JP2002111349A - Chip antenna element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chip antenna element capable of improving variation in frequency characteristics and the like at resonance. SOLUTION: A chip antenna 10 is provided with a radiation electrode 13, ground electrodes 15 and 17 and the like on an insulating substrate 11. Here, a recessed part 19 such as a groove is provided between the radiation electrode 13 and the ground electrodes 15 and 17. The recessed part 19 such as a groove specifies the distance between the radiation electrode 13 and the ground electrode 15 and 17 while a large width is selected to be an appropriate value depending on the depth and/or width of the recessed part 19 such as a groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip antenna element suitable for a microwave radio communication device such as a portable radio telephone and a wireless LAN (local area network).

[0002]

2. Description of the Related Art In a microwave radio communication device, especially a portable communication device such as a cellular phone, a monopole antenna or a microstrip antenna suitable for miniaturization and reduction in height is frequently used as an antenna element. The structure or principle of the microstrip antenna is described in detail in Antenna Engineering Handbook (p.109-111, edited by IEICE Ohmsha). These antenna elements are also called chip antenna elements.

[0003] As a chip type antenna element suitable for a cellular phone or the like, a configuration in which a radiating electrode is arranged on the upper surface of a rectangular parallelepiped insulating substrate and a ground electrode is arranged on the lower surface and power is supplied by a coaxial cable is disclosed in JP-A-10-209740. It is described in. In such an antenna element, the main characteristics such as the resonance frequency and the directivity are determined by the shape and size of the radiation electrode. For example, if a square whose side length is equal to 1/2 of the resonance wavelength is used as the radiation electrode, the antenna can be made non-directional in the vertical plane of the radiation electrode, and an antenna element suitable for a mobile phone or the like can be obtained.

[0004]

The chip type antenna is
Although the antenna is much smaller than other antennas, the present inventors have developed a more compact and high-performance antenna element based on market requirements, and filed an application in Japanese Patent Application No. 2000-113686. FIG. 11 is a perspective view thereof. The trapezoidal radiation electrode 13 disposed on the main surface of the insulating base 11 is sandwiched between the ground electrodes 15 and 17 from both sides, but the ground electrode is not disposed on the lower surface. In addition, a power supply electrode 12 is provided near the center to supply power by capacitive coupling. In the conventional configuration, a radiation electrode and a ground electrode are disposed on both main surfaces of the insulating base so as to face each other. However, the improved antenna has the ground electrodes 15 and 17 around the radiation electrode 13 as shown in FIG. A shielding effect is obtained. Due to this shielding effect, the antenna element is hardly affected by noise or the like from the surroundings, and stable antenna operation is possible. Further, the trapezoidal radiation electrode is effective in improving the band characteristics.

At present, frequencies assigned to microwave radio communication devices are from 800 MHz to around 1 GHz, and application of higher frequencies is being studied. The plan calls for increasing the bandwidth as well as increasing the frequency. Bluetooth is expected to have a radio frequency of 2.4-2.5GHz and a bandwidth of at least 100MHz. However, it is difficult for the above-mentioned antenna element to achieve this high target performance, and drastic measures have been required. Specifically, there is a problem of variation in resonance frequency.
According to the measurement results, the bandwidth has a little over 100 MHz, but the center frequency at resonance has a variation of ± 30 MHz with respect to 2.45 GHz. Due to the variation width of ± 30 MHz, the resonance frequency may deviate from the target value.

Generally, the resonance frequency of an antenna element is inversely proportional to the square root of the product of the inductance of the radiation electrode and the capacitance to ground. Inductance and capacitance are almost determined by geometrical factors such as the arrangement between the electrodes. However, due to the three-dimensional arrangement and the effect of the skin effect in the high frequency band cannot be ignored, the cause of the variation in the resonance frequency Finding was not easy. However, the following problems of the prior art were clarified.

