vides a quadrature phase for 2.4 GHz and an octal phase for 5.2 GHz to generate an IQ signal for the sub-harmonic mixer. Figure 3 shows the sub-harmonic mixer schematic [3]. This mixer can also be used as a traditional Gilbert mixer if LO_0 port is con- nected to LO_180 port; and the LO_90 port is connected to LO_270 port simultaneously. Therefore, the circuit design can be simplified. There is an additional function of this mixer, which is a band selector. Depending on the receiving RF signal strength, a band-selecting control signal coming from the baseband can be used to control the on/off of this mixer. Because of this mecha- nism, we can easily select which band we chose before the band- pass filter. A 10 MHz center frequency and 20 MHz bandwidth polyphase band-pass filter is designed to provide the image rejec- tion and filtering out the unwanted high frequency signal. To save power consumption and chip area, gm-C cell is implemented for this polyphase band-pass filter. 3. MEASUREMENT RESULT This concurrent compact dual-band receiver is implemented using HHNEC 0.18-m CMOS 1P6M technology. For a 1.8 V power supply, the overall power consumptions is simulated to be 66.1 mW. Table 1 summarizes all the measurement results. The pro- posed dual-band receiver has a fairly good performance as com- pared with the conventional receivers of individual receiving paths (as shown in Table 2). For noise issue, differential design concept is introduced. In addition, we not only use double guard ring layout style (N-well and P-substrate) to surround each individual block, but also individual power supply is used for each block. Another layout consideration is the RF signal penetrating through substrate issue; therefore, a metal1-shielding layer is added to form an ideal ground plate. Figure 4 shows the die photo of the proposed RF front-end chip with a die size of 2450  1700 m 2 . Figure 5 shows the dual-band receiver and Figure 6 shows the measured results. 4. CONCLUSION A low-cost and low-power IEEE 802.11a/b/g compact dual-band radio receiver for wireless LAN applications has been designed in a standard 0.18-m CMOS 1P6M technology. To save chip area, sub-harmonic mixer is used so that only one multi-modulus syn- thesizer is needed for this compact dual-band receiver design. The receiver has a simulated 2.8 dB and 4.3 dB receiver chain noise figure at 2.45 GHz and 5.25 GHz, respectively. For a 1.8 V power supply, the overall power consumption was only 66.1 mW. REFERENCES 1. B.-U. Klepser, M. Punzenberger, T. Ruhlicke, and M. Zannoth, 5-GHz and 2.4-GHz dual-band RF-transceiver for WLAN 802.11a/b/g appli- cations, Proceedings of IEEE Radio Frequency Integrated Circuits (RFIC) Symposium, Philadelphia, PA 8 –10 June 2003, pp. 37– 40. 2. B. McFarland, A. Shor, and A. Tabatabaei, A 2.4 & 5 GHz dual band 802.11 WLAN supporting data rates to 108 Mb/s, Proceedings of Gallium Arsenide Integrated Circuit (GaAs IC) Symposium, 2002. 24th Annual Technical Digest, 20 –23 October 2002, pp. 11–14. 3. M. Goldfarb, E. Balboni, and J. Cavey, Even harmonic double-bal- anced active mixer for use in direct conversion receivers, IEEE J Solid-State Circuits 38 (2003), 1762–1766. 4. A. Abidi, Direct-conversion radio transceivers for digital communica- tions, IEEE J Solid-State Circuits 30 (1995), 1399 –1410. 5. S.A. Sanielevici, K.R. Cioffi, B. Ahrari, P.S. Stephenson, D.L. Sko- glund, and M. Zargari, A 900-MHz transceiver chipset for two-way paging applications, IEEE J Solid-State Circuits 33 (1998), 2160 – 2168. 6. K. Vavelidis, I. Vassiliou, T. Georgantas, A. Yamanaka, S. Kavadias, G. Kamoulakos, C. Kapnistis, Y. Kokolakis, A. Kyranas, P. Merakos, I. Bouras, S. Bouras, S. Plevridis, and N. Haralabidis, A Dual-Band 5.15–5.35-GHz, 2.4 –2.5-GHz 0.18-m CMOS Transceiver for 802.11a/b/g Wireless LAN, IEEE J Solid-State Circuits 39 (2004), 1180 –1184. 7. Z. Markus, R. Thomas, and K. Bernd-Ulrich, TA highly integrated dual-band multimode wireless LAN transceiver, IEEE J Solid-State Circuits 39 (2004), 1191–1195. 8. 802.11a/b/g Chip Set, Product Brief, Agere systems, 2003. 9. 802.11a/b/g Dual-Band Wireless LAN Transceiver, Product Brief, Agere systems WL54040, 2003. 10. Wireless LAN IEEE 802.11a/b/g Chipset, Product Brief, RFMD, RFCS5420. 11. Z. Li, R. Quintal, and K.K. O, A dual-band CMOS front-end with two gain modes for wireless LAN applications, IEEE J Solid-State Circuits 39 (2004), 2069 –2073. 12. H. Hashemi and A. Hajimiri, Concurrent multiband low-noise ampli- fiers-theory, design, and applications, IEEE J Solid-State Circuits 50 (2002), 288 –301. © 2009 Wiley Periodicals, Inc. EFFICIENT TENSOR BASED FDTD SCHEME FOR MODELING SLOPED INTERFACES IN LOSSY MEDIA Gurpreet Singh, 1 Eng Leong Tan, 1 and Zhi Ning Chen 2 1 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798; Corresponding author: gurp0002@ntu.edu.sg 2 Institute for Infocomm Research, Singapore Received 5 October 2008 ABSTRACT: This article presents an efficient tensor based finite-differ- ence time-domain (FDTD) scheme for modeling sloped interfaces in lossy media. The formulated scheme achieves its improved efficiency by implicitly solving the internal fields affected by an interface. This per- mits the reduction of updating coefficients in the scheme. FDTD simula- tions that are generally used to compute scattering parameters or radar cross sections gain from this implicit computation. The scheme is formu- lated without assuming any single frequency approximation, previously assumed in the literature. This permits FDTD simulation results over a wide frequency bandwidth in a single FDTD simulation run. To allow a more accurate and conformal approximation, the scheme extends the use of cell filling ratio to lossy media. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1530 –1537, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 24398 Key words: finite-difference time-domain (FDTD) method; 2-dimension tensor; sloped interfaces; lossy media 1. INTRODUCTION The finite-difference time-domain (FDTD) method has been widely used to obtain solutions of Maxwell’s equations in complex geometries with complex materials. However, a significant flaw is its staircase approximation of planar, sloped or curved interfaces between different media on a Cartesian FDTD grid. Various meth- ods [1, 2] have been proposed to minimize the errors caused by the staircase approximation. One such class of methods is based on properly constructing an average of the material’s properties in the vicinity of the interface and using it to accurately solve the affected field components. For dielectrics, various effective permittivities have been determined in previous literature [2–5]. However, these permittivites do not completely account for the effective anisot- ropy induced by sloped or curved interface. 1530 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 6, June 2009 DOI 10.1002/mop