Patent Publication Number: US-2022239008-A1

Title: Common aperture antenna and communication device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/120444, filed on Oct. 12, 2020, which claims priority to Chinese Patent Application No. 201910999336.6, filed on Oct. 18, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of wireless communication technologies, and in particular, to a common aperture antenna and a communication device. 
     BACKGROUND 
     In the design process of a dual-band or multi-band array antenna, a common aperture technology is usually used to arrange array antennas of two frequency bands or even a plurality of frequency bands on the same mouth surface, so that the size of the multi-band array antenna can be greatly reduced. This feature provides advantages of small-scale, lightweight, and easy deployment. However, in a common aperture antenna design, antenna units of different frequency bands need to be arranged closely to each other. In this case, because of the large size and height of a low frequency antenna, a high frequency antenna is severely blocked, and a radiation pattern is greatly affected. 
     SUMMARY 
     Embodiments of this application provide a common aperture antenna and a communication device, to solve the problem that a low frequency antenna blocks a high frequency antenna in a dual-band or multi-band array antenna. 
     According to a first aspect, in an implementation, an embodiment of this application provides a common aperture antenna. The common aperture antenna includes: a reflection panel and a low frequency antenna unit, a frequency selective panel, and a high frequency antenna unit that are disposed on the same side as the reflection panel and that are arranged in sequence, where in the direction perpendicular to the reflection panel, the distance between the high frequency antenna unit and the reflection panel is greater than the distance between the low frequency antenna unit and the reflection panel, the frequency selective panel is disposed between the high frequency antenna unit and the low frequency antenna unit, and the frequency selective panel is a reflection ground of the high frequency antenna unit and has the total reflection characteristic for the working frequency of the high frequency antenna unit. In the solution in this embodiment, the high frequency antenna unit is disposed at a larger distance to the reflection panel than the low frequency antenna unit does, the frequency selective panel is disposed between the high frequency antenna unit and the low frequency antenna unit, and the frequency selective panel is used as an alternative reflection panel of the high frequency antenna unit, so that the distance between the high frequency antenna unit and its reflective surface is reduced. Therefore, the problem that the radiation pattern of the high frequency antenna unit is distorted due to an excessively large distance between the high frequency antenna unit and the reflection panel and the working bandwidth becomes narrow is avoided. 
     In an implementation, the transmittance of the frequency selective panel for high frequency signal is not greater than 10%. When the transmittance of the frequency selective panel for the high frequency signal is not greater than 10%, total reflection may be performed on the high frequency signal, so that the frequency selective panel serves as a reflection panel. 
     In an implementation, the frequency selective panel has a partial reflection characteristic for a low frequency signal. By using the partial reflection characteristic of the frequency selective panel, the signal radiated by the low frequency antenna unit is reflected back, and the signal reflected back by the frequency selective panel is counteracted with the reflected signal of the low frequency antenna unit, thereby loading the low frequency antenna unit, enhancing radiation performance and the working bandwidth of the low frequency antenna unit, further reducing the height of the low frequency antenna unit, and miniaturizing the common aperture antenna. 
     In an implementation, the transmittance range of the frequency selective panel for a low frequency signal is 20% to 80%. When a transmittance of the frequency selective panel for the low frequency signal ranges from 20% to 80% (including endpoints), the signal radiated by the low frequency antenna unit can be effectively reflected back, so that the reflected signal is counteracted with the reflected signal of the low frequency antenna unit, thereby loading the low frequency antenna unit. If the transmittance is less than 20%, the reflectance is too high. Consequently, the signal reflected back by the frequency selective panel is far stronger than the reflected signal of the low frequency antenna unit, and the two signals cannot be well counteracted with each other. If the transmittance is greater than 80%, the reflectance is too low. Consequently, the signal reflected back by the frequency selective panel is far weaker than the reflected signal of the low frequency antenna unit, and the two signals cannot be well counteracted with each other. 
     In an implementation, the frequency selective panel is disposed in parallel to the reflection panel, a vacuum wavelength corresponding to the working frequency of the low frequency antenna unit is λ, and the distance between the high frequency antenna unit and the low frequency antenna unit in the direction perpendicular to the reflection panel is less than or equal to 0.5 λ. When the distance between the high frequency antenna unit and the low frequency antenna unit in the direction perpendicular to the reflection panel is less than or equal to 0.5 λ, the distance between antenna units can become shorter, thereby reducing the array size and miniaturizing the antenna. 
