Automated CAD of coupled resonator filters

A gradient-based optimization technique along with a new definition of cost function is applied to the CAD of coupled resonator filters. The topology of the structure is enforced at each step of optimization and its physical dimensions are used as optimization variables. The cost function is defined using location of zeros and poles of the filter's transfer and reflection functions. Numerical tests show that with the new definition of the cost function, the optimization process converges from an arbitrarily selected starting point. This allows one to design filters even without a rough microwave synthesis which usually provides initial dimensions.     

Direct synthesis of folded symmetric resonator filters withsource-load coupling

A direct synthesis technique of coupled symmetric resonator filters with source-load coupling is presented. An examination of the implications of power conservation on the possible solutions to the synthesis problem is examined. It is shown that at least two different coupling matrices whose entries differ not only in signs but in magnitude, as well, can be extracted. The two matrices have the same coupling and routing scheme. Typical examples of synthesized filters are presented to document the validity of the technique     

Optimum filters for narrow-band frequency modulation

A computer search was made for the optimum second- and third-order bandpass filters for use in narrow-band FM and PM systems. The optimum filter for minimum distortion was found to be near the Bessel filter. The results were fairly independent of modulation index and bandwidth.     

A tri-section stepped-impedance resonator for cross-coupled bandpass filters

We report a new tri-section stepped-impedance resonator (SIR) that features a short and low-impedance section inserted in a two-section SIR. The inserted section not only makes the resonator more compact, but also enables the flexibility of introducing cross coupling in a filter configuration. Using the tri-section SIR, a cascaded triplet bandpass filter is demonstrated, featuring sharp roll-off at the high edge of the passband.     

A novel ultra-compact resonator for Superconducting thin-film filters

This paper proposes a novel thin-film resonator structure, which combines the microstrip resonator and the coplanar resonator to form an integrated resonator. This resonator structure has an extremely compact size, as compared to the thin-film resonator structures from the literature, and its resonant frequency was shown theoretically to be less sensitive to, or even insensitive to, the thickness of the substrate. An eight-pole quasi-elliptic filter based on this novel resonator was designed. The exact filter layout was simulated and optimized by full-wave electromagnetic simulation using IE3D software. The full-wave simulated filter response was in good agreement with the theoretical filter response. A filter was fabricated on a double-sided YBa/sub 2/Cu/sub 3/O/sub 7/ thin film epitaxially grown on a 2-in-diameter MgO wafer. The measured filter response showed a bandwidth of 1.5 MHz and a center frequency of 850.3 MHz at 78 K. The insertion loss at the passband center was 1 dB, corresponding to a filter Q of 28 000. Steep rejection slopes were obtained at the band edges and rejections reached over 70 dB in approximately 300 kHz from the passband edges. No pronounced changes were observed for input power levels between -20-0 dBm, indicating a relatively high power-handling capability of the filter.     

On the sensitivity of coupled resonator filters without some direct couplings

This paper presents an analysis of the sensitivity of coupled resonator filters in which some direct couplings are missing. The effect of changes in the coupling coefficients and resonant frequencies of the resonators is investigated by directly computing the gradient of the scattering parameters. It is shown that structures that are modular in the input-to-output direction are much less sensitive than those with modularity in the orthogonal direction for the same frequency response.     

Adaptive synthesis and design of resonator filters with source/load-multiresonator coupling

The paper presents a universal and comprehensive synthesis technique of coupled resonator filters with source/load-multiresonator coupling. The approach is based on repeated analyses of a circuit with the desired topology; no similarity transformation is needed. Restrictions imposed by the implementation on the coupling coefficients such as signs and orders of magnitudes are straightforwardly handled within this technique. The technique is then used to synthesize and design filters with full or almost full coupling matrices by selecting, among the infinite number of solutions, the matrix that corresponds to the actual implementation. In such cases, analytical techniques and those based on similarity transformations cannot be used since they provide no mechanism to constrain individual coupling coefficients in order to discriminate between two full coupling matrices, which are both solutions to the synthesis problem. Using the technique described in this paper, a filter designer can extract the coupling matrix of a filter of arbitrary order and topology while enforcing relevant constraints. There is no need to master all the different existing similarity-transformation-based techniques and the topologies to which they are applicable. For the first time, detailed investigations of parasitic coupling effects, for either compensation or utilization, are made possible. The method is applied to the synthesis of a variety of filters, some of which are then designed and built and their response measured.     

