Krzysztof Sachse

Quasi-ideal multilayer two- and three-strip directional couplers for monolithic and hybrid MICs

In this paper, the properties of multilayer two- and three-strip asymmetric coupled lines are described using their coupled-mode parameters. Examples of quasi-ideal, microstrip, and coplanar directional couplers designed in monolithic and hybrid microwave integrated-circuit technology, consisting of various layered structures of bilevel and trilevel coupled lines, are presented together with experimental results for two 3-dB couplers on ceramic-filled polytetrafluoroethylene and polyimide laminates.

Design of Compensated Coupled-Stripline 3-dB Directional Couplers, Phase Shifters, and Magic-T's—Part I: Single-Section Coupled-Line Circuits

The problem of discontinuities in coupled-stripline 3-dB directional couplers, phase shifters, and magic-Ts, regarding the connections of coupled and terminating signal lines, has been comprehensively investigated for the first time. The proposed equivalent circuit of these discontinuities, of which parameters can be computed in a process of fitting curves of the circuit and electromagnetic analyses, has been used for accurate modeling of coupled-stripline circuits. It has been shown that parasitic reactances, which result from connections of signal and coupled lines, severely deteriorate the return losses and the isolation of such circuits, and that these discontinuity effects can be substantially reduced by connecting compensating shunt capacitances to both coupled and signal lines. Results of measurements carried out for various designed and manufactured coupled-line circuits are most promising and prove the efficiency of the proposed compensation technique. This paper describes the technique of capacitive compensation of discontinuity effects in single-section coupled-line circuits

The scattering parameters and directional coupler analysis of characteristically terminated asymmetric coupled transmission lines in an inhomogeneous medium

The scattering matrix of asymmetric coupled two-line structures in an inhomogeneous medium terminated in a set of impedances that are equal to the characteristic impedances of the individual, uncoupled lines is derived in terms of the coupled-mode parameters. It is shown that the structures can compose an ideal backward-coupling directional coupler, perfectly matched and isolated at all frequencies, if the inductive k/sub L/ and capacitive k/sub C/ coupling coefficients of the coupled lines are equal. The effect of the nonideal equalization of the coupling coefficients on the coupler critical parameters is investigated. The normal-mode parameters (mode numbers and mode impedances) in the proximity of the point when k/sub L/=k/sub C/ and at that point are also examined. Numerical results confirm the validity of the analysis and prove the possibility of an asymmetrical coupler design with very high directivity. >

Design of Compensated Coupled-Stripline 3-dB Directional Couplers, Phase Shifters, and Magic-T's—Part II: Broadband Coupled-Line Circuits

The problem of discontinuities in broadband multisection coupled-stripline 3-dB directional couplers, phase shifters, high-pass tapered-line 3-dB directional couplers, and magic-Ts, regarding the connections of coupled and terminating signal lines, is comprehensively investigated in this paper for the first time. The equivalent circuit of these discontinuities proposed in Part I has been used for accurate modeling of the broadband multisection and ultra-broadband high-pass coupled-stripline circuits. It has been shown that parasitic reactances, which result from the connections of signal and coupled lines, severely deteriorate the return losses and the isolation of such circuits and also-in case of tapered-line directional couplers-the coupling responses. Moreover, it has been proven theoretically and experimentally that these discontinuity effects can be substantially reduced by introducing compensating shunt capacitances in a number of cross sections of coupled and signal lines. Results of measurements carried out for various designed and manufactured coupled-line circuits have been very promising and have proven the efficiency of the proposed broadband compensation technique. The theoretical and measured data are given for the following coupled-stripline circuits: a decade-bandwidth asymmetric three-section 3-dB directional coupler, a decade-bandwidth three-section phase-shifter compensator, and a high-pass asymmetric tapered-line 3-dB coupler

Novel coupled-line conductor-backed coplanar and microstrip directional couplers for PCB and LTCC applications

Novel coupled-line conductor-backed coplanar and microstrip directional couplers, convenient for manufacturing in standard printed circuit board (PCB) or low-temperature co-fired ceramic (LTCC) technology, are proposed. The coplanar coupler, consisting of a layered structure with four strips and covering a -10 to -2.6 dB coupling coefficient, is theoretically ideally impedance matched and perfectly isolated at all frequencies under the assumption of validity of quasi-static approximation and two-mode propagation. The microstrip coupler, a modification of the coplanar one, can be ideally compensated only in an area of strong coupling coefficients. The novel couplers are not sensitive to lateral misalignment of conductive layers, and not sensitive to thickness and dielectric permittivity tolerances of applied dielectric substrates. Preliminary experimental results for 2.7-, 3-, and 8.34-dB couplers, designed both in PCB, as well as LTCC technology are presented.

Broadband Planar Fully Integrated 8

An innovative approach that allows for realization of broadband planar fully integrated 8 × 8 Butler matrices is presented. Coupled-line directional couplers have been utilized, which enable broad operational band. A novel arrangement of the network has been proposed that allows the creation of an entirely planar design having two metallization layers and no interconnections between these layers. Four selected crossovers have been realized as a tandem connection of two 3-dB/90° coupled-line directional couplers, which, together with reference lines having appropriate electrical lengths, perform simultaneously crossovers of signal lines, and all needed broadband constant value phase shifters. Moreover, two of the needed 3-dB/90° directional couplers have been designed as tandem connections of two 8.34-dB directional couplers, acting as 3-dB/90° directional couplers having crossed outputs. With such a modification, a fully planar design with no inter-layer connections is possible. The proposed network arrangement has been experimentally tested with the design of an 8 × 8 Butler matrix operating at the center frequency of 3 GHz. The obtained measurement results fully confirm the validity of the proposed approach.

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The elements of the matrix - 3 dB/90/spl deg/ coupled-line directional couplers and cross-overs - have been designed in multilayer technology, optimised and tested individually, and then merged to form the whole integrated 4 /spl times/ 4 Butler matrix. A good performance of the manufactured matrix, operating in the frequency band 2-4 GHz, encouraged us to design a four-channel amplifier with four input- and four output ports, in which monolithic amplifiers are surface-mounted into 50 /spl Omega/ microstrip lines connecting the input and output Butler matrices. Very promising experimental results are shown.

8 Butler Matrix Using Coupled-Line Directional Couplers

The analysis and design of a 4 × 4 Butler matrix that utilizes tapered-coupled-line directional couplers is presented. As a basic element of the matrix, the previously designed and measured 3.3-dB directional coupler has been used. Two different realizations of a 4 × 4 Butler matrix are considered, i.e. a network consisting of tapered-line couplers and a Schiffman phase shifter, and a network in which the appropriate phase characteristics have been ensured by substituting one of the 0/180° directional couplers by a 3-dB/90° directional coupler. In this solution, the needed coupler has been designed as a 5-section symmetrical coupled-line coupler in which the tightly coupled section is designed with the use of tapered-coupled-lines. The proposed technique allowed for achieving very good amplitude characteristics of the designed directional coupler due to the fact that the large discontinuity between coupled-lines having different coupling coefficients is avoided. The operational bandwidth of the presented 4 × 4 Butler matrices exceeds two frequency octaves.

An integrated Butler matrix in multi-layer technology for multi-port amplifier applications

The scattering matrix of asymmetrical coupled two-line structure in an inhomogeneous medium, terminated in a set of impedances which are equal to the characteristic impedances of the individual, uncoupled lines, has been derived in terms of the coupled-mode parameters. It has been proved that the structure can compose an ideal, backward-coupling directional coupler, perfectly matched and isolated at all frequencies, if the inductive kL and capacitive kC coupling coefficients of the coupled lines are equal each other. The effect of the non-ideal equalization of the coupling coefficients on the coupler critical parameters is then investigated. The normal-mode parameters (mode numbers and mode impedances) in the proximity of the point when kL = kC and at that point are also examined. The numerical results presented confirm the validity of the developed analysis and prove the possibility of a very high directivity asymmetrical coupler design.

Broadband 4 × 4 Butler matrices utilizing tapered-coupled-line directional couplers

The paper discusses the properties of new microstrip transmission lines using a slot in the ground-plane. These lines have high characteristic impedance and their attenuation and frequency dispersion as well are small. A very tightly coupled cross-section of microstrip lines may be constructed using the new structures of coupled-lines. The numerical computations of the characteristic impedance and phase velocity of the single-and coupled-lines are given. In the variational method an approximated functions of the charge density on the strip and the potential in the slot in order to fulfil of the complicated boundary conditions caused by the slot and the multi-layered dielectric are evaluated. Then the potential distribution on the strip and the capacitance are computed using the variational expression in the Fourier-transformed domain. The applications of the new microstrip lines in MIC and some experimental results are presented.