Wave transmission lines and networks – Plural channel systems – Having branched circuits
Patent
1997-02-06
1998-08-04
Gensler, Paul
Wave transmission lines and networks
Plural channel systems
Having branched circuits
333128, H01P 512
Patent
active
057899975
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/ FI96/ 00325 filed May, 31, 1996 which designated the U.S.
BACKGROUND OF THE INVENTION
The invention relates to high-frequency engineering, more exactly to power dividers used in microwave and radio engineering.
On high frequencies, especially in microwave and radio engineering, it is often necessary to split a signal into two or more output ports or to combine several signals into one output port. In some solutions the same switching device has to be used either as a power divider from one input port into two output ports or as a lossless transmission line from one input port into one output port as required at each time. This is conventionally implemented by selection devices, such as bridges, placed on circuit boards. For example, a surface-mounted resistor of zero ohms can operate as a bridging component suitable for industrial mass production. Standard junction lines (also conventionally called bond wires) can also be used.
One generally used passive switching device is a so-called Wilkinson divider. The operation of a standard Wilkinson divider appears from FIG. 1A. The figure shows a situation in which the signal splits from one input port into two output ports. With respect to the present invention, the divider can be used also in the opposite way for combining a signal from two input ports into one output port.
When operating as a power divider, the Wilkinson divider comprises an input port IN, output ports OUTI and OUT2, a T-junction 1, a transmission line 2 connecting the input port IN and the output port OUT1, and a transmission line 3 connecting the input port IN and the output port OUT2. The output ports OUT1 and OUT2 are further connected by a resistor R. The length of the transmission lines is a quarter of wavelength.
The characteristic impedance of the input port IN is Z.sub.0. The characteristic impedances of the output ports OUTI and OUT2 are Z.sub.1 and Z.sub.2, respectively. In a simple case, when Z.sub.0 =Z.sub.1 =Z.sub.2, the characteristic impedance of the transmission lines is Z.sub.0 .sqroot.2 and the impedance of the resistor R is 2Z.sub.0.
In a general case, when Z.sub.0 =Z.sub.1 =Z.sub.2 does not necessarily hold true, the characteristic impedance of the transmission line 2 is .sqroot.2Z.sub.0 Z.sub.1 and, correspondingly, the characteristic impedance of the transmission line 3 is .sqroot.2Z.sub.0 Z.sub.2 The impedance of the resistor R is then 2.sqroot.Z.sub.1 Z.sub.2 .
A known arrangement for transforming the Wilkinson divider into a lossless transmission line is disclosed in FIGS. 1A, 1B, 2A and 2B. The circuit in FIG. 1B comprises a transmission line 5 with respect to FIG. 1A and bridging devices B1 to B5. FIG. 2A shows how the Wilkinson divider thus transformed is transformed into a Wilkinson divider according to FIG. 1A. In this case, the resistor R and the bridges B1, B4 and B5 are installed, but not the bridges B2 and B3. The transmission line 5 has in this case no effect on the operation of the divider.
It is shown in FIG. 2B how the Wilkinson divider is bypassed, that is, transformed into a lossless transmission line. In this case, the resistor R is not installed, nor the bridges B1, B4 and B5. When only the bridges B2 and B3 are installed, the circuit shown in FIG. 2B is a lossless transmission line between the input port IN and the output port OUT1.
A disadvantage of the circuit according to FIG. 1B is e.g., the great number (five in this embodiment) of bridging places operating as selection devices and the great number of installed bridges (three in divider use, two as a transmission path). A further disadvantage of the prior art circuit is that the bridges B2 and B3 required for operating as a transmission path cannot be easily produced with small stray impedances since they combine wide lines. Another disadvantage of the prior art circuit becomes evident when the input port IN and the output ports OUTI and OUT2 are not opposite to one another, especially when the Wilkinson divider is folde
REFERENCES:
patent: 3904990 (1975-09-01), La Rosa
patent: 4616196 (1986-10-01), Sharma
patent: 4901042 (1990-02-01), Terakawa et al.
Gensler Paul
Nokia Telecommunications Oy
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