EP2482383A2

EP2482383A2 - Microstrip antenna

Info

Publication number: EP2482383A2
Application number: EP11746883A
Authority: EP
Inventors: Zujian Feng; Zhenyu Tang; Xing LIAO; Zhili Guo
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2011-04-19
Filing date: 2011-04-19
Publication date: 2012-08-01
Also published as: CN102959801A; WO2011103841A3; WO2011103841A2; EP2482383A4

Abstract

Embodiments of the present invention provide a microstrip antenna, which includes: four layers of dielectric slabs disposed in parallel, where a first microstrip patch is disposed at a central position of an upper surface of a first layer dielectric slab; a second microstrip patch is disposed at a central position of an upper surface of a second layer dielectric slab; a first ground layer is disposed on an upper surface of a third layer dielectric slab, a coupling aperture is opened at a central position of the first ground layer, a central conductor is disposed at a central position of a lower surface of the third layer dielectric slab; and a second ground layer is disposed on a lower surface of a fourth layer dielectric slab. The third layer dielectric slab and the fourth layer dielectric slab are of asymmetric dielectrics, so that an electric field above the central conductor is greater than an electric field below. The microstrip antenna provided in the embodiments of the present invention improves energy coupling efficiency, ensures bandwidth of the antenna, and reduces backward radiation of the microstrip antenna, thereby improving the F/B of the microstrip antenna. Moreover, the overall size of the microstrip antenna is greatly reduced, which is beneficial to the transmission of the antenna and the integration of receiving circuits.

Description

FIELD OF THE INVENTION

The present invention relates to the field of mobile communications technologies, and in particular, to a microstrip antenna.

BACKGROUND OF THE INVENTION

With the development of the radio frequency technology, due to a low cost and easy processing and manufacturing, microstrip antennas are widely applied in fields of microwave and millimeter wave. The microwave antenna is thin and easy to be integrated. With the development of the antenna technology, the technology for expanding antenna bandwidth is widely applied, for example, L-probe feeding, a parasitic patch, U-type groove loading, aperture coupling and other technologies. An aperture-coupled multilayer microstrip antenna is most widely applied, and has the best combination property as well as advantages such as high bandwidth, low cross polarization and small size.
A sectional view of the microstrip antenna in the prior art is shown in FIG 1, which is usually formed by a dielectric slab 1a, a dielectric slab 2a and a dielectric slab 3a that are disposed in parallel. A microstrip patch 11a is disposed at a central position of an upper surface of the dielectric slab 1a, a microstrip patch 21a is disposed at a central position of an upper surface of the dielectric slab 2a, and a ground layer 31a is disposed on an upper surface of the dielectric slab 3a. A coupling aperture 32a is opened at a central position of the ground layer 31a, and a central conductor 33a is disposed on a lower surface of the dielectric slab 3a. In the microstrip antenna with such a structure, feeding is performed by a microstrip line formed by the ground layer 31 a, the dielectric slab 3a and the central conductor 33a. Backward radiation and spurious radiation of the microstrip antenna occur in the coupling aperture 32a, therefore affecting a ratio between forward radiation energy and backward radiation energy of the antenna, namely, affecting the F/B of the antenna. As shown in FIG 2, in another microstrip antenna in the prior art, a reflection board 4a of the aluminum honeycomb material is usually added at a position with 1/4 dielectric wavelength away from the antenna dielectric slab 3a, to offset the backward radiation. Foam 5a is filled between the dielectric slab 3a and the reflection board 4a.
However, a size of the microstrip antenna in the prior art is bulky, which makes transmission of the antenna and integration of receiving circuits difficult.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a microstrip antenna, to solve a problem in the prior art that the bulky size of the microstrip antenna makes transmission of the antenna and integration of receiving circuits difficult.
An embodiment of the present invention provides a microstrip antenna, including four layers of dielectric slabs disposed in parallel, where a first microstrip patch is disposed at a central position of an upper surface of a first layer dielectric slab; a second microstrip patch is disposed at a central position of an upper surface of a second layer dielectric slab; a first ground layer is disposed on an upper surface of a third layer dielectric slab, a coupling aperture is opened at a central position of the first ground layer, and a central conductor is disposed at a central position of a lower surface of the third layer dielectric slab; and a second ground layer is disposed at a lower surface of a fourth layer dielectric slab; and
the third layer dielectric slab and the fourth layer dielectric slab are of asymmetric dielectrics, so that an electric field above the central conductor is greater than an electric field below.
In the microstrip antenna provided in the embodiments of the present invention, the third layer dielectric slab and the fourth layer dielectric slab are of asymmetric dielectrics, so that in a strip line, an upper-part electric field strength is far greater than a lower-part electric field strength, which improves energy coupling efficiency, ensures bandwidth of the antenna, reduces the backward radiation of the microstrip antenna, thereby improving the F/B of the microstrip antenna. Moreover, the overall size of the microstrip antenna is greatly reduced, which is beneficial to the transmission of the antenna and the integration of the receiving circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical solutions according to the embodiments of the present invention or in the prior art more clearly, the accompanying drawings required for describing the embodiments or the prior art are introduced below briefly. Apparently, the accompanying drawings in the following description merely show some of the embodiments of the present invention, and persons of ordinary skill in the art can obtain other drawings according to the accompanying drawings without creative efforts.

