Helix for Offset Dish - help

  • Hello,

    the calculation (HDL_ANT2_WinForms by W1GHZ) for my offset dish pruduced following results:

    - f/D = 0,36, illumination small axis = 68,1deg and a recommendation for -3dB beamwidth = 38,8deg.

    With that in mind various helices were calculated. The best result was with 9turns:

    So far,this result does not match the recommendation. Compared with all the publications in the net and here in the forum the amout of turns is more or less doubled. I also couldn`t find any discussion about matching the helix and dish illumination. It is clear that this should match, but nobody does take care of this subject.

    Further more, I think that a patch antenna will not be acceptable for this f/D because of the broad overspill.

    My concern is, that such a helix will creat troubles with my neighbors wlan.

    What are your experience and recommendations:?:

  • Hi Hebert,

    leider nein. Dort wird eine Helix mit 3 Windungen und einem -10dB Öffungungswinkel von 105 Grad gearbeitet. Angegeben wird auch für ein f/D=0,66 ein Winkel von ca.70Grad. Das stimmt mit meinen Infos überein. Leider hat mein offset Spiegel ein f/D von 0,36.

    DL6YCL has an offset-dish with f/D=0,66 and an illumination angle of 105deg. He mentioned that a Poty has an angle of 110deg.