GB2435720A

GB2435720A - Liquid antenna with an adjustable liquid level

Info

Publication number: GB2435720A
Application number: GB0625704A
Authority: GB
Inventors: Hyun Hak Kim; Jae Chan Lee
Original assignee: Samsung Electro Mechanics Co Ltd
Current assignee: Samsung Electro Mechanics Co Ltd
Priority date: 2006-03-03
Filing date: 2006-12-22
Publication date: 2007-09-05
Anticipated expiration: 2026-12-22
Also published as: GB2435720B; GB0625704D0; DE102006060563A1; FI20065850L; FI20065850A0; ITMO20060422A1; KR20070090487A; DE102006060563B4; KR100771819B1

Abstract

A liquid antenna comprises a casing 100 with an inner space 110, suitable for containing polar liquid 400. A radiator 200 is located in the inner space 110, a feed 300 for applying a signal to the radiator 200 and a polar liquid 400 partially filling the inner space 110 are provided. Means for adjusting the level of polar liquid 400 in the inner space 110 is provided to vary the contact length of the radiator 200 and the polar liquid 400. The means for adjusting the liquid level may be a heat transfer system 510 to heat and/or cool the said liquid 400. Alternatively, a liquid injection pump or piston liquid displacement means or a casing made of flexible material such that pressurised gas may be used to change the inner space within the casing 100, may be used to adjust the liquid level 400. The polar liquid 400 may be water or an electrolyte containing magnetic powder, alcohol, ethylene glycol-based liquid or mixtures thereof. The liquid-coupled antenna is intended to provide high gain, broadband and/or improved low frequency performance for a compact antenna structure which may be readily used in folding mobile hand-held devices which allows restoration of an original frequency band when the frequency band is changed by the surrounding environment.

Description

FREQUENCY TUNABLE LIQUID ANTENNA

CLAIM OF PRIORITY

[0001] This application claims the benefit of Korean Patent Application No. 2006-0D2025 filed on March 3, 2006, in the Korean Inte]Jectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002) The present invention relates to a liquid antenna and, more particularly, to a liquid antenna which adjusts the level of polar liquid to vary the length of contact between a radiator and the polar liquid, thereby raising or lowering an entire frequency band.

Description of the Related Art

[0003] In general, an antenna adopts a conductor oscillating in a particular frequency band as a radiator. For example, a chip antenna has a structure in which a predetermined pattern of conductor is formed on a body made of a dielecLric or magnetic material.

E0004] Such an antenna has a unique resonant frequency according to a structure (length) of the conductor and/or a permittivity of a dielectric material. Therefore, once a Page 1 particular material for the conductor and/or the dielectric body is decided, the resonant frequency is adjustable only by geometrically changing the structure of the conductor.

[0005] Currently, there has been a demand for a chip antenna mainly used in a mobile communication terminal, which is miniaturized as well as capable of achieving a low frequency band. Recently, with development of a special magnetic material, there have been attempts to fabricate a small-sized antenna of a low frequency band. Still, due to limitation in space, it is difficult for a typical chip antenna to secure a sufficient resonant length.

[0006] In general, a typical antenna covers only a particular narrow band, but it is known to be more effective to use an antenna that covers a wide band even if gain is less. Ideally, it may be most advantageous if the antenna can cover all bandwidths while maintaining high gain, which however is almost impossible to achieve with a conventional antenna adopting a conductor radiator.

[0007] As described above, a typical antenna such as the chip antenna adopts a particular structure of conductor radiator, which hinders adjusment of the frequency to achieve a wide band and/or a low band.

[0008] To overcome such a drawback, a novel concept of liquid antenna adopting polar liquid as a radiator has been developed recently. Suchaliquidantennaadoptsvarioustypesofliquid, Page 2

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adjusts the density and types of electrolyte, and regulates the content and types of conductor powder mixed in the liquid, thereby obtaining more broadly designed characteristics. This advantageously allows the antenna to achieve a low band, and further a wide band as well as to adjust its frequency.

ST.Th4ARY OF THE INVENTION [0009] The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a liquid antenna which can restore a frequency band to an initial level through a mechanical operation without requiring an additional impedance matching device or frequency conversion device when the frequency band is changed by surrounding environment.

