RU2234169C1 - Controllable step attenuator - Google Patents

Abstract

FIELD: microwave technology.

SUBSTANCE: proposed step attenuator designed to vary microwave-signal transfer constant has its input and output formed by parallel connection of two transmission line sections. One of sections has signal attenuation unit connected through diodes to input and output, respectively. Second transmission line section has diode connected at distance of quarter-wavelength relative to input and output that shorts out this section with respect to microwave. Like-polarity connection is used for all diodes of device on dc end. There is also device mode control circuit. In addition diode is inserted in forward path at distance of quarter-wavelength from output and input of device that shorts out the latter.

EFFECT: enlarged operating frequency range of device.

2 cl, 2 dwg

Description

The invention relates to microwave technology, in particular to controlled step attenuators designed to change the transmission coefficient of the microwave signal.

Known attenuator [1], containing several segments of the transmission line with a length of a quarter of the wavelength at the selected average operating frequency. Line segments are included between the output and the input of the microwave signal. Parallel to the input and output terminals of the device, as well as parallel to the segments of the transmission line at their junctions, diodes are included that selectively absorb part of the microwave power passing through the transmission lines. The bias circuit supplies bias currents of various sizes to these diodes in such a way that the microwave impedance of the diodes included at the junction of the segments of the transmission line and the characteristic impedance of the transmission line are within the working attenuation range.

The disadvantages of such an attenuator are:

- a strong temperature dependence of the parameters in the “locking” mode (diodes operate at low currents in the linear section of the current-voltage characteristic);

- complexity of tuning (individual selection of control currents for each of the diodes);

- non-uniformity of the amplitude-frequency characteristic in the “attenuation” mode.

An attenuator is known (adopted as a prototype [2]), consisting of a transmission line with minimal transmission loss (“direct” path) and a transmission line with a given fixed attenuation (“bypass” path). The “direct” path contains a line segment connected to the transmission line using a pair of diodes connected by the same electrodes. The “bypass” path contains a resistive block. One arm of the resistive unit is grounded by microwave, the other two are connected to the transmission line using a pair of diodes connected by the same electrodes and in reverse polarity to the first pair of diodes. By direct current, the device is isolated by capacitors.

A stepwise change in the microwave signal transfer coefficient is achieved by alternately connecting a “direct” path or a “return” path to the input and output devices, changing the polarity of the control voltage and opening or closing the corresponding pair of diodes.

The disadvantages of such devices are:

- additional losses in the diodes connecting the “direct” path;

- insufficient isolation on the “direct” path when the device is in the “attenuation” mode due to the diode's own capacities;

- bipolar control of the operating modes of the device.

The technical result of the invention is as follows:

- reduced transmission loss (loop-through diodes are excluded from the “direct” path);

- high isolation between input and output along the “direct” path in the “locking” mode, which allows to obtain higher values of the required attenuation;

- the possibility of using unipolar power, which simplifies the design of the device.

In the proposed step attenuator, the input and output are formed by parallel connection of two segments of transmission lines. One of the segments contains a signal attenuation unit, connected through diodes to the input and output, respectively. The second segment of the transmission line contains a diode, which is connected at a distance of a quarter of the wavelength with respect to the input and output and shunts the segment along the microwave. All diodes of the device are switched on by direct current in the same polarity. There is also a device mode control circuit.

When no power is supplied, all diodes are in the closed state and the attenuation unit is disconnected from the transmission line. The microwave signal is transmitted along the second segment of the transmission line (direct path) with minimal transmission loss. When current is supplied through the control circuit, all diodes open. In the direct path, the diode shunts a segment of the transmission line, a microwave short circuit occurs, and the signal does not pass along the direct path. Other diodes at this time connect the attenuation unit to the transmission line. The microwave signal passing through the attenuation unit is attenuated to a predetermined value and is output to the device.

To expand the operating frequency range of the device in the "attenuation" mode, a diode is additionally included in the direct path at a distance of a quarter of the wavelength from the output or input of the device and shunting it. All diodes of the device are switched on by direct current in the same polarity.

The invention is illustrated by drawings.

In FIG. 1 shows a diagram of the proposed controlled step attenuator. In a step attenuator, the input and output are formed by parallel connection of two segments of transmission lines. The signal attenuation unit 5 is connected via diodes 4, 6 to the input and output, respectively. Diode 1 is connected through line segments 2, 3 at a quarter-wavelength distance with respect to the input and output. The control signals are supplied through the control circuit 7.

When no power is supplied, all diodes 1, 4, 6 are in the closed state and the attenuation unit 5 is disconnected from the transmission line. The microwave signal is transmitted on a direct path 2, 3 with minimal transmission loss. When a current is supplied through control circuit 7, all diodes 1, 4, 6 open and diode 1 shunts a section of transmission line 2, 3, a microwave short circuit occurs, and the signal does not pass along direct path 2, 3. Diodes 4, 6 at this time connect the attenuation unit 5 to the transmission line. The microwave signal, passing through the attenuation unit 5, is attenuated to a predetermined value and is output to the device.

In FIG. 2 is a diagram of the proposed attenuator according to claim 2. In a direct path 2, 3, 9, an additional diode 8 is included at a distance of a quarter of the wavelength from the output of the device. All diodes 1, 4, 6, 8 of the device are connected by direct current in the same polarity.

The fabricated samples of the proposed attenuator made it possible to reduce losses in the “transmission” mode to 0.5 dB, to achieve uneven amplitude-frequency characteristics in the “attenuation” mode of not more than 0.5 dB with a working bandwidth of at least 25% for a given attenuation of 15 dB in 3 centimeter wavelength range.

Sources of information

1. US patent No. 3859609, MKI H 01 P 1/22, publ. 01/07/1975.

2. US Patent No. 4138637, MKI H 01 P 1/22, publ. 02/06/1979, Fig.5.

Claims (2)

1. A controlled step attenuator, the input and output of which is formed by parallel connection of two segments of transmission lines, one of which contains a signal attenuation unit connected through diodes, and the second contains a diode, characterized in that the diode of the second segment of the line is connected at a quarter wavelength distance with respect to the input and output and shunts the segment along the microwave, and all the diodes of the device are turned on by direct current in the same polarity. 2. The controlled step attenuator according to claim 1, characterized in that a diode is additionally included in the second segment of the transmission line at a quarter of the wavelength from the output or input and shunting it along the microwave, all the diodes of the device are connected in direct current in the same polarity.

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