JP2008098769A - Frequency-variable antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small antenna capable of easily obtaining a desired irradiation pattern and easily performing variable control with broad resonance frequencies. <P>SOLUTION: A bias voltage feeded by a variable power voltage means E<SB>V</SB>is superimposed and applied onto a connection terminal 8 where an RF signal flows. Thereby, Dc current flows from a low pass filter 7, a feed point 1a, a wire 2a (right portion of a main wire), a wire AA' (right end turning portion), a wire 3 (sub wire), a wire B'B (left end turning portion), a wire 2b (left end turning portion), a feed point 1b to an inductor 5 sequentially, and falls to a chassis ground. All of four variable capacitance units 4 are the one where a varactor diode and resistor are connected in parallel. However, the direction of the varactor diode is respectively oriented to the one where reverse bias applies to. The variable capacitance units 4 are arranged at equal distance from a centerline (y-axis) in left-right symmetry, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a folded antenna equipped with a variable capacitance element and capable of variably controlling a resonance frequency.

As a dipole antenna that enables variable control of a communication frequency using a variable capacitance element, for example, a small antenna described in Patent Document 1 below is known. In this conventional antenna, a reactance variable element is inserted on a conductor line constituting the aerial line itself, and the reactance component is variably controlled by using a DC voltage variable power source and a bias line. The effective length of the (conductor line) is freely changed to variably control the resonance frequency of the antenna.
JP-A-9-130132

However, in the case of the above-described conventional antenna, a sufficiently high radiation characteristic cannot be obtained because the high frequency leaking to the bias line adversely affects the radiation pattern shape of the antenna. In addition, such an adverse effect due to high-frequency leakage is not always easy to predict, so it is difficult to design an antenna having desired radiation characteristics based on such a conventional technique.
For example, when an antenna is mounted on a window glass of a vehicle, a method using a dedicated bias line for variably controlling the resonance frequency is not always desirable from the viewpoint of the aesthetics of the antenna. . Further, for example, a choke inductor can be used to reduce high-frequency leakage to the bias line, but this method makes the above-mentioned aesthetic problem more pronounced. Even if such a choke inductor is used, high-frequency leakage to the bias line cannot be completely prevented.

  On the other hand, a method of mounting a reactance variable element such as a varactor diode in the matching circuit connected to the power feeding unit instead of on the aerial line is also conceivable, but when such a method is adopted, the effective length of the antenna is directly Therefore, it is not possible to variably control the antenna, and it is difficult to widen the antenna band by variably controlling the resonance frequency.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to realize a small antenna in which both a desired radiation pattern and a wide variable control of the resonance frequency are easy. It is.

In order to solve the above problems, the following means are effective.
That is, the first means of the present invention includes a single main wire having a single power supply portion consisting of a pair of left and right power supply points in the center, and the left and right ends arranged in parallel to the main wire. In a folded dipole antenna having a secondary wire connected to each of the left and right ends of the main wire, variable voltage means for variably controlling the DC voltage between the two feeding points is provided, A variable capacity unit is provided between each of the left and right ends and the power supply part, and another variable capacity unit is provided at each corresponding part of the slave wires arranged opposite to each of the variable capacity units. Each variable capacitance unit is constituted by a parallel connection of a varactor diode and a resistor, and each of these varactor diodes has a direction in which a reverse bias is applied by the variable voltage means. It is to connect to.

  However, the above-mentioned wire refers to a conductor line (metal wiring) such as a linear shape, a rod shape, a cylindrical shape, or a plate shape. In addition, the above-mentioned parallel means that the sub wires are arranged along the main wire and their respective parts are arranged in substantially the same direction at a substantially constant interval. Therefore, both are not necessarily straight and straight. It does not have to be and does not necessarily have to be exactly parallel. That is, these wires may be bent, folded, or wound spirally. Therefore, for example, a helical antenna can be manufactured based on the present invention.