[0010] According to an aspect of the invention, the invention provides a liquid anLenna. The liquid antenna includes: an antenna casing having ari inner space formed therein for containing polar liquid; a radiator provided inside the inner space; a feeder for applying a voltage to the radiator; polar liquid partially filled in the inner space; and means for adjusting the level of the polar liquid to vary a contact length of the radiator with the polar liquid.

[0011] The level-adjusting means can adopt a temperature controlling device which heats or cools the polar liquid filled in the inner space of the antenna casing to change the volume Page 3 of the polar liquid.

[0012] The temperature controlling device includes: a heat transmitting member connected to the antenna casing, the heat transmitting member for heating or cooling the polar liquid in the inner space; and a temperature regulator for regulating the temperature of the heat transmitting member.

[0013] The temperature controlling device includes: a temperature-changing chamber connected the inner space, the temperature-changing chamber having the polar liquid stored therein; a heat transmitting member coupled to the temperature-changing chamber to heat or cool the polar liquid; and a temperature regulator for regulating the temperature of the heat-transmitting member.

[0014] The level-adjusting means includes a supply unit having a pump for additionally injecting the polar liquid into the inner space or drawing out the polar liquid from the inner space.

[0015] The level-adjusting means includes a moving device having a piston adapted to move in a longitudinal direction of the inner space with a circumferential surface thereof attached to an inner wall of the inner space to thereby push the polar liquid to one side.

[0016] The feeder has one end inserted into the inner space along a longitudinal direction of the inner space, the radiator is connected to one end of the feeder, and the piston has the feeder penetrated therethrough to move in a longitudinal Page 4

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direction of the feeder.

[0017] The liquid antenna according to the present invention is coupled to a folder-type mobile communication terminal including an upper folder and a lower folder or a slide-type mobile communication terminal including a sliding part and a body. nd the moving device further includes a connecting rod having one end coupled to the piston and the other end coupled to the mobile communication terminal, thereby moving the piston according to opening or closing of the upper folder or the sliding part.

(0018] The antenna casing is made of a flexible material in order for the inner space to be changed in a volume thereof due to the pressure generated by gas therein according to the level change of the polar liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

(0019] The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: (0020] FIG. 1 is a schematic perspective view illustrating a liquid antenna related to the present invention; (0021] FIG. 2 is a schematic perspective view illustrating another liquid antenna related to the present invention; [0022] FIG. 3 is a schematic perspective view illustrating Page 5

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further another liquid antenna related to the present invention; [0023] FIG. 4 is a sectional view illustrating a liquid antenna according to a first embodiment of the present invention; [0024] FIG. 5 is a sectional view illustrating a liquid antenna according to a second embodiment of the present invention; [0025] FIG. 6 is a sectional view illustrating a liquid antenna according to a third embodiment of the present invention; [0026] FIG. 7 is a graph showing the frequency change according to the amount of polar liquid; [0027] FIG. 8 is a sectional view illustrating a liquid antenna according to a fourth embodiment of the present invention; and [0028] FIGS. 9 and 10 are sectional views illustrating the liquid antenna according to the exemplary embodiment of the present invention applied to a folder-type mobile communication terminal.

DETAILED DESCRIPTION OF THE PREFERRED EODIbNT

[0029] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

(0030] FIG. 1 is a schematic perspective view illustrating a liquid antenna related to the present invention.

[0031] Referring to FIG. 1, the antenna 10 includes polar liquid 15, a container 11 for containing the polar liquid 15, Page 6

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and a feeder 17 penetrated through one end of the container 11 so as to be connected to the liquid 15.

[0032] The polar liquid 15 is adopted in the liquid antenna as a novel type of radiator. The polar liquid 15 has a constant conductivity ratio as well as high permittivity due to ion bonding or molecule bonding, thereby having various current distribution. Therefore, the polar liquid 15 can act as a radiator with a particular resonant frequency in response to the current supplied through the feeder 17. For example, it is known that water has a permittivity of about 80 and a conductivity ratio of about 3 S/rn. Having different electromagnetic characteristics from the typical dielectric body and metal conductor as just described, it has been confirmed, in terms of frequency characteristics, that the polar liquid contributes to achieving a wide band or a low band to a degree unexpected from a typical antenna.

[0033] Inferences have been made as follows as to how the polar liquid contributes to frequency adjustment.

[0034] First, when the polar liquid is exposed to an electric wave of a particular frequency, it changes its polarity and oscillates. This is similar to the observation in which ultra-short wave is applied to food in the microwave oven and liquid (mostly water) in the food oscillates, which in turn heats the food. Such oscillation of the polar liquid may interfere with the electric wave passing therethrough.