     In an implementation, the distance between the low frequency antenna unit and the frequency selective panel in the direction perpendicular to the reflection panel is less than or equal to 0.1 λ. When the vertical distance between the low frequency antenna unit and the frequency selective panel is less than or equal to 0.1 λ, the frequency selective panel can achieve a maximum phase reversal of 72 degrees (0.2*360) for the reflected signal reflected by the frequency selective panel. This facilitates reversal of the reflected signal, and the reflected signal is counteracted with the reflected signal of the low frequency antenna unit, thereby improving the radiation performance of the low frequency antenna unit. 
     In an implementation, there are a plurality of high frequency antenna units, and the plurality of high frequency antenna units are distributed in a form of an array. The common aperture antenna further includes a plurality of first feeding units and a second feeding unit, the plurality of first feeding units respectively feed the plurality of high frequency antenna units, the second feeding unit feeds the low frequency antenna unit, the low frequency antenna unit includes at least one radiation arm, the radiation arm forms a hollow-out area, and a part of the first feeding unit passes through the hollow-out area and extends to electrically connect to the high frequency antenna unit. In this implementation, the first feeding unit is disposed to pass through the hollow-out area of the low frequency antenna unit. This helps to reduce the distance between the high frequency antenna unit and the low frequency antenna unit and miniaturize the common aperture antenna. 
     In an implementation, the reflection panel includes a top surface and a bottom surface. The low frequency antenna unit is located on the side of the top surface of the reflection panel. The first feeding unit passes through the reflection panel from the side of the bottom surface of the reflection panel and extends to electrically connect to the high frequency antenna unit to feed the high frequency antenna unit. The second feeding unit passes through the reflection panel from the side of the bottom surface of the reflection panel and extends to electrically connect to the low frequency antenna unit to feed the low frequency antenna unit. The low frequency antenna unit and the high frequency antenna unit are fixedly connected to the reflection panel by using the first feeding unit and the second feeding unit, to ensure a positional relationship between the low frequency antenna unit and the high frequency antenna unit. 
     In an implementation, the high frequency antenna units are distributed in the form of an array on a first plane, and the first plane is parallel to the frequency selective panel. The first plane on which the high frequency antenna unit is located is disposed in parallel to the frequency selective panel to ensure consistency of radiation performance of all high frequency antenna units and help miniaturize an entire architecture of the antenna. 
     In an implementation, the low frequency antenna unit includes a first group of dipole units and a second group of dipole units, the first group of dipole units and the second group of dipole units each include two radiation arms, the four radiation arms are distributed in a form of a 2×2 array architecture, and the two radiation arms of the first group of dipole units and the two radiation arms of the second group of dipole units are respectively located at opposite corners of the array architecture. In this embodiment, the low frequency antenna unit uses a bilinear polarized dipole unit, to enhance the radiation performance when being loaded on the frequency selective surface. 
     In an implementation, the radiation arm is a hollow-out annular structure. In a vertical projection of each radiation arm on the reflection panel, a projection area corresponding to the hollow-out area formed the radiation arm is an inner-arm area, and the first feeding unit passing through the inner-arm area extends toward the low frequency antenna unit and passes through the hollow-out area. Because the height of the low frequency antenna unit in the direction perpendicular to the reflection panel is lower than that of the high frequency antenna unit and the size of the low frequency antenna unit is larger than that of the high frequency antenna unit, to facilitate an array layout of the low frequency antenna unit and the high frequency antenna unit, a radiation arm of the low frequency antenna unit is designed as a hollow-out structure, so that the first feeding unit of the high frequency antenna unit can pass through the hollow-out area of the radiation arm to connect to the high frequency antenna unit. 
