Micro-strip antenna

Abstract: The antenna includes a first micro-strip antenna (204), a second micro-strip antenna (206) spaced away from and facing the first micro-strip antenna (204), a ground plate (208) located between the first and second micro-strip antennas (204, 206), a first dielectric material (210a) sandwiched between the first micro-strip antenna (204) and the ground plate (208), and a second dielectric material (210b) sandwiched between the second micro-strip antenna (206) and the ground plate (208), the ground plate (208) being formed with an opening (205) overlapping both the first and second micro-strip antennas (204,206).

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to an antenna comprised of micro-strip antennas and having bi-directional or non-directional characteristic. DESCRIPTION OF THE PRIOR ART Fig. 1 is a perspective view illustrating a conventional antenna comprised of micro-strip antennas and having bi-directional or non-directional characteristic. As illustrated in Fig. 1, the conventional antenna 102 is comprised of a first micro-strip antenna 104, a second micro-strip antenna 106 spaced away from and facing the first micro-strip antenna 104, a ground plate 108 located between the first and second micro-strip antennas 104 and 106, a first dielectric plate 110a composed of insulating material and sandwiched between the first micro-strip antenna 104 and the ground plate 108, a second dielectric plate 110b composed of insulating material and sandwiched between the second micro-strip antenna 106 and the ground plate 108, and an electric power distributor 112 for feeding electric power to the first and second micro-strip antennas 104 and 106. A first micro-strip line 114 is formed on a surface of the first dielectric plate 110a and is connected to the first micro-strip antenna 104, and a second micro-strip line 116 is formed on a surface of the second dielectric plate 110b and is connected to the second micro-strip antenna 106. Electric power supplied to a feeding terminal 118 is distributed by the electric power distributor 112 to the first and second micro-strip antennas 104 and 106 through the first and second micro-strip lines 114 and 116, respectively. However, the antenna 102 is accompanied with a problem that since the first and second micro-strip antennas 104 and 106 are positioned at opposite sides of the ground plate 108, the electric power distributor 112 for feeding electric power to the first and second micro-strip antennas 104 and 106 has to be three-dimensional. Specifically, the electric power distributor 112 has to have a width equal to or greater than a total width of the first and second dielectric plates 110a and 110b. As a result, the antenna 102 cannot avoid being larger in size due to the three-dimensional distributor 112. Japanese Unexamined Patent Publication No. 6-120729 having been published on April 28, 1994 has suggested an antenna comprised of a first dielectric plate, a second dielectric plate adhered to the first dielectric plate, a first planar electrical conductor formed on a surface of the first dielectric plate, and a second planar electrical conductor formed on a surface of the second dielectric plate. The antenna suggested in the above-mentioned Publication is accompanied with the same problem as that of the antenna illustrated in Fig. 1. Namely, since the first and second planar electrical conductors are positioned at opposite sides of the dielectric plates, an electric power distributor for feeding electric power to the first and second planar electrical conductors has to be three-dimensional, due to which the antenna cannot avoid to be larger in size. Japanese Unexamined Patent Publication No. 7-46028 having been published on February 14, 1995 has suggested an antenna comprised of a dielectric plate, and radiation slots formed on opposite surfaces of the dielectric plate. Since the radiation slots are formed at opposite surfaces of the dielectric plate, the antenna suggested in the above-identified Publication is accompanied with a problem that an electric power distributor for feeding electric power to the radiation slots has to be three-dimensional, due to which the antenna cannot avoid to be larger in size. An antenna according to the preamble of claim 1 is known from document JP-A-08/116211. This document discloses an antenna system provided with a first ground conductor plate, a first dielectric board provided adjacent the first ground plate, and a third dielectric board provided on the first dielectric board, whose thickness is thinner than that of the first dielectric board, and also with strip conductors being first and second feed lines used to feed power to first and second radiation conductors. Feeding points of the radiation conductors provided to first and second major sides of the second dielectric board are located at positions deviated by an angle of 90° thereby allowing the directions of currents flowing to the surface of the radiation conductors to be orthogonal to each other. Furthermore, plural slits with a prescribed width are provided to the radiation