Further, for example, an inductor such as a helical coil may be inserted into the main wire or the subwire at any position. Originally, a wire (metal wiring) has an inductance component in each part as a distributed constant, so naturally such deformation is allowed. In particular, in the case of configuring a small antenna, when an inductor is inserted into a wire, it is not easy to form a flat surface of the antenna.
Further, these inductors arranged by such insertion or the like may be considered as a part of the above-mentioned main wire or sub-wire, and all of the above-mentioned main wire or sub-wire are constituted by such an inductor. May be.
The above situation is the same for the third means (in the case of a folded monopole antenna) described later.

The second means of the present invention is that, in the first means, the folded dipole antenna is formed symmetrically about the feeding portion.
However, the orientation of the varactor diode is not left-right symmetric but is left in a direction in which reverse bias is applied.

  The third means of the present invention includes a main wire having one end as a feeding point, and a slave wire arranged in parallel to the main wire and having one end connected to one end that is not the feeding point of the main wire. Folded monopole antenna having variable voltage means for variably controlling the DC potential at the feeding point, a variable capacitance unit in the middle of the main wire, and grounding the other end of the slave wire not connected to the main wire In addition, other variable capacitance units are provided in the corresponding portions of the secondary wires arranged opposite to the variable capacitance units, and each of these variable capacitance units is configured by parallel connection of a varactor diode and a resistor. Each varactor diode is connected in the direction in which a reverse bias is applied by the variable voltage means.

  The fourth means of the present invention is to provide a plurality of the above-mentioned slave wires in any one of the above-mentioned first to third means.

  The fifth means of the present invention is to set the value of the resistance to 10 kΩ or more and 100 MΩ or less in any one of the first to fourth means. This value is more preferably 100 kΩ or more and 10 MΩ or less. If this value is too large, the action and effect obtained by disposing the resistor in the variable capacitance unit of the present invention is undesirably reduced. If this value is too small, the power consumption of the antenna becomes too large, which is not desirable.

According to a sixth means of the present invention, in any one of the first to fifth means, the length of the main wire from the end where the main wire and the secondary wire are connected to the feeding point is set to L. When / 4, the above varactor diodes are disposed on the respective wires at positions separated from the end by 7 L / 40 or more and 9 L / 40 or less.
Here, for example, in the case of a folded dipole antenna, it may be considered that the wire length between the folded portions at the left and right ends coincides with L / 2.

  In the case of a folded dipole antenna, the above distance (7L / 40 to 9L / 40) is the distance from the end closer to the varactor diode. That is, the position of the right varactor diode is defined by the distance from the right end, and the position of the left varactor diode is defined by the distance from the left end.

The seventh means of the present invention is to make the vertical cross-sectional area of the main wire smaller than the vertical cross-sectional area of the slave wire in any one of the first to sixth means.
However, the cross-sectional area of the wire is not necessarily limited to two types, and may be changed in three or more steps, or may be changed continuously.

The eighth means of the present invention is to make the diameter of the main wire 1/8 or more and 1/2 or less of the diameter of the slave wire in the seventh means.
However, the cross-sectional shape of each wire need not be exactly circular. When these cross-sectional shapes are arbitrary, it is desirable that the vertical cross-sectional area of the main wire is about 1/64 to 1/4 of the vertical cross-sectional area of the slave wire.

According to a ninth means of the present invention, in any one of the first to third means, both the main wire and the secondary wire are folded an arbitrary number of times.
However, the number of times of folding may be arbitrary, but usually about 1 to 3 times is optimal. Further, it is not always necessary to fold back in the reverse direction, and it is sufficient to fold back in a direction in which a sufficient resonance component (resonance direction current) can be obtained.

  However, as a more preferable folded form, for example, in the case of a folded dipole antenna having a single planar configuration, the secondary wire is surrounded by the primary wire above the antenna, that is, on the opposite side of the feeding portion. It is better to fold the folded parts at the left and right ends to the position of the power feeding part so that they are folded inward. It is good to fold to the position of the power feeding part inside.