     In an implementation, the second feeding unit includes: a first feeder, a second feeder, and four printed circuit boards in a one-to-one correspondence with the radiation arms, the printed circuit boards are connected between the radiation arms and the reflection panel, each printed circuit board includes a ground panel, a signal cable, and a feeding welding plate, two of the printed circuit boards are first boards, the first boards are connected to the radiation arms of the first dipole units, the other two printed circuit boards are second boards, the second boards are connected to the radiation arms of the second dipole units, there is a first gap between the two first boards, signal cables on the two first boards are connected across the first gap, there is a second gap between the two second boards, signal cables on the two second boards are connected across the second gap, each radiation arm is electrically connected to the ground panel through the feeding welding plate, an external conductor of the first feeder is electrically connected to the ground panel of one of the first boards, an inner conductor of the first feeder is electrically connected to the signal cable of the first board, an external conductor of the second feeder is electrically connected to the ground panel of one of the second boards, and an inner conductor of the second feeder is electrically connected to the signal cable of the second board. For the same group of dipole units, two printed circuit boards correspondingly connected to the same group of dipole units serve as a radiation arm and a reflection panel. In this case, the two printed circuit boards correspondingly connected to the same group of dipole units are connected to reverse a phase of an electromagnetic signal and load an electromagnetic signal in the low frequency antenna unit. In addition, the communication signal is transmitted to the low frequency antenna unit through an inner chip and a ground cable of the external conductor and the printed circuit boards. In this way, a signal of the low frequency antenna unit is transmitted. 
     In an implementation, the two first boards are coplanar, the two second boards are coplanar, and the direction in which the first boards extend is orthogonal to the direction in which the second boards extend. The coplanar first boards and the coplanar second boards help signal cables in the printed circuit boards stably transmit a signal to the low frequency antenna unit. 
     According to a second aspect, in an implementation, this application provides a communication device. The communication device includes a signal transceiver and the foregoing common aperture antenna, where the common aperture antenna is connected to the signal transceiver through a plurality of radio signal transceiver channels. Signals are transmitted between the signal transceiver and the common aperture antenna through the radio signal transceiver channels. 
     In the common aperture antenna provided in the embodiments of the present disclosure, the high frequency antenna unit is disposed on the side of the low frequency antenna unit far away from the reflection panel, and the frequency selective panel is disposed between the high frequency antenna unit and the low frequency antenna unit, to solve a problem that the low frequency antenna blocks the high frequency antenna in a dual-band or multi-band array antenna. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe technical solutions in embodiments or the background of this application more clearly, the following describes the accompanying drawings used in embodiments or the background of this application. 
         FIG. 1  is a principle diagram of signal transmission of a communication device; 
         FIG. 2  is a schematic diagram of an array antenna according to a conventional technology; 
         FIG. 3  is a principle diagram showing that second radiation occurs in an array antenna according to a conventional technology; 
         FIG. 4  is a schematic diagram of a structure of a common aperture antenna according to an implementation of this application; 
         FIG. 5  is a top view of the common aperture antenna in  FIG. 3 ; 
         FIG. 6  is a main view of the common aperture antenna in  FIG. 3 ; 
         FIG. 7  is an enlarged view of the E portion of the common aperture antenna in  FIG. 5 ; 
         FIG. 8  is a diagram of a signal transmission path of a low frequency antenna unit of a common aperture antenna according to an embodiment; 
         FIG. 9  is a distribution diagram of printed circuit boards of a common aperture antenna according to an embodiment; 
         FIG. 10A  and  FIG. 10B  are a direction pattern of a corresponding high frequency antenna unit in a common aperture antenna according to an embodiment; and 
         FIG. 11  is a frequency response diagram of a corresponding frequency selective panel in a common aperture antenna according to an embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments of this application with reference to the accompanying drawings in the embodiments of this application. 
     With the advent of information age, communication devices propose higher requirements on information exchange. As shown in  FIG. 1 , a communication device includes a radio signal transceiver device and a radio signal transceiver antenna, which transmit signals between each other through a radio signal transceiver channel. The radio signal transceiver device may transmit a radio signal through the radio signal transceiver antenna, and may further receive an external radio signal through the radio signal transceiver antenna. As an important carrier of information transmission, the performance of wireless antenna determines an information transmission speed of the communication device. To meet diversified demands of information exchange, in actual antenna design and production, the common aperture technology is usually used to arrange array antennas of two frequency bands or even a plurality of frequency bands on the same mouth surface, so that the size of a multi-band array antenna can be greatly reduced. This feature provides advantages of small-scale and lightweight. However, as shown in  FIG. 2 , in a design of a common aperture antenna, the distance between an antenna radiator (a low frequency antenna unit  20  or a high frequency antenna unit  30 ) to a reflection panel  10  is ¼ wavelength of the respective working frequency. Because the working frequency of the low frequency antenna unit  20  is low and a corresponding wavelength is long, the vertical distance between the low frequency antenna unit  20  and the reflection panel  10  is large. On the contrary, the vertical distance between the high frequency antenna unit  30  and the reflection panel  10  is small. 