FIG. 12 is an equivalent circuit of a chip antenna element. Of the circuit elements in FIG, Ci represents the feeding electrode coupling capacitance between the radiation electrode, C _G is the equivalent capacitance between the ground electrode and the radiation electrode, Rr is the radiation equivalent resistance, Lr is the equivalent inductance. Also, Cs is the stray capacitance, is obtained by collectively capacitance can not be identified other than C _G. Therefore, Cs is C _G
Will take a considerably smaller value than. During antenna operation, the resonant circuit of Lr and C _G is formed, the frequency is proportional to _{1 / (√ Lr C G)} . Also, at resonance Rr
Is equivalently the electromagnetic energy radiated from the antenna or the energy incident on the antenna.

[0008] Next, when the facing portion of the radiation electrode and the ground electrode at the upper left corner of FIG. 11 is enlarged, a schematic diagram as shown in FIG. 13 is obtained. This portion has a large effect on the value of C _G, considered approximately C _G is inversely proportional to Gd. As shown
The boundary between the ground electrode 15 and the radiation electrode 13 on the insulating base 11 is considerably irregular and intricate, and is not linear as shown by the broken line in the figure. Therefore, even in the design set in separation distance Gd, the effective will differ from values and Gd, the result C _G is not constant. C _G in the equivalent circuit is
The parameters such as the shape and arrangement of the electrodes and the physical properties of the insulating substrate are related. Among them, Gd has the largest influence, and Gd can be regarded as a main parameter. On the other hand, there is little variation in production of Lr. Therefore, variations in the resonant frequency greatly involved C _G, separation between the radiation electrode and the ground electrode, i.e., Gd is because it is not accurately formed.

When forming electrodes on an insulating substrate, a screen printing method is widely used. As is well known, the screen printing method is a method in which a pattern film made of a conductive paste is formed on an insulating substrate by screen printing, and then the electrodes are sintered at a required temperature, thereby producing small circuit components such as chip resistors and capacitors. Mass production technology used for
However, since the wettability between the conductive paste and the base material is not constant in the screen printing method, it is difficult to determine the boundaries of the electrodes to be constant as shown in FIG.
Gd formation was prevented.

Furthermore, in addition to the problem of wettability between the base and the conductive paste, there is expansion and contraction due to the temperature and / or stress of the screen sheet itself, which is one of the factors causing errors. Generally, in the screen printing method, a tolerance of about ± 20 μm is regarded as a practically allowable value. When converted to frequency, a tolerance of ± 20 μm corresponds to an error of ± 10 MHz. As a result of integrating the error factors described above, the resonance frequency is ± 30 MHz
z will vary.

On the other hand, Japanese Patent Application Laid-Open No. 10-256825 discloses a method for adjusting the variation in the resonance frequency of the antenna.
The method described in Japanese Patent Application Laid-Open No. H11-274839 and Japanese Patent Application Laid-Open No. H11-274839 is generally used. These methods use a duuter, laser, sandblast, or the like to trim the electrodes. Although this method is simple and easy to turn, it mainly involves manual work of mechanically removing the electrode and a part of the insulating base for each antenna element, and requires skill and many man-hours. In addition, it is difficult to standardize the position or amount of trimming, and there is a problem that the characteristics of the processed antenna element are slightly changed.

[0012]

Means for Solving the Problems The present inventors have sought a method that can suppress the variation of the resonance frequency, which is a problem of the prior art, and has good workability, and as a result, has arrived at a new electrode processing method. Furthermore, as a result of examining this electrode processing method in detail,
The present inventors have found that the present invention is very effective for widening the antenna element and the like, and completed the present invention.

A first aspect of the present invention is a method for determining a separation distance Gd between electrodes by providing a concave portion such as a groove between at least the radiation electrode and the ground electrode. Specifically, after the electrode pattern is formed on an insulating substrate, a groove having a Gd width is provided to physically separate both electrodes. By providing such a concave portion such as a groove, the interval between the radiation electrode and the ground electrode is made constant, and the variation in the resonance frequency is greatly suppressed.
In addition, the concave portion such as the groove used in the present invention includes a concave groove cut linearly or a local concave groove, and even a conceptually small depth formed on the surface of the insulating substrate. Including. This is because it is practically impossible to remove only the electrode on the insulating substrate, and the effect of the invention can be obtained even by a slight removal of the insulating substrate as a base material.

