Dynamic power adjustable S parameter test module and vector network analyzer
By designing a dynamic power adjustable S-parameter test module, the problems of power tuning and signal purity in millimeter-wave terahertz band testing were solved, achieving accuracy and stability in high-frequency band testing and meeting the requirements of high-frequency band testing.
Patent Information
- Application Number
- CN202511463415.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-14
- Publication Date
- 2026-02-24
AI Technical Summary
Existing millimeter-wave terahertz band S-parameter testing modules have difficulty achieving power tuning, linear large dynamic range, and high-purity signal output in high-frequency band testing, resulting in inaccurate test results.
A dynamically adjustable S-parameter test module is adopted, including a reference channel unit, a test channel unit, a local oscillator drive unit, and a signal generation unit. Through the combined design of attenuators, isolators, directional couplers, filter amplification units, and mixers, signal power tuning and crosstalk suppression are achieved. By using low-noise amplifier gain, signal purity is ensured and signal interference from the reverse receiver is reduced. The reference channel unit of the low-noise amplifier and the reference mixer of the test channel unit achieve signal reflection and filtered output.
It achieves high signal purity under small signal conditions, enables precise testing of linear receivers with minimal insertion loss, and provides accurate testing of devices under real large dynamic conditions, meeting the testing requirements of high frequency bands.
Smart Images
Figure CN121559178A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of signal testing technology, specifically relating to a dynamically adjustable S-parameter testing module and a vector network analyzer. Background Technology
[0002] With the rapid development of applications such as 5G / 6G communication, high-resolution radar, and biological / pharmaceutical spectral analysis, the operating frequency bands required for testing and measurement have expanded to millimeter-wave and even terahertz bands. Considering the transmission loss at higher frequencies, testing and measurement in the millimeter-wave and terahertz bands often employs a host computer with a frequency extension module to achieve higher frequency band expansion, bringing the test port as close as possible to the object under test and reducing transmission loss. S-parameter testing modules, which can be used with microwave frequency band vector network analyzers to perform S-parameter testing in the millimeter-wave and terahertz bands, are among the most widely used instruments in daily scientific research and engineering applications. The performance indicators of the S-parameter testing module directly determine the accuracy and stability of the corresponding millimeter-wave and terahertz band test results.
[0003] When testing passive devices in the millimeter-wave and terahertz bands, such as filters, it is necessary to simultaneously meet the requirements of extremely low in-band insertion loss (≤0.1dB) and high bandwidth rejection (≥100dB). This requires the S-parameter testing module to have a linear dynamic range, enabling insertion loss testing below 0.1dB, and also to possess a true dynamic range above 100dB, enabling out-of-band characteristic testing of high-order filters. When testing active devices in the millimeter-wave and terahertz bands, such as amplifiers undergoing small-signal testing, the output power of the S-parameter testing module needs to be tuned. Simultaneously, it is required to eliminate leakage, spurious, and parasitic interference signals as much as possible during small-signal output to maintain the purity of the output signal and ensure accuracy in small-signal testing of the amplifier. These requirements present significant challenges to the design of millimeter-wave and terahertz S-parameter testing modules, necessitating the simultaneous achievement of power tuning, linear large dynamic range, and high-purity signal output. Summary of the Invention
[0004] Based on the above problems, this application proposes a high-channel isolation, high-linearity, dynamic millimeter-wave terahertz power adjustable S-parameter test module architecture, the technical solution of which is as follows: A dynamically adjustable S-parameter test module includes a reference channel unit, a test channel unit, a local oscillator drive unit, and a signal generation unit. The signal from the signal generation unit passes through an attenuator and an isolator before entering the directional coupler. The quantitatively coupled output passes through two filtering and amplification units. One signal is output through the reference mixer and IF amplification and filtering unit of the reference channel unit and is received by the external host. The other signal is output to the object under test and simultaneously coupled through the directional coupling channel to the test mixer of the test channel unit for mixing. The test mixer reflects the signal to the IF filtering and amplification unit, where it is filtered and output. The local oscillator drive unit provides drive for the reference mixer in the reference channel unit and the test mixer in the test channel unit.
