JP2003110344A - Surface-mounting type antenna and antenna device mounting the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface mounting type antenna, to which directivity and bandwidth which are optimum to an antenna for Blue tooth are imparted, and an antenna device mounting the surface-mounting type antenna. SOLUTION: In the surface-mounting type antenna, a main radiation electrode and an auxiliary radiation electrode are arranged facing each other on dielectric or magnetic base material and are connected by using a connecting conductor. Since a style is used, where power feeding is performed to a junction part between the connecting conductor and the radiation electrodes by using a strip line, an impedance matching circuit is unnecessary, and very compact mounting is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna in which a radiation electrode is arranged on a substrate made of a dielectric material or a magnetic material and an antenna device having the antenna, and more particularly to a Bluetooth or wireless LA.
The present invention relates to a surface mount antenna suitable for N (Local Area Network).

[0002]

2. Description of the Related Art Surface mount type chip antennas in which a radiation electrode or the like is arranged on a dielectric or magnetic substrate and can be directly mounted on a circuit board are widely used in wireless communication devices such as mobile phones. On the other hand, Bluetooth (short-range wireless standard) for wirelessly connecting mobile phones and PCs
th) has started full-scale operation. As is well known, Bluetooth in wireless LAN is approximately 2.44GHz ± 40MHz.
It is said that it is sufficient to cover a close range with a radius of about 10 m. Antennas built into personal computers, etc. are not only characteristic in terms of directivity and bandwidth,
Excellent mountability is required. Conventionally, wireless LA
As an antenna for N or Bluetooth, a microstrip antenna or an inverted F-type antenna has been used.

FIG. 10 is a plan view showing the basic structure of a microstrip antenna, and a sectional view taken along the line AA.
In FIG. 10, 101 is a radiation conductor, 102 is a dielectric substrate, and 103 is a ground conductor. The dielectric substrate 102 is placed on the ground conductor 103, and the radiation conductor 101 is formed on the dielectric substrate 102 by etching or the like. And
A feeding point 104 is provided at a position where the input impedance on the radiation conductor 101 becomes equal to the impedance of the feeding point system.

Further, FIG. 11 is a plan view showing the structure of a one-side short-circuited microstrip antenna and its BB cross-sectional view. The one-side short-circuited microstrip antenna is such that the zero potential surface of the radiation conductor 101 in the above-described microstrip antenna is short-circuited to the ground conductor 103 by the short-circuit conductor 105. This way,
Despite operating at the same resonant frequency, it can be half the length of the radiating conductor.

Next, FIG. 12 is a plan view showing the structure of a plate-shaped inverted F antenna, and a sectional view taken along the line CC. Since the width Ws of the short-circuit conductor 105 is made smaller than the width Wb of the radiation conductor 101, the plate-shaped inverted F antenna can be downsized because the resonance frequency is lowered. Regarding the offset amount of the center of the short-circuit conductor 105 from the center line of the radiation conductor, it is advantageous to set the offset frequency at the end of the radiation conductor to lower the resonance frequency and reduce the size.

[0006]

The conventionally used wireless LAN system or Bluetooth antenna has the following technical problems. That is, it is a problem in terms of mounting and a problem in terms of characteristics such as directional characteristics and bandwidth. As shown in FIGS. 10 to 12, in the conventional antenna, the feeding point 104 is located inside the radiation conductor 101. This is a measure to be taken because impedance matching can be obtained only at the position shown in the figure, and impedance is mismatched at other points. Although not shown in the figure, a coaxial cable is used for power feeding, and the center conductor of the coaxial cable is inserted from the rear surface of the ground conductor 103. Therefore, at the time of mounting, the number of assembly work steps such as fixing the antenna, inserting the coaxial cable, and fixing the connection with the radiation conductor is increased, and it is necessary to become familiar with the work. On the other hand, there is also a mounting method that does not use a coaxial cable, but in this case, since a matching circuit or the like is inserted at the feeding point, the antenna device becomes large and complicated, and the wireless LA
It is not compatible with the N system.

Regarding the directivity, there are the following problems. For example, between mobile devices such as mobile phones, an omnidirectional antenna that does not depend on the relative posture between the devices is desirable. On the other hand, in a system that communicates between OA devices via a ceiling base station in an office or the like, an antenna having omnidirectionality in a horizontal plane is suitable so that the direction of each OA device on the desk is not restricted. . On the other hand, in order to perform stable communication between each OA device and the ceiling base station, an antenna having directivity in the ceiling direction with respect to the horizontal plane is suitable. Considering obstacles, ceiling base stations, and the like, it is considered that giving the directivity in the direction of 45 degrees to the horizontal plane is most suitable for the needs. However, in the conventional microstrip antenna and inverted F antenna, no consideration was given to the directivity described above, or the antenna had only insufficient characteristics.

