WO2008030021A1

WO2008030021A1 - Antenna with adjustable resonant frequency using metamaterial and apparatus comprising the same

Info

Publication number: WO2008030021A1
Application number: PCT/KR2007/004242
Authority: WO
Inventors: Byung Hoon Ryou; Won Mo Sung; Jeong Pyo Kim; Dong Ryul Shin
Original assignee: E.M.W. Antenna Co., Ltd.
Priority date: 2006-09-04
Filing date: 2007-09-04
Publication date: 2008-03-13

Abstract

There is herein disclosed a miniature antenna with an adjustable resonant frequency without any change of the radiation performance, and an apparatus including the same. The antenna comprises two radiation conductors connected to a feed section and a ground plane, respectively, and a resonant circuit section as a zero-order resonator including inductors, transmission lines and a capacitor. The inductors and/or capacitor are configured of a variable element so that the impedance of the variable element can be controlled to adjust the resonant frequency of the antenna. In addition, the installation position and the size of the ground plane within the apparatus with respect to the transmission lines can also be controlled to adjust the resonant frequency of the antenna. Alternatively, the antenna may further comprise a variable capacitor connected to the inductors so as to adjust the effective inductance and change the resonant frequency. The radiation lines of the antenna are not related with determination of the resonant frequency, and thus the radiation performance is not affected by the adjustment of the resonant frequency.

Description

ANTENNA WITH ADJUSTABLE RESONANT FREQUENCY USING METAMATERIAL AND APPARTUS COMPRISING THE

SAME

Technical Field

[1] The present invention relates to an antenna with an adjustable frequency, and more particularly, to a miniature antenna with a resonant frequency which can be adjusted by adopting a zero-order resonator (ZOR) using a metamaterial structure. Background Art

[2] An antenna is an indispensable constituent element of a wireless communication apparatus for transmitting/receiving electromagnetic waves, and is configured to resonate electromagnetic waves of a specific frequency to transmit/receive the electromagnetic waves of the frequency. As used herein, the term "resonance" generally refers to a state in which an impedance of a circuit at a specific frequency is an purely imaginary number, and substantially refers to a phenomenon in which there is a sharp decrease in an Sl 1 parameter as a reflection coefficient of a circuit at the specific frequency.

[3] A conventional antenna has a resonant structure of a first order mode. In other words, the conventional antenna is composed of a conductive wire (transmission line) which has an electrical length of λ/2 of a wavelength λcorresponding to a desired frequency and is opened or short-circuited at one end thereof. As such, an electromagnetic wave guided along the conductive wire forms a standing wave inside the conductive wire to generate a resonance. The electrical length of such an antenna with the resonant structure of a first order mode is determined depending on a resonant frequency, and hence the size of the antenna also depends on the resonant frequency. Particularly, disadvantageously as a desired resonant frequency decreases, the size of the antenna increases.

[4] In order to address such a shortcoming, there has been proposed a monopole antenna formed above a ground plane to have an electrical length of λ/4. Also, an antenna having various complex shapes such as a helix shape, a meander shape, etc., has been proposed to further reduce the size of the monopole antenna. However, the proposed antennas still has a limitation in that their sizes are determined depending on the resonant frequency. There occurs a problem in that as an antenna is miniaturized, the shape of the antenna is more complicated so as to form an antenna of a fixed length at a narrow space. In addition, as the shape of the antenna becomes complex, there is a difficulty in maintaining the performance of the antenna due to an increase of an influence by the coupling between conductive wires being formed, etc.

[5] Besides these, a method has been suggested in which a dielectric substance having a high dielectric constant is additionally provided to increase an effective electrical length of the antenna. However, this method is disadvantageous in that an additional cost is required for fabrication and additional provision of the dielectric substance.

[6] In the meantime, a metamaterial theory is known in the art as a new theory associated with the resonant structure.

[7] The metamaterial refers to a material or an electromagnetic structure designed artificially to exhibit a special electromagnetic characteristic which cannot be generally found in the nature. The term "metamaterial" as defined herein and in the present art, generally refers to a material or an electromagnetic structure having permittivity and permeability whose values are all negative numbers.

