WO2008051044A1

WO2008051044A1 - Multi resonant antenna

Info

Publication number: WO2008051044A1
Application number: PCT/KR2007/005302
Authority: WO
Inventors: Je-Hoon Yun
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2006-10-26
Filing date: 2007-10-26
Publication date: 2008-05-02
Also published as: KR20080038031A; KR100989064B1; EP2087551A1; EP2087551A4

Abstract

Provided is a small multi-resonant antenna, which includes an antenna element; a plurality of feeders for supplying power to the antenna element; a parasitic device disposed in a dielectric region between a board where an antenna circuit is positioned and the antenna element; a feed switch for selectively connecting any one among the feeders to the antenna element to supply power to the antenna element; and a parasitic device switch for controlling the parasitic device. Herein the feeders are disposed in such a manner that a total length of the antenna element is different individually. The present invention provides an antenna that can widely vary resonant frequency and delicately control frequency within a randomly selected resonant frequency, and a manufacturing method thereof.

Description

DESCRIPTION

MULTI RESONANT ANTENNA

TECHNICAL FIELD The present invention relates to a small multi- resonant antenna; and, more particularly, to a small multi-resonant antenna having a wideband characteristic and capable of widely varying resonant frequencies and delicately adjusting frequency within a randomly selected resonant frequency.

This work was supported by IT R&D program of MIC/IITA. ["Development of Antenna Measurement System Technology. "]

BACKGROUND ART

In general, antennas have narrowband characteristics and when they are miniaturized, their antenna radiation patterns have omni-directional characteristics and their antenna gains decrease. Also, input resistance of an antenna becomes very small and reactance becomes very high. Thus, the bandwidth of the antenna becomes narrow.

Following Digital Television (DTV) services, audio, video and broadcasting services using ultrahigh frequency (UHF) bands such as Terrestrial Digital Multimedia Broadcasting (T-DMB) , Digital Video Broadcasting-Handheld (DVB-H), Satellite Digital Multimedia Broadcasting (S- DMB) , and Digital Audio Broadcasting (DAB) have been launched recently. The frequency bands used in the services belong to low frequency bands, whose wavelength is longer than the length of a mobile phone. A conventional 1/4 wavelength monopole antenna (for example, the wavelength of T-DMB is about 40cm) is longer than a mobile phone. Thus, it is inconvenient to use the antenna and the antenna can be hardly embedded inside a mobile phone.

In an effort to resolve the problems, researchers are accelerating development of small antennas.

Since small antennas occupy physically small space, the bandwidth of small antennas is limited so as to maintain excellent antenna efficiency. Herein, antenna efficiency is a ratio between power radiated from an antenna and power supplied to the antenna.

The audio, video and broadcasting services have a problem that radio frequency (RF) signals have too wide frequency band to be covered with one small antenna. In other words, since small antennas have limited maximal bandwidth, a single small antenna cannot afford receiving RF signals of entire bandwidths. For example, the maximal bandwidth that a 1/25 wavelength small antenna can acquire while maintaining fine antenna efficiency lies within about 3% around center frequency. On the other hand, the bandwidth of T- DMB (which ranges from 174MHz to 216MHz) occupies about 22% around the center frequency. Therefore, one antenna cannot accommodate the frequency bandwidth.

In addition to T-DMB, DVB-H, S-DMB, and DAB, recent mobile phones provide diverse wireless communication services such as Code Division Multiple Access (CDMA) , Global System for Mobile Telecommunication (GSM), Personal Communication Services (PCS), voice communication, an active/passive Radio Frequency Identification (RFID) reader function, a reception function of an FM radio broadcasting service, Bluetooth service and so forth. To support such technologies, an antenna capable of transmitting/receiving signals in multiple bands is required.

Fig. 1 shows T-DMB frequency bandwidth and channel bandwidth that are used currently. Referring to Fig. 1, the T-DMB frequency bandwidth includes a plurality of channel bandwidths . Although the T-DMB frequency bandwidth is 42 MHz, one channel bandwidth is very narrow, i.e., 1.536MHz. When one channel is received, the channel bandwidth of another channel is not used. Therefore, it is possible for one small antenna to receive signals of wideband by switching channels .

In other words, it is possible for one small antenna to receive signals of multiple channels by independently generating multiple resonant frequencies. This makes it possible for a single small antenna to receive signals of wideband. If any, the bandwidth of the small antenna should be wider than the channel bandwidth shown in Fig. 1. According to a prior art, the resonant frequency of an antenna is controlled by installing a parasitic device or an RF module and varying inductance or capacitance to make a reactance value of the antenna to be 0. Fig. 2 is a view showing a typical small antenna employing a parasitic device.