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[0035] Secondly, when the polar liquid itself is exposed to an electric wave, it forms a closing path for the current, interfering with the electric wave.

[0036] Thirdly, liquid such as water lengthens the wavelength of an electric wave in general to cause loss of the electric wave. It is possible that such change in the wavelength of the electric wave ultimately causes frequency change.

[0037] Such polar liquid 15 may include various types such as ethylene glycol-based liquid, electrolyte or synthetic liquid, besides water. In particular, the polar liquid 15 may have other electrolytes dissolved therein to change its conductivity ratio with the assistance of dissociated ions, thereby attaining a low band or a wide band to a degree not achievable by the conventional antenna. Besides using electrolyte, conductor powder attractable by magnetic force, for example, metal powder such as Fe can be mixed into the liquid to obtain similar effects.

[0038] The liquid antenna can have broadly designed antenna characteristics by varying types of liquid, densities and types of electrolytes and contents and types of conductor powders.

This is disclosed in Korea Patent Application No. 10-2005-0062352 (entitled "Antenna Using Liquid Radiator") filed by the inventor of the present invention, and is incorporated in the present invention by reference.

[0039] FIG. 2 is a schematic perspective view illustrating Page 8

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another liquid antenna related to the present invention.

(0040] s shown in FIG. 2, a rnonopole antenna 20 has an L-shaped radiator 25. The radiator 25 has one end provided as a feeder 25a connected to an external circuit. The radiator 25 is disposed inside the container 27 which is for containing the liquid. The container 27 is filled with polar liquid 29.

[0041] In addition, the polar liquid 29 adoptable in the present invention may include but is not limited to at least one selected from the group consisting of water, alcohol, ethylene glycol-based liquid and mixtures thereof. The polar liquid 29 has a constant conductivity ratio as well as a high permittivity due to ion bonding or molecule bonding. Thus, the polar liquid 29 can have various current distribution affecting the characteristics of the antenna 20, thereby changing the unique resonant frequency of the radiator 25. In general, polar liquid has a higher permittivity and a low conductivity ratio compared to typical dielectric material or conductive material such as metal, and thus tends to affect the resonant frequency to achieve a wide band unlike dielectric material or metal.

[0042] To adjust the resonant frequency, the radiator 25, which is a conductor, is lengthened or geometrically altered to change the resonant frequency in the conventional monopole antenna.

However, using the polar 1iqud 29 tself allows achieving a wide band as well as adjusting the resonant frequency.

{0043] In this configuration shown in FIG. 2, most part of the Page 9

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radiator 25 is inserted in the container 27 to impart electromagnetic effects of the polar liquid 29 to an entire radiation region. However, since it will be satisfactory enough to allow the polar liquid 29 contained in the container 27 to have electromagnetic effects on at least a part of the radiator 25, it will also be possible to dispose only a part of the radiator in the container or provide the container adjacent to the radiator.

[0044) In this case, electrolyte or conductor powder can be mixedintothepolarliquid29usedas a frequency changingmeans to obtain additional improvement in electromagnetic characteristics of the polar liquid. In general, in the case of adding the conductor powder or electrolyte, the conductivity ratio increases, thus resulting in a greater degree of adjustment of the frequency. Therefore, the density (content) and type of the electrolyte and/or conductor powder mixed in the polar liquid 29 can be varied to yield various frequency changing effects. Various types of electrolyte such as NaC1, etc. can be used. For the conductor powder, metal attractable by magnetic force such as Fe and Ni. can be used.

E0045] Using the polar liquid to adjust the resonant frequency of the antenna as described above, a wide band as well as a low band or a high band can be selectively achieved according to the structure of the antenna.

[0046] FIG. 3 illustrates a helical antenna 30 having a spiral Page 10

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radiator 35. The radiator 35 has one end provided as a feeder 35a connected to an external circuit.

(0047] The radiator 35 of the helical antenna 30 is disposed inside a container 37 similar to the antenna shown in FIG. 2.

The container 37 is filled with polar liquid 39. The polar liquid may include but is not limited to at least one selected from the group consisting of water, alcohol, ethylene glycol-based liquid and rnitures thereof. The polar liquid 39 is provided as a novel current distribution source to adjust the unique resonant frequency of the radiator 35.

