JP4933020B2 - Slot antenna with folded cavity at the back - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna. In particular, the present invention relates to slot antennas used in high power applications.
[0002]
[Prior art]
The individual antenna elements of a wide scan phased array antenna (eg, capable of scanning very wide angles such as ± 45 °) typically must be spaced very close together. In particular, the individual antenna elements must generally be spaced from each other by approximately half the free space wavelength. There are various antenna elements with such a compact design. However, none of the currently available antennas that are sufficiently compact for use in wide scan phased array antennas can handle very high average power levels, while at the same time being very accurate, eg circularly polarized Polarization cannot be supplied to a fairly wide angle area (eg ± 50 ° in both planes). In this regard, there are many applications that require very compact antenna designs that satisfy these constraints, including high power wide scan phased array antennas. The following brief overview of currently available antenna technologies will help illustrate its limitations and drawbacks. Circularly polarized pitch antennas can only be made smaller than half the free space wavelength by using dielectrics, which makes them unsuitable for high power applications . A circularly polarized ridge waveguide antenna with a slot formed on the surface can be formed to be smaller than half of the free space wavelength. Such antenna designs can handle high power levels, but cannot provide accurate circular polarization.
[0003]
A slot antenna (i.e., no dielectric is required) can be constructed with a square cavity on the rear side that can handle high power levels. However, in order for the device to be operable, the cavity cross-sectional dimension must be greater than half the free space wavelength (typically 7/10 of the wavelength on the edge). The reason why the cavity dimension must be greater than 1/2 the free space wavelength is that the square dimension must be equal to 1/2 the waveguide wavelength longer than the free space wavelength in order for the cavity to resonate. .
[0004]
A slot antenna with a regular cavity at the back can reduce its dimensions by filling the cavity with a dielectric material, but this leads to substantial losses, so the antenna has a high average power application It would be inappropriate.
[0005]
Other known antenna designs include US Pat. No. 3,573,834 (issued to McCabe et al.), US Pat. No. 4,130,823 (issued to Hoople), US Pat. No. 4,132,995 (issued to Monser), and Those described in US Pat. No. 5,461,393 (issued to Gordon) are included. However, the antennas disclosed in these patent specifications are too large and have poor circular polarization performance and / or cannot handle high power levels.
[0006]
[Problems to be solved by the invention]
Thus, very compact that can handle high power levels over a very wide angular range (eg ± 50 ° in both planes) and provide a very accurate circular polarization, such as a wide scan phased array antenna Antennas are technically needed.
[0007]
[Means for Solving the Problems]
This problem is solved by the slot antenna of the present invention with a compact and folded cavity at the rear. In one of its features, the present invention provides a housing having a plurality of walls forming an enclosure, a slot formed in the first wall of the housing, and a second wall of the housing opposite the first wall. And an antenna including a formed folded cavity. The folded cavity is a composite cavity composed of a first cavity part and a second cavity part, and the entire circumference of each of the first cavity part and the second cavity part is joined by a folded part or a shelf. Is preferred. Any convenient RF transmission line, such as a waveguide or coaxial cable, can be used to inject RF energy into the folded cavity.
[0008]
In one embodiment, the slot is cruciform, and a coaxial cable carrying RF signals that are 90 ° out of phase is used to feed in each direction orthogonal to the folded cavity, thereby removing the cruciform slot from Produces accurate circularly polarized radiation.
[0009]
In another embodiment constructed and tested in detail, the slots are crossed dumbbell shaped and a ridge waveguide is used to power the folded cavity. In this embodiment, the amount of folding of the cavity in the first direction is greater than in the second direction, so that the folding cavity resonates at different frequencies for RF energy of different polarizations. In addition, a coupling post is provided to couple the RF energy of the first polarization to the RF energy of the second polarization, whereby the slot generates accurate circularly polarized radiation.
[0010]
In both embodiments, it is preferred that at least one of the width and length dimensions of the housing is less than 7/10 of the free space wavelength, and both the width and length of the housing are each less than 1/2 of the free space wavelength. With either of these embodiments, the antenna can generate a very accurate circular polarization and can handle very high average power levels, eg, 10 kW, and thus, for example, wide It is suitable for high power applications that require very compact antenna elements such as scan phased array antennas.
[0011]
In another aspect, the present invention also includes a phased array antenna that includes a plurality of antenna elements each configured in accordance with the present invention.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION Exemplary embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the effective teachings of the present invention.
Although the present invention is described herein with reference to illustrative embodiments for particular applications, it should be appreciated that the invention is not so limited. Those skilled in the art will recognize additional modifications, applications and embodiments within the scope of the invention, as well as additional areas where the invention will be very useful.