The gist of the present invention is that the peripheral portion of the electrode is processed and processed into a line or a plane. The present invention is a method based on a different idea and intention from a spot processing method such as conventional electrode trimming. Therefore, a special tool or device is not required for carrying out the processing, and it can be dealt with by a partial improvement of a generally used machining device, laser processing machine, sand blast or etching device. When a rotary cutter is applied as an example of the machining method, a processing tolerance of about several μm in width can be easily obtained. Compared with the conventional method using the screen printing method, the accuracy can be improved by one digit or more. Further, if it is desired to obtain an accuracy higher than that of the mechanical processing, etching or sandblasting using a mask with a resist film is an option.

[0015] In addition, the trimming method removes not only the electrode material but also the insulating substrate at the same time, which may cause unexpected results. However, according to the method of the present invention, since it is possible to perform a certain processing only at a necessary place, it is possible to minimize a change in characteristics due to the adjustment of the resonance frequency. In addition, the standardization of work is easy, and this is a processing method suitable for mass production. Further, it is not necessary to limit the concave portion such as a groove only between the radiation electrode and the ground electrode. Providing the concave portion such as the groove along the outer shape of the electrode has an effect of specifying the shape and dimensions of the electrode. It is in line with the technical philosophy.

A second aspect of the present invention is that the bandwidth of the antenna element can be arbitrarily controlled by appropriately selecting the cross section of the concave portion such as the groove. In the above-described invention, the invention mainly relates to the electrodes, but the invention includes not only the electrodes but also the insulating substrate. According to the present invention, an antenna element having a changed bandwidth can be easily manufactured.

A third aspect of the present invention is a configuration in which a dielectric is disposed or filled in a concave portion such as the groove. Providing a concave portion such as a groove between the radiation electrode and the ground electrode can be considered physically the same as replacing the dielectric between the radiation electrode and the ground electrode with air. When the space occupied by the air is replaced with a dielectric, it is possible to impart unique characteristics that are not limited to the physical properties of the insulating base. As is clear from the equivalent circuit, _CG is related to the resonance frequency and the bandwidth characteristics. However, as described in the above-mentioned invention, the characteristics of the antenna greatly depend on the material of the insulating base. Only a limited degree of change is obtained. Currently used insulating substrates are mainly limited to sintered materials such as titanium oxide and alumina. According to the present invention, desired antenna performance can be easily provided irrespective of the dielectric properties of the insulating base.

For example, if a low dielectric material such as polyethylene or glass is filled in a concave portion such as a groove, the resonance frequency is increased, and a wider bandwidth characteristic is obtained. If a thin film such as a non-linear or ferroelectric material is formed and arranged in a concave portion such as a groove, the resonance frequency may be lowered and the bandwidth may be narrowed. Documents describing the grooves or recesses described above,
Or, there is no prior art that suggests an effect. Hereinafter, embodiments of the present invention will be described in detail.

[0019]

FIG. 1 shows an embodiment according to the present invention. FIG. 3A is a top view of the antenna element, and FIG. 3B is a cross-sectional view taken along line AA ′. 11 differs from the conventional configuration shown in FIG. 11 in that a recess 19 such as a groove having a width Gd is provided between the radiation electrode 13 and the ground electrode 15. This antenna element can be manufactured by a processing method as shown in FIG. First, the radiation electrode 13 is placed on the insulating base 11.
In the step of forming the gate electrode 15 and the ground electrode 15, the gap between them is set to be smaller than Gd. After firing the electrode, a concave portion 19 such as a groove is cut in parallel to the ground electrode 15 with an appropriate depth d using a rotary cutter 21 having a cutter width Gd as shown in the figure. The concave portion 19 such as a groove includes the ground electrode 15 and the radiation electrode 13.
At the distance of Gd. In the conventional trimming method, a limited portion of the electrode is locally removed by a deuterer or the like.In this embodiment, however, the boundary of the electrode is trimmed linearly and to a constant width. Gd, which has been a problem in technology, can be finished with high precision. Therefore, it is clear that the variation in the resonance frequency can be significantly reduced.

