Using time domain is the best method. Time domain is available on the analyzer. Characteristic impedance measurments can be a bit difficult because the impedance may vary along the line, so that must be taken into account.

Thanks Dr. Joel. Can you explaine more about the time domain method? I saw the ENA has a analysis function. Under the convertion function there's Z:reflection, Z:transmission....etc. may I know what are these and how do they work? As I had try to seach on the web but was unable to locate the manual guide for these function.

Z:reflection and Z:transmission are intended for discrete elements; here is a description I wrote for another publication: 2.5 Modeling Circuits using Y and Z Conversion One common desire in evaluating the performance of a component is to model that component as a single series or shunt element. These desire was furthered by some built-in transformation functions on VNAs, first introduced with the HP8753A but common now on many models. The goal was to model a device in such a way that the S-parameters mapped to a single resistive and reactive element, in the Z-transform case, or a single conductance and susceptance in a the Y-transform case. These were quite simple models, and represented in Figure 2.41. Figure 2.41 Y and Z conversion circuits 2.5.1 Reflection Conversion Reflection conversions are computed from the S11 trace, and are essentially the same values a presented by impedance or admittance readouts of the Smith chart markers. Thus, Z-reflection conversion would be used with the circuit description from Figure 2.41a, and display the impedance in the real part of the result and the reactance in the imaginary part of the result. Y-reflection would be used with the circuit of Figure 2.41b, and display the conductance in the real part and the susceptance in the imaginary part of the result. The computations for these conversions are (2.27) Typically, these conversions would be used on 1-port devices and measurements. If it is used on a 2-port device, one must remember that the load impedance will affect the measured value of the Z- or Y- reflected conversion. 2.5.2 Transmission Conversion These reflection conversions are already well known as the models represented by the Smith chart, but a similar conversion can be performed for a simple transmission measurement. In this case, the circuits of Figure 2.41 c and d are the reference circuits for these conversions. They are useful when analyzing the series element models such as coupling capacitors, and the models for series resistors and inductors. The underlying computation for the transmission conversions are (2.28) The Z-transmission conversion would be well suited to view the series resistance of a coupling capacitor. The Y-transmission would show the resistive value of a series mounted SMT resistor with a shunt capacitance as a constant conductance with a reactance increasing as , forming a straight reactance line. These conversions are often confused with conversion to Y- or Z- parameters, but they are not, in general, related. These provide simple modeling functions based on a single S-parameter, whereas the Y-, Z- and related parameters provide a matrix result and require knowledge of all four S-parameters as well as the reference impedance. These other matrix parameters are described in the next section.

Z:reflection and Z:transmission are intended for discrete elements; here is a description I wrote for another publication:

2.5 Modeling Circuits using Y and Z Conversion

One common desire in evaluating the performance of a component is to model that component as a single series or shunt element. These desire was furthered by some built-in transformation functions on VNAs, first introduced with the HP8753A but common now on many models. The goal was to model a device in such a way that the S-parameters mapped to a single resistive and reactive element, in the Z-transform case, or a single conductance and susceptance in a the Y-transform case. These were quite simple models, and represented in Figure 2.41.

Figure 2.41 Y and Z conversion circuits

2.5.1 Reflection Conversion

Reflection conversions are computed from the S11 trace, and are essentially the same values a presented by impedance or admittance readouts of the Smith chart markers. Thus, Z-reflection conversion would be used with the circuit description from Figure 2.41a, and display the impedance in the real part of the result and the reactance in the imaginary part of the result. Y-reflection would be used with the circuit of Figure 2.41b, and display the conductance in the real part and the susceptance in the imaginary part of the result. The computations for these conversions are

(2.27)

Typically, these conversions would be used on 1-port devices and measurements. If it is used on a 2-port device, one must remember that the load impedance will affect the measured value of the Z- or Y- reflected conversion.

2.5.2 Transmission Conversion

These reflection conversions are already well known as the models represented by the Smith chart, but a similar conversion can be performed for a simple transmission measurement. In this case, the circuits of Figure 2.41 c and d are the reference circuits for these conversions. They are useful when analyzing the series element models such as coupling capacitors, and the models for series resistors and inductors. The underlying computation for the transmission conversions are

(2.28)

The Z-transmission conversion would be well suited to view the series resistance of a coupling capacitor. The Y-transmission would show the resistive value of a series mounted SMT resistor with a shunt capacitance as a constant conductance with a reactance increasing as , forming a straight reactance line.

These conversions are often confused with conversion to Y- or Z- parameters, but they are not, in general, related. These provide simple modeling functions based on a single S-parameter, whereas the Y-, Z- and related parameters provide a matrix result and require knowledge of all four S-parameters as well as the reference impedance. These other matrix parameters are described in the next section.