[0013]
Referring to FIG. 1, there is shown a perspective view of a slot antenna 20 with a folded cavity at the back of one exemplary embodiment of the present invention. A slot antenna 20 with a folded cavity at the rear includes a housing 22 in which a folded square cavity 24 is formed in the lower cavity wall 26 in accordance with a new feature of the present invention, and a slot 28 formed by machining in the upper cavity wall 30. Is included. The housing 22 can be composed of aluminum or other suitable conductive material.
[0014]
The folded square cavity 24 is considered to be formed by folding the edge of a standard square cavity in two dimensions on the back side. This folded cavity design allows the antenna 20 to be smaller than ½ wavelength with respect to the edge, thus making it sufficiently compact to be used as an antenna element in a wide range scanning phased array antenna. This dimensional reduction with respect to the prior art standard square cavity design is done without the use of dielectric material, thereby enabling the antenna 20 to be used in high power applications.
[0015]
The antenna 20 can be powered by a waveguide, coaxial cable or any other RF transmission line. The antenna 20 can be configured to generate a circularly polarized radiation pattern. For example, in the embodiment shown in FIG. 1, slot 28 is cruciform, thereby producing a circularly polarized radiation pattern. Of course, the slot 28 can be formed by machining two orthogonal slots in the upper cavity wall 30 into a cross shape.
[0016]
FIG. 2 is a cross-sectional view of a prior art standard square cavity 32 in one dimension, such as the width dimension. The width of the cavity 32 is indicated by “w”.
[0017]
FIG. 3 is a one-dimensional cross-sectional view of the folded square cavity 24 of the present invention, for example, the width dimension. The width of the folded cavity 24 is indicated by “<< w” to indicate that the width of the folded square cavity 24 of the present invention is significantly smaller than the width of the “unfolded” cavity 32 of the prior art. Note that the entire folded width is approximately equal to "w", as shown in FIG. Of course, this same dimensional reduction occurs in an orthogonal dimension, for example the length dimension of the folded cavity 24, because the folded cavity is “folded” along its length as well as its width.
[0018]
Of course, by folding a standard square cavity with orthogonal dimensions in this way, it consists of a first cavity portion 32 and a second cavity portion 34, each of which is surrounded by a turn or shelf 36. A joined “composite” cavity results. Of course, the particular shape of the cavity is not limited in the broad aspect of the invention.
[0019]
FIG. 4 is a perspective view of an embodiment of the antenna 20 with the folded cavity shown in FIG. 3 on the rear side, showing that it is fed by a pair of coaxial cables 40. Each coaxial cable 40 feeds the folded cavity 24 in each of its two orthogonal directions. When the phase of the coaxial signal is shifted by 90 °, the slot 28 provided with the folded cavity on the rear surface radiates circularly polarized waves.
[0020]
FIG. 5 is a perspective view of another embodiment of an antenna 20 ′ with a folded cavity at the rear of the present invention. In this embodiment, the antenna 20 ′ is fed by a ridge waveguide 44. The ridge waveguide 44 is narrower than a standard waveguide, and can be formed, for example, approximately ½ wavelength at the edge. Furthermore, in this embodiment, intersecting “dumbbell” shaped slots 28 ′ were used to generate a very wide radiation pattern. The ridge waveguide feed 44 only couples energy into the cavity with a single polarization. In order to obtain circular polarization, the folded cavity 24 'needs to resonate in both polarizations. This is achieved in this embodiment of the invention by including a coupling post 48 that energy couples from one polarization to another.
[0021]
Furthermore, in order to obtain circularly polarized waves, the two polarized waves in the folded cavity 24 'need to resonate at slightly different frequencies. This is achieved in this embodiment of the invention by making the amount of cavity folding for one polarization greater than for the other polarization. This is achieved by making the base of the folded cavity 34 'asymmetrical.
[0022]
An antenna 20 ′ (ie, the one shown in FIG. 5) with the folded cavity of this embodiment on the rear surface was constructed and tested in detail.
