Broadband radio frequency noise high-precision measurement system and method

Abstract

The invention provides a broadband radio frequency noise high-precision measurement system and method, and belongs to the technical field of terahertz detection. The system comprises a matching load module, a radio frequency link, a cold and hot load switching module, a superconducting detector module, an intermediate frequency module, an intelligent driving module, a bias module and a computer, firstly, the equivalent noise temperature of a system is represented for the first time through cold and hot load switching in a low-temperature Dewar; and then, after the radio frequency optical path is introduced, the second characterization of the equivalent noise temperature of the system is realized through cold and hot load switching again. Based on two characterization results, the broadband radio frequency noise temperature of the system can be accurately measured in combination with a noise cascade theory, so that the measurement precision and reliability are improved. The method has the remarkable advantages of high stability, efficient measurement, high precision, expanded application and the like.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz detection technology, and specifically relates to a high-precision measurement system and method for broadband radio frequency noise, which is suitable for noise measurement and optimization of high-sensitivity radio frequency receivers. Background Art

[0002] Superconductor-Insulator-Superconductor (SIS) mixers, with their ultrahigh sensitivity approaching the quantum limit, are widely used in high-resolution detection from millimeter waves to terahertz bands, radio astronomy spectral line observations, and deep-space Doppler remote sensing. In most superheterodyne superconducting SIS mixer receiver systems, equivalent noise temperature (ENT) is a core performance metric that directly determines the system's ability to detect weak cosmic radiation signals.

[0003] Typically, system noise primarily originates from RF noise caused by quasi-optical transmission loss, superconducting SIS mixer noise, and IF noise introduced by the mixer's cascaded IF components. However, despite fully accounting for the mixer's inherent noise and IF link noise contributions, measured RF noise can still be on the high side. During RF noise measurement, RF device loss and optical path characteristics each have varying degrees of impact on RF noise. Accurately evaluating system performance requires precise testing of the system's RF noise to measure the combined impact of RF device loss and optical path characteristics on system performance.

[0004] At present, the main method for measuring RF noise is the RF cross-line method, such as Figure 1 The superconducting SIS mixer receiver RF noise measurement system shown in the figure can be divided into three key components: RF, superconducting SIS mixer and intermediate frequency. The gains of these three components are G RF , G m and G IF , the corresponding noise temperature is T RF 、T m and T IF If a matching load equivalent to T is placed at the front end of the system, the total system power output after cascading is

[0005] Although this method can measure RF noise temperature, it still has certain limitations: (1) The system stability requirement is extremely high: Since the local oscillator power must be adjusted very low, small fluctuations may cause deviations in the measurement results, or even cause instability in the intersection position, thus affecting the final accuracy. (2) Low measurement efficiency: This method requires repeated fine-tuning of the local oscillator power and multiple measurements. The process is cumbersome and time-consuming, and is not suitable for rapid testing needs. (3) Low measurement accuracy: The core assumption of the RF cross-line method is that the mixer noise temperature T mThis assumption is only valid when the mixer gain is low; when the gain is high, the assumption fails and the measurement accuracy deteriorates. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a broadband RF noise high-precision measurement system and method for more accurately and efficiently measuring RF noise, so as to meet the extremely low sensitivity requirements of modern superconducting SIS mixer receivers.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a high-precision measurement system for broadband RF noise, comprising: a matching load module, a RF link, a hot and cold load switching module, a superconducting detector module and an intermediate frequency module connected in sequence, as well as an intelligent driving module, a bias module and a computer; the matching load module is composed of a black body, used to generate an RF signal, and transmit it through the RF link; the hot and cold load switching module realizes switching between three working modes: hot black body, cold black body and no load through the intelligent driving module; the local oscillator signal source is used to provide a local oscillator signal, and the local oscillator signal and the RF signal are transmitted to the superconducting detector module for mixing. The superconducting detector module is designed based on superconducting tunnel junction technology, and the intermediate frequency signal generated during the mixing process is transmitted to the intermediate frequency module for amplification and acquisition; the computer exchanges data with the bias module, the intermediate frequency module and the intelligent driving module, and the bias module acts on the superconducting detector module.

[0009] Optionally, the bias module includes a bias circuit and a bias power supply, the bias circuit is used to provide a DC bias and an output path of an intermediate frequency signal to the superconducting detector module, and the bias power supply is used to stabilize the bias operating point of the superconducting detector module.