[8] Such material is also referred as to a "Double-negative (DNG)" material in terms of having two negative parameters. The metamaterial is also referred to as a "Negative refractive index material (NRI)" in terms of having a negative reflection coefficient by negative permittivity and permeability. The metamaterial was originally researched by V.Veselago, a physicist of the Soviet Union in 1967, but after 30 years have passed since that, the research and application on a concrete implementing method is currently in progress.

[9] It is possible to implement a zero-order resonator (ZOR) using the metamaterial. An example of an implementation of the zero-order resonator using the metamaterial is disclosed in the U.S. Patent Application Serial No. 11/092,143 by Itoh, et, al. The zero- order resonator permits its resonant frequency to be determined irrespective of the electrical length of the resonant structure unlike the conventional resonant structure. The zero-order resonator substantially has the same resonant structure as that of an LC resonant circuit so that the inductance and the capacitance of an inductor and a capacitor included in the circuit determine the resonant frequency of the zero-order resonator. Thus, the resonant frequency can be changed by adjusting the inductance and the capacitance of the inductor and the capacitor. Also, even if the resonant frequency decreases, the antenna is not up-scaled.

[10] However, the metamaterial and the zero-order resonator theory are still not applied to electronic elements, particularly their applications to an antenna-related field are merely in an early stage. Disclosure of Invention Technical Problem

[11] Accordingly, an object of the present invention has been made to overcome the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide an antenna which adopts a zero-order resonator so as to be manufactured compactly regardless of the resonant frequency of the zero-order resonator.

[12] Another object of the present invention is to provide a miniature antenna which enables adjustment of its resonant frequency even without affecting its radiation performance. Technical Solution

[13] To accomplish the above object, according to one aspect of the present invention, there is provided an antenna comprising: a first radiation line connected at one end thereof to a feed circuit; a second radiation line grounded at one end thereof to an earth ground; and an at least one zero-order resonant circuit section connected at one end thereof to the first radiation line and connected at the other end thereof to the second radiation line.

[14] In one embodiment of the present invention, the zero-order resonant circuit section comprises: a first inductor connected to the first radiation line; a first transmission line connected in series to the first inductor; a first capacitor connected in series to the first transmission line; a second transmission line connected in series to the first capacitor; and a second inductor connected in series between the second transmission line and the second radiation line.

[15] In another embodiment of the present invention, the zero-order resonant circuit section comprises: a first inductor connected to the first radiation line; a transmission line connected in series to the first inductor; and a second inductor connected in series between the transmission line and the second radiation line.

[16] At least one of the first inductor and the second inductor may be a variable inductor.

The first capacitor may be a variable capacitor. In addition, at least one of the first inductor and the second inductor is connected to a variable capacitor whereby an effective inductance is adjustable. The zero-order resonant circuit section may further comprise a variable capacitor connected between one end of one of the first inductor and the second inductor and a ground plane. The first radiation line or the second radiation line may be formed in a helix shape so as to improve the gain of the antenna and adjust the resonant frequency of the antenna.

[17] The antenna may comprise two or more zero-order resonant circuit sections having different resonant frequencies.

[18] According to another aspect of the present invention, there is also provided a wireless communication apparatus having an antenna for transmitting/receiving a radio signal, wherein the antenna comprises: a first radiation line connected at one end thereof to a feed circuit; a second radiation line grounded at one end thereof to an earth ground; and an at least one zero-order resonant circuit section connected at one end thereof to the first radiation line and connected at the other end thereof to the second radiation line.

Advantageous Effects

[19] As described above, according to the present invention there is provided an antenna which can be manufactured compactly regardless of the resonant frequency and enables adjustment of its resonant frequency. Also, according to the antenna according to the present invention, there is provided a miniature antenna which enables adjustment of its resonant frequency even without affecting its radiation characteristics, and can exhibit a uniform radiation characteristic with respect to various resonant frequencies. Brief Description of the Drawings

[20] FIG. 1 is a circuit diagram showing an antenna according to one embodiment of the present invention;

[21] FIG. 2 is an equivalent circuit diagram showing the antenna of FIG. 1;

[22] FIG. 3 is an equivalent circuit diagram obtained by the adjustment of L , L , and

CO values of FIG. 2;

[23] FIG. 4 is a side view showing an antenna according to another embodiment of the present invention for adjustment of the capacitance;

