Full-wave Mode-matching Method Research Articles

An Elliptical Bandpass Frequency Selective Structure Based on Microstrip Lines

A high-performance bandpass frequency selective structure (FSS) is presented, which consists of a 2-D periodic array of shielded microstrip lines. It exhibits stable elliptical filtering response under large variation of the angle of incidence. Its operating principle and design guidelines are discussed through equivalent circuit models. An efficient full-wave mode-matching method has been developed to analyze the proposed FSS. The proposed structure provides a simple and practically feasible solution to high-performance FSS since it can be fabricated using readily available microstrip line technology.

Scattering by a Two-Dimensional Periodic Array of Vertically Placed Microstrip Lines

Scattering by a two-dimensional (2-D) array of vertically placed microstrip lines is important for a number of recently proposed interesting applications. We investigate this scattering problem using an efficient full-wave mode-matching method. Our analysis comprises two parts. First, the propagation characteristics of the 2-D array are studied by solving a unit-cell of this structure, which is a microstrip line sandwiched between two periodic boundaries. In the second part, an air-to-array discontinuity is solved using Floquet modes in the air-region. Based on our full-wave analysis, we then present two frequency selective surfaces using this array, which exhibit stable quasi-elliptic filtering response under a large variation of the angle of incidence. Results of our full-wave analysis are in excellent agreement with those obtained from measurements and CST Microwave Studio.

A Novel Band-Reject Frequency Selective Surface With Pseudo-Elliptic Response

A novel frequency selective surface (FSS) exhibiting pseudo-elliptic band-reject response is presented. The proposed FSS consists of a two-dimensional periodic array of microstrip lines. For an incident wave of linear polarization perpendicular to the printed lines, virtual magnetic walls are formed between the microstrip lines. Since a microstrip line shielded with magnetic side walls supports two quasi-TEM modes, the two-dimensional array effectively forms a dual-mode resonator. The elliptic response is thus realized by coupling the incident wave to both modes of the resonator. A wideband pseudo-elliptic response is achieved by including higher-order modes of the array. To analyze this FSS, we treat it as a cascaded junction of air-to-microstrip line discontinuities, and investigate the problem using the full-wave mode-matching method. We provide useful design guidelines for both narrow-band and wide-band FSSs, while explaining the effect of various geometrical parameters on the performance of this FSS. Narrow-band and wideband FSS prototypes are fabricated and measured results validate our design concept. This new class of FSS is easy-to-assemble, exhibits a superior performance, and is thus potentially useful for many practical applications.

Effect of a Finite Ground Plane on Rectangular Waveguide Slot Antennas' Radiation Patterns

This paper examines the effect of a finite ground plane on the radiation patterns of waveguide slot antennas. A hybrid geometrical theory of diffraction (GTD) method is presented to calculate the radiation patterns of slot antennas on both air-filled and partially dielectric-loaded rectangular waveguides with a finite wall size. The electric field distribution along the slot is obtained by a full-wave mode-matching method and then employed to calculate the geometrical optics (GO) field. The GTD is then applied to evaluate the diffraction from all the waveguide wall edges. Radiation patterns are finally obtained by the vectorial summation of the GO field and the diffracted fields. Numerical results obtained by our method are compared with measured data and those simulated by Ansoft's high frequency structure simulator (HFSS). Good agreement is observed for all the cases considered. The backward radiation is also examined for different sizes of waveguide wall on which the slots are cut.

Full-wave modeling of electric coupling probes in comb-line resonators and filters

An electric coupling probe in comb-line resonators and filters is rigorously modeled by full-wave mode matching method. The coupling structure is considered as a cascaded network of the resonator and strip-line discontinuities and is solved by cascading the generalized scattering matrices of all the discontinuities. As a result, the electric probe couplings of both rectangular and cylindrical comb-line resonators and filters can be accurately determined. The validation and accuracy of the method are verified by comparing the numerical results with the measured data and are shown to be in good agreement.

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.

Comments on "Study of whispering gallery modes in double disk sapphire resonators

For the original paper see ibid., vol. 44, no. 6, p. 848-853 (1996). In the above paper is presented a simplified, but quite accurate, method for the calculation of the resonant frequencies of whispering gallery modes in dielectric resonators. Abramowicz et al. have compared the result obtained by the author with the results of the full-wave radial mode-matching method, finding very good agreement. However, a part of the paper describing a model of coupled resonators and, particularly its solution were, in the commenters' opinion, faulty.

Design of compact waveguide twists

A new geometry for compact twist components composed of rectangular and circular waveguide sections is presented. The proposed twist geometry presents several advantages: 1) It can be designed for any rotation angle; 2) it is extremely short and, therefore, well suited for satellite communication applications; 3) its electrical behaviour is excellent for either narrow or broad frequency bands; and 4) a very accurate and efficient full-wave mode-matching method can be used to analyze these twists. A software package has been developed to design the proposed compact twist structure in a full-wave method.

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.

Full-wave analysis of coplanar waveguides for LiNbO/sub 3/ optical modulators by the mode-matching method considering nonideal conductors on etched buffer layers

Rigorous analysis of traveling-wave coplanar waveguide electrodes for LiNbO/sub 3/ optical modulator applications is presented by using an extended full-wave mode-matching method. The microwave propagation characteristics under the composite influence of substrate anisotropy, uniform or etched buffer layers, finite electrode thickness and conductivity, and metallization undercutting are accurately assessed by employing a network equivalent formulation. Variations of the coplanar waveguide microwave effective index and the characteristic impedance at low frequencies due to finite electrode conductivity are illustrated, and are important even though the mode is quasi-TEM in nature. The effect of etching the SiO/sub 2/ buffer layer is shown to be one possible method for lowering the microwave effective index while keeping the conductor loss at a fixed level.

Calculation of CPW AC resistance and inductance using a quasi-static mode-matching approach

The AC resistance and inductance of a coplanar waveguide with nonideal conductivity are computed by means of a quasi-static mode-matching method. Convergence is examined and the numerical results are compared to those obtained by a full-wave mode-matching method. Regarding the frequency dependence, significant influence of the conductor losses is found.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer assisted determination of K0- diagram in the vane-type coaxial magnetron

A full wave mode matching method is implemented on the basic structure of the vane-type coaxial Magnetron to obtain the eigenvalue equation in this structure. With the aid of a computer, the K0- diagram is obtained, which can be used to determine the phase velocity of propagating waves. The results are also compared with the admittance matching method. The accuracy of the admittance approach is justified for engineering design.

Effect of finite-width backside plane on overmoded conductor-backed coplanar waveguide

The full-wave mode-matching method is utilized to investigate the transmission characteristics of a conductor-backed coplanar waveguide (CBCPW) with a finite backside plane. Experimental results on the scattering parameters of the CBCPW through line are presented. The theoretical results obtained with the model, considering a finite backside-plane CBCPW to be a system of coupled transmission lines, are shown to agree very well with the experimental ones. The anomalous resonant phenomena in the transmission characteristics of a CBCPW through line and the effect of the finite-width backside plane are obtained and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rigorous modal analysis of the asymmetric rectangular iris in circular waveguides

The rigorous field theory analysis is presented for the rectangular iris in circular waveguides as well as for rectangular iris coupled circular waveguide resonators. The theory is based on the full-wave mode-matching method for the key-building block discontinuity circular waveguide to a noncentric smaller rectangular waveguide, associated with the generalized S-matrix technique. Arbitrary iris location and finite thickness are rigorously taken into account. The scattering parameters of a single transition and of a rectangular iris coupled one-resonator filter of about 12 GHz resonance frequency are presented as calculation examples. The theory is verified by comparison with measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field theoretical computer-aided design of rectangular and circular iris coupled rectangular or circular waveguide cavity filters

