CN102780535B - A kind of vector network analyzer Poewr control method based on intermediate frequency detection - Google Patents

Abstract

A kind of vector network analyzer Poewr control method based on intermediate frequency detection, driving source is divided into two-way by coupler, one tunnel is exported by port through coupler as test signal, another road is as reference signal, mixing is carried out with local vibration source, the intermediate-freuqncy signal exported is divided into two-way again, one tunnel enters receiver and carries out network parameter calculating, another road is through bandpass filtering, intermediate frequency detection, after logarithmic amplification, integration is carried out with control voltage, the output feedack of integrator is to the variable attenuator in driving source, like this, a closed loop auto level control link is formed between driving source and intermediate frequency.

Description

A Power Control Method of Vector Network Analyzer Based on IF Detection

technical field

The invention relates to a power control method of a vector network analyzer based on intermediate frequency detection.

Background technique

The importance of vector network analyzers in the field of RF, microwave and millimeter wave testing is obvious to all. One of the typical applications is the index test of a wide variety of amplifiers. For example, when measuring the compression point of a high-precision amplifier, it is hoped that the accuracy of the source power output by the test instrument is as high as possible; The source power has a wide power sweep range; when the pulse modulation signal is excited, it is hoped that the pulse power can be accurately controlled.

The power control technology of existing test instruments basically adopts the automatic level control (ALC) technology based on the internal source port for broadband detection. Since the wideband detection is directly performed from the source port, the noise power increases with the increase of the bandwidth. , the accuracy drops obviously, especially in the small signal state, the deterioration of power accuracy is more serious. In addition, pulse sources are more and more widely used, such as pulse radar, cable distribution characteristics test based on time domain reflectometry, etc., all need to transmit pulse signals, and the stability of pulse signals has always been a problem.

The block diagram of the traditional automatic level control principle is shown in Figure 1. At the source output end, a signal is divided by a power divider for detection. In order to increase the control range of the power, the detection signal is logarithmically amplified. The reference level is output by D/A, which is used to realize the power setting of the host. The reference level is integrated with the logarithmically amplified output voltage, and finally fed back to the electronically adjustable attenuator on the source path, thus forming a negative feedback loop to realize automatic amplitude stabilization and control of the source power.

In order to ensure the absolute power accuracy of the source output, a power meter is used to calibrate the port power at last. To obtain higher power flatness, more calibration points are required, but the more calibration points, the longer it takes. If the source output is in the pulse state, from the frequency domain, the wideband detection is aimed at all the frequency components of the pulse, not just the carrier power in the pulse. From the time domain, the detection output will have a change for the pulse switch, It is difficult to stabilize the power at the power set by the reference level. The traditional pulse power control method is to use software compensation after opening the loop, that is, disconnect the switch in Figure 1, set the loop to an open loop state, use a power meter to calibrate the output power of the port, and constantly adjust the reference voltage during the calibration process. Level until the port power reaches the set power value, and save the calibration data. This method cannot guarantee the accuracy of uncalibrated frequency points or power points. Due to the slow calibration time, usually we only calibrate a few test points, so the power accuracy in the pulse state cannot be guaranteed.

Since the existing power control technology uses broadband detection directly from the output port of the microwave signal source, the noise will inevitably increase with the increase of the bandwidth, and it is easily affected by the harmonic clutter of the signal source. This directly affects the accuracy of the source power, linearity, power sweep range and other indicators. And for the test of some high-power devices, when an additional drive amplifier needs to be added outside the network analyzer, the power accuracy of the output of the external amplifier will be more difficult to guarantee. In addition, this amplitude stabilization method cannot realize automatic amplitude stabilization in the pulse state.

Contents of the invention

For the above-mentioned shortcoming, the present invention makes full use of the characteristics of the vector network analyzer, namely the vector network analyzer comprises two parts of the excitation source and the receiver, and the frequency deviation of the excitation source and the receiver local oscillator source is always constant, and proposes a method based on The power control method of intermediate frequency detection, because the intermediate frequency of the vector network analyzer is fixed and very low, generally a few MHz, so the narrowband intermediate frequency detector can be used to control the power of the broadband microwave signal source, and the pulse source can be extracted by intermediate frequency filtering The carrier realizes the automatic amplitude stabilization of the closed loop in the pulse state.

One of purpose of the present invention is achieved through the following technical solutions:

The excitation source is divided into two paths through the coupler, one path is used as a test signal and output through the port through the coupler, the other path is used as a reference signal, which is mixed with the local oscillator source, and the output intermediate frequency signal is divided into two paths, and one path enters the receiver for network parameters calculation, the other path is band-pass filtered, intermediate frequency detection, logarithmic amplification, and integrated with the control voltage, and the output of the integrator is fed back to the variable attenuator in the excitation source. In this way, a closed loop is formed between the excitation source and the intermediate frequency. level control link.

Utilize the characteristics of the vector network analyzer itself, that is, the excitation source and the local oscillator source of the vector network analyzer are always scanned synchronously with the frequency deviation of the intermediate frequency. The intermediate frequency power has a linear relationship with the excitation source power, so that the direct source port broadband detection method can be replaced by intermediate frequency detection. Since the intermediate frequency is a fixed point frequency and the frequency is low, it can be filtered by a band-pass filter for narrow-band detection, reducing noise power, improving the signal-to-noise ratio, and reducing harmonic clutter outside the band-pass filter band influence on detection.

In order to ensure the absolute accuracy of the port power, the port power is calibrated with a power meter. Since the intermediate frequency of the vector network analyzer is low and fixed, it is easy to design a bandpass filter to filter the intermediate frequency. In this way, the noise added to the detector is smaller, the power control precision is higher, and the detection processing of smaller signals can be realized, and the power scanning range can be increased. And there is a high-performance logarithmic amplifier specifically for intermediate frequencies, which can greatly simplify circuit design.

