QFH-Antenna design

  • Good Morning,

    I built a 403-QFH-Antenna for weather balloon reception. After taking some measurements, I wonder that the best ajustment is not at the design frequency, but at about 1.5 fr=630MHz. At the design frequency S11=-13,5dB and at 630MHz S11 is about -30dB. How can I get the best match at the design frequency?. What did I wrong?

    Who can help?


  • Hi Achim,

    the design is according to jcoppens with his calculator at "https://jcoppens.com/ant/qth/calc.en.php" with 2.5mm conductor. I made another one for 137MHz with 10mm conductor and got S11=22dB. But I addmit at that time I didn´t look for other resonant points at higher frequencies. The function of the QFH-Antenna is similar to the patch antenna to get a circular polarisation discussed in this forum.

    Vy 73 Georg

  • Hi,

    I think my problem is solved. After a new construction the result is acceptable.

    The physical dimensions of the small loop were wrong. This was the reason, why it was not possible to get an unique match. Further more a critical point is the connection of the coax cable to the feed point.

    Vy73, Georg