The analysis and design of microwave circuits realized with planar technology (hybrid and monolithic microwave integrated circuits, (M)MIC) has been a very active research area since the concept of integrated circuit moves to high frequency signal processing at the middle of the sixties. The Microwaves Group at the University of Seville (Seville, Spain), also called GMUS using Spanish initials, has been contributing to this research field - from the point of view of Applied Electromagnetics - during the last 20 years. This project intends to continue the most "classical" lines of research of the group. In the project we deal with a variety of topics sharing analytical/numerical methodology, the nature of the involved electromagnetic systems and the lab facilities required to perform experimental measurements. We have grouped the topics of interest into three big blocks:
During the last few years a lot of research (mainly of theoretical nature) has been conducted on te topic of the study of the continuous spectrum (related with radiation) of planar printed lines. [Oli84, Oli87, Shi91, Ngh93, Mesa95b, Das96, Lin97, Marques97, DiNallo98, Carin99, Mesa99, Oli00]. This study distinguishes between two kind of contributions to radiation coming from guided systems: leaky wave radiation and residual wave radiation [Jackson00, Mesa01, Mesa02a]. Generally speaking, residual radiation is related with direct radiation of the source to the environment, although due to the translational symmetry of the printed line, this radiation exhibits a longitudinal propagation factor. Leaky wave radiation can be viewed as travelling waves (such as bound modes of the ideal line) which transversally lose energy while propagate. In this research some members of the GMUS have intensely collaborated with the Applied Electromagnetism Group (University of Houston, TX, USA) to develop and apply methods to obtain, in a quasi-analytical way, currents and fields excited by lumped voltage sources - such as delta-gaps or dipoles - along infinite printed lines [Langston01, Mesa02b, Bernal04]. The excitation of the continuous spectrum often gives place to spurious effects which can meaningfully degrade the performance of the printed line as transmission system [Freire99, Mesa02b] or to cause undesired couplings with neighbor lines [Bernal03]. In spite of big advances in this field since the seminal works by Arthur Oliner [Oli87], there are still many theoretical and practical aspects requiring a detailed study for full understanding or predictive value. Among these, we can mention circuital modeling to make easy the manipulation of the phenomenon by the circuit designer or the study of time domain response of such systems. Part of the effort we are developing in this project intends to solve these problems.
We are also interested on the analysis of leaky waves supported by planar multilayered dielectric waveguides (which may include ferrite or (bi)anisotropic materials). These waveguides are the typical guiding systems at optical or quasi-optical frequencies [Tamir90]. Spurious effects associated to the unavoidable excitation of the continuous spectrum can also appear in this type of waveguides. In spite of the continuous effort to characterize leaky waves on dielectric waveguides [Lee95, Mesa95a, Ane99, Petra02], we still face important numerical problems when the dispersion relation of the structure has to be solved [Rod04]. Indeed, we have to find out where are the complex zeros of a complex function having poles and branch points. This mathematical task has been attacked by the GMUS in several occasions (see, for instance [Mesa95a, Rod04]) but we want now to develop a definitive tool able to deal with virtually any kind of layered planar structure (open/closed, (bi)anisotropic, lossy, ...).
References for Block I:
[Ane99] E. Anemogiannis, E. N. Glytsis, and T. K. Gaylord, "Determination of Guided and Leaky Modes in Lossless and Lossy Planar Multilayer Optical Waveguides: Reflection Pole Method and Wavevector Density Method," Journal of Lightwave Technology, vol. 17, pp. 929-941, May 1999.
[Bernal04] J. Bernal, F. Mesa, and D. R. Jackson, "Crosstalk between two microstrip lines excited by a gap voltage source," IEEE Transactions on Microwave Theory and Techniques, vol. 52, n. 8, pp. 1770-1780, August 2004.
[Das96] N. K. Das, "Methods of suppression or avoidance of parallel-plate power leakage from conductor backed transmission lines," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-44, pp. 169-181, February 1996.
[Carin98] L. Carin, G. W. Slade, and K. J. Webb, "Mode coupling and leakage effects in finite-size printed interconnects," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-46, pp. 450-457, May 1998.
[DiNallo98] C. Di Nallo, F. Mesa, and D. R. Jackson, "Excitation of leaky modes on multilayer stripline structures," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-46, pp. 1062-1071, August 1998.
[Freire99] M. J. Freire, F. Mesa, C. DiNallo, D. R. Jackson, and A. A. Oliner, "Spurious transmission effects due to the excitation of the bound mode and the continuous spectrum on stripline with an air gap," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-47, pp. 2493-2502, December 1999.
[Jackson00] D. R. Jackson, F. Mesa, M. J. Freire, D. P. Nyquist, and C. DiNallo, "An excitation theory for bound modes, leaky modes, and residual-wave currents on stripline structures," Radio Science, vol. 35, pp. 495-510, March 2000.
