JP2011193362A - Antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a compact and high-gain antenna for two frequency bands. <P>SOLUTION: This antenna 101 is equipped with: a radiation element RE; a series inductor L2; an inductor L1; and a capacitor C1. The series inductor L2 is serially connected to the radiation element RE. The inductor L1 and the capacitor C1 form a parallel resonance circuit. The inductance of the series inductor L2 is a value by which a resonance frequency by the series inductor L2 and the radiation element RE is set at a frequency f0 between a VHF high band (207.5-222 MHz) being a first frequency band and a one-segment broadcasting frequency band (470-770 MHz) being a second frequency band. The parallel resonance circuit splits the resonance frequency f0 of the circuit when viewing the radiation element RE side from a power feed end FP into a center frequency f1 of the first frequency band and a center frequency f2 of the second frequency band by using the resonance frequency of the parallel resonance circuit as a boundary by splitting a resonance point by the series inductor L2 and the radiation element RE into two. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a small and high gain antenna for two frequency bands.

  Patent Documents 1 and 2 disclose an antenna in which a matching circuit including a variable capacitive element is added to a radiating element so as to correspond to a predetermined frequency band.

  Here, the configuration of the antenna of Patent Document 1 will be described with reference to FIG. The antenna shown in FIG. 1 includes a radiating element 1, a first inductive element 11, a second inductive element 13, and a variable capacitive element 14. The first inductive element 11 shifts the fundamental resonance frequency of the radiating element 1 to a frequency lower than the frequency of the radiating element 1 alone by increasing the reactance component of the radiating element 1. The second inductive element 13 and the variable capacitive element 14 constitute a variable reactance circuit. The variable capacitive element 14 changes its capacitance according to the applied voltage, and the radiating element 1 and the first inductive element 11. And the basic resonance frequency of the radiating element 1 is varied within a range including a predetermined frequency.

  The antenna disclosed in Patent Document 2 is a radiating element (whipped antenna) so that the resonance frequency comes between the two resonance frequencies f1 and f2 when operating at two separate resonance frequencies f1 and f2. The length is adjusted, an LC parallel resonance circuit is inserted in the middle of the radiating element, and the resonance frequency is divided into f1 and f2.

JP 2008-113233 A No. 07-046969

  The antenna of Patent Document 1 adds a tuning circuit for tuning with respect to a single frequency band, and does not cover two separate frequency bands. Also, the design method of the parallel resonant circuit is not clearly shown.

  In the antenna of Patent Document 2, since the lumped constant circuit is directly inserted into the radiating element, the assembling process is complicated and variations tend to occur. Moreover, the design method of a parallel resonant circuit is not clearly shown.

  An object of the present invention is to provide a small and high-gain antenna for two frequency bands.

The present invention includes a radiating element and a matching circuit connected between the radiating element and a feeding end, and includes a VHF high band (207.5 to 222 MHz) as a first frequency band and a second frequency band. An antenna for two frequency bands of a one-segment broadcasting frequency band (470 to 770 MHz),
The matching circuit includes a series inductor (L2) connected in series to the radiating element, and a parallel resonant circuit of an inductor (L1) and a capacitor (C1) connected in series to the inductor (L2). ,
The inductance of the series inductor (L2) is such that the resonance frequency of the series inductor (L2) and the radiating element is a frequency (f0) between the first frequency band and the second frequency band. And
The parallel resonant circuit divides a resonance point by the series inductor (L2) and the radiating element into two with a resonance frequency (antiresonance point) of the parallel resonant circuit as a boundary, and the radiating element from the feeding end A circuit having a resonance frequency of the circuit viewed from the side, the center frequency (f1) of the first frequency band and the center frequency (f2) of the second frequency band;
The reactance change rate dX / df at the center frequency (215 MHz) of the first frequency band of the parallel resonant circuit is 2.5 or less and the frequency at the lower end of the second frequency band (470 MHz) The inductance of the series inductor (L2) is selected so that the reactance change rate dX / df in FIG.

  As a result, the ISDB-Tmm (VHF high band, 207.5- 222 MHz) and one-segment band (UHF band, 470 to 770 MHz) can be matched simultaneously in a balanced manner while suppressing the passage loss of the matching circuit.