[0010] Optionally, the intermediate frequency module includes an amplifier and a spectrum analyzer, and the intermediate frequency signal is amplified by the amplifier and then collected by the spectrum analyzer.

[0011] In a second aspect, the present invention provides a method for high-precision measurement of broadband radio frequency noise, which is performed using the high-precision measurement system for broadband radio frequency noise described in the first aspect, comprising the following steps:

[0012] Step 1: Use the bias module to scan the DC characteristic IV curve of the superconducting detector module and set the bias voltage point;

[0013] Step 2: Turn on the local oscillator signal source and set the parameters so that the current of the superconducting detector module is pumped to a certain height;

[0014] Step 3: Calculate the equivalent radiation temperature based on the physical temperature of the cold black body and the physical temperature of the hot black body;

[0015] Step 4: Collect the intermediate frequency output power under the equivalent radiation temperature conditions of the hot blackbody physical temperature and the cold blackbody physical temperature respectively to characterize the equivalent noise temperature of the system;

[0016] Step 5: Introduce the RF optical path and collect the intermediate frequency output power under the equivalent radiation temperature conditions of the hot blackbody physical temperature and the cold blackbody physical temperature respectively to characterize the equivalent noise temperature of the system after the introduction of the RF optical path;

[0017] Step 6: Based on the characterization results of steps 4 and 5 and combined with the noise cascade theory, calculate the RF gain and corresponding RF noise temperature of the RF link.

[0018] Optionally, in step 3, the equivalent radiation temperature T C-W The calculation formula is:

[0019]

[0020] Among them, T is the physical temperature, h is Planck constant, f is the frequency, k is the B is the Boltzmann constant.

[0021] Optionally, step 4 specifically includes:

[0022] The temperature of a hot black body is T h The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected h :

[0023]

[0024] Among them, k B is the Boltzmann constant, Δf is the test bandwidth, G is the equivalent gain of the system, T rrx is the equivalent noise temperature of the system;

[0025] Use the hot and cold load switching module to switch to the cold black body. When the physical temperature of the cold black body is T c The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected c :

[0026]

[0027] Define Y = P h / P c , using the Y factor method, the equivalent noise temperature T of the system is obtained rx :

[0028]

[0029] Optionally, step 5 specifically includes:

[0030] Introducing the radio frequency optical path, when the physical temperature of the thermal black body is T h1 The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected h1 :

[0031]

[0032] Among them, T rx1 is the equivalent noise temperature of the system after the RF optical path is introduced;

[0033] Use the hot and cold load switching module to switch to the cold black body. When the physical temperature of the cold black body is T c1 The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected c1 :

[0034]

[0035] definition Using the Y factor method, the equivalent noise temperature T of the system after the RF optical path is introduced is obtained. rx1 :

[0036]

[0037] Optionally, in step 6, the RF gain G of the RF link RF for:

[0038]

[0039] The corresponding RF noise temperature is:

[0040]

[0041] The beneficial effects of the present invention are:

[0042] (1) High stability: This invention overcomes the problem of system susceptibility to interference under low local oscillator power conditions and breaks through the traditional method's reliance on extremely high system stability;

[0043] (2) Efficient measurement: The present invention reduces the number of steps, shortens the test time, and improves the convenience of the test process;

[0044] (3) High precision: The present invention does not rely on the specific value of the mixer gain and can maintain good measurement accuracy even under high gain conditions, thus having wider applicability;

[0045] (4) Expanded application: Based on the existing system, the present invention can also accurately measure the gain and RF noise of external RF components, expanding the application range of the system while having the advantages of simplicity, high efficiency, and stability.

[0046] The present invention is of great value for the design and performance improvement of high-performance terahertz receiving systems, and can be widely used in cutting-edge fields such as radio frequency noise characterization and low-noise receiver optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of a prior art superconducting SIS mixer receiver radio frequency noise measurement system.

[0048] Figure 2 It is a schematic diagram of the broadband radio frequency noise high-precision measurement system of the present invention.

[0049] Figure 3 It is an equivalent schematic diagram of the superconducting SIS mixer receiver of the present invention. DETAILED DESCRIPTION

[0050] The present invention will now be described in further detail with reference to the accompanying drawings.

[0051] Example 1

[0052] This embodiment proposes a high-precision measurement system for broadband radio frequency noise. Figure 2 The system mainly consists of a hot and cold load switching module, an intelligent drive module, a matching load module, a radio frequency link, a local oscillator signal source, a superconducting detector module, a bias module, an intermediate frequency module, and a computer.