[0048] As described above, the helical antenna 30 can adjust its resonant frequency by changing the interval of the loop of the spiral radiator. Due to such structural characteristics, the polar liquid 39 renders electromagnetic effects between the loop, achieving a wide band as well as a high band of the resonant frequency.

[0049] The above described liquid antennas 10, 20 and 30 are mounted to various electric wave tranceivers such as mobile communication terminals, which transmit and receive electric waves. However, in the case where the user comes in contact with the electric wave transceiver, the overall frequency band of the antenna may rise or fall, and the frequency band of the liquid antenna may deviate from the transmission frequency band or the reception frequencyband. In particular, when the liquid antennas 10, 20 and 30 are applied to a folder-type mobile Page 11 communication terminal, the overall frequency band of the antenna rises or falls not only when the user comes in contact with the terminal but also when the folder is opened. When the overall frequency band of the antenna rises or falls, impedance matching does not occur normally, decreasing the transmission energy and deteriorating the capacity of the antenna.

[0050] In addition, when the frequency band of the liquid antenna deviates from the transmission frequency band or the reception frequency band, the liquid antenna requires additional devices for impedance matching since it cannot adjust the frequency band by a mechanical method. Inclusion of the additional devices for impedance matching, however, complicates the configuration of the circuits and increases the volume of the electric wave transceiver.

[0051] To overcome the above described problem, the frequency band of the liquid antenna may be designed wider. However, too wide a frequency band results in radiation of not only the effective transmission/reception electric waves including the transmission and reception frequencies but also spurious waves coexisting in the frequency band. This can result in a serious problem where the overall communication quality is deteriorated due to interference by the spurious waves.

[0052] Now, exemplary embodiments of the present invention will be explained in greater detail with the accompanying Page 12 drawings [0053) FIG. 4 is a sectional view illustrating a liquid antenna according to a first embodiment of the present invention.

[0054] The most signilicant feature of the liquid antenna according to the prcsent invention is capability of adjusting a resonant frequency of a radiator 200 by changing a length of contact between the radiator 200 andpoiar liquid 400. As shown in FIG. 4, the liquid antenna includes an antenna casing 100; a radiator 200 provided inside the inner space 110; a feeder 300 for applying a voltage to the radiator 200; polar liquid 00 filled partially in the inner soace 110 so as to be in contact with the radiator 200, to thereby change the resonant frequency of the radiator 200; and a level-adjusting means for adjusting the level of the polar liquid to change the length of contact between the radiator 200 and the polar liquid 400.

[0055] The antenna casing 100 has an elongated form in one direction, and the inner space 110 also has an elongated form along a longitudinal direction of the antenna.

[0056] In addition, the radiator 200 is formed in a shape insertable into the inner space 11C, and is provided apart in a predetermined interval from an inner wall of the inner space 110. The interval between the radiator 200 and the inner wall of the inner space 110 is set narrow in such a way that the polar liquid 400 filled between the inner wall of the inner space 110 and the radiator 200 does not drip or spill by tension even if Page 13 the antenna is inclined or turned over. Therefore, the liquid antenna according to the present invention can maintain a regulated ength of contact between the radiator 200 and the polar liquid 40.0 irrespective of slope or directionality of the antenna. At this time, the interval between the radiator 200 and the inner wall of the inner space 110 can be modified variously according to various conditions such as viscosity of the polar liquid 400 and material of the radiator 200, the antenna casing 100, etc. (0057] The polar liquid 400 has a certain conductivity ratio and a high perrnittivity due to ion bonding or molecule bonding, and can include but is not limited to at least one selected from the group consisting of water, alcohol and ethylene glycol-based liquid. The polar liquid 400 can have diverse current distribution affecting the characteristics of the liquid antenna, thereby altering the resonant frequency of the radiator 200. At this time, the resonant frequency of the radiator 200 is changed according to the length of contact between the radiator 200 and the polar liquid 400. With a longer length of contact between the radiator 200 and the polar liquid 400, that is, with a higher level of the polar liquid 400, the resonant frequency of the radiator 200 becomes low. Conversely, with a shorter length of contact between the radiator 200 and the polar liquid 400, that is, with a lower level of the polar liquid 400, the resonant frequency of the radiator 200 becomes Page 14 high.