FIG. 3 shows another embodiment in which the radiation electrode 13 extends not only on the main surface but also on the side surface 14 of the insulating base 11. By arranging the radiation electrode 13 on the side surface 14, the radiation efficiency can be increased, and a more practical antenna element can be provided. As shown, the head 41 of the radiation electrode 13 has a stepped shape due to the concave portion 19 such as a groove. FIG. 4 shows an embodiment in which a concave portion 19 ′ such as a groove is provided on the side surface 14 in order to increase the effect of the present invention.

Further, when the characteristics of the sample were evaluated in detail, it was found that changing the shape of the concave portion such as the groove changed the bandwidth characteristic of the antenna, and a search was made for a practical shape of the concave portion such as the groove. FIG. 5 shows a result calculated by simulation in a relationship between the depth d of the concave portion such as the groove and the bandwidth BW. In the figure, the broken line is the case of the embodiment shown in FIG.
The solid line is the embodiment of FIG. As a matter of course, the longer the length of the concave portion such as the groove between the radiation electrode and the ground electrode, the greater the effect of d. Also, d and BW are almost in a proportional relationship, and d = 0.3 mm
In this case, the BW can be doubled or more as compared with the case where there is no groove at d = 0. When only trimming of the electrode is necessary, no groove is provided, and d is as close as possible to zero. FIG. 6 shows the relationship between the width W of the concave portion such as a groove and the bandwidth BW. As in the case of FIG. 5, when W increases, BW also increases. If W = 0.2 mm, the BW can be increased by about twice or more. On the other hand, the width W of the concave portion such as the groove has a greater effect on the bandwidth WB than the depth d of the concave portion such as the groove.

The provision of a concave portion such as a groove between the electrodes can be physically considered as follows. In FIG.
It is assumed that the radiation electrode 13 is positively charged with respect to the ground electrode 15. Since the relative permittivity of the insulating base 11 is usually at least one order of magnitude higher than that of air, most of the lines of electric force are distributed around the recess 19 such as a groove as shown in FIG.
Pass through one. Therefore, it can be understood that the concave portion 19 such as a groove can control the number of lines of electric force in the insulating base 11 and the density distribution thereof. As the concave portion 19 such as a groove is made deeper or wider, the wraparound of the lines of electric force is reduced, and as a result, the number of lines of electric force is reduced. This appears as a decrease in capacitance between the electrodes, and is equivalent to an increase in bandwidth. further,
As the concave portion 19 such as a groove becomes deeper, the electrode separation distance Gd has almost no influence on the distribution of lines of electric force.
The same effect can be obtained with a smaller width. Phenomenologically, the same applies to the case where the recess 19 such as a groove is widened.

FIG. 8 shows an embodiment in which a dielectric having characteristics different from those of the insulating base is provided in the concave portion such as the groove of the above-described embodiment. In this example, the dielectric 25 is filled with a low dielectric constant material such as polyethylene or glass, but it is not necessary to completely fill the dielectric 25 in some cases. Further, it is also possible to form a film, and the selection of the arrangement or the material in which the dielectric 25 in the recess 19 such as the groove can contribute to the improvement of the antenna element is included in the technical idea of the present invention.

FIG. 9 shows a case where the cross section of a concave portion such as a groove is trapezoidal. By inclining the side surface of the concave portion 19 such as a groove, groove processing becomes easier as compared with the case where the groove wall surface shown in FIG. 1 is vertical. As the inclination of the side surface becomes gentler, the characteristics deviate from the characteristics shown in FIGS. 5 and 6, but a large deviation does not occur unless it becomes extreme. As can be seen from this example, in implementing the present invention, the cross-sectional shape of the concave portion such as the groove is a secondary choice, and it is considered that workability or workability should be given priority.

