JP2015053548A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact antenna device resonating at a plurality of frequencies.SOLUTION: An antenna element Ant of the antenna device includes, on a dielectric, one end P1, another end P2 and an extension section ext extending between the one end P1 and the other end P2. The one end P1 is coupled with a power supply section OC and the extension section ext is formed in a loop. The other end P2 is coupled with the extension section ext, and a capacitor Ci is provided in the middle of the loop. The antenna element operates at a frequency resonating with the length of the extension section ext and a resonant frequency determined by the loop inductor and the capacitor Ci.

Description

  The embodiment relates to an antenna device and the like.

  In the technical field of mobile communications, various technologies have been developed for the purpose of high speed, large capacity, low delay, and the like. For example, in a communication system such as Long Term Evolution (LTE) Advance (LTE-Advance), it is allowed to increase the throughput by simultaneously using a plurality of carrier frequencies. The simultaneous use of a plurality of carrier frequencies is called carrier aggregation (CA).

  Since a plurality of carrier frequencies are used simultaneously in carrier aggregation (CA), the antenna of the communication apparatus must be a multiband antenna that resonates with a plurality of carrier frequencies. An example of a multiband antenna accommodates a plurality of antennas that resonate at a specific carrier frequency in a communication device.

JP 2006-42190 A International Publication No. 2006/030708 JP 2008-141739 A International Publication No.2012 / 124248

Kuo-Liang Wu, et al., "Wire Antenna for Dual Wideband Cellular Phone Application", Asia Pacific Microwave Conference, 2009. APMC 2009. pp.1796-1798

  However, when a separate antenna is accommodated in a communication device for each of a plurality of carrier frequencies, the area or volume occupied by the plurality of antennas (that is, the antenna device) in the communication device increases, and the communication device is downsized, etc. It becomes difficult to plan.

  In one aspect, an object of the present invention is to reduce the size of an antenna device that resonates at a plurality of frequencies.

An antenna device according to an aspect includes:
One end, the other end, and an extending portion extending between the one end and the other end, the one end is coupled to a power feeding portion, the extending portion is formed in a loop shape, and the other end is An antenna device coupled to the extending portion and provided with a capacitor in the middle of the loop.

  It is possible to reduce the size of an antenna device that resonates at a plurality of frequencies.

The figure which shows an example of a communication apparatus. The figure which shows an example of the antenna device by embodiment. The figure which shows a mode that the capacitor is formed of the distributed constant circuit. The figure which shows the example which the extending | stretching part ext is bent at the point F. It shows how the antenna device is resonating at the fundamental frequency f _1. It shows how the antenna device is resonating at the resonance frequency f _2. Diagram showing the frequency dependence of the S parameter S ₁₁ for the antenna device. Shows a comparative example of the frequency dependence of the S parameter S ₁₁ for monopole antenna capacitor is not provided. The figure which shows the monopole antenna in which the capacitor is not provided. Diagram showing the frequency dependence of the S parameter S ₁₁ for various capacitor C _{i (i} = 1,2,3,4,5). The figure which shows the model by which the antenna element Ant was cut | disconnected physically at a certain place (alpha). In disconnected model diagram showing the frequency dependence of the S parameter S ₁₁ for various capacitor C _{i (i} = 1,2,3,4,5). The figure which shows electric current distribution in case the antenna apparatus by the model which is not a separation model is resonating at the resonance frequency. The figure which shows electric current distribution in case the antenna apparatus by a separation model is resonating at the resonance frequency. The figure which shows the antenna apparatus shown in FIG. 2 for the comparison with another example. The figure which shows the antenna apparatus with which the capacitor | condenser Ci was provided between the point E and the point B of an extending _| stretching part. The figure which shows the antenna apparatus with which the point F and the point K were couple | bonded. The figure which shows the antenna apparatus with which two loops were piled up. The figure which shows the antenna apparatus which extended the monopole antenna from the point B. The figure which shows a mode that the extending | stretching part ext was formed with the plate-shaped track. The figure which shows the example which formed the antenna apparatus with the dipole antenna. The figure which shows the example of the antenna device which can switch a capacitor using switch S. The figure which shows the frequency dependence of efficiency (eta) in a state without matching loss. Resonant frequency resulting S-parameter S ₁₁ of the smaller value is a diagram showing a state which is not the maximum efficiency η in the absence of consistent loss. The frequency dependence of the S parameter S ₁₁ and the efficiency η after the matching circuit is adjusted so that the S parameter S ₁₁ when the capacitance value of the capacitor is _Cy is a small value at the desired carrier frequency f _x is shown. Figure. The figure which shows the design procedure which designs an antenna apparatus. The figure which shows the state in which the antenna element Ant is not couple | bonded with the electric power feeding part OC, and the capacitor is not connected. Diagram showing the frequency dependence of the S parameter S ₁₁ of the antenna device. The figure which shows the Smith chart about an antenna apparatus. The figure which shows the antenna which provided the electric power feeding part OC and the capacitor in series in one loop, and formed the loop. The figure which shows the antenna by which the extending | stretching part ext extended from electric power feeding part OC did not form the loop, and the capacitor was provided in the middle of the loop. The figure which shows the antenna apparatus which made two monopole antennas coexist.

  Embodiments will be described from the following viewpoints with reference to the accompanying drawings. In the figures, similar elements are given the same reference numbers or reference signs.

1. 1. Communication device 2. Antenna device Operation 3.1 Basic operation 3.2 Detachment model 4. 4. Modification 4.1 Modification of antenna shape 4.2 Modification using plate antenna 4.3 Modification using dipole antenna 4.4 Modification using switch 5. Correlation between S parameter, efficiency and resonance frequency Design method Comparison with other antennas

<1. Communication device>
FIG. 1 shows an example of a communication device. The communication device 1 has an antenna space 2 that accommodates an antenna device such as a multiband antenna. The antenna space 2 is not limited to the example of FIG. 1, and may be, for example, above the communication device 1. The communication device 1 may be any suitable device capable of performing wireless communication using one or more carrier frequencies. For example, the communication device 1 is a mobile phone, a user device, an information terminal, a high-performance mobile phone, a smartphone, a tablet computer, a personal digital assistant (PDA), a portable personal computer, a palmtop computer, a laptop computer, a desktop computer, etc. It may be. Furthermore, the communication device 1 may be a mobile terminal or a fixed terminal. For example, the communication device 1 may be a base station or an access point. Since the antenna device according to the embodiment occupies substantially the same space as the monopole antenna, it is particularly advantageous for a portable terminal that can use only a limited antenna space.

