Dielectric filter, dielectric duplexer, and communication apparatus

1. Field of the Invention

The present invention relates to a dielectric filter for use in microwave bands and the like, a dielectric duplexer, and a communication apparatus using them.

2. Description of the Related Art

Conventional filters for use in microwave bands and the like include a dielectric filter that is formed by providing an inner-conductor-forming opening or inner-conductor-forming openings in a dielectric block to form one resonator or a plurality of resonators, and by providing an outer conductor on outer faces of the dielectric block.

In the conventional dielectric filter using the dielectric block, terminal electrodes coupled by electrostatic capacitance to the inner conductors are provided to perform unbalanced-type input and/or output of signals. Therefore, to feed signals to, for example, a balanced-input/output-type amplifier circuit, a balun (balanced-unbalanced converter) is needed to convert unbalanced-type signals to balanced-type signals. However, the dielectric filter of this type gives rise to problems. Insertion loss because of the balun is large. Also, spacing must be secured for arranging the balun on a circuit substrate, and miniaturization cannot therefore be implemented.

To solve the above-described problems, Japanese Unexamined Patent Application Publication No. 7-254807 discloses a dielectric filter capable of performing balanced-type input and/or output of signals. In this balanced-type dielectric filter, however, to electrically connect an inner conductor to terminal electrodes on an outer face of a dielectric block, openings must be formed perpendicular to an inner-conductor-forming opening. It is very difficult to form the openings perpendicular to the inner-conductor-forming opening in the dielectric block. Therefore, manufacturing costs are increased. In addition, since both balancing characteristics and the degree of external coupling are influenced by the positions of the openings that form the aforementioned connecting conductors, high forming accuracy is required to obtain predetermined characteristics. Also, adjustment after forming is difficult.

The present invention provides a dielectric filter, a dielectric duplexer, and a communication apparatus using them, which allow balanced-type input and/or output of signals to be implemented, and concurrently, allow manufacturing costs to be easily reduced.

According to one aspect of the present invention, a dielectric filter is made by forming a conductor film on a single dielectric material to provide at least two λ/2 resonators that individually have two ends being open-circuited, that resonate at ½-wavelength at a predetermined frequency, and that are coupled together. Terminals are individually coupled by electrostatic capacitance to vicinities of the two open-circuit ends of each of the λ/2 resonators and are used for balanced input and/or output of signals.

According to the above aspect of the invention, without a balun being used, direct connection can be made to a balanced-input/output-type amplifier circuit, since balanced terminals are used to perform input and/or output of signals. Concurrently, either passage or attenuation of a predetermined frequency band can be performed. Therefore, the dielectric filter can be miniaturized, and production costs therefor can be reduced. In this case, since the resonators and the balanced terminals are coupled by the electrostatic capacitance, filter characteristics can easily be adjusted.

Also, according to the above aspect of the invention, each of the two λ/2 resonators may either be formed using a microstrip line or a strip line, or be formed of a dielectric coaxial resonator made by providing the conductor films in and on a dielectric block. In this case, no balun needs to be formed, and a filter for performing balanced input and/or input of signals can be easily formed on a dielectric substrate.

In addition, each of the two λ/2 resonators may be formed of a dielectric coaxial resonator made by providing the conductor films in and on a dielectric block. In this case, despite the dielectric filter being formed of the coaxial resonators, mounting of only the dielectric filter on a mounting substrate or the like allows a circuit for performing balanced input and/or output of signals and a circuit having the filter to be concurrently formed. Therefore, the area occupied on the mounting substrate can be reduced, and the mounting efficiency can be improved.

Furthermore, according to another aspect of the present invention, a dielectric duplexer is formed by providing a transmission filter and a reception filter that have the above-described configuration. In this case, the dielectric duplexer can be used as an antenna-sharing unit that performs balanced input and/or output of transmission signals and/or reception signals. In addition, miniaturization can be implemented for amplifier circuits and the like that perform balanced input and/or output as well as a high-frequency circuit section in the vicinity of the antenna.

According to still another aspect of the present invention, a communication apparatus is formed by using one of the above-described dielectric filters and/or the above-described dielectric duplexer. Therefore, a small and light communication apparatus can be constructed.

Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references indicate like elements and parts.