conductors along the feeding direction with respect to the feeding points and the pattern is formed to be interdigital. Also in this antenna device, power is fed to both antennas. For this purpose, each of the two antennas is provided with its own micro-strip line, so that also in this case, the electric power distributor has to be 3-dimensional, leading to a considerable antenna size. Document EP 0735610 discloses a similar device with a square patch antenna electromagnetically coupled to a signal reception feed line. This signal reception feed line is connected to two output feed lines, which makes this device also quite large in size. SUMMARY OF THE INVENTION In view of the above-mentioned problem, it is an object of the present invention to provide an antenna which is capable of operating without a three-dimensional electric power distributor, and hence, making it possible to fabricate an antenna equipment including the antenna, in a smaller width. According to the invention, this object is solved by an antenna according to claim 1. Preferable embodiments are defined in dependant claims. In accordance with the invention, when electromagnetic wave is supplied to the first micro-strip antenna, the first micro-strip antenna resonates and radiates electromagnetic waves to atmosphere therearound. The second micro-strip antenna is electromagnetically coupled to the first micro-strip antenna through the opening formed at the ground plate. As a result, the second micro-strip antenna resonates to the first micro-strip antenna to thereby radiate electromagnetic waves to atmosphere similarly to the first micro-strip antenna. Hence, the antenna is able to have bi-directional or non-directional characteristic. In addition, since electric power is supplied only to the first micro-strip antenna, it is no longer necessary for the antenna to include a three-dimensional power distributor unlike a conventional antenna, ensuring that the antenna can be fabricated in a smaller size. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view illustrating a conventional antenna. Fig. 2 is a perspective view illustrating an antenna in accordance with the first embodiment, which is an example useful for understanding the invention. Fig. 3 is a cross-sectional view of the antenna illustrated in Fig. 2, showing an operation of the antenna. Fig. 4 is a cross-sectional view taken along the line IV-IV in Fig. 2. Fig. 5 is a graph showing directional characteristic of the antenna illustrated in Fig. 2. Fig. 6 is a perspective view illustrating an antenna in accordance with the second embodiment, which is another example useful for understanding the invention. Fig. 7 is a perspective view illustrating an antenna in accordance with the third embodiment, which is an antenna according to the invention. Fig. 8 is a perspective view illustrating an antenna in accordance with the fourth embodiment, which is an antenna according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Fig. 2 illustrates an antenna in accordance with the first embodiment. As illustrated in Fig. 2, an antenna 202 in accordance with the first embodiment is comprised of a first micro-strip antenna 204, a second micro-strip antenna 206 spaced away from and facing the first micro-strip antenna 204, a ground plate 208 located between the first and second micro-strip antennas 204 and 206, a first dielectric plate 210a composed of insulating material and sandwiched between the first micro-strip antenna 204 and the ground plate 208, and a second dielectric plate 210b composed of insulating material and sandwiched between the second micro-strip antenna 206 and the ground plate 208. The first and second micro-strip antennas 204 and 206 are formed rectangular, and composed of electrical conductor in the form of a plate. The first micro-strip antenna 204 is coextensive with the second micro-strip antenna 206. The ground plate 208 is composed of electrical conductor. The first dielectric plate 210a makes close contact at one of surfaces thereof with one of surfaces of the ground plate 208, and the second dielectric plate 210b makes close contact at one of surfaces thereof with the other surface of the ground plate 208. The first micro-strip antenna 204 is adhered to the other surface, that is, an outer surface of the first dielectric plate 210a, and the second micro-strip antenna 206 is adhered to the other surface, that is, an outer surface of the second dielectric plate 210b. The ground plate 208 is formed with a rectangular opening 205 in an area overlapping both the first and second micro-strip antennas 204 and 206. The opening 205 has a smaller area than an area of the first or second micro-strip antenna 204 or 206. However, it should be noted that the opening 205 may be designed to have an area equal to or greater than an area of the first or second micro-strip antenna 204 or 206. The opening 205 has four sides each of which is parallel to an associated side of the first and second micro-strip antennas 204 or 206. A micro-strip line 214 composed of electrical conductor is formed on a surface of the first dielectric plate 