[Langston01] W. Langston, J. T. Williams, D. R. Jackson, and F. Mesa, "Spurious radiation from a practical source on a covered microstrip line," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-49, pp. 2216-2226, December 2001.
[Lee95] S.-L. Lee, Y. Chung, L. A. Coldren, and N. Degli, "On leaky mode approximation for modal expansion in multiplayer open waveguides," IEEE Journal of Quantum Electronics, vol. 31, pp. 1790-1802, October 1995.
[Lin97] Y. Lin and J. Shen, "Mode distinction and radiation efficiency analysis of planar leaky wave line source," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-45, pp. 1672-1680, October 1997.
[Marques97] R. Marqués and F. Mesa, "Spectral domain analysis of higher order leaky modes in microstrip lines: a new spectral-gap effect," Journal of Electromagnetic Waves and Applications, vol. 11, pp. 1367-1384, October 1997.
[Mesa95a] F. Mesa and M. Horno, "Computation of proper and improper in multilayered bianisotropic waveguides," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-43, pp. 233-235, January 1995.
[Mesa95b] F. Mesa and R. Marqués, "Integral representation of spatial Green's function and spectral domain analysis of leaky covered strip-like lines," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-43, pp. 828-837, April 1995.
[Mesa99] F. Mesa, C. DiNallo, and D. R. Jackson, "The theory of surface-wave and space-wave leaky mode excitation on microstrip lines," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-47, pp. 207-215, February 1999.
[Mesa01] F. Mesa, D. R. Jackson, and M. J. Freire, "High-frequency leaky mode excitation on microstrip line," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-49, pp. 2206-2215, December 2001.
[Mesa02a] F. Mesa, D. R. Jackson, and M.J. Freire, "Evolution of leaky modes on printed-circuit lines," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-50, pp. 94-104, January 2002.
[Mesa02b] F. Mesa and D. R. Jackson, "The danger of high-frequency spurious effects on wide microstrip line," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-50, pp. 2679-2689, December 2002.
[Ngh93] D. Nghiem, J. T. Williams, D. R. Jackson, and A. A. Oliner, "Proper and improper dominant mode solutions for stripline with an air gap," Radio Science, vol. 28, pp. 1163-1180, December 1993.
[Oli84] A. A. Oliner, "Historical perspectives on microwave field theory," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-32, pp. 1022-1045, September 1984.
[Oli87] A. A. Oliner, "Leakage from higher modes on microstrip line with application to antennas," Radio Science, vol. 22, pp. 907-912, November 1987.
[Petra01] J. Petrá¢cek and K. Singh, "Determination of Leaky Modes in Planar Multilayer Waveguides," IEEE Photonics Technology Letters, vol. 14, pp. 810-812, June 2002.
[Shi91] H. Shigesawa, M. Tsuji, and A. A. Oliner, "Dominant mode power leakage from printed-circuit waveguide," Radio Science, vol. 26, pp. 559-564, March 1991.
[Oli00] F. Mesa, A. A. Oliner, D. R. Jackson, and M.J. Freire, "The influence of the top cover on the leakage from microstrip line," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-48, pp. 2240-2248, December 2000.
[Rod04] R. Rodríguez-Berral, F. Mesa, and F. Medina, "Systematic and efficient root finder for computing the modal spectrum of planar layered waveguides," International Journal of RF and Microwave Computer-Aided Engineering, vol. 14, n. 1, pp. 73-83, January 2004.
[Tamir90] T. Tamir, ed., Guided-Wave Optoelectronics, Springer-Verlag, New York, 2nd ed. 1990.
In GPS or DBS receivers circular polarization antennas are required [Jam89, cap. 19]. There are two kind of circularly polarized patch antennas: those having single feed and those having with double feed. THose having a single feed point are very simple but the polarization bandwidth uses to be very narrow. Those having too feed points have a much better bandwidth for the axial ratio but the require a rather complex feed circuit [Poz97], and this can be an important problem if those antennas are part of large arrays. In the frame of our project we want to study two types of single feed circularly polarized patch antennas: elliptically shaped patch antennas on dielectric substrate [Lon81,Jun02] and square patch antennas printed on normally biased layered ferrite substrates [Poz92, Tsa98, Leo05a]. In the case of elliptical shaped patches, our purpose is to develop an accurate and efficient algorithm for the rigurous full-wave analysis of such antennas with coaxial probe feed. This algorithm will probably be based on the method of moments formulated in the spectral domain. In order to get high numerical efficiency, current density basis functions should incorporate edge condition, apart from an "attachment mode" [Pin89, Jun02] to ensure probe-patch current continuity and to account for the quasi-singular behavior of patch current density around the point of contact of the coaxial probe [Pin89]. In the past, members of the GMUS have been successful when analyzing resonances of microstrip circular patches [Los99], the scattering of plane waves by circular patches [Los01], and the electrostatic analysis of elliptical patches [Boi90]. Note that, while low eccentricity elliptical patches are expected to be useful radiating circular polarized waves, it has been verified that high eccentricity patches radiate two orthogonal linear waves at two different frequencies [Lon81]. Taking this into account, we want to study the behavior of elliptical antennas as dual band/dual polarization radiators. Theoretical and numerical predictions are expected to be confirmed by the experimental results obtained in our anechoic chamber.
