Theoretical and experimental research on nonradiative dielectric waveguide directional couplers

A practical design of nonradiative dielectric (NRD) waveguide directional couplers is presented. The dispersion characteristics of coupled NRD-guides and the scattering coefficients of NRD-guide directional couplers are studied as well as the transitions from metal rectangular wave-guide to NRD-guide couplers. Experiments of 3-dB and 10-dB NRD-guide couplers in ka-band show that the couplers are of good performance and promise in millimeter-wave integrated circuits.     

Directional couplers in trapped image guide configuration

Dispersion characteristics and wave impedance of trapped coupled image guides are computed by using mode matching techniques. Dispersion curves for trapped coupled image guide are plotted for various dielectric materials and dimensional parameters. The hybrid directional couplers in the above configuration have been theoretically designed by computing the normalization propagation constant.     

The Calculation and the Measurement of the Coupling Properties of Dielectric Image Lines of Rectangular Cross Section

In this paper the coupling properties of uniformly coupled dielectric image lines of rectangular cross section are calculated employing an exact method for the determination of the phase constants of the even and the odd mode. The theoretical results are verified experimentally. The results are also applied to the calculation of the coupling characteristics of practical dielectric image line directional couplers.     

Broadside coupled strip inset dielectric guide and its directionalcoupler application

A theoretical and numerical method is presented for the analysis of broadside-coupled strip inset dielectric guide. The method of analysis is based on an integral equation formulation and Galerkin's procedure. Besides propagation constants for two fundamental and higher order modes, the characteristic impedances for the two fundamental modes are calculated using the total propagating power and the longitudinal strip currents. The propagation characteristics of the two fundamental modes are then used to compute 4-port circuit parameters that are essential for accurate analysis and design of coupled line circuits. The effects of various structural parameters on the S-parameters are investigated and it is found that this broadside coupled strip IDG structure is useful for the realization of the directional couplers. Examples of strong and weak directional couplers are given. Furthermore, the propagation constants and S-parameters of coaxially excited coupled strips are measured, and are in good agreement with the theoretical analysis     

3dB directional couplers on image dielectric waveguides of 80–110 GHz frequency band

The effective dielectric permittivity method is applied, generalized and modified to determine image guide dielectric rods configurations for directional couplers with maximum bandwidth in 3-mm wavelengths range. Optimization problem of directional coupling, splitting and summing signals in image guide directional couplers with distributed coupling in the 80–110 GHz frequency range was solved using CST Microwave Studio software. Optimization results were been experimentally confirmed     

Image guide couplers used in millimeter wave integrated circuits

The dispersion and coupling characteristics of the coupled image guides are studied by using the odd-even mode principle and effective dielectric constant method. The practical design of the image guide directional couplers is presented. The experiments of 3-dB and 10-dB couplers in ka band show several good features which are very useful to millimeter wave integrated circuits with flat coupling, easy design and fabrication, mechanical stability and low losses.     

Broadband overlaid inset dielectric guide coupler with very flatcoupling

In this paper overlaid parallel coupled inset dielectric guides are proposed for broadband applications to directional couplers. This structure provides much flatter and higher coupling than the conventional one without an overlay. The propagation and coupling characteristics of the coupled guides are obtained by using the integral equation formulation and Galerkin's procedure. Numerical results for two limiting cases are compared with available measured data, showing good agreement. Effects of thickness and dielectric constant of the overlay are examined on coupling and bandwidth. It is found that by suitable choice of these parameters very flat coupling can be achieved for a wide frequency range which is still within the fundamental-mode bandwidth. Examples of couplers with the bandwidth exceeding 45% for the coupling of 3±0.25 dB are presented     

Coupled-Transmission-Line Directional Couplers with Coupled Lines of Unequal Characteristic Impedances

A new class of coupled-transmission-line directional couplers, called "nonsymmetrical directional couplers," is described. Unlike conventional directional couplers, nonsymmetrical directional couplers use coupled lines of unequal characteristic impedances. The principal difference between the performance of nonsymmetrical directional couplers and that of conventional designs is the impedance level of the coupled waves, which may be changed to higher or lower impedance levels than that of the incident wave. These directional couplers may be designed to have infinite directivity and to be matched at all frequencies, or they may be designed to have infinite directivity at all frequencies and a specified maximum VSWR. Coupling relationships and design equations for both cases are presented, and the relative properties of both cases are discussed. The theoretical limitation on the maximum coupling and the maximum impedance transformation that can be obtained simultaneously are derived. Techniques for broadbanding by cascading additional sections of coupled limes are described. Experimental results of a trial --10-dB coupler with coupled lines of 50 and 75 ohms are presented.     

A new variational method of incorporating loss in the analysis ofcoupled multiple-quantum well three-dimensional waveguides

We have developed a simple method of calculating the imaginary part of the propagation constant in a lossy waveguide that closely follows the effective-index method of finding the real propagation constant of a rectangular dielectric guide. The method gives values much in agreement with the exact values obtained by the circular-harmonics method. The method has been used in the improved coupled-mode analysis of coupled-multiple-quantum-well waveguides developed by Tsang and Chuang. Three different configurations of coupled waveguides have been considered: slab, buried-channel, and strip-loaded waveguide directional couplers, where excitonic electrorefraction in multiquantum wells has been utilized to accomplish the switching. The output power-electric field curves calculated by using the above method agree closely in all three cases with similar curves obtained by using a complex propagation constant calculated by a numerical two-dimensional root-searching technique. The present method simplifies the design and optimization of coupled-waveguide devices and its application is illustrated in the case of multiple-quantum-well directional couplers     

Suspended Coupled Slotline Using Double Layer Dielectric

This paper presents a rigorous analysis of coupled slotline a) on a double-layer dielectric substrate, and b) sandwiched between two dielectric substrates. The dielectric substrates are of arbitrary thickness and permittivity and the structure is assumed to be suspended inside a conducting enclosure of arbitrary dimensions. The odd- and even-mode dispersion and characteristics impedance, along with the effect of shielding on these, are illustrated. These structures should find extensive applications in the fabrication of MIC components, such as directional couplers, phase shifters, and mixers.     

