<Linear TDR>

Linear TDR Measurements

This project demonstrates how to use the linear TDR measurement capability of MWO.  This capability is the same as using a Vector Network Analyzer to do TDR measurements, so the frequency span and frequency steps should match lab equipment when comparing results to measured data.  It also demonstrates the use of equations to convert simulated reflection coefficient to impedance.

Overview
A simple circuit has been employed to study the standard TDR measurement problem when a length of transmission line is terminated with a resistance.  The resistance is coupled to the transmission line using two reactive elements that can represent discontinuities.  For example, these discontinuities could be found in a typical coaxial to microstrip transition.  Other elements can be added to suit the needs of the designer.

The primary elements, R, L and C can be tuned (Simulate > Tune).  The terminating resistance is defined using the vector equation capability of MWO.  Here we see that the resistance has a fixed set of values, ranging from 0 - 200W.  If required, this list (or vector) can be edited and other resistance values can be added or removed.   The equations for the resistance values are found in the main schematic window.  The equations used to collect the reflection coefficient and convert this to impedance are found in the output equations window.

Simulation Plots

Reflection TDR
This graph displays the results from the TDR measurement directly.   The reflection coefficient vs. time is being displayed.  The two traces show the TDR measurements for step (blue) and impulse (magenta) response.

Impedance TDR
This graph displays the results from the equation used to convert between reflection coefficient and impedance.

<Class E Amplifier>

Class E Amplifier

This is a basic Class E power amplifier designed using the procedures in "RF Power Amplifiers for Wireless Communications (Cripps/Artech), Chapter 6.

Overview
The waveforms show the typical Class E asymmetrical current pulse, and highly peaked voltage.

Tuning the drain capacitor shows a sharp tradeoff between efficiency and RF power. The PAE can approach 90%.

The RF power is nominally around 1 watt for 4.8v supply. It should be noted that the MESFET transistor used in this example has a power capability of about 3Watts if used in a conventional Class AB mode. This is the "power efficacy" issue, also discussed in the reference.

This is a good template project showing all the characteristics of the circuit that can be simulated.  

<AMR Example>

This project compares a simple microstrip line simulated in the available Analyst (3D FEM), AXIEM (2.5D Method of Moments) and Linear (Closed Form) solvers.

Download
Simulating this project is time-consuming.  This example, with the datasets included, is available at:  http://kb.awr.com/display/Examples/AMR_Example

Overview
The purpose of this example is to see how changing the Adaptive Mesh Refinement (AMR) in Analyst will affect the simulation results.

This example consists of a microstrip line simulated in the Analyst, AXIEM and linear simulation. Depending on what AMR you select in the Analyst, the simulation results will vary from the AXIEM and linear simulation.

There are three different Analyst EM structures of the same microstrip line with different AMR tolerances of low, medium and high. The AMR tolerance can be changed by right clicking on the structure and selecting Options and then go to Analyst tab. The structure with the low tolerance is the closest to AXIEM and linear simulation results.em:Analyst_Line_High_Tolerance

Once the Analyst simulation starts, if you look at the simulation dialog window you would see that the simulation goes through two stages. First is the Ports Only AMR which the simulator refines the mesh until a converged port solution is obtained. Second stage is the Full Solve AMR which happens after Ports Only AMR and the convergence criteria is based on the scattering matrix. If an asterisk appears next to an item, it means that that item is converged.

Simulation Plots
There are two graphs in the project. The first one shows the difference of the phase of S21 between the AXIEM structure, the 3 Analyst structures, and the schematic. gph:Delta Phase The second graph shows the weighted difference between the s-parameters of the AXIEM structure and the Analyst structures.gph:SModel

Refining the Solution
Once a simulation is completed, you can simulate again in a special model telling the simulator to refine the solution one more time.   Right click on any Analyst EM Structure and select "Refine Solution".  This will start at the previous solution saving the time it would have taken to get to start from the beginning.