BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a schematic diagram of the microstrip reflectarray antenna of the prior art.
FIG. 1B shows the IE3D software simulation result of the plane wave scattering field of the microstrip reflectarray antenna of the prior art.
FIG. 2A shows a schematic diagram of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention.
FIG. 2B shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention.
FIG. 3A shows the simulation result of the plane wave scattering field of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention.
FIG. 3B shows a schematic diagram resulting from the combination of FIG. 1B and FIG. 3A.
FIG. 4 shows a schematic diagram of the measurement result of both the bore-sight co-polarized radiation gain and the cross polarized radiation gain of the microstrip reflectarray antenna of the prior art and those of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, wherein the operating frequencies of the two microstrip reflectarray antennas both range from 9 GHz to 12 GHz.
FIG. 5 shows a schematic of the measurement result of both the co-polarization radiation pattern in H-plane and the cross-polarization radiation pattern in H-plane of the microstrip reflectarray antenna of the prior art and those of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, as the two microstrip reflectarray antennas both operate at 10.4 GHz.
FIG. 6 shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the second preferred embodiment of the present invention.
FIG. 7 shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the third preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 2A shows a schematic diagram of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention. In the present preferred embodiment, the microstrip reflectarray antenna comprises a ground plate 21, a reflecting plate 22, four supporting units 23, and a horn antenna 24. The reflecting plate 22 is supported by the four supporting units 23 being composed of at least one insulating material, and thus a predetermined distance between the reflecting plate 22 and the ground plate 21 being composed of copper is maintained. In the present preferred embodiment, the distance between the reflecting plate 22 and the ground plate 21 is about 6 mm. But, as in different operation environments, the distance between the reflecting plate 22 and the ground plate 21 can be varied by adjusting the length of the four supporting units 23. With reference to FIG. 2B, the microstrip reflectarray antenna according to the first preferred embodiment of the present invention comprises a plurality of microstrip antenna units 25 locating on the upper surface 221 of the reflecting plate 22, and each of the microstrip antenna units 25 has an inner ring 251 and an outer ring 252.
FIG. 2B shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention. In the present preferred embodiment, the size of each of the microstrip antenna units 25 (the length of the first diameter of the outer ring 252) corresponds to the location thereof on the upper surface of the reflecting plate of the microstrip reflectarray antenna of the present invention. Therefore, as the microstrip reflectarray antenna in its “transmitting state”, the reflecting plate 22 can correctly reflect the high frequency signal from the horn antenna 24 to the ambient space; and as the microstrip reflectarray antenna is in its “receiving state”, the reflecting plate 22 can also correctly reflect the high frequency signal from the ambient space to the horn antenna 24.
In the present preferred embodiment, the microstrip antenna unit 25 locating on the upper surface 221 of the reflecting plate 22 of the microstrip reflectarray antenna further comprises some characteristics, as described as below:
1. There is a predetermined ratio relationship between the length of the first diameter of the outer ring 252 and the length of the second diameter of the inner ring 251 of the same microstrip antenna unit, and the ratio relationship is applied to all of the microstrip antenna units 25 locating on the upper surface 221 of the reflecting plate 22 of the microstrip reflectarray antenna of the present invention. Besides, the ratio relationship can be varied for the different operation environments of the microstrip reflectarray antenna of the present invention. Generally speaking, the ratio of the second diameter of the inner ring 251 to the first diameter of the outer ring 252 of the same microstrip antenna unit 25 is preferably in the range of 0.4 and 0.8. In the present preferred embodiment, the ratio of the second diameter of the inner ring 251 to the first diameter of the outer ring 252 of the same microstrip antenna unit 25 is about 0.6.
2. In one of the microstrip antenna units 25, the outer ring 252 has two first slots 253 at one direction and the inner ring 251 of the same microstrip antenna unit also has two second slots 254 at the same direction (such as the Y direction of FIG. 2B). Thus, both the outer ring 252 and the inner ring 251 of the same microstrip antenna unit are divided equally into two portions.
3. In one of the microstrip antenna units 25, the outer ring 252 and the inner ring 251 both have the same width. In the present preferred embodiment, the width of the outer ring 252 and the width of the inner ring 251 of each of the microstrip antenna units 25 are both about 4 mm.
In addition, by presenting the results of the IE3D software simulation and the measurement of both the microstrip reflectarray antenna of the prior art (as shown in FIG. 1A) and the microstrip reflectarray antenna according to first preferred embodiment of the present invention (as shown in FIG. 2A) as described in the following, the lower cross polarization level characteristic of the microstrip reflectarray antenna according to first preferred embodiment of the present invention will be verified. As a result, by using the microstrip reflectarray antenna of the present invention, the available channel number of the satellite communication system will be increased significantly.
