Background Art Conventional antennas for portable phones includes a whip antenna comprising of a straight metallic antenna rod, a helical antenna comprising of a helically wound antenna element, and a retractable antenna including the whip antenna and the helical antenna so that the helical antenna operates when the whip antenna is in a retracted position while the whip antenna operates when it is in an extended position. Since all the antennas are protruded from the housing of the phones, however, they may be inharmonious with external appearance of the phones and easily broken by hitching on users or other bodies.

On the other hand, the portable phones are getting smaller in their size and lighter in their weight. However, one of the biggest restraint in the miniaturization of the phone is the antenna. Being exposed to the outside of the phone, the conventional antenna increases the overall size of the phone while occupying significant volume inside the phone.

In a whip antenna or a retractable antenna, for example, some space must be provided inside the phone for receiving the whip antenna when the whip antenna is inserted or retracted into the phone.

Accordingly, in order to solve the space problem caused by the size of the external antenna, internal antennas which may be installed inside the phone by surface mounting technologies are being contemplated. However, the bandwidth of the internal antenna is generally proportional to the thickness of the dielectric substrate. That is, the thinner the substrate is, the narrower the bandwidth is. Thus, in the case that the internal antenna is employed in a portable terminal, the bandwidth may be insufficient for facilitating signal transmission and reception due to the reduction of the size of the antenna.

Disclosure of the Invention To solve the above problems, an object of the present invention is to provide an internal patch antenna which has sufficiently wide bandwidth and can be installed easily by the surface mounting technology.

The internal patch antenna according to the present invention to achieve the above object is installed in the portable terminal to transmit and receive wireless signals. The internal patch antenna of the present invention includes a substrate, a dielectric layer, a ground plane, and a feeding microstrip transmission line. The dielectric layer, made of ceramic material having high dielectric constant, is formed on the substrate and has multiple radiator patterns for transmitting and receiving the signals on its upper side. The ground plane is disposed beneath the substrate. The feeding microstrip is inserted between the substrate and the dielectric layer to feed electrical signals to the radiator patterns by electromagnetic coupling. The feeding microstrip preferably runs through the center position between the substrate and the dielectric layer. The radiator patterns may be

arranged asymmetrically between the region above the feeding microstrip and the other regions.

It is preferable that a via hole filled with conductive material is formed through the substrate so that a feeding microstrip is fed from the rear through conductive material of the via hole. The feeding microstrip includes a feeding point connected to the via hole; a main feeding portion connected electrically to the feeding point ; and a termination portion which terminates the feeding microstrip. Additionally, multiple microstrip patches having rectangular shapes are arranged of series along the main feeding portion.

In a preferred embodiment, the internal patch antenna further includes a waveguide which connects the feeding point to a main feeding portion. In particular, it is preferable that the width of the main feeding portion is narrower than the width of a common microstrip transmission line of 50 ohm (Q). However, the waveguide part and the termination portion may have the same width as the common microstrip transmission line of 50 ohm. When the width of the main feeding part narrower, it is preferable to dispose a first impedance matching portion between the waveguide and the main feeding portion and a second impedance matching portion between the main feeding portion and the termination portion. The first and the second impedance matching portion may be implemented by tapering corresponding portions of the line. Meanwhile, to save the area of the microstrip transmission line, the feeding microstrip line may include portion bent into a'L'-or'U'-shape.

In one embodiment, a plurality of screw holes are formed on the ground plane, so that the ground plane is attached to a ground line of a circuit board of the portable terminal

by screwing into the screw holes. Alternatively, however, the ground plane may be attached to a ground line of a circuit board by soldering or using conductive adhesive.

It is preferable to arrange small patches periodically in series along the feeding microstrip transmission line and adjust the arrangement to combine adjacent modes and wide operation bandwidth.

