JP2002532928A - Transition from broadband microstrip to parallel-plate waveguide - Google Patents

Abstract

(57) Abstract: A broadband transmission device (20) used between a shielded microstrip (24) and a parallel plate waveguide (21). The broadband transition has a metal taper (26) with one end electrically connected to the microstrip feedline (24) of the microstrip circuit and the other end electrically connected to the waveguide wall. ). The metal taper may be optimized to cancel the reflection caused by the discontinuity between the microstrip circuit and the parallel plate waveguide over a wide operating frequency band. An antenna system (10) that uses a broadband transition is also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to waveguide transitions, and more particularly, to broadband microstrip to parallel plate waveguide transitions.

[0002]

[Prior art]

Typical microwave transitions associated with the present invention require the use of a waveguide operating in the fundamental mode rather than a parallel plate or over-mode waveguide. Thus, prior art waveguide transition designs do not provide the broadband and low VSWR capabilities provided by the present invention.

[0003]

[Problems to be solved by the invention]

Therefore, it is effective to have a transition from a broadband microstrip to a parallel-plate waveguide that improves the normal waveguide transition.

[0004]

[Means for Solving the Problems]

The present invention includes a broadband transition used between a shielded microstrip and a parallel plate waveguide. The broadband transition includes a metal taper having one end electrically connected to the conductive strip of the microstrip and the other end electrically connected to the waveguide wall. The metal taper may be optimized to cancel reflections caused by discontinuities between two completely different transmission media, including microstrip and parallel plate waveguides, over a wide operating frequency band.

A low VSWR transition between a linear array of shielded microstrip circuits (eg, phase shifters) and a parallel plate waveguide structure (eg, a continuous transverse stub array antenna) due to a broadband transition. Is realized with a wide operating bandwidth and wide-angle scanning capability. Shielded microstrip lines minimize cross-coupling between adjacent circuits, thereby allowing their individual amplitude and phase excitation to be imposed on line sources along the parallel plate waveguide interface. Metal tapers are also suitable for constructing a flat in-line transition between the microstrip and the square waveguide with full band coverage of the fundamental guided mode.
No technical literature describing this particular type of transition has been found.

The present invention may be used in applications requiring a low VSWR, broadband, flat in-line transition between a microstrip and a parallel plate or rectangular waveguide structure. In particular, the present invention relates to a method for connecting a linear array of microstrip circuits (eg, RF feed networks, ferrite or PIN diode phase shifters, microwave amplifiers, or mixers) to a parallel plate or overmoded waveguide line feed. Enables metastasis in The present invention can be used to provide inexpensive two-dimensional scanning capabilities by combining this type of electronic scanning line feed in one plane with mechanical rotation in orthogonal planes.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Various features and advantages of the present invention will be more readily understood from the following detailed description and the accompanying drawings. In the drawings, the same reference numerals indicate the same structural elements. Referring to the drawings, FIG. 1 illustrates the use of a broadband microstrip to parallel plate waveguide transition 20 in an antenna system 10 in accordance with the principles of the present invention. FIG. 1 is a simplified block diagram of an antenna system 10 illustrating a general application of a broadband transition 20. FIG.

The antenna system 10 includes a planar antenna 30 in which the transition 20 is used. This planar antenna 30 has a line feed input including a parallel plate or overmoded waveguide section. Planar antenna 30 also includes a linear array of phase shifters 13 each having a microstrip RF port 13a. The broadband transition 20 provides an RF interface between the phase shifter 13 and the antenna 30. A combiner / divider 12, which receives the input signal at the RF input 11, sets the amplitude distribution along the line feed input 30a of the antenna, and the linear array of phase shifters 13 allows the antenna 30 to have the desired The angle output is adjusted to produce a phase front suitable for scanning the output beam.

FIG. 2 shows a solid dielectric continuous transverse stub array antenna 30 as a typical example of the planar antenna 30. The continuous transverse stub array antenna 30 has a parallel plate waveguide horizontal line feed 31. The 8-way vertical collective feed 32 arranged behind the aperture plate 33 feeds eight continuous transverse stab radiators 34. N-way combiner / divider shown in FIG.
The horizontal aperture distribution provided by 12 and phase shifter 13 is provided to parallel plate line feed 30a along the rear of antenna 30.

