Antenna module whose antenna characteristics are not adversely affected by a mother board

[0001] 1. Field of the Invention

[0002] The present invention relates to an antenna module that is mounted on the mother board of an electronic apparatus such as a personal computer. In particular, the invention relates to an antenna module that is suitable for short-distance radio data communication.

[0003] 2. Description of the Related Art

[0004] In recent years, radio data transfer methods that enable short-distance information exchange by transmitting and receiving radio waves in a prescribed frequency band (e.g., a 2.4-GHZ band) have come to attract much attention. With the spread of such a technology, in the future, it will become more necessary to provide an antenna module for transmission and reception of communication data on the mother board of an electronic apparatus such as a personal computer.

[0005] FIG. 2 illustrates a conventional antenna module of the above kind. As shown in FIG. 2, the antenna module is generally configured in such a manner that a chip-type antenna 2, a circuit unit 3, and a connector 4 are mounted on an insulative substrate 1 that is mounted on the mother board (not shown) of a personal computer or the like and that a ground conductor 5 is formed on the back surface of the insulative substrate 1. In the chip-type antenna 2, a band-shaped conductor 2b is formed spirally on the surface of a chip-shaped dielectric member 2a. The spiral, band-shaped conductor 2b is connected to a feeder line 6. One end, near the feeding point, of the spiral, band-shaped conductor 2b is connected to the ground conductor 5 through a through-hole (not shown). The overall length of the spiral, band-shaped conductor 2b is set slightly shorter than ¼ of the free space wavelength λ of radio waves used, that is, λ/4, with wavelength shortening by the dielectric member 2a taken into consideration. The circuit unit 3 is such that a transmission/reception circuit in which electronic parts such as amplifiers and an oscillator are arranged is covered with a shield case. The transmission/reception circuit is connected to the feeder line 6. The connector 4 is to connect, to a mother-board-side external circuit, lead lines leading from the transmission/reception circuit of the circuit unit 3.

[0006] The above conventional antenna module functions as what is called a monopole antenna in which one end of the spiral, band-shaped conductor 2b is grounded. That is, it utilizes a mirror principle: the spiral, band-shaped conductor 2b resonates as if an equivalent radiation element existed on the opposite side of the ground conductor 5. Therefore, unlike the case of a dipole antenna, it is not necessary to provide a pair of radiation elements. The antenna module is fabricated in this manner to decrease the occupation area of the radiation element on the insulative substrate 1 and hence the entire module can easily be miniaturized.

[0007] Compactness has become increasingly important for antenna modules to permit mounting of an antenna module on a mother board of an electronic apparatus such as a personal computer. The compactness of the above conventional antenna module is satisfactory. However, the very reason that the above conventional antenna module is compact enough to be useful, i.e. the antenna module is of a monopole type that utilizes a mirror principle in which the presence of the ground conductor 5 allows the spiral, band-shaped conductor 2b to resonate in the same manner as in a half-wave dipole, creates a problem. More specifically, because the resonance frequency of the antenna module shown in FIG. 2 depends on the positional relationship between the chip-type antenna 2 and the ground conductor 5, the antenna characteristics are affected by mother-board-side ground conductor. Moreover, as the ground conductor is relatively close to the antenna module, the antenna characteristics are highly sensitive to the position of the ground conductor with respect to the antenna module. This means that it is difficult to attain high reliability in both manufacturability, in addition to operability as it is not unlikely that the relative position may vary significantly, for example due to temperature fluctuations.

[0008] The present invention has been made in view of the above, and an object of the invention is therefore to provide a compact antenna module whose antenna characteristics are not affected by the position of a mother board/ground plane.

[0009] To attain the above object, an antenna module according to the invention comprises an insulative substrate to be mounted on a mother board; a pair of radiation elements that are mounted on the insulative substrate and fed at the center of the pair of radiation elements; a circuit unit that is mounted on the insulative substrate and has a reception circuit and/or a transmission circuit that are connected to feeder lines for the respective radiation elements; and a connector that is mounted on the insulative substrate and connects, to an external circuit, lead lines leading from the circuit unit, wherein at least one of the pair of radiation elements is a snaked, band-shaped conductor that is patterned in “meander” form on the insulative substrate.

[0010] In the above-configured antenna module, since the antenna structure is not of a monopole but of a half-wave dipole in which the pair of radiation elements are fed at the center, its antenna characteristics are not adversely affected by a mother-board-side ground conductor. Since the overall length of the snaked, band-shaped conductor extending in “meander” form may be set to about ¼ of the free space wavelength λ of radio waves used, the longitudinal dimension of a patterning region of the snaked, band-shaped conductor can be much smaller than λ/4. That is, one of the pair of radiation elements of the dipole antenna can be patterned in a relatively narrow region, whereby increase in the size of the insulative substrate can be avoided. Further, since the capacitance of the snaked, band-shaped conductor increases as its “meandering” pitch is decreased, impedance matching can be attained easily.

[0011] In the above configuration, the pair of radiation elements may be arranged so as to generally assume an L-shape in a plan view. In this case, since the radiation element scan bear ranged along two adjoining sides of the insulative substrate, the circuit unit and the connector can be arranged in the remaining region on the insulative substrate without being forced to be confined there, which means improvement in the space factor. This is favorable for miniaturization of the insulative substrate. The pair of radiation elements may be the snaked, band-shaped conductor and a chip-type antenna. In this case, the miniaturization of the insulative substrate is made easier than in the case where both of the radiation elements are a snaked, band-shaped conductor.

