Wave transmission lines and networks – Miscellaneous – Multipactor applications
Reexamination Certificate
2001-08-29
2003-03-04
Wamsley, Patrick (Department: 2819)
Wave transmission lines and networks
Miscellaneous
Multipactor applications
C505S210000, C331S1070SL
Reexamination Certificate
active
06529092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a superconductor filter for transmitting-receiving signals used in a radio transmitter-receiver apparatus and a radio transmitter-receiver apparatus using a superconductor filter.
2. Description of the Related Art
In, for example, a radio transmitter-receiver apparatus used in a base station for mobile communication, a receiver filter and a transmitter filter are housed as constituents important for selecting a desired frequency band alone. In general, transmitter signals are generated by dividing into at least two channels and are finally synthesized by using a synthesizer so as to be sent from an antenna. In recent years, a frequency around 2 GHz is used in a mobile communication that is rapidly propagated. However, the frequency band assigned to each carrier is only 20 MHz. In order to use the entire frequency band, it is necessary to attenuate at least 40 dB with a width of 1 MHz. It follows that a filter is required to be excellent in attenuation characteristics and to be low in an insertion loss. For obtaining such a filter, required is a resonator element having a high Q-value.
In addition, an individual amplifying system and a collective amplifying system are known to the art as an amplifying system in the transmitter section of a radio transmitter-receiver apparatus that synthesizes signals of at least two carrier frequencies for transmission.
The individual amplifying system is a system in which sets of signal generator, transmitter amplifier and transmitter filter are prepared in accordance with the number of carrier frequencies used, and the signals of the carrier frequencies outputted from each signal generator are individually amplified by the transmitter amplifiers and allowed to pass through the filters, followed by synthesizing signals in a power synthesizer so as to send the synthesized signals.
The collective amplifying system is a system in which signals of a plurality of carrier frequencies outputted from a plurality of signal generators are synthesized in a power synthesizer, followed by. collectively amplifying the synthesized signals in a single transmitter amplifier and subsequently allowing the amplified signals to pass through a filter and, then, sending the filtered signals.
The individual amplifying system is expected in principle to produce various advantages described below over the collective amplifying system.
Specifically, in the collective amplifying system, signals of a plurality of carrier frequencies simultaneously enter a single amplifier, with the result that mutual interference is brought about among the signals of each carrier frequency. What should be noted is that the power of a distorted signal caused by the mutual interference is likely to give adverse influences to the signal of another carrier frequency. In the individual amplifying system, however, only the signal of one carrier frequency enters a single amplifier, with the result that mutual interference is not brought about among the signals of each carrier frequency. Also, in the individual amplifying system, it is possible to prevent interference caused by turning of the signal of another carrier frequency by setting the pass band of the transmitter filter in the bands corresponding to the separate carrier frequencies. As a result, it is possible to power synthesize easily the signals of each channel in a synthesizer.
In general, in an amplifier, modulation distortion is generated when a modulating signal is amplified, with the result that it is possible for power to leak into the adjacent channel so as to bring about interference with the signal of that channel. Such being the situation, the upper limit of the leaking power into the adjacent channel is determined in the specification. For example, in the modulation system in which signal is contained in the amplitude component like QPSK, the modulation system is backed off and operated at a low efficiency so as to ensure a linearity of the amplifier. In this respect, only the signal of one carrier frequency is allowed to pass through the amplifier in the individual amplifying system so as to suppress the leaking power into the adjacent channel caused by the modulation distortion. It follows that it is possible to operate the amplifier at a high efficiency. Since the power consumption of the amplifier occupies a very large proportion in the entire radio transmitting apparatus, the improvement in the efficiency of the amplifier greatly contributes to the power saving of the radio transmitting apparatus.
In the collective amplifying system, it is possible to achieve about 40% of the maximum efficiency when the allowable maximum channels are contained. However, even where the number of channels used is small, required is power substantially equal to that in the case of using all the channels, leading to low power efficiency. In the individual amplifying system, however, it is possible to turn off the power supplies of the amplifiers for the channels that are not used so as to make effective that channels alone which are being used. It follows that it is possible to achieve the power saving.
It should also be noted that, in the collective amplifying system, the heat generation is concentrated on the amplifier so as to make it necessary to take a large-scale measure for the heat dissipation. In the individual amplifying system, however, a plurality of amplifiers forming heat sources are dispersed, making it unnecessary to take a large scale measure for the heat dissipation.
In order to make the synthesizer simple in construction in the individual amplifying system, it is necessary to use a filter satisfactory in selectivity. It should be noted this connection that it is difficult for the filter of the conventional waveguide type (dielectric cavity resonator type) to meet the required selectivity. On the other hand, the linearity of the amplifier is important in the collective amplifying system in order to avoid the mutual interference among the signals. In recent years, the linearity of the amplifier has been improved by various technical improvements. As a result, the collective amplifying system is used nowadays. However, it is desirable to use the individual amplifying system that has various advantages in principle as described above.
Under the circumstances, proposed in, for example, Japanese Patent Disclosure (Kokai) No. 2000-68958 is the idea of using the individual amplifying system, in which is used a filter comprising resonator elements having a high Q value formed thereon by using a superconductor so as to achieve a sharp cut.
It is conceivable to use a bulk and a thin film for utilizing a superconductor as the conductors of the filter, and it is convenient to use a thin film in view of the cooling method and the freedom of design. In particular, it is well known to the art to form a thin film on a substrate material of a very low loss such as sapphire or MgO and to process the thin film into a planar transmission line. A microstrip line structure, a strip line structure and a coplanar structure are used in many cases as the structure of the planar transmission line. These structures are compact and, thus, are advantageous over the filter structure of the conventional waveguide type (dielectric cavity resonator type).
However, the planar transmission line is exposed to the air in the free space, with the result that the transmitter signal is radiated into the free space so as to possibly give rise to the phenomenon that the electromagnetic field tends to leak from the transmission line. Under the circumstances, where a plurality of filters are arranged adjacent to each other, a serious problem is generated that the undesired radiation and the electromagnetic field leaking from the transmission line of one filter are allowed to interfere with the other filter, resulting in failure to obtain a sufficient SN ratio.
In particularly, in the base station of, for example, a cellular phone, both the transmitter signal and the receiver signa
Aiga Fumihiko
Fuke Hiroyuki
Kato Riichi
Kayano Hiroyuki
Terashima Yoshiaki
Kabushiki Kaisha Toshiba
Wamsley Patrick
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