A method for testing a receiver noise figure based on high-precision radiation measurement

Abstract

A kind of receiver noise figure test method based on high-precision radiation measurement, different brightness temperature signals of calibration source output are used to calibrate receiver in real time, and high-precision measurement of receiver noise figure can be realized by calculating equivalent noise temperature.The whole simulates actual brightness temperature scene, and radiation measurement method is more accurate, which improves test precision;Calibration source realizes accurate and stable cold source and heat source based on liquid nitrogen refrigeration and physical heating, has the advantages of high output precision and long stability time, and long-time stability precision can reach 0.1k / 3 days;At the same time, the output brightness temperature of high-precision calibration source is between 90K and 330K, which is closer to actual brightness temperature scene, and can avoid the large non-linear error of receiver caused by the non-linearity of its internal amplifier, greatly improving the test precision.

Description

Technical Field

[0001] This invention belongs to the field of space microwave remote sensing technology, specifically relating to a receiver noise figure testing method based on high-precision radiation measurement. Background Technology

[0002] A microwave radiometer is a passive remote sensing instrument used to measure the microwave radiation energy of an object. It acquires characteristic information of the ground object by receiving its own microwave noise radiation, and then inverts the output data to obtain specific target parameters (mainly brightness temperature), thereby understanding the physical characteristics of the detected target. Essentially, it is a highly sensitive noise receiver. Currently, there are no publicly reported studies on methods for measuring the noise figure of microwave radiometer receivers using radiometric methods.

[0003] Traditionally, the noise figure of a microwave radiometer receiver is tested under laboratory conditions using a noise figure analyzer. The principle of the noise figure analyzer is to use an external noise head to generate hot and cold noise. The hot noise is calculated based on the over-noise ratio (UNR) on the noise head (typically 1000K–10000K), while the cold noise is calculated based on the thermal noise generated by the attenuator inside the noise source (Tc ≥ 273.15 + T0), where T0 represents the ambient temperature of the device. Finally, the receiver noise figure is measured using the Y-factor method. However, because the noise figure analyzer operates in frequency sweep mode, its hot and cold output noise values ​​are selected based on the UNR value of the receiver under test. This means the noise figure measured only represents the value at that specific frequency. When a microwave radiometer system performs ground-based observations, the target scene is a broadband signal. The measurement results from the noise figure analyzer cannot reflect the receiver's noise figure in the actual observed scene. Furthermore, the accuracy of the noise figure measured by the noise figure analyzer is typically 0.1 dB, corresponding to a brightness temperature uncertainty of approximately 4K. More importantly, noise figure analyzers, which measure receiver noise figures, typically utilize thermal and cold temperature noise levels between 290K and 1000K. However, spaceborne microwave radiometer systems observe the intrinsic energy radiation of ground objects, generally between 3K and 350K. When measuring the noise figure of a microwave radiometer receiver using a noise figure analyzer, the receiver's internal amplifier nonlinearity introduces a significant nonlinear error, approximately 0.2dB, corresponding to a brightness temperature of about 8K. In conclusion, noise figure analyzers fall far short of meeting the requirements for microwave radiometer noise figure measurements (generally, the quantitative measurement requirements for microwave radiometers vary depending on the frequency band, ranging from approximately 0.2K to 1K, corresponding to a power accuracy of 0.002dB to 0.01dB).

[0004] The shortcomings of existing receiver noise figure testing methods are as follows: First, the testing accuracy is determined by the noise figure analyzer and can only be controlled at around 0.1 dB, which cannot meet the increasingly demanding application requirements; Second, when the noise figure analyzer uses cold and hot temperature noise (290K~1000K) to measure the receiver noise figure, there is a significant difference from the actual ground object radiation brightness temperature (3K~350K), which will introduce a relatively large nonlinear error; Third, the noise figure analyzer operates in frequency sweep mode, while the scene signal is a broadband signal, which will cause the testing error to be large. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a receiver noise figure testing method based on high-precision radiation measurement, thereby solving the technical problems of insufficient measurement accuracy and large errors in existing methods.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0007] A receiver noise figure testing method based on high-precision radiation measurement specifically includes the following steps:

[0008] S1, Configure the calibration source and data acquisition unit connected to the receiver; switch the calibration source to a cold source to provide cold source noise, and acquire the output brightness temperature T of the cold source noise at the current moment. c and the output response V of the data acquisition unit c Simultaneously, the receiver's current temperature value t is obtained. 01 The calibration source is switched to a heat source to provide heat source noise, and the output brightness temperature T of the heat source noise at the current moment is recorded. h and the output response V of the data acquisition unit h Simultaneously record the receiver's temperature value t at the current moment. 02 ;

[0009] S2, the receiver gain G and equivalent noise temperature T are calculated using equations (1) and (2). r ;

[0010] V h =G·(T) h +T r )

[0011] V c =G·(T) c +T r (1)

[0012] G = (V h -V c ) / (T h -T c )

[0013]

[0014] S3, the noise figure F of the receiver is calculated using equation (3);

[0015]

[0016] Among them, T 01 T is the physical brightness temperature when the calibration source is switched to the cold source. 01 =t 01 +273.15; T 02 T is the physical brightness temperature when the calibration source switches to the heat source. 02 =t 02 +273.15.

[0017] Preferably, the time interval between switching the calibration source from a cold source to a hot source or from a hot source to a cold source does not exceed 1 minute.

[0018] Preferably, the brightness temperature of the calibration source output is between 90K and 330K.

[0019] Preferably, the calibration source in S1 is switched to a cold source, and the output brightness temperature is 90K.

[0020] Preferably, the calibration source in S1 is switched to a heat source, and the output brightness temperature is 330K.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) The receiver noise figure test method based on high-precision radiation measurement of the present invention simulates the actual brightness temperature scenario, and the radiation measurement method is more accurate, which can improve the test accuracy.

[0023] (2) The receiver noise figure test method based on high-precision radiation measurement of the present invention uses a calibration source based on liquid nitrogen cooling and physical heating to achieve a precise and stable cold source and heat source. It has the advantages of high output accuracy and long stabilization time. The long-term stabilization accuracy can reach 0.1k / 3 days. At the same time, the output brightness temperature of the high-precision calibration source is between 90K and 330K, which is closer to the actual brightness temperature scenario. This can avoid the large nonlinear error caused by the nonlinearity of the receiver's internal amplifier, and greatly improve the test accuracy. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 This is a comparison chart of the noise figure test results between the method of this application and existing methods;

[0026] Figure 2This is a comparison chart of the gain test results of the method in this application and existing methods. Detailed Implementation

[0027] The invention is not limited to the specific embodiments described below. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of this invention. Unless otherwise specified, all components and devices in this invention utilize components and devices known in the prior art.

[0028] A microwave radiometer system mainly consists of an antenna, a receiver, and a data acquisition unit. The noise figure of a microwave radiometer system is mainly composed of two parts: one part caused by the antenna and the other part caused by the receiver. Since the antenna is a passive device, its radiation efficiency affects the antenna's noise figure. This can be achieved by measuring the radiation efficiency in an anechoic chamber. The noise figure of a microwave radiometer system is mainly determined by the receiver, and the performance indicators of the receiver are mainly determined by its gain and noise figure. In particular, the noise figure is a key focus for microwave radiometer receivers. This invention proposes a receiver noise figure testing method based on high-precision radiation measurement for microwave radiometer receivers.

[0029] Example

[0030] This embodiment discloses a receiver noise figure testing method based on high-precision radiation measurement, which specifically includes the following steps:

[0031] S1 includes a calibration source and a data acquisition unit connected to the receiver. The input port of the receiver is connected to the calibration source, and the output port of the receiver is connected to the data acquisition unit. It also includes a temperature measuring resistor connected to the receiver, a host computer that transmits the acquired data to the host computer for processing, and a power supply that provides stable power to the receiver and the data acquisition unit.

[0032] In this embodiment, the receiver is an L-band microwave radiometer receiver; the preferred temperature measuring resistor is a PT100 platinum resistance thermometer, which can be directly attached to the corresponding housing of the receiver amplifier; the calibration source is a high-precision Maury MT155J06, which achieves high-precision and stable cold and hot source noise through liquid nitrogen cooling and physical heating; the data acquisition unit is a NI-PX1095, which digitally samples the signal amplified by the receiver, generates a clock signal through a highly stable clock chip, integrates the data in the FPGA, and then transmits it to the host computer at high speed via a serial port protocol to ensure the real-time performance and accuracy of the data.

