ization operating angle  cp , characterized as the angle off boresight direction ( = 0°) for which AR is lower than 3 dB, is about 110°. In y–z plane measured HPBW of RHCP is 105°. Measured  cp is about 105°. Measured peak cross polarization level and back lobe level are about -23.5 dB and -34.4 dB, respectively. From these measured results we can find that the proposed antenna behaves a satisfactory circularly polarized radiation performance. 3. CONCLUSIONS A novel realization of cavity backed crossed slot antenna for circularly polarized application has been presented in this article. The proposed antenna has low profile and can be conveniently manufactured because its backed cavity is constructed by metal- lized vias array at a single substrate. It provides promising circu- larly polarized radiation performance, which has been validated by measurements. ACKNOWLEDGMENTS This work was supported in part by NSF of Zhejiang Province of China under grant Y107550, in part by NSFC under grant 60506015. REFERENCES 1. H. Morishita, K. Hirasawa, and K. Fujimoto, Analysis of a cavity- backed annular slot antenna with one point shorted, IEEE Trans An- tennas Propag 39 (1991), 1472–1478. 2. Q. Li and Z. Shen, An inverted microstrip-fed cavity-backed slot antenna for circular polarization, IEEE Antennas Wireless Propag Lett 1 (2002), 190 –192. 3. D. Sievenpiper, H. Hsu, and R.M. Riley, Low-profile cavity-backed crossed-slot antenna with a single-probe feed designed for 2.34 GHz satellite radio applications, IEEE Trans Antennas Propag 52 (2004), 873– 879. 4. G.Q. Luo, W. Hong, Q.H. Lai, K. Wu, and L.L. Sun, Design and experimental verification of compact frequency selective surface with quasi-elliptic bandpass response, IEEE Trans Microwave Theory Tech 55 (2007), 2481–2487. © 2008 Wiley Periodicals, Inc. NEW THz EXCITATION OF PLANAR GOUBAU LINE Anthony Treizebre ´, 1 Bertrand Bocquet, 1 Yansheng Xu, 2 and Renato G. Bosisio 2 1 IEMN, Institut d’Electronique, de Microe ´ lectronique et de Nanotechnologie, UMR CNRS 8520, USTL Universite ´ des Sciences et Technologies de Lille, BP 69, Villeneuve d’Ascq 59652, France; Corresponding author: Bertrand.Bocquet@iemn.univ-lille1.fr 2 POLY-GRAMES, Centre de recherches avance ´ es en microondes et en e ´ lectronique spatiale, De ´ partement de ge ´ nie e ´ lectrique, Ecole Polytechnique de Montre ´ al, C.P. 6079, succursalle “centre-ville”, Montre ´ al, QC, Canada H3C 3A Received 19 March 2008 ABSTRACT: Quite recently, it has been found that conducting wires lying on a flat dielectric substrate can propagate Terahertz (THz) waves in the same way as conducting wires entirely coated with a dielectric (Goubau line). This phenomenon is interesting because it is a basic re- quirement to fabricate integrated circuits at THz frequencies. The exci- tation of planar Goubau line (PGL) waves was found to have a very strong Goubau mode on conducting wire. The excitation was made with a coplanar waveguide transition fed with a THz signal obtained from a vector network analyzer. The Goubau mode on PGL was excited with high efficiency (up to 75%.). This is a first step in the design of THz BioMEMS dedicated to living cell investigations. © 2008 Wiley Periodi- cals, Inc. Microwave Opt Technol Lett 50: 2998 –3001, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ mop.23850 Key words: BioMEMS; CPW PGL transition; planar Goubau line; terahertz; transmission line 1. INTRODUCTION Biological molecular interactions must be studied and well under- stood to achieve a basic understanding of biological systems. Related research projects directly lead to observe and study mo- lecular formations. Observation on groups of molecules by means of living cell membranes is a good and accepted approach to understand biological systems. Many physical principles are in- volved to carry out such studies including the use of nonionizing electromagnetic radiation. However, the optical approach, cur- rently in use, requires fluorescent tags that can modify biomolec- ular interactions. On the other hand, the use of lower frequency microwaves lacks the spatial resolution of optical waves. It is noted that terahertz (THz) waves are still not widely used. The use of such waves could be very interesting to study molecular interactions because THz photon energy is at the same level as low Figure 5 Measured radiation patterns at 10 GHz Figure 1 Schematic view of the PGL excitation structure 2998 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 11, November 2008 DOI 10.1002/mop