Antenna device

Provided is a compact antenna for installment in a portable terminal and adjusting a resonant frequency. The compact antenna device includes an antenna unit including first and second elements, the first element including a first antenna terminal having at least one of meandering and curved patterns wholly or partially, and the second element including an end connected to another end of the first element and another end having a second antenna terminal, a feeding unit exciting the antenna unit through the first and second antenna terminals, a switching circuit connected between the antenna unit and the feeding unit and selectively switching one or both of the first and second elements in order to connect one or both of the first and second elements to the feeding unit. A resonant frequency of the antenna unit varies during feeding by the feeding unit depending on the switching operation of the switching circuit.

PRIORITY

This application claims the benefit of Japanese Patent Application No. 2005-370029, filed in the Japanese Intellectual Property Office on Dec. 22, 2005, and Korean Patent Application No. 10-2006-0078761, filed in the Korean Intellectual Property Office on Aug. 21, 2006, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an antenna device, and more particularly, to a compact antenna device suitable for installment in a portable terminal and tunable to a resonant frequency.

2. Description of the Related Art

Portable devices such as notebooks and portable terminals require compact antennas in order to receive television (TV) signals and other signals. In this case, antennas having meandering or helical shapes may be considered as compact high performance antennas. However, since conventional helical antennas or monopole antennas are compact, they provide narrow bands and are difficult to match with portable terminals.

European Patent No. EP1,176,663A1 discloses a helical antenna technique used in a portable terminal. In the disclosure, a terminal is installed in an intermediate or front part of an element of a helical antenna. A filter including strip lines having different lengths, an inductor, and a capacitor are connected to the terminal using a switch.

However, a helical antenna circuit is complicated, and it is difficult to minutely tune to a resonant frequency. Accordingly, there exists a need for further development of the circuitry.

SUMMARY OF THE INVENTION

The present invention provides a compact antenna device suitable for installment in a portable terminal and tunable to a resonant frequency.

According to the present invention, there is provided an antenna unit including first and second elements, the first element including a first antenna terminal having at least one of meandering and curved patterns wholly or partially, and the second element including a first end connected to a first end of the first element and a second end having a second antenna terminal, a feeding unit exciting the antenna unit through the first and second antenna terminals, a switching circuit connected between the antenna unit and the feeding unit and selectively switching one or both of the first and second elements in order to connect one or both of the first and second elements to the feeding unit, wherein a resonant frequency of the antenna unit varies during feeding by the feeding unit depending on the switching operation of the switching circuit.

The antenna device further includes a matching adjusting circuit connected to the switching circuit and adjusting the resonant frequency of the antenna part, wherein the switching circuit connects one of the first and second elements to the feeding unit and the other one of the first and second elements, which is not connected to the feeding unit, to the matching adjusting circuit.

According to the present invention, there is provided an antenna unit including first and second elements, the first element including a first antenna terminal having at least one of meandering and curved patterns wholly or partially, and the second element including a first end connected to a first end of the first element and a second end having a second antenna terminal, a matching adjusting circuit connected to one of the first and second antenna terminals and adjusting a resonant frequency of the antenna unit, and a feeding unit exciting the antenna part through the other one of the first and second antenna terminals which is not connected to the matching adjusting circuit.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. A detailed description of known functions will be omitted for the sake of clarity and conciseness.

FIG. 1illustrates an antenna device according to the present invention. Referring toFIG. 1, the antenna device includes an antenna unit8including first and second elements10and12and a feeding unit26exciting the antenna unit8.

A first end of the first element10is electrically connected to a top end13of the second element12at a top part13. The second element12may be shorter than the first element10. A portion of or the entire first element10may have at least one of meandering and curved patterns. For example, the first element10may be formed in a helical structure. Also, the second element12may be formed in a linear structure.

The first element10includes a first antenna terminal at a second end thereof, and the second element12includes a second antenna terminal at a bottom end thereof. The first and second antenna terminals are respectively connected to first and second input and output terminals14and16of a RFAN18, which includes three or more high frequency signal input and output terminals and one or more control signal input and output terminals. The feeding unit26excites the antenna unit8, and a control circuit20controls the RFAN18.

FIG. 2illustrates a first RFAN18according to the present invention. Referring toFIG. 2, the RFAN18includes a switching circuit22that switches on the first and second input and output terminals14and16in order to connect the first and second input and output terminals14and16to the feeding unit26. The switching circuit22will be described later in more detail.

FIGS. 3A and 3Billustrate second and third RFANs18according to embodiments of the present invention. Referring toFIGS. 3A and 3B, the RFAN18includes a matching adjusting circuit24. As shown inFIG. 3A, the matching adjusting circuit24controlled by the control circuit20is connected to the first input and output terminal14, and the feeding unit26is connected to the second input and output terminal16. Alternatively, as shown inFIG. 3B, the matching adjusting circuit24controlled by the control circuit20is connected to the second input and output terminal16, and the feeding unit26is connected to the first input and output terminal14.

