MICROSTRIP ANTENNA AND FABRICATOIN METHOD THEREOF

FIELD OF THE INVENTION

The present invention relates to a microstrip antenna, and particularly to a microstrip antenna having defect ground structure on the ground plate.

BACKGROUND OF THE INVENTION

In various electronic devices such as wireless communication, radar, electronic navigation and electronic counter measure (ECM), there is an increasing requirement for small and light antenna, and the microstrip antenna has thus become a focus of the antenna research. The early microstrip antenna with a mainly rectangular or circular radiant plate has the defects of narrow bandwidth and low power. In order to improve the performance of antenna and to extend the bandwidth of antenna, many efforts have been exerted.

One approach is a microstrip antenna with a triangular radiant plate. Since the triangular microstrip antenna structure has a smaller size and a wider half-power bandwidth (HPBW) than structures of rectangular shape and the like, the bandwidth of the triangular antenna can be extended from several percentages of a common microstrip antenna to 18%, and therefore has found wide application in various antennas. However, in broad band communication, electronic counter measure (ECM) and broad band radar antenna systems, the triangular antenna still cannot meet the requirement.

In order to further improve the performance of antenna, it is proposed that a "U"- shape cut is provided on an isosceles triangular radiant plate such that the opening of the "U"-shape cut planes towards the bottom side of the triangle, thereby improving the performance of antenna significantly. However, regardless of how the parameters of radiant plate, such as the shape, change, since there are other high-order secondary waves existing on the ground plate in addition to the dominant wave required by the radiation, and the energy consumed by the secondary waves is completely lost for the radiation, the existence of such secondary waves significantly decreases the antenna bandwidth, and degrades the performance of the antenna.

Defect Ground Structure (DGS) is first proposed in the field of solid-state physics. Recently, in the fields involving optics and microwave, the aperiodic structure in the planar

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circuits of microstrip and coplanar waveguide (CPW) is generally referred to as the Defect Ground Structure (DGS). The defect ground structure can improve the performance of microwave circuit and resonant cavity, and has found a certain application in the optical and microwave fields.

OBJECT AND SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a microstrip antenna and fabrication thereof to improve the bandwidth of the antenna and reduce the cross coupling between the antenna units. A microstrip antenna in accordance with the present invention comprises a ground plate; a radiant plate, wherein said radiant plate being an isosceles triangular having a "U"- shape cut thereon with the opening facing towards the bottom side of the triangle; and a connector connected to the radiant plate via a feeding point disposed on the radiant plate, through which the radiant plate can be excited from beneath the ground plate to form electromagnetic radiation; wherein said ground plate comprises at least two notches at the positions corresponding to the edge or external of the radiant plate, and the distance between said notches is substantially half of the wavelength of the antenna dominant wave.

A method for fabricating a microstrip antenna according to the present invention comprises the following steps: providing a ground plate ; providing a radiant plate, said radiant plate being an isosceles triangular having a "U"- shape cut thereon with the opening facing towards the bottom side of the triangle; and providing at least one connector connected to the radiant plate via a feeding point disposed on the radiant plate, through which the radiant plate can be excited from beneath the ground plate to form electromagnetic radiation; wherein said ground plate comprises at least two notches at the positions corresponding to the edge or external of the radiant plate, and the distance between said notches is substantially half of the wavelength of the antenna dominant wave. Theoretically, since a substrate defect structure of a unit cycle is employed, the size of the antenna unit is relatively small. The defect structure is disposed on the ground plate of the antenna, which has a simple structure and is easy to manufacture and at the same time has a reduced weight. With such an antenna with a resistance bandwidth up to 21 %, half-

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power bandwidth greater than 90°, when consisting an antenna array, the substrate defect structure is used to suppress the surface wave, so as to reduce the cross coupling between the antenna units, to improve the efficiency of the antenna and to reduce the side lobe of the antenna, as well as to improve the standing wave ratio bandwidth. For dual polarized antenna, according to the law of conservation of energy, if the secondary wave is weakened, its energy will be superposed into the dominant wave, such that the dominant wave is further enhanced, and the bandwidth of the antenna is improved significantly. By using two sets of apertures on the ground plate, the present invention not only solves the problem that the energy of the secondary wave cannot be used, but also reduces the cross coupling between the antenna units, improves the performance of the antenna, and reduces the side lobe of the antenna and improves the standing wave ratio bandwidth simultaneously since defect ground structure (DGS) is formed on the ground plate due to the two sets of apertures. DGS structure is designed on the metal ground plate of the antenna, which has a simple structure and is easy to manufacture for mass production and at the same time has a reduced weight. Since a Defect Ground Structure

(DGS) of a unit cycle is employed, the size of the antenna unit is also relatively small.

