Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
1999-05-06
2001-04-24
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C333S033000
Reexamination Certificate
active
06222500
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to impedance matching of antenna units, and particularly to matching of antennas in small radio units.
BACKGROUND OF THE INVENTION
Radio units, and especially small radio units for mobile radio communication, are occasionally equipped with small antennas. This means that the center of radiation and the most powerful field of radiation from the antenna and the housing of the radio unit is situated close to the user's ear. In order to get around this problem, it is desirable to lift off the center of radiation some distance from the user's ear.
It is previously known that if a radio unit is supplied with a half-wave dipole antenna, the axis of the field of radiation lies in the middle of the antenna. Consequently, by making the antenna sufficiently long, the field will be moved away from the ear and the intensity of radiation will be considerably reduced near the user's ear and head.
Drawbacks associated with half-wave dipoles and other types of high-impedance fed dipoles are that they are difficult to match in impedance, especially if the intention is that the antenna should cover two or more harmonic bands. If, for example, a half-wave dipole is fed at one of its ends, it requires very high feeding impedances, in the magnitude of 800 ohms. If the dipole is fed at its center part, the feeding impedance is considerably lower, in the magnitude of 70 ohms. With small mobile radio units the antenna is as a rule fed from one of its ends. Simultaneously, the power stage, which is feeding the antenna, is provided with a much lower output impedance, in the magnitude of 50 ohms. To prevent the occurrence of reflections and a low degree of efficiency, the low output impedance of the power stage is to be matched to the high feeding impedance of the antenna. This requires an impedance-matching device be coupled up between the antenna and the power stage. The impedance-matching device may also be called a impedance-adapting device, or shorter, impedance-adapting, impedance-matching or just matching.
Different types of impedance-matching devices are previously known. One previously known type of matching constitutes a transformer with resonant circuits. In principle, a primary part is associated with the output of the power stage and a secondary part, comprising the tuned resonant circuits, with the antenna. The resonant circuits contain a parallel coil and a capacitance. The coil may occasionally be provided with an air core. In one variation of resonant circuits, the core is formed by means of a strip line, which means that a printed board pattern is produced to form the coil. In another variation, the primary winding is omitted and the conductors from the power stage are directly connected to any suitable position on the secondary winding. This solution involves advantages, such as fewer and smaller components which saves space and costs compared to a transformer circuit with both primary and secondary windings. One considerable drawback associated with this solution is its narrow bandwidth.
A further type of impedance-matching involves the use of a helix resonator, which in fact is a filter component, which in extreme cases may function as a tuned oscillation circuit.
In small apparatuses, as for example mobile radio equipment, however, only a small space is offered for an impedance-matching device.
SUMMARY OF THE INVENTION
In order to prevent reflections and a low degree of efficiency, the output impedance of the power stage must be matched to the input impedance of the antenna.
Matching will be needed irrespective of the fact that the power stage/feeding stage is provided with a substantially higher or lower output impedance compared to the input impedance of the input stage. A quotient of the highest and the lowest impedance gives an impedance quotient I. Accordingly, a high impedance quotient means a great difference between the impedances of the input and the output. Previously known impedance-matching devices frequently require a lot of space and/or are complicated in their design. However, in small apparatuses, such as a mobile radio equipment, only a small space is offered for an impedance-matching device.
The present invention offers a solution to an impedance-matching problem, namely impedance-matching of an antenna in a small space with short distances.
Another problem which is solved by the present invention is that sufficient bandwidth is achieved by means of the impedance-matching device.
Still another problem which is solved by the present invention is that an impedance-matching device should be simple and cheap to manufacture.
An object of the invention is to provide an impedance-matching in a strongly limited length and still keep up high demands on precision and bandwidth, and that the invention should be simple and cheap to manufacture.
Briefly, the proposed solution involves matching in several steps by using quarter-wave transformers.
In more detail, the solution is obtained in that quarter-wave transformers are stacked, the dielectric material of which comprises of a material with a dielectric coefficient ∈ exceeding the value of 10.
By this solution of the problems, a number of advantages are achieved. The impedance-matching device may be manufactured sufficiently small, so as to make it possible to mutually integrate the antenna and the matching device—even in the same housing. The device is especially appropriate for use in radio equipment having junctions with a high impedance quotient (I>3) between circuit-/module stage. It will be clear from the following presentation that the impedance-matching device is simple to manufacture, consists of few parts and therefore is also cheap to manufacture. Despite its small dimensions it provides good frequency characteristics, such as good precision, is easy to tune and is provided with a sufficient bandwidth. Designers and manufacturers are spared from the drawbacks of working with circuits and coils, as these circuit elements are difficult to manufacture with precise values and therefore are associated with severe losses.
The invention will now be described in more detail by means of examples of embodiments and with reference to the accompanying drawings.
REFERENCES:
patent: 2438915 (1948-06-01), Hansen
patent: 2518665 (1950-08-01), Collard
patent: 2531437 (1950-11-01), Johnson et al.
patent: 2533239 (1950-12-01), Gent et al.
patent: 2767380 (1956-10-01), Zobel
patent: 3157845 (1964-11-01), White
patent: 3909755 (1975-09-01), Kaunzinger
patent: 4617539 (1986-10-01), O'Shea et al.
patent: 4694264 (1987-09-01), Owens et al.
patent: 5065819 (1991-11-01), Kasevich
patent: 5369367 (1994-11-01), Eisenhart
patent: 5508669 (1996-04-01), Sugawara
patent: 5563615 (1996-10-01), Tay et al.
patent: 5847625 (1998-12-01), Gillette
patent: 0 359 361 A1 (1990-03-01), None
patent: WO 97/30489 (1997-08-01), None
Koitsalu Evald Arvid
Wallin Lars
Dinh Trinh Vo
Jenkens & Gilchrist
Telefonaktiebolaget LM Ericsson (publ)
Wong Don
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