According to a tenth means of the present invention, in any one of the first to ninth means, the feeding point includes a balun that separates a high-frequency current and a direct current, and the balun is a low-pass filter. It is configured by parallel connection with a high-pass filter.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

The effects obtained by the above-described means of the present invention are as follows.
That is, according to the first or third means of the present invention, since a reverse bias is applied to the varactor diodes, these varactor diodes function as variable capacitance elements, and their capacitance values are the above-mentioned variable voltage. It can be determined by the DC power supply voltage from the means. For this reason, if the variable voltage means described above is used as the control means, it is possible to variably control the phase transition of the high frequency at the insertion location of each variable capacitance unit of the antenna, so that the effective length of the antenna is effectively reduced. Thus, it is possible to variably control.

In addition, when a reverse bias is applied to a varactor diode, the DC resistance between the two terminals becomes very large, and the two terminals are substantially insulated from the direct current. When one DC power source is connected in series, it is difficult to apply equal voltages to each varactor diode or to maintain the equal state.
For this reason, if the above-described resistance is not provided in the above-described variable capacitance unit, it is difficult to apply an equal DC voltage to each of the varactor diodes connected in series. That is, it is difficult to obtain a design value. In this case, the voltage applied to each varactor diode changes (drifts) with time, and the operation of the antenna becomes unstable. As a cause of such a phenomenon, it is considered that local accumulation of charges on a series connection circuit of a plurality of varactor diodes, uneven distribution, or temporal change of the charge distribution are involved.

  However, according to the first or third means of the present invention, the resistors connected in parallel to the varactor diodes are further connected in series with each other. With the direct current energizing action, the voltages applied to the varactor diodes can be allocated substantially evenly and can be stably maintained. Therefore, according to the above means, the capacitance value indicated by each varactor diode becomes uniform as the design value, so that the resonance frequency of the antenna can be set as the design value without causing a frequency shift over time toward the low frequency side. Can be stabilized.

For this reason, according to the first or third means of the present invention, it is possible to realize a small antenna in which both desired radiation characteristics and variable control of the communication frequency are easy, and the operation is also designed. It can be stabilized according to value.
In addition, according to the first or third means of the present invention, since a dedicated bias line is not required, it is possible to avoid deterioration of the radiation pattern shape and aesthetics of the antenna.

  Further, according to the second means of the present invention, when the folded antenna is a dipole antenna, the feeding point can be arranged at the position where the current is maximized, so that the impedance matching of the antenna is the best. It becomes easy, and it becomes possible to constitute the most sensitive antenna.

Further, according to the fourth means of the present invention, the current in the transmission mode passing through the power feeding section is further increased by multiplexing the current in the transmission mode (differential mode) based on the action of the slave wire. Therefore, it is possible to configure an antenna with higher sensitivity.
Further, according to the fifth means of the present invention, it is possible to apply a voltage to each of the above varactor diodes uniformly at all times, and to effectively suppress power consumption due to the direct current.

  According to the sixth means of the present invention, the resonance frequency of the antenna can be adjusted over a wide range with respect to a small change in capacitance. At the same time, since the change in impedance with respect to the change in capacitance can be suppressed to a sufficiently small value, it is possible to effectively suppress reflection loss.

  Further, according to the seventh means of the present invention, since the impedance of the antenna viewed from the feeding point is increased, even when a small antenna is configured, the reflection loss at the feeding point can be reduced. In particular, according to the eighth means of the present invention, the compatibility with a general rated coaxial cable or the like can be extremely improved.