210a, and connects the first micro-strip antenna 204 to a feeding terminal 218 for feeding electric power to the first micro-strip antenna 204 therethrough. Hereinbelow is explained an operation of the antenna 202 in accordance with the first embodiment. Fig. 3 illustrates an electric field generated around the antenna 202. Electro-magnetic waves supplied to the feeding terminal 218 pass through the micro-strip line 214, and reach the first micro-strip antenna 204. As a result, the first micro-strip antenna 204 resonates and radiates electro-magnetic waves 207a to atmosphere. The second micro-strip antenna 206 is electro-magnetically coupled to the first micro-strip antenna 204 through the opening 205 formed at the ground plate 208. As a result, the second micro-strip antenna 206 resonates to the first micro-strip antenna 204, and thus, radiates electro-magnetic waves 207b to atmosphere, similarly to the first micro-strip antenna 204. Thus, electro-magnetic waves supplied to the feeding terminal 218 are fed to both the first and second micro-strip antennas 204 and 206, and then, radiated at opposite sides of the ground plate 208. As a result, the antenna 202 can have a bi-directional characteristic. As illustrated in Fig. 4, if the ground plate 208 is designed to have a sufficiently small width W, the first micro-strip antenna 204 would have a directional characteristic having a pattern 16 illustrated in Fig. 5 with a solid line, and the second micro-strip antenna 206 would have a directional characteristic having a pattern 18 illustrated in Fig. 5 with a broken line. Accordingly, the antenna 202 would have a directional characteristic 20 obtained by combining the patterns 16 and 18 with each other. As is obvious in view of Fig. 5, the thus obtained directional characteristic 20 is non-directional. According to the results of the experiments the inventor conducted, it is preferable that the ground plate 208 has a width W equal to or smaller than a double width 2T of the first or second micro-strip antenna 204 or 206. In Fig. 4, an X-axis extends in a direction in which the ground plate 208 extends, and an Y-axis extends in a direction perpendicular to the direction in which the ground plate 208 extends. In Fig. 5, an axis of abscissa corresponds to the X-axis in Fig. 4, and an axis of ordinate corresponds to the Y-axis in Fig. 4. The antenna 202 radiates such vertically polarized, bi-directional or non-directional waves as mentioned above in X-Y plane in Fig. 4. In the antenna 202 in accordance with the above-mentioned first embodiment, electric power is supplied only to the first micro-strip antenna 204. Hence, it is no longer necessary for the antenna 202 to include a three-dimensional electric power distributor such as the distributor 112 illustrated in Fig. 1, which ensures that an antenna equipment including the antenna 202 can be fabricated in a smaller size. The above-mentioned antenna 202 can be employed not only as a transmitting antenna for radiating electro-magnetic waves as mentioned earlier, but also as a receiving antenna, by virtue of invertibility of electro-magnetic waves. When the antenna 202 is employed as a receiving antenna, it is possible to take out electro-magnetic waves received only through the first micro-strip antenna 204. Hence, there can be obtained the same advantages as those obtained when the antenna 202 is employed as a transmitting antenna. [Second Embodiment] Fig. 6 illustrates an antenna in accordance with the second embodiment. As illustrated in Fig. 6, an antenna 302 in accordance with the second embodiment is comprised of a first micro-strip antenna 304, a second micro-strip antenna 306 spaced away from and facing the first micro-strip antenna 304, a ground plate 308 located between the first and second micro-strip antennas 304 and 306, a first dielectric plate 310a composed of insulating material and sandwiched between the first micro-strip antenna 304 and the ground plate 308, and a second dielectric plate 310b composed of insulating material and sandwiched between the second micro-strip antenna 306 and the ground plate 308. The first and second micro-strip antennas 304 and 306 are formed rectangular, and composed of electrical conductor in the form of a plate. The first micro-strip antenna 304 is coextensive with the second micro-strip antenna 306. The ground plate 308 is composed of electrical conductor. In the antenna 302 in accordance with the second embodiment, the first micro-strip antenna 304 is formed with first cut-outs 304a at corners located on a first diagonal line 304b thereof. Similarly, the second micro-strip antenna 306 is formed with first cut-outs 306a at corners located on a second diagonal line 306b thereof. The second diagonal line 306b of the second rectangular micro-strip antenna 306 is perpendicular to the first diagonal line 304b of the first rectangular micro-strip antenna 304. The first and second cut-outs 304a and 306a both make an angle of about 45 degrees relative to a direction in which the micro-strip line 10 extends. The first and second dielectric plates 310a and 310b make close