[0005] A vector network analyzer includes at least two S-parameter test modules with identical structures, namely S-parameter test module one and S-parameter test module two. Both S-parameter test module one and S-parameter test module two have signal transmission and reception functions. When measuring transmission characteristic S21, S-parameter test module one acts as a signal transmitter and S-parameter test module two acts as a signal receiver; when measuring transmission characteristic S11, S-parameter test module one acts as both a signal transmitter and a signal receiver; when measuring transmission characteristic S12, S-parameter test module two acts as a signal transmitter and S-parameter test module one acts as a signal receiver; when measuring transmission characteristic S22, S-parameter test module two acts as both a signal transmitter and a signal receiver.
[0006] When testing the S21 parameters, S-parameter test module one acts as the signal transmitter and S-parameter test module two acts as the signal receiver. During testing, the signal generation unit in S-parameter test module one generates a millimeter-wave band signal, which passes through an attenuator and an isolator to the directional coupler and then to the device under test (DUT). Simultaneously, the signal output from the signal generation unit is coupled to the reference mixer in the reference channel unit for reception. The reference mixer down-mixes to generate a reference intermediate frequency (IF) signal R1, which is returned to the host. When the signal from the directional coupler channel reaches the DUT, a portion of the signal is reflected and returns to S-parameter test module one. This reflected signal is then input to the test mixer in the test channel unit via the directional coupler for reception. The test mixer down-mixes to generate a test IF signal, which passes through a filtering and amplification unit and enters the test mixer in the test signal channel unit of S-parameter test module two. The signal is then output after passing through the filtering and amplification unit of the test signal channel unit.
[0007] Preferred stopband S21 test analysis: The crosstalk between channels mainly includes the interference of the test channel of S-parameter test module one to the test intermediate frequency B, and the interference of the reference channel of S-parameter test module two to it. The interference from the test channel of S-parameter test module one will affect the test signal at this time. Because the filtering and amplification unit generates a strong reflection, this reflected signal is mixed with the local oscillator signal in the test mixer, resulting in the following parasitic signal. ,as follows: ; To test the mixer's operating frequency; The signal leaks into the test channel through the isolation port of the directional coupler during forward transmission. Since the filter contains a passband or parasitic passband at this frequency, the parasitic signal can pass through the filter and enter the second S-parameter test module. It then enters the test receiver through the reverse receiving coupling channel of the directional coupler in the second S-parameter test module, where it undergoes second harmonic mixing with the local oscillator signal, generating a parasitic intermediate frequency, as follows: ; The parasitic signal and the intermediate frequency generated by the S-parameter test module 2 are the same, so they cannot be filtered out.
[0008] Preferably, to simplify the analysis process, it is assumed that the fundamental frequency conversion loss of all mixers is... The second harmonic mixing and frequency conversion loss is The mixer itself has a fundamental rejection ratio of S, and the coupler has the same insertion loss and coupling degree at the operating frequency band and at twice the frequency. Therefore, the power of the intermediate frequency during normal testing is... According to the transmission path, it should be: ; Secondly, based on the propagation path of the parasitic signal, its power can be obtained. It should be: ; in: To test the reflection coefficient of the filter in the channel unit, Here, C represents the insertion loss of the coupler, C represents the coupling degree of the directional coupler, and ISO represents the isolation degree of the directional coupler. For the filter under test in f O insertion loss, For the test piece in Insertion loss at point (PO-ISO) is the leakage through each channel during forward transmission.
[0009] Preferably, the reference mixer signal of the reference channel of the S-parameter test module two is limited by the local oscillator-to-RF port rejection ratio of the mixer local oscillator. The signal will leak to the test channel through the reference channel of the coupler in S-parameter test module two, similar to the original test signal. Mixing generates a new parasitic intermediate frequency: ; The power of the intermediate frequency signal can be calculated based on its generation and transmission path as follows: ; When testing a filter, if there is a passband at 2 times the frequency, the test value of S21 mainly depends on the amplitude of the test intermediate frequency and the parasitic intermediate frequency. If the stopband rejection ratio is large enough, the amplitude of the parasitic intermediate frequency is greater than the actual test intermediate frequency, and the true test result cannot be obtained. If the stopband rejection ratio is not large enough, the amplitude of the parasitic intermediate frequency is smaller than the actual test intermediate frequency, and the test result is normal.
