Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-01-28
2001-07-17
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06262682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro-strip antenna for use in a mobile communication apparatus, such as an airborne communication apparatus, a mobile telephone, or a cellular phone.
2. Description of the Related Art
A micro-strip antenna in which a radiation conductor is disposed on one main face of a dielectric substrate, and a ground conductor is disposed on the opposite main face of the substrate is compact, light, and thin. Therefore, such a micro-strip antenna is suitably used as an antenna member for use in a small-sized mobile communication apparatus, such as an airborne communication apparatus, a mobile telephone, or a cellular phone.
As shown in
FIG. 7
, a rectangular micro-strip antenna a includes a dielectric substrate b, a radiation conductor c formed on one main face of the substrate b, and a ground conductor d formed on the opposite main face of the substrate b. A through-hole e is formed in the dielectric substrate b and serves as a feed line to the radiation conductor c. Being energized via the through-hole e (feed point), the radiation conductor c radiates electromagnetic waves from its peripheral open ends. The thus-radiated electromagnetic waves are in the form of, for example, linearly polarized waves.
Reflection characteristics of the micro-strip antenna having the above structure vary greatly with input impedance. If input impedance fails to suitably match a 50&OHgr; feed line, reflection characteristics will be degraded. As a result, the center frequency of a signal to be transmitted or received may deviate from the resonance frequency of the micro-strip antenna, potentially failing to efficiently transmit or receive electromagnetic waves.
For the reasons set forth above, a micro-strip antenna of the kind being considered here must employ means for matching its input impedance to the 50&OHgr; feed line. Such a means is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 62-66703. According to this publication, a dielectric substrate is sandwiched between a radiation conductor b and a ground conductor c. A conductive plate is embedded in the dielectric substrate in parallel with the conductors b and c, and a feed line is electrically connected to the conductive plate and the ground conductor c. The conductive plate serves as a reactance compensation circuit element for changing the input impedance characteristics of the micro-strip antenna so as to suppress reflection characteristics in a predetermined band assigned to mobile communication apparatus and thus enabling implementation of a wide-band micro-strip antenna.
An important disadvantage of the above-described matching means is that the conductive plate must be embedded in the dielectric substrate, so that the resultant structure is relatively complex. As a consequence, fabrication of such micro-strip antennas is also relatively complex and difficult. Further, because the conductive plate is embedded in the dielectric substrate, the conductive plate cannot be adjusted from the outside.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems associated with conventional micro-strip antennas.
To achieve the above object, according to the present invention, a micro-strip antenna is provided comprising: a dielectric substrate; a radiation conductor disposed on one main face of the dielectric substrate; a ground conductor disposed on the opposite main face of the dielectric substrate; and a reactance compensation electrode disposed on a side face of the dielectric substrate and connected to the radiation conductor or the ground conductor. The reactance compensation electrode is adapted to match the input impedance of the micro-strip antenna to a feed line.
The reactance compensation electrode creates or generates an inductance component by itself and generates a capacitance component in cooperation with an opposed conductor, and thus the compensation electrode essentially functions as a reactance compensation circuit element. Varying the length or shape of the reactance compensation electrode varies the reactance component X of input impedance Z (Z=R+jX). Accordingly, through adjustment of the length or shape of the reactance compensation electrode, the input impedance of the micro-strip antenna can be made to match a 50&OHgr; feed line.
Instead of using a single reactance compensation electrode connected to either the radiation conductor or the ground conductor, an advantageous implementation of the invention employs a first reactance compensation electrode connected to the ground conductor and a second reactance compensation electrode connected to the radiation conductor, with electrodes disposed in a mutually opposing manner. In this configuration, stray capacitance is generated between the first and second reactance compensation electrodes, and the input impedance of the micro-strip antenna can be adjusted through modification of the length of either compensation electrode, thus increasing the number of parameters that can be varied in providing the input impedance adjustment, and thereby facilitating fine adjustment of the input impedance.
Preferably, the reactance compensation electrode has the shape of a strip electrode disposed in parallel with the main faces of the dielectric substrate. Through adjustment of the length of the strip electrode, the input impedance of the micro-strip antenna can be readily adjusted. The reactance compensation electrode may be of any other shape so long as the electrode creates or generates an inductance component in association with that shape and a capacitance component in cooperation with a conductor and so long as these components can be varied or changed to adjust the input impedance.
According to the present invention, the reactance compensation electrode serves as a reactance compensation circuit element, as indicated above. Through modification of the length or shape of the reactance compensation electrode, the reactance component of input impedance can be adjusted, and, in particular, the input impedance can be adjusted to match the 50&OHgr;feed line. By virtue of this match, the resonance frequency of the micro-strip antenna is made to equal the center frequency of a signal transmitted through the feed line, thereby improving efficiency in transmission or reception of electromagnetic waves.
Because the input impedance can be matched to the 50&OHgr; feed line through the provision of the reactance compensation electrode having an appropriate length or shape on a side face of the dielectric substrate, the basic micro-strip antenna construction remains the same, i.e., the resultant micro-strip antenna is a simple structure which is easy to fabricate. Since the reactance compensation electrode is formed on the outer surface in an exposed manner, the length of the reactance compensation electrode can be readily adjusted after fabrication of the micro-strip antenna.
Thus, the micro-strip antenna of the invention has a simple structure and excellent operating characteristics, and is optimized for use in a mobile communication apparatus.
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Clinger James
Larson & Taylor PLC
NGK Spark Plug Co. Ltd.
Wong Don
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