According to the ninth means of the present invention, the occupied area of the antenna can be transformed into an arbitrary shape, or the entire length of the occupied area of the antenna can be effectively shortened. For this reason, according to the ninth means of the present invention, the mountability of the antenna can be flexibly optimized.
In addition, it is appropriate that the number of turns is about 1 to 3 times. Even if this number is further increased, the current component in the direction perpendicular to the resonance direction in the folded portion does not contribute to the resonance effect of the antenna effectively, so even if this number is increased further, the antenna is straightened. However, it is difficult to effectively contribute to miniaturization simply by increasing the length of the line at that time.

  Further, according to the tenth means of the present invention, the direct current and the high frequency signal can be satisfactorily separated with sufficiently small loss based on the action of both filters connected in parallel. Therefore, the variable voltage means for variably controlling the DC current can variably control the capacitance value of the varactor diode and can ensure high sensitivity of the antenna with respect to the target high-frequency signal. .

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

(Example 1)
FIG. 1A is a circuit diagram of a folded dipole antenna A1 according to the first embodiment. The operating frequency of the antenna A1 was about 200 MHz, and the dimensions of the rectangular area occupied by the aerial line portion were 332 mm in the left-right direction (x-axis direction) and 30 mm in the vertical direction (y-axis direction).
The main wire constituting the antenna A1 is composed of a wire 2a and a wire 2b, and a power feeding unit 1 is provided between them (that is, in the central portion of the main wire). The wire 2a that connects the point 1a and the end point A of the power feeding unit 1 composed of a pair of two power feeding points (1a, 1b) has six right-angled bent portions. Similarly, the wire 2b connecting the other end 1b of the power feeding unit 1 and the end point B also has six right-angled bent portions.

  Further, the wire 3 having the end point A ′ as the right end and the end point B ′ as the left end constitutes a slave wire of the antenna A1, and each part thereof is along the main wire (wires 2a, 2b) paired therewith. They are arranged substantially parallel to these. That is, the wires 2a and 2ba are arranged substantially parallel to the wire 3, respectively. The points A and A ′, and the points B and B ′ are connected to each other by wires constituting the folded portions at the left and right ends of the antenna A1, respectively.

Based on these configurations, that is, by providing the bent portion as described above, the pair of the primary wire and the secondary wire that were initially extended in the x-axis direction in parallel and arranged in parallel on both the left and right sides is on the upper side of the drawing. They are folded twice symmetrically.
That is, the antenna A1 is configured such that, on the opposite side (that is, the upper side of the drawing) of the power feeding unit 1, the secondary wire 3 is folded inward while being surrounded by the main wires (2a, 2b). (Wire AA 'and Wire BB') are folded to the position of each feeding point (1a, 1b), and similarly, on the opposite side of feeding part 1, both wing tips of the antenna are folded again to the feeding part 1 position. It is a thing.
On the wires 2a, 2b, and the wire 3, variable capacity units 4 are loaded at a total of four locations where the distance in the x-axis direction from the power feeding unit 1 is equal. The wires 2a and 2b have the same radius, but the ratio of the radii of the main wires (2a, 2b) and the sub wires 3 is set to 1: 4.

Further, in order to connect the balanced antenna A1 to the unbalanced coaxial line, the balun 10 is disposed in the power feeding portion. The configuration of the balun 10 will be described in detail later using FIG. 1-C.
Variable voltage means E _V is for outputting the arbitrarily control the DC voltage of 0V～20V, in its negative electrode is chassis ground, the positive electrode is connected to one end of the choke coil L _BT . The other end of the choke coil L _BT is the connection terminal 8 connected directly to the T-junction 9 is connected to one end of the capacitor C _BT, the other end of the capacitor C _BT is a RF output terminal t Yes.

Bias voltage supplied by the variable voltage means E _V is applied superposed on the connection terminal 8 RF signal flows, whereby direct current, low pass filter 7, the feeding point 1a, the wire 2a (the right portion of the main wire) , Wire AA '(right end folded portion), wire 3 (secondary wire), wire B'B (left end folded portion), wire 2b (main wire left portion), feed point 1b, and inductor 5 sequentially Fall to chassis ground above.
The inductor 5 and the choke coil _LBT may be replaced with resistors.