[0014] An embodiment of the present invention will be hereinafter described with reference to FIG. 1, which illustrates an antenna module according to the embodiment of the invention. Components in FIG. 1 having corresponding components in FIG. 2 are given the same reference symbols as the latter.

[0015] The antenna module shown in FIG. 1 is generally configured in such a manner that a chip-type antenna 2 and a snaked, band-shaped conductor 7 as a pair of radiation elements that are fed at the center, a circuit unit 3 in which a transmission/reception circuit connected to feeder lines 8 and 9 for the respective radiation elements 2 and 7 is covered with a shield case, and a connector 4 that connects, to a mother-board-side external circuit, lead lines leading from the transmission/reception circuit are arranged on an insulative substrate 1 that is mounted on the mother board (not shown) of a personal computer or the like.

[0016] The chip-type antenna 2 is of a known type in which a band-shaped conductor 2b is formed spirally on the surface of a chip-shaped dielectric member 2a. The feeder line 8 is connected to one end of the spiral, band-shaped conductor 2b. The overall length of the spiral, band-shaped conductor 2b is set slightly shorter than ¼ of the free space wavelength λ of radio waves used, that is, λ/4, with wavelength shortening by the dielectric member 2a taken in to consideration. The snaked, band-shaped conductor 7 is a band-shaped conductor that is patterned on the insulative substrate 1 so as to snake in “meander” form, and its overall length is set to about λ/4. The chip-type antenna 2 and the snaked, band-shaped conductor 7 (meander conductor) extend along two adjoining sides of one face of the insulative substrate 1 so as to generally assume an L-shape in a plan view. The two terminals of a radio-frequency power source are connected to the respective feeder lines 8 and 9.

[0017] The antenna structure of the above-described antenna module is of a half-wave dipole in which the pair of radiation elements 2 and 7 are fed at the center of the pair. This substantially eliminates the effect of the mother-board-side ground conductor on the antenna characteristics of the antenna module and permits a high reliability antenna module to be produced. The snaked, band-shaped conductor 7 (one radiation element) occupies a slightly wider area on the insulative substrate 1 than the chip-shaped antenna 2 (the other radiation element) does. However, the longitudinal dimension of the patterning region of the snaked, band-shaped conductor 7 in “meander” form is still much smaller than λ/4. Further, in this embodiment, since the pair of radiation elements 2 and 7 extend along the two adjoining sides of one face of the insulative substrate 1 so as to generally assume an L-shape in a plan view, the circuit unit 3 and the connector 4 can be arranged in the remaining region on the same side of the insulative substrate 1 without increasing the overall area of the insulative substrate 1 necessary to contain all of this circuitry present on the face. That is, in this antenna module although the pair of radiation elements 2 and 7 of the dipole antenna are provided to increase the reliability, it is not necessary to increase the size of the insulative substrate 1, thereby permitting a compact antenna module to be more easily mounted on the mother board of a personal computer or the like.

[0018] Impedance matching, which is indispensable in manufacturing the above-type of antenna module, can be conducted relatively easily by selecting a pattern shape of the snaked, band-shaped conductor 7 as appropriate. That is, since the capacitance of the snaked, band-shaped conductor 7 increases as the pitch of its “meandering” is decreased, impedance matching can easily be attained by varying the capacitive reactance component as appropriate.

[0019] In another possible embodiment, a snaked, band-shaped conductor that is similar to the snaked, band-shaped conductor 7 may be provided in place of the chip-type antenna 2, that is, two snaked, band-shaped conductors in “meander” form are used as the pair of radiation elements of the dipole antenna. However, this will increase the overall size of the antenna module, even if the conductors are formed in an L shape in plan view, and thus, from the viewpoint of miniaturizing the insulative substrate 1, it is preferable to employ a chip-type antenna as one radiation element. To further decrease the overall size of the insulation substrate required, in an additional embodiment, two chip-type antennas may be used as the pair of radiation elements of the dipole antenna. However, this embodiment is not preferable because while the insulative substrate is further miniaturized from that shown in FIG. 1, such an embodiment complicates the impedance matching and increases both the manufacturing costs as well as increases the parts cost as the cost of the second chip-type antenna exceeds that of the meander conductor.

[0020] Practiced in the above-described manner, the invention provides the following advantages.

[0021] Since the antenna structure is not of a monopole but of a half-wave dipole in which a pair of radiation elements is fed at the center of the pair, there the antenna characteristics are not adversely affected by a mother-board-side ground conductor. Since the snaked, band-shaped conductor in “meander” form can be patterned in a relatively narrow region, increase in the size of the insulative substrate can be avoided by arranging the pair of radiation elements so that they generally assume an L-shape, for example, in a plan view. Further, the capacitance of the snaked, band-shaped conductor varies in accordance with its “meandering” pitch, impedance matching can be attained easily. Therefore, a highly practical antenna module can be provided that is highly reliable in that its antenna characteristics are not adversely affected by a mother board while being compact enough to permit it to be mounted on the mother board of an electronic apparatus such as a personal computer.