Finite-Difference Time-Domain Design of Compact Devices With

Computational Electromagnetics (CE)

Finite-Difference Time-Domain Design of Compact Devices with Improved Characteristics

M. G. Banciu National Institute of Materials Physics, Atomiştilor 105 bis, Măgurele, jud. Ilfov, Postal Code 077125, Romania E-mail Address: [email protected]

Abstract— A FDTD software was developed in order to analyze and design compact devices for mobile communications systems. A 3-D non-uniform Perfectly Matched Layer (PML) was implemented as absorbing boundary conditions. Advanced methods of digital signal processing were successfully applied with the purpose of reduce the iterations number when simulating structures with high-Q factors.

Keywords— FDTD, Bérenger’s perfectly matched layer, dual mode filters, cross-coupled filters, mobile communications

I. INTRODUCTION Grace to its accuracy and versatility, the Finite-Difference Time-Domain (FDTD) method was already applied to microstrip devices [1, 2].

II.NON-UNIFORM PML Fig. 1. Surface plot of the Ez component below the dielectric air-interface after In this paper, the Bérenger’s Perfectly Matched Layer 1200 iterations for the meander loop 2-pole dual-mode filter. (PML) was extended to a 3-D non-uniform boundary. The electric (magnetic) conductivity was obtained by the integration of the geometric profile between two electric

(magnetic) field grid points. Then, the electric conductivity l on the electric field points is given by l  0 r ( g 1)  g   l   l0  (1  l0 )( g 1)  (1) ln g  g  where l=0,1,2… represents the grid point index inside PML,

0 is the electrical conductivity at PML interface, g is the geometric progression ratio and l0 is the Kronecker symbol. The PML exhibits nl distinct layers. The magnetic absorption Fig. 2. Cross-coupled band-pass filter for 900 MHz GSM / GPRS systems was described by a magnetic conductivity applied on the design by using the FDTD method. magnetic field grid points, which are shifted half a cell relative to electric grid points By using the same FDTD method, cross-coupled filters were designed. These filters exhibit sharp filter-skirt due to the   (g 1)  *  0 r g l (2) attenuation poles on each side of the pass-band. l  2 ln g ACKNOWLEDGEMENT

III. DEVICES WITH IMPROVED CHARACTERISTICS FOR MOBILE This work was supported from the CEEX 1490 / 2006 COMMUNICATIONS project. Modern communications systems demand selective narrow- IV. REFERENCES band filters of about 2% fractional bandwidth. A solution to this requirement is given by compact size dual-mode filter as [1] M. G. Banciu, R. Ramer and A. Ioachim, “Microstrip filters using new compact resonators”, Electron. Lett., vol.38, no.5 pp.228-229, 2002. the meander loop dual mode filter shown in Fig. 1. For a [2] M. G. Banciu, R. Ramer and A. Ioachim, “Compact microstrip narrow-band filter, an accurate simulation usually involves resonators for 900 MHz frequency band”, IEEE Microwave Wireless about 64,000 time steps. However, an autoregressive moving- Components Letters, vol.13, no.5, pp.175-177, 2003. average (ARMA) signal estimation technique was developed [3] S. Shen, R. Ramer, M. G. Banciu, R. R. Mansour, “Design and realization of star-geometry dual-mode bandpass filter”, Optics Express, in order to reduce up to five times the number of iterations. vol. 13, No. 24, 2005, 9753-9757.