Antenna System Parameters

This calculator worksheet allows one to examine the relationships of antenna system parameters and their impact on antenna system operation. If one runs a sufficient number of example calculations, it becomes clear that any combination of transmission line loss and SWR, Return Loss, or forward and reflected (FWD/Ref'D) power which causes the percent of power reflected at the load to approach 100% can make the system marginal, or worse. Use the figure below for reference:

NOTE1:  All selections MUST be made, and applicable entries completed, before the calculator will work. Additionally, "Reset/Clear" action between caluclations is not absolutely necessary for all cases, but every so often the javascript "hangs" after a calculation; if your results are not as expected, use the Clear/Reset function and start over.

NOTE2:  The forward and reflected powers in the "results" will always be in Watts but, in parenthesis, these powers will also be in the units selected. For calculations based on SWR and Return Loss, reflected power will be in the units selected for entered forward power. When calculations are based on entered forward and reflected power, units will be those entered for each.

To start, Select units of forward power:   mW       W       dBm
Click on box and enter Forward Power :    

Select whether or not you wish to include transmission line losses in calculations:
  YES       NO
    If "YES" enter loss and select location of measurement:
    If "NO" go directly to "PARAMETER ENTRY" below.
    Click on box and enter line loss in dB:  
    Select location of measurement:  Line Input      Load (e.g., antenna)

Select desired Base Parameter and follow the entry instruction(s) for that parameter:
SWR:  Click on box and enter SWR:   :1

Return Loss:   Click on box and enter Return Loss:   dB
NOTE:  Return Loss must be = or > 0dB.  If including line loss & measuring at line input, value must be = or > twice the line loss.

Forward & Reflected Power:
Select units of reflected power:   mW       W       dBm
Click on box and enter Reflected Power :  
NOTE:  Reflected Power must be < or = Forward Power.

Click on and scroll down for results!                                    

An ND2X javascript calculator

Note that Reflection Coefficient is the VOLTAGE form of Return Loss. Note also that Mismatch Loss is the amount of power lost due to reflection; it is as if an attenuator with value = Mismatch Loss is placed in line. The result is that the power actually getting to the antenna is the forward power shown minus the reflected power shown.

Some Interesting Mathematic Relationships:
Reflection Coefficient (r), SWR and Return Loss (R.L.) are related as follows:

r = (SWR - 1)/(SWR + 1) R.L. = |20log(r)|
SWR = (1 + r)/(1 - r) r = 10(R.L./20)


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