Novel compact elliptic-function narrow-band bandpass filters usingmicrostrip open-loop resonators with coupled and crossing lines

Novel compact elliptic-function narrow-band bandpass filters have been designed and fabricated. This new configuration consists of two identical microstrip open-loop resonators with coupled and crossing lines. A theoretical investigation has confirmed that this novel configuration is capable of providing elliptic-function filtering. Furthermore, the feasibility of this filter is verified experimentally. Centered at 2.039 GHz, the fabricated microstrip bandpass filter shows a measured 3-dB bandwidth of 2% and two deep notches in its stopband. In addition, the main circuit of this filter occupies only 2.5 cm×1.5 cm using a substrate with dielectric constant of 10.5, making it very attractive for applications in the mobile and personal communication systems (PCS's)     

Analysis of multichannel narrow-band filters for image texturesegmentation

A model for texture analysis and segmentation using multiple oriented channel filters is analyzed in the general framework. Several different arguments are applied leading to the conclusion that the two-dimensional Gabor filters possess strong optimality properties for this task. Properties of the multiple-channel segmentation approach are analyzed. In particular, perturbations of textures from an ideal model are found to have important effects on the segmentation that can usually be ameliorated by simply preceding the segmentation process by a logarithmic operation and using a low-pass postfilter prior to making region assignments. The difficult problems of space-variant textures and multiple component textures are also considered. Local spatial frequency estimation approaches are suggested that use the responses as constraints in estimating the locally emergent texture frequencies. Complex texture aggregates containing multiple shared frequency components can be analyzed if the textures are distinct and few in number     

A GaInAsP-InP double-ring resonator coupled laser

A monolithic single-mode GaInAsP-InP double microring resonator coupled laser is demonstrated for the first time. The laser comprises two passive ring resonators, semiconductor optical amplifiers in the bus waveguides, and 3-dB codirectional couplers. The laser has an output power of 0.5 mW with a sidemode supression ratio of >35 dB. The tunability is demonstrated using integrated platinum resistors on top of the waveguides in the rings.     

Very high-order microring resonator filters for WDM applications

High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.     

Adaptive nonlinear filters for narrow-band interference suppressionin spread-spectrum CDMA systems

This paper presents a novel nonlinear filter and parameter estimator for narrow band interference suppression in code division multiple access spread-spectrum systems. As in the article by Rusch and Poor (1994), the received sampled signal is modeled as the sum of the spread-spectrum signal (modeled as a finite state independently identically distributed (i.i.d.) process-here we generalize to a finite state Markov chain), narrow-band interference (modeled as a Gaussian autoregressive process), and observation noise (modeled as a zero-mean white Gaussian process). The proposed algorithm combines a recursive hidden Markov model (HMM) estimator, Kalman filter (KF), and the recursive expectation maximization algorithm. The nonlinear filtering techniques for narrow-band interference suppression presented in Rusch and Poor and our proposed HMM-KF algorithm have the same computational cost. Detailed simulation studies show that the HMM-KF algorithm outperforms the filtering techniques in Rusch and Poor. In particular, significant improvements in the bit error rate and signal-to-noise ratio (SNR) enhancement are obtained in low to medium SNR. Furthermore, in simulation studies we investigate the effect on the performance of the HMM-KF and the approximate conditional mean (ACM) filter in the paper by Rusch and Poor, when the observation noise variance is increased. As expected, the performance of the HMM-KF and ACM algorithms worsen with increasing observation noise and number of users. However, HMM-KF significantly outperforms ACM in medium to high observation noise     

Frequency transform synthesis method for cross-coupled resonator bandpass filters

In this letter, an improved synthesis method for equal-ripple cross-coupled resonator bandpass filter is proposed based on the frequency transform method and Atia's method. In this method, the conventional lowpass prototype method is revised by replacing the low pass prototype with the frequency transform method. The detailed element extraction procedure in z-domain is given. Also the coupling matrix reduction implemented by optimization algorithm is described. This method is powerful for filter synthesis with asymmetric frequency response and complex transmission zeros. The design examples are presented and the experimental results validate its effectiveness.     

