4.65° with standard deviation of 3.21°. It means that the precision of our DOA ﬁnder is approximately 5°. 5. CONCLUSION This article has presented the low proﬁle of 2.4 GHz DOA ﬁnder. The ﬁnder is constituted by 2  2 rectangular array, beamforming network, power detector and economic microprocessor. To be compatible with 2D array antenna and achieve uniformly beam distribution, the modiﬁed Butler matrix utilized in beamforming network has been originally proposed in this article. The experi- mental results have conﬁrmed the direction ﬁnding capability of the prototype. This DOA ﬁnder has been found very attractive for com- mercial in WLAN positioning system or other system providing location-based services. This is because it is not complex and costly. ACKNOWLEDGMENT The authors acknowledge the ﬁnancial support from Thailand Research Fund and Suranaree University of Technology, Thailand. REFERENCES 1. Available at: http://itresearch.forbes.com/detail/RES/1051538795_191. html, White paper IEEE 802.11g. 2. P. Bahl and V.N. Padmanabhan, RADAR: An in-building RFbased user location and tracking system, IEEE Infocom (2000), 775–784. 3. Y. Wang, X. Jia, H.K. Lee and G.Y. Li, An indoor wireless positioning system based on WLAN infrastructure, 6th International Symposium on Satellite Navigation Technology Including Mobile Positioning and Location Services, Melbourne, Australia, 2003, p. 54. 4. Available at: http://www.geocities.co.jp/Athlete-Acropolis/4678/bea- con.html. 5. T. Ohira and K. Gyoda, Hand-held microwave direction-of-arrival ﬁnder based on varactor-tuned analog aerial beamforming, Asia-Pa- ciﬁc Microwave Conf, Taipei, Taiwan (2001), 585–588. 6. C. Plapous, J. Cheng, E. Taillefer, A. Hirata, and T. Ohira, Reactance domain MUSIC algorithm for electronically steerable parasitic array radiator, IEEE Trans Antennas Propag 52 (2004), 3257–3264. 7. M.F. Bondarenko and D.I. Lekhovitsky, Combined direction ﬁnders of point noise radiation sources based on adaptive lattice ﬁlters, IEEE Int Workshop Comp Adv Multi-Sensor Adapt (2005), 213–216. 8. P. Parvazi, A.B. Gershman, and Y.I. Abramovich, Detecting outliers in the estimator bank-based direction ﬁnding techniques using the like- lihood ratio quality assessment, IEEE Int Conf Acoustics Speech Signal Process (2007), II-1065–II-1068. 9. T. Matsumoto and Y. Kuwahara, Experiments of direction ﬁnder by RBF neural network with post processing, IEEE Antennas Propag Soc Int Symp, Washington, D.C., 2005, 10 –13. 10. Y. Kuwahara and T. Matsumoto, Experiments on direction ﬁnder using RBF neural network with post-processing, Electron Lett 41 (2005), 602– 603. 11. W.A.U. Titze, P.V. Brennan, and R. Benjamin, Direction ﬁnding system using symmetric-pair antenna arrays, IEEE Proc—Radar Sonar Navigat (1995), 130 –136. 12. W.G. Diab and H.M. Elkamchouchi, A deterministic real-time DOA- based smart antenna processor, IEEE 18th Int Symp Personal Indoor Mobile Radio Commun (2007), 1–5. 13. J.C. Liberti, Jr. and T.S. Rappaport, Smart antennas for wireless communications: IS-95 and third generation CDMA applications, Prentice Hall PTR, NJ, 1999. 14. J.S. Wight, W.J. Chudobiak, and V. Makios, A microstrip and stripline crossover structure, IEEE Trans Microwave Theory Tech 24 (1976), 270 –270. © 2008 Wiley Periodicals, Inc. COMPACT HARMONIC CONTROL NETWORK FOR DOHERTY POWER AMPLIFIER Paolo Colantonio, Franco Giannini, Rocco Giofre ` , and Luca Piazzon Electronic Engineering Department, University of Roma Tor Vergata, via del, Politecnico 1, Roma 00133, Italy; Corresponding author: giofr@ing.uniroma2.it Received 8 May 2008 ABSTRACT: In this contribution, an innovative design solution to realize small size Doherty power ampliﬁer is presented. The idea consists in the realization of a unique output matching network for both carrier and peak- ing devices without losing the Doherty behavior. Experimental results per- formed on uneven Doherty ampliﬁer using GaN HEMT device is given to demonstrate the proposed approach. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 256–258, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 23983 Figure 10 Absolute power differences between two output ports having neighbor main beam vs. DOA. [Color ﬁgure can be viewed in the online issue, which is available at www.interscience.wiley.com] Figure 11 Estimated DOA vs. DOA of source. [Color ﬁgure can be viewed in the online issue, which is available at www.interscience.wiley.com] 256 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 1, January 2009 DOI 10.1002/mop