FIG. 1A is a plan view of a dielectric filter according to a first embodiment;

FIG. 1B is an equivalent circuit diagram of the dielectric filter according to the first embodiment;

FIG. 2A is a perspective view of a dielectric filter according to a second embodiment;

FIG. 2B is a cross-sectional view of the dielectric filter according to the second embodiment;

FIG. 3A is a perspective view of a dielectric filter according to a third embodiment;

FIG. 3B is a cross-sectional view of the dielectric filter according to the third embodiment;

FIG. 3C is an equivalent circuit diagram of the dielectric filter according to the third embodiment;

FIG. 4A is a perspective view of a dielectric duplexer according to a fourth embodiment;

FIG. 4B is a cross-sectional view of the dielectric duplexer according to the fourth embodiment;

FIG. 4C is an equivalent circuit diagram of the dielectric duplexer according to the fourth embodiment; and

FIG. 5 is a block diagram showing a configuration of a communication apparatus according to a fifth embodiment.

Referring to FIGS. 1A and 1B, a description will be given of a configuration of a dielectric filter according to a first embodiment of the present invention.

FIG. 1A is a plan view of the dielectric filter. The individual reference symbols 15 and 16 denote strip line electrodes; 11 , 12 , 13 , and 14 denote terminal electrodes. These electrodes are formed on an upper face of a dielectric substrate 20 . A ground electrode is formed on substantially the entirety of a lower face of the dielectric substrate 20 . The dielectric substrate 20 , the strip line electrodes 15 and 16 , and the ground electrode form individual microstrip-line resonators. Electrostatic capacitance is generated between each of the terminal electrodes 11 and 12 and the vicinity of corresponding ends of the strip line electrode 15 . Similarly, electrostatic capacitance is generated in between each of the terminal electrodes 13 and 14 and the vicinity of corresponding ends of the strip line electrode 16 .

The aforementioned microstrip-line resonators comprising the strip line electrodes 15 and 16 work as two-end-open-circuited λ/2 resonators. The centers of the strip line electrodes 15 and 16 are equivalent to short-circuit points. The widths of the strip line electrodes at the short-circuit points are reduced, and the widths thereof at the open-circuit ends are increased. Thereby, the two resonators with the strip line electrodes 15 and 16 are permitted to couple together by electrostatic capacitance. Also, by forming each of the strip line electrodes in a stepped shape, the line length required to obtain a predetermined resonant frequency is reduced, to obtain overall miniaturization.

FIG. 1B is an equivalent circuit diagram of the dielectric filter shown in FIG. 1 A. In the state shown in the figure, the two resonators having the strip line electrodes 15 and 16 are coupled together by capacitance, and the terminal electrodes 11 to 14 and the two resonators are also coupled by capacitance to each other. The potentials of the two ends of each of the resonators have the relationship of a 180-degree phase difference. Therefore, the terminal electrodes 11 and 12 and the terminal electrodes 13 and 14 can individually serve as balanced input/output terminals. For example, the terminal electrodes 11 and 12 can be used as balanced input terminals, and the terminal electrodes 13 and 14 can be used as balanced output terminals. In this case, the dielectric filter can be used as a two-stage bandpass filter.

As described above, the external coupling between the resonators and the terminal electrodes is by electrostatic capacitance. Therefore, the external coupling can be easily adjusted by adjusting the distances and the areas between the resonators and the terminal electrodes. In addition, since an external terminal is formed in the vicinity of each end of each resonator, symmetry of the electrode patterns can be improved, and stabilized balancing characteristics can thereby be obtained.

In the example shown in FIGS. 1A and 1B, although the adjacent resonators are coupled by capacitance, they may also be coupled by using lumped-parameter elements such as capacitors and inductors. In addition, resonators made of strip lines may be formed by providing the individual electrode patterns shown in FIGS. 1A and 1B on two dielectric substrates.

Hereinbelow, referring to FIGS. 2A and 2B, a description will be given of a configuration of a dielectric filter according to a second embodiment.

FIG. 2A is a perspective view of the dielectric filter, and FIG. 2B is a cross-sectional view taken in a plane extending through the central axes of inner-conductor-forming openings 2 a and 2 b that are shown in FIG. 2 A. The upper face in the state shown in FIG. 2A is a mounting face for mounting on a substrate. In FIGS. 2A and 2B, 1 denotes a dielectric block that is substantially rectangular parallelepiped, and the two inner-conductor-forming openings 2 a and 2 b are provided therein. An outer conductor 3 is provided on four peripheral faces, excluding the faces at the end portions of the inner-conductor-forming openings 2 a and 2 b (four faces). Terminal electrodes 5 , 6 , 7 , and 8 are individually formed to be isolated from the outer conductor 3 . Inner conductors 4 a and 4 b are provided on inner faces of the inner-conductor-forming openings 2 a and 2 b.

