Figure 6 shows the measured and simulated response at wavelength of 1.296 m (peak wavelength under perpendicular light incidence) with respect to the incident light angle. The quantum efficiency is seriously dependent on the incident light angle. When the incident light angle less than 3°the decrease is slight and can be neglected (change from 0.55 to 0.54). When the light incident angle is larger than 5°, the quantum efficiency decreases rapidly. So the incident light angle must be taken into account when the PD is packaged. Figure 7 shows the measured full width at half maximum (FWHM) of photocurrent response with respect to incident light angle. The experimental results are almost independent on the light incident angle. When light illuminating the device is at a slant, the TM and TE waves have different refractive indexes. The responses of the TM and TE waves are different for the device. Thus response spectra are broadened. But the phenomenon induced by this mechanism is very slight (about 10 Ϫ5 nm). From the experimental results, an increase of FWHM is also not observed. SUMMARYIn this Letter characteristics with respect to the incident light angle of RCE PD were analyzed. Experiment were also carried out on a 1.3-m GaInNAs quantum-well RCE PD. Both theoretical analysis and experimental results show that the influence can be neglected when the light incidence angle is less than 3°. This is a requirement for the RCE PD to be applied in WDM systems.

A compact hairpin stepped-impedance resonator structure is proposed using large-ratio impedance steps to increase the first harmonic resonance frequency. The new resonator is used to design a novel microstrip bandpass filter by a simple and accurate CAD technique, using a commercial electromagnetic field solver. A high degree of miniaturisation is achieved by fabricating the filter on a BaO-PbO-Nd2O3-TiO2 ceramic substrate, with a dielectric constant of 90.9. Measurements on a filter at 1.8 GHz show close agreement with simulations and demonstrate a significant improvement in stopband performance. The centre frequency of the first harmonic passband is increased to approximately 4.3 GHz.

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A simple design procedure is described for miniaturized microstrip bandpass filters on high-ε r substrates. Costs and design times are reduced by replacing experimental measurements with EM simulations. The procedure is confirmed through the design of a miniaturized microstrip hairpin-coupled bandpass filter at 1.8 GHz on BaO PbO Nd 2 O 3 TiO 2 (ε r = 90 9) ceramic substrate.

High‐dielectric‐constant (high‐εr) ceramic materials provide opportunities for developing ultra‐miniaturized microstrip circuits. This paper investigates the properties of high‐εr microstrip transmission lines on (Zr, Sn)TiO4 (εr=37) and BaO–PbO–Nd2O3–TiO2 (εr=88) substrates. An electromagnetic (EM) field solver is used to determine the frequency‐dependent characteristic impedance and effective dielectric constant of a range of microstrip lines up to 5 GHz. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 313–314, 2001.