  The communication device 1 can perform wireless communication using one or more carrier frequencies. In particular, performing wireless communication using a plurality of carrier frequencies is referred to as carrier aggregation (CA). A plurality of carrier frequencies used together by carrier aggregation (CA) may belong to different frequency bands or may belong to the same frequency band. Frequency bands are extremely long wave (30-3kHz), very long wave (3-30kHz), long wave (30-300kHz), medium wave (300kHz-3MHz), short wave (3-30MHz), ultra short wave (30-300MHz), micro A classification such as a wave (300 MHz or more) may be used. In particular, the frequency band may be an I, G, P, L, S, C, X, Ku, K, Ka, V, or W band of microwaves. These are only examples of frequency bands, and frequency bands based on other classification methods may be used.

  As an example, the frequencies used simultaneously by carrier aggregation (CA) may be two carrier frequencies belonging to different frequency bands such as a carrier frequency of 800 MHz band and a carrier frequency of 2 GHz band. As another example, the frequencies used simultaneously by carrier aggregation (CA) may be two carrier frequencies belonging to the same frequency band such as a carrier frequency in the 800 MHz band and a carrier frequency in the 700 MHz band. Not only two but also three or more carrier frequencies may be used simultaneously.

<2. Antenna device>
The communication device 1 may perform wireless communication by carrier aggregation (CA). Therefore, the antenna device of the communication device 1 is preferably a multiband antenna that can simultaneously transmit and receive radio waves of a plurality of carrier frequencies.

  FIG. 2 shows an example of the antenna device according to the embodiment in terms of a plan view, a UU line cross-sectional view and a VV line cross-sectional view. However, it should be noted that the dielectric is not drawn in the plan view. Such an antenna device is accommodated in the antenna space 2 of FIG. The antenna device includes a ground plane G, a power feeding section OC, an antenna element Ant, and a matching circuit M.

  The power feeding unit OC supplies a signal for generating a radio wave having a predetermined frequency on the ground plane G.

The antenna element Ant is a quarter-wave antenna having one end P1, the other end P2, and an extending portion ext extending between the one end P1 and the other end P2. The antenna element Ant may therefore be referred to as a monopole antenna. Quarter wave antenna Ant resonates at a certain fundamental frequency f _1, 1 a length of a quarter of the fundamental wavelength lambda ₁ corresponding to the fundamental frequency f ₁ (= speed of light _{/ f 1) (λ 1/} 4 ) Corresponds to the length of the extension part ext. The antenna element Ant is formed by a line bent at a right angle at three points of points A, B, and D. One end P1 is coupled to the power feeding section OC via the matching circuit M. The other end P2 of the antenna elements Ant is, of point E of the extending portion ext, point B, as a point D, point F draw one loop is coupled to the point E via a capacitor C _i.

  In addition, point A, point B, point D, point E, and point F in FIG. 2 are only drawn with emphasis to clearly indicate the location in the middle of the extension part ext, and actually have a structure like a black circle. Note that does not exist.

Capacitor C _i is a the other end P2 and the point E in the middle of the stretched section ext capacitively coupled. The capacitor C _i may be formed as an individual element as shown in the VV line sectional view, or may be formed as a distributed constant circuit as shown in FIG. For distributed constant circuit, the capacitance of the capacitor C _i is or gap or gap d between the lines is determined by the area and the like of the length R, or line of the line.

In the case the capacitor C _i is discrete elements, as shown in FIG. 4, so that the distance between the other end P2 and the point E matches the length of the individual elements, the stretching portion ext is bent at the point F The distance between the other end P2 and the point E may be shortened. In the example shown in FIG. 4, the line width of the extending portion ext is about 1 mm, the distance between the points BD and EF is about 2 mm, and the distance between both ends of the capacitor Ci is about 0.6 mm. It is not limited to this.

As will be described later for specific operations, loop, the resonance frequency f ₂ = [2π√ (L · formed in terms of FIG. 2 E, point B, point D, point F, by the other end P2 and the capacitor C _i C _i )] ^-1 to resonate. L represents the inductance of the loop. The resonance frequency f ₂ is different from the fundamental frequency f _1. That is, the antenna element Ant forms an antenna device that resonates not only at the fundamental frequency f ₁ but also at the resonance frequency f ₂ .

  The matching circuit M adjusts the impedance so that the energy loss is substantially zero between the antenna element Ant and the power feeding section OC. Furthermore, by adjusting the impedance of the matching circuit M, the frequency (resonance frequency or matching frequency) of radio waves transmitted and received via the antenna element Ant can be adjusted to some extent.

As shown in the UU line sectional view of FIG. 2, the antenna element Ant may be realized as a linear line on a dielectric provided on the ground plane G. Forms other than the linear line will be described in “4.2 Modification Using Plate Antenna”. The dielectric may be made of any suitable material. As an example, the dielectric may be made of a material such as FR4 (Flame Retardant Type 4), ceramics, Teflon (registered trademark), etc. formed of glass epoxy resin. The pattern of the antenna element Ant may be formed of any suitable conductive material. As an example, the pattern of the antenna element Ant may be formed by plating a conductive material such as copper (Cu), gold (Au), silver (Ag), stainless steel or the like on the dielectric. The conductivity of the conductive material is, for example, 5.8 × 10 ⁵ (S / m).

<3. Operation>
<< 3.1 Basic Operation >>
The operation of the antenna device shown in FIG. 2 will be described. As described above, the antenna element Ant resonates not only at the fundamental frequency f ₁ but also at the resonance frequency f ₂ .

