What is RF modeling?

Discussion in 'Wireless & RF Design' started by Highlight, Sep 28, 2011.

  1. Highlight

    Thread Starter New Member

    Nov 26, 2010
    Sorry if this is a dumb question but what exactly is "RF modeling and Simulation"?..As in what does an RF modeling engineer do. Does it simply mean to model how a circuit or circuit component works at RF frequencies? Thank you for your info.
  2. mixed_signal

    New Member

    Dec 5, 2009
    Not a dumb question...

    You have pretty much explained it. At "low" frequencies, circuits can be reasonably accurately modeled as "lumped elements" of R, L, C and source components.

    A few examples of changes as you move to higher frequencies:

    The behavior of "small" parasitic capacitance and inductance packages, PC board pads and traces, bond wires, etc. become more important to circuit behavior (higher series or lower shunt impedance). So circuit component models become more complicated to account for the parasitic elements.

    As circuit dimensions approach a significant portion of a wavelength at the operating (or relevant) frequencies, traces and wires no longer act as "shorts" between elements. They start behaving like transmission lines. S-parameters that describe transmitted and reflected power at different "ports" of the circuit elements are often used. Network analyzers are often used to measure S-parameters. Smith Charts are often used to plot s-parameters and to make calculations or aid understanding.

    An RF design engineer learns and develops methods to make accurate measurements of devices and boards or layouts to "extract" the parasitics and measure a component's s-parameters. Even if one doesn't spend much time doing modeling or extraction, a good RF designer will understand how this is done and understand what is needed to have accurate models for their circuit simulations.

    There are a number of topics somewhat unique to RF design: RF low-noise amplifier (LNA) design, frequency conversion circuits (mixers), impedance matching circuits, antenna design, microstrip and stripline filter design, LC and other types of resonator based oscillator design, transmitter and RF power amplifier design, non-linear behavior of devices and circuits (intermodulation distortion), etc. This study is also closely related to RF system and communication system design (receiver system design, modulation formats, multiple access schemes, protocols, etc.). Each of these topics have a long history and large volume of literature around them.

    A few good intro texts are below. Even early editions of are quite worthwhile.
    Modern Communication Circuits, Jack Smith
    Digital and Analog Communications Systems, Leon Couch