JPS6338137B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave band linear modulator used in PCM communication devices and the like.

A modulator in which the relationship between modulation voltage and output signal voltage is linear as shown in FIG. 1 is called a linear modulator. Such a modulator is used as a modulator in a transmitter of a PCM communication system. This type of linear modulator is used in the PCM communication system because it can reduce the spread of the frequency spectrum of the modulated wave.

FIG. 2 is a graph showing the frequency spectrum of the modulated wave.

In the figure, the solid line indicates the use of a two-phase phase modulator;
This figure shows the frequency spectrum of a modulated wave when microwaves are directly modulated with a pseudo-random pattern wave.

As described above, the spread of the out-of-band spectrum is large, and interference with adjacent channels becomes a problem, and it is necessary to insert a bandpass filter for band limitation to reduce unnecessary waves. On the other hand, a linear modulator has linear input/output characteristics, so the modulated wave can be waveform-processed through a filter before being applied to the linear modulator, and the frequency spectrum of the modulated wave can be expanded by As shown by the dotted line in FIG. 2, there is an advantage that a bandpass filter for limiting the microwave band is not required.

FIG. 3 is a circuit diagram showing the configuration of a conventional linear modulator.

In the figure, 1 is the input terminal, 2 is the output terminal, and 10
is branch line 3dB hybrid, 20,2
0' is a diode, and 30 is a modulation signal terminal.

A microwave signal entering from input terminal 1 enters branch line 3 dB coupler 10 and is modulated by diodes 20, 20'. The diode used is a shotgun barrier diode.

The modulation characteristics are shown in FIG. If used where the modulation voltage is small, it operates as a linear modulator. However, since it is used where the modulation voltage is low, the loss of the microwave signal is large, about 15 dB. In addition, since a shot barrier diode is used as the diode, the maximum modulator input power is low at +10 dBm, and the output power is -5 dBm.
In order to obtain the required output power, it is necessary to increase the number of amplifier stages.

An object of the present invention is to provide a microwave band linear modulator that uses a PIN diode with a high allowable input power and can increase the modulator input power.

In order to achieve the above object, a microwave band linear modulator according to the present invention has a microwave modulator in which two diodes are connected to a coplanar slot conversion section with opposite polarities, and the input signal side of the diodes is connected to the coplanar slot converter. A fixed bias voltage is connected to one of the diodes, and a fixed bias voltage and a modulation signal are applied to the other diode in a superimposed manner.

According to the above configuration, the object of the present invention can be completely achieved.

The modulator according to the present invention will be explained in detail below in comparison with a conventional two-phase modulator for direct microwave modulation.

FIG. 5 is a schematic diagram showing the configuration of a conventional two-phase phase modulator for direct modulation of microwaves.

In the figure, 1 is an input terminal and 2 is an output terminal. 3 is a coplanar line, and 5 is a DC blocking capacitor. 20 and 20' are diodes, respectively.
4 is a slot line.

When the diode 20 in this modulator becomes conductive, an electric field as shown by the arrow in FIG. 6a is formed and a signal is transmitted from the coplanar line to the slot line. The vector of this output signal is designated as vector a in FIG. When diode 20' conducts,
An electric field as shown by the arrow in FIG. 6b is formed, and the electric field is in the opposite direction to that in FIG. 6a, and the signal is transmitted. That is, the phase of the output signal when the diode 20 is conductive is opposite to the phase of the output signal, and is represented by vector b in FIG. The modulation characteristics of this two-phase phase modulator are shown in FIG. 8, and it is clear that it cannot be used as a linear modulator.

The present invention improves nonlinearity by applying a fixed bias to one of the two diodes and applying a modulation signal to the other diode, so that it can be used as a linear modulator. be.

FIG. 9 is a schematic diagram illustrating an embodiment of a modulator according to the invention. Portions common to those explained in FIG. 5 are given the same reference numerals.

1 is an input terminal, 2 is an output terminal, 3 is a coplanar line, 4 is a slot line, 5 is a DC blocking capacitor, 20, 20' are diodes, 30 is a modulation signal terminal, and 40 is a fixed bias terminal. In addition,
PIN diodes are used as the diodes 20, 20'.

The operation of this modulator will be explained with reference to the vector diagram in FIG. Diode 20' has a vector
A fixed bias is applied such that an output signal corresponding to b′ is obtained, and in this state diode 2
A voltage c shown in FIG. 8 is applied to 0. However, since diode 20 is mostly off, the output signal is only vector b'. Also diode 2
When voltage d shown in Figure 8 is added to 0, the output at this time is the composite vector of vector b' and vector a.
becomes a′. That is, if the modulation voltage is used between c and d, it operates as a linear modulator.

The modulation characteristics of this linear modulator are shown in FIG.

As is clear from FIG. 10, it can be seen that linear modulation is realized between c and d.

By using PIN diodes, the input power can be increased by more than 10 times compared to conventional ones. Additionally, the loss of this modulator is about 13 dB, which is lower than conventional modulators.

As described in detail above, the modulator according to the present invention is capable of applying only a fixed bias voltage to one diode, and applying a modulation signal superimposed on the fixed bias voltage to the other diode,
Since each diode is isolated in terms of direct current, a linear modulator can be realized.

Furthermore, since the PIN diode can be used as a linear modulation element, the input power to the modulator can be improved by more than 10 times compared to a conventional linear modulator using a shot barrier diode.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the modulation characteristics of a conventional linear modulator, Fig. 2 is a graph showing the frequency spectrum of a modulated wave, Fig. 3 is a circuit diagram showing a configuration example of a conventional linear modulator, and Fig. 4 is a graph showing the modulation characteristics of a conventional linear modulator, FIG. 5 is a schematic diagram showing the structure of a conventional two-phase phase modulator, and FIG. 6 is an explanatory diagram showing the state of the electric field of the transmission signal in the coplanar slot conversion section. , FIG. 7 is a vector diagram for explaining the operation of the modulator, FIG. 8 is a graph showing the modulation characteristics of the two-phase modulator, FIG. 9 is a schematic diagram showing the structure of the linear modulator according to the present invention, and FIG. FIG. 10 is a graph showing the modulation characteristics of the linear modulator according to the present invention. 1... Input terminal, 2... Output terminal, 3... Coplanar, 4... Slot line, 5... DC blocking capacitor, 10... Branch line 3dB hybrid, 20, 20'... Diode, 30...
Modulation signal terminal, 40...Fixed bias terminal.

Claims (1)

[Claims] 1. In a microwave modulator in which two diodes are connected to a coplanar slot conversion section with opposite polarities, the input signal side of the diodes is separated, a fixed bias voltage is connected to the one diode, and the other diode is connected to a fixed bias voltage. A microwave band linear modulator characterized in that a fixed bias voltage and a modulation signal are applied in a superimposed manner to the diode.