FIG. 5 schematically shows how the antenna device resonates at the fundamental frequency f ₁ . The arrow corresponds to the current flow. The length of the extending portion ext extending from one end P1 to the other end P2 of the antenna element Ant is equal to _one quarter (= λ 1/4) of the fundamental wavelength λ ₁ corresponding to the fundamental frequency f ₁ . The fundamental wavelength λ ₁ satisfies the relationship of λ ₁ = light speed / f ₁ . When the antenna device is resonating at the fundamental frequency f ₁ , the part of one end P1, point A, point E, point B, point D, point F and the other end P2 of the antenna element Ant is a monopole antenna. It is working.

Figure 6 shows how the antenna device is resonating at the resonance frequency f ₂ schematically. The arrow corresponds to the current flow. Of the antenna element Ant, the portion of the loop formed by point E, point B, point D, point F, the other end P2, and the capacitor C _i is the resonance frequency f ₂ = [2π√ (L · C _i )] ⁻ Resonates at ¹ . L represents the inductance of the loop. The resonance frequency f ₂ is different from the fundamental frequency f _1. That is, when the antenna device is resonating at the resonance frequency f _2, part of the loop, forms a LC resonant circuit as shown in an equivalent circuit diagram of the right side.

FIG. 7 shows simulation results of calculating the S parameter S ₁₁ of the antenna apparatus shown in FIG. 2 for various frequencies. In the simulation, the distance from point A to point B in the extension part ext shown in FIG. 2 is about 49 mm, the distance from point B to point D is about 2 mm, and the line width of the extension part ext is about 1 mm. There, the capacitance value of the capacitor C _i has to be about 3.6PF. Of the S parameters, S ₁₁ corresponds to the intensity of the reflected radio wave among the radio waves input to the antenna device, and may be referred to as return loss or reflectance. S ₁₁ indicates that radio waves with a high frequency are reflected, while S ₁₁ indicates that radio waves with a low frequency are not reflected. That is, the reflected radio wave is not output from the antenna and cannot be used for communication. Conversely, unreflected radio waves form a current distribution in the antenna device. Therefore, it is possible to transmit and receive radio waves at a frequency (resonance frequency) resulting in small S _11.

In the example shown in FIG. 7, the fact that S ₁₁ is small near 0.8 GHz (800 MHz) corresponds to the fact that the antenna device resonates at the fundamental frequency f ₁ . Further, the S ₁₁ being small in the vicinity of 0.7 GHz (700 MHz) corresponds to the fact that the antenna device resonates at the resonance wave number f ₂ . Accordingly, the antenna device showing the characteristics of the S parameter S ₁₁ shown in FIG. 7, a frequency carrier belonging to 700MHz band, it is possible to perform radio communication by using a frequency carrier belonging to the 800MHz band simultaneously.

FIG. 8 shows a comparative example with respect to the example shown in FIG. Figure 8 shows the antenna of S parameter S ₁₁ shown in FIG. Structure shown in FIG. 9 is similar to the structure shown in FIG. 2, that the capacitor C _i to couple the other end P2 in point E is not provided are different. This antenna resonates only at the fundamental frequency f ₁ as shown in FIG.

The antenna device as shown in FIG. 2, by a simple structure of the other end P2 binds to a point E of the stretch portion ext via a capacitor C _i, in the monopole antenna is substantially the same size, a plurality of frequency Can resonate.

FIG. 10 shows a simulation result when the capacitance value of the capacitor C _i (i = 1, 2, 3, 4, 5) is changed. The S parameter S ₁₁ is calculated for five types of capacitance values of C ₁ = ₁ pF, C ₂ = ₂ pF, C ₃ = 3 pF, C ₄ = 4 pF, and C ₅ = 5 pF. In the simulation, the distance from the point A to the point B in the extended part ext shown in FIG. 2 is about 49 mm, the distance from the point B to the point D is about 2 mm, and the line width is about 1 mm. This is the same as in the simulation of FIG.

As shown in FIG. 10, S parameters S ₁₁ for each of the values of the capacitors C _i indicates a low value at the two frequencies of the fundamental frequency and the resonance frequency, that resonates at two frequencies I understand. For example (in the case where the value of the capacitance changes in the order of _{C 1, C 2, C 3} , C 4, C 5) as increases from the capacitance value 1pF capacitor C _i to 5 pF, so the frequency of resonance gradually decreases Yes. For example, in the case of resonance related to the fundamental frequency, the fundamental frequency when the capacitance is C ₁ = ₁ pF to 5 pF gradually decreases within a range of about 1.2 GHz to 1.7 GHz. The resonance frequency also gradually decreases within the range of 0.75 GHz to 1.2 GHz as the capacitance increases from C ₁ = ₁ pF to 5 pF. These agree with the theory that the resonant frequency follows [2π√ (L · C _i )] ⁻¹ .

Although only shown capacitance value five capacitors C _i in the example shown in FIG. 10, for a variety of other capacitance values, it is possible to draw a graph of S-parameters. That is, for any value of the capacitance of the capacitor C _i, there are S-parameter S ₁₁ becomes lower frequency (resonant frequency), the resonance frequency as the capacitance value increases is lower, the resonance frequency as the capacitance value decreases is higher . Conversely, as a certain frequency is the resonance frequency, there is capacitance value to lower the S parameter S _11, the capacitance value as the resonance frequency becomes higher is reduced and the capacitance value as the resonance frequency becomes lower increases .

<< 3.2 Separation model >>
Among the antenna elements Ant in FIG. 2, point E, point B, and point D, point F, the portion of the loop formed by the other end P2 and the capacitor C _i resonating, from the portion of the loop other portions When it sees, it is in a high impedance state (state where impedance is high). If a circuit is in a high impedance state, that circuit (ie, the portion of the loop) should be in the same state as it was physically disconnected from the other portion. In order to verify this, as shown in FIG. 11, a simulation is performed on a model (detached model or separated model) in which the antenna element Ant is physically cut at a certain location α. The structure shown in FIG. 11 is the same as the structure shown in FIG. 2 except that the structure is cut at a location α. The location α exists in the antenna element Ant at the boundary between the point E, the point B, the point D, the point F, the other end P2, and the part of the loop formed by the capacitor C _i and the other part.

