High Stopband Rejection Research Articles

A high stopband-rejection LTCC filter with multiple transmission zeros

A low-temperature-cofired ceramic (LTCC) bandpass filter with high stopband rejection is presented for multistandard coexisted wireless communication applications, such as the integrated wireless local area network (WLAN)/wavelength code-division multiple access handset, the dual-band triple-mode WLANs, and the global system for mobile communications/global positioning system receivers. By improving the filter cell structure, 2n transmission zeros can be generated to achieve wide-band suppression from cascading n filter cells. The presented method provides the design flexibility of locating these transmission zeros distributed in the lower and upper stopbands. An LTCC bandpass filter with four transmission zeros has been implemented for experimental demonstration. The measured insertion loss is less than 1.5 dB at 2500 MHz, and four transmission zeros are obtained at 1.64, 1.88, 4.36, and 5.32 GHz, respectively. These result in 48-59 dB for lower stopband suppression and 38-55 dB for higher stopband reduction. This paper demonstrates that the proposed filter is extremely suitable for the multiband RF transceivers where the cross-band interference must be adequately reduced.

Frequency response of a focused SAW device based on concentric wave surfaces: simulation and experiment

Focused interdigital transducers (FIDTs) based on concentric wave surfaces can excite surface acoustic wave (SAW) with high intensity, high beamwidth compression ratio and small localized area. In this paper, we developed a model to analyse the frequency response of a SAW device with FIDTs based on concentric wave surfaces. First, we constructed a focused SAW device by adopting a pair of FIDTs shaped as the concentric wave surface. To calculate its frequency response, a simulation model was established based on the 2D SAW filter model, effective permittivity approach and perturbation theory. Further, the focused SAW devices were designed and fabricated via the microelectromechanical system process technique. A good agreement between the simulated and measured results was found. Finally, the frequency responses of focused SAW devices based on concentric wave surfaces were discussed and some attractive features were found, such as less ripples of pass-band and high stop-band rejection. In addition, in comparison with the conventional SAW devices with uniform interdigital transducers, the focused SAW devices are more sensitive to variations in the focal area, instead of the whole delayline region. Accordingly, they are suitable to be applied to detect or manipulate some localized variations, such as acousto-optic or acousto-electric effects.

Sidelobe cancellation technique for achieving high rejection in SAW filters.

A new technique called sidelobe cancellation technique (SCT) to achieve high stopband rejection in SAW filters is described, for varying requirements of shape factor and sidelobe levels, by using an eigen function approach. Cosine series functions with improved sidelobe levels are employed. Each design is characterized by the order of the cosine series and the number of functions used to obtain a particular shape factor and rejection. Limited trimming of shape factor also can be achieved in each design. The filters described here are compared with the Kaiser window filter and are found to be efficient. Measured response of a prototype SAW filter using the approach given in this paper is plotted, and it is in good agreement with the simulated response.

SAW filters with high stopband rejection based on a cascade connection of selective elements

To achieve a high stopband rejection in surface acoustic wave (SAW) filters a construction that includes a cascade of some elements (interdigital transducers (IDT) and multistrip couplers (MSC)) is used. In this case each element has to maintain a comparatively low frequency selectivity, and this permits a simple model and a high-speed calculation process to be employed for its design. The proposed constructions have an apodized transducer with a metal coating instead of a passive electrode region as the input IDT and broadband withdrawal weighted unapodized transducer as the output IDT. One or two group-type multistrip couplers (MSC) provide an additional frequency selectivity. The original synthesis algorithms have been developed for design of IDT and MSC structure. >

Guided-wave multi/demultiplexers with high stopband rejection

A new guided-wave multi/demultiplexer with high stopband rejection is made using high-silica embedded channel waveguides. This consists of three directional couplers of the same structure, that is, the second and third directional couplers are connected with two output waveguides from the first directional coupler, which suppresses undesired optical signals. This optical device is fabricated using low temperature CVD, lithography, and a reactive ion etching process. It is possible to apply a high-reliability fail-safe module, two-way repeater transmission module using wavelength division multiplexing; it also has other uses.

Guided-wave multi/demultiplexers with high stopband rejection

A new guided-wave multi/demultiplexer with high stopband rejection is realised using high-silica embedded channel waveguides. This consists of three directional couplers of the same structure. That is, the second and third directional couplers are connected with two output waveguides of the first directional coupler. This multi/demultiplexer is fabricated using chemical vapour deposition, lithography and reactiveion-etching processes. Its structure is convenient for applying a stand-by module to improve reliability and for accommodating a two-way repeater transmission module using wavelength division multiplexing, as well as for other various uses.