Abstract:
A method of inhibiting cross-polarization of a microstrip antenna and a device thereof. Increase of a microstrip antenna array not only increases co-polarization, but also increases cross-polarization. When the microstrip antenna is designed and fabricated, the fabricated antenna is tested first. That is, intensity distribution of the cross-polarization in a radiation frequency band is tested first, and a radiation frequency that the cross-polarization is corresponding change with is found out when an antenna radiation unit is broken. A slot is fabricated in the corresponding antenna radiation unit to break the symmetry of the antenna radiation unit, so as to effectively inhibit the cross-polarization without influencing the co-polarization of the antenna radiation unit at a corresponding radiation frequency.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a method of inhibiting cross-polarization of a microstrip antenna and a device thereof, and more particularly to a method of inhibiting cross-polarization by fabricating a slot on a microstrip antenna and a device thereof to break symmetry thereof. 
         [0003]    2. Related Art 
         [0004]    With the progress of wireless communication technology, new communication products and technology have been developed. The progress of the technology enables the products to become light, thin, small, and short. Hence, the size antennae for receiving or transmitting signals in the communication products decides whether the products can become light, thin, small, and short or not. Among various technologies, the microstrip antenna technology is the most rapidly developing one in the antenna field. The microstrip antennae have advantages of small size, low weight, flexibility, and convenient combination with other elements and circuits. 
         [0005]    In a normal microstrip antenna design, the method of coupling power into antenna radiation units is roughly classified into direct-feed mode and indirect-feed mode. Typically, the direct-feed mode uses a coaxial cable or a microstrip line to connect a signal transmission line and the antenna radiation units, so the basic characteristics of the antenna is related much to the position of feed points. In another aspect, the indirect-feed mode provides more space for the combination of a feeding network and a related microwave circuit without breaking the structure of an antenna radiation element. Moreover, the increase of the antenna radiation units on the antenna radiation element not only increases the co-polarization, but also has increased influence on the cross-polarization as well. 
         [0006]    Therefore, it has become a problem for researchers to provide a microstrip antenna that inhibits the cross-polarization. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, the present invention is directed to provide a method of inhibiting cross-polarization of a microstrip antenna and a device thereof. The method inhibits the cross-polarization by fabricating a slot in a microstrip antenna and a device thereof to break symmetry thereof. 
         [0008]    The present invention is directed to provide a method of inhibiting cross-polarization of a microstrip antenna, including a microstrip antenna having a plurality of antenna radiation units for testing; the microstrip antenna is detected the intensity distribution of cross-polarization in a radiation frequency band for obtaining the relation of the area of the antenna radiation unit to the radiation frequency that is corresponding to the antenna radiation unit; the symmetry of any one of the antenna radiation units on the microstrip antenna are broken, so as to test a radiation frequency segment in which the cross-polarization is inhibited when the symmetry of the antenna radiation unit is broken in the radiation frequency band; a radiation frequency segment in which the cross-polarization is determined to be inhibited, and a slot is formed in the antenna radiation unit corresponding to the radiation frequency segment. 
         [0009]    The method of inhibiting cross-polarization of the microstrip antenna, wherein an area of the antenna radiation unit is inversely proportional to a corresponding radiation frequency, and the slot is fabricated by using a lithography process. The plurality of antenna radiation units is arranged in an array on the microstrip antenna. 
         [0010]    The method of inhibiting cross-polarization of the microstrip antenna is used to lies in effectively inhibiting the cross-polarization without influencing co-polarization of the radiation frequency corresponding to the antenna radiation unit. 