FIG. 12 shows a simulation result when the capacitance value of the capacitor C _i (i = 1, 2, 3, 4, 5) is changed in the separation model as shown in FIG. The S parameter S ₁₁ is simulated for five types of capacitance values, C ₁ = 0.5 pF, C ₂ = 1.125 pF, C ₃ = 1.75 pF, C ₄ = 2.375 pF, and C ₅ = 3 pF. In the simulation, the distance from the point A to the point B in the extended part ext is 50 mm, the distance from the point B to the point D is 5 mm, and the line width is 1 mm. This is the same as in the simulation of FIG.

As shown in FIG. 12, the S parameter S ₁₁ for each value of the capacitor C _i indicates that the antenna device resonates at a fundamental frequency of about 1.7 GHz. In the case of an antenna device that is not physically separated as shown in FIG. 2, a quarter of the wavelength λ ₁ ^{(non-separated)} corresponding to the fundamental frequency f ₁ ^{(non-separated)} is from one end P1 to the other end P2. Equal to the length of In contrast, in the case of the separation model shown in FIG. 11, a quarter of the wavelength λ ₁ ^(separation) corresponding to the fundamental frequency f ₁ ^(separation) is the length from one end P1 to the separation point α. be equivalent to. Accordingly, the wavelength λ ₁ ^{(non-separated)} is longer than the wavelength λ ₁ ^(separated) by the amount of the loop (wavelength λ ₁ ^{(non-separated)} > wavelength λ ₁ ^(separated) ). This means that f ₁ ^{(non-separated)} <f ₁ ^(separated) . In fact, if the value of the capacitor C _i was 3.36PF, fundamental frequency f ₁ ^{(non-separation)} as shown in FIG. 10 was about 1.3GHz. On the other hand, in the case of the separation model, as shown in FIG. 12, the fundamental frequency f ₁ ^(separation) is about 1.7 GHz, and f ₁ ^{(non-separation)} <f ₁ ^(separation) holds.

Furthermore, the antenna apparatus shown in FIG. 11, as shown in FIG. 12, resonating at a resonance frequency corresponding to the value of the capacitor C _i. As the value of capacitance C _i increases from 0.5 pF to 3 pF (when the value of capacitance changes in the order of C ₁ , C ₂ , C ₃ , C ₄ , C ₅ ), the frequency causing resonance gradually decreases. Yes. For example, the resonance frequency when the capacitance is C ₁ = 0.5 pF is about 2.1 GHz, the resonance frequency when the capacitance is C ₂ = 1.125 pF is about 1.5 GHz, and the capacitance is C ₃ = 1.75 pF, As C ₄ = 2.375 pF and C ₅ = 3 pF, the fundamental frequency gradually decreases. This is consistent with the theory that the resonant frequency follows [2π√ (L · C _i )] ⁻¹ .

Capacitance value of the capacitor C _i has not been shown only five in the example shown in FIG. 12, but for a variety of other capacitance values, it is possible to draw a graph of S-parameters S _11. That is, for any value of the capacitance of the capacitor C _i, there are S-parameter S ₁₁ becomes lower frequency (resonant frequency), the resonance frequency as the capacitance value increases is lower, the resonance frequency as the capacitance value decreases is higher . With respect to the relationship between the resonance frequency and the capacitance value, the example shown in FIG. 12 shows the same properties as the example shown in FIG. 10, and thus the validity of the separation model is supported.

FIG. 13 shows a current distribution when the antenna device as shown in FIG. 2 resonates at the resonance frequency. FIG. 14 shows a current distribution when the antenna device based on the separation model as shown in FIG. 11 resonates at the resonance frequency. However, in any of FIGS. 13 and 14, but the other terminal P2 is connected to the point E via a capacitor C _i, for convenience and ease of illustration, note that the capacitor C _i is not shown Cost. Referring to FIGS. 13 and 14, it can be seen that both are quite similar. Also from this, it can be said that the separation model appropriately represents the resonance state of the antenna device according to the embodiment.

According to the antenna device of the embodiment, a simple configuration of the other end P2 of the monopole antenna which resonates at the fundamental frequency f ₁ (antenna elements Ant) is coupled to the extending portion ext via a capacitor C _i, the fundamental frequency Resonance can be achieved even at a resonance frequency f ₂ different from f ₁ . Since members to be added relative to the monopole antenna is only the capacitor C _i, an antenna device according to the embodiment, requires only monopole antenna is substantially the same size. In particular, even when the antenna device has to resonate with a plurality of carrier frequencies belonging to the same frequency band, the size of the antenna device can be reduced.

<4. Modification>
<< 4.1 Modified Example of Antenna Shape >>
The antenna device according to the embodiment is not limited to the example shown in FIG. 2, and may be realized in various forms.

FIG. 15 shows the same form as the antenna device shown in FIG. 2 for comparison with other examples. On the other hand, a matching circuit M actually exists between the end P1 and the power feeding section OC, but it should be noted that the matching circuit M is not shown for the sake of simplicity. As described above, the antenna device resonates at the fundamental frequency f ₁ by the extending portion ext extending from one end P1 to the other end P2, while the point E, point B, point D, point F, the other end P2, and the capacitor C _i. Resonance occurs at the resonance frequency f ₂ = [2π√ (L · C _i )] ⁻¹ due to the loop portion.

Figure 16 shows an example in which capacitor C _i is provided between the E and the point B in terms of extending portion. In the case of this example, the antenna device resonates at the fundamental frequency f ₁ by the part from one end P1 to point A, point E, capacitor C _i , point B, point H, while point E, capacitor C _i , point B Resonant at a resonance frequency f ₂ = [2π√ (L · C _i )] ⁻¹ by the loop portion of the point D, the point F, the other end P2, and the point E.

FIG. 17 shows an example in which point F and point K are combined in the example shown in FIG. In the case of this example, the antenna device has a part extending from one end P1 to point A, point K, point E, point B, point D and one end P1, point A, point K, point J of the extension part ext. , And the portion reaching point F and point D resonates at the fundamental frequency f ₁ . That is, the current from point A to point K branches to the point E side and the point J side and reaches point D, while the current from point J to point K and the current from point E to point K Joins at point K and reaches point A. Further, the point E, the point B, the point D, the point F, the other end P2, and the loop portion of the capacitor C _i resonate at the resonance frequency f ₂ = [2π√ (L · C _i )] ⁻¹ .