[24] FIG. 5 is an equivalent circuit diagram showing an antenna according to another embodiment of the present invention for adjustment of the inductance;

[25] FIG. 6 is a graph showing a change of the reflection coefficient according to a change of the capacitance of a variable capacitor;

[26] FIG. 7 is a graph showing the dual-band operation of an antenna according to one embodiment of the present invention;

[27] FIG. 8 is a perspective view showing an example of an implemented antenna of the present invention;

[28] FIG. 9 is a perspective view showing an antenna according to another embodiment of the present invention; and

[29] FIG. 10 is a block diagram showing the construction of a wireless communication apparatus according to another embodiment of the present invention. Best Mode for Carrying Out the Invention

[30] Description will now be made in detail of a preferred embodiment of the present invention with reference to the attached drawings. For the sake of convenience of explanation, respective constituent elements are represented by circuit symbols, but any known element can be used in their concrete implementation and the adopted concrete elements can be modified within the scope of the present invention. Also, it is assumed that respective constituent elements in the drawings are connected to an ideal conductor.

[31] FIG. 1 is a circuit diagram showing an antenna according to one embodiment of the present invention. The antenna of this embodiment includes a first radiation line Tl connected at one end thereof to a feed section and adapted to be operated as a radiator, and a second radiation line T4 grounded at one end thereof to an earth ground and adapted to be operated as a radiator. The first radiation line Tl and the second radiation line T4 are connected to each other by means of a resonant circuit section RC. The resonant circuit section RC includes a first inductor Ll, a first transmission line T2, a first capacitor CO, a second transmission line T3, and a second inductor L2, which are connected in series with one another.

[32] Herein, although an embodiment of only one resonant circuit section RC has been described for the convenience of explanation, two or more resonant circuit sections RC may be configured to be connected in parallel with one another and to be operated. However, it will be obvious to a person skilled in the art that the following description can be similarly applied to the case where two or more resonant circuit sections RC are included. Particularly, in case where two or more identical resonant circuit sections are included, respective circuits are operated in the same manner, and thus the following description will be identically applied to the case.

[33] The radiation lines Tl and T4 are operated as radiators, and hence can be represented as radiation resistances. The transmission lines T2 and T3 can be represented as concentrated constant equivalent circuits of a serial inductor and a parallel capacitor. In FIG. 2, there is shown a circuit in which the radiation lines Tl and T4, and the transmission lines T2 and T3 are converted into the equivalent circuits.

[34] Referring to FIG. 2, the radiation lines Tl and T4 are represented as radiation resistances R and R , respectively. The values of the radiation resistances R and R ,

Tl T4 Tl T4 are determined depending on the material and length of the radiation lines Tl and T4, preferably the radiation lines Tl and T4 have identical radiation resistances. In the meantime, the transmission lines T2 and T3 can be represented as a set of a parallel ca fpacitor and a serial inductor C _τ2 and L _τ2 and C _τ3 and L _τ3 ,' res rpectively j . At this time, the inductance of the inductors L and L and the capacitance of the capacitors C

T2 T3 T2 and C depend on the length of the transmission lines T2 and T3 and the distance from a ground plane to the transmission line, and thus the construction of the transmission lines T2 and T3 can be controlled to adjust the inductance and capacitance values.

[35] The synthetic impedance Zeq of the inductors L and L and the first capacitor CO which are connected in series with each other can be represented as a phasor in the following Equation 1 :

[36] MathFigure 1

[37] Therefore, the values of the first capacitor CO or the inductors L and L can be

T2 T3 adjusted to allow the synthetic impedance Zeq to be equal to 0 (Zeq = 0). Specifically, CO can be made equal to

J to obtain

CO = ω (/^+Z₇₃) to allow the synthetic impedance Zeq to be equal 0 (Zeq = 0). An equivalent circuit, which is obtained given that Zeq is zero, is shown in FIG. 3.