Analysis of coupled inset dielectric guides under LSE and LSMpolarization

The inset dielectric guide (IDG) represents an easy-to-fabricate alternative to the image line that is also less sensitive to loss radiation at discontinuities. Two IDG geometries were analyzed, the so-called deep and shallow IDG structures, operating in the LSE and LSM polarizations, respectively. The propagation constants of single and coupled symmetrical IDGs have been calculated as well as the coupling coefficients of coupled guides. The transverse resonance diffraction method with variational formulation was used. Measured values show very good agreement with predicted values for the propagation constants of coupled deep slot IDGs. The information is a prerequisite for the design of directional couplers in IDG     

Novel directional couplers using broadside-coupled coplanarwaveguides for double-sided printed antennas

Two types of tight-coupling, broadband directional couplers employing open broadside-coupled coplanar waveguides (BC CPWs) are proposed which can easily be integrated with printed strip antennas. The first type uses the BC CPWs with dielectric overlays above and below the center substrate, while the second type uses the nonuniform BC CPWs. The scattering parameters of these directional couplers are derived with the even-odd mode analysis method based on the quasi-TEM wave approximation. Two 3-dB directional couplers, one for each type, are designed and measured characteristics are compared with theoretical results     

Effect of Loss and Frequency Dispersion on the Performance of Microstrip Directional Couplers and Coupled Line Filters (Short Papers)

The effect of ohmic and dielectric losses, conductor thickness, and frequency dispersion on the performance of edge-coupled microstrip directional couplers and interdigital filters have been determined in this short paper. The odd- and even-mode attenuation constants due to ohmic losses in the conductor have been calculated using Wheeler's inductance formula. The theoretical results for the characteristic impedance and propagation constants are in good agreement with the experimental results of Napoli and Hughes. Among the parameters that can be calculated from this theory are the isolation, directivity, and coupling coefficients of lossy directional couplers and the midband insertion loss of interdigital filters.     

Aperture Coupling Between Dielectric Image Lines

Aperture coupling between dielectric image lines is used develop a design technique for directional couplers at millimeter-wave frequencies. Expressions for coupling coefficients and directivity, employing coupling between image lines through apertures in the common ground plane are developed. The design procedure is illustrated by application 10-, 20-, and 30-dB directional couplers in rectangular image lines with circular aperture coupling.     

Determination of the coupling length in directional couplers fromspectral response

A novel technique to determine the coupling length as a function of wavelength in directional couplers, especially in the case of weakly coupled, symmetrical directional couplers is described. The technique is illustrated by using Ag⁺-Na⁺ ion-exchanged directional couplers in BK7 glass. Application of this technique to asymmetrical directional couplers is also addressed     

Accurate Wide-Range Design Equations for the Frequency-Dependent Characteristic of Parallel Coupled Microstrip Lines

In this paper, closed-form expressions are presented which model the frequency-dependent even- and odd-mode characteristics of parallel coupled microstrip lines with hitherto unattained accuracy and range of validity. They include the effective dielectric constants, the characteristic impedances using the power-current formulation, as well as the open-end equivalent lengths for the two fundamental modes on coupled microstrip. The formulas are accurate into the millimeter-wave region. They are based on an extensive set of accurate numerical data which were generated by a rigorous spectral-domain hybrid-mode approach and are believed to represent a substantial improvement compared to the state-of-the-art and with respect to the computer-aided design of coupled microstrip filters, directional couplers, and related components.     

Effect of transition waveguides on dielectric waveguide directionalcouplers

The coupling of energy between two curved dielectric waveguides is investigated by the staircase approximation method, which combines the building-block approach of multimode network theory with a rigorous mode-matching procedure. Particular attention is directed toward two major effects of transition waveguides on the performance of directional couplers composed of dielectric waveguides: one is the change in the coupling length, the other is the radiation loss. The coupling problem is analyzed in terms of the scattering of an incident guided mode by the coupler structure as a whole. Numerical results are given to illustrate the coupling characteristics of various structures and to establish useful guidelines for the design of directional couplers     

Integrated directional couplers with photodetectors by hydridevapour phase epitaxy

The hydride vapour-phase-epitaxial crystal growth technique has been used to realise integrated waveguide-photodetectors and, for the first time, integrated directional coupler-photodetectors for detection in the 1.3 μm to 1.55 μm wavelength range. The GaInAsP waveguides which formed the directional couplers had propagation losses of 2±0.5 dB/cm and more than 90% of the guided light was coupled into the photodetectors. The directional couplers were symmetric with respect to the launch port and had 3 dB coupling lengths of about 1.45 mm     

Microstrip line directional couplers with high directivity

Novel uniplanar backward directional couplers are analysed and designed. Microstrip parallel coupled lines and asymmetrical delay lines enable a multi-sectioned coupler to enhance directivity as well as the coupling. Single and multi-sectioned couplers at 1.8 GHz have been designed and measured, providing excellent directivity.