FIG. 10 shows a partially improved embodiment. This is a case where a concave portion 19 ″ such as a half-open groove is provided in a portion facing the radiation electrode 13 and the ground electrode 15, and a side groove 73 is provided around the uncut portion 71 and the radiation electrode 13. As in this embodiment, the present invention can be applied to a portion where the ground electrode and the radiation electrode do not face each other, and the stray capacitance Cs in the equivalent circuit shown in FIG. 13 can be minimized, which is effective in suppressing variations. Further, if the tip parallel portion 75 of the radiation electrode 13 is provided with a step as shown in the drawing, it is possible to further contribute to the improvement of the characteristics.
In addition, the uncut portion 71 is useful for improving mechanical strength and improving adjustment accuracy.

[0026]

According to the present invention, the variation of the resonance frequency, which has been a problem in the past, can be greatly suppressed, which contributes to the improvement of the yield at the time of manufacturing the antenna. Further, the wave number bandwidth characteristic and the like can be controlled by the shape of the concave portion such as the groove or the filling of the dielectric material, and various antennas having different characteristics can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a top view and a sectional view showing one embodiment of the present invention.

FIG. 2 is a schematic view of a method for processing a concave portion such as a groove according to the present invention.

FIG. 3 is a perspective view showing a second embodiment according to the present invention.

FIG. 4 is a perspective view of a main part showing a third embodiment according to the present invention.

FIG. 5 shows the relationship between the depth of a concave portion such as a groove and the bandwidth when the present invention is implemented.

FIG. 6 shows the relationship between the width of a concave portion such as a groove and the bandwidth when the present invention is implemented.

FIG. 7 is a distribution diagram of lines of electric force near concave portions such as grooves.

FIG. 8 is a cross-sectional view when a dielectric is arranged in a concave portion such as a groove.

FIG. 9 is a sectional view of a concave portion such as a groove according to the present invention.

FIG. 10 is a fourth embodiment of the present invention.

FIG. 11 is a perspective view of a conventional chip antenna element.

FIG. 12 is an equivalent circuit diagram of the chip antenna element.

FIG. 13 is an enlarged schematic view of a conventional electrode portion.

[Explanation of symbols]

10: antenna element, 11: insulating base, 12: feed electrode, 13: radiation electrode, 14: side surface, 15, 17: ground electrode, 19: recess such as groove, 21: cutter, 25: dielectric, 71: off Remaining part, 73: side groove, 75: tip parallel part

Claims (8)

[Claims] 1. A chip antenna element having a power supply electrode, a radiation electrode, a ground electrode, and the like disposed on an insulating substrate, wherein at least a concave portion such as a groove is provided between the radiation electrode and the ground electrode. A chip-type antenna element characterized by regulating the following. 2. The chip type antenna element according to claim 1, wherein the concave portion such as the groove has a required shape and a required cross-sectional area. 3. The method according to claim 1, wherein
A chip-type antenna element, wherein a concave portion such as the groove coincides with a part of an outer shape of the radiation electrode and / or the ground electrode. 4. The chip-type antenna element according to claim 1, wherein the recess such as the groove defines a separation distance between the radiation electrode and the ground electrode. 5. The chip-type antenna element according to claim 2, wherein the recess such as the groove has a rectangular cross section, and the bandwidth is controlled by the width and / or the depth. 6. The chip type antenna element according to claim 1, wherein a part or all of the concave portion such as the groove is filled with a dielectric. 7. The ground electrode according to claim 1, wherein the radiation electrode of the antenna element is an electrode disposed on at least a main surface of the insulating base and continuously and / or stepwise reduced in width. Are chip antenna elements arranged on both end surfaces of an insulating base and connected to one end of the radiation electrode. 8. The method for manufacturing an antenna element according to claim 1, further comprising a step of forming a concave portion such as the groove at a predetermined position after forming a radiation electrode and a ground electrode on the insulating base. A method for manufacturing a chip antenna element, comprising: