FI98105C - The microstrip-waveguide transition - Google Patents

Description

98105 MICROLIUS CURVE TUBE 11STRUCTION

The present invention relates to a microstrip waveguide displacement as defined in the preamble of claim 1.

5 Some microstrip waveguide transitions are already known by means of which power is transferred from a microstrip to a waveguide in the micro- and millimeter-wavelength range. There are at least three types of such known displacements: the ribbed waveguide type displacement, the fin line type displacement, and the probe type displacement. Common to transitions is that they are cumbersome to manufacture and are not hermetic.

On the other hand, a microstrip waveguide displacement is already known, in which the displacement is developed by the so-called

15 A patch antenna and comprising a microstrip arranged on a planar substrate above a ground-level connection opening. Further, the displacement includes a dipole element (patch antenna) arranged in the waveguide below the coupling opening, which is supported by a second planar substrate. A rectangular strip plate (dipole element) on the substrate forms a radiating resonator. Such a transition is described in German patent publication DE 4208 458.

In the transition shown in said publication, the power is coupled from the microstrip to the waveguide by means of a dipole element. Furthermore, according to the publication, the switching aperture must be dimensioned so that the resonant frequency of the aperture is clearly above the operating frequency of the displacement. Such sizing is considered in the literature to be typical of patch antenna coupling openings. Thus, the physical size of the opening becomes relatively small. In addition, in the transition shown in the above-mentioned publication, it is essential that the dielectric constant of the substance between the coupling opening and the dipole element 35 is as small as possible, most preferably there is air between the coupling opening and the dipole element 98105 2.

Such a microstrip antenna is characterized by a very low bandwidth, especially when a material with a high dielectric constant is used as a substrate.

Thus, the problem with the transition using the patch antenna is the small bandwidth, i.e. the power transfer has to be limited to a small frequency band.

10 However, many applications require broadband operation, in which case a narrowband transition cannot be used. On the other hand, the displacement requires precise sizing to agree, in which case the manufacturing process must be precise.

It is an object of the present invention to obviate or at least significantly alleviate the above problems. In particular, it is an object of the present invention to provide a new type of microstrip waveguide displacement which can be easily made hermetic and has a high bandwidth.

It is a further object of the present invention to provide a microstrip waveguide displacement which is simple and cost effective to implement.

For features characteristic of the present invention, reference is made to the claims.

The present invention is directed to microstrip waveguide displacement in the micro and / or millimeter wavelength range. The displacement includes a waveguide, a microstrip arranged at one end of the waveguide, and a ground plane arranged between the microstrip and the waveguide with its connection openings. According to the invention, a resonator of dielectric material 35 is arranged in the waveguide below the switching opening for switching power through the switching opening to the resonator and from there to the waveguide. Preferably, the resonator extends to the ground plane, so that there is no air gap between the 3 98105 resonator and the ground plane, which affects the dimensioning of the resonator. However, it should be noted that in some solutions it may be advantageous to leave an air gap between the resonator and the ground plane.

The bandwidth can be further improved by increasing the thickness of the dielectric plate. As the thickness increases, the displacement requires a larger connection opening to accommodate. The resonant frequency of the switching aperture then comes close to the operating frequency of the transition. When the thickness of the dielectric piece is λ / 4, λ corresponds in this application to the wavelength at the operating frequency of the transition, it has been found that the displacement fits best when the resonance of the aperture is below the operating frequency of the transition. Known aperture-fed Tilk cantennas generally have an aperture resonance at a frequency significantly higher than the operating frequency of the transition.

An advantage of the present invention is that the bandwidth of the operating frequency is significantly higher than with the corresponding hermetic and production structures. In addition, the displacement of the present invention is not as sensitive to changes in the manufacturing process as the known microstrip waveguide displacements.

Thus, thanks to the present invention, the microstrip-to-waveguide displacement becomes more economically viable to manufacture.

In one embodiment of the invention, the dielectric constant, εΓ, of the resonator is about 5 to 15, preferably about 6 to 10, and most preferably about 7.5. The value of the dielectric constant can be selected within the limits allowed by the available materials according to the desired properties in each case, depending on the other dimensioning of the displacement.

In one embodiment of the present invention, the resonator comprises a metal strip arranged on the opposite side of the resonator to the coupling 98105. Typically, the metal strip is very thin and can be made by patterning the metal to the desired shape on the surface of the resonator. Further preferably, the ground plane with its connection openings can be arranged on the microstrip on the opposite surface of the substrate to the microstrip. This avoids the addition of one separate component, the ground plane, to the transition structure.