[0010] Preferably, channel leakage analysis: the passband of the filter amplification unit is the operating frequency band of the S-parameter test module, the stopband covers approximately three times the passband, and it can provide the highest possible suppression within a frequency range of approximately two times the passband, achieving the desired level of suppression. Suppress, so that: ; For actual testing, the intermediate frequency, This represents the mid-frequency amplitude of the parasitic medium.
[0011] Compared with the prior art, the beneficial effects of this application are as follows: 1. Tunable power and high output signal purity under small signal conditions: The port power is tunable by adding a mechanically adjustable attenuator, and reverse isolation is achieved by a low-noise amplifier on the test / reference channel, reducing signal leakage from the test / reference receiver to the signal output path, improving the port output signal purity under small signal conditions, which is beneficial for accurate testing of active devices under small signal conditions; 2. Linear receivers enable precise testing with minimal insertion loss: Through integrated design of the coupling degree of the directional coupler, the gain of the low-noise amplifier in the receiving channel, and the compression point of the mixer, the receiver is ensured to be in a state of no compression distortion, enabling precise testing of devices with minimal insertion loss of less than 0.1dB. 3. Realistic large dynamic range enables accurate testing of high transmission loss devices: By adding a low-pass filter to the test / reference channel, the "pseudo" intermediate frequency signal generated by the crosstalk between the two module test / reference receivers can be effectively reduced, realizing realistic and parasitic-free large dynamic range characteristics, meeting the accurate testing requirements of high transmission loss devices such as filters and attenuators. Attached Figure Description
[0012] Figure 1 Here is the architecture diagram of the S-parameter testing module; Figure 2 For S 21 Schematic diagram of crosstalk in each channel during testing; Figure 3 Two typical cases for filter S21: (a) filter stopband test and (b) filter passband test. Figure 4 For S 21 Schematic diagram of leakage suppression in each channel during testing; Figure 5 This is a schematic diagram of crosstalk and leakage suppression. Detailed Implementation
[0013] The technical solution of this application will be described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of this application, rather than limitations thereof. Specific technical features can be combined with each other.
[0014] Figure 1 As shown, a dynamic power adjustable S-parameter test module includes a reference channel unit, a test channel unit, a local oscillator drive unit, and a signal generation unit. The signal from the signal generation unit passes through an attenuator and an isolator before entering the directional coupler. The quantitatively coupled output passes through two filtering and amplification units. One signal is output through the reference mixer and IF amplification and filtering unit of the reference channel unit and is received by the external host. The other signal is output to the object under test and simultaneously coupled through the directional coupling channel to the test mixer of the test channel unit for mixing. The test mixer reflects the signal to the IF filtering and amplification unit, where it is filtered and output. The local oscillator drive unit provides drive for the reference mixer in the reference channel unit and the test mixer in the test channel unit.
[0015] Figure 2 As shown, a vector network analyzer employs the dynamically adjustable S-parameter test module device as described in claim 1, characterized in that it includes at least two S-parameter test modules with identical structures, namely S-parameter test module one and S-parameter test module two. When testing S21, S-parameter test module one acts as the signal transmitter, and S-parameter test module two acts as the signal receiver. During testing, the signal generation unit in S-parameter test module one generates a millimeter-wave band signal, which passes through an attenuator and an isolator to the directional coupler and then to the device under test (DUT). Simultaneously, the signal output from the signal generation unit is coupled to the reference mixer in the reference channel unit for reception. The reference mixer down-mixes to generate a reference intermediate frequency (IF) signal R1, which is returned to the host. When the signal from the directional coupler channel reaches the DUT, a portion of the signal is reflected and returns to S-parameter test module one. This reflected signal is then input to the test mixer in the test channel unit via the directional coupler for reception. The test mixer down-mixes to generate a test IF signal, which passes through a filtering and amplification unit and enters the test mixer in the test signal channel unit of S-parameter test module two. The signal is then output after passing through the filtering and amplification unit of the test signal channel unit.