[0053] The hot and cold load switching module has three operating modes: hot blackbody radiation signal, cold blackbody radiation signal, and no load. Mode switching is achieved through an intelligent driver module, and the Y-factor method is used to perform a first characterization of the system's noise temperature. The intelligent driver module controls the hot and cold load switching module's operating state switching and collects blackbody temperature data in real time. The matched load module, consisting of a room-temperature or low-temperature blackbody, generates an RF signal for a second characterization of the system's equivalent noise temperature. The RF link, consisting of one or more RF devices, achieves efficient signal transmission by constructing a transmission path that conforms to Gaussian optical properties. The local oscillator signal source provides an excitation signal with adjustable base frequency and power to meet the coupling power requirements of the detector in the superconducting detector module. The superconducting detector module (i.e., the superconducting SIS mixer) is designed based on superconducting tunnel junction technology and is specifically designed for weak signal detection. The bias module consists of a superconducting SIS mixer bias circuit and a precision bias power supply. The intermediate frequency (IF) module includes a low-noise preamplifier, a room-temperature IF amplifier, and a spectrum analyzer, enabling IF signal amplification and spectrum detection and analysis. The computer exchanges data with the intelligent drive module, bias module and intermediate frequency module through standard communication methods to realize automatic operation of the system.

[0054] The basic working principle of the system: The local oscillator signal and the radio frequency signal are synthesized and transmitted to the superconducting detector module. The intermediate frequency signal generated during the mixing process is first amplified by a low-noise preamplifier. Subsequently, the amplified intermediate frequency signal is transmitted to a room-temperature intermediate frequency amplifier for further amplification and finally collected and read by a spectrum analyzer.

[0055] Example 2

[0056] Based on the measurement system proposed in Example 1, this embodiment proposes a high-precision measurement method for broadband radio frequency noise, including the following steps:

[0057] Step 1: Using the bias module, the computer program automatically scans the DC characteristic IV curve of the superconducting SIS mixer and sets the appropriate superconducting SIS mixer bias voltage point.

[0058] Step 2: Turn on the local oscillator signal source and set the output frequency, power and other parameters to pump the current of the superconducting SIS mixer to a certain level.

[0059] Step 3: Calculate the equivalent radiation temperature T C-W Taking the physical temperature of hot and cold black bodies as the benchmark, and according to the Callen-Welton black body equivalent radiation formula, the equivalent radiation temperature T is derived. C-W :

[0060]

[0061] Among them, T is the physical temperature, h is Planck constant, f is the frequency, k is the B is the Boltzmann constant.

[0062] Step 4: First characterization of the equivalent noise temperature T of the cryogenic dewar system rx ; The equivalent schematic diagram of the superconducting SIS mixer receiver is as follows Figure 3 As shown, in this pumping state, the physical temperature of the thermal black body is T h The equivalent radiation temperature Under these conditions, the corresponding intermediate frequency output power P is collected. h :

[0063]

[0064] Then, the hot and cold load switching module is used to switch to the cold black body. When the physical temperature of the cold black body is T c The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected c :

[0065]

[0066] Where Δf is the test bandwidth and P is the equivalent gain of the measurement system. The power ratio of the blackbody heat load at room temperature to the blackbody cold load at low temperature is defined as the Y factor (i.e. Y = P h / P c ), using the Y factor method, the equivalent noise temperature T of the system is obtained rx :

[0067]

[0068] Step 5: Second characterization of the system equivalent noise temperature T after the introduction of the RF optical path rx1 After the introduction of the radio frequency optical path, under the same setting conditions, first the thermal blackbody physical temperature is T h1 The equivalent radiation temperature Under these conditions, the corresponding intermediate frequency output power P is collected. h1 :

[0069]

[0070] Then, at a cold blackbody physical temperature of T c1 The equivalent radiation temperature Under these conditions, the corresponding intermediate frequency output power P is collected. c1 :

[0071]

[0072] Using the same Y factor method as in step 4 (i.e. ), and the equivalent noise temperature T of the system under this condition is obtained rx1 :

[0073]

[0074] Step 6: Based on the two characterization results and combined with the noise cascade theory, calculate the RF gain G RF ; For an equivalent radiation temperature of The RF gain is G RF For the system, based on the above two characterization results and combined with the noise cascade theory, that is:

[0075]

[0076] Get the gain G of the RF link RF :

[0077]

[0078] Further obtain the RF noise temperature T RF for:

[0079]

[0080] This embodiment can also accurately measure the gain of an external radio frequency component by using this method on an existing system, and has the advantages of simplicity, high efficiency, and stability.

