Wave transmission lines and networks – Plural channel systems – Having branched circuits
Patent
1997-03-03
1998-11-03
Ham, Seunhgsook
Wave transmission lines and networks
Plural channel systems
Having branched circuits
333134, 333202, 333235, H01P 512, H01P 118, H01P 710
Patent
active
058314903
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This application is the national phase of international application PCT/F196/00370 filed Jun. 26 1996 which designated the U.S.
The invention relates to a method for tuning a summing network of a base station. The invention also relates to a connecting means and a band-pass filter.
The invention particularly relates to a summing network of combiner filters of a base station in a cellular radio system. A combiner filter is a narrowband band-pass filter which is in resonance (tuned) precisely at the frequency of the carrier wave of the transmitter connected to it. The adjustment range of band-pass filters is usually 2 to 10% of the center frequency. The signals obtained from the outputs of the combiners are added together by a summing network and fed to the antenna of the base station. A summing network usually comprises a coaxial cable leading to the antenna of the base station, combiner filters being connected to the cable via connecting means and T-branches. In order that a maximum portion of the transmission power of the transmitters would be transferred to the antenna, the summing network must be tuned with respect to the frequency channels used by the transmitters of the base station. In fact, the summing network is tuned only on one frequency, but with movement away from the optimal frequency, the mismatching does not increase very abruptly at first. In the base stations of a cellular radio system, a summing network can thus usually be used at a frequency band the breadth of which is about 1 to 3% of the center frequency of the frequency band.
The tuning of known summing networks is based on the use of transmission lines having an accurate length in proportion to the wavelength. This sets high requirements for cabling of a summing network, since the transmission lines must be of exactly the right length so that the summing network will be optimized to the correct frequency. As automatically (by remote control) adjustable combiner filters have become more general, a need has arisen to find a way of changing the tuning of a summing network in a simple and quick manner. The useful frequency band of a summing network is too narrow to allow major changes in the frequency channels of the transmitters of a base station without that the tuning of the summing network has to be changed. The previously known solution, in which a mechanic goes to the location of a base station and replaces the cabling of a summing network with cabling designed for a new frequency band, is obviously too expensive and time-consuming.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a solution to the above problem. The object is achieved by the method, connecting means and band-pass filter provided by the invention.
The term `generally tubular` here refers to a conductor that has been shaped as a tube and may have apertures, e.g. one or more slits lengthwise of the tube, on its sleeve surface. The tubular conductor may also be at least partly conic.
The invention is based on the idea that by adjusting, in a fixed summing network, the reflection coefficient of the connecting means by which the cabling of the summing network is connected to a filter belonging to the summing network, it is possible to compensate in the summing network for the wavelength error generated at different center frequencies, the error causing a phase angle error between the waves advancing and reflecting in the summing network. In other words, by adjusting the reflection coefficient of the connecting means to accomplish a phase shift, the combined electrical length of the filter and the summing cable connected to the summing point of the summing network can be maintained correct (n.times..lambda./4), whereby the reflecting and the advancing wave are in phase, as seen from the summing point.
With regard to the tuning of a summing network, it is essential that the output port of the filter can be adjusted. With regard to summing, the adjustment of the input port of the filter is not as important. Yet the
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Ahonpaa Timo
Sarkka Veli-Matti
Ham Seunhgsook
Nokia Telecommunications Oy
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