Antenna structure and multi-beam antenna array using the same

An antenna structure comprises a substrate, a first antenna unit and a second antenna unit. The substrate comprises a first surface and a second surface opposing the first surface. The first antenna unit is disposed on the first surface, and comprises at least a first slot with a wider inside and narrower outside at the edge of the first antenna unit. The second antenna unit is disposed on the second surface, and is connected to the first antenna unit through a hole in the substrate. The radius of the at least one first slot is one-fourth the wavelength of the central frequency of the antenna structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosure is related to an antenna structure.

An antenna array is composed of a plurality of isotropic radiators. Amplitude and phase difference of radiation are caused by a current flowing through the antenna array. An antenna array exhibits better controllability than a single antenna. Therefore, antenna arrays are suitable for many applications.

For example, a multi-beam antenna array is often used in near-field microwave imaging applications. In the near-field microwave imaging applications, the radiated electromagnetic wave is in a spherical wave and is focused through a lens on a focus plane of an antenna array. To generate an image of larger size, the required curvature of the focus plane becomes greater. Accordingly, the receiving antenna array on the focus plane is required to be rotated to match the adjusted curvature. However, if the focus plane is rotated, not only do the radiation patterns of each array unit interfere with one another, but the layout of the transmission lines of the radio frequency circuit at the back end become extremely complicated, which results in reduced resolution and consumption of a great amount of energy.

Accordingly, there is a need to design an antenna structure which can be arranged as a multi-beam antenna array. The direction of the radiation beam of the antenna structure is configurable, and the noise of the operating frequency can be eliminated. The multi-beam antenna array does not need to be moved or rotated. In addition, the antenna structure can suppress side lobe level to maintain the spatial resolution of the lens.

BRIEF SUMMARY OF THE INVENTION

One embodiment discloses an antenna structure comprising a substrate, a first antenna unit and a second antenna unit. The substrate comprises a first surface and a second surface opposing the first surface. The first antenna unit is disposed on the first surface and comprises at least a first slot with a wider inside and narrower outside at the edge of the first antenna unit. The second antenna unit is disposed on the second surface and is connected to the first antenna unit through a hole in the substrate. The radius of the at least one first slot is one-fourth wavelength of the central frequency of the antenna structure.

Another embodiment discloses a multi-beam antenna array comprising a substrate and a plurality of antenna structures. The substrate comprises a first surface and a second surface opposing the first surface. The plurality of antenna structures are disposed on the substrate and arranged in an array, and each of the plurality of antenna structures comprises a first antenna unit and a second antenna unit. The first antenna unit is disposed on the first surface and comprises at least a first slot with a wider inside and narrower outside at the edge of the first antenna unit. The second antenna unit is disposed on the second surface and is connected to the first antenna unit through a hole in the substrate. The radius of the at least one first slot is one-fourth the wavelength of the central frequency of the antenna structure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a schematic view of an antenna structure according to an exemplary embodiment of this disclosure. As shown inFIG. 1, the antenna structure100comprises a substrate102, a first antenna unit104and a second antenna unit106. The substrate102comprises a first surface170and a second surface180opposing the first surface170. The first antenna unit104is in a blade form with an edge facing outside. In addition, the first antenna unit104is disposed on the first surface170and comprises at least a first slot150with a wider inside and narrower outside at the edge of the first antenna unit104. The second antenna unit106is in a blade form with an edge facing outside. In addition, the second antenna unit106is disposed on the second surface180and is connected to the first antenna unit104through a hole190in the substrate102. The layout of the first antenna unit104and the second antenna unit106on the substrate102is symmetrical. In addition, the first antenna unit104is partially overlapped with the second antenna unit106. As shown inFIG. 1, the arrangement of the first antenna unit104and the second antenna unit106forms a tapered slot antenna. It should be noted that the radius of the at least one first slot150is one-fourth the wavelength of the central frequency of the antenna structure100.

FIG. 2shows a partially enlarged schematic view of the first antenna unit104shown inFIG. 1. As shown inFIG. 2, the first antenna unit104comprises three first slots150, wherein the radius of each first slot150is one-fourth the wavelength of the central frequency of the antenna structure100. The virtual center of each first slot150is located outside of the first antenna unit104. In some embodiment of this disclosure, the fan angle of each first slot150is between 10 and 30 degrees. According to the impedance transformer principle, since the radius of each first slot150is one-fourth the wavelength of the central frequency of the antenna structure100, the corresponding equivalent circuit acts as a closed circuit. In other words, the three first slots150act as closed circuits for the current flowing through the first antenna unit104. Since a closed circuit draws currents, the current flowing through the first antenna unit104flows along the edges of the three first slots150, as indicated by the arrow shown inFIG. 2. Referring toFIG. 1, since the second antenna unit106does not have such a slot, the length of the path the current flowing through the first antenna unit104is shorter than that of the current flowing through the second antenna unit106. Therefore, the phase of the electromagnetic wave generated by the current flowing through the first antenna unit104falls behind that of the electromagnetic wave generated by the current flowing through the second antenna unit106. Accordingly, the radiation pattern of the antenna structure100is changed.