FIG 1 is a sectional view of an aperture-coupled multilayer microstrip antenna in the prior art;
FIG 2 is a sectional view of another aperture-coupled multilayer microstrip antenna in the prior art;
FIG 3 is a sectional view of a microstrip antenna provided in an embodiment of the present invention;
FIG. 4 is a sectional view of a microstrip antenna provided in another embodiment of the present invention;
FIG 5 is a perspective diagram of the microstrip antenna shown in FIG 4;
FIG 6 is a schematic diagram of return loss obtained through HFSS emulation of a microstrip antenna provided in the present invention;
FIG. 7 is a far-field directional diagram obtained through HFSS emulation of a microstrip antenna provided in the present invention; and
FIG. 8 is a schematic diagram of an in-band gain obtained through HFSS emulation of a microstrip antenna provided in the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions of the present invention will be clearly and comprehensively described in the following with reference to the accompanying drawings. It is obvious that the embodiments to be described are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by persons skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
FIG. 3 is a sectional view of a microstrip antenna provided in an embodiment of the present invention. As shown in FIG 3, the microstrip antenna includes: four layers of dielectric slabs that are disposed in parallel; where
a first microstrip patch 11 is disposed at a central position of an upper surface of a first layer dielectric slab 1; a second microstrip patch 21 is disposed at a central position of an upper surface of a second layer dielectric slab 2; a first ground layer 31 is disposed on an upper surface of a third layer dielectric slab 3, a coupling aperture 32 is opened at a central position of the first ground layer 31, a central conductor 33 is disposed at a central position of a lower surface of the third layer dielectric slab 3; and a second ground layer 41 is disposed on a lower surface of a fourth layer dielectric slab 4; and
the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of asymmetric dielectrics, so that an electric field above the central conductor 33 is greater than an electric field below.
As the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of asymmetric dielectrics, the first ground layer 31, the third layer dielectric slab 3, the central conductor 33, the fourth layer dielectric slab 4 and the second ground layer 41 together form an asymmetric dielectric strip line.
Specifically, an entire microstrip antenna is formed by four layers of dielectric slabs, namely, the first layer dielectric slab 1, the second layer dielectric slab 2, the third layer dielectric slab 3 and the fourth layer dielectric slab 4. As a feasible process for forming the microstrip antenna, a double-sided copper-clad dielectric slab may be adopted. Undesired copper foil is discarded and a desired pattern is reserved after photoetching of the copper foil, and the entire microstrip antenna is obtained through a laminating technology.
The first microstrip patch 11 is reserved at the central position of the upper surface of the first layer dielectric slab 1 through photoetching, and a copper foil on a lower surface of the first layer dielectric slab 1 is completely etched off. The second microstrip patch 21 is reserved at the central position of the upper surface of the second layer dielectric slab 2, and a copper foil on a lower surface of the second layer dielectric slab 2 is also completely etched off. A copper foil on the upper surface of the third layer dielectric slab 3 is reserved and served as the first ground layer 31 of the asymmetric dielectric strip line. The coupling aperture 32 is etched on the first ground layer 31. The central conductor 33 is reserved at the central position of the lower surface of the third layer dielectric slab 3. Other parts of the lower surface of the third layer dielectric slab 3 are completely etched off. An upper surface of the fourth layer dielectric slab 4 is completely etched off, and a copper foil on the lower surface of the fourth layer dielectric slab 4 is reserved and served as the second ground layer 41 of the asymmetric dielectric strip line.
The first ground layer 31, the third layer dielectric slab 3, the central conductor 33, the fourth layer dielectric slab 4 and the second ground layer 41 together forming the asymmetric dielectric strip line refers to that: the third layer dielectric slab 3 above the central conductor 33 and the fourth layer dielectric slab 4 below are different and asymmetric. Specifically, the difference and asymmetry may be that: the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of different sizes, or of different dielectric constants, or of different sizes and dielectric constants. In the embodiment of the present invention, it is required that the dielectric constant of the third layer dielectric slab 3 is greater than that of the fourth layer dielectric slab 4, and the size of the third layer dielectric slab 3 is less than that of the fourth layer dielectric slab 4.