     Although such a product determined by its physical characteristics can facilitate a common aperture design of a multi-band antenna, such a design also brings other problems. As shown in  FIG. 3 , in a design in which a low frequency antenna unit  20  is lower than a common aperture antenna above a high frequency antenna unit  30 , antenna units of different frequency bands need to be arranged closely to each other. In this case, because of the large size and height of the low frequency antenna unit  20 , the high frequency antenna unit  30  is severely blocked, and its radiation pattern is greatly affected. In  FIG. 3 , arrow a represents the direction of the main radiation current on the high frequency antenna unit  30 . In this case, the main radiation current generates main radiation c. Arrow b represents the direction of the induced current generated by the low frequency antenna unit  20  due to the mutual coupling when the low frequency antenna unit  20  and the high frequency antenna unit  30  are close, and the induced current correspondingly generates an induced radiation d. The induced radiation d is superimposed on the main radiation c. Consequently, the direction pattern of the high frequency antenna unit  30  is distorted, and antenna performance is deteriorated. Therefore, how to prevent the low frequency antenna unit  20  from blocking the high frequency antenna unit  30  becomes a focus in designing the common aperture antenna. 
     In view of this, as shown in  FIG. 4  to  FIG. 6 , this application provides a common aperture antenna  100 , including a reflection panel  10  and a low frequency antenna unit  20 , a high frequency antenna unit  30 , and a frequency selective panel  60 , namely, a frequency selective surface (FSS), that are disposed on a same side as the reflection panel  10  and that are arranged in sequence. In the direction perpendicular to the reflection panel  10 , the distance between the high frequency antenna unit  30  and the reflection panel  10  is greater than the distance between the low frequency antenna unit  20  and the reflection panel  10 , the frequency selective panel  60  is disposed between the high frequency antenna unit  30  and the low frequency antenna unit  20 , and the frequency selective panel  60  is a reflection ground of the high frequency antenna unit  30  and has a total reflection characteristic for the working frequency of the high frequency antenna unit  30 . In this embodiment, as shown in  FIG. 6 , the used technical solution is that the high frequency antenna unit  30  is disposed above the low frequency antenna unit  20 , in other words, the distance between the high frequency antenna unit  30  and the reflection panel  10  is greater than the distance between the low frequency antenna unit  20  and the reflection panel  10 . In this way, the low frequency antenna unit  20  can be prevented from blocking the high frequency antenna unit  30 . However, if only upper and down positions of the high frequency antenna unit  30  and the low frequency antenna unit are switched, other problems arise. For example, the larger distance between the high frequency antenna unit  30  and the reflection panel  10  causes distortion of the direction pattern of the high frequency antenna unit and narrowing of the working bandwidth. In view of this, in this embodiment, the frequency selective panel  60  is further disposed between the high frequency antenna unit  30  and the low frequency antenna unit  20 . The frequency selective panel  60  has a spatial filtering function. The frequency selective panels may be classified into four basic types based on passing and blocking characteristics of surfaces for different frequencies of electromagnetic waves: a high-pass type, a low-pass type, a band-pass type, a band-stop type. The frequency selective panel  60  in this embodiment has a band-stop characteristic for a high frequency signal, and a transmittance of the frequency selective panel  60  for the high frequency signal is below 10% (including 10%). In this case, the frequency selective panel  60  serves as the reflection panel  10  to reflect the high frequency signal, thereby avoiding distortion of the radiation pattern of the high frequency antenna unit  30  and narrowing of the bandwidth. Furthermore, the total reflection effect of the frequency selective panel  60  for the high frequency signal shows a band-stop characteristic for the working frequency of the high frequency antenna unit  30 , so that the high frequency signal does not generate an induced current due to coupling to the low frequency antenna unit  20 , thereby avoiding generating induced radiation, which affects main radiation of the high frequency antenna unit  30 . 
     In the design in this embodiment, the high frequency antenna unit  30  is designed on the side of the low frequency antenna unit  20  far away from the reflection panel  60 , and the frequency selective panel  60  impedance to a high frequency signal is disposed between the high frequency antenna unit  30  and the low frequency antenna unit  20 . This prevents the low frequency antenna unit  20  from blocking the high frequency antenna unit, and furthermore, avoids distortion of the direction pattern caused by an excessively large distance between the high frequency antenna unit  30  and the reflection panel. In addition, the frequency selective panel  60  further blocks coupling of the high frequency signal to the low frequency antenna unit. 