The rigorous CAD of a class of rectangular and circular waveguide cavity filters which are coupled by rectangular and/or circular irises is described. The design theory is based on the full-wave mode-matching method for three key building block elements (asymmetric rectangular double-step, asymmetric rectangular-to-circular and circular-to-circular waveguide junctions) associated with the generalized S-matrix technique for composite structures. The waveguide filters may be arbitrarily composed of the key building block elements and the rectangular or circular waveguide sections between them. Finite iris thicknesses, higher-order mode interactions, and asymmetric structures are rigorously taken into account. The theory is verified by measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Full-wave analysis of a lossy rectangular waveguide containing rough inner surfaces

The full-wave mode-matching method employing the similarity transformation is used to derive the eigenvalue equation for the periodic bumpy regions that model the surface roughness of a WR-10 (75-110-GHz) waveguide. For the case study reported, attenuation losses increased by approximately 60% (36%) at 75 GHz (110 GHz).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field theoretical CAD of open or aperture matched T-junction coupled rectangular waveguide structures

The rigorous computer-aided design of rectangular waveguide structures coupled by open or rectangular iris loaded E- or H-plane T-junctions is described. The design theory is based on the full wave mode-matching method for the key-building-block T-junction element associated with the generalized S-matrix technique for composite structures. The waveguide structures may be arbitrarily composed of the T-junction and already known key-building-block elements (such as the double step and the septum discontinuity) combined with homogeneous waveguide sections between them. The E- or H-plane T-junction effect, large apertures, finite iris or septum thicknesses, and higher-order mode interactions at all step discontinuities are rigorously taken into account. Typical design examples, like rectangular iris coupled T-junctions, narrow-stopband waveguide filters, high return loss E-plane T-junction diplexers, an elliptic function E-plane integrated metal insert filter and a simple ortho-mode transducer demonstrate the efficiency of the method. The theory is verified by measurements. >

Full-wave analyses of composite-metal multidielectric lossy microstrips

The full-wave mode-matching method is extended to analyze composite-metal multidielectric microstrips commonly used in monolithic microwave integrated circuits (MMICs). The theoretical data obtained by the present approach agree favorably with the available experimental data for GaAs-SiN-Ti-Au finite-width, composite-metal, and multidielectric microstrips. Specifically, the case of a microstrip line with composite-metal Ti-Au configuration on multidielectric GaAs-SiN layers, where ground plane conductor loss is also considered, is analyzed. The effect of the thickness of the Ti layer (t/sub 2/) on the dominant-mode complex propagation constant is plotted against a fixed-thickness SiN layer (d/sub 1/) of 2000 AA at 1 GHz and 70 GHz, and 50 GHz, respectively. The results of the total loss alpha computed using a simplified analysis technique are compared to results of the full-wave analysis. It is noted that as the frequency is increased to 50 GHz or even higher, the simplified analysis overestimates the total loss alpha because the currents on the edges of Ti and Au metal layers can no longer be neglected.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of Circularly Cylindrical Resonator Filled With Axially Magnetized Stratified Gyromagnetic Medium

A rigorous analysis of a circularly cylindrical resonator containing an axially magnetized stratified gyromagnetic medium is presented. The full-wave mode matching method is used. The field inside a cavity is expanded into series of transverse mode functions of a layered gyromagnetic parallel-plate line. An exemplary ferrite-air resonator is investigated numerically and experimentally showing good agreement of computed resonant frequencies with measured values.

Investigations of complex modes in a generalized bilateral finline with mounting grooves and finite conductor thickness

A generalized bilateral finline with mounting grooves and finite conductor thickness is analyzed by a full-wave mode-matching method. The final nonstandard eigenvalue equation is derived from the unknown coefficients in the slot regions to reduce the size of the matrix equation. The convergence studies of the mode-matching method is first studied for the fundamental mode of a symmetric bilateral finline. Both the propagation constant and the characteristic impedance as defined by the power-voltage relationship are analyzed and compared to the existing data. Excellent agreement is obtained. The effects of metallization thickness and mounting grooves are discussed. The accurate results obtained for the fundamental mode by the mode-matching method with respect to both relative and absolute convergence were also obtained for the complex modes of the finline. The dispersion characteristics of the fundamental, higher order, evanescent, and complex modes are presented for an asymmetric bilateral finline. The effects of mounting grooves and metallization thickness on the complex mode propagation constants are investigated and discussed. >