Besides, prior to the execution of the IE3D software simulation and the measurement, some limitations must be set. These limitations are described below:
1. The plane wave transmitted from the horn antenna to the reflecting plate is polarized, and the polarization direction of the plane wave is parallel to the Y direction of the FIG. 1A, FIG. 2A, and FIG. 2B. Besides, the cross polarization level (XPL) of the polarized signal at the bore sight angle is about 30 dBi.
2. The reflecting plate is composed of an FR-4 microwave substrate, the size of which is about 24 cm by 24 cm, and the thickness of the reflecting plate is about 0.8 mm.
3. The distance between the reflecting plate and the ground plate is about 6 mm.
4. There are 256 microstrip antenna units locating on the upper surface of the reflecting plate, wherein every two adjacent microstrip antenna units are separated by a pitch of 1.5 cm. Each of the microstrip antenna units comprises an inner ring and an outer ring, respectively. The thickness of the inner ring and the outer ring are both about 0.4 mm. Moreover, in all 256 microstrip antenna units, the length of the second diameter of the inner ring is 0.6 times the length of the first diameter of the outer ring.
5. In the microstrip reflectarray antenna of the prior art, each of the microstrip antenna units does not have any slot in the inner ring, nor outer ring. Besides, the inner ring and the outer ring are concentric.
6. In the microstrip antenna units of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, the outer ring has two first slots at one direction, while the inner ring also has two second slots at the same direction (such as the Y direction of FIG. 2B). Besides, the widths of the two first slots and the two second slots are about 0.4 mm.
The results of the completed IE3D software simulation are shown in FIG. 1B and FIG. 3A. FIG. 1B indicates the plane wave scattering field of the microstrip reflectarray antenna of the prior art. FIG. 3A shows the simulation result of the plane wave scattering field of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention. Furthermore, FIG. 3B shows a schematic diagram resulting from the combination of FIG. 1B and FIG. 3A, for easy identification of the difference between these two figures.
With reference to FIG. 3B, the plane wave scattering field of the two high frequency signals reflected by the microstrip reflectarray antennas in the Y-polarization direction are substantially equivalent in all angles, and there is no obvious difference between the two curves representing the two high frequency signals in the operation frequency range of the two microstrip reflectarray antennas (from 9 GHz to 12 GHz), which are shown by “⋄” and “−” in FIG. 3B, respectively. Moreover, since the signals transmitted by the horn antennas of the two microstrip reflectarray antennas to their corresponding reflecting plates are Y-polarized high frequency signals, the aforesaid two substantially equivalent curves indicate that these two microstrip reflectarray antennas have similar co-polarization level in all angles(θ).
Referring to FIG. 3B again, as shown in the lower half of the figure, the plane wave scattering fields of the two high frequency signals reflected by the two microstrip reflectarray antennas in the X-polarization direction are significantly different from each other in all angles. Besides, the curve representing the high frequency signal of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention (as shown by the “◯” in FIG. 3B) is significantly lower than the curve representing the high frequency signal of the microstrip reflectarray antenna of the prior art (shown by the “*” in FIG. 3B). Moreover, since the signals transmitted by the horn antennas of the two microstrip reflectarray antennas to their corresponding reflecting plates are Y-polarized high frequency signals, the aforesaid two curves indicate that the cross polarization level (XPL) of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention is lower than the cross polarization level (XPL) of the microstrip reflectarray antenna of the prior art in all angles (θ).
FIG. 4 shows a schematic diagram of the measurement result of both the bore-sight co-polarized radiation gain and the cross polarized radiation gain of the microstrip reflectarray antenna of the prior art and those of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, wherein the operating frequencies of the two microstrip reflectarray antennas both range from 9 GHz to 12 GHz. As shown in the figure, there is no obvious difference between the two curves representing the bore sight co-polarization gains of the two microstrip reflectarray antennas, which are respectively shown by the “∇” and “−” in FIG. 4. Therefore, the bore sight co-polarization gains of these two microstrip reflectarray antennas are substantially equivalent within the whole operation frequency range (from 9 GHz to 12 GHz).
Referring to FIG. 4 again, as shown in the lower half of the figure, the curve representing the cross-polarized gain of the microstrip reflectarray antenna according to the present preferred embodiment of the present invention (as shown by the “◯” in FIG. 4) is totally different from and obviously lower than the curve representing the cross-polarized gain of the microstrip reflectarray antenna of the prior art (as shown by the “*” in FIG. 4) within the whole operation frequency range (from 9 GHz to 12 GHz). Therefore, the cross-polarized gain of the microstrip reflectarray antenna according to the present preferred embodiment of the present invention is obviously lower than the cross-polarized gain of the microstrip reflectarray antenna of the prior art.