     In one embodiment, as shown in  FIG. 6 , the transmittance of the frequency selective panel  60  for a low frequency signal ranges from 20% to 80%, and the frequency selective panel  60  has a partial reflection characteristic for the low frequency signal. The frequency selective panel  60  in this embodiment not only has a band-stop characteristic for the high frequency signal, but also has a partial reflection characteristic for the low frequency signal, in other words, the transmittance for the low frequency signal ranges from 20% to 80%. By properly designing the reflectance of the frequency selective panel  60  for the working frequency of the low frequency antenna unit  20 , the frequency selective panel  60  reflects a signal transmitted by the low frequency antenna unit  20 , and the signal reflected back by the frequency selective panel  60  is counteracted with the signal of the low frequency antenna unit  20 , thereby loading the low frequency antenna unit  20 , and enhancing radiation performance and the working bandwidth of the low frequency antenna unit  20 . In one embodiment, to help load the low frequency antenna unit  20 , the distance between the low frequency antenna unit  20  and the reflection panel  10  may be adjusted, to miniaturize the common aperture antenna. 
     To clearly explain that the loading function of the frequency selective panel  60  can reduce the height of the low frequency antenna unit  20  and implement a miniaturization design, the following provides a detailed description by using an embodiment.  FIG. 10A  and  FIG. 10B  and  FIG. 11  are respectively the direction pattern of a high frequency antenna unit of a common aperture antenna and a frequency response diagram of a frequency selective panel according to one embodiment. In the embodiment, the working frequency of the high frequency antenna unit is 3.5 GHz to 4.5 GHz, and the working frequency of a low frequency antenna unit is 0.69 GHz to 0.96 GHz. As can be learned from  FIG. 11 , a reflection loss of the frequency selective panel is less than 0.1 dB in the frequency range of 3.5 GHz to 4.5 GHz. The effect is approximately equivalent to total reflection. The reflection loss of the frequency selective panel is approximately 4 dB in the frequency range of 0.69 GHz to 0.96 GHz, showing a partial reflection characteristic. As shown in  FIG. 6 , an antenna structure design corresponding to the frequency selective panel with the performance is that the distance between the low frequency antenna unit  20  and the reflection panel  10  is 36 mm, the distance between the low frequency antenna unit  20  and the frequency selective panel  60  is 10 mm, and the distance between the frequency selective panel  60  and the high frequency antenna unit  30  is 18 mm. In this case, the height of the entire common aperture antenna is 64 mm. According to a design in a conventional technology, the height of the entire common aperture antenna is determined by the height of the low frequency antenna unit. However, the height of the low frequency antenna unit working on the frequency band of 0.69 GHz to 0.96 GHz usually ranges from 70 mm to 90 mm, which is greater than 64 mm. In other words, by properly designing the frequency selective panel  60  to load the low frequency antenna unit  20 , the radiation performance and the working bandwidth of the low frequency antenna unit  20  can be enhanced, and further, the distance between the low frequency antenna unit  20  and the reflection panel  10  is reduced to miniaturize the entire antenna. 
     It should be noted that a process principle of loading the low frequency antenna unit  20  by the frequency selective panel  60  is shown in  FIG. 8 . S 1  is a signal fed to the low frequency antenna unit. A part of the signal enters the low frequency antenna unit  20 , and another part of the signal is reflected by the low frequency antenna unit  20  due to impedance mismatch, to form a first reflected signal S 2 . After receiving a signal, the low frequency antenna unit  20  converts the received signal into a low frequency electromagnetic signal for radiation. The radiated electromagnetic signal is reflected back by the frequency selective panel  60 , is received by the low frequency antenna unit  20 , and is transmitted to a feeding port (which is a feeding terminal of the low frequency antenna unit  20 ), to form a second reflected signal S 3 . By properly designing and adjusting the reflectance and the reflection phase of the frequency selective panel  60  for the low frequency signal, the distance between the frequency selective panel  60  and the low frequency antenna unit  20 , and a structure of the low frequency antenna unit  20 , amplitudes of the second reflected signal S 3  and the first reflected signal S 2  (two reflected signals) can become the same, the phase difference is 180 degrees, and the two signals are counteracted with each other. In this way, reflection is reduced. The reflection reduction means that the radiation signal is enhanced, thereby enhancing the radiation performance and the working bandwidth of the low frequency antenna unit  20 . After the low frequency antenna unit  20  provided in this application is adjusted, the reflected signals are counteracted with each other. In a working process, because there is no reflected signal or reflected signals are reduced, a signal radiation capability of the low frequency antenna unit  20  is improved. 