Square patch antennas on ferrite substrates will be studied from the experimental point of view. Theoretical study of this type of antennas has been already carried out in the frame of a former project (TIC2001-3163). The GMUS has some experience on the fabrication and measurement of circuits printed on ferrites, such as coupled line tunable filters [Leo05]. In the case of antennas, these must be magnetized using permanent magnets placed below the ground plane (we do not want to interfere with the radiating side of the antenna [Tsa98]). It is well known that standard microstrip patch antennas are narrow band devices from the point of view of input impedance [Jam89, cap. 1] and that circularly polarized single feed patch antennas are also narrow band from the point of view of axial ratio. But recently, Waterhouse has shown that a single fed patch antenna printed on a high permittivity substrate with a stacked parasitic patch printed over a low permittivity substrate presents a 20 % bandwidth both for input impedance and axial ratio [Wat99]. Starting from this idea, we hope to improve the bandwidth of circularly polarized antennas using stacked patches and a combination of high permittivity (such as ferrites) and low permittivity substrates.
Concerning the presence of ferrites, it is necessary to state that commercial electromagnetic simulators do not often incorporate this kind of materials. Our group has done many contributions to the numerical simulation of planar transmission lines and planar circuits including ferrite layers (see publications in the group web page). These codes will be used in the design of the above mentioned antennas. Nevertheless, we intend to introduce new improvements in this software because, due to the anisotropic nature of ferrites, still requires a lot of computational effort. A research line that has proven to be useful is the adaptation of the Mixed Potentials Integral Equation (MPIE) method [Rao82, Mich90] (MPIE is the heart of many electromagnetic simulators for planar structures) to the analysis of structures with ferrite layers. The GMUS has already contributed to this topic by obtaining the MPIE Green´s functions in the space domain for ferrite layers [Mesa04]. Including these Green´s functions in a MPIE scheme (previously solving those problems arising from the existence of special singularities) would provide a useful code able to deal with arbitrarily shaped patches (thanks to the use of Rao-Wilton-Glisson basis functions) in a relatively fast way.
References for Block II:
[Boi90] R. R. Boix, M. Horno, "Capacitance computation of elliptic microstrip disks in biaxial anisotropic multilayered substrates", IEEE Transactions on Microwave Theory Techniques, vol. MTT-38, pp. 30-37, January 1990.
[Jam89] J. R. James, P. S. Hall, "Handbook of microstrip antennas", Peter Peregrinus Ltd., London, 1989.
[Jun02] H. Jung, C. Seo, "Analysis of elliptical microstrip patch antenna considering attachment mode", IEEE Transactions on Antennas and Propagation, vol. AP-50, pp. 888-890, June 2002.
[Leo05] G. León, R.R. Boix, M.J. Freire, F. Medina, "Experimental Validation of Analysis Software for Tunable Microstrip Filters on Magnetized Ferrites," IEEE Transactions on Microwave Theory and Techniques, vol. 53, n. 5, pp. 1739-1744, May 2005.
G. León, R. R. Boix, M. J. Freire, F. Medina, "Experimental Validation of Analysis Software for Tunable Microstrip Filters on Magnetized Ferrites," IEEE Transactions on Microwave Theory and Techniques, vol. 53, n. 5, pp. 1739-1744, May 2005.
[Lon81] S. A. Long, L. C. Shen, D. H. Schaubert, F. G. Farrar, "An experimental study of the circular-polarized elliptical printed-circuit antenna", IEEE Transactions on Antennas and Propagation vol. AP-29, pp. 95-99, January 1981.
[Los99] V. Losada, R. R. Boix, M. Horno, "Resonant modes of circular microstrip patches in multilayered substrates", IEEE Transactions on Microwave Theory Techniques, vol. 47, pp. 488-498, April 1999.
[Los01] V. Losada, R. R. Boix, F. Medina, "Evaluation of the radar cross section of circular microstrip patches on anisotropic and chiral substrates", IEEE Transactions on Antennas and Propagation vol. AP-49, pp. 1603-1605, November 2001.
[Mesa04] F. Mesa and F. Medina, "Numerical computation of the Mixed Potential space-domain Green's functions for planar layered structures with arbitrarily magnetized ferrites," IEEE Transactions on Antennas and Propagation, vol. 52, n. 11, pp. 3019-3025, November 2004.
[Mich90] K. A. Michalski and D. Zheng, "Electromagnetic scattering and radiation by surfaces of arbitrary shape in layered media, Par I: Theory," IEEE Transactions on Antennas Propagation, vol. AP-38, pp.335-344, Mar. 1990.
