[天线]New approximate formulations for EM scattering by dielectric objects

684 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 3, MARCH 2004 , tb\^  
New Approximate Formulations for EM Scattering (Xv'Te?  
by Dielectric Objects Tt\h#E  
Tie Jun Cui, Senior Member, IEEE, Weng Cho Chew, Fellow, IEEE, and Wei Hong, Member, IEEE sjIUW$  
Abstract—The extended Born approximation (ExBorn) has <g3)!VR^q  
been shown an efficient formulation in the electromagnetic (EM) _'Rzu'$`  
scattering by dielectric objects in both free-space and air-earth .0]\a~x  
half-space problems. In most cases, ExBorn is much more accurate ckhU@C|=*  
than the conventional Born approximation at low frequencies. Z(c3GmY  
When the frequency is high or the contrast of dielectric objects is g*]/HS>e<G  
large, however, the ExBorn approximation becomes inaccurate. vj,OX~|  
In this paper, new approximations are proposed for the EM 8urX]#  
scattering by dielectric objects buried in a lossy earth, which are b;k3B7<  
also suitable for the case of free space. It has been shown that the J,SP1-L  
zeroth-order form of new approximations is completely equivalent su\iUi  
to ExBorn. Hence, high-order approximations can be regarded mtd ,m  
as high-order ExBorn. Closed-form formulations are derived lNRGlTD%  
for the new approximations. Using the fast Fourier transform ~dz,eB  
(FFT), these formulations can be implemented efficiently at a 7G]v(ay  
cost of log , where is the number of unknowns and rU!QXg]uD  
is a small number. Numerical simulations show that high-order rK@XC +`S  
ExBorn approximations are much more accurate than the ExBorn g:rjt1w`D  
approximation. L5j%4BlK/  
Index Terms—Born approximation, buried dielectric obj .. jRGslak;  
R!Lh~~@{(  

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