The third layer dielectric slab 3 and the fourth layer dielectric slab 4 in the asymmetric dielectric strip line are of different sizes, or of different material, which results in different dielectric constants, or the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of different sizes and material. By adopting the asymmetric dielectric strip line, an electric field strength above the central conductor 33 is far greater than an electric field strength below. Energy is mainly concentrated in a region of the third layer dielectric slab 3 between the central conductor 33 and the first ground layer 31. In this manner, energy exchange near the coupling aperture 32 has small influence on the electric field strength of the fourth layer dielectric slab 4, and overall energy can be effectively transmitted to the first microstrip patch 11 and the second microstrip patch 21. Therefore, the asymmetric strip line can better ensure effective transmission of the energy, and reducing backward radiation and spurious radiation of the energy. At the same time, the second ground layer 41 has a function of shielding energy, and is capable of preventing backward radiation of the energy, so as to ensure that most energy is radiated from the front of the microstrip antenna.
In the microstrip antenna provided in this embodiment, the third layer dielectric slab and the fourth layer dielectric slab are of asymmetric dielectrics, so that in the strip line, an upper-part electric field strength is far greater than an lower-part electric field strength, so as to improve energy coupling efficiency, ensure bandwidth of the antenna, and reduce the backward radiation of the microstrip antenna, thereby improving the F/B of the microstrip antenna. Moreover, the overall size of the microstrip antenna is greatly reduced, which is beneficial to the transmission of the antenna and the integration of the receiving circuits.
FIG 4 is a sectional view of a microstrip antenna provided in another embodiment of the present invention. As shown in FIG 4, the microstrip antenna includes: four layers of dielectric slabs that are disposed in parallel; where
a first microstrip patch 11 is disposed at a central position of an upper surface of a first layer dielectric slab 1; a second microstrip patch 21 is disposed at a central position of an upper surface of a second layer dielectric slab 2; a first ground layer 31 is disposed on an upper surface of a third layer dielectric slab 3, a coupling aperture 32 is opened at a central position of the first ground layer 31, a central conductor 33 is disposed at a central position of a lower surface of the third layer dielectric slab 3; and a second ground layer 41 is disposed on a lower surface of a fourth layer dielectric slab 4; and
the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of asymmetric dielectrics, so that an electric field above the central conductor 33 is greater than an electric field below.
The first ground layer 31, the third layer dielectric slab 3, the central conductor 33, the fourth layer dielectric slab 4 and the second ground layer 41 form an asymmetric dielectric strip line. The asymmetric dielectric strip line mainly refers to that: the third layer dielectric slab 3 above the central conductor 33 and the fourth layer dielectric slab 4 below are of asymmetric dielectrics, which specifically may be that: the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are of different sizes, or of different dielectric constants, or of different sizes and dielectric constants. In the embodiment of the present invention, the dielectric constant of the third layer dielectric slab 3 is greater than that of the fourth layer dielectric slab 4, and the size of the third layer dielectric slab 3 is less than that of the fourth layer dielectric slab 4.
Centers of the first microstrip patch 11 and the second microstrip patch 21 may overlap with each other, to ensure that energy transmitted towards a position above the microstrip antenna is the greatest. The first microstrip patch 11 and the second microstrip patch 21 may be both set to squares. A length of a side of the first microstrip patch 11 may be slightly greater than 1/2 dielectric wavelength, and a length of a side of the second microstrip patch 21 may be slightly less than 1/2 dielectric wavelength, which results from two resonances of the first microstrip patch 11 and the second microstrip patch 21. The length of the side of the first microstrip patch 11 is slightly greater than 1/2 dielectric wavelength, and the length of the side of the second microstrip patch 21 is slightly less than 1/2 dielectric wavelength, so as to ensure that energy between two resonances can be transmitted well, and facilitate the expansion of the bandwidth of the microstrip antenna.