[38] Since the synthetic impedance Zeq is equal to 0, L , CO and L are offset. Thus, if the capacitors C and C connected in parallel with each other are combined into an equivalent capacitor

^ eq ^ Tl\ 1 ^- 73

, the equivalent circuit of FIG. 3 is obtained. This circuit becomes an LC resonant circuit composed of two inductors and one capacitor which are connected in parallel with one another ignoring the radiation resistances R and R , to give a resonant

Tl T2 frequency (w ) by the following Equation 2: [39] MathFigure 2

1

[40] From the review of the above Equation 2, it can be seen that the resonant frequency of the circuit is solely determined depending on a capacitance (Ceq) by the inductors Ll and L2 and the transmission lines T2 and T3, and is not related with the electrical length of the circuit. Thus, in the circuit of FIG. 3, the resonant circuit section RC constitutes a zero-order resonator (ZOR). In addition, electromagnetic radiation is made by a current flowing through the radiation resistances RTl and RT4 in the resonant frequency (w ).

[41] As such, the antenna of this embodiment includes the zero-order resonator (ZOR) so that the size of the antenna can be determined independently of the resonant frequency of the zero-order resonator (ZOR) and each element can be miniaturized to fabricate the antenna compactly. For the purpose of miniaturization of the antenna, each element can employ a surface-mounted device (SMD), and an integrated circuit may also be adapted to achieve a still smaller antenna.

[42] In the antenna of this embodiment, a value of each element can be controlled to freely adjust the resonant frequency. Particularly, a variable element can be employed to freely adjust the resonant frequency of the resonant circuit depending on applications even after the fabrication of the circuit.

[43] First, the values of the capacitors C and C can be controlled to adjust the resonant frequency given by the Equation 2. However, the capacitance values of the capacitors C and C are determined depending on the length and the area of the transmission lines T2 and T3, and the distance from the ground plane to the transmission lines, and hence adjustment of the capacitors C and C is relatively difficult as compared to other elements. Preferably, during installation of the antenna, the formation position and the size of the ground plan are controlled to adjust the resonant frequency.

[44] A capacitance value of a first capacitor CO may be controlled to adjust the resonant frequency of the resonant circuit. The explanation on conversion to the equivalent circuit of FIG. 3 is oversimplified for the sake of convenience. In fact, although the synthetic impedance Zeq given by the Equation 2 is not equal to 0, if its value is not so large, the zero-order resonant characteristic of the resonant circuit section (RC) is maintained. Nevertheless, the value of the synthetic impedance Zeq minutely affects the resonant frequency of the resonant circuit. Therefore, a variable capacitor can be used as the first capacitor CO to control its capacitance value so as to minutely the resonant frequency of the resonant circuit.

[45] In another embodiment of the present invention, for the purpose of adjustment of the resonant frequency, the variable capacitor may be connected between one end of the inductor and the ground plane. An example of this embodiment will be described hereinafter with reference to FIG. 4.

[46] FIG. 4 is a side view showing an antenna according to another embodiment of the present invention for adjustment of the capacitance. The antenna includes transmission lines 230 and 250 serving as radiators, and inductors 220 and 240 connected at one ends thereof to one ends of the transmission lines 230 and 250. The transmission line 230 is connected at other end thereof to a feed section 290, and the transmission line 250 is grounded at the other end thereof to an earth ground. In addition, the inductors 220 and 240 are connected to each other by a transmission line 210. In this case, the transmission line 210 has a capacitace induced between the transmission lie 210 and the ground plane. In other words, in this embodiment, CO of FIG. 1 is implemented by the transmission line 210, and thus the antenna of FIG. 4 has a similar electrical construction to that of the equivalent circuit shown in FIG. 3.

[47] Meanwhile, the transmission line 210 has a protrusion 270 extending downwardly to the ground plane in such a fashion as to be branched off from a given portion thereof. The protrusion 270 is connected at a distal end thereof to one end of a variable capacitor 260. The variable capacitor 260 is connected at the other end thereof to a ground portion 280 so as to be short-circuited to the ground plane. Although not shown in FIG. 4, it will be obvious to a person skilled in the art that a bias circuit for controlling the variable capacitor 260 can be formed additionally.

[48] The change in the capacitance by the variable capacitor 260 can substantially bring about a change in the capacitance value of the capacitor (C of FIG. 3) between the eq transmission line 210 and the ground plane to thereby adjust the resonant frequency of the resonant circuit section.