A novel coupled method for dual-mode dielectric resonators andwaveguide filters

A novel method for coupling dual-mode waveguide or dielectric resonator cavities is described and analyzed. The method has advantages of providing a practical, flexible, economic means of replacing irises, of offering easy tunability of the coupling over a wide range of coupling values, and of reducing the length of the coupling structure. Calculation of the resonator's coupling parameters using the mode-matching method yields accurate results and is verified by measurements. Experimental four-pole dual-mode elliptic function filters using the coupling method for empty cavities and dielectric-resonator-loaded cavities were constructed and tested. The test results showed excellent agreement with theoretical analysis     

New calculations for coupling laser diode to multimode fiber

A simple and useful method is presented for calculating characteristics of a laser diode to a multimode fiber coupling. Attenuation of higher order modes in multimode fiber is introduced into ray tracing. Maximum coupling efficiencies and misalignment tolerances of optical circuit components are computed for utilization of a relatively large spherical lens and combination of two relatively large spherical lenses. It is clarified that attenuation of higher order modes strongly affects both maximum coupling efficiency and misalignment tolerances. Agreement between theoretical and experimental coupling characteristics is greatly improved compared with the case for conventional ray tracing.     

Interresonator coupling for overtone monolithic quartz filters

The traditional expression for interresonator coupling in monolithic quartz filters is extended to cover operation at overtone frequencies. Interresonator couplings calculated from the proposed expression are checked against computed results from a vibrational mode analysis.     

Three-dimensional propagation analysis of coupling efficiency using segmentation and local normal mode expansion for vertically coupled microring resonator filter

A novel three-dimensional (3-D) propagation analysis of coupled waveguides using local normal modes and the segmentation along the propagation axis was developed. The coupling efficiency of vertically coupled microring resonators was optimally designed using this analysis. The computation time is much faster and the required memory capacity is much smaller than those of the 3-D finite-difference time-domain (FDTD) method.     

High-silica multimode channel waveguide structure for minimizing fiber-waveguide-fiber coupling loss

The optimum structure for high-silica channel waveguides which are connected to input and output graded-index fibers having a 50-μm core diameter and a 1.0-percent refractive-index difference is studied theoretically and experimentally. Theoretical optimum waveguide structure is obtained on the basis of ray optic analysis. For the step-index waveguide with 1.0-percent refractive-index difference, the theoretical minimum coupling loss (input coupling loss + output coupling loss) is 1.7 dB for an optimum core of 38 μm both in depth and width. For the graded-index waveguide with parabolic-index profile in the depth direction and step-index profile in the width direction, the theoretical coupling loss is 1.1 dB for an optimum core of 38 μm in width and 50 μm in depth. These estimations were in good agreement with the experimental results, which were 1.8 dB for the step-index waveguide and 1.3 dB for the graded-index waveguide.     

Technique for improving coupling between microstripline anddielectric resonator antenna

A cylindrical dielectric resonator antenna fed by a microstripline is studied. By connecting a vertical strip at the end of the microstripline, the input matching of a dielectric resonator antenna can be improved substantially. Moreover, it offers an impedance bandwidth as wide as 19% and a stable radiation pattern across the operating frequency range     

High-Q helical resonator for oscillators and filters in mobile communications systems

A high-Q helical resonator is described which is directly coupled and resonant for lengths of approximately lambda /2. This resonator is extremely easy to fabricate, and is used to demonstrate high-Q filtering and low-noise oscillator operation as the resonator in state-of-the-art L-band oscillators.<>