[Pin89] S. Pinhas, S. Shtrikman, D. Treves, "Moment-method solution of the center-fed microstrip disk antenna invoking feed and edge singularities", IEEE Transactions on Antennas and Propagation, vol. AP-37, pp. 1516-1522, December 1989.
[Poz92] D.M. Pozar, "Radiation and scattering characteristics of microstrip antennas on normally biased ferrite substrates", IEEE Transactions on Antennas and Propagation, vol. AP-40, pp. 1084-1092, September 1992.
[Poz97] D.M. Pozar, S. M. Duffy, "A dual-band circularly polarized aperture-coupled stacked microstrip antenna for global positioning satellite", IEEE Transactions on Antennas and Propagation, vol. AP-45, pp. 1618-1625, November 1997.
[Poz00] D.M. Pozar, "An overview of wireless systems and antennas", IEEE AP-S International Symposium, Salt Lake City (UT, USA), pp. 566-569, July 2000.
[Rao82] S. M. Rao, D. R. Wilton, and A. W. Glisson, "Electromagnetic scattering by surfaces of arbitrary shape," IEEE Transactions on Antennas Propagation, vol. AP-30, pp. 409-418, May 1982.
[Tsa98] K. K. Tsang, R. J. Langley, "Design of circular patch antennas on ferrite substrates", IEE Proceedings., Pt. H, Microwaves, Opticas and Antennas, vol. 145, no. 1, pp. 49-55, February 1998.
[Wat99] R. B. Waterhouse, "Stacked patches using high and low dielectric constant material combinations", IEEE Transactions on Antennas and Propagation vol. AP-40, pp. 1767-1771, December 1999.
The third central topic of this project is electromagnetic periodic structures. Our purpose is to study two kind of periodic structures: frequency selective surfaces (FSS)and periodic planar transmission lines. Frequency selective surfaces consist of 2D periodic arrays of metallic patches (which act as stop band filters for impinging planar electromagnetic waves) or 2D periodic arrays of slots practiced on a metallic plane (bandpass filters). FSS are used as selective radomes, dichroic subreflectors for parabollic antennas with several feeders operating in several frequency bands or as polarizers [Mun00]. On the other hand, periodic planar lines show two interesting features that make them very useful. First, they are slow wave structures potentially allowing significant reduction of the size of circuits built using these lines as building blocks [Yan98,Sor01]. Second, periodic transmission lines exhibit stop and pass bands that make them useful for filter design [Rad98, Kim00, Sor01]. In the last few years a lot of attention has been paid to two types of planar periodic lines. The first type is made of a conventional microstrip line with a periodically perforated ground plane [Rad98, Kim00] (they have been also called 1D "photonic" or "electromagnetic band gap" structures). The second kind of periodic lines is obtained by introducing periodic perturbations along the plane with metallic patterns of a coplanar waveguide [Sor01]. In Spain, the research group of the Public University of Navarra (Prof. Mario Sorolla Ayza) has been very active in the design of microstrip [Las99, Lop02] and CPW [Mar03] filters based on periodic transmission lines. We hope to make contributions in this research line. Concerning 2D periodic structures, our group intends to develop a fast solver for the analysis of multilayer FSSs. By the end of the eighties Chan and Mittra [Cha88] developed a fast algorithm for the analysis of FSSs based on the spectral domain method of moments in conjunction with FFT techniques. Nevertheless, this algorithm was limited to metal patterns in the unit cell that can be fit to a uniform rectangular mesh. Recently our group has developed a faster algorithm working with nonuniform rectangular meshes [Boi03]. This algorithm is based on interpolations of the spectral Green´s function [Boi96] and the use of suitable transformations of double series slowly convergent into exponentially convergent double series. The most serious drawback of the algorithms in [Cha88] and [Boi03] is the use of the formulation in the spectral domain. Working in this domain force us to use rectangular support basis functions which are not amenable yo arbitrary geometry patches. Space domain formulations, in contrast, would allow us to use triangular support basis functions (RWG functions [Rao82]) suitable for arbitrarily shaped patches. However, a fast method to generate the required space domain Green´s functions should be first developed. Unfortunately, space domain Green´s functions for periodic structures are known in the form of slowly convergent double infinite numerical series. Mathematical extrapolation techniques such as Shank´s transformation [Sin90] have been proposed, but our experience tells us that these techniques are not stable when applied to sophisticated alternating series such as those involved in this problem. On the other hand, Spanish researchers Alvarez-Melcón and J.R. Mosig have reported on two strategies to accelerate the summation of these series [Alv00]. Recently it has been also proposed to use the discrete complex images method (DCIM) in conjunction with Ewald´s transformation [Yu00]. This is a fast method, but our previous research [Shu02] and some other reports state that DCIM presents some problems that should be solved before generating results with confidence. We propose to apply fast summation techniques previously developed for the obtaining of method of moments matrix entries [Boi03] to the computation of Green´s functions. Interpolation/extrapolation methods different from DCIM will be also investigated. Once this problem is solved, moment method schemes using RWG basis functions will be applied. The techniques commented in the previous paragraph can be adapted to deal with periodic planar lines. However, we should take into account that whereas 2D periodic structures are considered in the case of FSSs, 1D periodic structures are now of interest. In this case, Green´s functions involve infinite series of infinite integrals. In spite of this subtle difference (which implies some mathematical challenges) we also intend to develop a code to compute the propagation parameters (propagation constant and Bloch impedance) of the periodic lines. The transmission matrix of the unit cell will be also computed. Although some attention was paid to this problem by the end of the eighties [Gla87, Kia89], there is an important lack of information in the recent literature (an important exception is the paper by Zhu [Zhu03] where the periodicity of the problem is not explicitly exploited). This is a very curious fact if we consider the recent explosion of research on periodic structures!. Note that the scattering parameters of a finite section of periodic transmission line can be easily obtained from the transmission matrices of the input and output discontinuities (these can be computed using a commercial simulator) and from the transmission matrix of the unit cell [Ong02]. This procedure allows us to avoid the electromagnetic analysis of the electrically large whole structure. Important savings of CPU time can be then achieved. The last step of this research is obviously the design, fabrication and measurement of planar filters based on periodic structures.
