JPH0679048B2 - Digital radiometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital radiometer used for measuring electromagnetic waves ranging from high frequency, microwave to optical frequency band, and particularly to spectroscopic analysis of noise electromagnetic waves naturally emitted from an object. It is intended to improve the stability and functionality of the radiometers that are measured in.

[Conventional technology]

 The circuit configuration of a conventional stabilized radiometer is shown in FIG.

In FIG. 5, reference numeral 1 is an antenna for receiving an electromagnetic wave, and the electromagnetic wave is taken into the device by switching the electronic switch 2a. Reference numeral 2b is an electronic switch that works in conjunction with the electronic switch 2a and switches between the reference noise sources 3a and 3b. The reference temperatures of the reference noise sources 3a and 3b are, for example, T ₁ = 414.7K and T ₂ = 350.2K, respectively. A high frequency amplifier 4 amplifies a high frequency component of the electromagnetic wave captured by the antenna 1. Reference numeral 5 is a local oscillator, and 6 is a frequency mixer.
Signals are mixed, and the intermediate frequency component is amplified by the intermediate frequency amplifier 7 in the next stage. 8 is a bandpass filter (BPF)
In the group, BPF8 ₁ , 8 ₂ with a predetermined frequency difference,
…, 8 _n . An intermediate wave amplifier 9 amplifies the intermediate frequency component of the wave filtered by the BPF group 8. 10 is a square-law detector whose output is fed back by the AGC circuit 11 to adjust the gain of the intermediate frequency amplifier 9. The AGC circuit 11 is a video amplifier 11
It is composed of a, a synchronous detector 11b, an integration and averaging circuit 11c, and a feedback amplifier 11d. 12 is a video amplifier, 13 is a synchronous detector,
14 is an integration and averaging circuit, 15 is a pulse generator, and frequency ₀
Generates a square wave of. 16 is a multiplier, pulse generator 15
Double the frequency of.

Next, the operation principle will be described.

The reference noise sources 3a and 3b and the antenna 1 are controlled by the electronic switches 2a and 2b.
Switch between and to perform measurement. The signal noise temperature T ₃ from the antenna 1 is amplified by the high frequency amplifier 4, mixed with the signal oscillated by the local oscillator 5 by the frequency mixer 6 and converted into an intermediate frequency, and the intermediate frequency component is amplified by the intermediate frequency amplifier 7. The BPF group 8 filters and the intermediate frequency amplifier 9
When amplified by, an output Vd is obtained at the square detector 10. Then, the signal Vs is output via the video amplifier 12, the synchronous detector 13, and the integration / averaging circuit 14. On the other hand, the AGC feedback voltage V _agc (= C ₂ (T ₁ −T ₂ ); where C ₂ is a proportional constant) is output from the feedback amplifier 11d of the AGC circuit 11, which controls the gain of the intermediate frequency amplifier 9. To be done. Thus, the reference noise temperature
Since the difference between T ₁ and T ₂ (T ₁ −T ₂ ) is constant, only the fluctuation of C ₂ due to the gain fluctuation is detected and the influence of the internal noise temperature _Tr is eliminated.

[Problems to be solved by the invention]

Conventionally, this is a Dicke type radiometer that compares and detects the average noise temperature of two reference noise sources and the noise input to be measured. This Dicke type radiometer is characterized by two reference noise sources 3a and 3b. The constant noise temperature difference (T ₁ -T ₂ ) of ( ₁ ) is used to automatically control the gain variation of the intermediate frequency amplifier 9 of the radiometer for stabilization.

However, due to the structure of the apparatus, the above-mentioned conventional example has the following problems.

As described above, the reference noise source 3 is generated by the electronic switches 2a and 2b.
When switching between a and 3b and the antenna 1 for measurement and performing internal noise elimination and control of the amplifier gain, it is necessary to switch the electronic switch at equal time intervals. It depends on the limits of the methods available for analog signal processing. Therefore, the radiometer can measure the signal from the antenna to be measured to 1/3 of the total time, increasing the uncertainty of the measurement. On the other hand, when the above-mentioned gain limitation is not performed, the uncertainty of measurement due to gain fluctuation increases. Analog radiometers have limitations in improving measurement accuracy.

Since two synchronous detectors 13 and 11b and two integrating and averaging circuits 14 and 11c are required, the device becomes large.

When spectroscopic measurement is performed using the Dicke type radiometer shown in Fig. 1, many BPF groups 8 are installed at the location corresponding to the intermediate frequency amplifier section, and the BPF groups 8 are switched by switching means such as switches. However, since it is difficult to keep the characteristics of each BPF group 8 constant, a measurement error occurs.

In the measurement operation, the automatic gain control must be stopped and the BPF group 8 must be switched, and the AGC circuit 11 must be turned on while balancing the circuits, which makes the switching operation very cumbersome when performing continuous measurements. Become.

When performing the spectroscopic measurement using the Dicke type radiometer shown in FIG. 1, when changing the resolution and frequency range of the spectroscopic measurement, the BPF group 8 must be replaced with one that satisfies the frequency range.

