This section performs a variety of the functions most associated with the Vector Network Analyzer. This instrument measures a complex set of values these parameters are knows as S-Parameters. This function set will perform S-Parameter conversions of units and also for impedance change of the measurement system or DUT. These functions also include ones for phase length, and all the basic calibration kit definition suite of functions. I also included the coax, waveguide and stripline calculators to make them convenient for the waveguide cutoff, the Offset Length, and other parameters.
This section covers the majority of the cal kit definition functions of Offset Loss, Offset Delay and Offset Zo.
Offset loss is used by Agilent to characterize the loss of the calibration kit component so the VNA can model the loss. Enter the RF Loss in dB at 1Ghz, The Offset Zo calculated using Offset Zo, the physical length and the dielectric constant Er. Press calculate to perform calculation and “Clear” to clear and start over, Er defaults to 1.0.
Offset delay is the electrical delay of the cal kit component based on it’s physical length and the Dielectric constant Er. It can also be determined from the Frequency and Phase delta. In the case shown, I entered the physical length and the frequency and used the default Er of 1.0 (air). Pressing “Calculate” it computed the Phase in degrees and the delay in nanoseconds. Press “Clear” to clear the text boxes and start over, Er defaults to 1.0.
Offset Zo is a simplified version of the Coax impedance calculator on another tab. I am presenting the version here Agilent has in their Application notes. Enter the Inner and Outer diameter and the Dielectric Constant Er and Ur if non-unity. Press “Calculate” to calculate Zo in ohms or press “Clear” to clear and start over again Er and Ur default to 1.0.
Figure 77 – VNA Cal Kit Definitions
This section covers the remainder of the cal kit definition functions of C Effective, Waveguide Actual Delay and the Frequency Resolution.
This function will compute the C effective for the phase shift of the cal kit standard. Enter the Phase offset, the frequency, the Zo characteristic impedance of the standard and the Cx capacitive Impedance. Press “Calculate “ to compute the C-effective in pF and press “Clear” to start over. This function again has many multifunction possibilities. Enter in the Ceff and it will figure one of the other missing values.
The waveguide delay figures the true delay of waveguide that changes as the frequency of operation gets closer or beyond waveguide cut-off. Use the pull down combo box to select the waveguide type, enter the delay of the waveguide when it is in TEM 01 mode and finally enter the frequency of the measurement in GHz. Press “Calculate” to figure the Actual waveguide delay in nS or “Clear” to clear text boxes and rerun.
The frequency resolution is a simpler version of the Frequency tool. I put this here to aid in figuring the VNA setup while working in this section. By entering any three of the four variables it will calculate the missing one. So you can use it to calculate Start, Stop, Stop frequency and or number of points. Keep in mind that the Agilent VNA like to see 51, 101, 201, 401, 801 and 1601 points. My fuller tool on another screen has features to see each frequency and even search for nearest lower, higher or closest frequency point to the trace point frequencies. So enter any three variables in MHz or points and press “Calculate” to compute the missing one or “Clear” to clear and start over.
Figure 78 – VNA More Cal Kits
This section will perform the Phase Length and delay and also the group delay.
Phase delay is the electrical length of a device based on it phase length in degrees and dielectric constant and frequency. Enter the Phase Delay in degrees, Frequency in MHz, Dielectric Constant Er and press “Calculate” to compute and “Clear” to start over. As an addition feature if the delay in air is known it will back compute the missing Phase Delay or frequency provide the other is known.
Group delay is the rates of change of the phase vs the frequency. This is also known as the first derivative of the phase vs frequency. Enter any two of the Delta Phase in degrees change, the frequency change in MHz and press Calculate the Group Delay in nS. If you know the group delay and frequency or phase you can calculate the missing value.
Figure 79 – VNA Phase and Group Delay
This section is for converting S-Parameter units from one to another. In my work we mostly use dB-Degrees for Magnitude and Angle measurements off the Vector Network Analyzer. Adding the frequency of the measurement allows one to convert to the Impedance and it’s inverse the Immitance.
This function will compute the Renormalized S Parameters when you convert Measured S-Parameters to another Impedance Plane for the System. Most VNA systems are 50Ohm system impedance. In many cases the impedance of the device and fixturing around it may be another impedance plane such as 75Ohm unbalanced line.
Selecting this tab the user can perform calculation for MicroStrip line width, height from ground plane or Dielectric Thickness, Characteristic Impedance - Zo and Dielectric Constant - Er. The user can input any three of these quantities and the program will compute the remainder and the velocity factor as a ratio of the speed of light. In addition, if the frequency of use is input then the full and quarter wavelengths are computed. I have defaulted to 1Ghz frequency input.
Figure 80 – VNA Microstrip
Selecting this tab the user can perform calculation for Waveguide by giving inputs of width, height, Dielectric Constant – Er and the wave mode to compute the rest. In addition, if the frequency of use is input then the full and quarter wavelengths are computed. I have defaulted to 1Ghz frequency input. Included in the calculations are the Cut-off frequency, the Upper and Lower Operating Range and the Velocity factor of propagation. By checking the PreDef Waveguide checkbox the user gets the calculations for all the predefined waveguide. Unchecking the box allows the user to input non-standard waveguide dimensions to calculate.
Figure 81 – VNA Waveguide
This tab selection gives the user the functions to compute the characteristics of Coax Cable. The user can select from Predefined Coax types by checking the Defined Coax box or Custom Inputs by unchecking. The user can input his own variables in custom input mode. The four basic inputs are Inner Diameter (in), Outer Diameter (in), Dielectric Constant-Er and Characteristic Impedance-Zo. Input any of these three and Press the “Calculate Coax” button to compute the remaining fourth main element. The rest of the calculations are performed from the basic inputs and the Frequency Input. It computes the Cut-off frequency, Capacitance and Inductance per foot, the Time Delay, Velocity of Propagation as percent of light. With the frequency input it will add the calculation of full and quarter wavelength. I have defaulted to 1Ghz frequency input.
Figure 82 – VNA Coax
This menu selection will give the operator the option of Reflection or Transmission Error analysis for Vector Network Analyzer measurements.
This section performs the Vector Network Analyzer Transmission Error Analysis. Enter the Source Match, Load Match, Crosstalk, Transmission Tracking and Device S11, S21 and S22 in dB format. Then press “Calculate” to give the upper and lower Return Loss (RL) error bounds for the measurement of Return Loss for the device under test. Press “Clear” to re-enter or “Close” to quit.
Figure 102 – Vector Transmission Error
This section performs the Vector Network Analyzer Reflection Error Analysis. Enter the Coupler Directivity, Source Match, Reflection Tracking and Device Return Loss all in dB format. Then press “Calculate” to give the upper and lower Return Loss (RL) error bounds for the measurement of Return Loss for the device under test. Press “Clear” to re-enter or “Close” to quit.
Figure 103 – Vector Reflection Error