DE2833772C2 - Directional coupler - Google Patents

Description

45

The invention relates to a directional coupler according to the preamble of claim 1.

Such directional couplers are microwave four-gates, (H. Brand, Circuit theory of linear microwave networks, Hirzel Verlag, Stuttgart 1970), which are required to turn a circuit path into a precisely defined Fraction of the microwave power that traverses this circuit path in a certain direction, decoupling, z. B. for measurement purposes. The goal at which the power is decoupled in a defined manner should be from the neighboring gate, which takes on an analogous function when the microwave power is used Circuit path passes through in the opposite direction, be decoupled as well as possible. A measure of this Decoupling is the so-called directional attenuation, which should be as high as possible in most applications, if possible also over a larger frequency range.

Today there are a lot of microwave circuits with smaller power using microstrip technology it is important that such directional couplers are microstrip compatible. Disadvantage in However, the microstrip technique is that the phase velocities of the even and the odd Quasi-TEM wave type (TEM = transversal electromagnetic) are different on coupled microstrip lines. Hence the realization of Microstrip directional couplers with high directional attenuation due to a technical problem (H.-J. Herzog, Microstrip couplers with high isolation, NTG technical reports in the VDE publishing house, Vol. 60 (1977): 191-195). The various ways of solving this problem are in the foregoing Briefly reproduced essay and consist in the fact that a phase compensation through various technical measures is brought about. This can be done through discrete compensation at the ends of the Coupling path or by adjusting the phase velocities.

These known solutions for the implementation of microstrip directional couplers have high directional attenuation However, disadvantages of a technological nature, which consist in the fact that the reproducibility of the component compared to the implementation in simple microstrip technology deteriorated or the stability of the arrangement is decreased.

However, the conductor widths and gaps required for the coupled compensation lines are relatively small (typically 100 micrometers), which leads to increased specimen variance in production. Of the In addition, the 20 dB directional coupler only achieves more than 25 dB directional attenuation in the measurement in a relatively narrow band (relative range approx. 10%). After all, they lead through the compensation measure at the ends The discontinuities present in the coupling link result in a broadband significantly increased reflection factor compared to the uncompensated case.

The invention is therefore based on the object of specifying a directional coupler with high directional attenuation, which is easier to manufacture and microstrip compatible. This object is achieved by the in claim 1 specified measures resolved. Refinements of the invention can be found in the subclaims will. To solve the problem, a quasi-planar line type is used, the technological Advantages of the microstrip technology and its high mechanical stability combines with the electrical Advantages of the »air-filled« stripline (suspended substrate line). On coupled striplines of this type exist with a certain dimensioning of the cable cross-section? one straight and one odd quasi-TEM wave type with the same phase velocity. When dimensioned appropriately, this equality of the phase velocities exactly at a predeterminable frequency and in a further one Range around this frequency can be reached with a good approximation.

The electrical advantages of the invention result from the equality of the phase velocity Quasi-TEM wave types on the coupled lines of the special type used. Herewith are very to achieve high directional attenuation and reflection attenuation due to the low dispersion (frequency dependence the phase velocity) of the two wave types also in a larger range around the Design frequency can be achieved.

It is technologically advantageous that the directional coupler can be manufactured using microstrip technology usual photo etching technique can be done on both sides of the substrate. This also applies to the

Production of the recess in the metal foil or metal disc, which has an intermediate floor between the Represents the underside of the substrate and the bottom of the closed metallic housing. on the other hand However, this recess can also be achieved by processing the metal foil in a different manner or Metal disc or in the form of a cutout in the housing base on which the substrate rests or is soldered or glued to be conductive, in particular if their depth is over 0.5 mm The dimensioning of the cross-sectional geometry of the coupled strip lines can be as follows be made that the line properties almost predominantly only from those with tight tolerances producible etch geometries depend on the two sides of the substrate. Technologically favorable is also, that the gap widths required for a certain coupling attenuation between the coupled striplines turn out to be significantly wider than with conventional microstrip couplers, usually with ceramic substrates about twice as wide.

The invention will now be explained in more detail with reference to drawings of an exemplary embodiment. It shows

1 shows a cross section through a partially illustrated directional coupler; F i g. 2 partially the top of the substrate;

F i g. 3 partially the underside of the substrate;

F i g. 4 is a plan view of the partially shown housing bottom and FIG

5 shows the course of the directional attenuation and the coupling attenuation.