     In one embodiment, as shown in  FIG. 6 , the vacuum wavelength corresponding to the working frequency of the low frequency antenna unit  20  is λ, and the distance between the high frequency antenna unit  30  and the low frequency antenna unit  20  in the direction perpendicular to the reflection panel  10  is less than or equal to 0.5 λ. On one hand, the distance between the high frequency antenna unit  30  and the low frequency antenna unit  20  in the direction perpendicular to the reflection panel  10  is set in consideration of an array antenna size design. This helps to miniaturize the antenna. On the other hand, because the antenna designed in this embodiment is applied to a wireless communication device, if the distance between the high frequency antenna unit  30  and the low frequency antenna unit  20  in the direction perpendicular to the reflection panel  10  is greater than 0.5 λ, the mutual effect between the high frequency antenna unit  30  and the low frequency antenna unit  20  becomes smaller, and a decoupling effect cannot be achieved. 
     In one embodiment, as shown in  FIG. 6  and  FIG. 8 , the distance between the low frequency antenna unit  20  and the frequency selective panel  60  in the direction perpendicular to the reflection panel  10  is less than or equal to 0.1 λ. Herein, λ is the vacuum wavelength corresponding to the working frequency of the low frequency antenna unit  20 . When the vertical distance between the low frequency antenna unit  20  and the frequency selective panel  60  is less than or equal to 0.1 λ, the frequency selective panel  60  can implement a maximum of 72 degrees (0.2*360) of phase adjustment on the second reflected signal S 3 , adjust the vertical position of the frequency selective panel  60  and the pattern structure within the range of 0.1 λ based on a simulation result, and then adjust the structure of the low frequency antenna unit  20 . In this way, a good loading effect can be achieved, and a miniaturized antenna structure can be obtained. 
     In one embodiment, as shown in  FIG. 6 , the common aperture antenna  100  further includes a first feeding unit  50  and a second feeding unit  40 . The reflection panel includes  10  a top surface  12  and a bottom surface  14 . The low frequency antenna unit  20  is located on the side of the top surface  12  of the reflection panel  10 . The first feeding unit  50  passes through the reflection panel  10  from the side of the bottom surface  14  of the reflection panel  10  and extends to electrically connect to the high frequency antenna unit  30  to feed the high frequency antenna unit  30 . The second feeding unit  40  passes through the reflection panel  10  from the side of the bottom surface  14  of the reflection panel  10  and extends to electrically connect to the low frequency antenna unit  20  to feed the low frequency antenna unit  20 . The low frequency antenna unit  20  and the high frequency antenna unit  30  are fixedly connected to the reflection panel  10  by using the first feeding unit  50  and the second feeding unit  40 , to ensure a positional relationship between the low frequency antenna unit  20  and the high frequency antenna unit  30 . In addition, the first feeding unit  50  and the second feeding unit  40  are electrically connected to the high frequency antenna unit  30  and the low frequency antenna unit  20  respectively for signal transmission. In another implementation, the first feeding unit  50  and the second feeding unit  40  may alternatively not pass through the reflection panel  10 . For example, the first feeding unit  50  and the second feeding unit  40  are disposed on the side of the reflection panel  10  facing toward the low frequency antenna unit  20 , and feeders of the first feeding unit  50  and the second feeding unit  40  may extend from the surface (the surface facing toward the low frequency antenna unit  20 ) of the reflection panel  10  to a feeding grid. 
     In one embodiment, as shown in  FIG. 5  to  FIG. 7 , the low frequency antenna unit  20  includes a first group of dipole units and a second group of dipole units, the first group of dipole units and the second group of dipole units each include two radiation arms  22 , the four radiation arms are distributed in the form of a 2×2 array architecture, and the two radiation arms  22  of the first group of dipole units and the two radiation arms  22  of the second group of dipole units are respectively located at opposite corners of the array architecture. In this embodiment, the low frequency antenna unit  20  uses a bilinear polarized dipole unit, to enhance the radiation performance when being loaded on the frequency selective surface  60 . 
