CN220040733U - System for calibrating noise coefficient - Google Patents

Abstract

The utility model provides a system for calibrating the noise coefficient, which includes a microwave signal source, a first fixed attenuator, a power divider, a coaxial attenuator, a microwave power sensor and a microwave power meter; the output end of the microwave signal source is connected to The input end of the first fixed attenuator is connected, the output end of the first fixed attenuator is connected to the input end of the power divider; the first output end of the power divider is connected to the input end of the coaxial attenuator, and the The output end is used to connect the instrument to be calibrated; the second output end of the power divider is connected to the input end of the microwave power sensor; the output end of the microwave power sensor is connected to the input end of the microwave power meter. The reflection coefficient of the system is small, which can make the microwave signal source at the input end less affected by device mismatch, enable continuous noise coefficient calibration of the instrument being calibrated in a wider frequency domain, and improve the calibration of the noise coefficient. accuracy of results.

Description

A system for calibrating noise figure

Technical field

The utility model relates to the technical field of instrument calibration, and in particular to a system for calibrating the noise coefficient.

Background technique

The noise figure of instruments such as noise figure analyzers and spectrum analyzers needs to be calibrated because the noise figure is one of the main parameters that directly affects the instrument's test accuracy. The noise figure analyzer can simply, quickly and non-destructively measure the noise figure of semiconductor devices, thereby distinguishing qualified semiconductor devices from unqualified semiconductor devices.

At present, the connection method shown in Figure 1 is usually used to calibrate the noise coefficient of the instrument to be calibrated. The system for calibrating the noise coefficient includes a microwave signal source, isolator, coaxial attenuator and isolator connected in sequence. The instrument to be calibrated and Isolator connection at rear end.

However, in the process of calibrating the noise figure of the instrument being calibrated using the connection method shown in Figure 1, the isolator increases the reflection coefficient of the system; in addition, due to the narrow working frequency band of the isolator, it cannot calibrate the measured instrument in the wide frequency domain. Noise coefficient is used for data comparison, which leads to inaccurate calibration results.

Utility model content

The utility model provides a system for calibrating the noise coefficient to solve the technical problem of inaccurate calibration results of the noise coefficient of the instrument being calibrated.

In order to solve the above technical problems, the utility model provides a system for calibrating the noise coefficient, including a microwave signal source, a first fixed attenuator, a power divider, a coaxial attenuator, a microwave power sensor and a microwave power meter;

The output end of the microwave signal source is connected to the input end of the first fixed attenuator, and the output end of the first fixed attenuator is connected to the input end of the power divider;

The first output end of the power divider is connected to the input end of the coaxial attenuator, and the output end of the coaxial attenuator is used to connect the instrument to be calibrated;

The second output end of the power divider is connected to the input end of the microwave power sensor; the output end of the microwave power sensor is connected to the input end of the microwave power meter.

Optionally, the system further includes a second fixed attenuator, the input end of the second fixed attenuator is connected to the output end of the coaxial attenuator, and the output end of the second fixed attenuator is connected to the Connect the detection terminal of the instrument being calibrated.

Optionally, the first fixed attenuator and the second fixed attenuator have the same specifications.

Optionally, both the first fixed attenuator and the second fixed attenuator are π-type balanced attenuators.

Optionally, the first fixed attenuator and the second fixed attenuator each include a first resistor, a second resistor and a third resistor; one end of the first resistor is connected to one end of the second resistor, The other end of the first resistor is connected to one end of the third resistor; the other end of the second resistor is connected to the other end of the third resistor; the resistance of the first resistor is equal to the third resistor. The resistance of the resistor.

Optionally, the resistance of the first resistor is equal to 96.25Ω, the resistance of the second resistor is equal to 71.15Ω, and the resistance of the third resistor is equal to 96.25Ω.

Optionally, the first fixed attenuator and the second fixed attenuator each include a stainless steel shell, and the first resistor, the second resistor and the third resistor are all installed inside the stainless steel shell.

