The invention concerns an impedance-controlled coplanar waveguide system.
b) shows examples of buried microstrips, in which the central conductor 100 has a flat design and is arranged between two ground planes. In this regard, it is possible for several central conductors 100 to run between the ground planes. Buried microstrips of this type are known, for example, by the name “triplate”. Triplate waveguides are preferably used in printed circuits in multilayer technology. The electrically conductive central plane 100 is uniformly spaced from the two parallel ground planes. Similarly to a coaxial cable, this type of design reduces radiation losses. Since the thickness of the dielectric 101 is predetermined by the thickness of the printed circuit board material, the characteristic impedance on a multilevel printed circuit board can be determined by the width of the central conductor 100. However, the impedance (wave resistance of a line to alternating current) depends not only on the spacings of the signal-conducting line but also on the dielectric constant of the surrounding insulating material. Polymer printed circuit boards or multilayer ceramics are usually used for multilayer microwave modules. Their individual layers can be formed in different layer levels.
c) shows three other previously known designs of high-frequency waveguides, namely, a strip line (left), a coplanar waveguide (middle) and a microstrip line (right).
DE 42 28 349 A1, for example, describes a coplanar waveguide that is suitable for MMIC (monolithic microwave integrated circuit). In order to achieve the lowest possible characteristic impedances, two identical coplanar lines are connected in parallel. Air-gap interfaces are incorporated at the branches of the parallel-connected coplanar lines.
U.S. Pat. No. 6,774,748 B1 discloses a high-frequency unit with a multilayer dielectric substrate, plate through contacts and metallic surfaces. A cavity in which a semiconductor element is mounted is provided between the dielectric layers. The plate through contacts connect the inside of the cavity with the outside.
DE 198 42 800 A1 discloses a surface-mountable casing that can be operated at frequencies in the K band as well as in higher frequency bands. The surface-mountable casing has a dielectric body, which consists essentially of a dielectric substance, a continuous and planar ground conductor, which covers most of the main surface and lateral surfaces of the dielectric body, and a plurality of signal paths in the embodiment of a coplanar line, which are arranged in or on sections of the main surfaces and lateral surfaces that are not covered by the ground conductor.
One problem of the previously known planar waveguides is that they can be optimized only for a limited range of wavelengths. The transmission of very broadband electromagnetic waves is associated with appreciable losses (attenuations) in the unoptimized wavelength ranges. The decreasing wavelength with increasing frequency causes disturbances (inhomogeneities) along the lines to become relatively larger. This leads to greater reflections and thus greater attenuations, i.e., to a weaker available signal at the end of the line. In addition, dispersion effects are produced (dependence of the speed of propagation of the waves on their wavelength) as well as interference effects, which are determined by the fact that additional (undesired) vibrational modes are excited and possibly propagated. The transit time differences of the individual modes result in disturbing, i.e., attenuating, interference effects. The signal energy contained in the unwanted excited modes is practically lost and disturbs neighboring circuit parts due to irradiation, which is a major problem of the previously known lines at higher frequencies.
The general requirements on good broadband signal transmission and good electromagnetic compatibility (EMC) demand exactly defined impedance behavior along the entire signal path (usually constant, e.g., 50 ohms) and later, during manufacture, exact reproducibility for small reflection sources, so-called discontinuities.
One of the objectives of the present invention thus consists in the creation of an impedance-controlled coplanar waveguide system for the three-dimensional, low-loss and shielded distribution of very broadband electromagnetic waves (direct current to microwave signals above 100 GHz, digital signals with very high data rates) in multilayer (at least two layers) circuit carriers.
In addition to this main objective, there are several secondary objectives or goals, including good transmission of higher data rates and signal frequencies and the fulfillment of increasing requirements on better electromagnetic compatibility of corresponding subassemblies.
The objective of the invention is achieved by a waveguide system according to the attached Claim 1.
The impedance-controlled coplanar waveguide system of the invention for the three-dimensional distribution of signals of high bandwidth consists of at least one coplanar waveguide integrated in multilayer circuit carriers. The coplanar waveguide and its associated ground conductors are arranged symmetrically or asymmetrically between at least two continuous or interrupted insulating layers of a multilayer circuit carrier. Associated ground conductors are understood here to be all metal surfaces and plate through contacts (vias) with the same electric potential that surround the signal conductors (waveguides). If the insulating layers have interruptions, the spaces are filled with gases, liquids or vacuum.