[0016] When a vector network analyzer processes intermediate frequency (IF) signals, it only receives and processes signals within a very narrow bandwidth (3MHz~10MHz) near the IF frequency. Therefore, most frequency components have almost no impact on the IF test results. However, in some specific situations, they can have a significant impact on the test results, especially when many frequency components generate parasitic IF signals with the same frequency as the normal test IF signal and enter the vector network analyzer host, thereby interfering with the test results.
[0017] As a typical passive device, filters generally feature low insertion loss and high bandwidth suppression. More importantly, the presence of parasitic passbands or multiple passbands makes signal crosstalk analysis more complex during filter testing. Figure 3 As shown, when testing filters with parasitic channels at twice the passband frequency or dual passbands, different situations will occur during the passband and stopband S21 tests. The specific analysis will follow.
[0018] Stopband S 21 test( Figure 3 a): Crosstalk between channels mainly comes from two parts, such as Figure 2 As shown, one is the interference from the test channel of S-parameter test module one to the intermediate frequency B in the test, and the other is the reference channel of S-parameter test module two. First, there is the interference from the test channel of S-parameter test module one; at this time, the test signal... f O Due to the high transmission rejection and strong reflection of the filter, the transmission is severely attenuated, resulting in a strong reflection. This reflected signal is mixed with the local oscillator signal in the mixer, producing the following parasitic signal. f H ,as follows ; The signal leaks into the test channel through the isolation port of the forward transmission of the dual directional coupler. Since the filter contains a passband or parasitic passband at this frequency, the parasitic signal can pass through the filter and enter the second S-parameter test module. It then enters the test receiver through the reverse receiving coupling channel of the directional coupler in the second S-parameter test module, where it undergoes second harmonic mixing with the local oscillator signal, generating a parasitic intermediate frequency, as follows: ; The parasitic signal is at the same frequency as the test intermediate frequency generated by the module itself, and therefore cannot be filtered out. To simplify the analysis, assume that the fundamental frequency conversion loss of all mixers is CL1, the second harmonic frequency conversion loss is CL2, the fundamental rejection ratio of the mixer itself is S, and the insertion loss and coupling degree of the directional coupler are the same in the operating frequency band and at twice the frequency. Then, the power of the normal test intermediate frequency should be as follows, based on the transmission path: ; Secondly, based on the propagation path of this parasitic signal, its power can be calculated as follows: ; Where ILc is the insertion loss of the directional coupler, C is the coupling degree of the directional coupler, and ISO is the isolation degree of the directional coupler. IL DUT For the filter under test in f O insertion loss, IL S For the test piece in f H Insertion loss at (P) O -ISO) refers to leakage through each channel during forward emission.
[0019] Since the filter is in a strong reflection state at this time, Γ is approximately close to 1. Because the waveguide coupler isolation is approximately 30-40 dB, the fundamental frequency conversion loss is approximately 10 dB, and the subharmonic frequency conversion loss is approximately 20 dB, while the insertion loss IL of the device under test is... DUT and IL S The difference in insertion loss can reach more than 100dB. Therefore, the amplitude of the parasitic intermediate frequency is much larger than that of the normal test intermediate frequency, and it becomes the main signal entering the intermediate frequency interface B of the vector network analyzer. At this time, the S21 obtained by the test has deviated from the correct result.
[0020] The reference channel mixer signal in S-parameter test module two is limited by the local oscillator rejection ratio of the mixer, which is similar to the rejection ratio of the local oscillator to the RF port. The signal will leak to the test channel through the reference channel of the directional coupler in S-parameter test module two, and at this time it can also be compared with the original test signal.f O Mixing generates a new parasitic intermediate frequency: ; The power of the intermediate frequency signal can be calculated based on its generation and transmission path as follows: ; As can be seen, compared to the normal test intermediate frequency (IF), when the insertion loss of the device under test (DUT) is large, the amplitude can also be greater than the normal test IF B, which will also have a significant impact on the test results. In this case, the maximum stopband of the filter that can be measured depends only on the maximum value of the parasitic IF, and the true stopband rejection characteristics of the filter cannot be obtained.
