A compact and simple CPW‐fed step‐shaped microstrip antenna for ultrawideband applications is presented. The antenna offers a wide bandwidth from 4.4 to 11 GHz with an impedance bandwidth of 85.7%. The antenna also offers an average gain of 4.65 dBi in the entire band with good radiation characteristics. The antenna posses an overall dimension of 30 × 25 × 1.6 mm3 when fabricated on FR4 epoxy substrate of dielectric constant 4.4 and thickness 1.6 mm. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:589–591, 2015

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give the limitation of high pump powers, all the devices present almost the same XL (around Ϫ1.5 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 (Ϫ3.7 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. It is probably the only known tunable filter capable of selecting several wavelengths simultaneously. This capability can be used to construct a multiwavelength router. ACKNOWLEDGMENTWe thank Funcap, CNPq, CAPES, and FINEP (Brazilian Agencies) for their financial support.

A broadband rectangular microstrip antenna utilizing an electromagnetically coupled L-strip feed is presented. Experimental study shows a 2:1 VSWR bandwidth of Ϸ 10% and excellent cross-polarization performance with a radiation coverage almost as same as that of the rectangular microstrip antenna fed by conventional methods. The variation of bandwidth for different feed param- ANTENNA GEOMETRYThe geometry of the proposed antenna is shown in Figure 1. Rectangular patch antenna of dimension L ϫ W is etched on a substrate of thickness h 2 and permittivity r2 . The patch is electromagnetically fed by the L-shaped 50⍀ microstrip feed fabricated on a substrate of thickness h 1 ϭ 1.6 mm and permittivity r1 ϭ 4.28. EXPERIMENTAL RESULTSA rectangular patch antenna with L ϭ 40 mm and W ϭ 20 mm is fabricated on a substrate with r2 ϭ 4.28, h 2 ϭ 1.6 mm. The parameters of the L-strip feed are optimized to obtain maximum percentage bandwidth. The variation of the return loss of the above antenna with the optimum feed parameters S 1 ϭ 8 mm, S 2 ϭ 6 mm and S 3 ϭ 25 mm is shown in Figure 2. The antenna operates in the 3.03-3.38-GHz band giving a 2:1 VSWR bandwidth of Ϸ 10% with a center frequency of 3.3 GHz. The experiment is repeated for antennas resonating at the same frequency, fabricated on different substrates. Variation in the percentage bandwidth with feed segment length (S 3 ) is shown in Figure 3. Radiation patterns of the antenna at the operating band edges and midband frequencies for the above feed parameters are shown in Figure 4. The HPBW of the antenna in the E and H planes are 92°and 66°, respectively, at the resonant frequency. The cross polarization of the antenna is better than Ϫ30 dB. CONCLUSIONSA microstrip antenna with an electromagnetically coupled L-strip feed giving large bandwidth is presented. The remarkable feature of the proposed antenna is its compact structure to achieve enhanced bandwidth. The feeding technique is very simple compared to the other methods. ANALYSIS AND DESIGN OF AN ADAPTIVE POLYNOMIAL PREDISTORTER WITH THE LOOP DELAY ESTIMATOR

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