  The radiating element is, for example, a linear antenna having a length in a range of 100 mm to 120 mm.

  The radiating element may have a radiating electrode folded portion formed at a tip. As a result, the value of the series inductor L2 can be reduced, the loss in the series inductor L2 can be reduced, and the antenna efficiency is improved. In addition, variations in the matching circuit can be reduced.

  If the radiating element is a multistage radiating element that can be expanded and contracted and a helical radiating electrode is formed in the first stage of the radiating element, the inductance value of the series inductor L2 can be reduced. Loss can be reduced, and antenna efficiency is improved. In addition, variations in the matching circuit can be reduced.

  If the radiating element has a radiating electrode formed on the surface of a cylindrical resin base material, the antenna itself can be easily manufactured and assembled into a wireless device.

  According to the present invention, it is possible to simultaneously match both the first frequency band and the second frequency band while using a radiating element shorter than the λ / 4 length necessary for resonating at the first use frequency, In addition, the passage loss of the matching circuit can be suppressed. Therefore, a small and high gain antenna can be configured.

It is a figure which shows the structure of the antenna of patent document 1. FIG. 1 is a block diagram of an antenna 101 according to a first embodiment. FIG. 3A is a diagram illustrating the frequency characteristics of the reflection coefficient (S11) measured with the radiation element RE alone shown in FIG. FIG. 3B is a frequency characteristic diagram of the reflection coefficient (S11) in a state where the series inductor L2 is connected to the radiating element RE illustrated in FIG. FIG. 3C is a frequency characteristic diagram of the reflection coefficient (S11) obtained by calculating the inductance required for the radiation element RE to be evenly matched at the band ends (207.5 MHz and 222 MHz) of the first frequency band. It is. FIG. 3D is a frequency characteristic diagram of the reflection coefficient (S11) obtained by calculation of a capacitor required for the radiation element to be evenly matched at the band ends (470 MHz and 770 MHz) of the second frequency band. FIG. 3E shows the inductance of the inductor L0 at the center frequency (214.75 MHz) of the first frequency band, and the capacitance of the capacitor C0 at the lower frequency (470 MHz) of the second frequency band. 3 is a frequency characteristic diagram of the reflection coefficient (S11) of the antenna 101 shown in FIG. 2 in which the inductance of the inductor L1 and the capacitance of the capacitor C1 are determined. It is a figure which shows the reactance X of the parallel resonant circuit by the inductor L1 and the capacitor C1, and its change rate dX / df. 5A is a frequency characteristic diagram of an antenna reflection coefficient (S11), and FIG. 5B is a frequency characteristic diagram of a forward transmission coefficient (S21) to the antenna. It is a figure which shows the relationship of the loss average value in a band with the reactance change rate dX / df. It is a figure which shows the frequency characteristic of the reactance by the combination of the inductor L1 and capacitor C1 of a parallel resonant circuit. 8A is a frequency characteristic diagram of the reflection coefficient (S11) of the antenna when three different whip antennas are used, and FIG. 8B is a frequency characteristic diagram of the forward transmission coefficient (S21) of the antenna. is there. It is a figure which shows the shape of the radiation element (whipped antenna) used with the antenna which concerns on 3rd Embodiment. It is a frequency characteristic figure of the reflection coefficient (S11) of an antenna by the presence or absence of return. 11A is a frequency characteristic diagram of antenna efficiency, and FIG. 11B is an enlarged view of a portion 207 to 222 MHz in FIG. 11A. It is a top view of a radiation element used for an antenna concerning a 4th embodiment. It is a top view of a radiation element used for an antenna concerning a 5th embodiment.

<< First Embodiment >>
The antenna according to the first embodiment will be described with reference to FIGS.
FIG. 2 is a block diagram of the antenna 101 according to the first embodiment. The antenna 101 includes a radiating element RE, a series inductor L2, an inductor L1, and a capacitor C1. The series inductor L2 is connected in series with the radiating element RE. The inductor L1 and the capacitor C1 constitute a parallel resonance circuit, and this parallel resonance circuit is inserted in series between the series inductor L2 and the power supply end FP.