[0021] Passband S 21 test( Figure 3 b): At this point, the filter should provide low-loss transmission and weak reflection for the test signal. In this case, the isolation of the coupler plays a crucial role. As can be seen from the relevant formulas for intermediate frequency and parasitic intermediate frequency, the parasitic intermediate frequency signal is much smaller than the test intermediate frequency, so it will not have any impact on the test results.
[0022] In summary, when testing filters, especially high-suppression stopbands, if a passband exists at twice the frequency, the measured value of S21 mainly depends on the amplitudes of the test intermediate frequency (IF) and the parasitic IF. If the stopband rejection ratio is large enough, the amplitude of the parasitic IF will be greater than the actual test IF, making it impossible to obtain a true test result. If the stopband rejection ratio is not large enough, the amplitude of the parasitic IF will be smaller than the actual test IF, and the test result will be normal.
[0023] Channel leakage analysis: When performing small-signal tests on power devices such as power amplifiers, it is necessary to attenuate the port output power using the adjustable attenuator built into the spread spectrum module. At this point, the port output power is approximately in the range of -20 to -50 dBm. The leakage effect from the two receivers inside the module is then significant and cannot be ignored. Figure 4 As shown, these leakage signals can leak into the test channel through the isolation channel of the coupler, and f H The parasitic components are similar, and are also combination frequency components of each RF and LO. At this time, the suppression of the mixer itself and the isolation of the coupler alone are no longer sufficient to meet the test requirements in small signal scenarios.
[0024] The S-parameter testing module proposed in this application suppresses crosstalk and performs leakage analysis: Based on the preceding analysis of crosstalk and leakage, the following explains how the architecture proposed in this patent suppresses crosstalk and performs analysis. For example... Figure 5As shown, to simplify the analysis process, we still use fundamental frequency mixing as an example. By adding low-pass and low-noise amplifier units, the passband of the low-pass filter is the operating frequency band of the S-parameter test module, the stopband covers approximately three times the passband, and it can provide the highest possible suppression within a two-times frequency range. This can fully address the issue of... f H Suppress, so that: ; In this situation, the crosstalk signal will no longer affect the test results, and the true stopband characteristics of the filter can then be tested. Secondly, the low-noise amplifier can effectively suppress the reverse leakage signal while amplifying the forward transmission signal, thus further improving its performance for... f H On the one hand, the suppression of parasitic signals reduces the leakage of spurious signals from each channel receiver to the main channel, thereby improving the overall stability and testing accuracy of the module.
[0025] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.
Claims
1. A dynamically adjustable power S-parameter testing module, characterized in that, It includes a reference channel unit, a test channel unit, a local oscillator drive unit, and a signal generation unit; The signal from the signal generation unit passes through an attenuator and an isolator before entering the directional coupler. The quantitatively coupled output passes through two filtering and amplification units. One signal is output through the reference mixer and IF amplification and filtering unit of the reference channel unit and is received by the external host. The other signal is output to the object under test and simultaneously coupled through the directional coupling channel to the test mixer of the test channel unit for mixing. The test mixer reflects the signal to the IF filtering and amplification unit, where it is filtered and output. The local oscillator drive unit provides drive for the reference mixer in the reference channel unit and the test mixer in the test channel unit.
2. A vector network analyzer, employing the dynamically adjustable S-parameter test module as described in claim 1, characterized in that, It includes at least two S-parameter test modules with the same structure, namely S-parameter test module one and S-parameter test module two; Both S-parameter test module one and S-parameter test module two have signal transmission and reception functions. When measuring transmission characteristic S21, S-parameter test module one acts as a signal transmitter and S-parameter test module two acts as a signal receiver; when measuring transmission characteristic S11, S-parameter test module one acts as both a signal transmitter and a signal receiver; when measuring transmission characteristic S12, S-parameter test module two acts as a signal transmitter and S-parameter test module one acts as a signal receiver; when measuring transmission characteristic S22, S-parameter test module two acts as both a signal transmitter and a signal receiver.