contact with the ground plate 308. The first micro-strip antenna 304 is adhered to an outer surface of the first dielectric plate 310a, and the second micro-strip antenna 306 is adhered to an outer surface of the second dielectric plate 310b. The ground plate 308 is formed with a rectangular opening 305 in an area overlapping both the first and second micro-strip antennas 304 and 306. The opening 305 has a smaller area than an area of the first or second micro-strip antenna 304 or 306. The opening 305 has four sides each of which is parallel to an associated side of the first and second micro-strip antennas 304 or 306. A micro-strip line 314 composed of electrical conductor is formed on an outer surface of the first dielectric plate 310a, and connects the first micro-strip antenna 304 to a feeding terminal 318 for feeding electric power to the first micro-strip antenna 304 therethrough. Whereas the antenna 202 in accordance with the first embodiment radiates vertically polarized waves by supplying electro-magnetic waves to the first micro-strip antenna 204 through the micro-strip line 214, the antenna 302 in accordance with the second embodiment radiates circularly polarized waves having bi-directional or non-directional characteristic in a plane defined by the X-and Y-axes illustrated in Fig. 4. In the antenna 302 in accordance with the second embodiment, electric power is supplied only to the first micro-strip antenna 304. Hence, it is no longer necessary for the antenna 302 to include a three-dimensional electric power distributor such as the distributor 112 illustrated in Fig. 1, similarly to the antenna 202 in accordance with the first embodiment. In addition, the antenna 302 can be employed not only as a transmitting antenna for radiating electro-magnetic waves, but also as a receiving antenna, by virtue of invertibility of electro-magnetic waves, similarly to the antenna 202 in accordance with the first embodiment. [Third Embodiment] Fig. 7 illustrates an antenna in accordance with the third embodiment. An antenna 402 in accordance with the third embodiment is comprised of a first antenna array 404A, a second antenna array 406A, a ground plate 408 located between the first and second antenna arrays 404A and 406A, a first dielectric plate 410a sandwiched between the first antenna array 404A and the ground plate 408, and a second dielectric plate 410b sandwiched between the second antenna array 406A and the ground plate 408. The first antenna array 404A is comprised of a plurality of first rectangular micro-strip antenna elements 404 arranged in a line, a plurality of micro-strip lines 411 for connecting adjacent first micro-strip antenna elements 404 to each other, and a micro-strip line 414 for connecting the first micro-strip antenna element 404 located at an end of the first antenna array 404A to a feeding terminal 418. The second antenna array 406A is comprised of a plurality of second rectangular micro-strip antenna elements 406. Each of the second micro-strip antenna elements 406 is spaced away from adjacent one, and faces an associated one of the first micro-strip antenna elements 404. The ground plate 408 is formed with a plurality of openings 405 in areas overlapping both the first micro-strip antenna elements 404 and the associated second micro-strip antenna elements 406. Each of the openings 405 has a smaller area than an area of each of the first or second micro-strip antenna elements 404 or 406. Each of the openings 405 has four sides each of which is parallel to an associated side of the first and second micro-strip antenna elements 404 or 406. The antenna 402 in accordance with the third embodiment provides the same advantages as those obtained by the first embodiment. In the antenna 402, electric power is supplied only to the first micro-strip antenna elements 404. Hence, it is no longer necessary for the antenna 402 to include a three-dimensional electric power distributor such as the distributor 112 illustrated in Fig. 1. In addition, the antenna 402 can be employed not only as a transmitting antenna for radiating electro-magnetic waves, but also as a receiving antenna, by virtue of invertibility of electro-magnetic waves. [Fourth Embodiment] Fig. 8 illustrates an antenna in accordance with the fourth embodiment. An antenna 502 in accordance with the fourth embodiment is comprised of a first antenna array 504A, a second antenna array 506A, a ground plate 508 located between the first and second antenna arrays 504A and 506A, a first dielectric plate 510a sandwiched between the first antenna array 504A and the ground plate 508, and a second dielectric plate 510b sandwiched between the second antenna array 506A and the ground plate 508. The first antenna array 504A is comprised of a plurality of first rectangular micro-strip antenna elements 504 arranged in a line, a plurality of micro-strip lines 511 for connecting adjacent first micro-strip antenna elements 504 to each other, and a micro-strip line 514 for connecting the first micro-strip antenna element 504 located at an end of the first antenna array 504A to a feeding terminal 