[49] In another embodiment of the present invention, the inductance values of the first and second inductors Ll and L2 can be controlled to adjust the resonant frequency of the resonant circuit section given in Equation 2. That is, a variable inductor can be used as the first inductor and/or the second inductor to control the inductance values of the first inductor Ll and/or second inductor L2. In this case, as the inductance value increases, the resonant frequency of the antenna decreases. Any known element can be used as the variable inductor, and the variable inductor may be implemented as a separate element or an integrated circuit.

[50] FIG. 5 is an equivalent circuit diagram showing an antenna according to another embodiment of the present invention for adjustment of the inductance. In FIG. 5, similar elements as those in the above embodiments are denoted by similar reference numerals and their detailed description will be omitted. In this embodiment, a first variable capacitor Cl and a second variable capacitor C2 for adjustment of the effective inductance of the first and the second inductors Ll and L2 are connected in parallel with the inductors Ll and L2.

[51] More specifically, the admittance G by the first variable capacitor Cl and the first inductor Ll is given by the following Equation 3:

[52] MathFigure 3

[53] Thus, the effective inductance is given by the following Equation 4:

[54] MathFigure 4

[55] That is, the capacitance value of the first variable capacitor Cl can be controlled to adjust the effective inductance so that the resonant frequency given by the above Equation 2 can be adjusted. As the capacitance value of the first variable capacitor Cl increases, the effective inductance increases and the resonant frequency of the resonant circuit section decreases. Likewise, the same is also applied to the second variable capacitor C2.

[56] The reflection coefficient (Sl 1) was measured by a simulation in order to confirm a variation of the resonant frequency of the resonant circuit section depending on a change in the capacitance values of the capacitors Cl and C2. In the simulation, Ll=L2=680 nH, CO = 0.5 pF, and the transmission lines T2 and T3 was 30 mm in length and 2 mm in width. In addition, the inductors Ll and L2 were connected in parallel with the variable capacitors. FIG. 6 is a graph showing a change of the reflection coefficient (Sl 1) according to a change of the capacitance of a variable capacitor. As shown in FIG. 6, as the capacitance of the variable capacitor increases from 0.2 pF to 0.8 pF, the resonant frequency decreases from about 0.21 GHz to about 0.16 GHz.

[57] In another embodiment of the present invention, the variable capacitors Cl and C2 may be connected in series with the inductors Ll and L2. In this case, the synthetic impedance of the first variable capacitor Cl and the first inductor Ll is given as

[58] MathFigure 5

1

L _^=Ll - ω C l

[59] Therefore, as the capacitance value of the first variable capacitor Cl increases, the effective inductance increases but the resonant frequency decreases. Likewise, the same is also applied to the second variable capacitor C2 connected to the second inductor L2. As such, it is also possible to adjust the resonant frequency through the series connection between the variable capacitors Cl and C2 and the inductors Ll and L2, respectively.

[60] The variable capacitors Cl and C2 can employs any variable capacitor which is known in the art. Preferably, a varactor diode or a variable diode can be used as the variable capacitors Cl and C2.

[61] The inductance and/or capacitance values/value of variable inductor and/or the variable capacitor can be changed depending on a control signal applied from the outside. For example, in case of using the varactor diode, a DC bias signal of the diode can act as the control signal. The control signal can be generated by the input of users or by generated automatically by a control circuit depending on the operation state of the device so as to be input to the variable inductor and/or the variable capacitor.

[62] In one embodiment in which the antenna of the present invention is applied to a receiver for a mobile broadcasting service such as DMB, DVB-H and so forth, a control circuit can generate a control signal depending on a channel selection signal of the users. Thus, even in case where a plurality of channels is not received simultaneously due to a narrow band width of an antenna, the broadcasting of various channels can be received. Likewise, the same scheme can also be applied to an FM/ AM radio broadcasting receiver or a wireless set.

[63] As described above, the adjustment of the resonant frequency of the antenna requires only a change of the resonant circuit section (RC) of the antenna without any change of the radiation lines Tl and T4. Therefore, the resonant frequency of the antenna does not have an effect on the radiation performance of the antenna. In other words, the antenna can maintain the same radiation characteristics with respect to various resonant frequencies.

[64] In the meantime, the antenna according to the present invention can be operated as a dual-band antenna. The antenna of this embodiment employs the resonant circuit section (RC) as a ZOR to thereby form a first resonant frequency. Moreover, the radiation lines Tl and T4 operating as radiators present a second resonant frequency.