         [0011]    The present invention is directed to provide another method of inhibiting cross-polarization of a microstrip antenna, including a model of a pre-fabricated microstrip antenna having a plurality of antenna radiation units is established with a simulation software; the relevant parameters including a frequency of a feed signal and impedance of a feeding network are inputted into the simulation software; a radiation field type of the microstrip antenna is simulated with the simulation software, so as to obtain intensity distribution of the cross-polarization in a radiation frequency band of the microstrip antenna, for obtaining the relation of the area of the antenna radiation unit to the radiation frequency that is corresponding to the antenna radiation unit; the symmetry of any one of the antenna radiation units on the microstrip antenna that is broken is tested with the simulation software, so as to test a radiation frequency segment in which the cross-polarization is inhibited when the symmetry of the antenna radiation unit is broken in the radiation frequency band; a radiation frequency segment in which the cross-polarization is determined to be inhibited, a slot is fabricated in the antenna radiation unit corresponding to the radiation frequency segment in the simulation software, and a radiation field type of the microstrip antenna is simulated with the simulation software, so as to make comparison to determine whether the cross-polarization of a radiation frequency corresponding to the antenna radiation unit is inhibited or not. 
         [0012]    The method of inhibiting cross-polarization of the microstrip antenna, wherein an area of the antenna radiation unit is inversely proportional to a corresponding radiation frequency. The plurality of antenna radiation units is arranged in an array on the microstrip antenna. 
         [0013]    A microstrip antenna, for inhibiting cross-polarization, comprising a substrate, a plurality of antenna radiation units, disposed on the substrate, for receiving and transmitting a radio signal through resonance, a metal circuit, disposed on the substrate, and connected with the plurality of antenna radiation units, a signal feed portion, disposed on the metal circuit, for feeding in a signal current to the metal circuit, and receiving a signal current fed out from the metal circuit, and a slot, formed on one of the plurality of antenna radiation units, for inhibiting cross-polarization of a radiation frequency corresponding to the antenna radiation unit. 
         [0014]    The plurality of antenna radiation units is arranged in an array on the substrate. 
         [0015]    As for features and examples of the present invention, preferred embodiments will be illustrated in detail with reference to the accompanying drawings. 
         [0016]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
           [0018]      FIG. 1  is a flow chart of the process of inhibiting the cross-polarization of a microstrip antenna of the present invention; 
           [0019]      FIG. 2  is a flow chart of another process of inhibiting the cross-polarization of a microstrip antenna of the present invention; 
           [0020]      FIG. 3  is a schematic view of a microstrip antenna of the present invention in which the cross-polarization is not inhibited; 
           [0021]      FIG. 4  is a schematic view of a microstrip antenna of the present invention in which the cross-polarization is inhibited; 
           [0022]      FIG. 5A  is a diagram showing horizontal cross-polarization gain of the microstrip antenna in which the cross-polarization is not inhibited measured at the frequency of 3.7 GHz; 
           [0023]      FIG. 5B  is a diagram showing horizontal cross-polarization gain of the microstrip antenna in which the cross-polarization is not inhibited measured at the frequency of 3.8 GHz; 
           [0024]      FIG. 5C  is a diagram showing horizontal cross-polarization gain of the microstrip antenna of the present invention in which the cross-polarization is inhibited measured at the frequency of 3.7 GHz; and 
           [0025]      FIG. 5D  is a diagram showing horizontal cross-polarization gain of the microstrip antenna of the present invention in which the cross-polarization is inhibited measured at the frequency of 3.8 GHz. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The features and examples of the present invention are illustrated in detail below with reference to the accompanying drawings. 
         [0027]    The microstrip antenna of the present invention includes, but is not limited to, using the shape, number, and arrangement positions provided in the embodiment. The accompanying drawings are only for reference and illustrative purposes, but are not used to limit the present invention. 
         [0028]      FIG. 1  is a flow chart of the process of inhibiting the cross-polarization of a microstrip antenna of the present invention. The process is described as follows. A microstrip antenna having a plurality of antenna radiation units is provided for testing (step S 11 ). The intensity distribution of the cross-polarization of the microstrip antenna in a radiation frequency band is detected, for obtaining the relation of the area of the antenna radiation unit to the radiation frequency that is corresponding to the antenna radiation unit (step S 12 ). This step is performed for detecting which frequency segment is most seriously affected by the cross-polarization. Then, the symmetry of any one of the antenna radiation units on the microstrip antenna is broken, so as to test a radiation frequency segment in which the cross-polarization is inhibited when the symmetry of the antenna radiation unit is broken in the radiation frequency band (step S 13 ). Thus, the radiation frequency segment corresponding to any one of the antenna radiation units on the microstrip antenna in the radiation frequency band is obtained. As each antenna radiation unit contributes different signal intensity for each frequency segment, any one of the radiation units of the antenna has different influence on the cross-polarization. Therefore, in order to improve the influence of cross-polarization on a certain radiation frequency segment, the antenna radiation unit corresponding to the frequency segment must be found out first. Then, the radiation frequency segment in which the cross-polarization is to be inhibited is determined (step S 14 ). Next, a slot is formed in the antenna radiation unit corresponding to the radiation frequency segment (step S 15 ). As the symmetry of current flowing in the antenna radiation unit is broken after the slot is formed in the antenna radiation unit, the cross-polarization in the corresponding frequency segment is inhibited. 