Referring to Fig. 2, the small antenna employing a parasitic device controls resonant frequency by using a varactor diode and varying capacitance to change inductance or capacitance.

The small antenna employing a parasitic device includes a conductor 201, a circuit output unit 203, a parasitic device 205, a parasitic device switch 207, and a Printed Circuit Board (PCB) edge plane (not shown) . Herein, the PCB edge plane (not shown) includes a circuit generally realized in antennas and a ground line.

The conductor 201 is an antenna element. It transmits or receives signals to or from the outside.

The circuit output unit 203 supplies power from the PCB edge plane (not shown) to the conductor 201. As for the parasitic device 205, a varactor diode or a varying capacitance may be used.

The parasitic device switch 207 connects the parasitic device 205 to a ground plane included in the PCB edge plane (not shown) based on a control signal under the control of the PCB edge plane (not shown) . In other words, the parasitic device 205 is connected to or disconnected from the antenna circuit upon on/off of the parasitic device switch 207. The varactor diode or the varying capacitance sensitively reacts with a surrounding environment (such as static electricity caused by hand or hair), and devices such as varactor diodes which require bias voltage supplied regularly for each product can hardly maintain a predetermined capacitance value. Therefore, it is hard to generate resonant frequency of a predetermined level. Also, when the parasitic device is connected to or disconnected from the ground plane, the reactance value varies so much that the resonant frequencies cannot be delicately adjusted to include all channels for T-DMB, S-DMB, DVB-H and D-TV. Furthermore, since the reactance value of the parasitic device is synthetically determined based on the aperture, shape and position of the parasitic device, capacitance, and inductance, it is difficult to predict the variance of the resonant frequency.

Fig. 3 is a graph showing an SIl parameter according to on/off of the parasitic device switch in the small antenna of Fig. 2. The antenna is a disconnected line. The ends of the antenna resonate in predetermined frequency. Thus, signals are not totally reflected and they are delivered to the outside as a specific electromagnetic energy. In short, an antenna is basically a one-port device whose input port is one. Thus, the antenna has only an SlI value which signifies an input reflection coefficient, and the antenna has the minimal SlI value (dB) in operation frequency. In the frequency where the SlI value is the minimum, signal power inputted to the antenna is radiated maximally. In other words, impedance is best matched at a point where the SIl value is the minimum.

Therefore, the smaller the SIl value is, the higher the radiation efficiency of the antenna grows high. Also, the smaller the quality factor of the SIl value is, the wider the frequency bandwidth used in the antenna becomes .

As shown in Fig. 3, A graph shows a case when the parasitic device switch is turned off, and B graph shows a case when the parasitic device switch is turned on. Both A and B graphs include a first resonant frequency area 301a or 301b and a second resonant frequency area 303a or 303b. Herein, the vertical axis indicates a SlI value (dB) , whereas the horizontal axis indicates frequency (MHz) .

In the first and second resonant frequency areas, the B graph (which is a case when the parasitic device switch is turned on) has smaller SIl value, compared to the A graph (which is a case when the parasitic device switch is turned off) . In short, the SIl value of the first resonant frequency area 301a is greater than the SIl value of the first resonant frequency area 301b. Also, the SIl value of the second resonant frequency area 303a is greater than the SIl value of the second resonant frequency area 303b. Therefore, when the parasitic device switch is turned on, impedance is matched well and the antenna radiation efficiency is high.

Although there is a minute difference in the first resonant frequency areas 301a and 301b according to whether the parasitic device switch is turned on or off, the frequency of the second resonant frequency area (between 303a and 303b) has a wide variance. Therefore, although it is possible to delicately control channel variance in the first resonant frequency area, it is impossible to delicately control channel variance in the second resonant frequency area.

To sum up, the small antenna employing a parasitic device, which is shown in Fig. 2, has a problem that it cannot delicately control transmitting/receiving signals in the second resonant frequency area, because the variance in the first resonant frequency area is minute whereas the variance in the second resonant frequency area is large according to on/off of the parasitic device switch. As described above, it is required to develop a small multi-resonant antenna that can generate multiple resonant frequencies and delicately control frequency within a randomly selected resonant frequency in order to overcome the problems of the conventional small antenna employing a parasitic device.

DISCLOSURE TECHNICAL PROBLEM

An embodiment of the present invention, which is devised to fulfill the above requirements, is directed to providing a small multi-resonant antenna that can widely vary resonant frequency and delicately control frequency within a randomly selected resonant frequency by using a parasitic device and multiple feeders.