[65] The second resonant frequency, which is generated by a first order resonance of the radiators, depends on the electrical lengths of the radiators. Thus, the second resonant frequency is advantageously set higher than the first resonant frequency for the purpose of miniaturization of the radiator. In case where the radiation lines Tl and T4 is formed in a helix shape, the electrical lengths of the radiaion lines Tl and T4 can be extended without increasing the size of the antenna to thereby reduce the second resonant frequency. But, even in this case, there is a limitation in extending the electrical lengths of the radiaion lines Tl and T4, and hence the low-frequency range is advantageously covered by the first resonant frequency for the sake of miniaturization of the antenna. Meanwhile, in case where the radiation lines Tl and T4 is formed in a helix shape, since the volume of the radiator is increased in the first resonant frequency band, an gain-increasing effect can be obtained even without any increase in the size of the antenna.

[66] On the other hand, since the first resonant frequency is determined only by the resonant circuit section (RC) and is not related with the electrical lengths of the radiation lines Tl and T4, it is possible to implement a subminiature antenna capable of resonating a desired frequency band irrespective of the size of the antenna.

[67] Also, the first resonant frequency and the second resonant frequency are formed by different mechanisms, and hence can be independently adjusted, respectively. The adjustment of the resonant frequency will be described hereinafter with reference to FIG. 7.

[68] FIG. 7(a) shows the adjustment of the second resonant frequency of the antenna in this embodiment. The adjustment of the second resonant frequency is performed by adjusting the electrical lengths of the radiation lines Tl and T4, which does not influence the operation of the resonant circuit section. Thus, as shown in FIG. 7 (a), a change of the second resonant frequency set to a frequency badn adjacent to 1.5 GHz does not have an effect on the first resonant frequency set to a frequency band adjacent to 250 MHz.

[69] Similarly, referring to FIG. 7(b), although the first resonant frequency adjacent to

250 MHz is changed, the second resonant frequency adjacent to 1.5 GHz is so slightly changed. Particularly, when taking into consideration the fact that there is a six times difference between the values of the second resonant frequency and the first resonant frequency, the resultant change of the second resonant frequency is negligible. In this case, the adjustment method of the first resonant frequency is the same as described above.

[70] The antenna of this embodiment can be used as a dual-band antenna as well as respective resonant frequencies thereof can be adjusted independently freely, and hence it can be applied to various fields. Furthermore, in the antenna according to this embodiment, since the resonant circuit section is a ZOR, a resonance does not occur at multiplied frequencies. Therefore, setting of the second resonant frequency is not affected by the multiples of the first resonant frequency, so that a combination of various resonant frequencies can be realized depending on applications.

[71] The antenna of the present invention can be implemented using the transmission lines, the capacitors and the inductors, and an example of the implemented antenna is shown in FIG. 8. Referring to FIG. 8, the antenna according to this embodiment is formed on an antenna substrate. The antenna can be readily fabricated using a printed circuit board (PCB) as the antenna substrate. Radiators 110 are disposed at both edges of the antenna substrate, and a ground plane 130 for the transmission line is partly formed on a rear surface of the antenna substrate. The ground plane 130 is formed on the rear surface of the antenna substrate and connected to a ground plane-extending line 120 that is connected to the ground plane, and hence can serves as an earth ground. A resonant circuit section 140 is formed at distal ends of the radiators 110.

[72] At both ends of the resonant circuit section 140 is disposed first and second inductors 170 and 180 respectively connected to the distal ends of the radiators (110), and a capacitor 190 is disposed at a central portion of the resonant circuit section 140. The resonant circuit section 140 includes a first transmission line 150 and a second transmission line 160 which are connected at one end to the capacitor 190 and are connected at the other end to the first and second inductors 170 and 180, respectively. The first and second inductors 170 and 180 may be inductor elements and the capacitor 190 may be a capacitor element.

[73] In the meantime, the radiator 110 is connected at one distal end thereof to a feed section and is connected at the other end thereof to the ground plane 130 so as to function as a loop antenna.

[74] In the above construction, it will be obvious to a person skilled in the art that so long as the connection relationship between respective constituent elements is maintained, the lengths and sizes of the radiators 110 and transmission lines 150 and 160 can be freely modified.