Brief Description of the Drawings The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: FIGS. 1A and FIG. 1B illustrate an example of a portable phone which employs an internal patch antenna according to the present invention; FIG. 2 is a perspective view of an embodiment of the internal patch antenna according to the present invention; FIG. 3 is an exploded perspective view of the internal patch antenna of FIG. 2; FIG. 4 shows the radiator patterns of the internal patch antenna of FIG. 2 in detail; FIG. 5 shows the feeding microstrip of the internal patch antenna of FIG. 2 in detail; FIG. 6 shows the radiator patterns overlapped with the feeding microstrip ; FIG. 7 is a plot of standing-wave ratio of the internal patch antenna of FIG. 2; FIGS. 8A through 8C are radiation pattern diagrams of the internal patch antenna of FIG. 2 in a first through a third frequency band, respectively;

FIG. 9 is a perspective view of another embodiment of the internal patch antenna according to the present invention; FIG. 10 is a exploded perspective view of an internal patch antenna of FIG. 9; FIG. 11 is a plot of standing-wave ratio of the internal patch antenna of FIG. 9; and FIGS. 12A and 12B are radiation pattern diagrams of the internal patch antenna of FIG. 9 in a first and a second frequency band, respectively.

Embodiments FIGS. 1A and FIG. 1B illustrate an example of a portable phone which employs an internal patch antenna according to the present invention. As shown in the drawings, the patch antenna 10 is installed on a main circuit board 4 inside the portable phone 2. As described below, a ground plane of the patch antenna 10 directly contacts the ground line of the circuit board 4 and the antenna radiator is fed from a signal line of the circuit board 4. Particularly, since the radiation plane of the antenna is installed to turn toward the rear of the phone, just a little electromagnetic wave is directed to the user and the effect of electromagnetic wave to the human body is reduced. In FIGS 1A and 1B, (phi) denotes the azimuth, for measuring radiation patterns of the antenna described below, with reference to the feeding point of the antenna. In a preferred embodiment, the patch antenna 10 has a size of 27X 27X 4.5 square millimeters (mm3) and occupies just a little volume in the phone 2. Even though a folder-type phone is illustrated in Fig. 1, it is obvious that the patch antenna of the present invention can be employed in the other kinds

of portable terminals such as a flip-type and a bar-type phone, and a personal digital assistant (PDA).

FIGS. 2 and 3 illustrate an embodiment of the internal patch antenna according to the present invention in detail. The internal patch antenna 10 according to the present embodiment includes a substrate 60 made of plastic, e. g., glass epoxy (FR-4), a ground plane 70 installed beneath the lower surface of the substrate 60, and a dielectric layer 30 deposited on the upper surface of the substrate 60. On the dielectric layer 30 is formed a conductive layer 20 for radiating and receiving electromagnetic wave. A feeding microstrip, which transmits and receives signals to and from the conductive layer 20 by electromagnetic coupling, is disposed between the dielectric layer 30 and the substrate 60.

The feeding microstrip is electrically connected to a signal line of the main circuit board 4 through a via hole formed through the ground plane.

In the internal patch antenna of FIGS. 2 and 3, the conductive layer 20 is comprised of multiple radiator patterns. The radiator patterns are shown in more detail in FIG. 4. A first pattern 22 having the largest size is disposed in the center of the conductive layer 20.

Eight second patterns 24 scaled down by 1/9 from the first pattern 22 are disposed radially around the first pattern 22. Eight third patterns 26 scaled down by 1/9 from the second pattern 24 are disposed around each of the second pattern 24. Multiple fourth patterns 28 scaled down further are disposed around the second pattern 24 above the path of the feeding microstrip 40, so that the perturbation is increased in the region where the electromagnetic coupling occurs from the feeding microstrip transmission line to result in wide bandwidth and high radiation efficiency characteristics.

The radiator patterns arranged as above has a property of a kind of an array antenna. Here, the size of each of the first through the fourth patterns 22-28 and distances therebetween are determined so as to widen the operation bandwidth and insure plural resonance frequencies by autocorrelation while enhancing reliability for antenna duplication. The specific dimension is determined according to the overall size of the antenna and material of each member, and can be optimized depending on the application.