TECHNICAL SOLUTION

In accordance with an aspect of the present invention, there is provided an antenna element; a plurality of feeders for supplying power to the antenna element; a parasitic device disposed in a dielectric region between a board where an antenna circuit is positioned and the antenna element; a feed switch for selectively connecting any one among the feeders to the antenna element to supply power to the antenna element; and a parasitic device switch for controlling the parasitic device. Herein the feeders are disposed in such a manner that a total length of the antenna element is different individually.

ADVANTAGEOUS EFFECTS

The present invention provides a small antenna with a parasitic device and multiple feeders inside. The antenna can widely vary resonant frequency, can receive signals of broad band, that is, signals of multiple bands, and delicately control frequency within a randomly selected resonant frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows T-DMB frequency bandwidth and channel bandwidth that are used currently.

Fig. 2 is a view showing a typical small antenna employing a parasitic device.

Fig. 3 is a graph showing an SIl parameter according to on/off of the parasitic device switch in the small antenna of Fig. 2.

Fig. 4 is a view illustrating a small antenna using a parasitic device and multiple feeders in accordance with an embodiment of the present invention.

Fig. 5 is a graph showing an SIl parameter according to a feeder when the parasitic device switch 413 is turned on in the small antenna of Fig. 4.

Fig. 6 is a graph showing an SIl parameter according to a feeder when the parasitic device switch is turned off in the small antenna of Fig. 4. Fig. 7 is a view illustrating a small antenna using a parasitic device and multiple feeders in accordance with another embodiment of the present invention .

BEST MODE FOR THE INVENTION

The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. Fig. 4 is a view illustrating a small antenna using a parasitic device and multiple feeders in accordance with an embodiment of the present invention.

Referring to Fig. 4, the small antenna of the present embodiment includes a conductor 401, a first feeder 403, a second feeder 405, a radio frequency (RF) switch 407, a circuit output unit 409, a parasitic device 411, a parasitic device switch 413, and a PCB edge plane (not shown) . The PCB edge plane (not shown) includes a circuit generally realized in antennas (for example, a structure connected to an RF device, such as an amplifier, a mixer, and an analog-to-digital (AD) converter) and a ground line.

The conductor 401 is an antenna element, and it transmits or receives signals to or from the outside. The first feeder 403 and the second feeder 405 connect the circuit output unit 409 to the conductor 401, and they are set up in such a manner that the total length (from a feed point to an end of the antenna) of the conductor 401 varies for each feeder. The RF switch 407 selectively connects the circuit output unit 409 to any one between the first feeder 403 and the second feeder 405 based on a control signal transmitted from the PCB edge plane (not shown) . As the circuit output unit 409 is connected to one between the first feeder 403 and the second feeder 405, the total length (from a feed point to an end of the antenna) of the conductor 401 is changed, which leads to a change in the resonance length of the antenna.

Although Fig. 4 shows two feeders, which are the first feeder 403 and the second feeder 405, the number of feeders may be 3, 4, 5 or any arbitrary number according to an embodiment of the present invention. Also, the total number of the conductor 401 should be varied according to the selected number of feeders. This will be described in detail hereafter with reference to Fig. 8. The circuit output unit 409 is a feed point. Power is supplied from the PCB edge plane (not shown) to the conductor 401 through the first or second feeders 403 or 405. To take an example, a varactor diode or a varying capacitance may be used as the parasitic device 411. Also, the parasitic device 411 is disposed inside a dielectric plate between the conductor 401 and the PCB edge plane (not shown) . Although Fig. 4 shows one parasitic device 411, a plurality of parasitic devices may be set up according to an embodiment of the present invention, and the parasitic devices may be controlled using the parasitic device switch 413. This will be described in detail hereinafter with reference to Fig. 7.

The parasitic device switch 413 connects the parasitic device 411 to a ground plane included in the PCB edge plane (not shown) based on a control signal under the control of the PCB edge plane (not shown) . In short, it connects or disconnects the parasitic device 411 to or from the ground plane according to on/off of the parasitic device switch 413.

Herein, when the parasitic device switch 413 is turned on, the gap between the conductor 401 and the PCB edge plane (not shown) becomes narrow and thus capacitance components increase, which leads to a decrease in the reactance value. Reversely, when the parasitic device switch 413 is turned off, the gap between the conductor 401 and the PCB edge plane (not shown) becomes wide and thus capacitance components decrease, which leads to an increase in the reactance value .

In short, the reactance value of the antenna varies according to on/off of the parasitic device switch 413 and this makes it possible to delicately control frequency.