FIG. 3shows the radiation pattern of the antenna structure100. As shown inFIG. 3, since the phase of the electromagnetic wave generated by the current flowing through the first antenna unit104falls behind that of the electromagnetic wave generated by the current flowing through the second antenna unit106, the radiation pattern of the antenna structure100rotates clockwise toward the first antenna unit104.

FIG. 4shows a schematic view of an antenna structure according to another exemplary embodiment of this disclosure. As shown inFIG. 4, the antenna structure400comprises a substrate402, a first antenna unit404and a second antenna unit406. The antenna structure400is similar to the antenna structure100shown inFIG. 1, except the second antenna unit406comprises three second slots460and the first antenna unit404does not comprise any slot. Therefore, the phase of the electromagnetic wave generated by the current flowing through the first antenna unit404lies ahead of that of the electromagnetic wave generated by the current flowing through the second antenna unit406.

FIG. 5shows the radiation pattern of the antenna structure400. As shown inFIG. 5, since the phase of the electromagnetic wave generated by the current flowing through the first antenna unit404lies ahead of that of the electromagnetic wave generated by the current flowing through the second antenna unit406, the radiation pattern of the antenna structure400rotates counterclockwise toward the second antenna unit406.

Referring to the above exemplary embodiments, developers can increase or decrease the number of the first slots and the second slots to achieve the desired radiation pattern. The number of the first slots may be equal to or not equal to the number of the second slots. In addition, the number of the first slots and the second slots is not limited to three, but could include any quantity.

Referring toFIG. 2, according to the impedance transformer principle, the equivalent circuit of each first slot150viewed from the outside of the first antenna unit104is an open circuit. An open circuit exhibits features opposite to those of a closed circuit. That is, the electromagnetic wave of the operating frequency is less likely to be received by the first antenna unit104from the side comprising the first slots150. Therefore, the first antenna unit104exhibits the capability to reject the noise of the operating frequency.

In near-field microwave imaging applications, spatial resolution is mostly determined by a lens antenna. If an image of large size is required, an antenna array is arranged at the focus plane of the lens. According to Snell's Law and Huygens' Principle, a high side lobe level of the radiation pattern affects the main lobe of the radiation pattern. Therefore, the radiation pattern on the focus plane is often required to be adjusted such that the radiation pattern after the lens maintains a low side lobe level. By combining the antenna structure of this disclosure, the radiation pattern of each antenna structure can be adjusted individually, and a lens antenna suitable for near-field microwave imaging applications can be achieved.

FIG. 6shows a schematic view of a multi-beam antenna array according to an exemplary embodiment of this disclosure. As shown inFIG. 6, the multi-beam antenna array600comprises a substrate602and a plurality of antenna structures604. Each antenna structure604is similar to the antenna structure100or the antenna structure400shown inFIGS. 1 and 4respectively. As shown inFIG. 4, the number of first slots of the antenna structures604at the left side of the multi-beam antenna array600is greater than the number of second slots of the antenna structures604at the left side of the multi-beam antenna array600. Conversely, the number of first slots of the antenna structures604at the right side of the multi-beam antenna array600is smaller than the number of second slots of the antenna structures604at the right side of the multi-beam antenna array600. Accordingly, the radiation pattern of the antenna structures604at the left side of the multi-beam antenna array600points slightly to the right, the radiation pattern of the antenna structures604at the right side of the multi-beam antenna array600points slightly to the left, and the radiation pattern of the antenna structures604at the middle of the multi-beam antenna array600is not rotated. A lens690is arranged above the multi-beam antenna array600. The layout of the multi-beam antenna array600is designed so that the radiation pattern thereof corresponds to the focus plane of the lens690.

Referring toFIGS. 3 and 5, since the radiation patterns of the antenna structures604at both sides of the multi-beam antenna array600are not symmetric, the level of the side lobes of the radiation pattern after the lens690is low, and thus the spatial resolution of the lens690can be maintained at a suitable level. In addition, since the equivalent circuits of the first slots and the second slots viewed from the outside of the antenna unit604are open circuits, the coupling effect between each antenna unit604is reduced, and hence the isolation between array units is enhanced.

In conclusion, the antenna structures provided by this disclosure utilize slots such that the radiation patterns of the antenna structures are changed. By adjusting the number of slots, the amount of shifting of the radiation patterns of the antenna structures can be adjusted accordingly. Therefore, the multi-beam antenna array combining a plurality of antenna structures provided by this disclosure is suitable for near-field microwave imaging applications in that the antenna array does not need to be rotated.

The above-described exemplary embodiments are intended to be illustrative only. Those skilled in the art may devise numerous alternative embodiments without departing from the scope of the following claims.