  The inductance of the series inductor L2 is a value at which the resonance frequency of the series inductor L2 and the radiating element RE becomes a frequency f0 between the first frequency band and the second frequency band.

  The parallel resonant circuit has a resonance point of the circuit when the radiating element RE side is viewed from the feeding end FP, with a resonance point of the series inductor L2 and the radiating element RE as a boundary from a resonance frequency (antiresonance point) of the parallel resonance circuit. This circuit divides f0 into a center frequency f1 in the first frequency band and a center frequency f2 in the second frequency band.

  Note that the series inductor L2 only needs to be electrically connected in series to the radiating element RE, and the parallel resonant circuit of the inductor L1 and the capacitor C1 only needs to be connected in series to the inductor L2. A parallel resonance circuit of the inductor L1 and the capacitor C1 may be connected to the radiating element RE side, and the series inductor L2 may be connected to the power supply end FP side. That is, the order of the parallel resonant circuit and the series inductor L2 may be reversed.

The series inductor L2 and the parallel resonant circuit are designed in the following order.
(1) The inductance of the inductor L0 to be added in series with respect to the series inductor L2, which is required for the radiation element RE to be evenly matched at the band ends (207.5 MHz and 222 MHz) of the first frequency band, is obtained.

  Here, “equal matching” is about the measurement error in the dark room and is usually within ± 5% of the input power.

(2) The capacitance of the capacitor C0 to be added in series with respect to the series inductor L2, which is required for the radiation element RE to be evenly matched at the band ends (470 MHz and 770 MHz) of the second frequency band, is obtained.

(3) An inductor that becomes the inductance of the inductor L0 at the center frequency (214.75 MHz) of the first frequency band and the capacitance of the capacitor C0 at the lower frequency (470 MHz) of the second frequency band. The inductance of L1 and the capacitance of capacitor C1 are determined from equations 3 and 4 shown later.

  However, the reactance change rate dX / df of the parallel resonant circuit at the center frequency (214.75 MHz) of the first frequency band is 2.5 or less, and the low frequency end frequency (470 MHz) of the second frequency band. The inductance of the series inductor L2 is selected so that the reactance change rate dX / df at 1) is 1 or less.

  The series inductor L2 and the parallel resonant circuit are designed by the above procedure.

Next, the action of the parallel resonant circuit and the series inductor L2 by the inductor L1 and the capacitor C1 and the method of determining the respective values will be specifically described with reference to FIG.
FIG. 3A is a diagram illustrating the frequency characteristics of the reflection coefficient (S11) measured with the radiation element RE alone shown in FIG. Here, the radiating element RE is a so-called multistage antenna, which is in the most extended state of 120 mm. In this radiating element RE, a return loss dip occurs in the vicinity of 480 MHz, which is a frequency between the first frequency band and the second frequency band.

  FIG. 3B is a frequency characteristic diagram of the reflection coefficient (S11) in a state where the series inductor L2 is connected to the radiating element RE illustrated in FIG. Curve C is a calculation result, and curve M is an actual measurement value. The inductance value of the series inductor L2 is obtained so that the resonance frequency by the series inductor L2 and the radiating element RE becomes a frequency f0 (about 350 MHz) between the first frequency band and the second frequency band. Here, the inductance of the series inductor L2 is 39 nH. Due to the action of the series inductor L2, a return loss occurs around the frequency f0.

  FIG. 3C is a frequency characteristic diagram of the reflection coefficient (S11) obtained by calculating the inductance required for the radiation element RE to be evenly matched at the band ends (207.5 MHz and 222 MHz) of the first frequency band. It is. Specifically, the inductance of the inductor L0 to be added in series with respect to the series inductor L2 is obtained. Here, the inductance of L2 is 39 nH, and the inductance of L0 is 82 nH. In this state, an equal return loss occurs at 207.5 MHz and 222 MHz.

  FIG. 3D is a frequency characteristic diagram of the reflection coefficient (S11) obtained by calculation of the capacitance required for the radiation element RE to be evenly matched at the band ends (470 MHz and 770 MHz) of the second frequency band. . Specifically, the capacitance of the capacitor C0 to be added in series with the series inductor L2 is obtained. Here, the inductance of L2 is 39 nH, and the capacitance of C0 is 3 pF. In this state, an equal return loss occurs at 470 MHz and 770 MHz.