The RF switch 407 or the parasitic device switch 413 is controlled based on resonant frequency information of an LC switch or local oscillation frequency information which is selected in an intermediate frequency (IF) converter and applied to a mixer. Also, the RF switch 407 or the parasitic device switch 413 may perform switching by feeding back a signal-to-noise ratio of RF signals or IF signals until the signal-to-noise ratio becomes the maximum.

When the RF switch 407 is simultaneously connected to a plurality of feeders, it can be regarded as one antenna. Therefore, it has a limited bandwidth according to the maximal bandwidth of a small antenna. Therefore, the circuit output unit 409 is connected to one feeder and disconnected from all the other feeders in the small antenna of the present invention.

Referring to Fig. 5, C graph shows a first resonant frequency area 501c and a second resonant frequency area 503c when the parasitic device switch is turned on and the circuit output unit 409 is connected to the first feeder 403. D graph shows a first resonant frequency area 501d and a second resonant frequency area 503d when the parasitic device switch is turned on and the circuit output unit 409 is connected to the second feeder 405. Herein, the vertical axis indicates an SIl value (dB) and the horizontal axis indicates frequency (MHz) .

When the parasitic device switch is turned on, the variance gap between the first resonant frequency areas 501c and 501d of the C and D graphs is small and the variance gap between the second resonant frequency areas 503c and 503d of the C and D graphs is small. Also, the SIl value of the first resonant frequency areas 501c and 501d of the C and D graphs is much smaller than -1OdB.

In short, when the parasitic device switch is turned on and the first feeder 403 or the second feeder 405 is in connection in the small antenna of Fig. 4, the variance gap of resonant frequency is so small that frequency can be delicately controlled. Furthermore, since the SIl values for the first resonant frequency 501c and 501d are small, impedance is matched well to thereby minimize reflection loss caused by impedance mismatch and increase the antenna efficiency.

Therefore, when the parasitic device switch is turned on, frequency can be delicately controlled for signals of the first resonant frequency and the antenna efficiency is high.

Fig. 6 is a graph showing an SIl parameter according to a feeder when the parasitic device switch is turned off in the small antenna of Fig. 4. Referring to Fig. 6, E graph shows a first resonant frequency area 601e and a second resonant frequency area 603e when the parasitic device switch is turned on and the circuit output unit 409 is connected to the first feeder 403. F graph shows a first resonant frequency area 601f and a second resonant frequency area 603f when the parasitic device switch is turned off and the circuit output unit 409 is connected to the second feeder 405. Herein, the vertical axis indicates an SIl value (dB) and the horizontal axis indicates frequency (MHz) .

When the parasitic device switch is turned off, the variance gap between the first resonant frequency areas 601e and 60If of the E and F graphs is small and the variance gap between the second resonant frequency areas 603e and 603f of the E and F graphs is small. Also, the SIl value of the second resonant frequency areas 603e and 603f of the E and F graphs is much smaller than -1OdB. In short, when the parasitic device switch is turned off and the first feeder 403 or the second feeder 405 is in connection in the small antenna of Fig. 4, the variance gap of resonant frequency is so small that frequency can be delicately controlled. Furthermore, since the SIl values for the second resonant frequency 603e and 603f are small, impedance is matched well to thereby minimize reflection loss caused by impedance mismatch and increase the antenna efficiency.

Therefore, when the parasitic device switch is turned off, frequency can be delicately controlled for signals of the second resonant frequency and the antenna efficiency is high.

To have a look at the variance according to on/off of the parasitic device switch with reference to Figs. 5 and 6 when the first feeder 403 is in connection, a variance gap between the first resonant frequencies 501c and 601e and a variance gap between the second resonant frequencies 503c and 603e are about 10 to 20 MHz, which is much wider than the channel variance gap shown in Fig. 1. Also, when the second feeder 405 is in connection, a variance gap between the first resonant frequencies 501d and 601f and a variance gap between the second resonant frequencies 503d and 603f are very wide.

To sum up, the capacitance value of the parasitic device varies according to on/off of the parasitic device switch and the reactance of the antenna is changed. This widely varies the resonant frequency.

Therefore, it is possible to widely vary frequency by using a parasitic device, and to delicately vary channels within the widely varied resonant frequency by using multiple feeders. In short, it is possible to change the channel both delicately and widely, and to change frequency band for another service by selecting a corresponding parasitic device.