[75] In another embodiment of the present invention, the antenna may comprise at least two resonant circuit sections which have different resonant frequencies and are connected in parallel with each other. In this case, it is possible to allow the antenna to serve as a multi-band antenna by concurrently operating the at least two resonant circuit sections. In other words, since the at least two resonant circuit sections are operated independently to each other, the antenna resonates at each resonant frequency. Preferably, the at least two resonant circuit sections may be connected through an isolation circuit. But, since the interference between the resonant characteristics of ZORs is small due to their indigenous resonance mechanism, the isolation circuit is not an indispensable element.

[76] Alternatively, the at least two resonant circuit sections may be selectively operated.

In this case, the antenna may be operated so as to allow the resonant frequency to be changed depending on the resonant circuit section selected by a switch, etc. Particularly, since the range of the resonant frequency adjustable by one resonant circuit section is limited, it is possible to extend the range of the resonant frequency adjustable through the provision of the at least two resonant circuit sections.

[77] The antenna according to this embodiment is shown in FIG. 9. The antenna according to this embodiment comprises two antenna sections 300 and 400, each of which includes a resonant circuit section. The construction of each of the antenna sections 300 and 400 is the same as that of the antenna shown in FIG. 1.

[78] For example, the antenna section 300 includes inductors 312 and 318 and a capacitor 316 which are connected to each other through transmission lines 314a and 314b. Thus, a resonant circuit section 310 including the inductors 312 and 318, the capacitor 316 and the transmission lines 314a and 314b has a similar electrical construction to that of the resonant circuit section (RC) shown in FIG. 1. In addition, such a resonant circuit section 310 is connected to radiation lines 320 and 330 which are connected to a ground plane and a feed section, respectively. These radiation lines 320 and 330 function as radiators. Although not shown, the antenna section 400 also has the same construction as that of the antenna section 300 and includes inductors 414a and 414b and a capacitor 416.

[79] It is possible to adjust the length of each transmission line, the inductance of each inductor, and the capacitance of each capacitor so as to allow the antennas 300 and 400 to have different resonant frequencies to thereby implement a multi-band antenna. Further, as described above, since each resonant frequency of the antenna sections can be independently adjusted, the resonant frequency of each antenna section can be set freely in conformance with the requirements of applications.

[80] In FIG. 9, there has been shown each antenna including both the resonant circuit section and the radiation serving as a radiator, but it is possible to allow the antenna to include only a pair of radiation lines and a plurality of resonant circuit sections. Also, the number of antenna sections is not limited and more than three antenna sections can be implemented.

[81] A radio signal transmitting and receiving apparatus according to another embodiment of the present invention will be described hereinafter with reference to FIG. 10. The radio signal transmitting and receiving apparatus according to this embodiment includes an antenna 510 which is connected to an RF module 520 for processing a radio signal. The RF module 520 suitably filters and amplifies a signal received through the antenna 510 to produce an analog signal suitable for the process.

[82] The signal output from the RF module 520 is converted into a digital signal by an analog-to-digital (A/D) converter 530, and then is suitably processed by a digital signal process (DSP) 540. The processed signal is supplied to a main circuitry 550 for use in communication.

[83] More specifically, the main circuitry 550 outputs an audio signal among the received signals as voice through a speaker, and applies an image signal thereamong to a display device 570 so as to be displayed thereon as an image. In this manner, the apparatus can receive multimedia contents and provide them to users.

[84] Moreover, the main circuitry 550 is allowed to receive a signal form an input device

560 such as a camera, a microphone, a keypad and the like, and convert the signal suitably for its transmission through the antenna 510. To this end, an analog signal from the input device 560 is converted into a digital signal by the A/D converter 590, and in turn is converted into an analog signal for application to the antenna so as to be transmitted.

[85] Particularly, the radio signal transmitting and receiving apparatus of this embodiment can employ the antenna as above described so as to have a multi-band characteristic which is indispensable for transmission/reception of a multimedia signal, and is suitable for provision of various services to users. Besides, since the characteristic of the antenna is easily adjusted, it is possible to appropriately modify the antenna in conformance to the requirements of other signal processing circuits such as the RF module 620, etc. A small-scaled apparatus can, of course, be implemented owing to the miniaturized antenna 510.