The first ground layer 31 is shared by the second microstrip patch 21 and the asymmetric dielectric strip line. The coupling aperture 32 is opened at the first ground layer 31. The coupling aperture 21 is an elongated gap. Seen from the perspective diagram shown in FIG 5, the coupling aperture 32 is located right below the second microstrip patch 21, and is perpendicular to the central conductor 33. The coupling aperture 32 and the central conductor 33 are etched at the opposite side of the center of the third layer dielectric slab 3, thereby ensuring alignment precision between the coupling aperture 32 and the central conductor 33. As a standing wave voltage on the central conductor 33 with an open end demonstrates a cosine distribution, and at a position with 1/4 dielectric wavelength away from an open end, a voltage amplitude is maximum. When the coupling aperture 32 is located at this position, the maximum coupling of the energy can be implemented, thereby ensuring effective transmission of the energy. A length of the coupling aperture 32 may be set to be less than 1/2 dielectric wavelength, so that the coupling aperture 32 is in a non-resonant state. The reason lies in that, the coupling aperture 32 is an elongated gap, and the gap in a resonant state may also radiate electromagnetic waves. As a result, the backward radiation of the microstrip antenna is caused, and further working energy of the entire antenna is mismatched and a normal working state of the microstrip antenna is affected. Therefore, the coupling aperture 32 is required to be in a non-resonant state.
As shown in FIG 5, the central conductor 33 is located right below the coupling aperture 32. A length of a part that is of the central conductor 33 and exceeds an edge of the coupling aperture 32 is less than 1/4 dielectric wavelength, and a length of a part that does not exceed the edge of the coupling aperture 32 is equal to 1/4 dielectric wavelength. A width of the part that is of the central conductor 33 and exceeds the edge of the coupling aperture 32 and a width of the part that does not exceed the edge of the coupling aperture 32 are both greater than widths of other parts of the central conductor 33. The reason lies in that: the energy coupling and antenna radiation exist, so that a transmission line impedance near the coupling aperture 32 changes. Impedance matching needs to be performed on the microstrip antenna, and capacitive reactance is introduced at an open end section of the central conductor 33 to offset inductive reactance generated by the coupling aperture 32. A condition for the open end section being capacitive is that, under a condition that the length is less than 1/4 dielectric wavelength, capacitivity increases as a width increases. On the central conductor 33, a section of conductor in front of the coupling aperture 32 functions to transform the antenna impedance to high impedance for implementing the matching. A length of an impedance transforming section is approximately 1/4 dielectric wavelength, a width is greater than that of the central conductor 33, and smaller antenna impedance is transformed to be consistent with impedance of the asymmetric dielectric strip line. Through fine tuning of the length and width of a reactance adjustment section and the impedance transforming section, optimal bandwidth of the microstrip antenna can be implemented.
In order to increase the bandwidth of the microstrip antenna, a non-resonant cavity may be set in the third layer dielectric slab 3 and the fourth layer dielectric slab 4 around the coupling aperture 32, where the non-resonant cavity connects the first ground layer 31 and the second ground layer 41. The non-resonant cavity may be formed by at least four metal columns 5, and the metal columns 5 connect the first ground layer 31 and the second ground layer 41.
As an exemplary implementation manner, the non-resonant cavity may be formed by four metal columns 5, and a distance between any two adjacent metal columns 5 in the non-resonant cavity is less than 1/2 dielectric wavelength, to prevent energy mismatch caused by extra resonance generated in a region near the central conductor 33.
Transverse electric and magnetic field (Transverse Electric and Magnetic Field; TEM) waves or quasi-TEM waves are transmitted in the asymmetric dielectric strip line, which is determined by a metal boundary condition and a dielectric boundary condition of a transmission line (which is formed by the central conductor 33, the first ground layer 31 and the second ground layer 41). If dielectric constants of the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are different, a vertical electric field component or a magnetic field component is generated at a boundary of the two dielectrics. However, the vertical component is weak, and therefore, it is the quasi-TEM waves that are transmitted in the asymmetric dielectric strip line. If the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are merely of different sizes, and the dielectric constants of the third layer dielectric slab 3 and the fourth layer dielectric slab 4 are the same, it is the TEM waves that are transmitted in the asymmetric dielectric strip line.
