[Moon-net] 13cm Septum measurements

[Rastislav Galuscak]

    Hello gentlemen,
       
      I would like to share with some  experiencies, I have acquired with the 13cm septum feed with  square cross-section /modeled according to  Zdenek, OK1DFC, dimension/ . The septum feed was modeled by CST Microwave  Studio software at the Czech Technical University in Prague and some computed analyzes  was verify with measurement on  real  feed on 23 cm in  university`s anechoic chamber.
       
      It possible to achieve good isolation /S21/  and good impedance match/S11/ since S paremeters  are good within the frq. range 2300 MHz (S21=26.5  dB, S11=23.7dB), 2350 MHz( S21=36dB ,S11=25dB), up to 2424 MHz where S21=32 dB,  S11=26 dB.
      For wide band impedance matching, probe with  high outer diameter must be used /up to 10 mm for 13cm/  
      For septum feed with round cross section what  is  our present project, conical shape of  probe is used with very good wideband impedance match /below 20 db within freq.  range 210 MHz on 23 cm band/
       
      Septum feed with square cross section has very  good axial ratio for main axes. The axial ratio does not exceed – 1 dB within  range Theta = -68 deg. Up to 68 deg. for Phi =0, 90 deg.in freq. range 2300/2424  Mhz.
      Axial ratio is becaming worser for cuts with Phi=  45, 135 deg. where -1 dB range Theta=         
        - 26.4  up to 26.4 is. This is the worst case for freq. 2424MHz.  
      This is the limitation of  square septum feed , since circular polarized  feed should have low axial ratio within feed substended angle for appropriate  f/D dish ratio.
      Better axial ratio and better copolarization  efficiency in parabolic antenna assembly is possible to achieve  with septum placed in wavegiude with round  cross- section.  This project is  finishing now with the tests in anechoic chamber. The results will be published  very soon in DUBUS.
       
      Noting the polarization properties of feed  described above is not possible to investigate with sun noise measurement  techniques.
       
          Detailed computed results / in 2D or 3D or ASCII format/ of square  septum feed I can send on request.
       
                73, Rasto OM6AA
    

peter blair <g3ltf at btinternet.com> wrote:   I would like to hear from anyone who has measured the match of a 13cm septum feed at 2304 or 2320 and also at 2424 MHz.
 thankyou.73 Peter G3LTF
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