The upper side and underside of the multilayer circuit carrier is provided with full-surface or partially closed (perforated/lattice-like) electrically conductive layers. Electrically conductive plate through contacts are provided as electric walls or shields on the other two opposite sides. The ground conductors, the electrically conductive layers and the plate through contacts are peripherally electrically connected. They are all at ground potential and thus form the shield for the waveguide.
A general advantage of the waveguide system of the invention is the lower noise radiation to surrounding circuit components and lines. At the same time, the signal energy that is not radiated is retained as useful energy. In addition, the coupling of (interfering) high-frequency radiation from the outside is improved (interference immunity). Therefore, the electromagnetic compatibility (EMC) of a system of the invention is greatly improved. This has advantageous effects on the achievable component density of the electronic circuits, for the better the EMC aspects of the line design are fulfilled, the smaller the minimum distances to surrounding electronic components can be and the smaller the minimum separations of the lines from one another can be.
In the waveguide system of the invention, the waveguide impedance can be adjusted by the conductor width, the conductor height or conductor shape, by the distance between these conducting coplanar layers, by the relative permittivities of the insulating substrate layers, and/or by the distance from the electrically conductive layers and the plate through contacts.
The insulating layers or dielectrics of the waveguide system of the invention in multilayer circuit carriers can consist of polymeric/organic and/or ceramic/inorganic substrate materials and/or of insulating composite materials and/or foams thereof and/or conductor supports thereof, and of vacuum, air and/or other gases. For example, circuit supports can be individually processed from so-called LTCC ceramic tapes (low-temperature co-fired ceramic), which are flexible in the raw state (print with metal paste, punch out holes for plate through contacts, and fill with metal paste). The layers (up to several tens of them) arc then stacked, pressed together, and sintered at about 900° C. into a compact and hermetically tight block, by which they acquire typical ceramic properties.
The solution according to the present invention has a series of advantages over the previously known high-frequency waveguides. The practically useful frequency range, which is characterized by low losses and mode purity, is increased considerably compared to buried microstrips of the same cross-sectional area. Whereas a useful frequency range of a few tens of GHz is available in triplate structures, the system of the invention now makes significantly more than 100 GHz available with low reflection loss. At the same time, the signal distribution does not have to be, as has been customary until now for high signal frequencies and signal bandwidths, realized in a planar way, i.e., in one plane with single-layer conduction structures that are usually shielded in only one direction, but rather is advantageously realized for miniaturized integration in a multilayer configuration in the third dimension (height) as well. In addition, the solution according to the invention and its embodiments make it possible to realize adjacent and crossed lines that are very well decoupled from one another.
Furthermore, compared to buried microstrips, advantages are obtained with respect to a lesser dependence of the reflection loss (adaptation) of the waveguide on variations of the height of the insulating layers (layer height) and the positioning (offset) of the ground-side plate through contacts surrounding the center signal lines.
In addition to the low-loss wave guidance of broadband signals, the waveguide system of the invention is also suitable for realizing a change in the direction of signal propagation at any desired angles by means of horizontal rotations or waveguide bends. It is likewise possible to bridge any height differences and/or angles of entrance or emergence of the waveguide within a circuit carrier.
Modified embodiments of the invention are fabricated in such a way that they can act as coupling members to conventional waveguides. For example, to this end, an external contact bank of the multilayer circuit carrier can be realized as a microstrip waveguide. The waveguide system is suitable for realizing a single-stage or multistage waveguide transition vertically to the outside and for realizing a waveguide transition laterally to the outside.
Further advantages, details and refinements of the present invention are apparent from the preferred embodiments described below with reference to the drawings.