The first ground layer 31 and the second ground layer 41 in the asymmetric dielectric strip line form a loop of a surface current together with the central conductor 33. A direction of the surface current on the first ground layer 31 and the second ground layer 41 is opposite to a direction of the surface current on the central conductor 33, while the total magnitude of the surface current on the first ground layer 31 and the second ground layer 41 is equal to that of the surface current on the central conductor 33. As the sizes and dielectric constants of the third layer dielectric slab 3 and the fourth layer dielectric slab 4 in the asymmetric dielectric strip line are different, the electric field strengths in the two layers of dielectric slabs are different. As a result, the magnitude of the surface current on the first ground layer 31 is different from that on the second ground layer 41. In the embodiment of the present invention, the dielectric constant of the third layer dielectric slab 3 is greater than that of the fourth layer dielectric slab 4, or the size of the third layer dielectric slab 3 is less than that of the fourth layer dielectric slab 4. Alternatively, it is possible that the dielectric constant of the third layer dielectric slab 3 is greater than that of the fourth layer dielectric slab 4, and the size of the third layer dielectric slab 3 is less than that of the fourth layer dielectric slab 4. Therefore, the surface current of the first ground layer 31 is far greater than that of the second ground layer 41.
When passing through the coupling aperture 32, the surface current on the first ground layer 31 is divided before the coupling aperture 32, and then combined after the coupling aperture 32. Such direction change of the surface current forms a non-TEM field near the coupling aperture 32. The coupling aperture 32 is located right above the central conductor 33 and may obtain the maximum non-TEM field strength. According to the boundary condition of the asymmetric strip line, under the influence of the non-TEM field, an induction current is generated on the second ground layer 41, corresponding to a mirror non-TEM field. A direction of the mirror non-TEM field is opposite to that of an original non-TEM field, functioning to offset the original non-TEM field.
It should be noted that, whether the coupling aperture 32 is in a resonant state has great influence on the induction current. Therefore, the length of the coupling aperture 32 may be reduced as much as possible, so that the length is less than a length in the resonant state, thereby decreasing the strength of the induction current. In addition, the change of a dielectric filling manner in the third layer dielectric slab 3 and the fourth layer dielectric slab 4 in the asymmetric strip line may also function to decrease the induction current.
A magnetic field part of the non-TEM field formed near the coupling aperture 32 is right consistent with a transverse magnetic field formed in the second layer dielectric slab 2 during radiation of the second microstrip patch 21. Therefore, the coupling aperture 32 is capable of exciting the radiation of the second microstrip patch 21. In the same way, the second microstrip patch 21 needs to be located right above the coupling aperture 32 to excite the most effective antenna radiation. The first microstrip patch 11 is also in a resonant state by coupling energy of the second microstrip patch 21, to radiate energy externally. As resonant frequencies for exciting the second microstrip patch 21 and the first microstrip patch 11 are different but close to each other, the bandwidth of the microstrip antenna is improved.
Due to the fast change of a magnetic field mode near the coupling aperture 32, many unnecessary transmission modes are excited in the asymmetric strip line, and a major one is a parallel wire TEM wave. As the parallel wire TEM wave exists, the antenna radiation efficiency may be decreased and the spurious radiation is brought, thereby reducing the cross polarization performance as well as side and backward radiation rejection capability of the antenna. The non-resonant cavity formed by the metal columns 5 may destruct the boundary condition of transmission of the parallel wire TEM wave and restrain the generation of the parallel wire TEM wave, thereby facilitating the reduction of interferences of antenna units in an antenna array, and facilitating the reduction of an interference of an active integrated antenna on active devices backward.