When the excitation source output is in a pulse state, in order to realize the stabilization of the amplitude of the intra-pulse carrier, it is necessary to obtain the carrier power. When the excitation source is mixed with the local oscillator, the carrier frequency is reduced to a lower intermediate frequency, and the intermediate frequency of the carrier can be obtained through a band-pass filter. Relatively speaking, the intermediate frequency filter is easier to design, and when the pulse frequency is higher , the greater the interval between the spectral lines of the pulse spectrum, the better the bandpass filtering effect, and the better the final amplitude stabilization effect. In this way, pulse amplitude stabilization can adopt the same closed-loop method as continuous wave amplitude stabilization to improve in-band power flatness.

The present invention improves the signal-to-noise ratio of the detection by adopting the narrow-band intermediate frequency detection method, thereby improving the power accuracy, expanding the power scanning range, and adding a band-pass filter to the intermediate frequency path, which can obtain the carrier wave of the pulse excitation source, thereby better Realize the closed-loop stabilization of the excitation source in the pulse state, and improve the power accuracy of the pulse source. Due to the use of intermediate frequency detection by the receiver, it is not limited by the bandwidth of the signal source, so the power of a wider bandwidth signal can be controlled. In addition, the power control method of intermediate frequency detection can also solve the problem of uncontrollable power accuracy when adding amplifiers outside the instrument and spreading to higher frequencies.

Description of drawings

Specific embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings.

Figure 1 Block diagram of automatic level control

Figure 2 Block diagram of network analyzer power control based on IF detection

Figure 3 Time-domain waveform when the excitation source output is in a pulse state

Figure 4 The frequency domain waveform when the excitation source output is in a pulse state

Detailed ways

The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings; it should be understood that the preferred embodiments are only for illustrating the present invention, rather than limiting the protection scope of the present invention.

As shown in Figure 2, the excitation source is divided into two paths through coupler 1, one path is used as a test signal and output through port 1 through coupler 2, and the other path is used as a reference signal, which is mixed with the local oscillator source, and the output R intermediate frequency signal is further divided into two One path enters the receiver for network parameter calculation, and the other path is band-pass filtered, intermediate frequency detected, logarithmically amplified, and integrated with the control voltage, and the output of the integrator is fed back to the variable attenuator in the excitation source. In this way, the excitation A closed-loop automatic level control link is formed between the source and the intermediate frequency.

Utilize the characteristics of the vector network analyzer itself, that is, the excitation source and the local oscillator source of the vector network analyzer are always scanned synchronously with the frequency deviation of the intermediate frequency. The intermediate frequency power has a linear relationship with the excitation source power, so that the direct source port broadband detection method can be replaced by intermediate frequency detection. Since the intermediate frequency is a fixed point frequency and the frequency is low, it can be filtered by a band-pass filter for narrow-band detection, reducing noise power, improving the signal-to-noise ratio, and reducing harmonic clutter outside the band-pass filter band influence on detection.

In order to ensure the absolute accuracy of the port power, the port power is calibrated with a power meter. Since the intermediate frequency of the vector network analyzer is low and fixed, it is easy to design a bandpass filter to filter the intermediate frequency. In this way, the noise added to the detector is smaller, the power control precision is higher, and the detection processing of smaller signals can be realized, and the power scanning range can be increased. And there is a high-performance logarithmic amplifier specifically for intermediate frequencies, which can greatly simplify circuit design.

When the output of the excitation source is in the pulse state, to realize the stabilization of the amplitude of the intra-pulse carrier, it is necessary to obtain the carrier. When the excitation source is mixed with the local oscillator, the carrier frequency is reduced to a lower intermediate frequency, and the intermediate frequency of the carrier can be obtained through a band-pass filter. Relatively speaking, the intermediate frequency filter is easier to design, and when the pulse frequency is higher , the greater the interval between the spectral lines of the pulse spectrum, the better the bandpass filtering effect, and the better the final amplitude stabilization effect.

Claims (3)

1. the vector network analyzer Poewr control method based on intermediate frequency detection, it is characterized in that: driving source is divided into two-way by coupler, one tunnel is exported by port through coupler as test signal, another road is as reference signal, mixing is carried out with local vibration source, the intermediate-freuqncy signal exported is divided into two-way again, one tunnel enters receiver and carries out network parameter calculating, another road is through bandpass filtering, intermediate frequency detection, after logarithmic amplification, integration is carried out with control voltage, the output feedack of integrator is to the variable attenuator in driving source, like this, a closed loop auto level control link is formed between driving source and intermediate frequency,

When driving source exports as pulse condition, realize the fixed ampllitude to arteries and veins intercarrier, need to obtain carrier wave, when after driving source and local vibration source mixing, carrier wave has been reduced to lower intermediate frequency, just can be obtained the intermediate frequency of carrier wave by band pass filter.

2. as claimed in claim 1 based on the vector network analyzer Poewr control method of intermediate frequency detection, it is characterized in that: intermediate frequency is by after bandpass filtering, carrier frequency in the arteries and veins that can obtain pulse condition, and then realize the closed loop fixed ampllitude under pulse condition, improve the fixed ampllitude precision of pulse condition.

3. as claimed in claim 1 based on the vector network analyzer Poewr control method of intermediate frequency detection, it is characterized in that: working band is wide, not by the restriction of signal source bandwidth, fixed ampllitude speed is fast, omits the software compensation for wave detector frequency response during the calibration of power.