Re: NEC-LIST: Modelling slot on large cylinder?

On Mon, 28 Apr 1997, Stanley Lim Hock Hin wrote:

> Good day everyone,
>
> Has anyone done any modelling of narrow slot on large cylinder (diameter
> of the cylinder greater than a wavelength) using NEC-2. Is there any
> particular discrepancy? Any response is appreciated.
>
> Thanks,
> Stanley

   Stan:

   For cylinder sizes greater than 3/4 lambda, the NEC2 code and the
   exact eigenfunction expansions hardly agree. Some years ago, I
   had the `misfortune' of computing the eigenfunction expansion for
   a PEC circular cylinder due to a line source. The formulas were from
   Jim Wait's classic monograph, and the series converged rather too
   slowly. The D'Alembert's ratio test actually could NOT work, and I
   was convinced that for ka > 5 the whole series was computationally
   useless, although it was the exact answer.
 
   To model a narrow axial slot (1/2 lambda in length), use the
   NEC-BSC3 code. That is, use a 1/2 lambda magnetic dipole to model
   the narrow slot, and locate it OFF the cylinder by 0.25*lambda.
   (This is necessary in order to be within the legal limits of the
   theory in the NEC-BSC3 code.) You may expect satisfactory results
   for ka=5 and above. Improved agreements may be obtained as the
   ka value increases. For our work here at the University of Kansas,
   we normally use NEC-BSC3 and the eigenfunction expansion for
   covering both low and high values of ka.

   I am not so sure about NEC2 code, and Jerry can provide more input
   on this.

  - cheers,
 =================================================================
  Deb Chatterjee

  Radar Systems and Remote Sensing Laboratory
  Department of Electrical Engineering and Computer Science
  Room 322, Nichols Hall
  2291 Irving Hill Road
  Lawrence, KS 66045-2969

  tel: (913)864-7742
  fax: (913)864-7789
  e-mail: dchatterjee_at_kuhub.cc.ukans.edu
Received on Fri May 02 1997 - 03:36:00 EDT