FIG. 5 shows a schematic diagram of the measurement result of both the co-polarization radiation pattern in H-plane and the cross-polarization radiation pattern in H-plane of the microstrip reflectarray antenna of the prior art and those of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, as the two microstrip reflectarray antennas both operate at 10.4 GHz. As shown in the figure, there is no obvious difference between the two curves representing the co-polarization radiation pattern of the two microstrip reflectarray antennas in all angles, which are respectively shown by “−” and “—” in FIG. 5. Therefore, the co-polarization radiation patterns of these two microstrip reflectarray antennas are substantially equivalent in all angles (θ).
Referring to FIG. 5 again, as shown in the lower half of the figure, the curves representing the cross-polarization radiation patterns of the two microstrip reflectarray antennas are different from each other in all angles (θ), wherein the curve representing the cross-polarization radiation pattern of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention (as shown by the “” in FIG. 5) is lower than the curve representing the cross-polarization radiation pattern of the microstrip reflectarray antenna of the prior art (as shown by the “◯” in FIG. 5). Therefore, the cross-polarization radiation pattern of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention is significantly lower than the cross-polarization radiation pattern of the microstrip reflectarray antenna of the prior art.
In the present preferred embodiment, the second diameter of the inner ring is 0.6 times the first diameter of the outer ring of each of the microstrip antenna units locating on the upper surface of the microstrip reflectarray antenna according to the first preferred embodiment of the present invention, but preferably the ratio of the second diameter of the inner ring to the first diameter of the outer ring is in the range of 0.4 and 0.8. Furthermore, once the ratio is changed, the cross polarization level of the microstrip reflectarray antenna is also changed accordingly. Taking the microstrip reflectarray antenna according to the first preferred embodiment of the present invention as an example, when the ratio is 0.6, the cross polarization level of the microstrip reflectarray antenna is about 36 dB. But when the ratio is changed from 0.6 to 0.8, the cross polarization level of the microstrip reflectarray antenna will decline to 20 dB as a result, that is, more noise (such as the signal with different polarization direction) will be received by the microstrip reflectarray antenna according to the first preferred embodiment of the present invention.
FIG. 6 shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the second preferred embodiment of the present invention. In the present preferred embodiment, each of the microstrip antenna units 61 locating on the upper surface of the reflecting plate has a square inner ring 62 and a square outer ring 63. Besides, in each of microstrip antenna units, the geometry center of the inner ring 62 overlaps the geometry center of the outer ring 63. In addition, the outer ring 63 has two first slots 64 and the inner ring 62 has two second slots 65, respectively. Therefore, the outer ring 63 and inner ring 62 of the same microstrip antenna unit are both divided into two equal portions. Moreover, the size of the outer ring 63 corresponds to the location of the outer ring 63 on the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the second preferred embodiment of the invention.
FIG. 7 shows a schematic diagram of the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the third preferred embodiment of the present invention. In this present preferred embodiment, each of the microstrip antenna units 71 locating on the upper surface of the reflecting plate has a hexagonal inner ring 72 and a hexagonal outer ring 73. Besides, in each of microstrip antenna units, the geometry center of the inner ring 72 overlaps the geometric center of the outer ring 73. In addition, the outer ring 73 has two first slots 74 and the inner ring 72 has two second slots 75, respectively. Therefore, the outer ring 73 and inner ring 72 of the same microstrip antenna unit are both divided into two equal portions. Moreover, the size of the outer ring 73 corresponds to the location of the outer ring 73 on the upper surface of the reflecting plate of the microstrip reflectarray antenna according to the third preferred embodiment of the invention.
In summary, as the microstrip antenna units of the microstrip reflectarray antenna of the present invention each consists of an outer ring having two first slots, and an inner ring having two second slots, wherein the connecting line connecting the two first slots (not shown in the figure) is parallel to the other connecting line connecting the two second slots (not shown in the figure), the microstrip antenna units of the microstrip reflectarray antenna of the present invention can prevent the current induced by a high frequency signal having a polarization direction perpendicular to the connecting line of the two first slots from flowing on the microstrip antenna units when the microstrip reflectarray antenna of the present invention is in its “receiving state”. As a result, the microstrip reflectarray antenna of the present invention can only receive the high frequency signals having the polarization direction parallel to the connecting line of the two first slots of the microstrip antenna units, and the cross polarization level of the microstrip reflectarray antenna is further reduced. Hence, by using the microstrip reflectarray antenna of the present invention, a satellite communication system can use one frequency channel to transmit two or more signals with different polarization directions at the same time. Thus, the capacity of the satellite communication system is enlarged, and the reception quality thereof is also improved.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.
Patent Application
20080024368