     In one embodiment, as shown in  FIG. 5 , there are a plurality of high frequency antenna units  30 , the plurality of high frequency antenna units  30  are distributed on a first plane in the form of an array, and the first plane is parallel to the frequency selective panel  60 . There are a plurality of first feeding units  50 , and the plurality of first feeding units  50  are in a one-to-one correspondence with high frequency antenna units  30 . The low frequency antenna unit  20  includes at least one radiation arm  22 . The radiation arm  22  forms a hollow-out area in the center. A part of the first feeding unit  50  passes through the hollow-out area and extends to electrically connect to the high frequency antenna unit. Specifically, in a vertical projection of each radiation arm  22  on the reflection panel  10 , a projection area corresponding to the hollow-out area in the center formed the radiation arm  22  is an inner-arm area, and the first feeding unit  50  passing through the inner-arm area extends toward the low frequency antenna unit  20  and passes through the hollow-out area. Because the height of the low frequency antenna unit  20  in the direction perpendicular to the reflection panel  10  is lower than that of the high frequency antenna unit  30  and the size of the low frequency antenna unit  20  is larger than that of the high frequency antenna unit  30 , to facilitate an array layout of the low frequency antenna unit  20  and the high frequency antenna unit  30 , the first feeding unit  50  is disposed to pass through the hollow-out area, to reduce the distance between the low frequency antenna unit  20  and the high frequency antenna unit  30  and miniature the antenna product. 
     In the common aperture antenna provided in this application, in the direction perpendicular to the reflection panel  10 , a part of the high frequency antenna unit  30  is disposed opposite to the low frequency antenna unit  20 . A feeding apparatus, namely, the second feeding unit  40 , of this part of the high frequency antenna unit  30  passes through the radiation arm  22  of the low frequency antenna unit  20  to form the hollow-out area and extends to electrically connect to the high frequency antenna unit  30 . In an implementation, the second feeding unit  40  is a coaxial cable, and the coaxial cable may be perpendicular to the reflection panel  10 . 
     As shown in  FIG. 4 , in one embodiment, the radiation arm  22  of the low frequency antenna unit  20  is designed as a hollow-out circular structure, so that the first feeding unit  50  of the high frequency antenna unit  30  passes through the hollow-out area of the radiation arm to connect to the high frequency antenna unit  30 . Specifically, as shown in  FIG. 4  and  FIG. 5 , in an embodiment, the first feeding unit  50  disposed on the inner-arm area passes through the circular structure to connect the high frequency antenna unit  30  and the reflection panel  10 . The design of the circular structure enables the high frequency antenna unit  30  to pass through the circular structure to be fastened to the reflection panel  10 , so that the high frequency antenna unit  30  and the low frequency antenna unit  20  have an overlap part in the projection interval of the reflection panel  10 , that is, horizontal space of the reflection panel  10  is fully utilized. 
     According to a conventional technology, a low frequency antenna unit  20  and a relatively large antenna spacing (including a horizontal spacing and a vertical spacing) are used in a coaxial unit technology to prevent the low frequency antenna unit from blocking the high frequency antenna unit. However, in this technical solution, a large distance needs to be kept between high frequency antenna units to ensure that a surrounding high frequency antenna unit is not blocked. In a common aperture array antenna designed by using such a solution, the distance between the high frequency antenna units is usually 0.8 times a high frequency wavelength. As a result, the size of the array antenna is large, and the integration degree is not high enough. Furthermore, the large-angle beam scanning requirement is not met. For an array antenna with a large scanning angle, the spacing between antenna units in the array needs to be approximately 0.5 times a wavelength to avoid a large appended lobe within the scanning angle. In the common aperture antenna in this embodiment, as shown in  FIG. 3  and  FIG. 4 , the high frequency antenna unit  30  is disposed on the side of the low frequency antenna unit  20  far away from the reflection panel  10 , and the frequency selective panel  60  is disposed between the high frequency antenna unit  30  and the low frequency antenna unit  20 . Such a design not only prevents the low frequency antenna unit  20  from blocking the high frequency antenna unit  30 , but also reduces electromagnetic couplings between the low frequency antenna unit  20  and the high frequency antenna unit  30 , so that the horizontal spacing between the low frequency antenna unit  20  and the high frequency antenna unit  30  that are located in an area outside the arm becomes smaller. Similarly, the frequency selective panel  60  is disposed between the high frequency antenna unit  30  and the low frequency antenna unit  20 , and the radiation arm of the low frequency antenna unit  20  is designed as a hollow-out structure. In this way, a design of the high frequency antenna unit  30  in the inner-arm area is implemented, thereby greatly improving a miniaturized design of the antenna. In this case, large space is saved when the same signal strength is obtained. 
