JP2009188910A - Vehicle-mounted antenna and resonant frequency adjusting method of the vehicle-mounted antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate adjustment of a resonant frequency. <P>SOLUTION: An antenna module 601 mounted on a vehicle body of a motor vehicle includes a slot 605 through which dielectric boards 602, 603, 604 can be inserted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mobile phone broadcast band in the United States (824 MHz to 894 MHz, 1850 MHz to 1990 MHz), a GPS artificial satellite GPS signal 1575.42 MHz band, an XM artificial satellite XM signal 2338.75 MHz band, and a combination of them. More particularly, the present invention relates to a mounting method for an antenna mounted on a dielectric material such as glass or a method for adjusting a resonance frequency of a vehicle-mounted antenna device suitable for a mixed-type antenna or a dual-band antenna operable at both high and low frequencies.

  There are a variety of mounting forms for in-vehicle antennas, such as a rod-shaped antenna on the roof outside the car, a glass-mounted antenna inside the car interior, and a box type that fits on the dashboard or inside a car part such as a room mirror. Has been.

  The characteristics (directivity characteristics, etc.) of the in-vehicle antenna change depending on various conditions such as the shape and size of the antenna element, the GND structure, the shape of the automobile, and the material. Therefore, a desired resonance frequency can be obtained when mounted on an individual vehicle. As shown in the figure, the best characteristics are ensured when mounted on the vehicle by making fine adjustments in the mounted state.

  Generally, the fine adjustment method of the resonance frequency that is often performed is to adjust the excitation frequency by changing the length of the antenna element in the mounted state or changing the path length of the current flowing through the antenna element by providing a notch. To do. Normally, when designing an in-vehicle antenna, evaluate the return loss characteristics in free space before mounting on the car body and make adjustments to bring the best characteristics. Since the resonance frequency fluctuates due to the influence of the body metal, etc., the antenna shape, dimensions, etc. are designed in advance to resonate at a frequency shifted from the desired resonance frequency in anticipation of this fluctuation. A method is sometimes used in which adjustment is performed so that the frequency is adjusted (resonated) to a desired frequency.

  For example, an antenna mounted on a windshield, such as a glass-mounted antenna or a box-type antenna, is an example of an antenna mounted on a windshield. Since glass is a dielectric, nearby antenna elements are affected by the glass, and the wavelength of the dielectric is shortened. It is generally known that the resonance frequency is lower than before mounting due to the effect. As shown in FIG. 1, the resonance frequency changes before and after mounting on an automobile body, but how much the resonance frequency is lowered is usually empirically determined from accumulated experimental data and the like. For this reason, the characteristic evaluation in the state affixed on the glass plate for evaluation of a windshield substitute etc. is performed in advance, and after mounting in a vehicle body, the step of performing further fine adjustment of a resonance frequency will be taken.

  The mounting method on the windshield is generally performed using a double-sided tape or an adhesive from the viewpoint of workability and cost. In addition, since the shape of a windshield of an automobile is usually a curved surface, an example of sandwiching a gasket that can be easily bent so that the antenna module can be flexibly adhered in accordance with the curvature can be seen.

  In-vehicle antennas mounted on the windshield are required to be compact and low-profile so as not to obstruct the field of view. In general, a reduction in the height of an antenna module results in a narrower band than a reduction in the volume of the antenna element. To improve this, the ground of the antenna itself is brought into contact with a part of a body metal such as a roof or a pillar in a pseudo manner. In addition, a device has been devised such as increasing the GND area or improving the radiation characteristics of a desired polarization plane by forming a three-dimensional shape.

  In addition, a so-called tunable antenna or the like that achieves matching by providing a variable capacitor in the matching circuit section and adjusting its capacitance has been put into practical use.

JP 2005-26783 A

  In mounting the vehicle-mounted antenna on the vehicle body, it is necessary to adjust the characteristics so that the resonance frequency is suitable for a specific vehicle type. The shape of the windshield, the curvature, the angle of inclination, the design of the metal parts such as the roof and the pillar are different for each vehicle type, and this is a factor that further increases the variation in in-vehicle antenna characteristics.

  When mounting a vehicle-mounted antenna on a vehicle body, it is necessary to perform fine adjustment of the resonance frequency for each vehicle model at the stage of mounting on the vehicle body in order to obtain sufficient antenna characteristics. There is an idea that the resonance frequency may be customized for each vehicle type so that it can be adapted to many types of vehicles. For example, in the case of a general-purpose antenna for an aftermarket, even if it is mounted, the quality varies due to the deviation of the resonance frequency. There may be a case where sufficient antenna characteristics cannot be obtained, and there is a problem that the individual difference increases depending on the mounted vehicle type or vehicle.

