NEC-LIST:Numerical errors on NEC radiation efficiency computation

I am modelling a small loop (circumference is wavelength/20). If the
loop is lossless, NEC correctly computes input resistance (radiation
resistance). When losses (copper wire) are added, the input resistance
is computed correctly, but radiation efficiency is overestimate. This
produces errors in directive gain computation, too. One way to overcome
this problem is to average the power gain over a sphere, then compute
the radiation efficiency end finally correct the directive gain.
Does anyone know a paper where the problem of NEC inaccuracy on
efficiency computation of small loops has been addressed?

Best regards
                        Piero Tognolatti

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Piero Tognolatti
Dipartimento di Ingegneria Elettrica - Universita' dell'Aquila
I-67040 Monteluco di Roio (AQ) - Italy
ph.: +39 0862 434412
fax: +39 0862 434414
e-mail: tognolatti_at_ing.univaq.it  or   p.tognolatti_at_ieee.org
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