In one embodiment of the present invention, the width of the metal strip is selected to be smaller than the width of the connection opening. Thus, the transition is broadband in a compact structure. The passband is steep at both edges, in which case the passband has at least two resonances - one resonance does not give a similar steepness to the passband.

In another application, the resonator may comprise a metal strip very wide with respect to the connection opening. In this case, the displacement is very wide, taking into account the small size of the structure. Figure 20 5 shows the measurement result of a structure with a wide metal strip. Electronically, many phenomena occur over a short distance, which together adapt the transition to broadband. The resonance of a wide metal strip is more broadband than that of a narrow one. The current distribution of the resonant small me-25 stable strip is centered on both edges as with the microstrip. The current distribution of the wide metal strip is distributed over a wider area, which fits well with the field pattern of the basic waveform of the waveguide. The wide metal strip also better excites the resonant waveforms in the die-30 electric resonator, which expand the bandwidth of the transition.

Parasitic elements can be added next to the metal strip, which can also be used to increase the bandwidth. With the help of the elements, the bandwidth 35 can be increased up to three times - four times the bandwidth obtained with a single, small metal strip, when the resonant frequencies of the elements added in parallel are tuned to slightly different frequencies.

Preferably, the waveguide may be rectangular, round, polygonal or el-5 Lips in cross section.

In the following, the invention will be described in detail by means of exemplary embodiments with reference to the accompanying drawing, in which: Figure 1 shows a transition according to the invention; Figures 2a and 2b show the quarter-wave transform effect of a dielectric piece in both the empty state and the waveguide; Figure 3 shows a transition according to the invention; Fig. 4 shows a mirror image of a resonator in a displacement according to the invention, and Fig. 5 shows a measured frequency response curve of a displacement according to the invention.

The microstrip-waveguide displacement shown in Fig. 1 comprises a waveguide 1, a microstrip 3 arranged at one end 2 of the waveguide, and a ground plane 4 with connection openings 5 arranged between the microstrip and the waveguide. , whereby the power is connected through the connection opening to the resonator and from there to the waveguide. The distance of the free end 9 of the microstrip, the so-called open stub length measured from the center of the switching opening 5 is about λ / 4, 30 whereby the maximum of the magnetic field enters the center of the switching opening 5 with the maximum electric field at the end of the open stub 9.

Referring to Figures 2a and 2b, a quarter-wave-thick dielectric piece acts as a transition to a four- to 35-wave transformer. The situation can be illustrated with an example of free space. The impedance η0 of the free space is 377 Ω, the impedance of the dielectric piece is t] 0 / Vs, and it is desired to see an impedance of about 50 Ω: η. Thus, the impedance of the dielectric resonator, i.e. the quarter-wave transformer, Fig. 2a, should now be: 5 -IjL · = τ] η0 x Z.; where (1) 4 £ r sr = resonator dielectric constant; Z2 = assumed impedance of the switching hole; and η0 = free state impedance, - 10 of which the appropriate dielectric constant is solved by aa: er = - = 7,5 (2) Z2

In the situation of Figure 2b, 15 are obtained for the waveguide, respectively:

Vr - ZXX -— ZXX, η ° X Z,; (3) where

Er = resonator dielectric constant; Zx = is the coefficient by which, when multiplying the waveguide impedance of a waveguide, the characteristic impedance of the waveguide is obtained; Z2 = assumed impedance of the switching hole; η0 = free space impedance; 25 f = operating frequency; and fc = cut-off frequency

On the left side of the equation is the impedance of a waveguide filled with a dielectric substance, on the left is the impedance of an air-filled waveguide at the square root multiplied by the assumed aperture impedance Z2. Zx is the coefficient by which the characteristic impedance of the waveguide is obtained by multiplying the wavelength impedance of the waveguide. Zx depends on the definition of impedance. The impedance of the aperture should be determined using the same impedance definition. Now we get a suitable dielectric-5 autumn constant: Z.r n, Ji- (j-y, v er = - \ --— Λ f <«> Z2 K f 10

For example, with the waveguide power-voltage impedance definition, a standard waveguide with a rectangular cross-section with cross-sectional dimensions a = 2b, Zx 15 is 1. One transition according to the invention is about 1.8 times the cut-off frequency. The square root expression then gives about 0.8. If the impedance visible at the aperture towards the waveguide is 50 Ω, a suitable dielectric constant of 20 is obtained. For example, the dielectric constant of Alumina is 9.8, so a quarter-wave transformer made from it lowers the impedance of the waveguide by about 35 Ω: ϋη. The aperture itself can be used as an impedance transformer, but as a high impedance adapter, the aperture becomes narrowband.