  Although the antenna device shown in FIGS. 15, 16, and 17 resonates at two frequencies, the embodiment is not limited to two resonances, and can resonate at three or more frequencies.

FIG. 18 shows an example in which two loops as shown in FIG. 15 are overlapped. In the case of the example shown in FIG. 18, the extending portion ext branches to form another loop between the one end P1 and the other end P2 (more precisely, between the point A and the point E). Another capacitor C _j is provided in the middle of another loop. The antenna device resonates at the fundamental frequency f ₁ by the part from one end P1 to point A, point E, point B, point D, point F, and the other end P2, while point E, point B, point D, point F Then, resonance occurs at the resonance frequency f ₂ = [2π√ (L _i · C _i )] ⁻¹ by the loop portion formed by the other end P2 and the capacitor C _i . L _i is the inductance of the loop portion. The steps so far are the same as the example shown in FIG.

Further, when the antenna device shown in FIG. 18, of the extending portion ext, point EE, point BB, the point DD, point FF, the portion of the loop by the other end PP2 and the capacitor C _j, the resonance frequency f ₃ = [2 ?? (L _j · C _j )] ^Resonates at ^-1 . L _j is the inductance of the loop formed by point EE, point BB, point DD, point FF, the other end PP2, and capacitor C _j . The inductances L _i and L _j may be the same or different. However, the fundamental frequency f ₁ , the resonance frequency f ₂ , and the resonance frequency f ₃ need to be different from each other.

FIG. 19 shows an example in which the monopole antenna is extended from point B in the example shown in FIG. In the case of the example shown in FIG. 19, the antenna device resonates at a fundamental frequency f ₁ by a portion from one end P1 to point A, point E, point B, point D, point F, and the other end P2, while point E, Resonance occurs at a resonance frequency f ₂ = [2π√ (L · C _i )] ⁻¹ by the loop of point B, point D, point F, the other end P2, and the capacitor C _i . The steps so far are the same as the example shown in FIG.

Further, in the case of the antenna device shown in FIG. 19, the extending portion ext branches at the point B to the point D side and the point BB side. Thus, whereas the point from the end P1 A, point E, point B, point BB, the point DD, point FF, the portion extending to the other end PP2 resonates at third resonant frequency f _3. The length of the quarter of the third resonance wavelength λ ₃ corresponding to the third resonance frequency f ₃ is from the one end P1, point A, point E, point B, point BB, point DD, point FF, the other Equal to the length of the path to the end PP2. As in the case of the example of FIG. 18, the fundamental frequency f ₁ , the resonance frequency f ₂ , and the resonance frequency f ₃ need to be different from each other.

  The examples shown in FIGS. 15 to 19 are merely specific examples, and various other forms of the antenna device are possible. However, in any example, a part of the extending portion ext forms a loop, and a capacitor is provided in the middle of the loop.

<< 4.2 Modification Using Plate Antenna >>
In the examples shown in FIGS. 2 to 6 and FIGS. 15 to 19, the extending portion ext may be formed by a linear line. Alternatively, as shown in FIG. 20, the cross-sectional shape of the extending portion ext formed by the plate-like line may be a shape as shown in FIGS. 2 to 6 and FIGS. 15 to 19. The other end P2 also in this case are capacitively coupled via a capacitor C _i to the extending portion ext. Although FIG. 20 shows an example of capacitive coupling by individual elements, capacitive coupling may be performed by a distributed constant circuit as shown in FIG. When a plate-like line is used, from one end P1 to point A (side A), point B (side B), point D (side D), point F (side F) and the other end P2 the distance, the sum of the width w of the line is equal to the length of one quarter of the fundamental wavelength lambda _1, the resonance of the fundamental frequency f ₁ is generated. Therefore, it is preferable to use a plate-like antenna from the viewpoint of further downsizing the antenna device.

<< 4.3 Modified Example Using Dipole Antenna >>
In the examples shown in FIG. 2 to FIG. 6 and FIG. 15 to FIG. 20, the antenna element Ant that resonates at the fundamental frequency f1 (fundamental wavelength λ1) forms a monopole antenna. Without limitation, a dipole antenna may be formed.

FIG. 21 shows an example in which an antenna device is formed by a dipole antenna. On the other hand, a matching circuit M actually exists between the terminals P1 and PP1 and the power feeding section OC, but it should be noted that the matching circuit M is not shown for the sake of simplicity. The antenna device is connected from one end P1 to point A, point E, point B, point D, point F, the other end P2 and one end PP1 to point AA, point EE, point BB, point DD, point FF, and the other end PP2. Resonant at the fundamental frequency f ₁ due to the extending part ext, while the resonance frequency f ₂ = [2π√ (L ・ C) due to the loop part by point E, point B, point D, point F, the other end P2 and capacitor C _{i i} )] ^Resonates at ^-1 . Similarly, the antenna device resonates at the resonance frequency f ₃ = [2π√ (L · C _i )] ⁻¹ due to the loop portion of the point EE, the point BB, the point DD, the point FF, the other end PP2, and the capacitor C _i. To do.

The length from one end P1 to point A, point E, point B, point D, point F and the other end P2 is equal to one quarter of the fundamental wavelength, and from one end PP1 to point AA, point EE, point The length from BB, point DD, point FF to the other end PP2 is also equal to a quarter of the fundamental wavelength. Therefore, the antenna device shown in FIG. 21 operates as a dipole antenna when resonating at the fundamental frequency f ₁ .

  From the viewpoint of reducing the size of the antenna device, it is preferable to form a monopole antenna as shown in FIGS. 2 to 6 and FIGS. 15 to 20.

<< 4.4 Modification Using Switch >>
FIG. 22 shows an example of an antenna device that can switch the capacitor that couples the other end P2 and the point E using the switch S. In the case of the illustrated example, the switch S can select any one of the five types of capacitance values C ₁ to C ₅ . The type of capacitance value of the capacitor is arbitrary.