  Further, even when the device is designed and manufactured with the resonance frequency shifted in advance before mounting and then mounted on the vehicle body, there is a possibility that the desired resonance frequency may not be satisfied for the following reason.

  1) Dielectric constants vary among dielectrics such as glass and antenna housing.

  2) The windshield 202 of the vehicle is normally curved, and a gap space 203 is formed between the glass surface and the antenna unit 201 to be mounted, resulting in variations (FIG. 2).

  3) The double-sided tape and the adhesive 302 are also a kind of dielectric, and this also has a variation in relative dielectric constant. In addition, the in-vehicle box-type antenna module 301 is attached to the windshield 303 of the automobile with the double-sided tape 302. There are variations in the air layer on the surface and the amount of adhesive (Fig. 3).

  4) Naturally, characteristic variations also occur in the antenna element itself.

  5) In the case of the adjustment method in which the antenna element is modified, the balance between the resonance frequencies on the high frequency side and the low frequency side of the dual band antenna may be lost.

  In an in-vehicle antenna, these conditions are complicatedly entangled, so it is very difficult to keep the characteristics of the entire in-vehicle antenna stable and to maintain reproducibility. Therefore, there is a problem that the manufacturing cost at the time of mass production tends to increase because complicated fine adjustment work such as cutting the antenna element is required.

  In particular, in a mounting method that adheres to a dielectric such as a glass pasting type, a low-profile antenna design, that is, a design close to a planar antenna is often adopted, and in particular, a dielectric such as glass or a nearby It is easily affected by metal and easily leads to product variations. Further, for the purpose of downsizing, it is assumed that the tendency is further strengthened in an antenna in which a dielectric having a high relative dielectric constant is a part of a component aiming at a wavelength shortening effect.

  FIG. 4 is a graph showing changes in the return loss 401 calculated by simulation when the gap between the antenna element (copper) and the dielectric is changed. It can be seen that a slight gap change with the dielectric greatly contributes to the characteristic change.

  FIG. 5 is a graph showing changes in the return loss 501 calculated by simulation when the relative dielectric constant of the dielectric is changed. It can be seen that there is a change in the resonant frequency of about 100 MHz that only changes the relative permittivity by 1.5.

  As described above, it is extremely difficult to accurately manage in advance the slight variations in relative permittivity, fine glass and antenna spacing, etc., and to compensate for this variation. Since it is difficult to formulate a simple design value, it can be said that there is a risk that the in-vehicle antenna itself becomes a work of art.

  With respect to the tunable antenna, a separate matching circuit is required, and the work is complicated from the viewpoint of the difficulty of the adjustment method, and the increase in manufacturing cost is unavoidable. it is conceivable that.

  The object of the present invention is to make it easy to adjust the resonance frequency and suppress manufacturing variations as much as possible when mounting an in-vehicle antenna that features a low profile and compact shape on an automobile window glass surface. Another object of the present invention is to provide a resonance frequency adjusting method that contributes to reduction of manufacturing cost.

  In order to achieve the above object, an in-vehicle antenna according to the present invention is provided with a slot into which a dielectric plate can be inserted in an antenna module mounted on the body of an automobile.

  The method for adjusting the resonance frequency of an in-vehicle antenna according to the present invention adjusts the resonance frequency by forming a slot in an antenna module mounted on the body of an automobile and inserting or removing a plurality of dielectric plates.

  The present invention exhibits the following excellent effects.

  (1) The resonance frequency can be easily adjusted.

  (2) The resonance frequency can be adjusted without breaking the balance between the high frequency side and the low frequency side.

  (3) Fine adjustment of the resonance frequency is possible.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The present invention relates to a case where an in-vehicle antenna mounted in a form in which a resonance frequency change is assumed by being affected by a dielectric such as a window glass or a body metal when mounted on the body of an automobile is mounted on the body of the automobile. This is a method for adjusting a resonance frequency, and is a method for adjusting the resonance frequency of a vehicle-mounted antenna in which a slot into which a dielectric plate can be inserted is provided in the antenna module.

  At that time, the resonance frequency can be easily adjusted by inserting or removing a plurality of dielectric plates from the antenna module.

