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This paper describes a design of a surface acoustic wave (SAW) ladder-type bandpass filter (BPF) for 2.4-2.5GHz ISM-band, based on the low temperature co-fired ceramic (LTCC) substrate, which can be used in 802.11b/g wireless LAN and Bluetooth applications. It obtains an excellent state-of-the-art performance in the ultra small package. The proposed architecture is based on a combination of SAW and low temperature co-fired ceramic (LTCC) technologies, where the multilayer LTCC substrate is used for integration of matching and passband-driving elements and for obtaining additional transmission zeros. It is comprised of three series and two parallel SAW resonators, realized on the LiTaO 3 piezoelectric substrate and connected accordingly to a ladder-type T-topology circuit design, and an additional resonator to obtain an attenuation at 2.57-2.62 GHz IMT-E (TDD) band. Two input/output matching inductors and three additional inductors, permitting to obtain a sufficient suppression level at 2.11-2.17 GHz UMTS (DL) band and harmonics, are completely integrated within ceramic.The described bandpass filter has ultra small dimensions of 1.1 x 1.4 x 0.9 mm, very low insertion losses of -1.5 dB max in the passband. This fully matched SAW bandpass filter has achieved excellent selectivity performance with the up-to-date smallest package size.Index Terms -Bandpass filter (BPF), ladder-type, surface acoustic wave (SAW), coexistence, low temperature co-fired ceramic (LTCC), wireless local area network (WLAN), systemin-package (SIP).

Error Vector Magnitude (EVM) is a key parameter for the design of digitally modulated communication systems. In the case of SAW filters, it is a measure for the caused intersymbol-or inter-chip interference. It can be mainly attributed to linear distortion. This paper will present a semi-analytical method for computing EVM based on the definition given in [ 11. The major goal of this work was to provide a precise, easy-touse and computationally efficient method to obtain EVM for UMTS SAW filters while avoiding discrete time system simulation or the use of special measurement equipment other than network analyzers. Therefore, time-and frequency domain formulas for EVM were derived without making simplifying assumptions or approximations. Because the former requires FFT to obtain the filter impulse response from a measured or simulated transfer function and the latter involves numerical integration, this method is called semianalytical.Numerical results based on the time-domain EVM formula will be compared to results from EVM measurement.

We demonstrate a novel concept for a mode selection mechanism in surface emitting laser diodes. This concept is based on a strong coupling process between the laser mode and a surface mode on top of the laser diode. The mode selection mechanism is the result of a strong feedback from the surface mode into the laser diode. Nearly single-modelike emission spectra are achieved from surface emitting GaAs/AlGaAs laser diodes and qualitatively explained by a model based on ray optics. The main advantage of this type of laser diode is its simple fabrication and the possibility of adjusting the desired wavelength independent of the growth process by external technological parameters.

Strongly improved surface emitting laser diodes based on surface mode emission are presented. A first-order-grating was utilized for the excitation of the surface modes. This results in an efficient quasi-single-beam surface emission with low divergence and a significant narrowing in the emission spectrum. A variation in the emission wavelength of up to 4 nm is achieved by adjusting the surface waveguide thickness, which demonstrates the wavelength selection mechanism of the SME technique. The decisive advantage of the SME laser diodes in comparison to DFB/DBR laser diodes is their high flexibility in fabrication, which makes them very suitable for wavelength division multiplexing applications.