Further, there is a problem that the bandwidth is narrowed due to the high frequency. Since the input impedance of the conventional antenna is low at the feeding point, the feeding method by capacitive coupling has been adopted as a countermeasure. However, in this power feeding system, the capacitance in series increases as the frequency increases, so the bandwidth becomes narrow. In particular, it is expected that it will be difficult to secure the required bandwidth in the high frequency range of 5 GHz or higher. An object of the present invention is to solve such conventional problems and provide a small and high-performance surface mount antenna and an antenna device suitable for mounting the same.

[0009]

In order to solve the above problems, an antenna having a completely new structure in which the radiation electrode is composed of a main radiation electrode and a sub-radiation electrode is devised based on the configuration of a conventional microstrip antenna. . Hereinafter, the solution means and the features will be described in detail for each claim. According to a first aspect of the present invention, in a surface mount antenna in which a radiation electrode is arranged on a dielectric or magnetic substrate, the radiation electrode includes main and sub-radiation electrodes, and the radiation electrodes are electrically connected by a connecting conductor. It is a surface-mounted antenna characterized in that Conventionally, an antenna having a plurality of radiation electrodes has a structure that is often found in an antenna intended for multiple resonance. The multiple resonance antenna is provided with a resonance circuit adapted to each frequency, and is configured so as not to be influenced by other resonance circuits. For this reason, a plurality of radiation electrodes are not connected to each other, and a method is generally adopted in which resonant circuits including the radiation electrodes are independently configured and gathered at one place. However, the antenna of the present invention is intended to operate as if the main and sub-radiation electrodes were only one electrode, and the main and sub-radiation electrodes are provided in order to improve the directional characteristics and the bandwidth. , And newly found a method of joining both electrodes with a connecting conductor.

Splitting the radiating electrode in two not only gives much more characterization choices than with a single radiating electrode, but it also makes it possible to remove constraints. For example, the directivity of a patch antenna or an inverted F antenna is determined by the relative relationship between the radiation electrode and the ground conductor. If a sub-radiation electrode is brought in here as the second electrode, a completely different state can be obtained. The distribution pattern of the electric field and the magnetic current is determined by the positions or shapes of the radiation electrode and the ground conductor, and is almost fixed by the configuration of the antenna. The introduction of the sub-radiation electrode gives the possibility of partially changing and controlling the fixed electric field or magnetic current pattern, and new characteristics can be expected for the surface-mounted antenna.

According to a second aspect of the invention, the main radiation electrode 11 is provided.
And the sub-radiation electrode 13 are opposed to each other via the base,
The surface mount antenna is characterized in that power is supplied to either of the joints between the main or sub-radiation electrode and the connection conductor 15. The purpose of making the main radiation electrode and the sub-radiation electrode face each other is to obtain an efficient resonant circuit. In order to operate the antenna most efficiently, it is preferable that the antennas are close to the parallel arrangement. However, it goes without saying that the effects of the present invention can be obtained if both electrodes face each other. Further, the radiation electrodes need only face at least partially, and do not need to face the entire surface. The crossing angle on both sides is 0
90 degrees is preferable, but considering that it depends on the surface configuration of the substrate, the case of 90 degrees or more is also possible.

The latter stage of the present invention is a power feeding method in which the joint between the radiation electrode and the connection conductor is used as a power feeding point in a broad sense. The effect of the present invention can be obtained only when it is combined with the electrode arrangement method in the preceding stage. The above-mentioned joint is not only suitable for work, but also has the necessary conditions for ensuring reliability. The surface mount type chip antenna is strongly required to have a compact power feeding structure, but the present invention enables power feeding on a circuit board by a method suitable for that purpose.

FIG. 1 is a principle diagram for explaining the basic elements of the antenna according to the present invention and the operation thereof. In the figure, reference numeral 10 is a surface mount antenna according to the present invention, and the base body is omitted so that the arrangement and bonding state of each electrode can be understood. The surface mount antenna 10 is arranged on the ground conductor 17 with a required gap. The radiation electrode is composed of a main radiation electrode 11 and a sub-radiation electrode 13, and both electrodes are joined by a connection conductor 15 arranged on the side surface to obtain conduction. However, this structure is basically different from the conventional microstrip antenna. In the conventional microstrip antenna, the radiation electrode is always arranged parallel to and facing the ground conductor. This is to form a resonance circuit using the electrostatic capacitance between the radiation electrode and the ground conductor. Therefore, the resonance current reciprocates between the radiation electrode and the ground conductor.

