Lambda/4 Loop Antenna

     I am modeling a quarter-wave loop antenna typically referred to in the
     Ham radio literature as a DDRR or Halo antenna. This loop is about a
     quarter-wave in circumference at 137 MHz and is mounted about 1" over
     a ground plane. The antenna is easily matched to a 50 ohm coax cable.
     
     I have had some problems modeling the input impedance of this antenna
     with NEC2D and NEC3D. Of particular concern is an erratic impedance
     behavior near resonance and negative resistance several MHz above
     resonance.
     
     I was wondering if anyone has modeled a similar antenna with similar
     problems. I would also like to know of any good references in the
     literature related to this type of antenna.
     
     Thanks for any input you may have,
     
     Jeff Fordham
     Associate Staff Engineer
     Scientific Atlanta
     (Jeff.Fordham_at_SciAtl.com)
     
     ============================================================
     CM Quarter-Wave Loop Antenna over Ground Plane
     CM Single Loop Designed @ 137.5 MHz
     CM Loop Radius(in) 3.5
     CE Ground Plane Space(in.) 1.0 in.
     GA,135,1,3.5,0,-8,0.125
     GM,100,43,0,8,0,0,0
     GM,0,0,90,0,0,0,0
     GM,0,0,0,0,0,0,0,1.0
     GW,52,3,3.5,0,1.0,3.5,0,0,0.125
     GW,53,1,3.36442,.9647,1.0,3.36442,.9647,0,0.025
     GW,54,1,3.46594,-.48711,1.,3.4915,-.244,1.,0.125
     GS,0,0,0.0254
     GE,1
     GN,1
     FR,0,20,0,0,130,1,0,
     PT,-2
     PL,3,1,0,3
     EX,0,53,1,1,1,0
     RP,0,37,3,1010,-90,0,5,45
     EN
     =============================================================
     
Received on Fri Mar 29 1996 - 19:39:00 EST