3. The vector network analyzer according to claim 2, characterized in that, S-parameter test module one serves as the signal transmitter, and S-parameter test module two serves as the signal receiver; During testing, the signal generation unit in S-parameter test module one generates a millimeter-wave band signal, which passes through an attenuator and an isolator to the directional coupler and then to the device under test (DUT). Simultaneously, the signal output from the signal generation unit is coupled to the reference mixer in the reference channel unit for reception. The reference mixer down-mixes to generate a reference intermediate frequency (IF) signal R1, which is returned to the host. When the signal from the directional coupler channel reaches the DUT, a portion of the signal is reflected and returns to S-parameter test module one. This reflected signal is then input to the test mixer in the test channel unit via the directional coupler for reception. The test mixer down-mixes to generate a test IF signal, which passes through a filtering and amplification unit and enters the test mixer in the test signal channel unit of S-parameter test module two. The signal is then output after passing through the filtering and amplification unit of the test signal channel unit.
4. The vector network analyzer according to claim 2, characterized in that, Stopband S21 test analysis: The crosstalk between channels mainly includes the interference of the test channel of S-parameter test module one to the test intermediate frequency B, and the interference of the reference channel of S-parameter test module two to it. The interference of the test channel of S-parameter test module one on it, at this time the test signal Because the filtering and amplification unit generates a strong reflection, this reflected signal is mixed with the local oscillator signal in the test mixer, resulting in the following parasitic signal. ,as follows: ； To test the mixer's operating frequency; The signal leaks to the input of the filter under test through the test channel of the directional coupler. If the filter has a passband or parasitic passband at that frequency, the parasitic signal can pass through the filter and enter the second S-parameter test module. It then enters the test receiver through the test channel of the directional coupler in the second S-parameter test module and undergoes second harmonic mixing with the local oscillator signal, generating a parasitic intermediate frequency, as follows: ； The parasitic signal is the same frequency as the test intermediate frequency normally generated by the S-parameter test module 2, and therefore cannot be filtered out.
5. The vector network analyzer according to claim 3, characterized in that, To simplify the analysis, assume that the fundamental frequency conversion loss of the mixer in all S-parameter test modules is... The second harmonic mixing and frequency conversion loss is The mixer itself has a fundamental frequency rejection ratio of S and a second harmonic rejection ratio of S. H To simplify the analysis, we assume that the insertion loss and coupling degree of the coupler are the same at the operating frequency band and at twice the frequency. Then, the power at the intermediate frequency during normal testing will be... According to the transmission path, it should be: ； Secondly, based on the propagation path of the parasitic signal, its power can be obtained. It should be: ； in: To test the reflection coefficient of the filter in the channel unit, Here, C represents the insertion loss of the coupler, C represents the coupling degree of the directional coupler, and ISO represents the isolation degree of the directional coupler. For the filter under test in f O Insertion loss, For the test piece in Insertion loss at point (PO-ISO) is the leakage through each channel during forward transmission.
6. The vector network analyzer according to claim 4, characterized in that, The reference mixer signal of the reference channel in S-parameter test module two is limited by the local oscillator-to-RF port rejection ratio of the mixer local oscillator. The signal will leak to the test channel through the reference channel of the coupler in S-parameter test module two, similar to the original test signal. Mixing generates a new parasitic intermediate frequency: ; The power of the intermediate frequency signal can be calculated based on its generation and transmission path as follows: ； When testing a filter, if there is a passband at 2 times the frequency, the test value of S21 depends on the amplitude of the test intermediate frequency and the parasitic intermediate frequency. If the stopband rejection ratio is large enough, the amplitude of the parasitic intermediate frequency is greater than the actual test intermediate frequency, and the true test result cannot be obtained. If the stopband rejection ratio is not high enough, the parasitic intermediate frequency amplitude will be smaller than the actual test intermediate frequency, and the test result will be normal.
7. The vector network analyzer according to claim 4, characterized in that, Channel leakage analysis: The passband of the filter amplification unit is the operating frequency band of the S-parameter test module, the stopband covers approximately three times the passband, and provides the highest possible suppression within a two-times frequency range, achieving [the desired level of suppression]. Suppress, so that: ； For actual testing, the intermediate frequency, This represents the mid-frequency amplitude of the parasitic medium.