The other objects and achievements of the present invention will be apparent from the description of the present invention with reference to the following figures and claims, to allow one to have a thorough understanding to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a single polarized microstrip antenna structure according to a first embodiment of the present invention.

FIG. 2 is a rear view of a single polarized microstrip antenna structure according to the first embodiment of the present invention.

FIG. 3 is a left view of a single polarized microstrip antenna structure according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a single polarized microstrip antenna structure according to the first embodiment of the present invention. FIG. 5 is an antenna pattern of a single polarized microstrip antenna structure according to the first embodiment of the present invention.

FIG. 6 is a standing wave test graph of a single polarized microstrip antenna structure according to the first embodiment of the present invention.

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FIG. 7 is a front view of a dual polarized triangular microstrip antenna structure according to a second embodiment of the present invention.

FIG. 8 is a rear view of a dual polarized triangular microstrip antenna structure according to the second embodiment of the present invention. FIG. 9 is a left view of a dual polarized triangular microstrip antenna structure according to the second embodiment of the present invention.

FIG. 10 is a sectional view of a dual polarized triangular microstrip antenna structure according to the second embodiment of the present invention.

FIG. 11 is a return loss graph of port A and port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention.

FIG. 12 is a two-port isolation graph of port A and port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention.

FIG. 13 is an H-plane pattern of port A of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention. FIG.14 an E-plane pattern of port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention.

FIG. 15 is a front view of a rectangular microstrip antenna structure according to a third embodiment of the present invention.

FIG. 16 is a rear view of a rectangular microstrip antenna structure according to a third embodiment of the present invention.

In the above drawings, the same reference symbol indicates the same, similar or corresponding characteristics or functions.

DETAILED DESCRIPTION OF THE INVENTION The technical approaches of the present invention will be described in detail hereinafter by way of embodiments with reference to the figures.

Referring to FIG. 1, a single polarized triangular microstrip antenna in a first embodiment of the present invention comprises: a metal ground plate 1; a substrate 3 disposed above the metal ground plate 1 and in parallel with the metal ground plate 1 ; a triangular metal patch 2 disposed on the upper surface of the substrate 3; a feeding point 12 on the center of the triangle, for electrically connecting with the exterior to excite the metal patch 2 to radiate electromagnetic wave.

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The triangular metal patch 2 is the radiant plate of a microwave antenna. The radiant plate of the present invention may have various disposing ways according to different applications. For example, the radiant plate can be a self-supported metal sheet, but does not necessarily include a substrate. Of course, the radiant plate can also be on a substrate as shown in FIG. 1, for example, by adhering, depositing, printing and fixing with screw on the edges. Likewise, the ground plate of the present invention may also be a self-supported metal sheet or formed on a substrate similarly with the radiant plate.

Particularly, the triangular metal patch 2 is of isosceles triangle shape, on which a "U"-shape cut 11 is disposed with an opening facing towards the bottom side of the triangle of the triangular metal patch 2.

Referring to FIG. 2, it can be seen that there are four circular apertures 21 and a feeding aperture 5 required for the connector to connect with a feeding point disposed on the ground plate of the triangular microstrip antenna in the embodiment of the present invention. Generally, the apertures 21 for enhancing the dominant wave should be located at the edge of the projection drawing of the radiant plate with a weak field intensity, or outside the projection drawing, and the distance between the circular apertures is the wavelength of the dominant wave. In order to enhance the dominant wave, the diameter of the first set of apertures is generally an integral multiple of the half-wavelength of the dominant wave. If the diameter of the apertures is other dimensions close to approximately an integral multiple of the half- wavelength, the effect of enhancing the dominant wave will be reduced. The openings on the ground plate of the present invention can be in shapes other than circular apertures or be narrow slits.

Referring to FIG. 3, it can be seen that the first embodiment of the present invention further comprises a coaxial connector 5. Referring to FIG. 4, an inner core 51 of the coaxial connector 5 is connected to the metal patch 2 via the substrate 3, while an outer core 52 of the coaxial connector is connected to the metal ground plate 1.

Referring to FIG. 3 and FIG. 4, it can be seen that there is further a layer of foamed material bulk 4 between the ground plate 1 and the substrate 3. The foamed material bulk 4 is mainly used for fixing and isolating. Because of the supporting of the foamed material bulk 4, the antenna of the present invention can be more secure and less likely to be broken.