<5. Interrelationship between S-parameters, efficiency and resonance frequency>
Next, a design procedure for designing an antenna device that can simultaneously transmit and receive radio waves of a plurality of desired carrier frequencies will be described. Before describing a specific design procedure, the correlation among S parameter S ₁₁ , efficiency η, and resonance frequency will be described.

As described with reference to FIG. 10, in the case of the antenna device having the structure as shown in FIG. 2, the S parameter S ₁₁ is not only the fundamental frequency f ₁ but also the resonance frequency f ₂ (= [2π√ (L · C _i )] ⁻¹ ) shows a low value. S parameter S ₁₁ is the result of the reflection of the incident wave, the communication indicates the intensity of the radio wave is not available, may be referred to as Lee turns loss or reflectance.

According to the frequency dependence of the S parameter S ₁₁ described with reference to FIG. 10, the following can be said. For some value of the capacitance of the capacitor C _i, there are S-parameter S ₁₁ becomes lower frequency (resonance frequency), becomes the resonance frequency decreases as the capacitance value increases, the resonance frequency as the capacitance value decreases is higher. Conversely, as a certain frequency is the resonance frequency, there is capacitance value to lower the S parameter S _11, the capacitance value as the resonance frequency becomes higher is reduced and the capacitance value as the resonance frequency becomes lower increases .

Frequency dependence of the S parameter S ₁₁ can to some extent controlled also by adjusting the impedance of the matching circuit M provided between the feeding portion OC and the antenna elements Ant. In other words, by adjusting the matching circuit M, it is possible to control the value of the frequency (resonance frequency) resulting in low S _11. Specifically, the graph as shown in FIG. 10 can be shifted to some extent in the frequency axis direction.

On the other hand, the ratio between the power P _in input to the antenna and the power P _out output from the antenna (more specifically, the common logarithm of the ratio (10log ₁₀ [P _out / P _in ])) It represents the efficiency η [dB] in the absence. “No matching loss” indicates that the antenna element Ant and the feeding section OC are connected in a matched state. Therefore, the efficiency η in a state where there is no matching loss is unchanged regardless of how the matching circuit M is adjusted.

FIG. 23 shows the frequency dependence of the efficiency η with no matching loss. When the power P _in input to the antenna is equal to the power P _out output from the antenna, the efficiency η is the maximum, indicating 0 [dB]. As shown in Figure 23, in the frequency range of 0.7 GHz (700 MHz) to 0.9 GHz (900 MHz), if the capacitance value of the capacitor is C ₁ = ₁ pF, C ₂ = ₂ pF or C ₃ = 3 pF Although a good efficiency η (a value near 0 dB) is shown, when the capacitance value of the capacitor is C ₄ = 4 pF, the efficiency η is poor near 850 MHz. Similarly, when the capacitance value of the capacitor is C ₅ = 5 pF, the efficiency η is degraded near 730 MHz. The threshold value for determining whether the efficiency η is good is, for example, −5 dB.

However, referring to FIG. 10, when the capacitance value of the capacitor is C ₄ = 4 pF, the frequency of 850 MHz is a resonance frequency that provides a small S parameter S ₁₁ . Similarly, when the capacitance value of the capacitor is C ₅ = 5 pF, the frequency of 730 MHz is also a resonance frequency that provides a small S parameter S ₁₁ .

Therefore, from the overall simulation results of FIGS. 10 and 23, the efficiency in the absence of integrity loss eta (Figure 23) shows only bad value at the resonant frequency resulting S-parameter S ₁₁ of small value, it means that I understand. Such a tendency applies not only when the capacitance value of the capacitor is C ₄ or C ₅ but also for any other capacitance value.

It can be considered as follows that the resonance frequency that results in a small value of the S parameter S ₁₁ does not yield the best efficiency η. When the antenna is resonating at the resonance frequency, as shown in FIG. 6, the point E, the point B, the point D, a point F, and the other end P2, and the portion of the loop formed by the capacitor C _i resonating . In this case, the current from the point E to the point B and the current from the point D to the point F are equal in magnitude and opposite to each other, and thus cancel each other. The power due to the currents that cancel each other is dissipated as thermal energy, leading to a bad efficiency η at the resonant frequency. The conductors forming the antenna element Ant ideally have infinite conductivity (and a resistivity that is zero), but in practice have a finite conductivity (and finite resistivity), and the antenna element Ant A part of the electric power flowing through is lost as heat energy.

FIG. 24 shows that the resonance frequencies f _x and f _y resulting in a small value of the S parameter S ₁₁ do not maximize the efficiency η (f = f _x ) and η (f = f ₇ ) without matching loss. A (slightly worsening) appearance is shown schematically. However, since attention is paid to the resonance frequency depending on the capacitance value, it should be noted that the graph regarding the fundamental frequency is omitted. f _x is a frequency (resonance frequency) that provides a small S parameter S ₁₁ when the capacitance value of the capacitor is C _x . f _y is the frequency that provides the small S-parameters S ₁₁ and the capacitance value of the capacitor is C _y (resonance frequency).

Therefore, to form a loop with a capacitor of capacitance value of C _x in the antenna device shown in FIG. 2, even when allowed to resonate at the frequency f _x, so as is the efficiency η is poor, to send and receive properly radio waves Can not. For example, if the desired carrier frequency was f _x, even to form a loop with a capacitor having a capacitance value C _x bring small S parameter S ₁₁ in the carrier frequency f _x, at the desired carrier frequency f _x It cannot properly transmit and receive radio waves.

Therefore, in the embodiment, when sending and receiving radio waves with a desired carrier frequency f _x, rather than C _x value of the capacitance of the capacitor is set to the capacitance value C _y resulting in different resonance frequency f _y. As shown in the graph of the efficiency η of Figure 24, (in the case of the graph indicated by "..." in FIG. 24) when the capacitance value of the capacitor is C _y, efficiency η good at frequency f _x Indicates the value.

