Non-plug-in device measurement

Due to the needs of microwave engineering, most of the ports of microwave radio frequency components are females, while the ports of the cable connection devices are one female and one male. These microwave radio frequency components cannot be directly connected to the vector network analyzer for direct test. It is a non-plug-in device. In the actual measurement, there are a large number of non-inserting devices, their port connection types are opposite, the cathode and anode characteristics are the same, and the direct measurement cannot be performed directly during calibration. In order to connect a non-plug-in device to the vector network analyzer, a double-female or double-male adapter must be added, so that the test value of the vector network analyzer is not the actual value of the DUT, but the value of the DUT plus the adapter .

    In general measurement, the influence of the adapter is ignored, and the measured result is considered to be the actual value of the DUT. The loss and delay of the adapter are added to the DUT invisibly, so that the accurate value of the DUT cannot be obtained. . Or use different calibration methods in the test, for example, the characteristic undetermined pass-through method, characteristic-determined pass-through method, adapter exchange method, adapter removal, etc., to reduce the impact of the adapter on the DUT, but these methods are both good and bad. It is not possible to directly remove the influence of the adapter on non-inserting devices. This article uses a single port to test adapters with unknown characteristics (such as double male and double female connectors). According to the algorithm and assumptions, the theoretical calculation value after cascading is close to the actual measured value, and then the value of the adapter is determined, and the measured value is finally obtained. The accurate value of the component, so as to eliminate the influence of the adapter on the component under test during the test.

    1 Principle

    The signal flow diagram (shown in Figure 1) combined with scattering parameters is a simple and effective method for analyzing microwave networks and microwave measurement systems. The flow graph formula is also called Mason’s non-touching loop rule (Mason’s non-touching loop rule), or Mason’s formula for short. According to the Mason formula, the transmission value between any two points in the signal flow graph can be directly calculated.

    2 Verification process

    There are many kinds of adapters. For research convenience and universality, this experiment uses double-female and double-female as verification. The principle and process of other types of adapters are also the same.

    In the experiment, one vector network analyzer (100 MHz～40 GHz), two cables, one set of 2.4 mm calibration kits (AV31123, calibration kits and cables must be high in accuracy, with small errors) are used in the experiment, programmable 1 step attenuator. Set the linear frequency range from 1 to 21 GHz, take one point every 100 MHz, the number of sweep points is 201, and the intermediate frequency bandwidth is 100 Hz. Connect the cables to the two ports of the vector network analyzer and perform full two-port SOLT calibration on the cable. The cable port is the calibration end face, and 12 system errors are eliminated. After the preparatory work is completed, use different methods to test. In method 1, the dual cathode and dual anode values are calculated by connecting a 50Ω matched load; in method 2, the dual cathode and dual anode values are calculated by connecting a programmable step attenuator. The following is the detailed process of the two methods.

    2.1 Method 1

    After connecting the double male connector to port 1, connect the opener, the short-circuiter, and the 50 Ω matched load (as shown in Figure 2), and the measured reflection coefficients are ΓAO, ΓAS, and ΓAL respectively. After connecting the double female connector to port 2, connect the opener, the short circuit, and the 50Ω matched load (as shown in Figure 3), and the measured reflection coefficients are ΓBO, ΓBS, and Γ BL. Then port 1 directly add an opener, a short circuit, and a 50 Ω matched load, and the measured reflection coefficients are Γ1O, Γ1S, and Γ1L (as shown in Figure 4). Port 2 is directly added with an opener and a short circuit, and the measured reflection coefficients are respectively Γ2O, Γ2S, and Γ2L (as shown in Figure 5).

    Figure 5 Port 2 is connected to circuit breaker, short circuit, and matching load

    From equation (2), the equations of double yang and double negative [SA] and [SB] can be obtained as follows:

    In the formula: m11, m12, m21, and m22 are the parameter values of the double male connector to be tested, and n11, n12, n21, and n22 are the S parameter values of the double female connector. Assuming that the network reciprocity has, m12 = m21 n12 = n21, the system of equations can be solved for the double-positive S-parameter matrix SA and the double-negative S-parameter matrix SB. They are:

    2.2 Method 2

    Use a 2O dB attenuator as the load to replace the 50 Ω matched load in Method 1, and use a vector network analyzer to measure the reflection coefficients ΓAL and ΓBL of the attenuator connected to the double cathode and double anode, and the measured reflection coefficients of the 20 dB attenuator are Γ 1L respectively. , Γ2L. The other steps are similar to Method 1. Calculate S and compare it with method 1.

    3 verification

    For the feasibility of the above method, two methods are used to verify the calculated value of the double male and double female connector.

    3.1 Cascade double positive and double negative

    First calculate the S parameter after the double-yin and double-yang cascade. The S parameter of the cascaded two-port network cannot be directly calculated. You need to convert the S parameter to the T parameter to find the cascading value [TAB]-[TA][TB], and then convert the cascaded [TAB] to [ SAB]. Cascade the double anode and double cathode (as shown in Figure 6).

    Figure 6 Double positive and double negative cascade

    The S parameters obtained by the above method are reference values, and these values are compared with the S parameters calculated by the Mason formula. All the test data are processed with MATLAB software, and the S-parameter curve after the final cascade is simulated and compared with the S-parameter curve tested in the vector network analyzer.

    It can be seen from Figure 7 that the difference between S12 and S21 is very small, but there are some differences between S11 and S22. The two curves of method 1 with 50 Ω matched load and method 2 with 20 dB attenuator are basically the same. No matter what kind of load is connected after double anode and double cathode cascade, the cascade value is a fixed value. The reason for the difference is that the 20 dB attenuator is not a standard device, and there is reflection when the double anode and double cathode are cascaded.

    Figure 7 S11, S22 calculated by double-anode and double-cathode 20 dB attenuator and tested by vector network analyzer

    The curve diagram of the theoretical calculation value of S11 is very close to the test curve of the vector network analyzer. In the low frequency band, the curve diagram of the theoretical calculation value of S22 is consistent with the test curve of the vector network analyzer. The curve diagram of the theoretical calculation value is better at high frequencies because the reflection coefficient is below -40 dB and the isolation is higher. In fact, the connection ports of double anode and double cathode are affected during the pass-through test. Therefore, the theoretical calculated value is more than the measured value.

    In the test, there are multiple connections to the standard parts, adapters and attenuators, and each connection will cause human errors to varying degrees. The value of the standard part is obtained by the test after calibration of the vector network, and no higher calibration system is used for testing. The measurement of the transmission parameters is indispensable for obtaining the s-parameters, but in the experiment, the transmission parameters are only obtained indirectly by measuring the reflection coefficient. Various factors cause certain errors in the results. Some corrections to these errors can get better results.

    3.2 Programmable step attenuator

    The following verification uses a programmable step attenuator. The DUT has attenuation values of 0, 10 dB, 20 dB, 30 dB, 40 dB, 50 dB, and 60 dB. The S parameters of the attenuator are calculated from experimental data (as shown in Figures 8-10).

    From the above calculation results, it can be seen that the S parameters of the programmable step attenuator calculated without the double-male and double-female connectors get the expected result. The calculated value of the attenuator is verified to be consistent with the transmission parameters and reflection parameters given by Agilent.

    4 Conclusion

    This article is a confirmatory experiment, by calculating double-female and double-female adapters to remove their impact on non-inserting devices in the test. Specialization and simplification of common adapter problems, but this has a theoretical breakthrough in the measurement of other adapters and further research on port extension and de-embedding technology.