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10334[loopantennas] RE: Receiving Phased Array with Small Electric or Magnetic Active Wideband Elements

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  • Andrew Ikin
    Dec 6, 2013
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      Dear Chavdar,

       

      Thanks for an interesting paper.

       

      I have a few comments to make: There is no provision to amplitude balance the antennas or to compensate for minor delay-line loss. One is therefore assuming that the antennas are always gain matched with frequency even when the presence of nearby objects could be affecting the gain. This will in some circumstances reduce the F/B as nearby objects (metal fences, power/phone line etc) affect the antennas near-field response especially at LF/MF.

       

      My experience with MW active dipole, active loop and active K9AY arrays using variable delay-line and switched delay-line phasing indicate that the provision to vary the antennas gain is just as important as having control over the phasing.

       

      I agree with your observation that a 1 to 10  frequency ratio is readily achievable. However, where the antenna spacing is very small, there is a further degrading in s/n due the amplifier noise not cancelling out in same way as the signal. This is more of an issue with small 1m diameter high gain loop antennas. Also with very close antenna spacing the array phasing and gain balance becomes very critical, causing pattern degradation. Therefore, it may be prudent for MW/LW use to allow for an increase in antenna spacing to over 30m.

       

      Using the above arrays at HF can be quite disappointing due to signals having too much angular variance. Loop arrays offer the worst performance because they offer little rejection of rear high angle signals.

       

      Additional Reference:

       

      Keen’s Wireless direction Finding, Third Edition 1938.

       

       

      Kind regards

       

      Andrew

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