518. The second antenna array 506A is comprised of a plurality of second micro-strip antenna elements 506. Each of the second micro-strip antenna elements 506 is spaced away from adjacent one, and faces an associated one of the first micro-strip antenna elements 504. Each of the first micro-strip antenna elements 504 is formed with first cut-outs 504a at corners located on a first diagonal line 504b thereof. Similarly, each of the second micro-strip antenna elements 506 is formed with first cut-outs 506a at corners located on a second diagonal line 506b thereof. The second diagonal line 506b of the second rectangular micro-strip antenna element 506 is perpendicular to the first diagonal line 504b of the first rectangular micro-strip antenna element 504. The first and second cut-outs 504a and 506a both make an angle of about 45 degrees relative to a direction in which the micro-strip lines 511 extend. The ground plate 508 is formed with a plurality of openings 505 in areas overlapping both the first micro-strip antenna elements 504 and the associated second micro-strip antenna elements 506. Each of the openings 505 has a smaller area than an area of each of the first or second micro-strip antenna elements 504 or 506. Each of the openings 505 has four sides each of which is parallel to an associated side of the first and second micro-strip antenna elements 504 or 506. The antenna 502 in accordance with the third embodiment provides the same advantages as those obtained by the first embodiment. In the antenna 502, since electric power is supplied only to the first micro-strip antenna elements 504, it is no longer necessary for the antenna 502 to include a three-dimensional electric power distributor such as the distributor 112 illustrated in Fig. 1. In addition, the antenna 502 can be employed not only as a transmitting antenna for radiating electro-magnetic waves, but also as a receiving antenna, by virtue of invertibility of electro-magnetic waves.

Claims: An antenna comprising: (a) a first micro-strip antenna (404A, 504A); (b) a second micro-strip antenna (406A, 506A) spaced away from and facing the first micro-strip antenna (404A, 504A); (c) a ground plate (408, 508) located between the first and second micro-strip antennas (404A, 504A; 406A, 506A) and being provided with at last one opening (405, 505); (d) a first dielectric material (410a, 510a) sandwiched between the second micro-strip antenna (406A, 506A) and the ground plate (408, 508); and (e) a second dielectric material (410b, 510b) sandwiched between the second micro-strip antenna (406A, 506A) and the ground plate (408, 508), characterized by that the first micro-strip antenna (404A, 504A) is comprised of a plurality of first micro-strip antenna elements (404, 504) arranged in a line and electrically connected to one another, that the second micro-strip antenna (406A, 506A) is comprised of a plurality of second micro-strip antenna elements (406, 506) each spaced away from and facing an associated one of the first micro-strip antenna elements (404, 504), and that the ground plate (408, 508) is formed with a plurality of openings (405, 505) overlapping each of the first micro-strip antenna elements (404, 504) and an associated second micro-strip antenna element (406, 506). The antenna as set forth in claim 1, wherein each of the first micro-strip antenna elements (504) is formed rectangular and is formed with first cut-outs (504a) at corners located on a first diagonal line (504b) thereof, and wherein each of the second micro-strip antenna elements (506) is formed rectangular and is formed with second cut-outs (506a) at corners located on a second diagonal line (506b) perpendicular to the first diagonal line (504b). The antenna as set forth in claim 1 or 2, wherein the first micro-strip antenna elements (404, 504) are electrically connected to one another through a micro-strip line (411, 511) formed on a surface of the first dielectric material (410a, 510a). The antenna as set forth in claim 1 or 2, wherein each of the openings (405, 505) has an area equal to or smaller than an area of each of the first or second micro-strip antenna elements (404, 504; 406, 506). The antenna as set forth in claim 1 or 2, wherein each of the openings (405, 505) is rectangular. The antenna as set forth in claim 5, wherein each of the openings (405, 505) has sides parallel to sides of each of the first and second micro-strip antenna elements (404, 504; 406, 506). The antenna as set forth in claim 1, 2 or 6, wherein the ground plate (408, 508) has a width equal to or smaller than a double width of the first or second micro-strip antenna elements (404, 504; 406, 506). The antenna as set forth in claim 2, wherein the first and second cut-outs (504a, 506a) are in parallel with each other. The antenna as set forth in claim 3 , wherein the first and second cut-outs (504a, 506a) make an angle of about 45 degrees relative to the micro-strip line (414, 514).

Inventors: HIRABE MASASHI, HIRABE, MASASHI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1998
Main classification: H01Q9
IPC codes: H01Q13, H01Q19, H01Q9, H01Q21