  FIG. 1B shows a circuit diagram of the variable capacitance unit 4 described above. As can be seen from this figure, these variable capacitance units 4 are obtained by connecting a varactor diode D and a resistor R in parallel. However, the direction of the varactor diode D is oriented in the opposite direction to the DC bias from the DC power source connected to the connection terminal 8, that is, in the direction in which the reverse bias is applied. Further, the variable capacitance unit 4 was arranged 150 mm away from the center line (y axis) passing through the center of the power feeding unit 1 in a bilaterally symmetrical manner as shown in FIG.

With these configurations, as shown in FIG. 1B, the direction of the DC current i fed from the DC power supply (variable voltage means E _V ) is always opposite to the direction of the varactor diode D. Here, for example, the DC voltage of the variable voltage means E _V and 20V, when the resistance value of the resistance R of the variable capacitance unit 4 and 1 M.OMEGA, on the wire of the antenna A1, since four of the variable capacitance unit 4 is connected in series, of the The direct current i is 5 μA. Since this current is very small, power consumption due to this direct current i does not become a problem. Although this current is very small, it is sufficient to maintain a uniform voltage applied to each varactor diode.
Also, changing the DC voltage of the variable voltage means E _V between 0V～32V, the DC voltage to the individual varactor diodes changes between 0V～8V, at this time, the individual varactor diodes in this embodiment Each capacitance value varies within a range of 13 pF to 0.5 pF.

FIG. 1C shows a circuit diagram of the balun 10 described above. The balun 10 includes a high-pass filter 6, a low-pass filter 7, and a T branch 9. Each input / output terminal is connected to the connection terminal 8 and the feeding points 1a and 1b of the antenna, respectively. The high-pass filter 6 is obtained by connecting the other ends of the coils L ₄ and L ₅ whose one ends are grounded between the stages of capacitors C ₁ , C ₂ and C ₃ connected in series. The low-pass filter 7 is formed by connecting the other ends of the capacitors C ₄ and C ₅ whose one ends are grounded between the series-connected stages of the coils L ₁ , L ₂ and L ₃ . These filters 6 and 7 are connected in parallel using a T-branch 9. Note that the DC current i in FIG. 1-C indicates the same current as the DC current i in FIG. 1-B.

  Since these circuits shown in FIG. 1-C including the choke coil 5 are portions further disposed on the base side of the antenna than the power feeding unit 1 of the antenna A1, for example, the antenna A1 is connected to the vehicle. When arranged on a windshield or the like, these circuits can be arranged in an invisible place or an area that is relatively difficult to enter.

  According to the above configuration, the same bias voltage can be applied to each variable capacitance unit 4 loaded on each wire without using a special bias circuit. Therefore, in the antenna A1 according to the first embodiment, the resonance frequency of the antenna can be variably controlled without deteriorating the radiation pattern.

  Also, normally, when configuring a folded dipole antenna, if the antenna size is made much smaller than half of the wavelength used, the input impedance of the antenna will be very small, a few ohms. In the antenna A1 according to the first embodiment, since the ratio of the diameters of the main wires (wires 2a and 2b) and the sub wires (wires 3) is set to 1: 4, the input impedance is raised to several tens of ohms. ing. For this reason, although the antenna A1 is sufficiently small, the reflection loss is small.

Hereinafter, the characteristics of the antenna will be described in more detail with reference to experimental results related to the folded dipole antenna A1.
FIG. 2-A shows the relationship between the variable capacitance of each varactor diode D of the antenna A1 and the resonance frequency. From this graph, it can be seen that the resonance frequency is changed by changing the capacitance value of the varactor diode D.
FIG. 2-B shows the relationship between the variable capacitance and impedance of the antenna A1. In general, if the change in impedance is large, a resonance frequency band in which the reflection loss is large is likely to be generated. However, as can be seen from FIG. 2-B, the antenna A1 greatly changes the capacitance value of the variable capacitance unit 4. The impedance does not change much even if it is made. Therefore, in this antenna A1, there is no resonance frequency at which the reflection loss becomes particularly large.