A section of this broadband transition 20 used for three adjacent elements is shown in FIG. A parallel plate waveguide 21 (shown on the left side of FIG. 3) having a height of 0.140 inches and filled with a dielectric is provided by a parallel plate line feed 30a of the continuous transverse stub array antenna 30. Corresponding to A plurality of microstrip circuits 22, each including a shielded microstrip feed line 24 (shown on the right side of FIG. 3), includes three phase shifter 13 output circuits, the height of which is the height of the interface. Parallel-plate waveguides to minimize physically discontinuities
Same as 12. The plurality of microstrip circuits 22 are fabricated on a substrate 23, such as a 0.025 inch thick Rexolite ™ substrate 23, which is
Is preferably the same dielectric material as that forming the parallel plate waveguide 21 and the continuous transverse stub array antenna 30.

In FIG. 3, a portion of the upper wall of the broadband transition 20 has been cut away so that one of the plurality of metal tapers 26 is visible. The taper 26 may be manufactured as a separate part or as a part in the parallel plate area by forming the required shape in a dielectric material, followed by metallizing the cavity walls. . The metal taper 26 has one end electrically connected to the microstrip feed line 24 of the microstrip circuit 22 and the other end electrically connected to the wall (upper wall or top wall) of the waveguide 21. Have been.

The broadband transition 20 has the capability of low VSWR performance over a multi-octave bandwidth, but the design relationship depends on the need to avoid grating lobes that appear in real space at the upper band edge for large scan angles. Is weighed. This relationship is obtained from the following equation: s / λ _h = (1-1 / n) / 1 + | sin θ _max | (1) where s = the distance between adjacent elements λ _h = the wavelength of the highest operating frequency n = number of elements θ _max = maximum scanning angle from the wide side of the waveguide As an example of the present invention, a Hewlett-Packard high-frequency structure simulator (HF
SS) A computer program was used to model the broadband transition 20 for a 32-element continuous transverse stub array antenna 30. The array antenna 30 operates over a frequency band of 6 to 18 GHz and generates ±
Designed to scan up to 60 °. From equation (1), the maximum allowable element spacing is 0
. A spacing of 0.325 inches was selected to give a margin of 340 inches, and therefore manufacturing tolerances.

FIG. 4 shows the calculated magnitude of reflectance | S ₁₁ | and transmittance | S ₂₁ | versus frequency. The calculated VSWR shown in FIG.
Lower than 1.50: 1 over Hz. However, when the array is scanned to ± 60 °, grating lobes occur above 22.7 GHz. 24 GHz
In that case, if no grating lobes are generated, the array may only be scanned to ± 27.8 °. Element spacing may be increased slightly (eg, 0.350 inches) to provide the desired low VSWR performance at 6 GHz, but ± 60 ° scan coverage without grating lobes can only be obtained up to 17.5 GHz. Can not. At higher frequencies, the available scan sectors become progressively smaller as represented by equation (1).

The broadband transition 20 of the present invention can also be used as a low VSWR transition between a microstrip circuit 22 and a rectangular waveguide 21 as shown in FIG. However, the broadband capability of this particular broadband transition 20 is limited by the fundamental mode cutoff at the lower frequency end and the propagation of higher order modes at the higher frequency end.

The methodology used to design the metal taper 26 includes the following steps. The width (Y direction) of the taper 26 is selected to be equal to the line width of the microstrip circuit 22. This eliminates the need for alignment in the Y direction, and this option is available for special design requirements.

The length of each taper 26 is determined by the operating bandwidth, the desired VSWR, and space limitations. The taper 26 is typically several wavelengths long at the lowest frequency for each medium. In an exemplary design, a taper 26 shorter than the wavelength length was required by physical constraints.

The curve of the taper 26, which is initially a parabola, is numerically optimized to minimize reflectivity for the desired band. Alternatively, an optimization routine may be used to calculate the curve.

