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relative excitation amplitudes of the modes. Three different cases were studied in terms of the relative permittivity r2 of the TM 02 patch, while keeping r1 ϭ 1.15 for the TM 11 mode. It was found that as r2 increased, the phase centre location of the antenna moved further away from its physical centre, over a given angular range of the far field. The largest phase centre displacement of about 0.3 was achieved, for a peak 50°phase variation, in Case III. The concept provides a simple and yet practical method for moving the antenna phase centre, without mechanically moving the antenna itself. This attractive feature can be useful in applications like beam shaping, global positioning systems, virtual arrays, adaptive pattern controls, and reflector antenna applications. ABSTRACT:The resonant modes and characteristics of a rectangular microstrip with a variable air gap are theoretically and experimentally examined. Effect of varying width to length ratio is another important aspect addressed and a computer aided design is presented. Thorough experiments are presented, a few of which are reported for the first time. ABSTRACT:We present a single-pass L-band erbium doped fiber amplifier (EDFA) based on a large mode area (LMA) fiber. A single transverse mode is maintained through restricted mode launch. Pump light near 974 nm is sent into the core and has high spatial overlap with the signal beam, helping to preserve single mode propagation. Up to ϩ27 dB of pump power limited small signal gain (30 W signal input) with a noise figure (NF) near 4.4 is achieved in a relatively short fiber [b].

The polymerization of thiophene (TP), in bulk and in solution in CHCl3 by FeCl3 resulted in the formation of a polymer which was characterized by FTIR as polythiophene (PTP). High yield was realized in the latter case. The polymerization of TP with FeCl3 and nanodimensional Al2O3 resulted in the formation of a nanocomposite which was partly dispersible in aqueous and non‐aqueous media. The dispersibility appeared to be higher when the polymerization was conducted in a suspension containing a higher amount of Al2O3. Scanning electron micrographs showed globular particles and the presence of clusters of composite particles. Transmission electron micrographic (TEM) analyses revealed the particle size of the composite to be in the range 22–74 nm. Thermal analyses (TG/DTA) revealed the outstanding stability of PTP–Al2O3 composites compared to that of PTP. The conductivity of PTP and of PTP–Al2O3 composite was of the order of 10−3 S cm−1 for samples doped with I2. © 2003 Society of Chemical Industry