  FIGS. 3A and 3B show changes in the resonance frequency and the input impedance when the insertion position of the variable capacitance unit 4 is changed. X, o, and * are values when the varactor diode D is set to 13 pF, 2.5 pF, and 1.5 pF, respectively. The horizontal axis is the distance from the aforementioned center line to the varactor diode D. From FIG. 3A and FIG. 3B, if the variable capacitance unit 4 is disposed in a range of about 14 cm to 19 cm from the center, the input impedance is not changed so much, that is, the reflection loss is not increased. It can be seen that the resonance frequency can be variably controlled over a wide range (about 190 MHz to 250 MHz).

  FIG. 4 illustrates four examples of the resonance frequencies and the standing wave ratio in the vicinity thereof when the capacitance value of the varactor diode D is changed. In this graph, the solid line is the calculated value, and the □, ●, ×, and ○ marks indicate the measured values. From this graph, it can be seen that the resonance frequency of the antenna can be controlled from at least 187 MHz to 230 MHz. Also, the standing wave ratio is sufficiently small. However, although only four examples are illustrated in FIG. 4, in practice, the resonance frequency to be variably controlled (that is, the frequency at the deepest part of the valley bottom of the graph showing a sharp convex shape downward) is at least 187 MHz to 230 MHz. The standing wave ratio is less than 2 at any resonance frequency.

FIG. 5 shows the directivity on the zx plane when the resonance frequency of the antenna A1 is adjusted to 190 MHz. From this graph, it can be seen that an ideal figure 8 directivity is obtained.
Further, FIG. 6 illustrates the relationship between each resonance frequency and gain of the antenna A1. From this graph, it can be seen that a sufficiently good gain of about −3 dBi is obtained on the average over a wide range, and that stable operation can be obtained at least from 187 MHz to 230 MHz.

As described above, in the antenna A1 according to the first embodiment, since a dedicated bias line is not used, the radiation pattern is greatly improved as compared with the conventional antenna. Moreover, despite the fact that each stage is smaller than the conventional one, a folded dipole antenna that can be easily matched can be realized.
Therefore, for example, based on this embodiment, if the antenna A1 is mounted on the top of a windshield of a car, for example, a digital radio that is expected to open in the near future in the car without obstructing the driver's field of view. Radio waves (188 MHz to 192 MHz) can be received very well. In addition, the reception band (187 MHz to 230 MHz) of the antenna A1 leaves a large margin on the higher side than the frequency band of the digital radio. For this reason, in the antenna A1, the resonance frequency to the low frequency side, which can be caused by a change in the arrangement state such as the arrangement target, arrangement position, orientation, or the approach of an obstacle such as a human body, etc. The shift phenomenon can be dealt with sufficiently well and flexibly.

  FIG. 7A is a circuit diagram of a folded monopole antenna A2 according to the second embodiment. This antenna A2 is obtained by modifying the folded dipole antenna A1 of the first embodiment into a monopole helical antenna, and exhibits substantially the same directivity as the graph of FIG. Further, portions corresponding to the first embodiment in the figure are indicated by using the same reference numerals or the same reference numerals with “″”. A variable capacitance unit pair DD shown in FIG. 7-B is connected to the circuit DD.