[0058] The level-adjusting means can adopt various configurations that allow adjusting the level of the polar liquid 400. This embodiment is exemplified by the level-adjusting means applied to a temperature controlling device 510. The temperature controlling device 510 includes a heat transmitting member 512 coupled to the antenna casing to heat or cool the polar liquid 400 in the inner space 110 and a temperature regulator 514 for regulating the temperature of the heat transmitting member 512. Thereby, the temperature controlling device 510 is configured to heat or cool the polar liquid 400 filled in the inner pace 110 of the antenna casing to change the volume of the polar liquid 400, thereby adjusting the level of the polar liquid 400.

[0059] That is, when the heat transmitting member 512 is heated by the temperature regulator 514, the heat generated from the heat transmitting member 512 is transmitted to the polar liquid 400 in the inner space 110, and the polar liquid 400 is expanded in its volume and increased in its level. If the level of the polar liquid 400 is increased, the length of contact between the radiator 200 and the polar liquid 400 is increased, and thus similar to when the length of a conventional antenna of solid material is increased, the frequency band of the radiator 200 is decreased overall.

[0060] On the contrary, when the heat transmitting member 512 Page 15 is cooled by the temperature regulator 514, the coolness generated from the heat transmitting member 512 is transmitted to the polar liquid 400, which is then constricted in its volume due to the temperature decrease and is lowered in its level.

VThen the level of the polar liquid 400 is decreased, the length of contact between the radiator 200 and the polar liquid 400 is decreased, and thus the frequency band of the radiator 200 is raised overall.

[0061] At this time, the option of whether to lower or raise the frequency of the radiator 200 is determined by the characteristics of the electric wave transceiver to which the liquid antenna is mounted. For example, when the user holds the electric wave transceiver with the liquid antenna mounted thereto with his/her hand and the frequency band of the radiator 200 is increased, the temperature regulator 514 heats the heat transmitting member 512 to lower the frequency band to thereby maintain the initial normal frequency band. At this time, it is preferable that the degree of increase in the frequency band of the radiator 200 by increasing the level of the polar liquid 400 is set to equal the degree of the decrease in the frequency band of the radiator 200 when the user holds the electric wave transceiver with his/her hand.

[0062] FIG. 5 is a sectional view illustrating a liquid antenna according to a second embodiment of the present invention.

Page 16 (0063] In the embodiment shown in FIG. 4, due to the very narrow inner space 110, a small amount of the polar liquid 400 is filled in the inner space 110. when the amount of the polar liquid 400 is small, even if the polar liquid.400 is heated, the total volume change of the polar liquid 400 is not so great, which is limited in increasing the level of the polar liquid 400.

[0064] Therefore, to increase the amount of level change of the polar liquid 400 by increasing the amount of the polar liquid 400 heated, as shown in FIG. 5, the temperature controlling device 510 is provided to include a temperature-changing chamber 516 having the polar liquid 400 stored therein and connected to the inner space 110, a heat transmitting member 512 coupled to the temperature-changing chamber 516 to heat or cool the polar liquid 400 in the temperature-changing chamber 516 and a temperature regulator 514 for regulating the temperature of the heat transmitting member 512.

[0065] The temperature controlling device 510 shown in FIG. is configured to heat a greater amount of the polar liquid 400 stored in the temperature-changing chamber 516, not just a portion of the polar liquid 400 filled in the inner space 110.

This facilitates increasing the amount of change in the total volume of the polar liquid 400, thereby resulting in a greater level change of the polar liquid 400.

[0066] At this time, when the volume of the polar liquid 400 is expanded, the portion where the polar liquid 400 is not filled, Page 17 that is, the portion filled with gas such as air, etc. is decreased, and thus the gas is compressed. However, when the gas is compressed to have a pressure greater than a certain level, the polar liquid 400 cannot expand due to the pressure of the gas.

[0067] Therefore, it is preferable that the antenna casing 100 is made of a flexible material to allow the volume of the inner space 110 to be changed according to the pressure generated in the gas in the inner space 110 with the level change of the polar liquid 400, i.e., with expansion of the polar liquid 400. with the antenna casing 100 made of a flexible material, when the gas is compressed due to the expansion of the polar liquid 400, the antenna casing 100 is expanded to have increased inner space 110. On the other hand, when vacuum pressure is generated due to the constriction of the polar liquid 400, the antenna casing is constricted to have decreased inner space 110 by the vacuum pressure of the gas. Therefore, the polar liquid 400 is expanded and constricted more freely.