Generally, the foamed material bulk 4 always chooses the material with a dielectric constant close to the air, e.g. foamed polystyrene plastic. If the dielectric constant of the

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chosen foamed material bulk 4 is not close to that of the air, the distance between the antenna ground plate and the radiant plate might be adjusted according to its dielectric constant.

Of course, plastic screws can be used to support and fix between the ground plate and the radiant plate, instead of a single bulk of foamed material bulk. Alternatively, in case of a less demanding requirement, a connector having support function can also be used to solve the problems of fixing and supporting.

The above embodiment employs a substrate defect structure of a unit cycle, and the size of the antenna unit is relatively small. The substrate defect structure disposed on the ground plate of the antenna has a simple structure and is easy for manufacture and mass production and at the same time with a reduced weight. When consisting an antenna array, the substrate defect structure can be used to restrain the surface wave, to reduce the cross coupling between the antenna units, to improve the performance of the antenna, to reduce the side lobe of the antenna, and to improve the standing wave ratio bandwidth. FIG. 5 shows an antenna pattern of the single polarized microstrip antenna in the first embodiment of the present invention. It can be seen from the figure that the side lobe of the antenna of the present invention is reduced.

FIG. 6 shows a standing wave test graph of the single polarized microstrip antenna according to the first embodiment of the present invention. It can be seen from the figure that the standing wave ratio bandwidth of the antenna of the present invention is broadened significantly.

The technique approach of the present invention will be described in detail hereinafter according to a second embodiment of a specific dual polarized triangular microstrip antenna of the present invention. Since the dual polarized microstrip antenna is formed by combining two single polarized microstrip antennas together, in terms of spatial field, it combines two antennas having orthogonal polarization directions of +45° and -45°. Therefore, for those skilled in the art, a single polarized microstrip antenna can be definitely realized from the following description of the dual polarized triangular microstrip antenna of the present invention, and the approach is also contemplated in the scope as claimed by the present invention.

Referring to FIG. 7, the dual polarized triangular microstrip antenna according to the second embodiment of the present invention comprises a metal ground plate 1 ; a substrate 3 disposed above the metal ground plate 1 and in parallel with the metal ground plate 1; a

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triangular metal patch 2 disposed on the upper surface of the substrate 3; and a first feeding point 21 and a second feeding point 22, for electrically connecting to the exterior, to excite the metal patch 2 to radiate the electromagnetic wave.

Referring to FIG. 8, which is a rear view of the dual polarized triangular microstrip antenna according to the second embodiment of the present invention, it can be seen that the there are two sets of apertures and a feeding aperture required for the connector to connect with the feeding point disposed on the ground plate of the triangular microstrip antenna according to the embodiment of the present invention. The first set of apertures, as indicated by the indication 11, positioned at three vertexes of the orthographic projection of the triangle metal patch 2 on the metal ground plate 1, are used for enhancing the dominant wave. The diameter of the first set of apertures is generally an integral multiple of the half-wavelength of the dominant wave. For the embodiment shown in FIG. 2, the wavelength of the dominant wave is 0.25 of the diameter of the aperture 11, i.e. λ = 0.25D.

If the diameter of the aperture is other sizes close to an integral multiple of the half- wavelength, the effect of enhancing the dominant wave will be weakened.

The second set of apertures of the present invention is used for eliminating the secondary wave. For the radiant antenna, the smaller the secondary wave on the ground plate is, the better the effect of the antenna is. Therefore, the second set of apertures should be located at a position where the secondary wave is the strongest, provided that the dominant wave is not influenced. In order to determine the position of the second set of apertures, the wave distribution on the ground plate should be obtained first, and the position where the secondary wave is the strongest on the wave distribution figure should be found without influencing the dominant wave. Then the radius thereof is determined with said position as the center, again without influencing the dominant wave. For the second embodiment, it can be seen from FIG. 8 that the second set of apertures are disposed on the midpoints of the three sides of the projection triangle of the radiant plate with a radius less than that of the first set of apertures. If the radius of the second set of apertures is larger than that of the first set of apertures, the dominant wave will be weakened, and the performance of the antenna will be degraded. It can also be seen from FIG. 7 and FIG. 8 the positions of the feeding points 21 and

22 of the second embodiment. For the single polarized microstrip antenna, the feeding point is located at the geometric centre of the radiant plate or in a region close to the

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geometric centre of the radiant plate, with a similar antenna performance. But if it deviates from this region, the performance of the antenna will be degraded significantly. Because of different shapes of radiant plate and various antenna sizes, this region cannot be defined by numerical intervals, but can be considered as a region where the geometric center of the radiant plate is included and the performance of the antenna will not be degraded significantly due to the change of the feeding point position in this region. For the dual polarization of this second embodiment, the feeding point 21 is a feeding point located at the central region of the triangle, and after the location of the feeding point 21 has been determined, the position of the other feeding point 22 should be chosen as an intersection point of zero potential lines on two dual polarized dominant waves.