However, in the present invention, the distribution of the resonance current i is different. Most of i passes through the connection conductor 15 and flows to the main radiation electrode 11 and the sub-radiation electrode 13 as shown by the arrow in the figure. Part of the current is shunted to the ground conductor 17 side, but this does not affect the characteristics. That is, the resonance circuit of the antenna of the present invention is formed between the main radiation electrode 11 and the sub-radiation electrode 13. In other words, a + b, which is the sum of the widths of the primary and secondary radiation electrodes, is
It will have a wavelength / 4 relationship. On the other hand, the radiation electrode length c is preferably close to a + b. Further, if a and b are equal or close to each other, the size of the antenna can be reduced to almost half.

Further, as shown in FIG.
Is placed above the ground conductor 17 with a required gap spacing. Since the impedance matching action is obtained by this arrangement, the matching circuit can be omitted. The conventional surface mount antenna is a method of feeding power to a position where impedance is matched or inserting a matching circuit, but the present invention is characterized in that impedance matching is obtained by the arrangement relationship between the ground conductor and the radiation electrode. However, there is no literature that discloses or teaches such an impedance matching method.

A third aspect of the present invention is an invention of a surface mount antenna, wherein the connection conductor is defined in a substantially trapezoidal shape. The substantially trapezoidal connecting conductor has the effect of widening the bandwidth. As will be described later, it was found that as the trapezoidal ratio (upper side length / lower side length) increases, the bandwidth broadens almost in proportion. This is related to the stray capacitance formed between the main radiating electrode and the sub radiating electrode, but the shape of the trapezoidal hypotenuse seems to have little influence, and rather depends on the lengths of the upper and lower sides.

Next, when the above-mentioned antenna is mounted to form an antenna device, the invention of claim 4 is a structure in which the effects of the present invention can be sufficiently brought out. That is, in the antenna device which transmits and receives high frequency radio waves in cooperation with the ground conductor, the surface mount antenna according to any one of claims 1 to 3,
The antenna device is characterized in that the radiation electrode is installed parallel to the ground conductor surface and at a required distance. In the wording, the setting of the parallel and the separation distance of the radiation electrode with respect to the ground conductor is specified, but the radiation electrode is not in contact with or close to the ground conductor as in the conventional surface mount antenna.

According to a fifth aspect of the present invention, there is provided a method for feeding power to the antenna by using a strip line provided on the ground conductor substrate. By using the junction between the connection conductor and the main radiation electrode or the sub-radiation electrode as the feeding point, it is possible to feed power without using a coaxial cable.
Furthermore, assembly and mounting is greatly simplified. However, the impedance matching is not limited to a myriad of places, and is limited to a very limited place that satisfies certain requirements as described later. The feeding point of the present invention is not a place where impedance matching is performed, but is a requirement in mounting.

The invention of claim 6 is the antenna device according to claim 4, wherein the ground conductor is removed in a space wider than the size of the antenna on the surface of the ground conductor substrate whose both surfaces are covered with conductors, and the antenna is placed in this space. Is an antenna device. The gist of the present invention is that the original characteristics of the antenna can be easily obtained by placing the surface-mounted antenna at a required distance from the ground conductor rather than by directly mounting it on the ground conductor surface. Suitable distances will be described in detail in the examples.

[0021] Claim 7 is an invention of a power feeding method. The antenna device is characterized in that a strip line formed on the ground conductor substrate is connected to a joint between a connection conductor and a radiation electrode, and impedance matching is obtained by a relative positional relationship between the strip line and the ground conductor. By this method, the insertion of the impedance matching circuit is unnecessary, and a practical surface mount antenna can be obtained with a simple configuration. As described above, the feeding point of the antenna of the present invention is the junction between the radiation electrode and the connecting conductor, but since the input impedance seen from this junction is low, the reflection of the voltage wave is large and impedance matching is required. The present invention is a method that provides a solution to this problem without the use of matching circuits.

[0021] Claim 8 is an invention relating to the directional characteristics as an antenna device. That is, the antenna device according to any one of claims 4 to 7 has almost 4
It has directional characteristics in the direction of 5 degrees and has an omnidirectional characteristic in a plane parallel to the ground conductor. Although such characteristics have not been taken into consideration in the conventional wireless LAN antennas, the present invention can provide an antenna having a directional characteristic that has not been obtained conventionally.