In the internal patch antenna of FIGS. 2 and 3, the radiator patterns exchange signals with the microstrip transmission line by electromagnetic coupling. To enhance the coupling efficiency between radiator patterns and transmission line, it is preferable to use ceramic of high dielectric constant, e. g., 80-120 for the dielectric layer 30. Use of multiple radiating patterns mentioned above contribute to the enhancement of the coupling efficiency as well. Since the internal patch antenna of the present invention basically uses resonance characteristics, the operation frequency band can be adjusted by changing dielectric material. On the other hand, if the coupling efficiency is increased, the bandwidth of the antenna is widened also.

FIG. 5 shows the feeding microstrip in the internal patch antenna. The feeding microstrip 40 includes a waveguide 44, a main feeding portion 48, and a termination portion 54. In such feeding microstrip 40, the signal feeding operation for the radiator patterns 22-28 of the conductive layer 20 is mainly carried out by the main feeding portion 48. The waveguide 44 provides a high frequency signal from the feeding point 42 to the main feeding portion 48 and the termination portion 54 terminates the feeding microstrip 40. FIG. 6 shows the radiator patterns overlapped with the feeding microstrip.

Meanwhile, the feeding microstrip 40 is connected to the main circuit board of the phone through a via hole adjacent to the feeding point.

In the antenna structure according to the present invention, since the feeding microstrip transmission line is not exposed to air and but buried between the plastic substrate and the ceramic dielectric layer, the high frequency signal propagating through the microstrip transmission line is influenced by the ceramic. Thus, the equivalent capacitance is increased compared with the case that the microstrip transmission line is exposed to air and the characteristic impedance is less than 50 ohm (Q). Therefore, it is preferable that the line bandwidth of the main feeding portion 48 is less than that of a common microstrip transmission line having a characteristic impedance of 50 ohm (Q) for the purpose of impedance matching. The specific width of the main feeding portion 48 can be optimized by a simulation.

Since the line width of the main feeding portion 48 is narrow, it is preferable to provide a first transition portion 46, between the waveguide 44 and the main feeding portion 48, having a taped aspect of which line width diminishes gradually, so that impedance is matched in this region. Similarly, it is preferable to provide a second transition portion 52, between the main feeding portion 48 and the termination portion 54, of which line width increases gradually so as to fulfill impedance matching.

Meanwhile, six microstrip patches 50 are arranged in series along the main feeding portion 48 so as to provide electrical signal efficiently to the radiator patterns and obtain wide bandwidth characteristic and effective mode coupling through the interferences between the patches. While the electromagnetic signal provided through the feeding point

passes the small microstrip patches, a lower-order mode of two adjacent modes moves upward to high frequency so that modes are coupled and a wide bandwidth characteristic is obtained in the resonance frequency.

On the other hand, the total length of the feeding microstrip 40 is closely related to the resonance frequency of the antenna. In this regard, the waveguide 44 or the termination portion is preferably bent into a'L'-shape or'U'-shape so that the feeding microstrip is implemented effectively in a limited area while maintaining required length.

It can be seen that the waveguide 44 is bent into the'U'-shape in the embodiment of FIG.

5. In the embodiment of FIG. 5, the electrical length of the waveguide 44 is 0.072Ro, the electrical length of the main feeding portion 48 is 0.063Ao, and the electric length of the termination portion 54 is 0.043A0. Here, , o is the resonance frequency of the antenna, or the central frequency of the highest frequency band in case of a multiple frequency band antenna. Additionally, each small patch arranged along the main feeding portion 48 has a size of0. 007Ao x 0.0033po and the space between adjacent patches is 0. 0033, 0.

