4. J.C. Batchelor, R.J. Langley, and H Endo, On-glass mobile antenna performance modeling, IEE Proc Microwave Antennas Propag 148 (2001), 233–238. 5. D.E. Goldberg, Genetic algorithms in search, optimization and machine learning, Addison-Wesley, Reading, MA, 1989. 6. Y. Rahmat-Samii and E. Michielssen, Electromagnetic optimization by genetic algorithms, Wiley, New York, 1999. 7. T. Hiroyasu, M. Miki, and S. Watanabe, The new model of parallel genetic algorithm in multi-objective optimization problems—Di- vided range multi-objective genetic algorithm, Proc Congr Evol Comput 1 (2000), 333–340. 8. EM Software & Systems–S.A. (Pty) Ltd., FEKO suite 5.3, EM Soft- ware and Systems, Stellenbosch, 2007. 9. 2006 KIA Grand Carnival. Available at: http://www.kia.co.kr. 10. Transmit antenna. Available at: http://www.ets-lindgren.com/ manuals/3121C.pdf. V C 2009 Wiley Periodicals, Inc. X-BAND HIGH-POWER AMPLIFIER WITH A MAGNETICALLY COUPLED POWER-COMBINER Kyung-Ai Lee, Changkun Park, Jong-Hoon Chun, and Songcheol Hong School of Electrical Engineering & Computer Science, Division of Electrical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-Dong, Yuseong-Gu, Daejeon 305-701, Republic of Korea; Corresponding author: schong@ee.kaist.ac.kr Received 9 April 2009 ABSTRACT: In this article, a high-power ampliﬁer for X-band application is studied, which consists of a two-stage ampliﬁer with magnetically coupled power-combiners and dividers. These are based on transmission line transformers, which has lower loss characteristics than spiral-type transformers at the frequencies. The proposed ampliﬁer utilizes the voltage-combining concept with the transformers and differential ampliﬁers. The size of the ampliﬁer is also minimized by using the virtual grounds of the differential structure. The saturated output power of the power ampliﬁer is 38.1 dBm (6.45 W), and the gain is 17 dB at 10 GHz. The area of the chip is 2.56 mm  3.13 mm and the power density of the ampliﬁer is 806 mW/mm 2 . V C 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 110–113, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24851 Key words: X-band power amplifier; tournament shaped; voltage combiner; binary combiner 1. INTRODUCTION Currently, there is an increasing demand for X-band radar T/R modules for military and public services use. One of the most important components of the module is a high-power ampliﬁer, which should preferably be developed as a microwave mono- lithic circuit (MMIC) for the minimization and reproducibility of the module [1–4]. The conventional ampliﬁers have their transistors arranged in a row using binary-tree-combining topol- ogy. With this topology, the summed output power is delivered to an output load by means of the power-combining. Figure 1 shows an example of a binary-combining topology. Mostly, an output impedance of a power transistor (R1) is lower than 50 X, which needs matching components like inductors and capacitors. These lumped devices have large power losses. To solve this problem, the voltage-combining topology has been studied with CMOS technology at a frequency band lower than 5 GHz [5, 6]. In this topology, the magnetically coupled lines substituted the inductors and capacitors (Fig. 2). If the magneti- cally coupled lines work well in X band, these help to reduce the power loss of the power-combiner. The differential struc- tures in the topology have virtual grounds, which eliminate k/4 drain bias lines. The concept of combining voltage is therefore introduced to improve the performance and to reduce the size of the high-power ampliﬁer. This paper describes the performance of the high-power am- pliﬁer at X band with the magnetically coupled power-combiner, which utilizes the voltage-combining concept. The concept of the voltage-combining was introduced with distributed active transformer [6], but it cannot be adopted in GaAs technology, where the gate must be aligned to the same direction. This is because it utilized the circular geometry to implement the power-combining and the output matching simultaneously. Therefore, the tournament-shaped magnetically coupled power- combiner is used for X-band high-power ampliﬁer. Figure 1 The binary-combining topology with eight transistors Figure 2 The voltage-combining topology with eight transistors 110 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 DOI 10.1002/mop