The surface-mounted antenna of the present invention described above can not only improve directivity and band characteristics, but also contribute to miniaturization of the antenna. Further, although the base body of the conventional microstrip antenna is usually flat, if the main radiation electrode and the sub-radiation electrode are arranged as in the present invention using a square pole base body, it has a strong directivity in a predetermined direction, Moreover, a small antenna can be manufactured. This can be easily understood by considering the distribution of electric force lines or magnetic currents between the main radiation electrode and the sub-radiation electrode.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, examples will be described.
FIG. 2 is a perspective view of a surface mount antenna according to the present invention mounted on a substrate having ground conductors on both sides. As shown in the figure, the surface mount antenna 10 of the present invention is mounted in a space where the ground conductor 17 is removed and the insulating layer 27 is exposed.
This space is wider than that of the surface mount antenna 10, and a ground conductor substrate processed into a size described later is used. Further, since the ground conductor is arranged on the back surface of the surface-mounted antenna 10, the sub-radiation electrode 13 faces the ground conductor on the back surface via the insulating layer 27. As a result, the sub-radiation electrode 13 is separated from the ground conductor with a required gap.

For feeding power to the surface mount antenna, a strip line 23 provided at the center of the ground conductor substrate is used. Since the strip line 23 is a method of extending and connecting to the joint portion of the sub-radiation electrode 13 and the connection conductor 15, after the surface mount antenna is fixed to a predetermined position on the ground conductor board, the continuity can be obtained by soldering or the like. For example, a power supply circuit can be formed. Since the conventional power feeding method is a method in which a through hole is provided in a substrate or the like by using a coaxial cable, the structure of the ground conductor substrate is complicated, and much time is required for assembly and adjustment. However, the surface-mounted antenna of the present invention does not have such a problem, and the antenna can be mounted on the substrate quickly and surely, and more robust connection can be made, so that a highly reliable antenna device can be provided. Incidentally, D ₁ , D ₂ and W ₄ shown in the figure
Is 1 mm. The ground conductor substrate has a thickness of 0.6 mm, and the copper plates for the ground conductor on both sides have a thickness of several tens of μm.

Further, the main radiation electrode 11 has an extension portion 29 extending to the back side surface, and this extension portion 29 is a conductor portion that can be used for adjusting the resonance frequency. By appropriately processing the extension portion 29 by trimming or the like, the capacitance between the main radiation electrode and the sub radiation electrode can be adjusted, and the resonance frequency can be finely adjusted. The extension 29 is arranged to such an extent that it does not affect the radiation characteristics of the antenna, but it should be formed if necessary.

FIG. 3A shows a surface mount type amplifier according to the present invention.
The equivalent circuit of Tena is shown. For comparison, the conventional case is also
It is shown in FIG. Compared with conventional cases, capacitors
C_Two, C_ThreeAnd inductance L_ThreeIs newly added,
Wired as shown. C _Two, C_ThreeAnd L_ThreeIs Figure 2
The parts shown in the figure are equivalently replaced. In addition,
L₁= L₁₁+ L₁₂+ L_Thirteen, C₁≫ C_TwoAlso C_Three≫
C_TwoHave a relationship. Impedance matching is C_Two, C_ThreeOh
And L_ThreeIt is possible by appropriately selecting the value of
To C_ThreeThe choice of is important. On the other hand, because of the above relationship, C
_Two, C_ThreeAnd L_ThreeEffect on resonance frequency is small
The impedance matching is independent of the resonance frequency.
It can be carried out.

As a sample, a surface-mounted antenna having a length of 6 mm, a width of 3 mm and a thickness of 3 mm was mounted on a printed board having a length of 30 mm, a width of 20 mm and a thickness of 0.6 mm and evaluated. At this time, the ground conductor pattern is arranged in all areas other than the developed product on the component mounting surface of the board, and the antenna sample on the upper side of the board and the coaxial connector on the lower side are connected by strip lines. For this antenna sample, a measuring instrument such as a network analyzer was connected to the other end of the coaxial cable, and VSWR and gain (radiation directivity) were measured. Here, VSWR (Voltage Standing Wave Ratio:
The voltage standing wave ratio) is a value defined by the ratio Vmax / Vmin of the standing wave voltage when the incident wave and the reflected wave are in phase and opposite phase, and is used as an index of the impedance matching state.

