Full version in "Microwave System Design Tools and EW Applications" published by Artech House, Inc.
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Antenna Near Field Power

 Applet Notes

Two plot options are given, Power Density, or Power Received by an antenna of defined aperture. The powers are determined by dividing the transmitting and receiving antennas into sub-elements and integrating the powers between the elements. To achieve a reasonable accuracy many elements are used which can make this applet somewhat slow.

Default values may be modified and the display updated using scroll bars and the 'Enter' Button. The display automatically scales, dependent on the parameter values selected. The Fresnel Zone range is calculated from the common formula, 2xDxD/lambda; where D is the transmitting antenna largest (width) dimension.

The red curves indicate the power responses using the long-range inverse square law formula.

Mouse movement in Range - Power space indicates the main plot values relative to the mouse x-axis position.

The Save Button saves plot data to the Java Console ( slow if the console is open) with a summary of the relevant component parameters. Data may be selected on the Console using the mouse (Shift-click) and copied to the clipboard ( Ctrl C ) and saved in a text file for a permanent record or transferring to Excel for example.

If visual plots are required, Alt-Printscreen, copies the current window to MS Clipboard.

To speed up response in the power received mode, whilst testing the effects of parameter ranges, choose coarse plot resolution (C radio button).
Once the wanted geometry is found, fine mode provides for increased accuracy. Also, for better detail in the very near zone adjust the upper scale range and use F, fine resolution.
The Fresnel zone range is calculated from the standard formula, 2D2/lambda, where D is the transmitting antenna largest (width) dimension.
Antenna width and height dimensions are in multiples of the signal wavelength (denoted by WL).
At close ranges, below about one-fifth of the Fresnel zone range and especially for low edge tapers, the power density flattens to approximately that expected by dividing the prime source power by the antenna physical area.

Because of the relatively coarse integration, accuracy no better than 1dB can be expected.