Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-06-11
2001-06-26
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219000
Reexamination Certificate
active
06252475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency circuit element including resonators as basic elements. Prominent examples of such a high-frequency circuit element are filters and duplexers used for high-frequency signal processors in communication systems.
2. Description of the Prior Art
In high-frequency communication systems, high-frequency circuit elements based on resonators, for which filters and duplexers are prominent examples, are indispensable elements. Especially in mobile communication systems, the efficient utilization of frequency bands requires filters with narrow passbands. In base stations for mobile communications systems and communication satellites, there is a great need for filters with low loss, that are small and that can withstand high levels of power.
The majority of high-frequency circuit elements, such as resonator filters that are presently in use includes, for example, elements using dielectric resonators, elements using transmission line structures, and elements using surface acoustic wave elements. Of these, elements using transmission line structures are small and can be used for frequencies up to millimeter waves and microwaves. They are widely used, because they are of two-dimensional structure and formed on a substrate, so that they easily can be combined with other circuits and elements. For these types of resonators, half-wavelength resonators based on transmission lines are most widely used, and high-frequency circuit elements such as filters can be obtained by coupling several half-wavelength resonators together.
Another conventional example is a planar circuit structure. Typical examples of such a structure are (i) chains of circular disk resonators and/or (ii) elements achieving filter characteristics by providing protrusions in a part of the periphery of a circular disk resonator and thereby coupling dipole modes (see for example “Low Loss Multiplexers with Planar Dual Mode HTS Resonators”, by Jerry Fiedziuszko et.al., IEEE Transactions on Microwave Theory and Techniques, Vol. 44, No. 7, pp. 1248-1257; article in IEICE Technical Digest, 1993, Vol. 93, No. 363 (XCE93 47-56) by Yasunari Nagai; “Analysis of Microwave Planar Circuit”, IEICE Technical Digest, 72/8 Vol. 55-B No. 8, Tanroku MIYOSHI and Takanori OKOSHI).
However, in resonators with the transmission line structure using, for example, half-wavelength resonators, high-frequency current concentrates partially in the conductor, so that the losses due to the resistance of the conductor are comparatively large, and the Q factor of the resonator deteriorates, which causes an increase of losses in the case of a filter. Furthermore, in the case of half-wavelength resonators with microstrip transmission line structure that are frequently used, there is the problem of losses due to radiation from the circuit into space.
These factors become even more conspicuous as the structure is miniaturized and the operation frequencies are increased. As resonators with comparatively low losses and high power handling capability, dielectric resonators are used. However, since dielectric resonators have a three-dimensional structure and are relatively large, it is difficult to miniaturize high-frequency circuit elements using them.
Using superconductors, it is possible to reduce losses in the high-frequency circuit element. However, in the above-noted conventional structures, superconductivity is easily lost by excessive current concentrations, and it is difficult to use superconductors for signals with high power. In actual measurements, the largest input power was on the order of 10 mW, which is far from practical levels.
In filters using planar circuit resonators, for which circular disk resonators are prominent examples, the current distribution becomes uniform over a large area, so that they have excellent power handling capability. However, elements where several circular disk resonators are lined up in a row have a very large surface area so that it becomes very difficult to design multistage structures to attain steep skirt. Moreover, in the case of resonator filters using a planar circuit structure with protrusions in a portion of the periphery, there has been, so far, no easy method of designing multistage structures of three or more stages.
Therefore, in order to obtain a two-dimensional high-frequency circuit element that can be matched well with other circuit elements in the microwave and millimeter wave range, using high-performance yet small resonator filters, it is very important to solve the above-noted problems for resonators of transmission line structure or planar circuit structure.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-noted problems of the prior art and provide a high-performance high-frequency circuit element with low losses, good power handling capability, and steep skirt.
In one or more embodiments, a high-frequency circuit element in accordance with the present invention includes n planar circuit resonators, wherein n is an integer greater than one, that are coupled to each other in sequence and each have two orthogonal resonant modes, and a first coupling terminal and a second coupling terminal, wherein the two coupling terminals are coupled to the two resonant modes of a first one of the planar circuit resonators. With a high-frequency circuit element of such a configuration, a resonant coupling type filter can utilize both orthogonal resonant modes of a plurality of planar circuit resonators, so that a multi-stage resonant filter can be obtained, in which the number of resonators has been reduced by half. Moreover, the planar circuit resonator has a more homogenous current distribution and therefore lower transmission losses than conventional transmission line resonators. Thus, a small, low-loss multi-stage resonator filter becomes possible.
In one or more embodiments, the high-frequency circuit element according to the present invention further includes a means for coupling the two resonant modes of an n-th one of the planar circuit resonators.
In one or more embodiments, the planar circuit resonators include a substrate, a strip conductor formed on a surface of the substrate, and a ground plane formed on a rear surface of the substrate. With this configuration, the circuit shape can be determined by the conductive pattern formed on one side of the substrate, which facilitates the design process and the manufacturing process. In this configuration, it is preferable that the shape of the strip conductor is circular or elliptical. With such a configuration, current concentrations in the contour portion of the strip conductor pattern can be reduced effectively, so that it becomes possible to reduce losses even further.
In one or more embodiments, the planar circuit resonators of the high-frequency circuit element according to the present invention include two substrates, a strip conductor sandwiched between the two substrates, and ground planes that are formed on the surfaces of the two substrates that are not in contact with the strip conductor. With this configuration, the influence of radiation of the electric field is negligible, so that a very stable high-frequency circuit element with little loss can be obtained.
Furthermore, in this configuration, it is preferable that the shape of the strip conductor is circular or elliptical.
In one or more embodiments, each planar circuit resonator includes one strip conductor, the n strip conductors are arranged on a line and separated by gap portions, the first coupling terminal is located at a position of the contour of a first one of the n strip conductors located at one end of the n strip conductors, which position is on an opposite side, with respect to a center of the first strip conductor, of a second one of the n strip conductors, which is adjacent to the first strip conductor, and the second coupling terminal is located at a position of the contour of the first one of the n strip conductors, which position shifted substa
Enokihara Akira
Setsune Kentaro
Jones Stephen E.
Matsushita Electric - Industrial Co., Ltd.
Pascal Robert
Rosenthal & Osha L.L.P.
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