     In one embodiment, as shown in  FIG. 6  to  FIG. 8 , the second feeding unit  40  includes: a first feeder, a second feeder, and four printed circuit boards  42  in a one-to-one correspondence with the radiation arms  22 , the printed circuit boards  42  are connected between the radiation arms  22  and the reflection panel  10 , each printed circuit board  42  includes a ground panel  424 , a signal cable  422 , and a feeding welding plate  426 , two of the printed circuit boards  42  are first boards, the first boards are connected to the radiation arms  22  of the first dipole units, the other two printed circuit boards  42  are second boards, the second boards are connected to the radiation arms  22  of the second dipole units, there is a first gap between the two first boards, signal cables  422  on the two first boards are connected across the first gap, there is a second gap between the two second boards, signal cables  422  on the two second boards are connected across the second gap, each radiation arm  22  is electrically connected to the ground panel  424  through the feeding welding plate  426 , an external conductor of the first feeder  150  is electrically connected to the ground panel  424  of one of the first boards, an inner conductor of the first feeder  150  is electrically connected to the signal cable  422  of the first board, an external conductor of the second feeder is electrically connected to the ground panel  424  of one of the second boards, and an inner conductor of the second feeder is electrically connected to the signal cable  422  of the second board. Specifically, as shown in  FIG. 7 , the first board is used as an example. One end of the signal cable  422  is connected to the inner chip of the first feeder  150 , and the ground cable of the first feeder  150  is electrically connected to the ground panel  424  to transmit a signal between the first feeder  150  and the low frequency antenna unit  20 . A communication signal is transmitted to the low frequency antenna unit  20  through the inner chip and the ground cable of the first feeder  150  and the printed circuit board  42 , thereby transmitting a signal of the low frequency antenna unit  20 . 
     According to the foregoing structure design, as shown in  FIG. 8 , a signal is transmitted to the printed circuit board  42  from the signal cable along the path  51 . The transmitted signal is received by the ground panel  424 , is delivered to the low frequency antenna unit  20 , and is radiated under the action of the low frequency antenna unit  20 . On one hand, the radiated signal is reflected back by the frequency selective panel  60  along the path S 3  and enters the printed circuit board  42 . On the other hand, a signal reflected by the low frequency antenna unit  20  to the printed circuit board  42  is transmitted along the path S 2 . According to the Balun principle, the transmission amplitudes of reflected signals on the path S 2  and the path S 3  are equivalent but the phase difference is  180  degrees. Therefore, the phase of the electromagnetic signal is reversed to load the low frequency antenna unit. 
     In one embodiment, as shown in  FIG. 9 , two first boards are coplanar, e.g., a printed circuit board  42   a  and a printed circuit board  42   c  are coplanar; and two second boards are coplanar, e.g., a printed circuit board  42   b  and a printed circuit board  42   d  are coplanar. The direction in which the first boards extend is orthogonal to the direction in which the second boards extend. The coplanar first boards and the coplanar second boards help signal cables in the printed circuit boards stably transmit a signal to the low frequency antenna unit. 
     In addition, this application further provides a communication device. The communication device has a built-in signal transceiver, configured to process a signal. An interface of the signal transceiver is connected to the feeding unit of the foregoing common aperture antenna to transmit and receive a signal. The signal transceiver may transfer a current signal to the feeding unit through the interface, and a current is transmitted to the low frequency antenna unit and the high frequency antenna unit through the feeding unit. Under the action of the low frequency antenna unit and the high frequency antenna unit, a change in the current is converted into an electromagnetic signal, and the electromagnetic signal is propagated outward in a form of an electromagnetic wave. Similarly, an external electromagnetic signal is converted into a current signal by using the low frequency antenna unit and the high frequency antenna unit, is fed back to the feeding unit, and then is transferred to the signal transceiver for processing. In one embodiment, the communication device may be a radar or a base station, and the signal transceiver may be an RRU (radio remote unit). The radio remote unit may be shown in  FIG. 1 , may send a plurality of signals to the antenna, to implement transmission of the plurality of signals. 
     The foregoing descriptions are merely example implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.