[0033] Before testing, turn on the above equipment and warm it up for at least 1 hour. Test it after it is working stably.

[0034] The calibration source is switched to a cold source to provide cold source noise, and the output brightness temperature T of the cold source noise at the current moment is obtained. c and the output response V of the data acquisition unit c Simultaneously, the receiver's current temperature value t is obtained. 01 The calibration source is switched to a heat source to provide heat source noise, and the output brightness temperature T of the heat source noise at the current moment is recorded. h and the output response V of the data acquisition unit h Simultaneously record the receiver's temperature value t at the current moment. 02 ;

[0035] In this embodiment, the output brightness temperature of the calibration source is 90K to 330K. When the calibration source is switched to a cold source, the output brightness temperature is 90K, and when the calibration source is switched to a hot source, the output brightness temperature is 330K. It is also ensured that the time interval between switching the calibration source from a cold source to a hot source or from a hot source to a cold source does not exceed 1 minute.

[0036] S2, the receiver gain G and equivalent noise temperature T are calculated using equations (1) and (2). r ;

[0037] V h =G·(T) h +T r )

[0038] V c =G·(T) c +T r (1)

[0039] G = (V h -V c ) / (T h -T c )

[0040]

[0041] S3, the noise figure F of the receiver is calculated using equation (3);

[0042]

[0043] Among them, T 01 T is the physical brightness temperature when the calibration source is switched to the cold source. 01 =t 01 +273.15; T 02 T is the physical brightness temperature when the calibration source switches to the heat source. 02 =t 02 +273.15.

[0044] like Figure 1As shown, the test method disclosed in this application, compared to the frequency sweep test method of a noise figure analyzer, simulates the actual brightness temperature scenario, and the radiation measurement method is more accurate, thus improving test precision. The calibration source in this application achieves precise and stable cold and heat sources based on liquid nitrogen cooling and physical heating, offering advantages such as high output accuracy and long stabilization time, with a long-term stabilization accuracy reaching 0.1K / 3 days. Simultaneously, the high-precision calibration source outputs a brightness temperature between 90K and 330K, more closely resembling the actual brightness temperature scenario, avoiding significant nonlinear errors caused by the receiver's internal amplifier nonlinearity, and greatly improving test precision.

[0045] Meanwhile, gain G, as an important indicator for evaluating receiver performance, can conventionally only be measured using a vector network analyzer. However, the method in this application can also directly measure it, and the results are more accurate. Specifically, as follows... Figure 2 As shown.

[0046] The above embodiments are merely specific application examples of the present invention. In actual operation, adjustments can be made according to the on-site geological conditions, detection requirements, and specific technical equipment to achieve the best detection effect.

[0047] Through the above steps, a novel receiver noise figure testing method based on high-precision radiation measurement has been realized, which effectively solves the problems existing in the prior art and plays a positive role in promoting atmospheric detection and application.

[0048] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0049] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0050] Furthermore, the various implementation methods disclosed in this solution can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content invented by this disclosure.

Claims

1. A method for testing the noise figure of a receiver based on high-precision radiation measurement, characterized in that, Specifically, the steps include the following: S1, Configure the calibration source and data acquisition unit connected to the receiver; The calibration source is switched to a cold source to provide cold source noise, and the output brightness temperature of the cold source noise at the current moment is obtained. and the output response of the data acquisition unit At the same time, the receiver's temperature value is obtained. ; The calibration source is switched to a heat source to provide heat source noise, and the output brightness temperature of the heat source noise at the current moment is recorded. and the output response of the data acquisition unit Simultaneously record the receiver's temperature value at the current moment. ; The calibration source in S1 is switched to a cold source, and the output brightness temperature is 90K. The calibration source in S1 is switched to a heat source, and the output brightness temperature is 330K. S2, the receiver gain is calculated using equations (1) and (2). and equivalent noise temperature ; （1） （2） S3, the noise figure of the receiver is calculated using equation (3). ; （3） in, The physical brightness temperature when the calibration source is switched to the cold source. ; The physical brightness temperature when the calibration source switches to the heat source. ; The time interval between switching the calibration source from a cold source to a hot source or from a hot source to a cold source shall not exceed 1 minute; The brightness temperature of the calibration source is 90K~330K.

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