FIG. 4illustrates a fourth RFAN18according to the present invention. The RFAN18includes the matching adjusting circuit24and the switching circuit22. The control circuit20controls the matching adjusting circuit24and the switching circuit22.

FIGS. 5A through 5C,6, and7illustrate first through fifth matching adjusting circuits24according to the present invention. The first matching adjusting circuit24may be realized as an inductor as shown inFIG. 5A. The second matching adjusting circuit24may be realized as a parallel circuit including an inductor and a capacitor as shown inFIG. 5B. The third adjusting circuit24may be realized as a switch as shown inFIG. 5C. Referring to the fourth adjusting circuit24isFIG. 6, an inductor L1is connected in series with a capacitor C1, a variable capacitor C2is connected in parallel with a circuit including the inductor L1and the capacitor C1, and a capacitor C3is connected to a circuit including the inductor L1, the capacitor C1, and the variable capacitor C2and to a power supply voltage VCC through an inductor L2so as to control the capacitor C2. The matching adjusting circuit24may be appropriately selected from the above examples to reduce a Voltage Standing Wave Ratio (VSWR) of the antenna unit8so as to transmit a signal at a high sensitivity. As shown inFIG. 7, the fifth matching adjusting circuit24may include a plurality of circuits as illustrated inFIGS. 5A through 5Cand inFIG. 6. A switch may select one of the plurality of circuits tuned to a resonant frequency. The matching adjusting circuit24is not limited to these examples.

FIGS. 8A through 8Cillustrate first, second and third connection states of the switching circuit22according to the present invention. As shown in the first state inFIG. 8A, when the switching circuit22switches off a linear element12but switches on a helical element10, the switching circuit22is connected to the feeding unit26. As shown in the second state inFIG. 8B, when the switching circuit22switches on the linear element12but switches off the helical element10, the switching circuit22is connected to the feeding unit26. As shown in third state inFIG. 8C, when the switching circuit22switches on both the helical element10and the linear element12, the switching circuit22is connected to the feeding unit26. Since the VSWR of the antenna unit8varies with a connection state of the switching circuit22, the connection state of the switching circuit22may be selected depending on the environment in which it is used.

The results of a simulation performed on an antenna device according to the present invention will now be described.

FIG. 9illustrates an antenna device used in a first simulation. An antenna unit8including a first element10having a helical shape and a second element12having a linear shape is installed on a board having a laptop computer shape. The first element10is connected to the feeding unit26, and the second element12is connected to the matching adjusting circuit24.

FIG. 10illustrates a sixth matching adjusting circuit24according to the present invention, andFIG. 11illustrates the results of a simulation performed on a VSWR of the antenna unit8illustrated inFIGS. 9 and 10.

In the present embodiment, a switch is turned on, a resonant frequency is f1, a wavelength of the resonant frequency is λ1, and a helical element has a diameter of about 0.008λ1, a pitch of about 0.014λ1, and a number of turns of 5.73. The antenna unit8has a length of about 0.08λ1. The size corresponding to a liquid crystal display is about 0.17λ1×0.23λ1, and the size corresponding to a keyboard is about 0.16λ1×0.23λ1, of a board30.

Referring toFIG. 10, (2) denotes an inductor of 3.9 microhenry (μH), (3) denotes a circuit including an inductor of 1.2 μH and a capacitor of 1.0 picofarad (pF), which are connected in parallel, and (4) denotes a circuit including capacitors of 6.0 pH and 5.0 pH which are connected in parallel with an inductor of 1.0 μH.

Referring toFIG. 11, a solid line (1) denotes the VSWR of the antenna unit8when the switch is turned on. Here, the resonant frequency is f1.

A bold broken line (2) denotes the VSWR of the antenna unit8when the antenna unit8is connected to the inductor (2) illustrated inFIG. 10. Here, the resonant frequency is about 0.88f1.

A slender broken line (3) denotes the VSWR of the antenna unit8when the antenna unit8is connected to the circuit (3) including the inductor and the capacitor illustrated inFIG. 10. Here, resonant frequency is about 0.68f1.

An alternating long and short dash line (4) denotes the VSWR of the antenna unit8when the matching adjusting circuit24is inserted into the circuit (4) illustrated inFIG. 10. Here, an intermediate frequency is 0.68f1.

As described above, a circuit of the matching adjusting circuit24may be selected in order to vary the resonant frequency of the antenna unit8. Also, a helical element and a linear element may be connected to each other in order to reduce a length of the antenna unit8to about 0.08λ1.