More specifically, one end A ′ of the slave wire 3 ″ is connected to the folded portion of the antenna A2 made of the wire AA ′, and the other end of the slave wire 3 ″ is a plate-like ground plate made of a conductor. G is connected. A cylindrical hole H is formed in the center of the ground plate G, and the feeding point 1a ″ constituting one end of the main wire 2a ″ is arranged at the center of one bottom surface of the cylindrical shape. However, this bottom surface is the bottom surface on the upper surface S of the ground plate G. The main wire 2a ″ is spirally wired between the feeding point 1a ″ and the end point A, and the secondary wire 3 ″ is also wired so as to maintain a substantially constant interval along this.
Output terminal t of the RF signal is connected to the feeding point 1a "through capacitor C _BT, to the other end of the capacitor C _BT to output terminal t is not connected, one end of the choke coil L _BT are connected. the capacitance C _BT and the choke coil L _BT is for separating the the DC current i RF Like the capacitor C _BT and the choke coil L _BT in FIG. 1-a (RF signal) and the other end of the choke coil L _BT is connected to a positive electrode of the variable voltage means E _V. Meanwhile, the negative electrode side of the variable voltage means E _V is connected to the ground plane G through the resistor r .

A pair of lines of the substantially parallel main wire 2a ″ and sub-wire 3 ″ extends in the x-axis direction while being spirally wound. The cross-sectional area of the secondary wire 3 ″ was set to 16 times the cross-sectional area of the main wire 2a ″.
FIG. 7B shows a circuit diagram of the variable capacitance unit pair DD of the antenna A2 of the second embodiment. In the circuit DD, the variable capacitance units 4 of the first embodiment are arranged in opposite directions, and the connection points a, b, c, and d in FIG. 7-B are the same points a and b in FIG. b, c, d are shown. Also, the direct current i in FIG. 7-B is the same current as the direct current i shown in FIG. 7-A. That is, also in the second embodiment, the varactor diode D is arranged in a direction in which a DC reverse bias is applied. The capacitance value of each varactor diode D, also in this second embodiment, substantially the same manner as Example 1 above, can be variably controlled freely on the basis of the variable control of a DC voltage the variable voltage means E _V outputs .
According to such a configuration, the antenna cannot be planarized, but a desired folded antenna capable of variably controlling the resonance frequency over a wide range can be further miniaturized.

[Other variations]
The embodiment of the present invention is not limited to the above-described embodiment, and other modifications as exemplified below may be made. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.

(Modification 1)
For example, in the first embodiment, no inductor is inserted into any of the wires (2a, 2b, 3), but an inductor such as a helical coil may be inserted into these wires. Moreover, you may comprise all the full length of these wires from arbitrary inductors, such as a helical coil, for example. These circumstances are the same when a folded monopole antenna is configured.

(Modification 2)
In the first embodiment, the configuration of the folded dipole antenna is exemplified. However, if the right half of the wire of the antenna A1 is used and connected to the surface S in the same manner as in the second embodiment, the above-described embodiment. A folded monopole antenna that can be tuned in the same manner as in FIG. Even in such a case, the operation and effect of the present invention can be obtained.
Also in such a modification, a helical coil or the like can be inserted into an arbitrary part of each wire.

(Modification 3)
Further, in the folded dipole antenna A1 (FIG. 1) of the first embodiment, the structure in which the main wire and the sub wire are arranged in parallel is shown in two stages of folding. However, the number of times of folding the antenna line may be arbitrary. It may be 0 times or 1 time. Further, the number of sub wires arranged in parallel to the main wire may be plural. By increasing the number of sub wires, the current in the transmission mode (differential mode) passing through the power feeding unit can be further increased.

(Modification 4)
Further, the vertical cross-sectional area of the wire is not necessarily limited to two types, and may be changed in three steps or more, or may be changed continuously. Therefore, for example, deformation such as changing the cross-sectional area of the wire continuously and monotonously in the folded portions (eg, the portions of the wires AA ′ and BB ′) at the left and right ends of the antenna, in the vicinity thereof, or in the vicinity thereof. Each may be done.

(Modification 5)
In addition, the above-described main and secondary wires can be replaced with, for example, a woven mesh-shaped conductor line that constitutes the ground line outside the coaxial cable, and of course, the same operation and effect as the above-described embodiment can be obtained. be able to.