In the present measurement, an anechoic chamber was used in which an electromagnetic wave absorber was laid on the inner wall of the shield room without any gap. Radio waves are transmitted from the antenna sample that rotates on the turntable,
Of these, only the direct wave was received by the horn antenna, and gain and radiation directivity were obtained based on the received power obtained. The printed circuit board is shown in FIGS. 4 and 5, and the mounting method thereof is shown in FIG.

FIG. 7 shows the measurement results of the directional characteristics. In FIG. 6A, it can be seen that high sensitivity appears in the vicinity of the 45 ° direction in the YZ plane, that is, in the plane perpendicular to the ground conductor 25 plane as shown in FIG. Similarly, (b) is the ground conductor 25
The directivity with respect to XZ parallel to that is omnidirectional so that it looks like a perfect circle. The prototype antenna sample was developed for 5GHz band wireless LAN.
This is a prototype made assuming that it can be used in the United States, Europe, and Japan.

FIG. 8 shows the frequency characteristics of the prototype antenna. A bandwidth of 123 MHz is obtained centering on a resonance frequency of 5.2 GHz, which is a characteristic that can be practically used. Further, FIG. 9 is a characteristic curve used when examining the shape of the connecting conductor. We simulated various shapes and found that they can be integrated into a trapezoidal shape. This time, we have adopted a trapezoidal ratio = 2 because of the balance between the center frequency and the ratio band.

[0031]

As described above, the present invention solves the conventional mounting problem of the surface mount antenna for Bluetooth and wireless LAN, and improves the directivity and band characteristic.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a perspective view of a surface-mounted antenna according to the present invention mounted on a substrate.

FIG. 3 is an equivalent circuit of a surface mount antenna.

FIG. 4 is a diagram of mounting a ground conductor substrate and an antenna.

FIG. 5 is a front view of a ground conductor substrate.

FIG. 6 is a schematic method of directivity measurement.

FIG. 7 is a measurement result of directivity.

FIG. 8 is a frequency characteristic of VSWR.

FIG. 9 is a trapezoidal ratio and a band ratio characteristic of a connecting conductor.

FIG. 10 is a plan view of a conventional stripline antenna.

FIG. 11 is a plan view of a conventional one-sided short-circuited microstrip antenna.

FIG. 12 is a plan view of a conventional plate-shaped inverted F antenna.

[Explanation of symbols]

10: (Surface mount type) antenna, 11: Main radiation electrode, 1
3: sub-radiation electrode, 15: connection conductor, 17: ground conductor, 1
9: signal source, 21: substrate, 23: strip line, 2
5: Ground conductor, 27: Insulating layer, 29: Extension part, 31: Coaxial connector, 33: Through hole, 101: Radiation conductor, 1
02: Dielectric substrate, 103: Ground conductor, 104: Feeding point,
105: Short-circuit conductor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidetoshi Hagiwara             Hitachi Metals, 70-2 Minamieicho, Tottori City, Tottori Prefecture             Tottori Factory Co., Ltd. F-term (reference) 5J045 AA01 AA21 AB05 AB06 DA08                       EA07 HA06 NA01                 5J046 AA04 AA07 AB13 PA07

Claims (8)

[Claims] 1. A surface-mounted antenna in which a radiation electrode is arranged on a dielectric or magnetic substrate, wherein the radiation electrode comprises a main and a sub-radiation electrode joined to each other by a connecting conductor. . 2. The surface mount antenna according to claim 1, wherein the main and sub-radiation electrodes are opposed to each other with the base interposed therebetween, and a joint portion with the connection conductor is a feeding point. 3. The method according to claim 1, wherein
The surface mount antenna, wherein the connecting conductor has a substantially trapezoidal shape. 4. An antenna device in which a surface-mounted antenna is mounted on a double-sided ground conductor substrate, wherein the surface-mounted antenna according to any one of claims 1 to 3 is arranged at a required distance from the ground conductor. And antenna device. 5. The antenna according to claim 4, wherein a strip line is provided on the ground conductor substrate, and the strip line is connected to a joint portion of either the main or sub radiation electrode and the connection conductor. apparatus. 6. The method according to claim 4 or 5,
At least the surface mount antenna is not directly mounted on the ground conductor of the ground conductor substrate. 7. The impedance matching between the strip line and the junction according to claim 4,
An antenna device obtained by appropriately combining electrostatic capacitances formed between a main radiation electrode, a sub-radiation electrode, or a ground conductor. 8. The method according to any one of claims 4 to 7, wherein the ground conductor surface has directional characteristics in a direction of approximately 45 degrees, and the surface parallel to the ground conductor is omnidirectional. Antenna device.