functions. To validate the technique, the example of scattering from a PEC cylinder with a slot illuminated by an obliquely incident plane wave is given. Comparing the results from the proposed method and those from the conventional BOR-FDTD, they show good agreement. And a substantial savings in compu- tational time is achieved. REFERENCES 1. C.L. Bitt, Solution of electromagnetic scattering problems using time domain techniques, IEEE Trans Antenna propag 37 (1989), 1181– 1192. 2. M.E. Moghaddam, J. Yannakakis, and W.C. Chew, Modeling of the subsurface interface radar, J Electromagn Waves Appl 5 (1991), 17– 39. 3. D.B. Davidson and R.W. Ziolkowski, Body-of-revolution finite-dif- ference time-domain modeling of space-time focusing by a three- dimensional lens’ J Opt Soc Am A 11 (1994), 1471–1490. 4. D.W. Prather and S.Y. Shi, Formulation and application of the finite- difference time-domain method for the analysis of axially symmetric diffractive optical elements, J Opt Soc Am A 16 (1999), 1131–1142. 5. Y. Chen and R. Mittra, Finite-difference time-domain algorithm for solving Maxwell’s equations in rotationally symmetric geometries, IEEE Trans Microwave Theory Tech 44 (1996), 832– 839. 6. W.H. Yu and R. Mittra, A technique for improving the accuracy of the non-uniform finite difference time domain (FDTD) algorithm, IEEE Trans Microwave Theory Tech 47 (1999), 353–356. 7. Taflove and S.C. Hagness, Computational electrodynamics: The finite- difference time-domain method, Artech House, Norwood, MA, 2000. 8. Y.S. Chung, T.K. Sarkar, B.H. Jung, and M. Salazar-Palma, An unconditionally stable scheme for the finite-difference time-domain method, IEEE Trans Microwave Theory Tech 51 (2003), 697–704. 9. S.G. Garcı ´a, A. Rubio Bretones, R. Go ´mez Martı ´n, and S.C. Hagness, Accurate implementation of current sources in the ADI-FDTD scheme, IEEE Antennas Wireless Propag Lett 3 (2004), 141–144. 10. D.E. Merewether, R. Fisher, and F.W. Smith, On implementing a numeric Huygen’s source scheme in a finite difference program to illuminate scattering bodies, IEEE Trans Nucl Sci 27 (1980), 1829 – 1833. 11. G. Mur, Absorbing boundary conditions for the finite-difference ap- proximation of the time-domain electromagnetic field equations, IEEE Trans Electromagn Compatibility 23 (1981), 377–382. © 2007 Wiley Periodicals, Inc. TRANSMISSION LINE DELAY-BASED RADIO FREQUENCY IDENTIFICATION (RFID) TAG Jeevan Vemagiri, Aravind Chamarti, Mangilal Agarwal, and Kody Varahramyan Institute for Micromanufacturing, Louisiana Tech University, 911 Hergot Ave, Ruston, LA-71272 Received 13 January 2007 ABSTRACT: This paper presents the design, simulation, fabrication, and characterization of a transmission delay line-based RFID tag. The ID generating circuit is designed based on the transmission delay line concept. A compact, inset-fed triangular patch antenna resonant at 915 MHz frequency is developed for integration with the tag application. The layout of the tag has been realized using conventional photolithog- raphy. Tags with a 5- and 10-ns delay ID generation circuits have been tested using input signals of 10-ns width. An OOK (On-Off Keying) modulation technique is employed for characterization of the tag. The received output consists of delayed signal from the tag added to the di- rect signal from the transmitter. Transmission delay line-based RFID technology can be exploited for low-end commercial applications that has a large market. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1900 –1904, 2007; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.22599 Key words: RFID; delay lines; distributed parameter circuits; micro- strip; UHF circuits; UHF RFID antennas Figure 3 Electric fields of z components (a) at p 1 , (b) at p 2 , and (c) at p 3 1900 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 8, August 2007 DOI 10.1002/mop