Next, S parameter S ₁₁ of the capacitance value of the capacitor is C _y are such that a small value at the desired carrier frequency f _x, the matching circuit M is adjusted. As described above, while the frequency dependence of the S parameter S ₁₁ is capable of some degree controlled by adjusting the matching circuit, the frequency dependence of the efficiency η in the absence of alignment loss, how adjusting a matching circuit Even so, it is unchanged. Therefore, when the matching circuit is adjusted so that the S parameter S ₁₁ when the capacitance value of the capacitor is _Cy is a small value at the desired carrier frequency f _x , the frequency dependence of the S parameter S ₁₁ and the efficiency η is As shown in FIG. The graph of efficiency η is the same as in FIG. For simplicity of illustration, the graph of the capacitance value of the capacitor is C _x is not depicted. Set the capacitance value of the capacitor C _y, a matching circuit by appropriately adjusting the antenna device, S parameter S ₁₁ at high efficiency indicates eta, and desired carrier frequency f _x at the desired carrier frequency f _x Can be made sufficiently low. By leveraging this way the matching circuit, it is possible to transmit and receive radio waves at a desired carrier frequency f _x.

<6. Design method>
With reference to FIG. 26, a design procedure 26 for designing an antenna device capable of transmitting and receiving radio waves of a desired carrier frequency will be described. The described design procedure 26 shows a procedure for setting the resonance frequency depending on the capacitance value. The design for the fundamental frequency determined by the length of the antenna element Ant or the extension part ext is performed separately. As a specific example, it is assumed that the fundamental frequency f ₁ is 800 MHz and the desired carrier frequency f _x is 700 MHz.

  For example, as shown in FIG. 27, an antenna element Ant that is not coupled to the power feeding section OC (that is, one end P1 is open) and is not connected to a capacitor is prepared.

In step 261, the impedance Z _C = R + jX viewed from between the point E and the other end P2 in the extending portion ext of the antenna element Ant is calculated. R represents a resistance component, and X represents a reactance component.

Next, at step 262, based on X = ωL, an inductance L of the loop by point E, point B, point D and the other end P2 is calculated. Here, ω is an angular frequency, and ω = 2πf. f represents the resonance frequency f _y . The resonance frequency f _y is a frequency that satisfies the following condition.

When the capacitance value of the (A) capacitor is set to C _y, a frequency resulting in small S parameter S _11.

When the capacitance value of the (B) capacitor is set to C _y, the efficiency η in the absence of alignment loss, showing a good value in the vicinity desired carrier frequency f _x.

(C) is a frequency close to the desired carrier frequency f _x. This is because when the capacitance value of the capacitor is set to C _y, by adjusting the matching circuit M, which means that it can be changed to f _x the resonant frequency from f _y.

In the above specific example, the desired carrier frequency f _x is 700 MHz. Referring to the frequency dependence of the near 700MHz S-parameters S ₁₁ shown in FIG. _{10, 850MHz (C 4),} S parameter S ₁₁ in 950 MHz (C ₃₎ indicates a sufficiently low value (condition A). Referring to FIG. 23, when the capacitance value of the capacitor is C ₄ = 4 pF (corresponding to the resonance frequency of 850 MHz), the efficiency η is better than that of C ₅ = 5 pF, but worse as it approaches the 800 MHz band The efficiency η is shown. When the capacitance value of the capacitor is C ₃ = 3 pF (corresponding to a resonant frequency of 950 MHz), the efficiency η shows a good value in both the 700 MHz band and the 800 MHz band (Condition B). Therefore, 950 MHz (C ₅ ) provides better efficiency η than 850 MHz (C ₄ ). 950MHz is relatively close to 700MHz (Condition C). Therefore, referring to the graphs corresponding to the five types of capacitance values shown in FIGS. 10 and 23, it can be seen that the resonance frequency f _y may be set to 950 MHz.

Meanwhile, as described with reference to FIG. 10, for any capacitance value of the capacitors C _i, there are S-parameter S ₁₁ becomes lower frequency (resonance frequency), such capacitance values exist numerous continuous To do. Conversely, as one frequency is a resonance frequency, to the capacitance value to lower the S parameter S ₁₁ is present, also there are many continuous such frequencies. Therefore, the frequency that can be set as the resonance frequency f _y is not limited to 950 MHz but may be other frequencies. Considering that 950 MHz (C ₅ ) provides better efficiency η than 850 MHz (C ₄ ), a frequency higher than 950 MHz can be set as the resonance frequency f _y . However, according to the condition C, the frequency set as the resonance frequency f _y needs to be relatively close to 700 MHz. Therefore, for convenience of calculation, the resonance frequency f _{y is set} to 1 GHz.

In the simulation, assuming that the resonance frequency f _y is 1 GHz, the impedance Z _C seen from between the point E and the other end P2 in the extension part ext of the antenna element Ant is Z _C = R + jX = 1.5 + j75.27 It became a value like this. Therefore, the inductance L of the loop formed by the point E, the point B, the point D, the point F, and the other end P2 is L = X / (2πf _y ) = 11.99 nH.

In step 263, the capacitance C _y for the loop resonates at the resonance frequency f _y is calculated on the basis of the _{f y = [2π√ (L ·} C y)] -1. C _y = [(2πf) ² L] ⁻¹ = 2.11 pF.

Next, in step 264, a capacitor having a capacitance value of C _y = 2.11 pF is inserted between point E and point F (the other end P2) in FIG. Frequency dependence of the S parameter S ₁₁ of the antenna in this state is shown in FIG. 28, the Smith chart of the antenna is shown in Figure 29. The frequency f is changed from 0.5 GHz (500 MHz) to 2 GHz. As can be seen from FIGS. 28 and 29, parallel resonance occurs when the frequency f is around 1 GHz, and monopole resonance occurs when the frequency f is 1.3 GHz.

Next, in step 265, one end P1 of the antenna element Ant is connected to the matching circuit M. In a desired carrier frequency f _x, so that the S parameter S ₁₁ becomes sufficiently small, the matching circuit is adjusted. Thus, through the matching circuit M and the antenna elements Ant, it is possible to properly transmit and receive radio waves of a desired carrier frequency f _x. Then, the design procedure 26 ends.

<7. Comparison with other antennas>
From the viewpoint of the difference between the antenna device according to the embodiment and another antenna, features of the antenna device according to the embodiment will be described.