  FIG. 3E shows the inductance of the inductor L0 at the center frequency (214.75 MHz) of the first frequency band, and the capacitance of the capacitor C0 at the lower frequency (470 MHz) of the second frequency band. FIG. 3 is a frequency characteristic diagram of the reflection coefficient (S11) of the antenna 101 shown in FIG. 2 in which the inductance of the inductor L1 and the capacitance of the capacitor C1 are determined. Curve C is a calculation result, and curve M is an actual measurement value.

  By calculating the inductance of the series inductor L2, the inductance of the inductor L1 of the parallel resonant circuit, and the capacitance of the capacitor C1 by the above procedure, the two return losses resulting from the splitting of the resonance into two by the action of the parallel resonant circuit are obtained. A dip appears in each of the first frequency band and the second frequency band.

Next, the reactance of the parallel resonant circuit and the rate of change thereof will be described.
FIG. 4 is a diagram showing the reactance X of the parallel resonant circuit including the inductor L1 and the capacitor C1 and the rate of change dX / df. Here, the horizontal axis represents frequency, and the vertical axis represents reactance and its rate of change.

  The reactance X (ω) is expressed by the following equation.

  Here, ω is an angular frequency, that is, ω = 2πf.

  The reactance change rate dX (ω) / dω is expressed by the following equation.

  Further, the inductor L1 has an inductance of the inductor L0 at the center frequency (214.75 MHz) of the first frequency band and a capacitance of the capacitor C0 at the lower frequency (470 MHz) of the second frequency band. And the capacitance of the capacitor C1 are expressed by the following equations.

  Here, ω1 is a value 2πf1 obtained by multiplying the frequency f1 satisfying the inductance desired to be realized by the parallel resonance circuit by 2π, and ω2 is a value 2πf2 obtained by multiplying the antiresonance frequency f2 of the parallel resonance circuit by 2π.

Next, the antenna reflection coefficient (S11) and forward transmission coefficient (S21) when the values of the series inductor L2, the inductor L1 of the parallel resonant circuit, and the capacitor C1 are changed will be described with reference to FIG. .
5A is a frequency characteristic diagram of the antenna reflection coefficient (S11), and FIG. 5B is a frequency characteristic diagram of the antenna forward transmission coefficient (S21). Here, the forward transmission coefficient (S21) of the antenna is obtained for the loss in the matching circuit with the efficiency of the antenna as 100%. The conditions of each characteristic curve [1], [2], [3] are as follows.

  All of these satisfy the conditions of the design procedures (1) to (3).

  The condition [1] is that the rate of change dX / df of reactance of the parallel resonant circuit at the center frequency (214.75 MHz) of the first frequency band is 2.5 or less and the low frequency of the second frequency band is low. The reactance change rate dX / df at the band edge frequency (470 MHz) is 1 or less. As is clear from FIGS. 5A and 5B and Table 1, when the condition [1] is satisfied, both the first frequency band and the second frequency band can be matched with good balance, and The passage loss of the matching circuit can be suppressed. On the other hand, in [2] and [3], the reactance change rate dX / df of 214.75 MHz is 2.50 or less, and the condition of change rate dX / df = 1 or less at 470 MHz is simultaneously satisfied. Therefore, both S21 and S11 are in poor balance.

  In general, the Q value of the parallel resonant circuit degrades and the loss increases as it approaches the antiresonance point, but the reactance of the parallel resonant circuit that satisfies the above conditions (the impedance of the inductor L1 and the capacitance of the capacitor C1) is selected. By doing so, it is possible to match both bands while minimizing the loss at the anti-resonance point frequency in the ISDB-Tmm band and the one-segment band located above and below the anti-resonance point.

  The reactance of the parallel resonant circuit in the one-seg band has the steepest rate of change at 470 MHz and approaches a low impedance (short) at higher frequencies, so it is not the “center frequency” of the second frequency band. As described above, the capacitance at 470 MHz, which is the “low end”, may be considered.