Apart from periodic filters, we plan also to work on other planar filter configurations. This will follow lines of research already started in a previous project. The general idea is to enhance the performance of conventional planar filters by making use of the patterning of the ground side of the substrate. The development of compact resonators for reduced size filter design will be also an objective of our research. Our group has made recent contributions in these areas, such as the improvement of the out-of-band response of coupled line filters [Vel04] or the development of compact filters of small electrical size (a fraction of a wavelength) based on split ring resonators [Mart04] (this work has been carried out in conjunction with the groups of Prof. Mario Sorolla, UPN, and Ferrán Martín, UAB). Our first goal is to explore the improvements that can be introduced in the behavior of various passive planar devices (mainly filters and couplers) taking advantage of the use of metallic "islands" or slots in the ground plane. Some authors use the term "defected ground structures" (DGS) to name this kind of circuits. Our second goal is to invent, design, simulate and measure compact printed resonators following the way of recent works such as [Ban03, Chen03, Hsi03a, Hsi03b, Zhu03]. We will combine home made software with commercial software so as to carry out this task.
References for Block III:
[Alv00] A. Álvarez Melcón, J. R. Mosig, "Two techniques for the efficient numerical calculation of the Green's functions for planar shielded circuits and antennas", IEEE Transactions on Microwave Theory Techniques, vol. 48, pp. 1492-1504, September 2000.
[Ban03] M. G. Banciu, R. Ramer, and A. Ioachim, "Compact Microstrip Resonators for 900 MHz Frequency Band", IEEE Microwave and Wireless Components Letters, vol. 13, n. 5, pp. 175-177, May 2003.
[Boi96] R. R. Boix, N. G. Alexopoulos, M. Horno, "Efficient numerical computation of the spectral transverse dyadic Green's function in stratified anisotropic media," Journal of Electromagnetic Waves and Applications, vol. 10, n. 8, pp. 1047-1083, August 1996.
[Boi03] R. R. Boix, M. J. Freire, F. Medina, "New method for the efficient summation of double infinite series arising from the spectral domain analysis of frequency selective surfaces," IEEE Transactions on Antennas and Propagation, vol. 52, n. 4, pp. 1080-1094, April 2004.
[Cha88] C. H. Chan, "A numerically efficient technique for the method of moments solution of electromagnetic problem associated with planar periodic structures", Microwave and Optical Technology Letters, vol. 1, No. 10, pp. 372--374, December 1988.
[Chen03] C.-C. Chen, Y.-R. Chen, C.-Y. Chang, "Miniaturized Microstrip Cross-Coupled Filters Using Quarter-Wave or Quasi-Quarter-Wave Resonators", IEEE Transactions on Microwave Theory Techniques, vol. 51, n. 1, pp. 120-131, January 2003.
[Gla87] F. J. Glandorf, I. Wolff, "A spectral-domain analysis of periodically nonuniform microstrip lines", IEEE Transactions on Microwave Theory Techniques, vol. MTT-47, pp. 336-343, March 1987.
[Hsi03a] L.-H. Hsieh, K. Chang, "Compact Elliptic-Function Low-Pass Filters Using Microstrip Stepped-Impedance Hairpin Resonators", IEEE Transactions on Microwave Theory Techniques, vol. 51, n. 1, pp. 193-199, January 2003.
[Hsi03b] L.-H. Hsieh, K. Chang, "Compact, Low Insertion-Loss, Sharp-Rejection, and Wide-Band Microstrip Bandpass Filters", IEEE Transactions on Microwave Theory Techniques, vol. 51, n. 4, pp. 1241-1246, April 2003.
[Kia89] J. F. Kiang, S. M. Ali, J. A Kong, "Propagation properties of striplines periodically loaded with crossing strips", IEEE Transactions on Microwave Theory Techniques, vol. MTT-37, pp. 776-786, April 1989.
