JPS6331057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave radiometer receiver for remote sensing that obtains electromagnetic waves radiated from an object to be observed and the state, characteristics, or related information of the object.

First, the configuration of a conventional microwave radiometer receiver, which is the basis of the present invention, will be briefly explained.

FIG. 1 is a system block diagram of a conventional total power type microwave radiometer receiver, which is the basis of the present invention. In the figure, 1 is a receiving antenna, 2 is a measurement and calibration switch, and 3 is a
RF/IF circuit, 4 is a square law detector, 5 is a step attenuator, 6 is an integrator, 7 is an A/D converter, 8 is a low temperature noise source for calibration, 9 is a high temperature noise source for calibration 10 is a calibration noise It is a changeover switch.

The electromagnetic waves now received by the receiving antenna 1 pass through the measurement and calibration switch 2 and are transferred to the RF/IF circuit 3.
The signal is frequency-converted and amplified by a square detector 4, and square-law detected by a square-law detector 4. Level adjustment is then performed by step attenuator 5. This step attenuator 5 is an A/D
The output of the converter 7 is fed back to form an AGC circuit. Next, integration is performed via an integrator 6 with a certain time constant. When the integration is completed, A/
The signal is A/D converted by the D converter 7 and output. It also has a calibration low noise source 8 and a calibration high temperature noise source 9 for system calibration, which are switched by a calibration noise source changeover switch 10 and further connected to a measurement and calibration changeover switch 2. Here, during measurement, the noise received by the receiving antenna 1 is connected to the receiver, and during calibration, one of the two noise sources for calibration is connected to the receiver.

Next, an overview of the operation of a conventional total power type microwave radiometer will be briefly explained. Figure 2 shows the A/D versus input noise temperature Ta in the conventional method.
The relationship between converter input voltage Va is shown. Square law detector 4
Since , the input-output relationship is a straight line. First, the high temperature noise source 9 for calibration is connected to the receiver, and the A/D converter input voltage Vo for the noise temperature To is
shall be. This input voltage Vo is always applied to the A/D converter 7.
The AGC circuit operates so that the maximum input voltage is reached, and the step attenuator 5 operates to set the amount of attenuation.
This sets the maximum input voltage of the A/D converter 6, so as to avoid saturation of the A/D converter 7 during measurement. A/ for this input noise temperature To
Let A be the intersection of the D converter input voltage Vo. next
The AGC circuit is opened and the receiver is connected to the low temperature noise source 8 for calibration. Input noise temperature at this time
Let the A/D converter input voltage with respect to Ts be Vs, and let this intersection be point B. These two points A and B are determined and the calibration of the system is completed. Next, connect the receiver to receiving antenna 1
A/D converter input voltage VM at this time
The input noise temperature is determined from the straight line connecting the above two points A and B.
TM is required.

However, in conventional microwave radiometer receivers, as shown in Figure 2, the voltage range of the A/D converter input voltage from Vs to OV is mostly due to noise generated from inside the receiver and is unnecessary for observation. voltage.

The voltage range due to noise components actually generated from the measurement target is from Vs to Vo. Therefore, in a conventional total power type microwave radiometer receiver, most of the input voltage to the A/D converter 7 is unrelated to antenna noise, which further deteriorates the resolution of the A/D converter 7. becomes. In addition, in order to improve the resolution and increase the measurement accuracy, the number of bits of the A/D converter 7 should be increased.
The drawback was that the maximum input voltage of the A/D converter had to be chosen large in order to increase the voltage per 1LSB.

Therefore, in this invention, by newly adding a differential amplifier, a memory circuit, and a D/A converter, the noise generated inside the receiver that is unrelated to the observation noise is removed, and the resolution of the A/D converter is increased. It is designed to eliminate the drawbacks of the conventional method.

FIG. 3 shows a system block diagram of a microwave radiometer receiver according to the present invention. First, the measurement and calibration switch 2 is switched to the calibration noise source side, and the calibration noise source switch 10 is switched to the low temperature noise source 8 side.

At this time, by setting the contents of the memory circuit 11 to O, one input of the differential amplifier 12 is set to O.V.
I'll leave it as that.