[86] While the invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is merely exemplary and not limited to the disclosed embodiments. The constituent elements described in the above embodiments can be implemented in various manners without departing from the scope of the present invention. For example, the capacitor may be implemented in the form of a chip or an integrated circuit (IC). Besides, each constituent element may be implemented by using a distributed constant circuit. In addition, a control signal for controlling the variable elements can be associated with any external signal, if necessary, and a control circuit for generating the control signal can be designed by a known technique to conform to a specified variable element. The embodiments disclosed herein have been proposed to allow a person skilled in the art to easily implement the present invention, and the person skilled in the art may implement the present invention by a combination of these embodiments. Therefore, the scope of the present invention is not limited by or to the embodiments as described above, and should be construed to be defined only by the appended claims and their equivalents.

[87]

Claims

[1] An antenna comprising: a first radiation line connected at one end thereof to a feed circuit; a second radiation line grounded at one end thereof to an earth ground; and an at least one zero-order resonant circuit section connected at one end thereof to the first radiation line and connected at the other end thereof to the second radiation line.

[2] The antenna as defined in claim 1, wherein the zero-order resonant circuit section comprises: a first inductor connected to the first radiation line; a first transmission line connected in series to the first inductor; a first capacitor connected in series to the first transmission line; a second transmission line connected in series to the first capacitor; and a second inductor connected in series between the second transmission line and the second radiation line.

[3] The antenna as defined in claim 1, wherein the zero-order resonant circuit section comprises: a first inductor connected to the first radiation line; a transmission line connected in series to the first inductor; and a second inductor connected in series between the transmission line and the second radiation line.

[4] The antenna as defined in claim 2 or 3, wherein at least one of the first inductor and the second inductor is a variable inductor.

[5] The antenna as defined in claim 2, wherein the first capacitor is a variable capacitor.

[6] The antenna as defined in claim 2 or 3, wherein at least one of the first inductor and the second inductor is connected to a variable capacitor whereby an effective inductance is adjustable.

[7] The antenna as defined in claim 2 or 3, wherein the zero-order resonant circuit section further comprises a variable capacitor connected between one end of one of the first inductor and the second inductor and a ground plane.

[8] The antenna as defined in claim 1, wherein the first radiation line or the second radiation line is formed in a helix shape.

[9] The antenna as defined in claim 1, comprising two or more zero-order resonant circuit sections, the zero-order resonants circuit sections having different resonant frequencies.

[10] A wireless communication apparatus having an antenna for transmitting/ receiving a radio signal, wherein the antenna comprises: a first radiation line connected at one end thereof to a feed circuit; a second radiation line grounded at one end thereof to an earth ground; and an at least one zero-order resonant circuit section connected at one end thereof to the first radiation line and connected at the other end thereof to the second radiation line.

[11] The wireless communication apparatus as defined in claim 10, wherein the zero- order resonant circuit section comprises: a first inductor connected to the first radiation line; a first transmission line connected in series to the first inductor; a first capacitor connected in series to the first transmission line; a second transmission line connected in series to the first capacitor; and a second inductor connected in series between the second transmission line and the second radiation line.

[12] The wireless communication apparatus as defined in claim 10, wherein the zero- order resonant circuit section comprises: a first inductor connected to the first radiation line; a transmission line connected in series to the first inductor; and a second inductor connected in series between the transmission line and the second radiation line.

[13] The wireless communication apparatus as defined in claim 11 or 12, wherein at least one of the first inductor and the second inductor is a variable inductor.

[14] The wireless communication apparatus as defined in claim 11, wherein the first capacitor is a variable capacitor.

[15] The wireless communication apparatus as defined in claim 11 or 12, wherein at least one of the first inductor and the second inductor is connected to a variable capacitor whereby an effective inductance is adjustable.

[16] The wireless communication apparatus as defined in claim 11 or 12, wherein the zero-order resonant circuit section further comprises a variable capacitor connected between one end of one of the first inductor and the second inductor and a ground plane.

[17] The wireless communication apparatus as defined in claim 10, wherein the first radiation line or the second radiation line is formed in a helix shape.

[18] The wireless communication apparatus as defined in claim 10, wherein the antenna comprises two or more zero-order resonant circuit sections having different resonant frequencies.