Optionally, the system further includes a metal plate, and the ground terminals of the microwave signal source, the first fixed attenuator, the power divider, the microwave power sensor and the microwave power meter are respectively connected to the Metal plate connection.

Optionally, the metal plate is a flat metal plate with a flat surface.

Optionally, the microwave signal source, the first fixed attenuator, the power divider, the coaxial attenuator, the microwave power sensor and the microwave power meter are connected through radio frequency cables.

The system for calibrating the noise coefficient provided by the utility model has a small reflection coefficient, which can make the microwave signal source at the input end less affected by device mismatch, and can continuously calibrate the instrument in a wider frequency domain. The noise figure calibration improves the accuracy of the noise figure calibration results.

Description of the drawings

Figure 1 is a schematic module diagram of a system for calibrating noise figures in the prior art.

FIG. 2 is a schematic connection diagram of a system for calibrating the noise figure provided by an embodiment of the present invention.

Figure 3 is a schematic diagram of the module corresponding to Figure 2.

Figure 4 is a partial network structure diagram corresponding to Figure 2.

FIG. 5 is a schematic structural diagram of a π-type balanced attenuator provided by an embodiment of the present invention.

FIG. 6 is a schematic module diagram of another system for calibrating the noise figure provided by an embodiment of the present invention.

Detailed ways

In order to make the purpose, advantages and characteristics of the present invention clearer, a system for calibrating the noise coefficient proposed by the present invention will be further described in detail below with reference to the accompanying drawings. It should be noted that the drawings are in a very simplified form and use imprecise proportions, and are only used to conveniently and clearly assist in explaining the embodiments of the present invention.

In the description of the present utility model, the terms "first", "second" and other qualifiers are added for convenience of description and reference, and cannot be understood as indicating or implying relative importance or implicitly indicating the indicated technical features. quantity. Therefore, features defined by qualifiers such as "first" and "second" may explicitly or implicitly include one or more of these features.

As shown in Figures 2 to 4, this embodiment provides a system for calibrating the noise figure, including a microwave signal source, a first fixed attenuator, a power divider, a coaxial attenuator, a microwave power sensor and a microwave power meter; the output end of the microwave signal source is connected to the input end of the first fixed attenuator, and the output end of the first fixed attenuator is connected to the input end of the power divider; the power divider's The first output end is connected to the input end of the coaxial attenuator, and the output end of the coaxial attenuator is used to connect the instrument to be calibrated; the second output end of the power divider is connected to the input end of the microwave power sensor. The output end of the microwave power sensor is connected to the input end of the microwave power meter.

Wherein, the first fixed attenuator means that the attenuation amount of the attenuator remains unchanged. Coaxial attenuator refers to an attenuator with adjustable attenuation. The power divider plays the role of keeping the output power of the two output channels completely equal, ensuring online real-time monitoring of the power changes of the instrument being calibrated without adding additional monitoring devices. Microwave power sensors and microwave power meters are mainly used to accurately capture microwave power changes, which can be traced to the microwave power benchmark with good accuracy. The instrument to be calibrated may be a noise figure analyzer or a spectrum analyzer, which requires noise figure calibration. The following embodiments mainly take a noise figure analyzer as an example for explanation.

The calibration principle of the system is as follows:

The coaxial attenuator can be regarded as a linear two-port network. The mathematical functional relationship between the noise coefficient of the linear two-port network and the source reflection coefficient is shown in Equation 1, which is generally called the noise parameter equation.

Among them, F is the noise coefficient; F _min is the minimum noise coefficient (a constant determined by the material environment, which can be obtained by looking up the table); R _n is the equivalent noise resistance (indicating how quickly the noise coefficient changes with the source reflection coefficient); Г _S is Source reflection coefficient; Г _opt is the optimal source reflection coefficient (the source reflection coefficient corresponding to the minimum noise coefficient).

