Re: NEC-LIST: calculating antenna bandwidth

Subject: NEC-LIST: calculating antenna bandwidth

Before working on methods of calculating bandwidth, there is need to be
precise in defining "antenna bandwidth".
It appears that the following must be considdered, and that they are really
independent:
- Gain bandwidth= at present, undefined, =bandwidth over which the antenna
gain varies by more then X dB. May be specified as a percentage of operating
frequency. X is commonly taken as 3 dB, and must be specified if another
value is used.
- SWR bandwidth=commonly taken as the range where the drive point SWR is
less than 2:1. This is a function of the antenna drive impedance, the line
impedance and loss and the matching method.
- Antenna bandwidth= at present, undefined. Possibly best is to develop from
the gain bandwidth , or defined in terms of antenna Q=the ratio of stored
energy to radiated energy. Note that penetration into the supergain regime
must be considered. See Chu, Physical Limitations od Omni-Directiional
Antennas, J Ap. Phys., v19, Dec. 1948, and Harrington, Time Harmonic
Electromagnetic Fields, McGraw-Hill, 1961
- Backlobe bandwidth= at present, undefined. May be taken as the bandwidth
over which the F/B exceeds a certain ratio. Note the the use of back=180
degrees from the nose of the main lobe does not give an acurate picture of
the interference/antenna temperature performance.

 We need some discussion then a proposal to the IEEE Standards Group

bob havikand w4mb

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