[0068] FIG. 6 is a sectional view illustrating a liquid antenna according to a third embodiment of the present invention.

[0069] The level-adjusting means for adjusting the level of the polar liquid 400 is not intended to be limited to the temperature controlling device 510 shown in FIGS. 4 and 5. As shown in FIG. 6, the level-adjusting means can also be Page 18 configured into a supply unit 520 including a pump 522 for retrieving the polar liquid 400 from the storage chamber 524 to inject into the inner space 110 or drawing out the polar liquid 400 nontained in the inner space 110 to feed to the storage chamber 524.

[0070] Using a pump 522 toinject or draw out the polar liquid 400 as described above, even if the polar liquid 400 has characteristics of small volume change according to the temperature change, the level change of the polar liquid 400 can be easily induced.

[0071] FIG. 7 is a graph illustrating the changes in the frequencies according to the injection amount of the polar liquid 400.

[0072] The liquid antenna according to the present invention exhibits frequency characteristics denoted by a curve a' when 0.2cc of the polar liquid 400 made of water and ethylene glycol-based solution is filled in the inner space 110. When the amount of the polar liquid 400 is increased to 0.6cc, 1.2cc and 2.6cc, the liquid antenna exhibits frequency characteristics denoted by b', c' and d', respectively.

That is, as the amount of the polar liquid 400 is increased from 0.2cc to 0.6cc, 1.2ccand2.6cc, the resonant point of the liquid antenna is gradually lowered to 2.6GHz, 2.1GHz, 1.7GHz and 1.5GHz, respectively.

Page 19 [0073] Therefore, it can be seen that the overall frequency band is decreased as the length of con:act between the radiator and the polar liquid 400 is increased.

E0074] FIG. 8 is a sectional view illustrating a liquid antenna according to a fourth embodiment of the present invention.

[0075] As shown in FIG. 8, the level adjusting means may also adopt a moving device 530 including a piston which is adapted to move in a longitudinal direction of the inner space 110 with its circumferential surface attached to an inner wall of the inner space 110 to thereby push the polar liquid 400 to one side.

(0076] The piston 532 is configured to seal the space between the inner wall of the inner space 110 and the radiator 200 such that the polar liquid 400 filled above does not leak to the bottom. The piston 532 has a connecting rod 534 coupled thereto so that it is

moved along the inner space 110 by external force. Here, the connecting rod 534 may be configured in the form of a pipe surrounding the feeder 300 or in the form of at least two pins arranged to evenly transmit driving power to a lower end of the piston 532.

[0077] When the piston 532 is moved upward along the inner space 110, the polar liquid 400 contained in the inner space 110 is pushed upward by the piston 532 and increased in its level.

Conversely, when the piston 532 is moved downward along the inner space 110, the polar liquid 400 contained in the inner Page 20 space 110 comes down together with the piston 532 and is decreased in its level.

[0078] At this time, even if the piston 532 is moved upward and thereby the polar liquid 400 is pushed upward, the volume of the polar liquid 400 is not changed. Thus, when only the radiator 200 is.provided to occupy an entire portion of the inner space 110, the length of contact between the polar liquid 400 and the radiator 200 is not changed. TI-ierefore, as shown in FIG. 7, it is preferable that the feeder 300 is also inserted intotheinnerspace 110 inalongitudinal direction of the inner space 110 with the radiator 200 connected to the one end of the feeder 300. It is also preferable that the piston 532 has the feeder 300 penetrated therethrough to move along the longitudinal direction of the feeder 300.

[0079] That is, in the state of the embodiment depicted in FIG. 8, when the piston 532 is moved upward, the length of contact between the polar liquid 400 and the feeder 300 is gradually decreased, and as much as the decrease in the length of contact between the feeder 300 and the polar liquid 400, the length of contact between the radiator 200 and the polar liquid 400 is increased, thereby lowering the frequency. On the contrary, in the state of the embodiment depicted in FIG. 8, when the piston 532 is moved downward, the length of contact between the feeder 300 and the polar liquid 400 is decreased while the length of contact between the radiator 200 and the polar liquid 400 is Page 21 increased, thereby raising the frequency.