  FIG. 6 is a diagram showing the relationship of the in-band loss average value to the reactance change rate dX / df. Here, the approximate line LB is a characteristic in the first frequency band (207 to 222 MHz), and the approximate line HB is a characteristic in the second frequency band (470 to 500 MHz, which is the section with the largest matching circuit loss in the one-segment band). It is. The loss of the matching circuit is calculated by correcting the loss due to the reflected power.

  FIG. 7 is a diagram showing frequency characteristics of reactance by the combination of the inductor L1 and the capacitor C1 of the parallel resonant circuit.

  For example, if L2 = 56 nH, L1 = 51 nH, and C1 = 4 pF, the rate of change of reactance of the parallel resonant circuit at 214.75 MHz is about 1.1, the average loss from 207 to 222 MHz is about 2.0 dB, and 470 MHz The rate of change at about 1.5 is about 1.5, and the average loss at 470 to 500 MHz is about 1.0 dB. That is, the matching for both bands is balanced.

  If L2 = 27 nH, L1 = 33 nH, and C1 = 13 pF, the change rate of reactance of the parallel resonant circuit at 214.75 MHz is about 7.7, and the average loss at 207 to 222 MHz is about 3.8 dB. The rate of change at 470 MHz is about 0.1, and the average loss at 470 to 500 MHz is about 0.5 dB. That is, the loss at 207 to 222 MHz is slightly large.

  Thus, it can be seen that the reactance change rate dX / df and loss at 215 MHz and 470 MHz are in a trade-off relationship.

  As described above, the average loss in the band by the matching circuit between 207 to 222 MHz at the antenna length of 120 mm and between 470 to 500 MHz (the section with the largest matching circuit loss in the one-segment band) is expressed by the reactance change rate dX / df. If it is 4.7 or less at 214.75 MHz and 3.7 or less at 470 MHz, the average loss is within -3 dB.

In FIG. 6, when the horizontal axis is represented by x and the vertical axis is represented by y, the straight line LB is
y = −0.273x−1.71
The straight line HB is
y = −0.689x−0.433
Respectively.

<< Second Embodiment >>
In the second embodiment, characteristic changes when the length of the whip antenna is changed will be described.
8A is a frequency characteristic diagram of the reflection coefficient (S11) of the antenna when three different whip antennas are used, and FIG. 8B is a frequency characteristic diagram of the forward transmission coefficient (S21) of the antenna. is there.

The conditions of each characteristic curve [1] [2] [3] are as follows.
All of these satisfy the conditions of the design procedures (1) to (3).

  In addition, the average loss value in each band of the matching circuit for the three antennas is as follows.

  As is apparent from this result, if the whip antenna has an average length of one-segment tuner antenna of 100 to 120 mm, the reactance change rate of the parallel resonant circuit is at least 214.75 MHz and 2.5 or less, 470 MHz. In the range of 1 or less, the passing loss of the matching circuit is well within 3 dB. Here, “3 dB” is a guide only. Since the reactance change rate dX / df and the loss are in a trade-off relationship, the number of 3 dB is not significant.

  The design range is defined by combining the result shown in the second embodiment and the relationship between the average loss value in the band and the change rate shown in FIG. 6 in the first embodiment.

  That is, the reactance change rate dX / df at the center frequency (215 MHz) of the first frequency band of the parallel resonant circuit is 2.5 or less and the reactance at the lower frequency (470 MHz) of the second frequency band. The inductance of the series inductor L2 may be selected so that the rate of change dX / df is in a range of 1 or less.

  The inductors L1 and L2 used in the matching circuit may be winding type inductors or multilayer type inductors. The only difference is the absolute value of the loss, and the idea is the same.

<< Third Embodiment >>
In 3rd Embodiment, it shows about the effect of folding of a radiation element (whipped antenna).
FIG. 9 is a diagram illustrating the shape of a radiating element (whipped antenna) used in the antenna according to the third embodiment. The radiating element RE is folded back by a predetermined length at the folded portion TE at the tip.

  The required inductance value of the series inductor L2 varies depending on the presence or absence of the folding. In the case of no folding, as shown in the first and second embodiments, the inductance of L2 is 33 nH. When folding is provided, the inductance value of the series inductor L2 becomes 24 nH as the inductance component increases.