[Kim00] T. Kim, C. Seo, "A novel photonic bandgap structure for low-pass filter of wide stopband", IEEE Microwave and Guided Wave Letters, vol. 10, No. 1, pp. 13-15, January 2000.
[Las99] M. A. G. Laso, M. J. Erro, D. Benito, M. J. Garde, T. Lopetegui, F. Falcone, M. Sorolla, "Analysis and design of 1-D photonic bandgap microstrip structures using a fiber grating model", Microwave and Optical Technology Letters, 22, No. 4, pp. 223-226, Aug. 1999.
[Lop02] T. Lopetegui, M. A. G. Lasso, M. J. Erro, M. Sorolla, M. Thumm, "Analsyis and design of periodic structures for microstrip lines by using the coupled mode theory", IEEE Mic. Wireless Comp. Letters, vol. 12, No. 11, pp. 441-443, November 2002.
[Mar03] F. Martín, F. Falcone, J. Bonache, T. Lopetegui, M. A. G. Lasso, M. Sorolla, "Dual electromagnetic bandgap CPW structures for filter applications", IEEE Microwave Wireless Components Letters, vol. 13, No. 9, pp. 393-395, September 2003.[
[Mart04] J. Martel, R. Marqués, F. Falcone, J.D. Baena, F. Medina, F. Martín, M. Sorolla "A new LC series element for compact bandpass filter design", IEEE Microwave and Wireless Components Letters, aceptado en November 2003.
[Mun00] B. A. Munk, "Frequency selective surfaces", Wiley Interscience, New York, 2000.
[Ong02] C. Y. Ong, M. Okoniewski, "A simple recursive formula for calculating the S-parameters of finite periodic structures", IEEE Microwave Wireless Components Letters, vol. 12, No. 7, pp. 264-266, July 2002.
[Rad98] V. Radisic, Y. Qian, R. Coccioli, T. Itoh, "Novel 2-D photonic bandgap structure for microstrip lines", IEEE Microwave and Guided Wave Letters, vol. 8, No. 2, pp. 69-71, February 1998.
[Rao82] S. M. Rao, D. R. Wilton, A. W. Glisson, "Electromagnetic scattering by surfaces of arbitrary shape", IEEE Transactions on Antennas and Propagation vol. AP-30, pp. 409-418, March 1982.
[Shu02] N. V. Shuley, R. R. Boix, F. Medina, M. Horno, "On the fast approximation of Green's functions in MPIE formulations for planar layered media", IEEE Transactions on Microwave Theory Techniques, vol. 50, pp. 2185-2192, September 2002.
[Sin90] S. Singh, W. F. Richards, J. Zinecker, D. R. Wilton, "Accelerating the convergence of series representing the free space periodic Green's function", IEEE Transactions on Antennas and Propagation vol. AP-38, pp. 1958-1962, December 1990.
[Sor01] J. Sor, Y. Qian, T. Itoh, "Miniature low-loss CPW periodic structures for filter applications", IEEE Transactions on Microwave Theory Techniques, vol. MTT-49, pp. 236-2341, December 2001.
[Vel04] M.C. Velázquez, J. Martel, F. Medina, "Parallel coupled microstrip filters with ground plane aperture for spurious band suppression", IEEE Transactions on Microwave Theory and Techniques, vol. 52, n. 3, pp. 1082-1086, March 2004.
[Yan98] F. Yang, Y. Qian, R. Coccioli, T. Itoh, "A novel low-loss slow-wave microstrip structure", IEEE Microwave and Guided Wave Letters, vol. 8, No. 11, pp. 372-374, November 1998.
[Yu00] Y. Yu, C. H. Chan, "Efficient hybrid spatial and spectral techniques in analyzing planar periodic structures with nonuniform discretizations", IEEE Transactions on Microwave Theory Techniques, vol. MTT-48, pp. 1623-1627, October 2000.
[Zhu03] L. Zhu, W. Menzel, "Compact Microstrip Bandpass Filter With Two Transmission Zeros Using a Stub-Tapped Half-Wavelength Line Resonator", IEEE Microwave and Wireless Components Letters, vol. 13, n. 1, pp. 16-18, January 2003.
[Zhu03] L. Zhu, "Guided-wave characteristics of periodic coplanar waveguides with inductive loading--unit-length transmission parameters", IEEE Transactions on Microwave Theory Techniques, vol. MTT-51, pp. 2133-2138, October 2003.
In this section we will include those book chapters, journal and conference papers reporting original results of the project. Please, note that
Abstract: This letter demonstrates the near-field imaging enhancement at microwave frequencies of two-dimensional sources by a ferrite slab magnetized to saturation. It is shown that this effect is based on the nonreciprocal amplification of magnetostatic surface waves (MSSW) across the ferrite slab. The inclusion of losses in our analysis has also made it possible to prove this effect for realistic yttrium iron garnet ferrite samples. For ferrite slabs of width d, the resolution at the image plane (at a distance 2d from the source) is better than the resolution in air at a distance d of the source, which leads to an equivalent air length of the ferrite slab less than zero. Since the constitutive parameters of saturated ferrites depend on the external magnetizing field, the operation frequency of the proposed imaging devices can be tuned by varying this biasing field.