The present invention has been made to solve such a problem. First, the input switch is set to an arbitrary unequal time interval, the measurement time of the measured amount T3 is increased, and the conventional drawbacks are eliminated. Also, digital signal processing is used to obtain a measured quantity of T3 from the switch input, which is not possible with analog processing.
Further, it is an object of the present invention to obtain a highly accurate digital radiometer which has a structure in which high accuracy of internal noise correction and gain fluctuation correction can be measured by digital signal processing, and a measurement range and resolution can be arbitrarily set.

[Means for solving problems]

A digital radiometer according to the present invention includes an A / D converter for A / D converting an output signal of a high frequency amplifier, a buffer memory for temporarily storing an output of the A / D converter, and an operation of the A / D converter. A timing command, two reference noise sources, and automatic signal processing means for controlling switching means for switching electromagnetic waves from the measured object are provided.

[Action]

Send the input signal conversion timing command to the A / D converter, and
A digital signal is read from the buffer memory that stores the D / D converted digital signal and temporarily stores it, and simple averaging is performed while eliminating the effect of gain fluctuation of the high frequency amplifier by using the noise temperature difference between two reference noise sources. , Correlation / Fourier transform or Fourier transform / square calculation is performed by the automatic signal processing means to calculate the signal power or the spectrum of the electromagnetic wave.

〔Example〕

FIG. 1 is a block diagram of a digital radiometer showing an embodiment of the present invention, in which 1,2a, 2b, 3a, 3b and 4 are the same as those in FIG. A / D converter for performing D / D conversion, 22 is a buffer memory, and 23 is a signal processing device that constitutes the automatic signal processing means of the present invention, and is configured so that desired signal processing can be programmed. Fourier analysis is performed, and the average power is output as a digital signal by the power spectrum or root mean square calculation. Reference numeral 24 is a D / A converter for D / A converting the output signal calculated by the signal processing device 23, and sends this analog signal to a display unit (not shown). The A / D converter 21 receives the input signal T _S and the reference noise temperature according to the command from the signal processing device 23.
A / D conversion is performed on T ₁ and T ₂ . Reference numeral 25 is a driver for driving the electronic switch 2a, and 26 is a driver for driving the electronic switch 2b.

Next, the operation will be described with reference to the timing chart of FIG.

The input signal T _S from the antenna 1 is amplified by the high frequency amplifier 4, then A / D converted by the A / D converter 21 in accordance with a command from the signal processing device 23, and stored in the buffer memory 22. Then, the signal processing device 23 causes the signal S ₁ (t) in the operation time section 0 ≦ t ≦ T ₀ of the electronic switch 2a and the signal S ₂ (t) in the operation time section T ₀ ≦ t ≦ T ₀ + ΔT of the electronic switch 2b. Is read from the buffer memory 22 and programmed, for example, the following calculation is executed.

First, in FIG. 2 (a), a plurality of signals S ₁ (t) and S ₂ (t) in each cycle T ₀ + 2ΔT are read out, and the root mean square calculation of each of them is performed. To execute. The results correspond to KG (T _s + T _r ) and KG (T ₁ + T _r ), respectively. In addition, the calculation of the following formula (1) that takes the difference between the two is executed.

However, K represents a proportional constant, and G represents the gain of the high frequency amplifier 4.

In the calculation of the equation (1), the signal S _d from which the influence of the fluctuation of the internal noise temperature T _r is removed is output.

The operation time interval ₀ ≦ t ≦ T 0 of the signal S ₁ (t) operation time interval from the data of _{T 0 ≦ t ≦ T 0 +} ΔT signal S ₂ (t) is averaged data And the calculation of the following formula (2) is executed.

Then, the signal S (t) is subjected to a correlation operation and a Fourier transform operation, or a Fourier transform operation and a square operation to obtain a power spectrum φ included in the signal S (t).
() Or the average power of the signal is obtained. The maximum frequency _max and frequency resolution Δ of the obtained power spectrum φ () are _max = 1 / 2Δτ (3) Δ =, where Δτ and T ₀ are the sampling period and measurement time of the A / D converter 21, respectively. 1 / T ₀ (4) The sampling period Δτ and the measurement time T ₀
Can be easily changed by the program.

Further, the operation represented by the following formula (5) is executed. This calculation is performed by switching the electronic switches 2a and 2b to obtain the reference noise temperatures T ₁ and T ₂ input from the two reference noise sources 3a and 3b.
Output signals of S ₂ (t) and S ₃ (t) are read out from the buffer memory respectively, and the root mean square calculation is performed for each of them, K ・ G (T ₁ + T _r ) and K ・ G
To obtain the difference ΔS of (T ₂ + T _r ), However, T ₁ -T ₂ is a constant value of the noise temperature difference between the two reference noise sources 3a and 3b, and K is a proportional constant.

The variation of the gain G of the high frequency amplifier 4 can be obtained by the calculation of the equation (5). Therefore, the signal Sd is divided by this difference ΔS by Sd / ΔS = (T ₁ −T _S ) / (T ₁ −T ₂ ) ... (6), and the gain G of the high frequency amplifier 4 varies. A digital signal Sd / ΔS from which the influence is removed is obtained.
In addition, the power spectrum φ () obtained from the equation (2)
By also performing the operation of dividing by ΔS, the digital signal φ () / ΔS from which the influence of the variation of the gain G of the high frequency amplifier 4 is removed can be obtained.