At this time, the network analyzer records the S parameters of the two-port network. Enter the formula to convert S parameters into T parameters. The formula is as follows:

At this time, the mismatch error of the two ports can be converted from the reflection coefficient equation:

Among them, a represents the parameters of the two-port network at the initial value, b represents the parameter at the final value, S _22a represents the S parameter of the two-port network at the initial value, S _22b represents the S parameter of the two-port network at the final value; Г _1a represents The reflection coefficient of the two-port network at the initial value, Г _1b represents the reflection coefficient of the two-port network at the final value.

The first fixed attenuator is a precision attenuator, and its parameter matrix m is After the first fixed attenuator and the two-port network are combined, it is assumed to have infinite reverse attenuation, so the sub-diagonal lines of the S matrices of these two attenuators are set to 0. However, the attenuator cannot guarantee complete matching, so the coefficients on the main diagonal are retained. The mismatch error at this time can be simplified to:

At this time, the more ideal attenuator parameters in the expression replace the original two-port S parameters for calculation, and the new S _22a and S _22b after synthesis also further reduce the impact of the reflection coefficient of the calibrated noise analyzer at the load end, so that The influence of the signal source reflection coefficient on the input end on the mismatch is also much smaller. It can be proved that the combination of the first fixed attenuator and the coaxial attenuator can in principle reduce the reflection coefficient of the calibration system and improve the accuracy.

The standard used in calibrating the system can be as follows:

1. Microwave signal source/vector signal source: frequency range: 250kHz~40GHz; frequency accuracy: 1×10 ^-7 ; output power: (-110~+20)dBm; output power flatness: ±0.1dB/10MHz.

2. Power meter/power probe: frequency range: DC~18GHz; measurement range (-35~+20)dBm; linearity <0.16%.

3. First fixed attenuator/precision attenuator: quantity 1; frequency range: DC~18GHz; attenuation: 10dB, voltage standing wave ratio: ≤1.1.

4. Network analyzer: frequency range is 9kHz~18GHz; the maximum allowable error in transmission coefficient amplitude measurement is ±0.01dB.

5. Power divider: Frequency range: DC~18GHz; the maximum allowable error in power distribution of the two output channels is ±0.02dB.

6. Coaxial attenuator: frequency range: DC ~ 18GHz; attenuation: 20dB, voltage standing wave ratio: ≤1.2.

Calibration steps for noise figure include:

a. When the output power of the recording signal source is 5dB, the readings of the calibrated noise figure analyzer and power meter are recorded into the original record as P ₀ and P _s,0 respectively. The output power range of the signal source is -6dB ~ +5dB, and the power output variation is 1dB.

b. Set the output power of the signal source, use the measured value of the power meter as the standard noise coefficient value, record P _s,i in the original record table, and calculate the noise coefficient standard value of the noise coefficient analyzer being calibrated according to Equation 5.

NFS _i : the standard value of the noise figure of the noise figure analyzer being calibrated, dB;

ENR: Noise source excess noise ratio setting value;

P _s,0 : Analog signal source output continuous wave power 5dBm, power probe measurement value, dBm;

P _s,i : noise power measurement value of the calibrated noise figure analyzer, dB;

i: The number of detection times is 1 to 11.

c. Adjust the output power of the signal source, and record that the value indicated by the noise coefficient analyzer being calibrated is the noise power of the instrument. The noise coefficient measurement value of the noise coefficient analyzer being calibrated can be obtained, and record P _i in the original record.

In the table:

NF _i : noise figure measurement value of the noise figure analyzer being calibrated, dB;

ENR: Noise source excess noise ratio setting value;

P ₀ : Analog signal source output continuous wave power 5dBm, power meter measurement value, dBm;

P _i : When the analog signal source outputs different continuous wave powers, the power probe measurement value, dBm;

i: The number of detection times is 1 to 11.

The difference between Equation 6 and Equation 5 can be used as the calibration error. If the error is within the specified range, it means the calibration result is acceptable.

The most obvious mismatch during calibration is that it causes large fluctuations and unevenness in the frequency domain during the noise figure measurement process. The system described can significantly eliminate mismatch errors, as shown in Table 1.