Abstract: This paper will study the most convenient way of formulating the characteristic equation for shielded, parallel-plate, grounded, and open reciprocal/nonreciprocal planar layered waveguides, including the possibility of different upper and lower half-spaces. A detailed study of the suitable mapping for each kind of waveguide will lead to the formulation of analytic characteristic equations for shielded/ parallel-plate/ grounded reciprocal/ nonreciprocal waveguides and also for open reciprocal ones. Although no mapping has been found to remove all the branch points of the characteristic equation for open nonreciprocal waveguides with different half-spaces, a robust approach will be proposed to overcome the main drawbacks caused by the multivalued nature of this problem. The combination of the suitable formulation of the characteristic equation with a systematic integral-nature root-searching strategy bears a reliable and efficient method. Some novel numerical results will be presented for open anisotropic reciprocal waveguides and for open magnetized ferrite slabs to illustrate the performance of the present proposal.
Abstract: Floating strip conductors printed on the backside of the substrate are shown to be useful to suppress the spurious transmission band appearing at twice the central frequency of coupledline microstrip filters. It is shown that proper adjustment of the dimensions of the floating conductors yields equal even and odd electrical lengths. An attractive feature of this design is its flexibility because the equalization of the modal electrical lengths can be achieved with various geometries. Additionally, the floating conductor provides an extra coupling mechanism that relaxes tolerances of strip width and spacing in those cases where tightly coupled sections are required. A fast quasi-TEM analysis is used to find the structure yielding equal mode phase velocities. Fine tuning to equalize the modal electrical lengths for each coupled stage is based on the use of a commercial electromagnetic simulator. Experimental verification is finally provided.
Abstract: The method of moments in the spectral domain is applied to the full-wave analysis of aperture coupled microstrip antennas in the case where the substrate of the antennas is a layered medium containing magnetized ferrites. The subsectional basis functions used in the analysis make it possible to handle patch antennas and coupling apertures with right angle corners of arbitrary shape. The numerical results obtained show that antennas on ferrite substrates fed by single microstrip lines can radiate both circular and linear polarization, the polarization state being dependent on the orientation of the ferrites bias magnetic field. For a given polarization state, the matching frequency band of the antennas can be tuned over a wide frequency range by adjusting the magnitude of the bias magnetic field. Also, the polarization state can be continuously tuned from circular to linear within the same frequency band by adjusting both the magnitude and the orientation of the bias magnetic field. Some measurements are presented in order to check the validity of the numerical algorithm developed.
Abstract: In this paper it is shown for the first time that a novel transition may occur for dominant (quasi transverse electromagnetic (quasi-TEM)) leaky modes on microstrip line, between a leaky mode that leaks into the TM0 surface wave mode and one that leaks both into the surface wave and into space. The modal evolution of leaky modes as a function of frequency is studied by means of a full-wave spectral domain approach, and it is shown that such transitions occur on microstrip lines that have a critical strip width, which is relatively large. When the strip width is equal to the critical value, a transition frequency will exist at which the attenuation constant of the leaky mode drops exactly to zero and the leaky mode has a real propagation wave number exactly equal to the free-space wave number. At this frequency, the leaky mode transitions from one that leaks into only the surface wave to one that also leaks into space. In a frequency neighborhood of the transition frequency, very large spurious effects may be produced because of interference between the fundamental quasi-TEM mode and the continuous spectrum current.
Abstract: This work presents an in-depth theoretical analysis of a planar layered dielectric waveguide with periodic side walls. It is shown that, apart from the conventional guided modes for which most of their energy travels within the dielectric dense medium, this guide presents other modes whose energy mostly travels in the air regions inside the side walls or outside them. In particular, the mode with its energy traveling inside the side walls is a low-loss and weakly dispersive mode that could be of interest for practical applications. Moreover, it has been demonstrated that this mode can be strongly excited by a realistic source, which has been done by showing that this mode is the main part of the spectrum radiated by a dipole line located within the air region inside the side walls.
Abstract: This paper presents a quasi-TM approach for the fundamental mode of transmission lines with semiconductor substrates and non perfect metallic conductors. The approach has allowed us to develop a transmission-line model by properly defining frequency-dependent parameters in terms of the quasi-static electric potential and the electric current density along the propagation direction in the line. The previous quasi-TM analysis avoids the involved numerical root finding process typical in full-wave analysis, and overcomes the limitations of the conventional quasi-TEM approach to account for the effects of the longitudinal currents present both in the lossy substrates and in the nonperfect conductors. The transmission-line parameters have been computed by a hybrid technique that combines the method of lines with the method of the moments (MoM). The total CPU effort has been considerably reduced thanks to the possibility of finding closed-form expressions for the reaction integrals appearing in the MoM. Comparisons with previous computed and measured results show the validity of the present model.