         [0029]    The method of inhibiting cross-polarization of the microstrip antenna, wherein an area of the antenna radiation unit is inversely proportional to a corresponding radiation frequency, and the slot is fabricated by using a lithography process. The slot is formed by a lithography process. The plurality of antenna radiation units is arranged in an array on the microstrip antenna. 
         [0030]    When the method of inhibiting cross-polarization of a microstrip antenna is designed and applied, the microstrip antenna must be tested. The testing is performed by using an anechoic chamber, in which metal walls are used to isolate the interference of external signals, and an electromagnetic wave absorption material is attached on the walls from inside to reduce the reflected energy in the chamber. In the test, the distribution of parameters (e.g., amplitudes and phases) of the electromagnetic waves radiated by an antenna under test (AUT) in a near field space is detected by a scanning probe (during the test in embodiments of the present invention, the distance between the AUT and the scanning probe is 4 m). The scanning mode may be planar, cylindrical, or spherical. The RF (or microwave) signals are transmitted to a vector network analyzer (VNA) through a coaxial cable, so as to obtain relevant data. Then, the data are processed with methods such as probe radiation field type correction and numerical Fourier transformation in the background, so as to obtain the desired radiation (far field) field type of the AUT. 
         [0031]      FIG. 2  is a flow chart of another process of inhibiting cross-polarization of a microstrip antenna of the present invention. The process is described as follows. Firstly, when the method of inhibiting cross-polarization of a microstrip antenna is designed and applied, simulation software is applied to establish a model of a pre-fabricated microstrip antenna (step S 21 ). Next, relevant parameters including a frequency of a feed signal and impedance of a feeding network are inputted into the simulation software (step S 22 ). Then, a radiation field type of the microstrip antenna is simulated with the simulation software, so as to obtain the intensity distribution of the cross-polarization in a radiation frequency band of the microstrip antenna, for obtaining the relation of the area of the antenna radiation unit to the radiation frequency that is corresponding to the antenna radiation unit (step S 23 ). Then, the simulation software is used to test the situation when symmetry of any one of the antenna radiation units on the microstrip antenna is broken, so as to test a radiation frequency segment in which the cross-polarization is inhibited when the symmetry of the antenna radiation unit is broken in the radiation frequency band (step S 24 ). Next, a radiation frequency segment in which the cross-polarization is to be inhibited is determined (step S 25 ). Next, a slot is formed in the antenna radiation unit corresponding to the radiation frequency segment in the simulation software (step S 26 ). Then, the simulation software is used to simulate the radiation field type of the microstrip antenna, so as to make comparison to determine whether the cross-polarization of the radiation frequency corresponding to the antenna radiation unit is inhibited or not. 
         [0032]    The method of inhibiting cross-polarization of the microstrip antenna, wherein an area of the antenna radiation unit is inversely proportional to a corresponding radiation frequency, and the slot is fabricated by using a lithography process. The plurality of antenna radiation units is arranged in an array on the microstrip antenna. 
         [0033]    Then, a final product is fabricated according to the simulation results and is tested. The testing is performed by using an anechoic chamber, in which metal walls are used to isolate the interference of external signals, and an electromagnetic wave absorption material is attached on the walls from inside to reduce the reflected energy in the chamber. In the test, the distribution of parameters (e.g., amplitudes and phases) of the electromagnetic waves radiated by an antenna under test (AUT) in a near field space is detected by a scanning probe (during the test in embodiments of the present invention, the distance between the AUT and the scanning probe is 4 m). The scanning mode may be planar, cylindrical, or spherical. The RF (or microwave) signals are transmitted to a vector network analyzer (VNA) through a coaxial cable, so as to obtain relevant data. Then, the data are processed with methods such as probe radiation field type correction and numerical Fourier transformation in the background, so as to obtain the desired radiation (far field) field type of the AUT. 
