JPH0472901A - Antenna for radio equipment - Google Patents

Abstract

PURPOSE:To realize a small sized antenna suitable for a small sized terminal equipment by providing a feeder between a conductor formed on a ground panel and the ground panel and repeating on/off of a switch short-circuiting a point on the conductor and the ground panel for a prescribed period. CONSTITUTION:An input impedance when viewing from a feeding point 4 toward the antenna is an impedance of an open stub 3b and a loop antenna formed with a ground panel and a strip conductor or line conductor 3a at switch ON. The input impedance at switch OFF is an impedance of the antenna comprising a resistive element 3b and a loop antenna comprising the ground panel and the strip conductor or line conductor 3a. The input impedance is changed continuously from the ON state impedance into the OFF state impedance according to the duty ratio depending on an external control signal 9. Thus, the antenna operated at a broad low frequency band equivalently is realized by using a small sized antenna with a narrow band.

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a small antenna that is applied to a small mobile terminal having a small volume, such as a portable mobile terminal. [Prior Art 1] Conventionally, inverted F-shaped antennas, helical antennas, and the like have been adopted for small terminals having a small volume, such as portable mobile terminals. When antennas are made smaller, their frequency characteristics become narrower, which is a key to further miniaturization of terminals. As a conceptual method to solve this problem, it is known to make the input impedance of a small, narrow-band antenna variable to maintain good matching with free space depending on the frequency band used for communication. In the conventional invention, a conceptual structure is described regarding the principle of varying the input impedance of the antenna by loading an active element in the middle or at the tip of the antenna. 63-294
Publication No. 107 can be mentioned. [Problems to be Solved by the Invention] The above-mentioned prior art does not discuss the specific structure of the antenna system, nor does it quantitatively examine the variable range of input impedance. An object of the present invention is to present a specific structure of an antenna with variable input impedance, and to realize a small antenna applied to a small terminal. Furthermore, conventional technology uses complex and power-consuming elements such as amplifiers and phase shifters as active elements loaded into antennas, but antennas applied to mobile terminals are required to consume as little power as possible. Therefore, it is not necessarily suitable. Another object of the present invention is to provide a variable input impedance antenna that can extremely reduce power consumption due to loading of active elements. Another object of the present invention is to provide a variable input impedance antenna that generates as few harmonics as possible even when the input impedance of the antenna is varied.

[Means to solve the problem]

The above purpose is to form a linear, plate-shaped, or strip-shaped conductor on the ground, provide a power feeding part between the conductor and the ground, and short-circuit the ground with a point on the conductor that is different from the power feeding part. This is achieved by providing a switch and means for repeating the on-off operation of the switch at a constant cycle. In mobile terminals, a portion of the housing serves as a grounding conductor. According to this means, when the antenna is used for transmission, harmonic components are excited in the antenna in addition to the frequency used. This problem is solved by forming a frequency selection plate opposite the ground or the housing, and forming the antenna between them.

