Telecommunications – Transmitter – Plural separate transmitters or channels
Reexamination Certificate
1999-02-25
2001-05-15
Maung, May (Department: 2681)
Telecommunications
Transmitter
Plural separate transmitters or channels
C455S126000, C455S562100
Reexamination Certificate
active
06233434
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to a system for transmitting/receiving an electrical signal, and more particularly to a system for transmitting/receiving a signal having a carrier frequency band for a radio base station.
In mobile communication of carrying out the communication utilizing an electromagnetic wave, in order that the limited frequencies may be repeatedly used at high efficiency and also the capacity of subscribers which are accommodated by a system may be increased, there is employed a method, called the cellular method, wherein the range of an electromagnetic wave which has been radiated from one base station is focused by sharpening the directivity of an antenna and the same frequency is spatially reutilized. In the current method, from the demand for miniaturization of the terminals, the information transmission amount which is required by the system, and the spatial attenuation characteristics of an electromagnetic wave, in the cellular mobile communication system, the range of the electromagnetic wave which has been radiated from a base station is in the range of about several km to about 20 km, the used frequency is in the range of several hundreds MHz to several GHz, and the radiation power of one terminal is in the range of several hundreds mW to about several W. Under such circumstances, in order that one base station may support the subscribers of several tens to several hundreds, the mean transmission electric power of several tens W to several hundreds W is required for the output of a transmission power amplifier of the base station. In addition, in order to realize the various communication services, currently, the mobile communication system for which the digital communication method is adopted is the main current. In this case, since the modulation method becomes the phase/amplitude modulation, the high linearity is required for the transmission power amplifier, and since the non-linearity of a semiconductor device used to realize that power amplifier needs to be compensated for, in general, the efficiency of the power amplifier of interest can not be enhanced, and the saturation output of several hundreds W to several kW is required for the power amplifier of interest. Then, it is desirable that the transmission power amplifier of the base station is installed in the vicinity of the associated antenna. If the electric power is supplied from the transmission power amplifier installed adjacent to an indoor base station at more than ten meters above the ground to the antenna which is installed at the height of 100 m, normally, the electric power loss of about 5 to about 6 dB occurs due to the loss of a high frequency cable such as a coaxial cable through which the antenna is connected to the transmission power amplifier. In order to compensate therefor, the output of the transmission power amplifier needs to be increased by about 5 times.
On the other hand, in order that the electromagnetic wave which has been radiated from a base station may be focused within a service area of one base station, the large gain is required for the antenna. In order that the transmission output may be focused within the service area having a diameter of about several m to about 10 km as in the current cellular system, the antenna gain of about 10 dBi to about 16 dBi is required. The gain of the antenna which can be realized by a single element is about 2 dBi, and hence in order to realize the larger gain of 10 dBi to 16 dBi, the technology, for an array antenna, of arranging a plurality of such single elements to increase the gain is required. In order to realize the gain of about 10 to about 16 dBi, the array in which eight to twelve single elements are arranged is required. In addition, in the normal operation of the system, by adjusting the area for which the base station provides the service, i.e., the area within which the electromagnetic wave is focused along with increase or decrease of the number of subscribers, the frequency utilizing efficiency of the overall system is enhanced. For this reason, the main beam of the antenna which is applied to the base station needs to be tilted downwardly and also the function of changing the tile angle is required.
SUMMARY OF THE INVENTION
In order to fulfill the demand for increasing the output power of the above-mentioned transmission power amplifier and the demand for increasing the gain of the antenna, in the prior art, for the former demand, the combining device is employed which utilizes the mode coupling of the electric power as the proximity operation, such as the combining circuit or the combiner for which a plurality of power amplifiers or a plurality of semiconductor amplifying devices used in the power amplifiers are prepared, thereby carrying out the power electric combining. Since a large amount of electric power is concentrated in the small space, and also since the proximity effect is utilized, in terms of necessity of ensuring the isolation between a plurality of input terminals of the combining circuit, those devices bring the loss in the power combining, and since the loss is increasing as increase in the number of combining, the efficiency of the overall power amplifier is degraded. This is a problem. In addition, for the latter demand, since in order to attain the large gain, a plurality of antennas are coupled to one another with the fixed phase relation while maintaining the impedance matching, the line through which the element antennas are coupled is increased, and as a result, the loss is also increased. This is another problem. For example, if the array in which ten element antennas are arranged is taken as an example, since in the normal array antenna, the spacing between the base elements is about 0.5 to about 1.0 wavelength, when ten elements are coupled to one another by the tournament method, the loss for 4 to 5 wavelength is measured for one basic element. In addition, in order to make the beam tilt angle of the antenna variable, the variable phase shifter needs to be inserted between the transmission power amplifier and the antenna. Then, since the output power of the transmission power amplifier is very large, the loss in the phase shifter can not be disregarded.
As described above, in the carrier band power feeding system for the mobile communication base station employing the transmission power amplifier and the array antenna according to the prior art, there arises the problem that the loss which the transmission electric power undergoes is large until the transmission electric power having the large output has been radiated to the space, and hence the efficiency of the carrier band power feeding system is degraded to cause increase in the power consumption.
In the light of the foregoing, the present invention was made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide, in a carrier band power feeding system for a communication base station including transmission power amplifiers and antennas, a system for transmitting/receiving an electrical signal which is capable of reducing the loss in the transmission electric power and the increase in the power consumption until the transmission electric power having the large output has been radiated to the space.
According to one aspect of the present invention, there is provided a system for transmitting/receiving an electrical signal, the system including: a plurality of transmission/reception signal amplifying devices each having a power amplifier, a variable phase shift circuit connected to an input portion of the power amplifier, a power detector connected to an output portion of the power amplifier, and a phase shifting amount table which is constructed on the basis of the characteristics of the power amplifier; a plurality of antennas which are respectively connected to the transmission/reception signal amplifying devices; and a tilt angle control circuit which is connected to the transmission/reception signal
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Maung May
LandOfFree
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