         [0034]      FIG. 3  is a schematic view of a microstrip antenna of the present invention in which the cross-polarization is not inhibited. Referring to  FIG. 3 , the microstrip antenna includes a substrate  10 , a metal circuit  20 , a plurality of antenna radiation units  30 , and a signal feed portion  40 . The substrate  10  has a first surface  101  and a second surface  102  opposite to the first surface  101 . The metal circuit  20  is formed on the first surface  101 . A plurality of antenna radiation units  30  is disposed on the first surface  101 , for receiving and transmitting a radio signal through resonance. The metal circuit  20  is disposed on the first surface  101 , and is connected with the plurality of antenna radiation units  30 . 
         [0035]    The plurality of antenna radiation units  30  is arranged in an array on the substrate. 
         [0036]    The substrate  10  normally is a PCB. Certainly, other types of substrates are also applicable, and the substrate  10  can be a hard board or a flexible soft board. A material of the hard board is glass fiber, Bakelite or other materials, and a material of the flexible soft board is polyimide (PI), polyethylene terephthalate (PET), or other materials. 
         [0037]    The metal circuit  20  receives a feed signal from the signal feed portion  40 , and transmits the feed signal to a plurality of corresponding antenna radiation units  30 . 
         [0038]    The plurality of antenna radiation units  30  converts the feed signal transmitted from the metal circuit  20  to a radiation signal. 
         [0039]      FIG. 4  is a schematic view of a microstrip antenna of the present invention in which the cross-polarization is inhibited. Referring to  FIG. 4 , the microstrip antenna includes a substrate  110 , a metal circuit  120 , a plurality of antenna radiation units  130 , a signal feed portion  140 , and a slot  150 . The substrate  110  has a first surface  111  and a second surface  112  opposite to the first surface  111 . The metal circuit  120  is formed on the first surface  111 . A plurality of antenna radiation units is formed on the first surface  111 , and is arranged in an array. The metal circuit  120  is disposed on the first surface  111 , and is connected with the plurality of antenna radiation units  130 . 
         [0040]    The substrate  110  normally is a PCB. Certainly, other types of substrates are also applicable, and the substrate  110  can be a hard board or a flexible soft board. A material of the hard board is glass fiber, Bakelite or other materials, and a material of the flexible soft board is polyimide (PI), polyethylene terephthalate (PET), or other materials. 
         [0041]    The metal circuit  120  receives a feed signal from the signal feed portion  140 , and transmits the feed signal to a plurality of corresponding antenna radiation units  130 . 
         [0042]    The plurality of antenna radiation units  130  receives the feed signal transmitted from the metal circuit  120 , and converts it to a radio signal. 
         [0043]    The slot  150  is formed in the first surface  111 , for breaking symmetry of the current flowing in the antenna radiation units  130 , so as to inhibit the cross-polarization. The shape of the slot  150  may be, but is not limited to, a rectangle, square, and round. The slot  150  is formed by using a lithography process. 
         [0044]      FIGS. 5A and 5B  are diagrams showing horizontal cross-polarization gain of the microstrip antenna in which the cross-polarization is not inhibited measured at the frequencies of 3.7 GHz and 3.8 GHz respectively.  FIGS. 5C and 5D  are diagrams showing horizontal cross-polarization gain of the microstrip antenna of the present invention in which the cross-polarization is inhibited measured at the frequencies of 3.7 GHz and 3.8 GHz respectively. Referring to  FIGS. 5A ,  5 B,  5 C, and  5 D, it is known that after the slot is formed in the antenna radiation unit, the gain of horizontal cross-polarization is obviously reduced by 4-6 dB in average at the frequencies of 3.7 GHz and 3.8 GHz respectively. 
         [0045]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.