  FIG. 10 is a frequency characteristic diagram of the reflection coefficient (S11) of the antenna depending on the presence or absence of folding. 11A is a frequency characteristic diagram of antenna efficiency, and FIG. 11B is an enlarged view of a portion 207 to 222 MHz in FIG. 11A. In the figure, a characteristic curve [1] indicates a characteristic without folding and a characteristic curve [2] indicates a characteristic with folding.

  As is apparent from these characteristics, by folding back the tip of the radiating element, the inductance value of the series inductor L2 can be reduced, and the loss due to the series inductor L2 can be reduced. Further, as the inductance value of the series inductor L2 becomes smaller, the variation in characteristics due to the variation in the inductance value of the series inductor L2 is reduced.

<< Fourth Embodiment >>
FIG. 12 is a plan view of a radiating element used for the antenna according to the fourth embodiment. The radiating element has a two-stage stretchable structure. The base side is a metal rod 51 and the tip side is a cylindrical resin molded body, and a radiating electrode 521 having a folded shape is formed along the resin molded body. One end 521C of the radiation electrode 521 is electrically connected to the metal rod 51, and the other is an open end 521T. Thus, even if it is a two-stage stretch type, it can be provided with a folded portion. The same effects as described in the embodiment are obtained. In addition, if the radiation electrode is formed on the surface of the cylindrical resin base material, the antenna itself can be easily manufactured and assembled into a wireless device.

<< Fifth Embodiment >>
FIG. 13 is a plan view of a radiating element used for the antenna according to the fifth embodiment. On the base side, a helical radiation electrode 611 is formed on a resin molded body 61. The tip side is a metal rod 62 and is electrically connected to the end of the helical radiation electrode 611.

  Thus, if it is set as the structure where the helical radiation electrode was formed in the root part, the inductance value of the series inductor L2 can be reduced, the loss in the series inductor L2 can be reduced, and antenna efficiency improves. In addition, variations in the matching circuit can be reduced.

In addition, if the radiation electrode is formed on the surface of the cylindrical resin base in this way, the antenna itself can be easily manufactured and assembled into a wireless device.
The radiation electrode may be provided in the resin molded body by insert molding.

L1 ... inductor L2 ... series inductor RE ... radiation element 51 ... metal rod 62 ... metal rod 61 ... resin molded body 101 ... antenna 521 ... radiation electrode 521C ... one end 521T ... open end 611 ... radiation electrode

Claims (5)

Two frequency bands including a radiating element and a matching circuit connected between the radiating element and the feeding end, a VHF high band as a first frequency band and a one-segment broadcasting frequency band as a second frequency band An antenna for which
The matching circuit includes a series inductor electrically connected in series to the radiating element, and a parallel resonant circuit of an inductor and a capacitor connected in series to the inductor,
The inductance of the series inductor is a value at which the resonance frequency by the series inductor and the radiating element is a frequency between the first frequency band and the second frequency band,
The parallel resonance circuit divides a resonance point by the series inductor and the radiating element into two with a resonance frequency of the parallel resonance circuit as a boundary, and a resonance frequency of a circuit when the radiating element side is viewed from the feeding end. Is a circuit having a substantially center frequency of the first frequency band and a substantially center frequency of the second frequency band,
The reactance change rate dX / df at the center frequency of the first frequency band of the parallel resonant circuit is 2.5 or less, and the reactance change at a low frequency in the second frequency band An antenna obtained by selecting an inductance of the series inductor so that a rate dX / df is in a range of 1 or less.   The antenna according to claim 1, wherein the radiating element is a linear antenna having a length in a range of 100 mm to 120 mm.   The antenna according to claim 1, wherein the radiating element has a folded portion of a radiating electrode formed at a tip.   The antenna according to any one of claims 1 to 3, wherein the radiating element is an expandable / contractible multistage radiating element, and a helical radiating electrode is formed on a first stage of the radiating element.   The antenna according to any one of claims 1 to 4, wherein the radiation element has a radiation electrode formed on a surface of a cylindrical resin base material.