[0081] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A high-precision broadband radio frequency noise measurement system, characterized in that: include: The matched load module, radio frequency link, hot and cold load switching module, superconducting detector module and intermediate frequency module, as well as the intelligent driving module, bias module and computer are connected in sequence; the matched load module is composed of a black body, used to generate radio frequency signals and transmit them through the radio frequency link; the hot and cold load switching module realizes the switching of three working modes: hot black body, cold black body and no load through the intelligent driving module; the local oscillator signal source is used to provide a local oscillator signal, and the local oscillator signal and the radio frequency signal are transmitted to the superconducting detector module for mixing. The superconducting detector module is designed based on superconducting tunnel junction technology, and the intermediate frequency signal generated during the mixing process is transmitted to the intermediate frequency module for amplification and collection; the computer exchanges data with the bias module, intermediate frequency module and intelligent driving module, and the bias module acts on the superconducting detector module.

2. A broadband radio frequency noise high-precision measurement system according to claim 1, characterized in that: The bias module includes a bias circuit and a bias power supply. The bias circuit is used to provide a DC bias and an output path of an intermediate frequency signal to the superconducting detector module. The bias power supply is used to stabilize the bias operating point of the superconducting detector module.

3. The high-precision broadband radio frequency noise measurement system according to claim 1, wherein: The intermediate frequency module includes an amplifier and a spectrum analyzer. The intermediate frequency signal is amplified by the amplifier and then collected by the spectrum analyzer.

4. A method for high-precision measurement of broadband radio frequency noise, comprising: The steps include: Step 1: Use the bias module to scan the DC characteristic IV curve of the superconducting detector module and set the bias voltage point; Step 2: Turn on the local oscillator signal source and set the parameters so that the current of the superconducting detector module is pumped to a certain height; Step 3: Calculate the equivalent radiation temperature based on the physical temperature of the cold black body and the physical temperature of the hot black body; Step 4: Collect the intermediate frequency output power under the equivalent radiation temperature conditions of the hot blackbody physical temperature and the cold blackbody physical temperature respectively to characterize the equivalent noise temperature of the system; Step 5: Introduce the RF optical path and collect the intermediate frequency output power under the equivalent radiation temperature conditions of the hot blackbody physical temperature and the cold blackbody physical temperature respectively to characterize the equivalent noise temperature of the system after the introduction of the RF optical path; Step 6: Based on the characterization results of steps 4 and 5 and combined with the noise cascade theory, calculate the RF gain and corresponding RF noise temperature of the RF link.

5. A high-precision measurement method for broadband radio frequency noise according to claim 4, characterized in that: In step 3, the equivalent radiation temperature T C-W The calculation formula is: Among them, T is the physical temperature, h is Planck constant, f is the frequency, k is the B is the Boltzmann constant.

6. A high-precision measurement method for broadband radio frequency noise according to claim 4, characterized in that: The step 4 specifically includes: The temperature of a hot black body is T h The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected h : Among them, k B is the Boltzmann constant, Δf is the test bandwidth, G is the equivalent gain of the system, T rx is the equivalent noise temperature of the system; Use the hot and cold load switching module to switch to the cold black body. When the physical temperature of the cold black body is T c The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected c : Define Y = P h / P c , using the Y factor method, the equivalent noise temperature T of the system is obtained rx :

7. A high-precision measurement method for broadband radio frequency noise according to claim 6, characterized in that: The step 5 specifically includes: Introducing the radio frequency optical path, when the physical temperature of the thermal black body is T h1 The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected h1 : Among them, T rx1 is the equivalent noise temperature of the system after the RF optical path is introduced; Use the hot and cold load switching module to switch to the cold black body. When the physical temperature of the cold black body is T c1 The equivalent radiation temperature Under the conditions, the intermediate frequency output power P is collected c1 : definition Using the Y factor method, the equivalent noise temperature T of the system after the RF optical path is introduced is obtained. rx1 :

8. A high-precision measurement method for broadband radio frequency noise according to claim 7, characterized in that: In step 6, the RF gain G of the RF link RF for: The corresponding RF noise temperature is:

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