give the limitation of high pump powers, all the devices present almost the same XL (around -1.5 dB). For the soliton regime, in all the devices there is a decrease of XL for pump powers around 1 W, which is the energy of the fundamental soliton. For high pump powers, all devices present a second peak, and decreased XL is detected. For the L/10 device, the minimum (-3.7 dB) is around 8 W. The increase of the pump power results in high-order solitons and pulse compression; in this situation the bandwidth of the pulse increases and we can extrapolate the bandwidth of the device as the XL increases. Our study of the XL on the AOTF, operating with ultra-short optical solitons, provides possibilities for achieving high efficiency in ultrafast all-optical signal processing, especially for optical switches, filters, and optical transistors. The AOTF has attracted much attention in recent years, in part because it appears to be a suitable basis for multiwavelength optical cross-connects. 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WIDE BAND RECTANGULAR MICROSTRIP ANTENNA USING SYMMETRIC T-SHAPED FEED Sreedevi K. Menon, B. Lethakumary, K. Vasudevan, and P. Mohanan Centre for Research in Electromagnetics and Antennas Department of Electronics Cochin University of Science and Technology Cochin 682 022, India Received 16 April 2002 ABSTRACT: Bandwidth enhancement of a rectangular microstrip antenna using a T-shaped microstrip feed is explored in this paper. A 2:1 VSWR impedance bandwidth of 23% is achieved by employing this technique. The far-field patterns are stable across the pass band. The proposed antenna can be used conveniently in broadband com- munications. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 235–236, 2002; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.10566 Key words: microstrip antennas; bandwidth enhancement; T-shaped feed; electromagnetic coupling 1. INTRODUCTION Narrow bandwidth available from printed microstrip patches is the major handicap factor which limits the widespread application of these classes of antennas. Several techniques for bandwidth wid- ening of microstrip antennas have been reported in literature, such as the use of thick substrates [1] and multiple dielectric resonators [2]. In all these cases the impedance bandwidth is found to be less than 10%. The usage of shorting pins [3], and high dielectric constant substrate and superstrates, [4] etc., can be used to reduce antenna size, but in these cases the bandwidth is found to be very narrow in nature. Recently, a T-probe-fed patch antenna used to enhance the impedance bandwidth up to 40% [5] was reported, however, its overall system is highly complex and bulky. In this paper, a novel approach of planar T-shaped feed for feeding microstrip antenna is presented with less complexity. This feeding technique gives a 2:1 VSWR bandwidth of 23.2%. 2. ANTENNA GEOMETRY A 50  T-shaped feed line is fabricated on a substrate of dielectric constant  r1 = 4.28 and thickness h 1 = 0.16 cm. An antenna of dimension L  W is fabricated on a substrate of  r2 and thickness h 2 and is electro magnetically coupled with the feed line as described in Figure 1. 3. EXPERIMENTAL RESULTS The performance of the patch with T-shaped feed is evaluated using HP 8510C Network Analyzer. A rectangular patch an- Figure 1 Geometry of the rectangular microstrip antenna with a sym- metric T-shaped feed MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 35, No. 3, November 5 2002 235