As shown in Figs. 5 and 6, the small antenna of the present invention can effectively use the first resonant frequency and the second resonant frequency according to on/off of the parasitic device switch. Also, it can receive signals of T-DMB (ranging from 174MHz to 216 MHz) and DVB-H (ranging from 400MHz to 600 MHz) by reducing the length of the antenna by half to thereby extend the used frequency twice as wide.

Referring to Figs. 4 to 6, the small antenna of the present invention can widely vary the resonant frequency by using a parasitic device and it can also delicately control the resonant frequency by varying the total length of the antenna with multiple feeders.

Fig. 7 illustrates a small antenna using a parasitic device and multiple feeders in accordance with another embodiment of the present invention. The antenna of the present embodiment includes a third feeder 701 and a second parasitic device 703 in addition to the structure of the small antenna shown in Fig. 4.

Referring to Fig. 7, the small antenna of the present embodiment includes multiple feeders and multiple parasitic devices. Herein, the parasitic device 411 will be referred to as a first parasitic device 411 to be distinguished from the second parasitic device 703.

The RF switch 407 selectively connects the circuit output unit 409 to any one among the first feeder 403, the second feeder 405, and the third feeder 701, and the parasitic device switch 413 controls the first parasitic device 411 and the second parasitic device 903. Since different resonant frequencies are selected according to the total length of the antenna which is variable, three resonant frequencies having delicate differences between them are generated according to the variance of the total length caused by the three feeders .

Differently from the RF switch 407 capable of connecting only one feeder, the parasitic device switch 413 can selectively connect one of the first parasitic device 411 and the second parasitic device 703 to the ground plane and, at the same time, connect both the first parasitic device 411 and the second parasitic device 703 to the ground plane. The parasitic device is connected to the ground plane selectively or simultaneously so as to selectively transmit/receive signals corresponding to the first resonant frequency 501c, 501d, 601e or 60If or signals corresponding to the second resonant frequency 503c, 503d, 603e or 603f, and to maintain impedance matched. The small antenna employing a parasitic device and multiple feeder, which is suggested in the present invention and described with reference to Figs. 4 to 7, can be applied to an inverted F antenna such as a Planar Inverted-F Antenna (PIFA), a meander-type antenna, a helical antenna, a spring-type loop antenna and so forth. Also, it can be applied to small antennas with less than 1/4 wavelength, such as a Spiral Top Loaded Monopole Antenna (STLA) , a capacitor-plate antenna, a multielement top-loaded monopole antenna and the like. The method of the present invention can be realized as a program and stored in a computer-readable recording medium such as CD-ROM, RAM, ROM, floppy disks, hard disks, magneto-optical disks and the like. Since this process can be easily implemented by those of ordinary skill in the art to which the present pertains, detailed description will not be provided herein.

While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Industrial Applicability

The present invention provides a small antenna that can widely vary resonant frequency and delicately control frequency within a randomly selected resonant frequency.

Claims

WHAT IS CLAIMED IS

1. An antenna, comprising: an antenna element; a plurality of feeders for supplying power to the antenna element; a parasitic device disposed in a dielectric region between a board where an antenna circuit is positioned and the antenna element; a feed switch for selectively connecting any one among the feeders to the antenna element to supply power to the antenna element; and a parasitic device switch for controlling the parasitic device, wherein the feeders are disposed in such a manner that a total length of the antenna element is different for each feeder.

2. The antenna of claim 1, wherein the number of the parasitic device is plural.

3. The antenna of claim 2, wherein the parasitic device switch controls at least any one of the parasitic devices to be turned on/off.

4. The antenna of claim 1, wherein the parasitic device is a varactor diode.

5. The antenna of claim 1, wherein the parasitic device is a varying capacitance.

6. The antenna of claim 1, wherein a reactance component of the antenna varies according to operation of the parasitic device switch.

7. The antenna of claim 6, wherein a capacitance value of the parasitic device varies according to operation of the parasitic device switch.

8. The antenna of claim 1, whose maximal radius is less than 1/4 wavelength.

9. The antenna of claim 1, wherein the antenna element is a Planar Inverted-F Antenna (PIFA) .

10. The antenna of claim 1, wherein the antenna element is a meander-type antenna.

11. The antenna of claim 1, wherein the antenna element is a helical antenna.

12. The antenna of claim 1, wherein the antenna element is a spring-type loop antenna.

13. The antenna of claim 1, wherein the antenna element is a Spiral Top Loaded Monopole Antenna (STLA) .

14. The antenna of claim 1, wherein the antenna element is a capacitor-plate antenna.

15. The antenna of claim 1, wherein the antenna element is a multi-element top-loaded monopole antenna.

16. The antenna of claim 1, wherein the antenna element is an inverted F antenna.