  FIG. 30 shows an antenna in which a power feeding unit OC and a capacitor are provided in series in one loop to form a loop. This antenna resonates only at one wavelength determined by the loop length. This is different from the antenna device according to the embodiment that resonates at a plurality of wavelengths or frequencies.

  FIG. 31 shows an antenna in which an extension part ext extending from the power feeding part OC does not form a loop, and a capacitor is provided in the middle of the loop. This antenna also resonates only at one wavelength determined by the loop length. This is different from the antenna device according to the embodiment that resonates at a plurality of wavelengths or frequencies.

  From the viewpoint of changing the frequency at which the antenna resonates, it is conceivable to switch the path through which the current flows in the antenna, or switch the impedance (particularly reactance) of an element in the path. However, when switching paths and impedances, it is not possible to resonate with multiple frequencies simultaneously. This is different from the antenna device according to the embodiment that resonates at a plurality of frequencies at the same time.

In FIG. 32, resonance occurs at the first wavelength λ ₁ by the portion from the power feeding section OC through point A, point B, and point C to point D, and from the power feeding section OC through point A, point B, and point C to point E. An antenna device that resonates at a _second wavelength λ ₂ is shown by the part extending to. The length from the power supply section OC through point A, point B, and point C to point D is equal to a quarter of the first wavelength λ ₁ . The length from the power feeding section OC to the point E through the points A, B and C is equal to a quarter of the second wavelength λ ₂ . This antenna is an antenna device that resonates at two wavelengths or frequencies, but it is necessary to provide a line between points C and E. Therefore, in order to resonate at similar frequencies such as 700 MHz and 800 MHz, the distance from the power supply section OC to the point D and the distance from the power supply section OC to the point E need to be made the same length. There is a concern that the antenna will be enlarged. In this respect, the antenna device according to the embodiment is advantageous from the viewpoint of miniaturization and the like because a capacitor is simply added.

  As described above, the embodiments of the antenna device that resonates at a plurality of frequencies have been described. However, the embodiments are not limited to the specifically described examples, and those skilled in the art will recognize various modifications, modifications, alternatives, Can understand substitution examples. Although specific numerical examples have been described to facilitate understanding of the embodiment, these numerical values are merely examples, and any appropriate values may be used unless otherwise specified. Further, although specific mathematical formulas have been used to facilitate understanding of the embodiment, these mathematical formulas are merely examples unless otherwise specified, and other mathematical formulas that yield similar results are used. May be. The classification of items in the above description is not essential to the embodiment. Unless there is a contradiction, the items described in two or more items may be used in combination as necessary, and are described in a certain item. A matter may apply to a matter described in another item.

Regarding the above embodiment, the following additional notes are disclosed.
(Appendix 1)
It has one end (P1), the other end (P2), and an extending portion (ext) extending between the one end and the other end, and the one end is coupled to the power feeding portion (FIG. 2, OC). The extending portion is formed in a loop shape, the other end is coupled to the extending portion, and a capacitor (C _i ) is provided in the middle of the loop.
(Appendix 2)
The antenna device resonates with an electromagnetic wave (f ₁ ) having a quarter wavelength length equal to the length of the extending portion, and a resonance frequency (determined by an inductor formed by the capacitor and the loop). The antenna device according to appendix 1, which also resonates with an electromagnetic wave of f ₂ = [2π√ (LC)] ⁻¹ ).
(Appendix 3)
The antenna device according to appendix 1 or 2, wherein the capacitor is formed by an individual element (FIGS. 2 and 4) or a distributed constant circuit (FIG. 3).
(Appendix 4)
The extension part is branched so as to form another loop between the one end and the other end, and another capacitor is provided in the middle of the other loop, according to appendix 1 or 2. Antenna device.
(Appendix 5)
Appendix 4 wherein the resonance frequency determined by the capacitor and the inductor formed by the loop is different from another resonance frequency determined by the another capacitor and another inductor formed by the another loop. The antenna device according to 1.
(Appendix 6)
The antenna device according to appendix 4 or 5, wherein the another capacitor is formed by an individual element or a distributed constant circuit.
(Appendix 7)
The antenna device according to any one of supplementary notes 1-6, further comprising a switch for changing a capacitance value of the capacitor.
(Appendix 8)
The antenna device according to appendix 7, wherein the switch is a changeover switch that selects any one of a plurality of capacitance values.
(Appendix 9)
The antenna device according to any one of appendices 1-8, wherein the one end (P1) is coupled to the power feeding unit (OC) through a matching circuit (M).
(Appendix 10)
The antenna device according to any one of appendices 1-9, wherein the frequency of the electromagnetic wave having a length of the quarter wavelength equal to the length of the extending portion and the resonance frequency belong to the same frequency band.
(Appendix 11)
The antenna device according to any one of appendices 1-10, wherein the quarter-wave antenna forms a linear inverted L antenna.
(Appendix 12)
The antenna device according to any one of appendices 1-10, wherein the quarter-wave antenna forms a plate-like inverted F antenna.

1 Communication device
2 Antenna space
G Ground plane
OC power supply
Ant antenna element
P1 one end
P2 other end
ext Extension part
C _i capacitor
M matching circuit

Claims (6)

  One end, the other end, and an extending portion extending between the one end and the other end, the one end is coupled to a power feeding portion, the extending portion is formed in a loop shape, and the other end is An antenna device coupled to the extending portion and provided with a capacitor in the middle of the loop.   The antenna device resonates with an electromagnetic wave having a quarter wavelength length equal to the length of the extending portion and also resonates with an electromagnetic wave having a resonance frequency determined by the inductor formed by the capacitor and the loop. The antenna device according to claim 1.   The antenna device according to claim 1, wherein the capacitor is formed of an individual element or a distributed constant circuit.   The extension part is branched so as to form another loop between the one end and the other end, and another capacitor is provided in the middle of the other loop. The antenna device according to claim 1.   The antenna device according to claim 1, further comprising a switch for changing a capacitance value of the capacitor.   The antenna device according to claim 1, wherein the one end is coupled to the power feeding unit via a matching circuit.

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