[Operation 1] A linear, plate-shaped, or strip-shaped conductor is formed on the ground, a power feeding part is provided between the conductor and the ground, and a switch is installed to short-circuit a point on the conductor different from the power feeding part and the ground. In the provided antenna system, the impedance seen from the feed point, that is, the input impedance, differs between the on and off states of the switch. When the feeding point is excited with a sine-sine wave, the current waveforms of the feeding section corresponding to the two states of the switch, On and Off, have different phases and amplitudes. Therefore, if we consider the on-off of the switch to be one period and make this period equal to the reciprocal of the excitation frequency, that is, the excitation period, and change the duty ratio, a current waveform different from a sine wave with the same period as the excitation period will be obtained at the feeding point. It can be obtained with The reciprocal of the fundamental wave component of this current waveform normalized by the excitation voltage is the input impedance, and the on-state of the switch depends on the duty ratio of the switch. It takes a value that continuously changes between the respective input impedance values corresponding to the two states of ff. In this case, the antenna also radiates second and higher harmonics with respect to the fundamental frequency. In wireless communications, the harmonic components not only cause interference to other wireless devices, but also cause a reduction in the power allocated to the fundamental wave out of the power consumption of the terminal, resulting in a decrease in antenna efficiency. This problem can be solved by making the frequency selection plate formed on the top of the antenna a low-pass type and making the first pass frequency band match the frequency band of the fundamental wave, so that the power of the harmonic components radiated from the antenna is converted to reactive power. , resolved. [Embodiment] An embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a perspective view of an embodiment of a radio antenna according to the present invention, in which a dielectric layer 2 is formed on a grounded ground or a portion 1 of a housing, and a strip is formed on the upper surface of the dielectric layer. Conductors or linear conductors 3a, 3b are formed. The conductor is unbalanced excited with the ground 1 via the coaxial line 6 by the excitation wave source 5 at the power feeding section 4 . A changeover switch 8 is inserted between the strip-like conductors or linear conductors 3a and 3b at an intermediate point 7 that is different from the power feeding section. The changeover switch is repeatedly turned on and off at the same period as the excitation frequency and while maintaining a constant duty ratio, and the duty ratio can be varied by an external control signal 9. According to this embodiment, the input impedance seen from the feed point 4 is the impedance of the ground and the loop antenna formed by the strip or linear conductor 3a and the open stub 3b when the switch is on, and the impedance of the ground and the open stub 3b when the switch is off. This is the impedance of the loop antenna formed by the strip-shaped conductor or linear conductor 3a and the antenna formed by the parasitic element 3b. According to the duty ratio determined by the external control signal 9, the input impedance continuously changes from the on-state impedance to the off-state impedance. - For example, excitation frequency IGHz, dielectric constant dielectric constant 1
, the band characteristics of the antenna having dimensions of 1/30th wavelength in thickness, 172 wavelengths in the 38th conductor part, and 1/10th wavelength in the 3b part will be explained with reference to FIG. Figure 6 shows the variation of the input impedance of the antenna from IGHz to 0.94GHz. The circle in the figure indicates that the signal source impedance is at the excitation frequency IGH.
When the impedance of the antenna at z is equal to the impedance of the antenna, the impedance at the input point satisfies the VSWR of 1.5. The black circles in the figure are values showing the relationship between the excitation frequency and antenna input impedance when the disconnection switch is not operated, and the white circles are the values when the disconnection switch is operated at a duty ratio of 0.7. If the disconnection switch is not operated, the above matching condition cannot be satisfied when the antenna excitation frequency is 0.94 GHz. Operate the switch and set the duty ratio to 0.
．． By setting it to 7, it becomes possible to fully satisfy the above matching condition even at 0°94 GHz. According to the above principle, it is possible to realize an antenna that can equivalently operate in a wide band by using a small antenna whose matching condition changes greatly with respect to the excitation frequency, that is, whose band is narrow. FIG. 3 is a perspective view of another embodiment of the radio antenna according to the present invention, in which a support conductor 10 is attached to the top of the structure shown in FIG.
with the addition of a frequency selective plate consisting of a metal patch supported by a support dielectric 13 and backed by a supporting dielectric 13. According to this embodiment, in order to make the input impedance of the antenna variable, the harmonic components generated when switching the switch 8 while maintaining a constant duty ratio are returned to the antenna side without being radiated into free space and converted into reactive power. It has the effect of Therefore, it is possible to suppress unnecessary radio waves for other wireless devices, and it is also possible to efficiently allocate the power supplied to the antenna to the fundamental wave component, resulting in the effect of improving the efficiency of the antenna. FIG. 4 is a perspective view of another embodiment of the radio antenna according to the present invention, in which instead of the frequency selection plate consisting of a metal grid in the structure shown in FIG. This is a configuration using a dielectric plate 12. According to this embodiment, the fundamental wave component is radiated in phase with the free space due to multiple reflections within the dielectric plate, but the second harmonic component is radiated with opposite phase, so the multiple reflected waves cancel each other out and become ineffective. It will be electrified. In the frequency range of the microwave band and submillimeter wave band, which are generally used for wireless communication, the amount of phase shift of the reflected wave generated at the boundary between the dielectric material and the free space is smaller than 180°, so harmonic components of the third order or higher are generated inside the dielectric layer. The multi-reflected waves cannot reach the co-phase condition, and their power will not be strongly radiated into free space. When a linear conductor that is sufficiently long and thin compared to the wavelength has a dielectric constant of 90, a thickness of 8.35 mm, a distance between the conductor and the ground of 0.635 mm, and an excitation frequency of IGHz, the fundamental wave, second harmonic, and third harmonic are generated. The ratio of far field strength is 1:1゜2X10-3: 1.3X10-2
It is. As described above, the spatial emission of harmonic component power is suppressed, and the efficiency of the antenna is improved as in the embodiment shown in FIG. Furthermore, dielectric materials are lighter than metal grids, making them suitable for use in mobile terminals. FIG. 1 is a perspective view of another embodiment of the radio antenna according to the present invention, in which the dielectric plate in the structure shown in FIG. It is formed in contact with the upper part. This embodiment has the effect of reducing the height of the antenna in the vertical direction relative to the ground or a part of the housing, and is effective in reducing the volume of the antenna. FIG. 5 is a perspective view of another embodiment of the radio antenna according to the present invention, which has an integrated structure in which the dielectric plate has the same dielectric constant as the dielectric layer in the structure shown in FIG. . According to this embodiment, it is possible to form a strip-shaped conductor or a linear conductor buried in a dielectric material, which eliminates the need to closely bond dielectric materials with different dielectric constants, and simplifies antenna production. It has the effect of