In addition, the switching timing of the electronic switches 2a and 2b is set to the second
The signal S ₁ (t) to be measured is measured in a short time period by changing as shown in FIG. (B), and the program of the signal processing device 23 can be used to change the operation mode such as enhancing the high-speed response of the measurement. It can be freely selected only by changing it. Even in this case, S once stored in the buffer memory
_The calculation processing method for each of the signals ₁ (t), S ₂ (t) and S ₃ (t) is as follows: Formula (1), Formula (2), Formula (5), Formula (6) It is the same.

Although the antenna 1, the high frequency amplifier 4 and the reference noise sources 3a and 3b are connected through the electronic switches 2a and 2b in the above embodiment, a total power type (see FIG. 3) in which the antenna 1 and the high frequency amplifier 4 are directly connected. (Shown in (a)), a noise injection type (shown in the third (b)) in which the antenna 1 and the high frequency amplifier 4 are connected to the electronic switch 2b to the directional coupler 31 to guide electromagnetic waves,
The electronic switch 2a and the reference noise source 3a may be connected via the variable voltage attenuator 32 to form a zero balance type (shown in FIG. 3C).

In the above embodiment, the case where the output of the high frequency amplifier 4 is directly input to the A / D converter 21 has been described, but as shown in FIG. 4 (a), the high frequency amplifier 4 and the A / D converter 2
A frequency mixer 6 is provided between the frequency converter 1 and 1 to mix the wave of the local oscillator 5 with the input signal, and the intermediate frequency amplifier 7 amplifies the signal for A / D conversion at the intermediate frequency, or FIG. As shown in (b),
The BPF group 8, the intermediate frequency amplifier 9, the square wave detector 10, and the video amplifier 12 may be connected in series with the A / D converter 21 to form a video digital type.

〔The invention's effect〕

As described above, the present invention is an A / D converter for A / D converting the output signal of a high frequency amplifier, a buffer memory for temporarily storing the output of this A / D converter, and an operation of the A / D converter. Since a timing command and a drive signal for switching the switching means are transmitted, an automatic signal processing means for reading out the digital signal stored in the buffer memory and performing signal processing for obtaining a spectrum spectrum or signal power is provided. It has the effects of 1) to 8).

(1) The structure can be simplified as compared with the conventional device, and the size and weight of the device can be reduced.

(2) Since the calculation program can be arbitrarily changed, the measurement range and resolution can be arbitrarily set, and high functionality can be achieved.

(3) The spectral spectrum obtained by the digital signal processing has a high resolution and can measure fine spectral, so that high accuracy can be achieved.

(4) Since internal noise correction and gain fluctuation correction are performed with high accuracy by digital signal processing, the output can be highly stabilized.

(5) Highly stable operation in environments with large changes in ambient temperature (outdoors, outer space).

(6) Targets that require long-term measurement (changes in the global environment, etc.)
It is possible to measure with high accuracy.

(7) The small size and light weight increase the degree of freedom in the installation location of the measuring instrument.

(8) Seismic resistance is improved by digital signal processing.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a digital radiometer showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are timing charts for explaining the operation of FIG. 1, and FIGS.
FIGS. 4 (c), 4 (a), and 4 (b) are diagrams for explaining the essential parts of another embodiment of the present invention, and FIG. 5 is a circuit diagram of a radiometer showing a conventional example. In the figure, 1 is an antenna, 2a and 2b are electronic switches, 3a and 3b are reference noise sources, 4 is a high frequency amplifier, 5 is a local oscillator, 6 is a frequency mixer, 7 and 9 are intermediate frequency amplifiers, and 8 is a BPF group. , 10 is a square-law detector, 11 is an AGC circuit, 12 is a video amplifier, 13 is a synchronous detector, 14 is an integration / averaging circuit, 15 is a pulse generator, 16 is a multiplier, 21 is an A / D converter, 22 Is a buffer memory, 23 is a signal processing device, 24 is a D / A converter, 25 and 26 are drivers, 31 is a directional coupler, and 32 is a voltage variable attenuator.

Claims (1)

[Claims] 1. An electromagnetic wave radiated from an object to be measured and these reference noise sources are switched by a switching means having two reference noise sources, and the influence of internal noise and gain variation of a high frequency amplifier on the electromagnetic waves is said. In a radiometer for measuring the spectral spectrum of the electromagnetic wave or the signal power while removing by utilizing the noise temperature difference between two reference noise sources, an A / D converter for A / D converting the output signal of the high frequency amplifier,
A buffer memory for temporarily storing the output of this A / D converter, an operation timing command for the A / D converter, and a drive signal for switching the switching means at arbitrary unequal intervals are sent and stored in the buffer memory. A digital radiometer, which is provided with an automatic signal processing means for reading out the digital signal and performing signal processing for obtaining the spectral spectrum or signal power.