DE3410730C2 - Directional measuring coupler - Google Patents

Description

The invention relates to a directional coupler in the preamble of Art.

Known directional couplers of this type have a lower limit frequency of their working range due to low frequencies occurring phase errors between those of the voltage on the line pro proportional proportions and the proportion of the current on the line len proportions for the formation of the two measuring voltages. For expansion of the working range towards low frequencies, it is known to additionally to compensate for frequency-dependent compensation elements hen (see e.g. DE 31 19 939 C2).

From US-PS 27 97 387 a directional measuring coupler is known which has a center-tapped current transformer. This current transformer consists of a winding with center tap, so that the coupling between the two current transformer outputs is 1 . This high coupling of the measuring branches means that every load change at one measuring output automatically causes an (unwanted) level change at the other measuring output.

The object of the present invention is the working range of Directional measuring couplers in the preamble of  Specified claim type without special compensation measures to extend to low frequencies.

The achievement of this task is by given the characterizing features of the claim.

The measuring directional coupler according to the invention has a simple Circuit construction one by eliminating the lower limit frequency significantly larger bandwidth than measurement directional coupler from the state of the art. Another advantage with that Measuring directional coupler according to the invention is the decoupling the measuring paths of the two measuring voltages through the separate one Arrangement of the two current transformers.

The invention is still based on the figures illustrated and related to known arrangements set. It shows

Fig. 1 is a schematic diagram

Fig. 2 is an equivalent circuit diagram for the voltage on the line measured voltage proportional share,

Fig. 3 is an equivalent circuit diagram for the current proportional to the measuring voltage on the line portion,

Fig. 4 frequency curves of phases and amplitudes ver different voltages each for a known measuring directional coupler and

Fig. 5 is a schematic diagram,

Fig. 6 is an equivalent circuit diagram for the voltage proportional to the measured voltage line portion,

Fig. 7 is an equivalent circuit diagram for the current proportional to the measuring voltage on the line portion,

Fig. 8 frequency curves of phases and amplitudes of different voltages each for a measurement directional coupler according to the invention.

The line L in Fig. 1 and Fig. 5 is terminated with a generally complex, variable and frequency-dependent resistor Z.

The tapped at the measuring resistors R _V and R _R measuring voltages U _V and U _R are composed of a voltage portion U _u proportional to the voltage U on the line L, which via the resistors R ₁ (and, if necessary, an adjustment network, not shown, for example as in the form of a capacitive voltage divider) is branched off from the line, and a voltage component U _i proportional to the current i on the line L, which is obtained by inductive current conversion, for example by means of toroidal current transformers W surrounding the line ( FIG. 1) or W ₁ and W ₂ ( Fig. 5). The voltage components U _u have the same polarity for both measuring voltages, the voltage components U _{i have} opposite polarities. The measuring voltages U _V and U _R thus result in

U _V = U _u U _i
U _R = U _u - U _i .

Of equivalent circuit diagrams of FIG. 2 and FIG. 3 is easy to see that in the known directional couplers (of FIG. 1), the voltage components U _u (U _UR and U _uV) in amplitude a and its phase angle Ψ to the voltage U independent of frequency are ( Fig. 4A, 4B), while the voltage components U _i (U _iV and U _iR ) have a strong frequency dependence of the amplitude and the phase position with respect to the current i at low frequencies ( Fig. 4B, 4D). Due to the frequency dependence of the amplitude ratio U _i / U _u and the relative phases

a lower limit frequency f _g is determined by a predetermined permissible measurement error.

In contrast, directional measurement couplers according to the invention (FIG. 5) as slightly from the equivalent circuits in Fig. 6 and Fig. 7 shows the clamping voltage components U _u (U _uV and U _{u R)} at the same frequency Dependency with regard to the phase position ( FIG. 8A) and the amplitude ( FIG. 8B), like the voltage components U _i (U _iV and U _iR ). The parameters of the relative phases that were important for the determination of the complex reflection factor were

and the amplitude ratio U _i / U _u ( FIG. 8D) are thus constant even at low frequencies.

Claims (1)

Directional measuring coupler for determining the complex reflection factor of a line terminated with a possibly variable resistance by comparing measuring voltages (U _v , U _R ) which are proportional to the leading or returning waves on the line, these voltages being superimposed by one of the Voltage on the line proportional portion (U _u ) and a portion proportional to the current on the line portion (U _i ) are formed, characterized in that two identical current transformers are arranged separately on the line, each connected to ground and at the other connection give the current on the line proportional portion (U _i ) with mutually opposite polarity to form the measuring voltages.