【Effect of the invention】

According to the present invention, the input impedance of the antenna can be made variable, and it is possible to compensate for changes in the matching state of the antenna due to changes in the excitation frequency. An antenna that can equivalently operate in a wide band can be realized using a small antenna. Therefore, it is possible to realize a small portable radio device that is convenient to carry. Furthermore, by adding a structure with a frequency selection function formed on the top of the antenna, it is possible to convert the power of harmonic components radiated from the antenna into reactive power by changing the above-mentioned input impedance. An efficient antenna can be realized. Therefore, the power consumption of the portable device can be reduced by employing a high-efficiency antenna, which has the advantage of extending the life of the battery.

[Brief explanation of the drawing]

1, 2, 3, 4, and 5 are all perspective views of a radio antenna according to an embodiment of the present invention, and FIG. 6 is a perspective view of a radio antenna according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the excitation frequency and the locus of impedance change. Explanation of symbols

Claims (1)

[Claims] 1. A linear, plate-shaped, or strip-shaped conductor formed on a grounded ground or a casing, a power feeding part existing between the conductor and the ground or the casing, and the power feeding part It is characterized by comprising a switch that short-circuits a point on a different conductor and a point on the ground or casing, and means for repeating on-off of the switch at a constant period. Antenna for radio equipment. 2. The radio antenna according to claim 1, wherein the switch is inserted in the middle of the linear, plate-shaped conductor or strip conductor, and electrically disconnects the conductor at that part. 3. The radio antenna according to claim 1, wherein the switch is also inserted in the middle of the linear, plate-shaped conductor, or strip conductor, and electrically disconnects the conductor at that part. 4. The antenna for radio equipment according to claim 1, 2 or 3, characterized in that a plurality of the switches are provided. 5. Above the wire, plate conductor or strip conductor (
When viewed from the antenna, the direction opposite to the casing or the ground)
5. The radio antenna according to claim 1, wherein the frequency selection plate made of a conductor is grounded. 6. The antenna for radio equipment according to claim 1, 2, 3 or 4, wherein a semiconductor element such as a transistor is used for the switch. 7. The radio antenna according to claim 5, wherein the frequency selection plate is formed of a grid of linear conductors or strip conductors. 8. The radio antenna according to claim 5, wherein the frequency selection plate is formed of a metal patch arrangement. 9. The radio according to claim 1, 2, 3, or 4, wherein the linear conductor or strip conductor is supported by a first dielectric layer formed on the ground or the casing. aircraft antenna. 10. The radio antenna according to claim 9, further comprising a second dielectric layer above the linear conductor or strip conductor. 11. The radio antenna according to claim 10, wherein the second dielectric layer is in contact with a linear conductor or a strip conductor. 12. The radio antenna according to claim 8, 9 or 10, wherein the thickness of the second dielectric layer, measured in the thickness direction, is smaller than a quarter wavelength of the excitation wavelength. 13. The first dielectric layer and the second dielectric layer have the same dielectric constant, that is, the linear conductor or strip conductor 13. The radio antenna according to claim 12, wherein the radio antenna is embedded in the antenna. 14. The radio antenna according to claim 13, wherein the thickness of the first dielectric layer and the second dielectric layer that are integrated is smaller than a quarter wavelength of the excitation wavelength. 15. The radio antenna according to claim 13 or 14, wherein the linear conductor or strip conductor has an inverted L-shaped antenna shape in a direction perpendicular to the ground or the housing. 16. The radio antenna according to claim 13 or 14, wherein the linear conductor or strip conductor has an inverted F-shaped antenna shape in a direction perpendicular to the ground or the housing. 17. The radio antenna according to claim 15 or 16, wherein the linear conductor or strip conductor has a zigzag shape in a direction horizontal to the ground or the housing. 18. The radio antenna according to claim 15 or 16, wherein the linear conductor or strip conductor has a crank shape in a direction horizontal to the ground or the housing.