Referring back to FIGS. 2 and 3, the ground plane 70 includes four screw holes for putting screws in the vicinity of four corners. The antenna may be installed solidly on the main circuit board of the phone while guaranteeing the ground state of the ground plane 70 by driving screws into the screw holes in a state that the ground plane 70 is closely stuck to the main circuit board. Meanwhile, the region 74 of the ground plane 70 near the via hole of the substrate 60 for feeding power to the feeding microstrip 40 is incised and partially filled with, or made of, non-conductive material for the insulation between the conductive material filled in the via hole and the ground plane 70. In an alternative

embodiment, however, the ground plane 70 can be fixed to the main circuit board of the terminal by soldering or using conductive adhesive.

FIG. 7 shows the standing-wave ratio of the internal patch antenna according to the present embodiment. The internal patch antenna shows excellent standing-wave ratio characteristics in three frequency bands of 900 MHz, 1.8 GHz, and 2.1 GHz, and thus can operate as a triple band antenna. Here, the frequency bands of 900 MHz, 1.8 GHz, and 2. 1 GHz correspond to bands for the Group Special Mobile (GSM) system, the Personal Communications Service (PCS), and the International Mobile Telecommunication 2000 (IMT-2000) system, respectively. Accordingly, the internal patch antenna of the present embodiment can be employed in any terminal suitable for one of the three systems without any adaptation process.

FIGS. 8A through 8C show radiation patterns of the internal patch antenna of FIG.

2 in the frequency bands of 900 MHz, 1.8 GHz, and 2.1 GHz, respectively. Combining the radiation patterns of phi=0 and phi=90, the three-dimensional radiation pattern has a shape of an ovum cut by a half and shows high radiation intensity evenly for the rear direction and the side direction of the terminal.

FIGS. 9 and 10 illustrates another embodiment of the internal patch antenna according to the present invention. The antenna of the present embodiment is resonated in dual frequency bands of 1.8 GHz and 2.1 GHz, and has the size of is 20 x 10 x 4.5 (mm).

The antenna shown in FIGS. 9 and 10 has a similar structure to that shown in FIGS. 2 and 3. To be more detail, the antenna of the present embodiment includes a

conductive layer 120 comprising of multiple radiator patterns, a dielectric layer 130, a feeding microstrip 160, and a ground plane 170. It can be said that the antenna of FIGS.

9 and 10 is a miniature of that shown in FIGS. 2 and 3 maintaining electric characteristics of the latter. In the present embodiment, however, the termination portion of the feeding microstrip transmission line 160 is bent into a'L'-shaped pattern to reduce the area of the feeding microstrip transmission line 160. Further, the lateral radiator patterns in FIGS. 2 and 3 are removed while the patterns above the feeding microstrip transmission line 160 are maintained, so that the size of the antenna is reduced. That is, the first pattern is disposed on the center of the dielectric layer 130, and the second and the third patterns are disposed only on the region the dielectric layer 130 above the feeding microstrip line.

FIGS. 11 through 12B show electric characteristics of a dual band internal patch antenna according to the present embodiment. Specifically, FIG. 11 shows standing-wave ratio of the internal patch antenna of FIG. 9, and FIGS. 12A and 12B show radiation patterns in a first and a second frequency band, respectively. Comparing FIGS. 11 through 12B with FIGS. 7 through 8C, it can be seen that the antenna of the present embodiment shows similar electric characteristics to the antenna of FIGS. 2 and s ws s a e Industrial Applicability The multiple band internal patch antenna of the present invention can be installed on the main circuit board of the portable terminal, and thus can enables the terminal manufacturer to increase the productivity of the terminals. The present invention increases the reproducibility of the antenna and thus facilitates mass production of the antenna and

portable terminal. Also, the present invention can effectively solve the space problem of the conventional antenna. Since some portion of the electromagnetic wave radiated from the antenna is shielded by the ground plane of the antenna and the circuit board of the terminal, electromagnetic interference exposed to the human body is reduced compared with the conventional omnidirectional antenna. Since the antenna of the present invention can operate in multiple frequency bands, the terminal manufacturer can employ the same antenna for various kinds of terminals.