  For example, as described above, the present invention is suitable for in-vehicle digital radio reception. However, the present invention is not limited to those uses (usage frequency band, mounting target, arrangement area, reception, etc.). The present invention should not be applied and can be used for any other communication purpose.

Circuit diagram of folded dipole antenna A1 of the first embodiment Circuit diagram of the variable capacitance unit 4 of the antenna A1 of the first embodiment. Circuit diagram of the balun 10 of the antenna A1 of the first embodiment A graph showing the relationship between the variable capacitance of the antenna A1 and the resonance frequency Graph showing the relationship between the variable capacitance and impedance of the antenna A1 Graph showing the relationship between the position of the varactor diode D and the resonance frequency A graph showing the relationship between the position of the varactor diode D and the impedance A graph illustrating the standing wave ratio in the vicinity of four resonance frequencies The graph which shows the directivity on zx plane of antenna A1 Graph illustrating the relationship between each resonance frequency and gain of antenna A1 Circuit diagram of folded dipole antenna A2 of the second embodiment Circuit diagram of variable capacitance unit pair DD of antenna A2 of the second embodiment

Explanation of symbols

A1: Folded dipole antenna A2: Folded monopole antenna
1: Power supply unit 2a, 2b: Main wire
3: Secondary wire
4: Variable capacity unit
D: Varactor diode
R: Resistance
E _V : Variable voltage means

Claims (10)

One main wire having a single power supply portion consisting of a pair of power supply points on the left and right, and a left and right end connected to the left and right ends of the main wire, respectively. In a folded dipole antenna having a follower wire,
Variable voltage means for variably controlling the DC voltage between the two feeding points;
The main wire is
Each has a variable capacity unit between the left and right ends and the power supply unit,
The secondary wire is
Each of the corresponding parts arranged opposite to each of the variable capacity units has another variable capacity unit,
Each of the variable capacity units is
Consists of parallel connection of varactor diode and resistor,
The varactor diode is
The folded dipole antenna is connected in a direction in which a reverse bias is applied by the variable voltage means. The folded dipole antenna according to claim 1, wherein the folded dipole antenna is formed symmetrically with respect to the feeding portion. In a folded monopole antenna having one main wire having one end as a feeding point, and a slave wire arranged in parallel to the main wire and having one end connected to one end that is not the feeding point of the main wire,
Variable voltage means for variably controlling the DC potential of the feeding point;
The main wire is
A variable capacity unit is in the middle,
The secondary wire is
The other end not connected to the main wire is grounded, and
Having another variable capacity unit in a corresponding part lined up against the variable capacity unit,
Each of the variable capacity units is
Consists of parallel connection of varactor diode and resistor,
The varactor diode is
A folded monopole antenna, which is connected in a direction in which a reverse bias is applied by the variable voltage means. The antenna according to any one of claims 1 to 3, comprising a plurality of the secondary wires. The value of the resistance is
The antenna according to any one of claims 1 to 4, wherein the antenna is 10 kΩ or more and 100 MΩ or less. When the length of the main wire from the end where the main wire and the sub wire are connected to the feeding point is L / 4,
Each of the varactor diodes is
The antenna according to any one of claims 1 to 5, wherein the antenna is disposed on each wire at a position separated from the end by 7L / 40 or more and 9L / 40 or less. The vertical cross-sectional area of the main wire is
The antenna according to any one of claims 1 to 6, wherein the antenna has a smaller vertical cross-sectional area than the secondary wire. The diameter of the main wire is
8. The antenna according to claim 7, wherein the antenna has a diameter of 1/8 or more and 1/2 or less of the diameter of the secondary wire. The antenna according to any one of claims 1 to 8, wherein both the main wire and the slave wire are folded an arbitrary number of times. At the feeding point,
It has a balun that separates high-frequency current and direct current,
The balun is
The antenna according to any one of claims 1 to 9, wherein the antenna is configured by connecting a low-pass filter and a high-pass filter in parallel.

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