[0080) PIGS. 9 and 10 are sectional views illustrating the liquid antenna according to the fourth embodiment of the present invention applied to a folder-type mobile communication terminal - [0081] In the case where the liquid antenna according to the present invention is applied to a folder-type mobile communication terminal composed of an upper folder 1 and a lower folder 2, not only when the user touches the mobile communication terminal with his/her hands but also when the user opens or closes the upper folder 1, the frequency of the liquid antenna is changed. Thus, it is preferable that the liquid antenna according to the present invention is configured such that the frequency is changed according to the operation of the upper folder 1.

[0082] The liquid antenna is typically coupled to an upper folder. Here, the connecting rod 534 has one end coupled to the piston 532 and the other end coupled to the lower folder 2 so that it moves the piston 532 as the upper folder 1 is opened.

[0083] That is, as shown in FTG. 9, when the upper folder 1 is folded, the connecting rod 534 is flexed at a hinge 3. Then as shown in FIG. 10, when the upper folder 1 is opened, it is stretched linearly and pushes the piston upward to change the frequency. To enable such an operation, it is preferable that Page 22 the connecting rod is made of a material having excellent flexibility such as a spring.

[0084] This embodiment is exemplified by the moving device 530 having a construction in which the piston 532 is mechanically moved by the connecting rod 53 according to the angle of the upper folder 1. However, the structure of moving the piston 532 according to opening and closing of the upper folder 1 is not intended to be limited to the aforementioned structure in this embodiment. Alternatively, the moving device 530 can be configured to sense the opening and closing of the upper folder 1 and move the piston 532 using an additional driving means.

[0085] In addition, the liquid antenna can be applied to a slide-type mobile communication terminal composed of a sliding part and a body.

[0086] The liquid antenna according to the present invention can adjust the level of polar liquid without an additional impedance matching device or frequency converting device when a frequency band is altered by surrounding environment, thereby restoring the frequency band to its original level. Further, when applied to a folder-type or slide-type mobile communication terminal, the liquid antenna can change the frequency band according to the opening and closing of the upper folder or the sliding part.

[0087] While the present invention has been shown and described Page 23

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in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

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Claims

What Is Claimed Is: 1. A liquid antenna comprising: an antenna casing

having an inner space formed therein for containing polar liquid; a radiator provided inside the inner space; a feeder for applying a voltage to the radiator; polar liquid partially filled in the inner space; and means for adjusting the level of the polar liquid to vary a contact length of the radiator with the polar liquid.

2. The liquid antenna according to claim 1, wherein the level adjusting means comprises a temperature controlling device which heats or cools the polar liquid filled in the inner space of the antenna casing to change the volume of the polar liquid.

3. The liquid antenna according to claim 2, wherein the temperature controlling device comprises: a heat transmitting member connected to the antenna casing, the heat transmitting member for heating or cooling the polar liquid in the inner space; and a temperature regulator for regulating the temperature of the heat transmitting member.

4. The liquid antenna according to claim 2, wherein the Page 25 temperature controlling device comprises: a temperature-changing chamber connected the inner space, the temperature-changing chamber having the polar liquid stored therein; a heat transmitting member coupled to the temperature-changing chamber to heat or cool the polar liquid; and a temperature reguietor for regulating the temperature of the heat-transmittin member.

5. The liquid antenna according to claim 1, wherein the evel-adjusting means comprises a supply unit including a pump for additionally injecting the polar liquid into the inner space or drawing out the polar liquid from the inner space.

6. The liquid antenna according to claim 1, wherein the level-adjusting means comprises a moving device including a piston adapted to move in a longitudinal direction of the inner space with a circumferential surface thereof attached to an inner wall of the inner space to thereby push the polar liquid to one side.

7. The liquid antenna according to claim 6, wherein the feeder has one end inserted into the inner space along a longitudinal direction of the inner space, the radiator is Page 26

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connected to one end of the feeder, and the piston has the feeder penetrated therethrough to move in a longitudinal direction of the feeder.

8. The liquid antenna according to claim 6, the antenna coupled to a folder-type mobile communication terminal including an upper folder and a lower folder or a slide-type mobile communication terminal including a sliding part and a body, wherein the moving device further comprises a connecting rod having one end coupled to the piston and the other end coupled to the mobile communication terminal, thereby moving the piston according to opening or closing of the upper folder or the sliding part.

9. The liquid antenna according to claim 1, wherein the antenna casing is made of a flexible material in order for the inner space to be changed in a volume thereof due to the pressure generated by gas therein according to the level change of the polar liquid.

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