In the described construction, the inner conductors 4 a and 4 b individually work as λ/2 resonators that resonate at a half wavelength and that have two ends being open-circuited. The terminal electrodes 5 and 6 are individually coupled by capacitance to the vicinities of open-circuit ends of the inner conductor 4 a on the inner surface of the inner-conductor-forming opening 2 a. Similarly, the terminal electrodes 7 and 8 are individually coupled by capacitance to the vicinities of open-circuit ends of the inner conductor 4 b on the inner surface of the inner-conductor-forming opening 2 b.

An equivalent circuit diagram of the dielectric filter shown in FIGS. 2A and 2B is similar to that shown in FIG. 1 B. The dielectric filter described above is used as a balanced-input/output-type dielectric filter that has characteristics of a two-stage bandpass filter.

As described above, the external coupling between the resonators and the terminal electrodes is made by electrostatic capacitance. Therefore, the external coupling can be easily adjusted by adjusting distances and areas between the resonators and the terminal electrodes. In addition, two pairs of the terminal electrodes, each performing balanced input and/or output, are formed in positions symmetrical both in the direction between the two open-circuited end faces and in the direction between the input and the output of signals. This allows stabilized balancing characteristics to be obtained.

Hereinbelow, referring to FIGS. 3A to 3 C, a description will be given of a configuration of a dielectric filter according to a third embodiment.

FIG. 3A is a perspective view of the dielectric filter. FIG. 3B is a cross-sectional view taken in a plane extending through the central axes of inner-conductor-forming openings 2 a, 2 b, and 2 c that are shown in FIG. 3 A. FIG. 3C is a circuit diagram of the dielectric filter shown in FIGS. 3A and 3B. The upper face in the state shown in FIG. 3A is a mounting face for mounting on a substrate.

In FIGS. 3A and 3B, 1 denotes a dielectric block that is substantially a rectangular parallelepiped and the three inner-conductor-forming openings 2 a, 2 b, and 2 c are provided therein. The inner-conductor-forming opening 2 b is arranged to be substantially half the length of each of the inner-conductor-forming openings 2 a and 2 c, one end thereof is arranged to be an open-circuited end face, and the other end is arranged to be a short-circuit-end face. Opening end portions of the inner-conductor-forming openings 2 a and 2 c are arranged to be open-circuited end faces. An outer conductor 3 is formed on all the outer faces except these open-circuited end faces, and terminal electrodes 5 , 6 , 7 , and 8 are formed so as to be isolated from the outer conductor 3 . Inner conductors 4 a, 4 b, and 4 c are formed on inner faces of the inner-conductor-forming openings 2 a, 2 b and 2 c, respectively.

In the described construction, the inner conductors 4 a and 4 c individually work as λ/2 resonators that resonate at a half wavelength and have two ends open-circuited. In addition, the inner conductor 4 b works as a λ/4 resonator that resonates at 1/4 wavelength and has one end open-circuited and the other end short-circuited. The adjacent resonators are coupled together by capacitance.

As shown in FIG. 3C, the terminal electrodes 5 and 6 are individually coupled by capacitance to the vicinities of the open-circuit ends of the inner conductors 4 a on the inner surface of the inner-conductor-forming opening 2 a. Similarly, the terminal electrodes 7 and 8 are individually coupled by capacitance to the vicinities of the open-circuit ends of the inner conductor 4 c on the inner surface of the inner-conductor-forming opening 2 c. Thus, the above arrangement produces a dielectric filter that has characteristics of a bandpass filter. This dielectric filter uses the terminal electrodes 5 and 6 as balanced input terminals and the terminal electrodes 7 and 8 as balanced output terminals.

In the example shown in FIGS. 3A to 3 C, the outer resonators are arranged to be λ/2 resonators, and the inner resonator is arranged to be a λ/4 resonator. However, the arrangement may be such that, conversely, outer resonators are λ/4 resonators, and an inner resonator is a λ/2 resonator. Also, the number of the resonators may be four or more.

