for a frequency range, within which range a certain antenna characteristic is maintained with respect to the center frequency.
In the fifth embodiment, specific band is obtained from a calculation, based on antenna impedance specified by resonance frequency of antenna, of frequency range which makes the antenna VSWR (Voltage Standing Wave Ratio) characteristic 3 or lower. VSWR is an index for showing how much of the energy inputted to an antenna is transmitted and radiated without being reflected due to mismatching of antenna and propagation path. As expediency, the specific band in the fifth embodiment has been calculated assuming that the VSWR characteristic is greater than 3.
Since it is disposed so that first power supply vertex 105 and second power supply vertex 111 have an acute angle, both of first oblique side 109 and second oblique side 115, which are contributing to the radiation, can be separated from base 116 for a certain distance. As the result, an undesirable coupling between first oblique side 109, second oblique side 115 and base 116 can be avoided, and the radiation characteristics of antenna system improved. Although the operation of antenna system has been described at its signal reception, the same description applies to its signal transmitting operation. Specific band of the above antenna system changes depending on an angle of first acute angle vertex 106 and second acute angle vertex 112.
Now, change in the specific band is described using practical examples.
When angle θ 106 of first acute angle vertex 106 and angle θ 112 of second acute angle vertex 112 are within a range of approximately 12 degrees to 48 degrees, it exhibited the characteristics that was superior to the specific band with conventional dipole antenna. Within the above angle range, the specific band further expanded when θ 106 and θ 112 are approximately 20 degrees to 40 degrees.
If angles θ 106 and θ 112 at first acute angle vertex 196 and second acute angle vertex 112 are made to be more than 20 degrees, the lengths of first oblique side 109 and second oblique side 115 become to be more different from the lengths of first triangle base 108 and second triangle base 114. As the result, the specific band becomes greater.
On the other hand, if the angles θ 106 and θ 112 are made to be smaller than 40 degrees, first oblique side 109 gets to be closer to a parallel arrangement with first triangle base 108, second oblique side 115 to be closer to a parallel arrangement with second triangle base 114. When the vector of reception current i 109 in first oblique side 109 and that of reception current i 115 in second oblique side 115 are decomposed, respectively, into parallel component and vertical component with respect to first triangle base 108 and second triangle base 114, the vertical component of current vector becomes smaller as the result of the above-described reduced angles θ 106 and θ 112. Direction of the vertical component of current i 109 in first oblique side 109 and that of the vertical component of current vector i 115 in second oblique side 115 is opposite to each other; so, they set off to each other. Therefore, it is desirable that the currents have smaller vertical components. In this way, first oblique side 109 and second oblique side 115 will exhibit improved radiation characteristics, and the specific band broadened.
The specific band is maximized by making angle θ 106 at first acute angle vertex 106 and angle θ 112 at second acute angle vertex 112 to be approximately 30 degrees.
Now, signal receiving operation of an antenna system in the sixth embodiment is described referring to
The receiving currents flowing in first conductor 102 and second conductor 103 remain the same as in the fifth embodiment. Reception current i 119 which contributes to the receiving on perpendicular line 119 flows, as illustrated in
The above-structured antenna has the combined appearance of a broad band triangular dipole antenna and a dipole antenna. The antenna system exhibits an improved radiation characteristic, and expands the specific band a step further.
An antenna system in accordance with seventh embodiment is described referring to
The point of difference as compared with the sixth embodiment is that it is further provided with third oblique side 120 connected with the connection point of first parallel line 117 and perpendicular line 119, and fourth oblique side 121 connected with the connection point of second parallel line 118 and perpendicular line 119. Thus, an approximate isosceles triangle is formed with perpendicular line 119, third oblique side 120 and fourth oblique side 121.
The signal receiving operation of an antenna system in the seventh embodiment is described referring to
Reception currents i 102, i 103 and i 119 in first conductor 102, second conductor 103 and perpendicular line 119, respectively, flow in the same manner as in the fifth and sixth embodiments. Reception current i 120 in third oblique side 120 flows from the connection point of first parallel line 117 and perpendicular line 119 towards the connection point of third oblique side 120 and fourth oblique side 121. Reception current i 121 in fourth oblique line 121 flows from the connection point of third oblique side 120 and fourth oblique side 121 towards the connection point of second parallel line 118 and perpendicular line 119.
In an antenna system of the above-described structure, which is further provided with third oblique side 120 and fourth oblique side 121, the specific band can be broadened a step further.
An on-vehicle antenna system in accordance with the present invention brings about a significantly improved receiving characteristic with the antenna installed at a vehicle's window glass. The antenna system can be mounted on various kinds of electronic apparatus; for example, as the antenna for on-vehicle TV receivers, radio receivers, portable telephone systems, etc., among other kinds of electronic apparatus. Thus, possible field of application seems to be substantial for the antenna system in the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-107250 | Apr 2005 | JP | national |
| 2005-294842 | Oct 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/307046 | 4/3/2006 | WO | 00 | 12/11/2006 |