Relative bandwidth of the antenna is an important index for measuring the antenna performance. The relative bandwidth of the microstrip antenna is a ratio between a frequency range of the electromagnetic wave of the microstrip antenna radiation and a central frequency of the electromagnetic wave of the microstrip antenna radiation. Under the premise that the antenna relative bandwidth is ensured, return loss of the antenna needs to be further considered. The return loss refers to a ratio between electromagnetic waves radiated by the microstrip antenna and electromagnetic waves reflected back to the antenna. The return loss may also be used to measure the electromagnetic wave radiation efficiency of the antenna. FIG. 6 is a partial schematic diagram of return loss obtained through HFSS emulation of a microstrip antenna provided in the present invention. In FIG. 6, a horizontal coordinate indicates the frequency of the electromagnetic wave radiated by the microstrip antenna, and a vertical coordinate indicates the return loss of the electromagnetic wave radiated by the microstrip antenna. The relative bandwidth of the microstrip antenna may be calculated according to the frequency range and central frequency of the electromagnetic wave of the microstrip antenna provided in the present invention. In FIG 6, according to the frequency range corresponding to the partial relative bandwidth of the microstrip antenna, the vertical coordinate of corresponding return loss may be found. It can be concluded that, the return loss of the microstrip antenna provided in the present invention is less than -20 dB within 10% of the relative bandwidth, and the return loss is less than -18 dB within 12% of the relative bandwidth. Therefore, the return loss of the microstrip antenna provided in the present invention meets most application scenarios.
FIG 7 is a far-field directional diagram obtained through HFSS emulation of a microstrip antenna provided in the present invention. In FIG 7, Theta and phi are both spherical coordinates. Two orthogonal sections of the electromagnetic wave energy radiated by the microstrip antenna are shown in FIG. 7, where two polarization components and four curves exist in the same section. According to a coordinate scale, it can be obtained from a difference between a maximum value of co-polarization with greater energy and a maximum value of cross polarization with smaller energy, or from a ratio between front (0 degree) and back (180 degrees) of the same co-polarization curve that, the cross polarization of the microstrip antenna provided in the present invention is about -27.2 dB, and the F/B of the microstrip antenna is about 16.5 dB. The magnitude of the second ground layer influences the F/B of the antenna to some extent, and generally, expanding the second ground layer can reduce the backward radiation. Therefore, a single microstrip antenna may be used as an array unit. The second ground layer is expanded by increasing the number of array units, so that energy hardly diffracts to the back of the microstrip antenna, namely, reducing the backward radiation, thereby improving the F/B of the microstrip antenna. For example, a 4*4 microstrip antenna array is adopted, that is, 4 rows by 4 columns of microstrip antennas are connected. Generally, the F/B of the microstrip antenna array may be improved to 30 dB, and the size of the microstrip antenna array is only 54mm*54mm. If the number of the array units of the microstrip antenna is further increased, it can be implemented that the F/B of the microstrip antenna may be improved to higher than 50 dB.
FIG 8 is a schematic diagram of an in-band gain obtained through HFSS emulation of a microstrip antenna provided in the present invention. In FIG 8, a horizontal coordinate indicates the frequency of the electromagnetic wave radiated by the microstrip antenna, and a vertical coordinate indicates the gain of the electromagnetic wave radiated by the microstrip antenna, where the gain is another important index of the antenna performance, embodying the energy bunching capability of the antenna that serves as an energy transceiver. It can be calculated from FIG. 8 that, the average gain value of the electromagnetic wave radiated by the microstrip antenna provided in the embodiment of the present invention is about 7.33 dB, and in each frequency point within the frequency band range of the microstrip antenna, a fluctuation amplitude around the average value, namely, an in-band flatness, is about 0.1 dB. It can be seen that, on each frequency point within the frequency band range of the microstrip antenna provided in the present invention, the gains of radiated electromagnetic waves are close.
Finally, it should be noted that the above embodiments are merely provided for describing the technical solutions of the present invention, but not intended to limit the present invention. It should be understood by persons of ordinary skill in the art that although the present invention has been described in detail with reference to the embodiments, modifications can be made to the technical solutions described in the embodiments, or equivalent replacements can be made to some technical features in the technical solutions, as long as such modifications or replacements do not depart from the idea and the scope of the present invention.

