Hui-Wen Yao

Full wave modeling of conducting posts in rectangular waveguides and its applications to slot coupled combline filters

A full wave model of conducting posts in rectangular waveguides yielding their generalized S-matrix is presented. By cascading the generalized scattering matrices of the posts and waveguide discontinuities, slot couplings between two combline resonators are obtained. The validation and accuracy of the method are confirmed by comparing the numerical results with measured data. It is shown that both electric and magnetic couplings can be obtained by changing the slot positions, and the electric coupling is more sensitive to the tuning screw than magnetic coupling. A 6-pole slot coupled combline filter with asymmetrical transmission zeros is designed and built. Excellent filter responses are obtained.

Wide-band waveguide and ridge waveguide T-junctions for diplexer applications

Scattering parameters of E- and H-plane stepped waveguide and E-plane ridge waveguide stepped T-junctions are obtained using an extension of the three-plane mode matching method. An optimization process is applied to find the T-junctions and step dimensions that yield a low reflection coefficient in one of the T-junctions arms over a wide frequency band. An example of the design of a wideband T-junction diplexer is presented. The diplexer filters are inductive window waveguide filters, and are rigorously modeled using mode matching and a novel two-dimensional curve fitting method, which greatly reduces the CPU time for optimization. The diplexer optimization procedure, as well as the filter modeling method, are described. Experimental results on the optimized T-junction and the diplexer are presented; both show excellent agreement with their computed optimum results, without any adjustments or tuning. >

Mixed modes cylindrical planar dielectric resonator filters with rectangular enclosure

A compact mixed modes cylindrical planar dielectric resonator filter in a rectangular enclosure is presented. Space coupling between the resonators excited in different modes and iris coupling between the identical resonators are realized in the filter. All the couplings and resonant frequencies of the DR cavities are computed by a rigorous full wave mode matching method and a cascading procedure using generalized scattering matrices. A 6-pole elliptic function filter is designed and constructed, and the measured filter frequency responses verify the theory.

Millimeter-wave Ka-band H-plane diplexers and multiplexers

Millimeter-wave H-plane diplexers/multiplexers are designed using modified H-plane waveguide T-junctions and modified inductive window bandpass filters. Modeling of the diplexers/multiplexers are performed using the full-wave mode-matching method to obtain the generalized scattering matrices of the building blocks and by the cascading procedure to provide the overall frequency response. A complete systematic optimization procedure leads to the desired diplexer/multiplexer design. The validity of employing the modified H-plane T-junctions in the diplexer/multiplexer configurations are demonstrated by the design examples. A millimeter-wave Ka upper band diplexer based on the simulated results was built and tested. Without any tuning, excellent experimental results are obtained, which verified the full-wave mode-matching-based precise design.

Computer-aided diagnosis and tuning of cascaded coupled resonators filters

A model for the determination of the individual resonant frequencies and inter-resonator couplings of a system consisting of cascaded coupled resonators is presented. Measuring or computing the phase of the reflection coefficient of short-circuit terminated networks synthesizes all the inter-resonator couplings and resonant frequencies. The loading effect on the last resonator due to the unknown position of the short-circuit reference plane is accurately accounted for by a systematic method. A deterministic finite steps tuning method based on the model is developed. The method is proven successful experimentally and the noniterative nature of the method makes fully automatic tuning of filters possible.

Synthesis of coupled-resonators group-delay equalizers

A systematic synthesis and design procedure for coupled-resonators cavity group-delay equalizers is presented. The procedure consists of solving the approximation problem by optimization and performing cascade synthesis. The error function for the optimization is computed from the given filters group delay and the zeros and poles of the input impedance of the equalizer. Convergence of the optimization is fast and insensitive to the initial guess even when the number of resonators is large. Two examples, together with experimental results, are presented; comparisons between the externally equalized and self-equalized filters are made. The effect of the isolation of the cascading devices (circulator or 3-dB hybrid) on the ripple of the final group-delay response is also extensively investigated. The good agreement between the theoretical simulation and the experimental results demonstrates the powerful nature and effectiveness of the proposed design procedure.

Improvement of spurious performance of combline filters

Methods to improve the spurious performance of combine filters are investigated. The first spurious passband of a conventional combine filter with uniform rods can be pushed to a higher frequency by using stepped rod resonators or suppressed by a careful design of the coupling slots without a noticeable sacrifice of filter insertion loss. Experiments verify the theory.

Accuracy of coupling computations and its application to DR filter design

Coupling of two circular cavities by a rectangular iris computed by the improved large aperture theory and by the full wave mode matching technique are compared. It is found that the improved large aperture approximation provides reasonable accuracy for a wide range of coupling values. The approximation is applied to design dielectric resonator (DR) filters in which rigorous computation of the couplings by the full wave mode matching method is quite difficult and time consuming. Excellent DR filter response is obtained with no adjustment of the coupling iris.<<ETX>>

A full wave analysis of microstrip-to-waveguide transitions

A wide band, low insertion loss transition from rectangular waveguide to shielded microstrip line is analyzed using a full wave mode-matching technique. The transition consists of a discontinuity between a ridge waveguide and the microstrip line and a ridge waveguide impedance transformer. The microstrip eigenmodes, including complex modes, are obtained by mode-matching method with LSE and LSM mode expansion. Computed results of a 17-22 GHz transition agree well with available experimental results. This rigorous approach provides a useful tool for the optimum design of microstrip to air filled waveguide or dielectric filled waveguide transitions.<<ETX>>

Modeling of generalized coaxial probes in rectangular waveguides

An new approach combining the orthogonal expansion method for modeling cylindrical posts in rectangular waveguides and the extension of the three short plane measurement technique is used to obtain the S-matrix for a general coaxial probe in a rectangular waveguide. The computed results are in excellent agreement with the measured results showing the usefulness of this method.<<ETX>>