In general, the power measurement uncertainty due to mismatch is given by:

Δ _miss ≈(20loge)·|Γ _S ||Γ ₁ |cos(Φ _s +Φ _L ) (Equation 7)

The maximum mismatch error is:

Δ _{miss_max} =(20loge)·r _S r ₁ =±8.686r _S r _L (Equation 8)

In the formula: r _S = |Γ _S |; r ₁ = |Γ ₁ |; Γ _S : voltage reflection coefficient of the microwave signal source; Γ ₁ : voltage reflection at the power input end of the first-level network (i.e., the first fixed attenuator) coefficient.

Table 1 Measured values and uncertainties of the voltage standing wave ratio of the calibration system before and after improvement

The reflection coefficient of the system for calibrating the noise coefficient provided by this embodiment is smaller, which can make the microwave signal source at the input end less affected by device mismatch, and can continuously calibrate the instrument in a wider frequency domain. The noise figure calibration improves the accuracy of the noise figure calibration results.

Optionally, as shown in Figure 6, the system further includes a second fixed attenuator, the input end of the second fixed attenuator is connected to the output end of the coaxial attenuator, the second fixed attenuator The output end is connected to the detection end of the calibrated instrument. Providing a second fixed attenuator can reduce the reflection coefficient of the system, thereby making the calibration results of the system more accurate.

Optionally, the first fixed attenuator and the second fixed attenuator have the same specifications. This facilitates the design and assembly of the system.

Optionally, as shown in Figures 5 and 6, both the first fixed attenuator and the second fixed attenuator are π-type balanced attenuators. Since the characteristic impedances of the input and output ends of the two-port network formed by the coaxial attenuator are equal, the use of a π-type balanced attenuator can reduce the mismatch error of the system.

Optionally, as shown in Figure 5 and Figure 6, the first fixed attenuator and the second fixed attenuator each include a first resistor, a second resistor and a third resistor; one end of the first resistor and One end of the second resistor is connected, the other end of the first resistor is connected to one end of the third resistor; the other end of the second resistor is connected to the other end of the third resistor; the first The resistance of the resistor is equal to the resistance of the third resistor. The π-type balanced attenuator can be customized. The π-type balanced attenuator provided in this embodiment has a simple structure and is easy to manufacture.

Optionally, as shown in Figure 5, the resistance of the first resistor is equal to 96.25Ω, the resistance of the second resistor is equal to 71.15Ω, and the resistance of the third resistor is equal to 96.25Ω. The characteristic impedance of devices in the microwave radio frequency field usually defaults to 50 ohms, so the characteristic impedance of the first fixed attenuator provided in this implementation is 50 ohms. In the case of microwave devices without impedance conversion, the input impedance and output impedance are usually equal. The attenuator has a good low standing wave coefficient because of its large attenuation insertion loss.

Specifically, Z is the characteristic impedance, Z _S is the source impedance, and Z _L is the load impedance. Where K is the impedance factor, R ₁ is the input impedance, which is the impedance of the first resistor, R ₂ is the impedance of the second resistor, and R ₃ is the output impedance, which is the impedance of the third resistor. The π-type balanced attenuator is composed of passive components, which makes the circuit design linear. R1 and R3, that is, the input and output terminal impedances, are interchangeable. Therefore, when the characteristic impedance is equal to the impedance of the first fixed attenuator, the π-type balanced attenuator can effectively reduce the signal level. The precision attenuator required for this calibration system is 10dB attenuation and matches the network impedance of 50Ω.

Z＝50Ω

K＝10dB＝10 ^10/20 ＝3.1623

Optionally, the first fixed attenuator and the second fixed attenuator each include a stainless steel shell, and the first resistor, the second resistor and the third resistor are all installed inside the stainless steel shell. . The stainless steel housing can reduce the impact of external signals on the calibration, thereby improving the calibration results of the system. The inner conductor of the attenuator can be made of nickel-plated brass, because the power is usually small and does not require aluminum fins for heat dissipation. If the power is improved later, additional additions can be made. The internal ceramic base attenuator material can be beryllium oxide, the lead-out film can be a thick film, and the lead-out strip on the coaxial can be a gold-plated copper strip.