Claims

A microstrip antenna, comprising: four layers of dielectric slabs disposed in parallel, wherein a first microstrip patch is disposed at a central position of an upper surface of a first layer dielectric slab; a second microstrip patch is disposed at a central position of an upper surface of a second layer dielectric slab; a first ground layer is disposed on an upper surface of a third layer dielectric slab, a coupling aperture is opened at a central position of the first ground layer, a central conductor is disposed at a central position of a lower surface of the third layer dielectric slab; and a second ground layer is disposed on a lower surface of a fourth layer dielectric slab; and
the third layer dielectric slab and the fourth layer dielectric slab are of asymmetric dielectrics, so that an electric field above the central conductor is greater than an electric field below.
The microstrip antenna according to claim 1, wherein a dielectric constant of the third layer dielectric slab is greater than a dielectric constant of the fourth layer dielectric slab, and/or the size of the third layer dielectric slab is less than that of the fourth layer dielectric slab.
The microstrip antenna according to claim 1 or 2, wherein a non-resonant cavity is disposed in the third layer dielectric slab and the fourth layer dielectric slab around the coupling aperture, and the non-resonant cavity connects the first ground layer and the second ground layer.
The microstrip antenna according to claim 3, wherein the non-resonant cavity is formed by at least four metal columns, and the metal columns connect the first ground layer and the second ground layer.
The microstrip antenna according to claim 4, wherein the non-resonant cavity is formed by four metal columns, and a distance between any two adjacent metal columns in the non-resonant cavity is less than 1/2 dielectric wavelength.
The microstrip antenna according to claim 1, wherein the coupling aperture is an elongated gap, and a length of the coupling aperture is less than 1/2 dielectric wavelength.
The microstrip antenna according to claim 6, wherein a length of the central conductor that exceeds an edge of the coupling aperture is less than 1/4 dielectric wavelength, and a length that does not exceed the edge of the coupling aperture is equal to 1/4 dielectric wavelength, a width of the central conductor that exceeds the edge of the coupling aperture and a width that does not exceed the edge of the coupling aperture are both greater than widths of other parts of the central conductor.
The microstrip antenna according to claim 1, wherein centers of the first microstrip patch and the second microstrip patch overlap with each other.
The microstrip antenna according to claim 1 or 8, wherein a length of a side of the first microstrip patch is slightly greater than 1/2 dielectric wavelength, and a length of a side of the second microstrip patch is slightly less than 1/2 dielectric wavelength.