Furthermore, since the low-temperature noise source 8 for calibration is connected to the other end of the differential amplifier 12, a corresponding voltage appears, but this voltage is based on the noise level from the low-temperature noise source 8 for calibration and the noise generated inside the receiver. This is due to the sum with the noise. At this time, a voltage proportional to the input voltage appears at the output of the differential amplifier 12, and the A/D
The data is newly stored in the memory circuit 11 via the converter 7. This voltage passes through the D/A converter 13 and enters one input of the differential amplifier 12 again. Next, switch the calibration noise source switch 10 to the calibration high temperature noise source 9.
The AGC consists of a step attenuator 5, an integrator 6, a differential amplifier 12, and an A/D converter 7.
The circuit adjusts the amount of attenuation of the step attenuator 5 so that the output of the differential amplifier 12 becomes the maximum input voltage of the A/D converter 7. After calibrating the system in this way, the measurement and calibration changeover switch 2 is switched to the antenna 1 side and the observation object is observed. A voltage appears after subtracting the noise voltage generated from the noise source. If the temperature of a known low noise source for calibration is corrected at the signal processing stage, an input noise temperature that does not include noise generated inside the receiver can be obtained.

FIG. 4 shows the relationship between input noise temperature and A/D converter input voltage in the method according to the present invention. The method for determining points A and B through calibration is as described above, but the difference from the conventional method is that the differential amplifier output becomes OV when the low temperature noise source 8 for calibration is connected to the receiver. This allows the resolution of the A/D converter 7 to be increased to the maximum. According to this method, the resolution of the conventional A/D converter 7 was Vo-Vs/To-Ts [V/K] (1), but according to the present invention, the resolution is Vo/To-Ts [V/K]. (2) and is improved by Vo/Vo−Vs (3).

As described above, the present invention can improve the resolution of the A/D converter 7 by subtracting unnecessary noise components generated from inside the receiver that are included in the conventional observation noise voltage.

[Brief explanation of the drawing]

Figure 1 is a system block diagram of a conventional total power type microwave radiometer receiver, which is the basis of this invention, and Figure 2 is a diagram showing the relationship of A/D converter input voltage to conventional input noise temperature. ,
FIG. 3 is a system block diagram of a total power type microwave radiometer receiver according to the present invention.
FIG. 4 is a diagram showing the relationship between the input noise temperature and the A/D converter input voltage according to the present invention, in which 1 is a receiving antenna, 2 is a measurement and calibration switch, 3 is an RF/IF circuit, 4 is a square law detector,
5 is a step attenuator, 6 is an integrator, 7 is an A/D converter, 8 is a low temperature noise source for calibration, 9 is a high temperature noise source for calibration, 10 is a calibration switch, 11 is a memory circuit, 12 is a differential The dynamic amplifier 13 is a D/A converter. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. A low noise source for calibration, a high noise source for calibration, a calibration noise source switching switch that switches the output of the low noise source for calibration and the output of the high noise source for calibration, and a calibration noise source switch that switches the output of the low noise source for calibration and the output of the high noise source for calibration, a measurement and calibration switch that switches between the reception output of the reception antenna and the output of the calibration noise source switch;
A frequency conversion/amplification means for inputting the output from the measurement and calibration switch, a step attenuator for adjusting the level of the output of the frequency conversion/amplification means, and an integrator for integrating the output of the step attenuator. It is composed of an A/D converter that converts the output of this integrator into a digital signal and feeds the output back to the step attenuator, the step attenuator, the integrator, and the A/D converter, and the calibration The step attenuator is configured such that when the high temperature noise source for calibration is connected to the frequency conversion/amplification means by the switch, the input voltage of the A/D converter with respect to the noise temperature of the high temperature noise source for calibration becomes the maximum input voltage. and an AGC circuit that adjusts the intersection of the input voltage of the A/D converter with respect to the noise temperature of the high noise source for calibration and the input voltage of the A/D converter with respect to the noise temperature of the low temperature noise source for calibration. and the input voltage of the A/D converter when the receiving antenna is connected to the frequency conversion/amplification means. , a differential amplifier having one input end connected to the output end of the integrator and an output end connected to the input end of the A/D converter; and the low noise source for calibration are connected to the frequency converter. a memory circuit configured to set the other input of the differential amplifier to OV when switched to the amplification means, and newly stores the output of the differential amplifier via the A/D converter; and this memory circuit. A microwave radiometer receiver comprising: a D/A converter that inputs the output of the differential amplifier to the other input terminal of the differential amplifier.