Optionally, the system further includes a metal plate, and the ground terminals of the microwave signal source, the first fixed attenuator, the power divider, the microwave power sensor and the microwave power meter are respectively connected to the Metal plate connection. Using the same reference ground plane improves the calibration results of the system.

Optionally, the metal plate is a flat metal plate with a flat surface. In this way, various components included in the system can be easily fixed.

Optionally, the microwave signal source, the first fixed attenuator, the power divider, the coaxial attenuator, the microwave power sensor and the microwave power meter are connected through radio frequency cables. RF cables can reduce the impact of external signals on calibration, thereby improving the calibration results of the system.

To sum up, the system for calibrating the noise coefficient provided by the present invention has a smaller reflection coefficient, which can make the microwave signal source at the input end less affected by device mismatch, and can calibrate the noise coefficient in a wider frequency domain. The instrument being calibrated performs continuous noise coefficient calibration, which improves the accuracy of the noise coefficient calibration results.

The above description is only a description of the preferred embodiments of the present utility model, and does not limit the scope of the present utility model in any way. Any changes or modifications made by those of ordinary skill in the art based on the above disclosures fall within the protection scope of the present utility model.

Claims (10)

1. A system for calibrating noise coefficient, characterized in that it includes a microwave signal source, a first fixed attenuator, a power divider, a coaxial attenuator, a microwave power sensor and a microwave power meter; The output end of the microwave signal source is connected to the input end of the first fixed attenuator, and the output end of the first fixed attenuator is connected to the input end of the power divider; The first output end of the power divider is connected to the input end of the coaxial attenuator, and the output end of the coaxial attenuator is used to connect the instrument to be calibrated; The second output end of the power divider is connected to the input end of the microwave power sensor; the output end of the microwave power sensor is connected to the input end of the microwave power meter. 2. A system for calibrating noise figure according to claim 1, characterized in that the system further includes a second fixed attenuator, the input end of the second fixed attenuator is connected to the coaxial attenuation The output end of the second fixed attenuator is connected to the detection end of the calibrated instrument. 3. A system for calibrating noise figure according to claim 2, characterized in that the first fixed attenuator and the second fixed attenuator have the same specifications. 4. A system for calibrating noise figure according to claim 3, characterized in that both the first fixed attenuator and the second fixed attenuator are π-type balanced attenuators. 5. A system for calibrating noise figure according to claim 4, characterized in that the first fixed attenuator and the second fixed attenuator each include a first resistor, a second resistor and a third resistor. Resistor; one end of the first resistor is connected to one end of the second resistor, the other end of the first resistor is connected to one end of the third resistor; the other end of the second resistor is connected to the third resistor. The other end of the resistor is connected; the resistance of the first resistor is equal to the resistance of the third resistor. 6. A system for calibrating noise coefficient according to claim 5, characterized in that the resistance of the first resistor is equal to 96.25Ω, the resistance of the second resistor is equal to 71.15Ω, and the resistance of the second resistor is equal to 71.15Ω. The resistance of the three resistors is equal to 96.25Ω. 7. A system for calibrating noise coefficient according to claim 5, wherein the first fixed attenuator and the second fixed attenuator each include a stainless steel shell, and the first resistor and the second fixed attenuator The second resistor and the third resistor are both installed inside the stainless steel housing. 8. A system for calibrating noise coefficient according to claim 1, characterized in that the system further includes a metal plate, the microwave signal source, the first fixed attenuator, the power divider The ground terminals of the microwave power sensor and the microwave power meter are respectively connected to the metal plate. 9. A system for calibrating noise coefficient according to claim 8, characterized in that the metal plate is a flat metal plate with a flat surface. 10. A system for calibrating noise figure according to claim 1, characterized in that the microwave signal source, the first fixed attenuator, the power divider, the coaxial attenuator, The microwave power sensor and the microwave power meter are connected through a radio frequency cable.