1 shows the basic structure of the cross section of the type of coupled stripline used, which, when dimensioned correctly, has the properties desired for the coupling mechanism and the generation of a high directional attenuation. The exemplary embodiment is a ² / .( directional coupler with a coupling attenuation C of approx. 1OdB at a frequency of 3 Hz and the highest possible directional attenuation D. mm with a housing base 6 and with a cover plate 8. The metallic housing base 6 has a, for example, 0.5 mm deep, milled rectangular recess 5, for example with the dimensions 3.5 mm × 15 mm.

This recess 5 is covered by a substrate 7 designed as a dielectric carrier plate, e.g. B. made of ceramic 0.64 mm thick and a dielectric constant 9, 7, which is produced by etching technology on the Top the striplines 1 and 2 and on the Underside 4 has a metallization 3. Like the strip lines 1, this metallization 3 has and 2 a thickness of e.g. B.! 0 micrometers and consists of chromium as an adhesive layer and of copper as Conductor material. The width of the lines 1 and 2 is z. B. 0.8 mm at a mutual distance of z. B. 0.4 mm. The metallization 3 on the underside 4 of the substrate 7 has a maximum size corresponding to the recess 5 in the housing base 6, metallization-free area 11 approx. 2 mm wide here. To change the electrical properties is if necessary, a screw 10 can be screwed into the housing base 6 from below. The cavity between the substrate and the cover plate 8 and the space of the recess 5 are here filled with air, but can also be filled with other dielectrics.

in Fig. 2 and F i g. 3 shows the top and bottom of the substrate 7. The etching structure arranged on the opposite side of the substrate 7 is shown in dashed lines. The substrate board, which is etched on both sides, is placed here on the housing base 6 without any further contact. The F i g. 4 shows a top view of the recess 5 in the housing base 6, which is milled there, for example. This recess under the area 11 in the metallization of the substrate in the supporting housing can also be achieved by placing a recessed metal foil or disk underneath. Measurement results which were recorded with a network analyzer are shown in FIG. 5. It must be said that the reflection attenuation (gate reflection factor) is so low that it can no longer be reliably resolved in the existing measurement setup. The measured directional attenuation D over the frequency f is mainly determined by the properties of the absorbers used in the measurement, which themselves have a finite reflection loss, and can therefore no longer be determined precisely when a certain value is exceeded. The theoretical value of D is here D = 63 dB at 3 GHz. The measurement shows that D = 30 dB is exceeded in a larger frequency range around 3 GHz (relative bandwidth approx. 30%). The coupling loss C is also shown as a function of the frequency /.

Areas of application of the directional coupler according to the invention are, for. B. the microwave measurement technology, the Microwave circuit technology of planar technology, for example in radar technology, radio relay technology, in satellite radio.

1 sheet of drawings

Claims (5)

Patent claims: ι. Directional coupler in stripline technology with two strip conductors running parallel over the coupling length with a small spacing on a substrate, the underside of which is metallized, characterized in that the metallization (3) is on the underside (4) of the substrate (7) at the location of the parallel strip conductors (1,2) and the space in between a metallization-free area (II) that with the metallized underside (4) of the substrate (7) directly on the floor (6) or a metallic intermediate floor of a closed metallic housing rests, which has a cover plate (8) over the top of the substrate that the adjoining bottom part under the metallized area (11) has a recess (5) having at least the same width as an area (11), and that its cross-section geometry (Fig. 1) depending on the thickness and the dielectric number of the substrate used as well as of the desired coupling attenuation and of the frequency is so dimensioned that at one given frequency the phase velocities of the two involved in the coupling mechanism Quasi-TEM wave types are the same size. 2. Directional coupler according to claim 1, characterized in that the housing bottom (6) has a Metal plate in which the recess (5) is milled. 3. Directional coupler according to claim 1, characterized in that the recess (5) consists of a There is recessed metal foil or disk on the housing base (6). 4. Directional coupler according to claims 1 to 3, characterized in that in the housing base (6) one extends into the recess (5) Tuning screw (10) is present. 5. Directional coupler according to claims 1 to 4, characterized in that the dielectric in the recess (5) and the cavity (> 3) between the housing and the conductor structure of the directional coupler is air or another dielectric.