Table 1 shows the X and Z coordinates of the lower and upper surfaces of the metal taper 26, while FIG. 6 shows the profile defined by these points.

[0019]

[Table 1] Thus, a transition from a broadband microstrip to a parallel plate waveguide is disclosed. It is to be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Obviously, various other devices can be readily devised by those skilled in the art without departing from the scope of the invention.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an exemplary embodiment of a transition from a broadband microstrip to a parallel plate waveguide in accordance with the principles of the present invention.

FIG. 2 is a perspective view of a solid dielectric continuous transverse stub array antenna shown as an example of a planar antenna.

FIG. 3 is a perspective view showing a section of a transition portion of three adjacent elements.

FIG. 4 is a graph illustrating VSWR calculated for an exemplary 32-element continuous transverse stub array antenna.

FIG. 5 is a perspective view illustrating an exemplary broadband transition that can be used as a low VSWR transition between a microstrip and a rectangular waveguide.

FIG. 6 is a profile diagram defined by the points shown in Table 1.

[Procedure amendment]

[Submission date] September 14, 2000 (2000.9.14)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Contents of correction]

[Claims]

Claims (15)

[Claims] A plurality of microstrip circuits each including a shielded microstrip feed line disposed on a parallel plate waveguide; a plurality of microstrip circuits disposed on a substrate; A first end coupled to one of the microstrip feedlines of
A plurality of metal tapers (26) each having a second end disposed adjacent to the waveguide.
Transition from broadband microstrip to parallel-plate waveguide coupled to 0). 2. The parallel-plate waveguide (21) comprises a dielectric-filled parallel-plate waveguide (21).
The transfer part according to claim 1, wherein 3. The transition according to claim 1, wherein the metal tapers include different metal parts. 4. The transition according to claim 1, wherein the metal taper is a dielectric material having a metal-coated taper. 5. The width of the metal tapers (26) is equal to the line width of the microstrip circuit (22), and the length of each taper (26) is determined by the operating bandwidth, the desired VSWR and space constraints, The transition of claim 1 wherein the taper curve is optimized to minimize reflectivity for the desired band. 6. An RF input (11), a combiner / divider (12) coupled to the RF input, and a microstrip RF port (13a) coupled to the combiner / divider (12). A linear array of phase shifters (13), a planar antenna (30) having a line feed input and a waveguide section, and a broadband microstrip coupled between the linear array of phase shifters and the planar antenna. A transition portion (20) to a parallel plate waveguide, wherein the transition portion (20) from the broadband microstrip to the parallel plate waveguide comprises a parallel plate waveguide (21) and a substrate (23). Shielded microstrip feedline located above (24)
A plurality of microstrip circuits each including: a first end coupled to one of the plurality of microstrip feed lines; and a second end disposed adjacent the waveguide. An antenna system comprising: a plurality of metal tapers (26) each having: 7. The antenna system according to claim 6, wherein the planar antenna has a parallel plate waveguide section. 8. The antenna system according to claim 6, wherein the planar antenna has an overmoded waveguide section. 9. The antenna system according to claim 6, wherein the planar antenna (30) comprises a solid dielectric continuous transverse stub array antenna (30). 10. The antenna system according to claim 6, wherein the continuous transverse stub array antenna (30) includes a parallel plate waveguide horizontal line feed (31). 11. A broadband transition (20) comprising a dielectric-filled parallel plate waveguide (21).
The antenna system according to claim 6, comprising: 12. The parallel plate waveguide (21) is a dielectric filled parallel plate waveguide (21).
The antenna system according to claim 6, comprising: 13. The antenna system according to claim 6, wherein the metal taper (26) includes separate metal parts. 14. The antenna system according to claim 6, wherein the metal taper (26) is made of a metal-coated tapered dielectric material. 15. The width of the metal tapers (26) is equal to the line width of the microstrip circuit (22), and the length of each taper (26) is determined by the operating bandwidth, the desired VSWR and space constraints; 7. The antenna system of claim 6, wherein the taper curve is optimized to minimize reflectivity for a desired band.