In this way, the arrangement of at least one of the plurality of resonators to be the λ/4 resonator produces an advantage in that the frequency that generates spurious-mode components can be adjusted. Furthermore, it produces an advantage that the spurious-mode frequency can be adjusted to a level (value) that causes no influence on the characteristics of the dielectric filter.

Hereinbelow, referring to FIGS. 4A to 4 C, a description will be given of a configuration of a dielectric duplexer according to a fourth embodiment.

FIG. 4A is a perspective view of the dielectric duplexer. FIG. 4B is a cross-sectional view taken in a plane extending through the central axes of individual inner-conductor-forming openings 2 a to 2 e in the dielectric duplexer. FIG. 4C is a circuit diagram of the dielectric duplexer. The upper face in the state shown in FIG. 4A is a mounting face for mounting on a substrate.

In FIGS. 4A and 4B, 1 denotes a dielectric block that is substantially a rectangular parallelepiped, and the five inner-conductor-forming openings 2 a to 2 e are provided therein. Two end faces of the inner-conductor-forming openings 2 a to 2 e are arranged to be open-circuited end faces. An outer conductor 3 is formed on the four outer faces excluding the open-circuited end faces. Terminal electrodes 5 to 10 are formed on the dielectric block and isolated from the outer conductor 3 . Inner conductors 4 a to 4 e are formed on inner faces of the inner-conductor-forming openings 2 a to 2 e, respectively.

In the described dielectric duplexer, two dielectric filters having similar constructions to those shown in FIGS. 2A and 2B are provided in the single dielectric block 1 , and terminal electrodes 7 and 8 are shared thereby. Specifically, a dielectric filter is configured with two resonators similar to those shown in FIGS. 2A and 2B corresponding to the inner-conductor-forming openings 2 a and 2 b, and another dielectric filter has three resonators corresponding to the inner-conductor-forming openings 2 c, 2 d, and 2 e.

Also, as shown in FIG. 4C, the terminal electrodes 5 and 6 are coupled by capacitance to the vicinity of open-circuited ends of an inner conductor 4 a provided on an inner surface of the inner-conductor-forming opening 2 a. The terminal electrodes 9 and 10 are coupled by capacitance to the vicinity of open-circuited ends of an inner conductor 4 e provided on an inner surface of the inner-conductor-forming opening 2 e. The terminal electrodes 7 and 8 are coupled by capacitance to the vicinity of both open-circuited ends of an inner conductor 4 b provided on an inner surface of the inner-conductor-forming opening 2 b, and open-circuited ends of an inner conductor 4 c provided on an inner surface of the inner conductor 2 c.

The described dielectric duplexer can be used as an antenna-sharing unit that uses the terminal electrodes 5 and 6 as a transmission-signal input port, the terminal electrodes 7 and 8 as an antenna port, and the terminal electrodes 9 and 10 as a reception-signal output port.

Hereinbelow, referring to FIG. 5, a description will be given of a configuration of a communication apparatus using one of the above described dielectric filters or the above dielectric duplexer.

In FIG. 5, ANT denotes a transmission/reception antenna; DPX denotes a duplexer; BPFa, BPFb, and BPFc each denote a bandpass filter; AMPa and AMPb each denote an amplifier circuit; MIXa and MIXb each denote a mixer; OSC denotes an oscillator; and DIV denotes a synthesizer.

The mixer MIXa uses modulation signals to modulate frequency signals outputted from the synthesizer DIV. The bandpass filter BPFa passes the signals only in a transmission-signal band. The amplifier circuit AMPa performs power-amplification of the signals, and transmits them via the antenna ANT via the duplexer DPX. The bypass filter BPFb passes only signals in a reception-signal band out of those outputted from the duplexer DPX, and the amplifier circuit AMPb amplifies them. The mixer MIXb mixes individual frequency signals outputted from the bandpass filter BPFc and reception signals and output mixed signals to intermediate frequency signals IF.

In a case where amplifier circuits AMPa and AMPb shown in FIG. 5 are balanced-input/output-type circuits, a duplexer having the construction as shown in FIG. 4 is used for the portion of the duplexer DPX. Also, for the bandpass filters BPFa and BPFb, dielectric filters of the constructions as shown in FIGS. 1 to 3 are used. In this way, with these balanced-type circuits, since signals can be filtered, and concurrently, can be inputted and/or outputted without a balun being used, a communication apparatus that is small in overall size can be constructed.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is not limited by the specific disclosure herein.