The dimensioning specifications for the waveguide and the associated ground conductors are basically well-known to those skilled in the art. In principle, the following rile applies to the arrangement of the plate through contacts: the smaller the separation, the better. In the ideal case, a completely metal-filled electrically conductive shielding wall is obtained, similar to the upper and lower ground plane. However, due to constraints related to production engineering, the plate through contacts are spaced some distance apart, and the vertically remaining space is unmetallized. In practical structures, the distance between the opposite outer surfaces can be about 300 micrometers. The greater this remaining window opening becomes, the poorer the microwave properties become. The appearance of new unwanted wave modes then begins in correspondingly lower frequency ranges. However, this effect is greatly reduced by the ground surfaces guided parallel to the actual (center) signal conductor (waveguide). The main part of the electrical field components is located between the center signal conductor and the coplanar ground planes (symmetrical division right/left). Another field component is present between the neutral conductor and the upper and lower ground planes. Therefore, only one other, very small field component (whose quantification depends on the specific dimensions) can still act at all through the windows or gaps between the plate through contacts. This interfering inverse amplification factor of the electromagnetic field increases with increasing frequency.
Proceeding from this basic design, additional embodiments of the invention are presented in the following figures. These embodiments make it possible to realize a three-dimensional signal distribution within a multilayer circuit carrier (module). The conductor heights, conductor shapes and conductor separations of the coplanar waveguide 2 and the ground conductors 3, 4 themselves and the distance to the surrounding electrically conductive layers of the electromagnetic shielding must be constant along the line in order to achieve constant impedance and minimal dispersion. Therefore, for impedance changes (matching circuit), these geometries (separations, widths and heights) of the line elements and/or the relative permittivities of the insulating substrate layers 5, 6 must be varied along the direction of propagation. This large number of adjustable parameters leads to far more variation possibilities and thus design possibilities for the impedance transformations and more complex matching circuits compared to conventional waveguides.
In this regard as well, those skilled in the art are aware of the rules for constructing the parameters, so that only a few examples for the wide variety of dimensioning will be given here. For example, the dimensioning of the gap between the center signal line (waveguide) and the coplanar ground surfaces on both sides depends essentially on the following parameters:
In practice, the individual design of a waveguide system prepared by an expert is optimized by subsequent iterative computer simulations. In this regard, the desired impedance is determined by parameter variation with the aid of a so-called 3D EM or full-wave field simulator.
a), for example, shows a symmetrical arrangement of the coplanar conductors 2, 3, 4 combined with a vertically asymmetrical arrangement of the insulating layers 5, 6 (insulating substrate layers). Other realized circuit functions in a total system can require, e.g., differently high individual layers of the dielectric, which lead to vertical asymmetries of the waveguide structure. However, a smaller distance to the ground plane at the top or bottom requires (local) adaptation to the dimensioning for constant impedance along the line. The gap between the neutral conductor and the coplanar ground plane must, e.g., be somewhat increased. The advantages of the invention (bandwidth, etc.) are then retained.
Other impedances can also be realized in line sections by the specified dimensionings. Impedance jumps of this type, much like the compensation structures described below, are used for better electrical and mechanical adaptations of certain connected components or for filter purposes.
The specified vertical asymmetry can be combined with a horizontal asymmetry. This serves the purpose, e.g., of avoiding other aligned components or realizing line sections of different impedance. Normally, however, both vertical and horizontal symmetry is strived for, since this offers the greatest useful bandwidth.
a) shows a two-row arrangement of the plate through contacts 9, 10 on both sides of the waveguide 2.
b) shows in two additional views a vertical line transition between two different and equally high conduction planes with simultaneous 180° rotation of the direction of wave propagation and corresponding compensation systems with defined line narrowing (cf.
The waveguide transitions shown in
For example,
For example, two-wire flat strip lines have long been known, which were used in older radio receivers as inexpensive antenna cable with characteristic impedances in the range of 120-300 ohms, e.g., as so-called “VHF strip line” with polyethylene as dielectric but without external shielding. On the model of this concept, an additional signal line is supplied in the cross section of the waveguide described above in order to realize differential signal transmission.
The embodiment shown in
The embodiment shown in
However, the embodiments shown in
For three-dimensional differential signal transmission, the two waveguide systems illustrated in
Therefore, especially differential vertical transitions according to
Analogously, at the respective transition and bending points (discontinuities), it is possible, for frequency response correction, to use the variants of compensation systems that have already been described in the case of the single-signal conductor system (cf.
Number | Date | Country | Kind |
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10 2007 028 799.4 | Jun 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP08/57666 | 6/18/2008 | WO | 00 | 12/18/2009 |