25 Since there is already a low impedance in front of the aperture, the aperture connection becomes more broadband. It is noteworthy that exploiting the quarter-wave transform effect requires a relatively large dielectric constant for the resonator.

Referring to Fig. 3, two parasitic elements 8 are arranged on the surface 30 of the resonator 6. Depending on the dimensioning and fitting requirements of the displacement, more parasitic elements 8 can be added. The resonant frequencies of the elements 8 are the same or are tuned to a slightly different frequency than the resonant frequency of the metal strip 7.

98105 8

Many waveforms can travel in a dielectric piece, if at all. Table 1 shows the cut-off frequencies of the waveforms m, n propagating in the dielectric piece of the example case in the waveguide R 5 58; sr = 10.5 and the frequency unit GHz.

Table 1 m, n 0 1 2 3 4 5 6 0 0 1,1461 2,2922 3,4383 4,5844 5,7305 6,8766 1 2,2924 2,5630 3,2418 4,1322 5,1256 6, 1720 7,2486 2 4,5849 4,7259 5,1259 5,7309 6,43036 7,3389 3 6,8773 6,9721 7,2492

According to one measurement, the wavy waveforms are those whose index n is even 10 and m is odd, since these shapes have symmetry in both horizontal and vertical planes of symmetry, such as the opening at the end of the waveguide and the metal strip. Some of these waveforms may resonate in a dielectric resonator. Figure 4 ha-15 illustrates such a resonator. The dielectric piece can be thought of seeing its mirror image behind the ground plane, to the right in Figure 4, wherein the piece becomes a half wave length.

Referring further to German patent publication DE 4208458, the publication starts with a patch antenna, i.e. a patch antenna from which a displacement has been developed. In the transition according to the present invention, it is possible to start by switching the power between the micro-strip and the waveguide in the structure through a switching opening. A plate with a high dielectric constant of about λ / 4 thickness is placed in front of the connection opening, which acts as a quarter-wave transformer and a dielectric resonator. The transition is already working well as such. The displacement can be further improved if a suitable metal strip is placed in front of the quarter-wave transformer, i.e. on top of the dielectric piece. An essential feature of the structure is to utilize the quarter-wave transform effect which is achieved with a high dielectric constant. Also, the utilization of the resonances generated by the quarter-wave thick plate as a bandwidth-enhancing phenomenon 5 is a significant improvement over the structure presented in said German publication.

The invention is not limited to the application examples presented above only, but many modifications are possible while remaining within the scope of the inventive idea defined by the claims.

Claims (9)

1. Micro strip guide offset within the micro and / or millimeter road area, to which offset belongs a guide strip (1), a micro strip (3) arranged at one end (2), a ground plane arranged between the micro strip and the guide (4) with associated coupling openings (5) and a substrate (6) arranged on the lower side of the coupling opening (5) in the guide (1), characterized in that the substrate (6) is a dielectric blank. ne and is arranged to act as a resonator for coupling the power through the coupling aperture to the substrate and thence to the guide; and that the size of the coupling aperture (5) is selected such that the resonant frequency is on the lower side of the offset operating frequency. 2. Micro-strip guide offset according to claim 1, characterized in that the substrate (6) is arranged as an impedance transformer, advantageously a quarter-way transformer, the thickness (d) of the substrate in the longitudinal direction of the guide (1) being approx. 1/6 - 1/3, preferably approx. Ί / 4, where 1 corresponds to the path length of the operating frequency. Micro-strip guide offset according to claim 1 or 2, characterized in that the substrate (6) extends all the way to the ground plane (4). Micro-strip guide offset according to any one of claims 1-3, characterized in that the dielectric constant of the substrate (6) is approx. 5 to 15, preferably ca. 6 to 10 and preferably approx. 7.5. Micro-strip guide offset according to any of claims 1-4, characterized in that the substrate (6) includes a metal strip (7) arranged on the opposite side of the substrate in relation to the connection opening (5). 98105 Micro-strip guide offset according to any of claims 1-5, characterized in that the ground plane (4) with associated coupling opening (5) is arranged on the micro-strip (3). 7. Micro-strip guide firing according to any one of claims 1-6, characterized in that at least two parasitic elements (8) are arranged on the surface of the substrate (6) next to the metal strip (7), whose resonance frequency is tuned to different frequencies in relation to metal. frequency. Micro-strip guide offset according to any one of claims 1-7, characterized in that the guide (1) for its intersection is rectangular, round, polygon or elliptically shaped. Micro-strip guide offset according to any of claims 1-8, characterized in that the cross-sectional shape of the coupling opening (5) and / or the metal strip (7) corresponds to the cross-sectional shape of the guide (1). 20 '