Such a compact antenna device may be installed in a portable terminal such as a laptop or a Personal Data Assistant (PDA) in order to transmit and/or receive a radio signal in a desired frequency band. In particular, a TV signal in a band between a Very High Frequency (VHF) band to an Ultra High Frequency (UHF) band may be easily received.

FIG. 12illustrates an antenna device used in a second simulation. An antenna unit8including a first element10having a helical shape and a second element12having a linear shape is installed on a board having a laptop computer shape. The antenna unit8is connected to the switching circuit22as shown inFIGS. 8A through 8C.

FIG. 13illustrates the results of a simulation of a VSWR of the antenna unit8illustrated inFIG. 12. Referring toFIG. 13, a solid line (a) denotes the VSWR of the antenna unit8connected to the feeding unit26when the first element10having the helical shape is switched on as illustrated inFIG. 8A. Here, a resonant frequency is f2.

A broken line (b) denotes the VSWR of the antenna unit8connected to the feeding unit26when the first element10having the helical shape is switched off as illustrated inFIG. 8B. Here, the resonant frequency is about 0.912f2.

An alternated long and short dash line (c) denotes the VSWR of the antenna unit8when the first and second elements10and12are switched on to be connected to the feeding unit26as illustrated inFIG. 8C. Here, the resonant frequency is about 1.86f2.

As described above, the resonant frequency can be adjusted. If a wavelength of the resonant frequency f2is λ2, the first element10having the helical shape may have a diameter of about 0.008λ2, a pitch of about 0.005λ2, and a number of turns of 12.92 as illustrated inFIG. 12. Also, the antenna unit8may have a length of about 0.07λ2. The size corresponding to a liquid crystal display is about 0.16λ2×0.23λ2, and the size corresponding to a keyboard is about 0.15λ2×0.23λ2, of a board30.

It has been described that the first element10has a helical shape, and the second element12has a linear shape. However, the present invention is not limited to these shapes. Hereinafter, modifications of shapes of the first and second elements10and12will be described. In the following, at least one element includes a part having a different shape from a linear shape. Thus, if an element is helical, another element may be linear, helical, meandering, or zigzag shaped.

If an element is meandering, another element may be linear, zigzag, or zigzag-linear. A part of the other element may have another shape. Referring toFIGS. 14Athrough to17B, a first element is helical, and a second element includes a part having a different shape from the other part of the second element. As shown inFIGS. 14A,15A,16A, and17A, the first element10may be disposed around a central axis of the second element12. As shown inFIGS. 14B,15B,16B, and17B, the second element12may be disposed outside the first element10.

Referring toFIGS. 14A and 14B, a part of the second element12may be meandering as indicated with a broken line. Referring toFIGS. 15A and 15B, the part of the second element12may be helical as indicated with a broken line. Referring toFIGS. 16A and 16B, part of the second element12may be zigzag shaped as indicated with a broken line. Referring toFIGS. 17A and 17B, a width or thickness of a conductor of part of the second element12may vary as indicated with a broken line.

Referring toFIGS. 18A through 22B, an element, for example, the first element10, is meandering, and another element, for example, the second element12, includes a part having a different shape from the other part of the second element12. A meandering shape is nearly planar. Referring toFIGS. 18A,19A,20A,21A, and22A, the second element12may overlap with the first element10. Referring toFIGS. 18B,19B,20B,21B, and22B, the second element12may be disposed parallel with the first element10on the same plane.

Referring toFIGS. 18A and 18B, the first element10has a meandering shape, and the second element12has a linear shape. Referring toFIGS. 19A and 19B, a part of the second element12is meandering as indicated with a broken line. Referring toFIGS. 20A and 20B, a part of the second element12is helical as indicated with a broken line. Referring toFIGS. 21A and 21B, the part of the second element12is zigzag shaped as indicated with a broken line. Referring toFIGS. 22A and 22B, a width or thickness of a conductor of a part of the second element12various as indicated with a broken line. Also, modifications of intervals and widths (diameters) of meandering, zigzag shaped, and helical shapes are within the scope of the present invention.

The first element10may not include a part having a different shape as shown inFIGS. 14A through 22Bor may include a part having a different shape. Also, in any of the above-described structures, two elements may be connected at the top part13and thus lengthened so as to reduce a resonant frequency and make the antenna device more compact. Also, two elements having different electric lengths may be installed, and any of the three ways of connecting terminals of the two elements to a feeding unit through a switching circuit may be selected. As a result, a resonant frequency may be selected in three different cases: In addition, a frequency may be tuned by a matching adjusting circuit including an inductor and a capacitor.

As described above, a compact antenna device according to the present invention is installed in a portable terminal and is tunable to a resonant frequency. The resonant frequency is adjusted using a switching circuit, and the frequency is tuned using the matching adjusting circuit. Thus, the compact antenna device widens a frequency band.