NEC-LIST: Re: Equivalent diameter

          Roy, and all:
          
          This subject has come up before and I have yet to be
          satisfied by any answers that I could apply, but the
          following is offered: In the paper, "Problems in Strip
          Transmission Lines" by S. B. Cohn (IRE Trans. on M.T.&T.,
          Vol. 3, pp119-126, March 1955) the relationship between
          circular and rectangular cross sections is cited in two
          references. Cohn uses this to determine the characteristic
          impedance of a rectangular center conductor in stripline
          (TEM-mode) when he has an analytic expression for a round
          one. One has to take Conh's use of the analyses as
          applicable to one's own problem. The reference I found,
          "Waveguide Handbook" by Marcuvitz, p.263, has some fairly
          complicated analytic functions which would require solving
          for the inverse elliptical integrals of first and second
          kinds. However, the same plot is given in both of the above
          references and is fairly smooth. It is tabulated below:
          
          d"/d' do/d' do = diameter of rod.
          ----- ----- rectangular bar is d" x d'.
          0 0.50 d" < d'.
          .1 0.59
          .2 0.67
          .3 0.74
          .4 0.81
          .5 0.875
          .6 0.94
          .7 1.00
          .8 1.06
          .9 1.12
          1.0 1.18
          
          The rectangular conductor is d' wide and d" thick, d"<d' and
          the circular conductor's diameter is do.
          
          I hope this helps; maybe someone can connect the dots with
          an equation.
          
          73, Paul Gili, AA1LL
          5 White St., Greenville, NH, 03048
          
          Sr. E.E., Electromagnetic Center Of Technology
          Sanders, A Lockheed Martin Co. (603)885-3938
          
          pgili_at_mailgw.sanders.lockheed.com
          
Received on Wed Mar 26 1997 - 09:35:49 EST