aperture surface of the circular antenna and the load of circular antenna is placed at the center [6]. Figure 3 shows the antenna factor of the EM sensor arranged with E-null configuration and H-null configuration as a function of frequency ranged from 50 MHz to 3 GHz. The antenna factor is about 98.18 (dB) and 100.0 (dB) for E-null configuration at 50 MHz and 3 GHz, respectively. Similarly, the antenna factor is about 115.21 (dB) and 110.3 (dB) for H-null configuration at 50 MHz and 3 GHz, respectively. For measuring the electric field and magnetic field, it can be seen that the antenna factor and associated sensitivity of the EM sensor are almost flat in the frequency range of 50 MHz and 3 GHz. There- fore, the linear performance of this EM sensor can be achieved. 4. CONCLUSION The electromagnetic field sensor using a LiNbO 3 Mach-Zehnder optical modulator and an antenna has been developed to measure the electromagnetic field. This sensor operated at a wavelength of 1.55 m, for which many fiber optical systems have been devel- oped. The minimum detectable filed intensity of this electromag- netic field sensor is 0.7 mV/m at 50 MHz and 1.2 mV/m at 3 GHz, respectively. The sensitivity was relatively flat from 50 MHz to 3 GHz and this frequency range uniquely covers all frequency bands involved in the cellular phones, mobile communication, and bluetooth technology. According to the experimental results, this electromagnetic field sensor so developed can be potentially em- ployed in sensory applications on electromagnetic compatibility and RF and microwave safety control. ACKNOWLEDGMENT This work was supported by the National Science Council of the Republic of China under contract No. NSC94 –2215-E-006 – 009. REFERENCES 1. I.Z. Huerta and J.R. Asomoza, Electro-optic E-field sensor using an optical modulator, in Pro CONIELECOMP’04 (2004), 220 –222. 2. C.G. Martinez, G.T. Garcia, and J.R. Asomoza, Electric field sensing system using coherence modulation of light, IEEE Trans Instrum Meas 51 (2002), 985–989. 3. K.W. Hui, K.S. Chiang, B. Wu, and Z.H. Zhang, Electrode optimization for high-speed traveling-wave integrated optic modulators, J Lightwave Technol 6 (1998), 232–238. 4. H.D. Yoon, S.K. Lim, C. An, Y.T. Han, C.M. Kim, K.H. Ku, and H.Y. Lee, Design and RF characteristics of traveling-wave electrodes for high –speed lithium niobate optical modulators, in Proc 1999 IEEE TENCON (1999), 35–38. 5. C.T. Lee, H.C. Lee, H.H. Lai, and L.G. Sheu, Complementary optical bistable operation with integration of two directional coupler on LiNbO 3 crystal, Jpn J Appl Phys Part 1 35 (1996), 2686 –2689. 6. T. Miyakawa, K. Nishikawa, and K. Nishida, An optical-waveguide- type magnetic field probe with a loop antenna element, Electron Com- mun Jpn Part 2 88 (2005), 18 –27. © 2006 Wiley Periodicals, Inc. A MULTI-LAYERED PROXIMITY COUPLED PATCH SUITABLE FOR MMIC INTEGRATION W. S. T. Rowe, 1 and R. B. Waterhouse 2 1 School of Electrical and Computer Engineering RMIT University, Melbourne, Australia 2 Pharad, Glen Burnie, MD Received 23 February 2006 ABSTRACT: In this paper, the authors present a highly efficient, broadband patch based antenna that is compatible with integrating into Monolithic Microwave Integrated Circuits. The antenna configuration is a proximity coupled stacked patch structure where the layer between the Monolithic Microwave Integrated Circuit and the first patch is an inex- pensive laminate. The impact of this layer on the performance of the antenna is investigated both theoretically and experimentally. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1899 –1902, 2006; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/mop.21775 Key words: printed antennas; efficient antenna integration; MMIC 1. INTRODUCTION With the recent interest in wideband wireless communications, the need for efficient, integrated base station terminals where all microwave circuitry and antenna technology can be developed into a “single chip ” solution is very pertinent. This strategy is very challenging as material suitable for microwave components, such as active devices or compact passive distribution networks, is not inherently compatible with efficient, conventional patch based antennas [1]. Another important requirement for wideband wire- less communication terminals is that the cost of the module must be low, to assist in the mass deployment of these systems. In Ref. [2], a highly efficient patch based antenna suitable for integration with Monolithic Microwave Integrated Circuits (MMICs) was introduced. The antenna structure was based on a proximity coupled stacked patch configuration where the feed layer was a MMIC-consistent substrate. The developed antenna had a 10 dB return loss bandwidth of 21% and an efficiency across this band of more than 85%. Importantly, the technique also enabled the first patch radiator not to be fabricated on the MMIC material, conserving expensive real estate. The key to the MMIC- compatible antenna presented in Ref. [2] was the thin laminate between the MMIC layer and the first patch, and it was postulated that this layer needed to be of similar dielectric constant value to that of the MMIC layer. This can be a potential setback for a low cost implementation of this design, as typically the higher the dielectric constant of the material, the more expensive it is (with the exception of some ceramics). This paper presents an extension of the work conveyed in Ref. [2]. In particular, the focus is on the relationship between the dielectric laminate between the MMIC feed layer and the lower patch and the overall performance of the stacked antenna. It was Figure 3 Antenna factor as a function of electromagnetic field fre- quency DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 1899