[0023]
FIG. 6 is a graph showing the reflection loss versus frequency at the input port of the ridge waveguide of the slot antenna 20 ′ having the folded cavity of the present invention shown in FIG. As will be appreciated with reference to this graph, the loss at the center (design) frequency is less than -20 dB and less than -20 dB over approximately 3% bandwidth. The double-resonance characteristic of the return loss must also be recognized and this double-resonance characteristic is the two polarizations of the folded cavity 24 'resonating at different frequencies to produce circularly polarized radiation as described above. Is due to. The radiated axial ratio for this embodiment (ie, the embodiment shown in FIG. 5) was also tested, with the axial ratio close to zero at the center frequency and an axial ratio for the folded cavity 24 'of approximately 2. It was determined to be less than 3 dB over a% bandwidth. In addition, this embodiment (ie, the embodiment shown in FIG. 5) was also tested under high power. In particular, average power exceeding 10 kW was supplied to the antenna 20 ', but no degradation occurred as a result.
[0024]
While the present invention has been described herein with reference to illustrative embodiments for particular applications, it should be appreciated that the invention is not so limited. Those skilled in the art will recognize additional modifications, applications and embodiments within the scope of the present invention and in additional fields where the present invention is very useful.
[0025]
Thus, the present invention has been described herein with reference to illustrative embodiments for particular applications. Those skilled in the art will recognize additional modifications, applications and embodiments within the scope of the invention. For example, while the present invention is particularly useful for use in phased array antennas, the present invention can also be used in many other applications, such as industrial heating and / or cooking applications.
[0026]
Accordingly, the appended claims are intended to cover any and all such applications, modifications and embodiments within the scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a perspective view of a slot antenna provided with a folded cavity on the rear surface according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a folded cavity of a slot antenna having a regular folded cavity on the rear surface.
3 is a cross-sectional view of a folded cavity of a slot antenna having the folded cavity shown in FIG. 1 on the rear surface.
FIG. 4 is a perspective view of a slot antenna having a folded cavity of the present invention fed by a coaxial cable on the rear surface.
FIG. 5 is a perspective view of another embodiment of a slot antenna with a folded cavity of the present invention fed by a ridge waveguide on the rear surface.
6 is a graph showing reflection loss versus frequency at the input port of the ridge waveguide of the slot antenna having the folded cavity of the present invention shown in FIG. 5 on the rear surface.

Claims (10)

A plurality of walls forming an enclosure, the plurality of walls having a rectangular first wall in which a radiating slot for radiating circularly polarized waves is formed, and facing and substantially parallel to the first wall; A rectangular housing having a second wall and a side wall which is perpendicular to the first wall and connects the first wall and the peripheral edge of the second wall, and in which a cavity is formed When,
Means for injecting RF energy into a cavity in the rectangular housing to radiate circularly polarized waves from the radiation slot ;
The second wall is
A flat outer lower cavity wall portion connected to the lower end of the side wall and extending inwardly from the connecting portion in parallel with the first wall;
Axial projection of rectangular cross-section with a rectangular opening protrudes to the upper portion in the direction of the vertical first wall from the inner edge of the outer lower cavity wall portion relative to the outer lower cavity wall portion and said first wall Part,
The shaft covers the rectangular opening in the upper end of the extending projection portions, rectangular, further extending from said axial projecting portion to the vicinity of the parallel pre-Symbol sidewall and said first wall toward the side wall direction of the outer is constituted by a flat top portion of,
Means for injecting RF energy into the cavity is provided in the flat outer lower cavity wall portion of the second wall ;
A first cavity portion is formed between the first wall and the flat upper portion of the second wall;
Second between the outer lower cavity wall portion and the flat top portion of said second wall between and the second wall of the outer edge portion of the Tan Taira upper portion of the side wall and the second wall A hollow portion is formed,
The antenna in which the first cavity portion and the second cavity portion are connected in the vicinity of the side wall, thereby forming a folded cavity.   The antenna of claim 1, wherein at least one dimension of the length and width of the housing is less than 7/10 of the free space wavelength.   The antenna according to claim 1, wherein at least one of the length and the width of the housing is equal to or less than ½ of a free space wavelength. Antenna of the means for injecting either one of claims 1 to 3 includes a coaxial transmission cable. It said means for injecting is any one antenna according to claims 1 to 3 includes a waveguide. Implantation means any one antenna according to claims 1 to 5 comprises a ridge waveguide.   The antenna according to any one of claims 1 to 6, wherein the slot provided in the first wall has a cross shape. The antenna according to any one of claims 1 to 6, wherein the slot provided in the first wall has an intersecting dumbbell shape. Further includes a coupling post that couples RF energy of a first polarization to RF energy of a second polarization, any one of claims 1 to 8 thereby generating a circularly polarized radiation from the slot The described antenna. Folded cavity, with respect to the first RF energy polarization resonate at a first frequency, claims and is configured to resonate at a second frequency for the second RF energy polarization 1 The antenna of any one of thru | or 8 .

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