IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 58, NO. 3, MARCH 2010 969 Fig. 8. (a) Fabricated back-to-back rat-race coupler/CPS transition, (b) mea- sured and for two different CPS lengths. the 180 hybrid coupler and the CPS line between Ref. planes 1 and 2 in Fig. 5(a) was then measured separately. Two back-to-back designs with different lengths of CPS line are built and the measured and of these back-to-back designs are shown (Fig. 8). The measured of the back-to-back design with 25 mm of CPS line is at 24 GHz. This results in a total loss of between Ref. planes 1 and 2 (Ansoft HFSS predicted 0.8 dB loss). The measured of the back-to-back design with 45 mm CPS line is at 24 GHz, which means that the CPS line has a loss of (HFSS pre- dicted a loss of 0.07 dB/cm). The measured gain agrees very well with simulated gain, but with some ripples due to the scattering effects from the measurement setup. The measured gain is from 21.5 to 25.9 GHz with a measured peak gain of 9.8 dB at 24 GHz. HFSS reports a directivity of 10.3 dB with a gain of 9.9 dB at 24 GHz, and this corresponds to a radiation ef- ficiency , which is collaborated by our experiment (within mea- surement error). III. CONCLUSION This communication presented a millimeter-wave CPS-fed Yagi-Uda antenna with a folded dipole feed, relatively wideband operation (21–25 GHz), medium gain (8–10 dB) and very low cross-polarization levels . The antenna can be scaled to 60–94 GHz for automotive radars and high data-rate communication systems, and is ideally suited for differential RFIC connections. REFERENCES [1] L. Zhu and K. Wu, “Model-Based characterization of CPS-fed printed dipole for innovative design of uniplanar integrated antenna,” IEEE Mi- crow. Guided Wave Lett., vol. 9, pp. 342–344, Sep. 1999. [2] N. Kaneda, W. R. Deal, Y. Qian, R. Waterhouse, and T. Itoh, “A broad- band planar quasi-Yagi antenna,” IEEE Trans. Antennas Propag., vol. 50, no. 8, pp. 1158–1160, Aug. 2002. [3] P. R. Grajek, B. Schoenlinner, and G. M. Rebeiz, “A 24-GHz high-gain Yagi-Uda antenna array,” IEEE Trans. Antennas Propag., vol. 52, pp. 1257–1261, May 2004. [4] G. Zheng, A. A. Kishk, A. B. Yakovlev, and A. W. Glisson, “Simplified feed for a modified printed Yagi antenna,” Electron. Lett., vol. 40, no. 8, pp. 464–465, Apr. 2004. [5] Y. Lee and S. Chung, “Design of a 38-GHz printed Yagi antenna with multiple directors,” in Proc. IEEE Antennas and Propag. Symp., Jul. 2001, vol. 3, pp. 606–609. [6] G. R. DeJean and M. M. Tentzeris, “A new high-gain microstrip Yagi array antenna with a high front-to-Back (F/B) ratio for WLAN and millimeter-wave applications,” IEEE Trans. Antennas Propag., vol. 55, pp. 298–304, Feb. 2007. [7] H. K. Kan, R. B. Waterhouse, A. M. Abbosh, and M. E. Bialkowski, “Simple broadband planar CPW-fed quasi-Yagi antenna,” IEEE An- tennas Wireless Propag. Lett., vol. 6, pp. 18–20, 2007. [8] S. Hsu, K. Wei, C. Hsu, and R. Chuang, “A 60-GHz Millimeter-Wave CPW-Fed Yagi Antenna Fabricated by Using 0.18-mm CMOS Tech- nology,” IEEE Electron. Device Lett., vol. 29, pp. 625–627, Jun. 2008. [9] R. A. Alhalabi and G. M. Rebeiz, “High-Gain Yagi-Uda antennas for millimeter-wave switched-beam systems,” IEEE Trans. Antennas Propag., vol. 57, pp. 3672–3676 , Nov. 2009. [10] W. L. Stutzman and G. A. Thiele, Antenna Theory and Design, 2nd ed. New York: Wiley, 1998. [11] Ansoft Corporation, Pittsburgh, PA. [12] Dorado International Seattle, WA. A Finite Edge GTD Analysis of the H-Plane Horn Radiation Pattern Maifuz Ali and Subrata Sanyal Abstract—The earlier geometrical theory of diffraction (GTD) approach to the H-plane horn radiation problem is reconsidered with spherical source excitation. Corner diffraction terms are included to provide a GTD model for the finiteness of the horn edges. A new heuristic corner slope diffraction (CSD) coefficient for a finite edge in a conducting plane is presented. The H-plane horn pattern, obtained with the addition of the corner diffraction and the new CSD terms to the earlier infinite edge GTD approach, is found to be in better agreement with measured results compared to earlier GTD formulations. Index Terms—Corner diffraction, corner slope diffraction, geometrical theory of diffraction (GTD), horn antenna, H-plane radiation pattern. I. INTRODUCTION The horn antenna invented by J. C. Bose [1] in the 1890s is a good canonical problem as it has a broad range of low response in the back- ward (LRB) directions [2]. Keller’s GTD and parallel plate waveguide mode approximation was used by Yu et al. to obtain the H-plane pat- tern in [3]. The GTD prediction was in good agreement with measure- ments in the forward direction. In the back lobe direction it was shown that the E-edge contributions were significant for observation angle at and around 180 . However, there remained wide differences in LRB region. For , better results in the average was obtained by taking into account the finite edge effect of the E-edges using current Manuscript received October 28, 2008; revised August 23, 2009. First pub- lished December 04, 2009; current version published March 03, 2010. The authors are with the Department of Electronics and Electrical Commu- nication Engineering, Indian Institute of Technology, Kharagpur-721 302, India (e-mail: maifuzali@lycos.com; ssanyal@ece.iitkgp.ernet.in). Digital Object Identifier 10.1109/TAP.2009.2037762 0018-926X/$26.00 © 2010 IEEE