Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2001-10-30
2004-01-20
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S7000MS
Reexamination Certificate
active
06680713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna, particularly a compact antenna suitable for inclusion in various devices having capabilities for processing radio signals, including various communication devices that can transmit and receive radio signals.
2. Description of the Related Art
In recent years, there have been increasing uses for antennas that can be used in frequency regions in a range of several hundreds of MHz to several tens of GHz due to increasing demand for various devices having capabilities for transmitting and receiving radio signals, including various communication devices for processing radio signals. Obvious uses for such antennas include mobile communications, next generation traffic management systems, non-contacting type cards for automatic toll collection systems, but in addition, because of the trend toward the use of wireless data handling systems that enable to handle data, without using cumbersome lengthy cables, such as cordless operation of household appliances through the Internet, Intranet radio LAN, Bluetooth and the like, it is anticipated that the use of such antennas will also be widespread in similar fields. Furthermore, such antennas are used in various systems for wireless data handling from various terminals, and the demand is also increasing for applications in telemetering for monitoring information on water pipes, natural gas pipelines and other safety management systems and POS (point-of-sale) terminals in financial systems. Other applications are beginning to emerge over a wide field of commerce including household appliances such as TV that can be made portable by satellite broadcasting as well as vending machines.
To date, such antennas described above used in various devices having capabilities for receiving and transmitting radio signals are mainly monopole antennas attached to the casing of a device. Also known are helical antennas that protrude slightly to the exterior of the casing.
However, in the case of monopole antennas, it is necessary to extend the structure for each use of the device to make the operation cumbersome, and, there is a further problem that the extended portion is susceptible to breaking. Also, in the case of the helical antennas, because a hollow coil that serves as the antenna main body is embedded in a covering material such as polymer resin for protection, the size of device tends to increase if it is mounted on the outside the casing and it is difficult to avoid the problem that the aesthetics suffers. Nevertheless, reducing the size of the antenna leads only to lowering of signal gain, which inevitably leads to increasing the circuit size for processing radio signals to result in significantly higher power consumption and a need for increasing the size of the battery, and ultimately leading back to the problem that the overall size of the device cannot be reduced.
On the other hand, when attempts are made to realize a high gain compact antenna comprised by resonance circuit having an inductance section and a capacitance section to transmit and receive radio waves, it is not sufficient to provide only one resonance section because of insufficient gain produced by such a design, and therefore, it is necessary to combine a plurality of resonance sections to produce one antenna working as a whole. However, if the gain in individual resonance sections is increased, the widths of the characteristic resonance curves become narrow, and a problem arises that it is not possible to resonate all the resonance sections at one frequency in nearly the same phase. Conversely, if the resonance widths are made wider so as to resonate all the resonance section at one frequency in nearly the same phase, it gives rise to a problems that Q values decrease, and consequently, sufficient gain cannot be obtained.
Particularly, when the size of the antenna is made smaller, variations in the inductance and capacitance values tend to increase, causing the individual resonance frequencies to differ to the extent that the widths of the resonance curves hardly superimpose. In practice, it is difficult at the present time to resonate a plurality of resonance sections at one frequency in nearly the same phase while obtaining sufficient gain in individual resonance sections. Even if it is supposed that production is possible with sufficient precision, the productivity inevitably suffers so that there has been a need to develop a new technology to resolve such problems.
SUMMARY OF THE INVENTION
The present invention is provided in view of the background information described above, and an object is to provide a compact antenna that can produce high gain.
The antenna according to the present invention is an antenna comprised by an antenna main body having a plurality of resonance sections connected electrically in series, wherein each resonance section has an inductance section and a capacitance section connected electrically in parallel and resonates at an normal vibration frequency; and the plurality of resonance sections are constructed in such a way that characteristic frequency curves overlap one another at least in the width portion of respective curves so that each resonance section resonates at nearly the same normal vibration frequency, and the antenna main body is constructed so as to have at least one resonance frequency different from the normal vibration frequency of the resonance sections which is produced by coupling of the individual resonance sections.
Furthermore, it is preferable that the resonance frequency is used as a center frequency for transmitting or receiving radio waves for the antenna.
In this case, it is preferable that the center frequency is selected to be higher than the normal vibration frequency.
Especially, it is preferable that the antenna is constructed so that the center frequency is higher than twice the normal vibration frequency.
Therefore, it is preferable that a frequency adjusting capacitance section is connected electrically in series to the antenna main body for adjusting the resonance frequency.
Particularly, it is preferable that the frequency adjusting capacitance section is mounted between the exit end of the antenna main body, which is opposite to the feed end, and a ground section connected to ground potential.
Especially, it is preferable that the ground section is connected electrically from the exit end of the antenna main body to a ground-side of a power line that supplies power to the antenna main body.
According to the present invention, by constructing the antenna in such a way that the antenna main body can resonate at the resonance frequency different from the characteristic individual normal vibration frequencies of the resonance sections, the resonance frequency different from the normal vibration frequency can be selected as the center frequency to be used for radio wave transmission and reception, thereby improving the antenna performance from the viewpoint of releasing the radiative energy from the resonance sections. The reason is that, if the normal vibration frequency itself is chosen as the center frequency, it is thought that a type of energy storage section, in which a current amounting to Q times the current flowing in the antenna main body is flowing, is created in the interior of the resonance sections (acting as a parallel resonance system), to impede the transfer of electromagnetic energy. Therefore, by selecting the center frequency different from the normal vibration frequency, the energy release is facilitated from the capacitance section connected to the inductance section in parallel, thus increasing the antenna gain.
From this viewpoint, the normal vibration frequency at which the resonance section resonates may be higher or lower than the center frequency for reception or transmission of radio waves, but it is preferable that the normal vibration frequency is selected from the low-frequency-side of the center frequency. This is due to the fact that, if the normal vibration frequency is made lower,
Chiba Toshiyuki
Kobayashi Hideki
Sugimura Shiro
Yokoshima Takao
Ho Tan
Mitsubishi Materials Corporation
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