Optenni Newsletter 3/2011

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Optenni Newsletter 3/2011

Optenni Ltd

Ranking of antennas by obtainable impedance bandwidth in Optenni Lab

Besides matching circuit design and optimization, Optenni Lab also includes several methods for estimating the obtainable impedance bandwidth of antennas. These functionalities can be used in an early antenna design phase to evaluate and rank differently matched antennas. The preferred method is the bandwidth potential approach that can be applied also to wideband and multiresonant antennas.

Bandwidth potential

The main tool for estimating the obtainable impedance bandwidth in Optenni Lab is called bandwidth potential. It implicitly constructs different two-component matching circuits for various frequencies and calculates the obtainable impedance bandwidth through the circuits. The bandwidth potential calculation is available in two variants:

  • Standard (for narrowband antennas): This is based on matching to 50 Ohms or conjugate matching at a point frequency and is a very quick computation that gives a reasonable estimate for narrowband antennas.
  • Optimized (for wideband and multiresonant antennas): Here the maximum impedance bandwidth through a two-component matching circuit is found out at each frequency. The calculation takes some tens of seconds and is more realistic than the standard approach as it can handle wideband and multiresonant antennas.

Optenni Lab also includes Q factor estimation directly from the impedance data using a formula derived by Yaghjian and Best. However, this formula can only be used for narrowband single resonant antennas as the Q factor is not even defined for multiresonant antennas. Thus, it is normally better to use the bandwidth potential calculation for the bandwidth estimation.

Ranking of antenna candidates

The bandwidth potential calculation gives a figure of merit that can be used in the antenna concept design phase to select best possible antenna candidates. Bandwidth potential normalizes the impedance matching so that differently matched antennas and also nonresonant antennas can be compared in a fair way.

The bandwidth potential calculation can be very useful in interpreting the results of parameter sweeps. In a parameter sweep, the impedance matching is typically changing in a complex way and only looking at the raw impedance data might lead to wrong conclusions about the antenna bandwidth. A better way of analyzing the parameter sweep is to compare the bandwidth potential curves calculated from the different parameter values of your antenna.

For more information about the Optenni Lab tools for estimating the impedance bandwidth, please visit this web page or contact us.

PS. The story goes on. The next Optenni Lab version (1.4) will include some additional functionality for antenna bandwidth estimation, but this will be covered in another newsletter.

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