Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2002-10-25
2004-09-21
Nguyen, Patricia (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S206000, C333S156000, C333S160000
Reexamination Certificate
active
06794959
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an in-band-flat-group-delay type dielectric filter having a uniform group delay time, which mainly is used in high-frequency radio equipment utilizing a high frequency band and to a linearized amplifier using the same.
BACKGROUND OF THE INVENTION
Recently, many linearized amplifiers have come to be used in base station radio equipment for mobile communication systems to reduce the sizes of base stations.
FIG. 32
is a block diagram showing a feedforward amplifier as a typical example of linearized amplifiers. The feedforward amplifier shown in
FIG. 32
includes delay circuits
321
, directional couplers
322
,
323
, and
325
, a main amplifier
324
, an error amplifier
326
, an input terminal
327
, and an output terminal
328
. Main signals are input from the input terminal
327
and are amplified in the main amplifier
324
. In the signals amplified in the main amplifier
324
, distortion occurs and only distorted components are detected in a carrier cancellation loop. The feedforward amplifier is a circuit in which only the distorted components are eliminated from the signals including the distortion, which has been amplified in the main amplifier
324
, in the distortion cancellation loop, and only signals including no distortion are extracted. The details of its operation are described in “High-Power GaAs FET Amplifiers” by John L. B. Walker (issued by Artech House (Boston, London), see 7.3.2 Linearized Amplifiers). In the carrier cancellation loop and the distortion cancellation loop, in order to allow the group delay times of the two signals divided in the directional coupler
323
to coincide exactly with each other and to synthesize them in the directional coupler
325
, strict and fine adjustment of the group delay times is required for the delay circuits
321
.
Conventionally, in a distortion compensating circuit in a linearized amplifier, for the purpose of adjusting group delay times, a delay device using a coaxial cable such as one with a diameter of about 2 cm and a length of at least 10 m has been used in general.
However, such a delay device is large and has a great insertion loss, which have been disadvantages. The great insertion loss requires the device to have a higher output power, thus causing various problems such as an increase in the size of equipment, a high power consumption, a further complicated configuration relating to radiation, or the like, which have been obstacles to obtaining small base station equipment. Furthermore, it is required to vary the physical length of a cable for carrying out the fine adjustment of the group delay time. Therefore, each time the length is varied, it is necessary to disconnect connectors and to cut the cable, resulting in a poor working efficiency, which has been a problem.
On the other hand, a dielectric filter mainly has been used for removing undesired signals as a bandpass filter or a band stop filter, and particularly, its amplitude transfer characteristics have received attention. Therefore, conventional dielectric filters have low losses, but a deviation in group delay time depending on frequencies is great. For this reason, it has been considered that the conventional dielectric filters cannot be used for delay devices providing uniform group delays. Moreover, it has been hardly intended to flatten both amplitude characteristics and group delay frequency characteristics at the same time. In addition, there has been no example of achieving both the low loss and the reduction in size using a dielectric.
SUMMARY OF THE INVENTION
The present invention is intended to provide an in-band-flat-group-delay type dielectric filter with a small size, a low loss, and uniform-group-delay frequency characteristics.
The present invention also is intended to provide a dielectric filter in which a fine adjustment of a group delay time can be carried out easily.
Furthermore, the present invention is intended to provide a small linearized amplifier using such a dielectric filter.
An in-band-flat-group-delay type dielectric filter according to a first basic configuration of the present invention includes a plurality of dielectric coaxial resonators, a coupling circuit comprising a combination of reactive elements, with which the respective dielectric coaxial resonators are coupled to one another, and input/output terminals connected to ends of the coupling circuit. The dielectric coaxial resonators coupled to the input/output terminals have a different characteristic impedance from that of the other inter-stage dielectric coaxial resonators. According to this configuration, a small filter with a low loss and uniform-group-delay frequency characteristics can be obtained. Therefore, for example, when a cable-type delay device used in a feedforward linearized amplifier or the like is replaced by the filter with the configuration described above, due to a lower loss, a load on the amplifier is reduced and a margin in heat radiation design can be obtained, and at the same time, the size of the amplifier can be reduced. Furthermore, broad-band characteristics can be obtained and thus uniform-group-delay frequency characteristics can be obtained together with the low-loss characteristics with a small amplitude deviation. In the above-mentioned configuration, it is preferred to set the characteristic impedance of the dielectric coaxial resonators coupled to the input/output terminals to be higher than that of the other inter-stage dielectric coaxial resonators.
In the above basic configuration, it is preferable that both deviations in group delay time and in amplitude between the input/output terminals fall within predetermined certain deviation values, respectively, at the center frequency and within a specified frequency band around the center frequency at the same time, and the minimum of the group delay time within a passband is at least one nanosecond.
In the above-mentioned basic configuration, preferably, the dielectric coaxial resonators coupled to the input/output terminals are half-wave dielectric resonators with their both ends opened. According to this configuration, the Q value indicating the performance of the resonators is high, thus obtaining the effects of reducing the size and loss.
In the above-mentioned basic configuration, preferably, the dielectric coaxial resonators coupled to the input/output terminals are quarter-wave dielectric resonators with their one ends short-circuited, and the inter-stage dielectric coaxial resonators are half-wave dielectric resonators with their both ends opened. According to this configuration, a slope parameter can be varied between the input/output stages and the interstages, thus facilitating the manufacture.
In the above-mentioned basic configuration, it is possible to allow the dielectric coaxial resonators coupled to the input/output terminals to have a different characteristic impedance from that of the other inter-stage dielectric coaxial resonators by using dielectric materials with different dielectric constants. According to this configuration, the characteristic impedance can be varied easily, multistage dielectric resonators can be obtained while excellent input/output matching is maintained, the broad-band characteristics can be obtained, and low-loss characteristics with a small amplitude deviation and uniform-group-delay frequency characteristics can be obtained.
The characteristic impedance of the dielectric coaxial resonators coupled to the input/output terminals may be made different from that of the inter-stage dielectric coaxial resonators by making diameter ratios of the dielectric coaxial resonators coupled to the input/output terminals and the inter-stage dielectric coaxial resonators different. According to this configuration, the resonators are allowed to have different characteristic impedances easily. Therefore, even when, for instance, dielectric ceramic materials with the same relative dielectric constant are used, the above-mentioned configuration can be achieved, resulting in an easier manufac
Ishizaki Toshio
Nakamatsu Hiroyuki
Nakamura Toshiaki
Tachibana Minoru
Yamada Toru
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Nguyen Patricia
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