Abstract: An equivalent circuit model for a gap voltage source on a microstrip line is developed. The model is valid at high frequency, and accounts for the reactive nature of the gap as well as the radiative nature of the currents on the line at high frequency. The model also accounts for the non-unique definition of the characteristic impedance associated with the bound mode at high frequency. The equivalent circuit models the excitation of the ound mode exactly even at high frequency where standard transmission-line theory is no longer accurate. The frequency behavior of the circuit parameters in the model is shown, together with some time-domain results that have been computed by using a very efficient approach based on the proposed circuit model.
Abstract: This work presents a new implementation of the Mixed-Potential Integral Equation (MPIE) for planar structures that can include ferrite layers arbitrarily magnetized. The implementation of the MPIE here reported is carried out in the space domain. Thus it will combine the well-known numerical advantages of working with potentials as well as the flexibility for analyzing non-rectangular shape conductors with the additional ability of including anisotropic layers of arbitrarily magnetized ferrites. In this way, our approach widens the scope of the space-domain MPIE and sets this method as a very efficient and versatile numerical tool to deal with a wide class of planar microwave circuits and antennas.
Abstract: Open split ring resonators (OSRRs) are used in this letter to design wide-band semi-lumped bandpass filters. OSRRs work as lumped LC series elements due to their small electrical size and can be then used as building blocks of reduced size band pass filters. The values of the capacitance, C, and inductance, L, of the OSRR are controlled by adjusting the geometrical parameters of the coupled open rings. In our design, the OSRRs are connected through quarter-wave lines which act as inverters. The impedance of these inverters have been conveniently calculated to achieve the filter specifications. Finally bending and/or meandering techniques have been applied so as to obtain highly compact designs. Experimental verification is provided and good agreement has been found between electromagnetic simulations and measurements.
Abstract: A novel implementation of stepped-impedance low-pass elliptic filters is presented in this paper. The filters are based on the well known technique of cascading high and low impedance sections to simulate the ladder LC lumped circuit prototype. Wepropose in this work a new approach to build up the constitutive circuit elements by taking advantage of the use of both sides of the substrate. The use of doublesided technology yields both design flexibility and good circuit performance. High impedance sections are achieved by using slots in the backside of the substrate whereas low impedance sections are obtained with parallel plate capacitors. In order to achieve the transmission poles corresponding to the elliptic design, these capacitors are series connected to the ground plane by means of high impedance coplanar waveguide (CPW) lines which mainly act as inductors. As a final step, meandering techniques have been applied to the high impedance sections of the filter to reduce the overall circuit size. The measurement of several fabricated filters shows fairly good agreement between theory and experiment.
Abstract: A new technique is presented for the numerical derivation of closed-form expressions of spatial domain Green’s functions for multilayered media. In the new technique the spectral domain Green’s functions are approximated by an asymptotic term plus a ratio of two polynomials, the coefficients of these two polynomials being determined via the method of total least squares. The approximation makes it possible to obtain closed-form expressions of the spatial domain Green’s functions consisting of a term containing the near-field singularities plus a finite sum of Hankel functions. A judicious choice of the coefficients of the spectral domain polynomials prevents the Hankel functions from introducing non-physical singularities as the horizontal separation between source and field points goes to zero. The new numerical technique requires very few computational resources, and it has the merit of providing single closed-form approximations for the Green’s functions that are accurate both in the near and far fields. A very good agreement has been found when comparing the results obtained with the new technique with those obtained via a numerically intensive computation of Sommerfeld integrals.
Abstract: This paper studies the effects of practical conductor and dielectric losses on the high-frequency current excited on a microstrip line by a gap voltage source. The analysis shows that whereas losses cause an exponential decay in the propagating bound mode (as expected), the continuous-spectrum current is much less influenced by the presence of material losses. As a consequence, the nature of the strip current far away from the source is dramatically affected by the presence of losses, and will be dominated by the continuous spectrum. This results in unusual behavior that is observed for the strip current far away from the source.
Abstract: In this paper we aim at rigorously studying the practical excitation of a shielded microstrip line periodically perturbed by gaps. In particular a delta-gap voltage source is considered in an environment shielded by lateral and top metallic walls. The excitation problem is solved through a numerical implementation of the array scanning method, in which the field excited by a nonperiodic source in a periodic environment is represented as an integral superposition of fields, which are solutions of suitable auxiliary Floquet-periodic problems. To solve the latter, a spectral-domain method-of-moments approach has been adopted, introducing original acceleration techniques to enhance the efficiency and accuracy of the method. The numerical performance of the spectral-domain approach is illustrated and fully validated. Results are presented both for the dispersive properties of Bloch modes supported by the structure in the absence of excitation and for the currents excited on the structure by a single delta-gap source, also discussing the modal representation of such currents in terms of Green's function singularities in the spectral plane of the longitudinal wavenumber.