  Specifically, an antenna housing (antenna module) to be mounted on a vehicle body, in which a multilayer or multiple rows of dielectrics are formed in a part of an antenna housing including an antenna element and made of a dielectric such as ABS resin or polycarbonate. Resonance frequency is easily adjusted by providing a slot for inserting a plate, and a configuration in which a dielectric plate or a dielectric rod having a different relative dielectric constant can be easily inserted into or removed from the slot for inserting a dielectric plate. be able to.

  The embodiment of the present invention will be specifically described with reference to FIG.

  The antenna housing (antenna module) 601 is a box type made of resin or the like. The antenna housing 601 is provided with a slot 605 for accommodating a plurality of thin dielectric plates 602, 603, 604. The slot 605 is basically provided at a position close to the built-in antenna element (including the element part and the GND part), and the return loss characteristic of the antenna is changed by inserting the dielectric plates 602, 603, and 604 into the slot 605. It is provided in the position to do.

  There is no limitation on the number of dielectric plates 602, 603, and 604 that can be accommodated in the slot 605, and about 1 to 5 sheets can be normally inserted. The resonance frequency can be finely adjusted as the number of inserted sheets increases. However, since the thickness of the antenna module 601 increases, it is not sufficient.

  Dielectric plates 602, 603, and 604 are received in slots 605. The degree of change in resonance frequency varies depending on the number of inserted sheets. If there is a deviation in the resonance frequency during mounting, adjustment is performed by increasing or decreasing the number of dielectric plates 602, 603, 604, and the dielectric plates 602, 603, 604 may be moved closer to or away from the antenna element. It is good also as a structure which can be adjusted by doing.

  The material and relative dielectric constant of the dielectric plates 602, 603, and 604 are not limited, and any dielectric material having a relative dielectric constant may be used. Needless to say, an inexpensive material is selected. For example, FR-4 glass epoxy or ceramic may be used. Adjustment may be made by mixing dielectric plates 602, 603, and 604 having different dielectric constants. In addition, not only solid but also liquid such as grease and oil may be sealed. In addition, a guide or a door stop may be provided so that the dielectric plates 602, 603, and 604 can be inserted.

  The antenna housing 601 is provided on the window glass 606 of the automobile.

  FIG. 7 shows another embodiment. In the case where there is a dimensional limitation in the thickness direction of the antenna housing 701, as shown in FIG. 7, a structure may be adopted in which slots 702 are provided in the lateral direction (that is, the plane perpendicular to the window glass 703 of the automobile).

  In any case, it is important to provide the slots 605 and 702 in the vicinity of the built-in antenna element (that is, the position where the return loss characteristic changes due to the proximity of the dielectric).

  According to the present invention, the following excellent effects are exhibited.

  1) When mounting on the vehicle body, no complicated work such as cutting or shaving the antenna element is required, so that the resonance frequency can be adjusted easily, leading to a reduction in work cost.

  2) Since characteristic variations due to the proximity of a dielectric material such as glass are corrected by the dielectric material, adjustment is possible without breaking the balance between the high frequency side and the low frequency side of a dual band antenna or the like.

  3) Since the insertion slot has a plurality of layers or a plurality of insertion slots, it becomes possible to insert dielectrics having different relative dielectric constants, so that fine adjustment is possible, and an antenna with high quality and high accuracy can be provided.

FIG. 4 is a diagram for explaining the return loss of the dual-band antenna before mounting on the vehicle body (above the arrow) and a diagram for explaining the return loss of the dual-band antenna after mounting on the vehicle body (below the arrow). It is a figure showing that a gap space is generated when a box-type in-vehicle antenna is mounted on a windshield having a curvature of an automobile. It is a figure showing sticking an in-vehicle box type antenna module on a windshield of a car with a double-sided tape or an adhesive. It is the graph explaining the change of the return loss at the time of changing the gap between an antenna element and a dielectric material. It is the graph explaining the change of the return loss at the time of changing the dielectric constant of a dielectric material. It is a figure showing the antenna module which has a dielectric material board insertion slot by this invention. It is a figure showing the antenna module which has a dielectric material board insertion slot by this invention.

Explanation of symbols

601 and 701 Antenna housing (antenna module)
602, 603, 604 Dielectric plate 605, 702 Slot 606, 703 Automotive window glass

Claims (2)

  An in-vehicle antenna, characterized in that a slot into which a dielectric plate can be inserted is provided in an antenna module mounted on a car body of an automobile.   A resonance frequency adjusting method for an on-vehicle antenna, characterized in that a resonance frequency is adjusted by forming a slot in an antenna module mounted on a car body of an automobile and inserting or removing a plurality of dielectric plates.

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