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AC Analysis of an RF System

This model shows how to use harmonic balance to calculate the AC steady-state frequency response curve for an LC bandpass filter built using blocks from the RF Blockset™ Circuit Envelope library.

System Architecture

The system consists of:

  • A Continuous Wave source and a series resistor, which model a voltage source with internal source impedance.

  • Inductor and Capacitor blocks configured to model a third-order Chebyshev filter with a center frequency of 2.4 GHz.

  • An Outport block acts as a voltage sensor, measuring the voltage across a load resistor.

  • The Configuration block, which sets up the circuit envelope simulation environment.

Running the Example

  1. Type open_system('simrfV2_ac_analysis') at the Command Window prompt.

  2. Double-click the block labeled 'Specify Frequency Values' to provide a vector of frequencies.

  3. Double-click the block labeled 'Calculate Frequency Response' to execute a script, simrfV2_ac_analysis_callback, that analyzes the model at the specified frequencies and plots the response.

Configuring a Model for Harmonic Balance

To configure a model with circuit envelope library blocks for harmonic balance:

  • In the Model Configuration parameters dialog box, set the Stop time parameter to zero.

  • Use a Continuous Wave block to drive the system.

  • Set the Carrier frequencies parameter in the Continuous Wave, Outport blocks, and the Fundamental Tones parameter in the Configuration block to the same vector of frequencies.


Ludwig, Reinhold and Pavel Bretchko, RF Circuit Design: Theory and Applications. Prentice-Hall, 2000.

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