FIG. 9 is a side view of a dual polarized triangular microstrip antenna structure in the second embodiment of the present invention. There are two coaxial connectors 5 and 6 included in the second embodiment of the present invention. The coaxial connectors 5 and 6 are connected to two feeding points 21 and 22 on the metal patch 2, respectively. Referring to FIG. 10, which shows a sectional view of the dual polarized triangular microstrip antenna structure in the second embodiment of the present invention (only one coaxial connector 5 is shown here), an inner core 51 of the coaxial connector is connected to the metal patch 2 through the substrate 3, while an outer core 52 of the coaxial connector is connected to the metal ground plate 1. The above coaxial connectors may be displaced by other connectors, such as exciting probes, as in the prior art known to those skilled in the art.

FIG. 11 shows a return loss graph of port A and port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention, wherein the port A is corresponding to the electromagnetic wave created by the feeding point 21, while the port B is corresponding to the electromagnetic wave created by the feeding point

22. Among the three curves shown in FIG. 5, the "antenna A simulated SH" curve is a simulated antenna return loss curve before the first and second sets of apertures are disposed on the ground plate, the "antenna B simulated SH" curve is a simulated antenna return loss curve after the first and second sets of apertures have been disposed on the ground plate, the "antenna B experimental SH" curve is a real measured antenna return loss curve after the first and second sets of apertures have been disposed on the ground plate. In the measurement of the antenna performance, the range corresponding to the return loss below - IOdb is defined as the bandwidth of the antenna. It can be seen from

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the figures that when the return loss is at - IOdb, the width of openings of the "antenna B simulated SH" curve and the "antenna B experimental SH" curve is obviously wider than that of the "antenna A simulated SH" curve, i.e., the bandwidth of the antenna is improved significantly. FIG. 12 is a two-port isolation graph of port A and port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention. Likewise, the "antenna A simulated S 12" curve is a simulated port isolation curve before the first and second sets of apertures are disposed on the ground plate, the "antenna B simulated S 12" curve is a simulated port isolation curve after the first and second sets of apertures have been disposed on the ground plate, and the "antenna B experimental S 12" curve is a real measured port isolation curve after the first and second sets of apertures have been disposed on the ground plate. For the port isolation curve, the more negative it is, the better the isolation effect is. It can be seen from the figure that the real measured isolation effect is much better than that of the two simulations, which improves the performance of the antenna significantly, and the result is not predictable.

FIG. 13 and FIG. 14 are respectively an H-plane pattern graph of port A and an E- plane pattern graph of port B of a dual polarized triangular microstrip antenna according to the second embodiment of the present invention. It can be seen from the figures that, although the performance of the antenna is improved significantly by disposing two sets of apertures on the ground plate, its directivity is not influenced. Therefore, the approach of the present invention is a practical improvement.

The technique approach of the present invention will be further described hereinafter by way of a single polarized microstrip antenna having a rectangular radiant plate.

FIG. 15 is a front view of the rectangular microstrip antenna structure according to a third embodiment of the present invention. The rectangular antenna also includes a ground plate 1, a substrate 3 disposed above the metal ground plate 1 and in parallel with the metal ground plate 1; a rectangular metal patch 7 disposed on the upper surface of the substrate 3; a feeding point 8 for electrically connecting to the exterior, to excite the metal patch 7 to radiate electromagnetic waves. FIG. 16 is a rear view of the rectangular microstrip antenna structure according to the third embodiment of the present invention. The first set of apertures 31 of this embodiment are located at four vertexes of the rectangle, and the distance between which is the half

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wavelength of the dominant wave. The second set of apertures 32 in this embodiment are located at the midpoints of the four sides of the rectangle. The feeding points 21, 22 are located at the positions offsetting from the center of the left and right, and top and bottom symmetric lines of the rectangle. The other parts of the third embodiment are similar to the second embodiment, and will not be repeated herein.

The above embodiments are described only illustrative, and not intended to limit the technique approaches of the present invention. Although the present invention is described in details referring to the preferable embodiments, those skilled in the art will understand that the technique approaches of the present invention can be modified or equally displaced without departing from the spirit and scope of the technique approaches of the present invention, which will also fall into the protective scope of the claims of the present invention.