Patent Publication Number: US-2023163467-A1

Title: Antenna module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110143604, filed on Nov. 23, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technology Field 
     The disclosure relates to an antenna module, and more particularly, to an antenna module having good antenna performance. 
     Description of Related Art 
     The frequency range of the antenna used for radar detection has, for example, a narrow bandwidth in 24 GHz (24.05 GHz to 24.25 GHz). How to provide such an antenna with good performance is a research direction in the art. 
     SUMMARY 
     The disclosure provides an antenna module having good antenna performance. 
     An antenna module of the disclosure includes a transceiver chip, a transmitting array antenna, a receiving array antenna, two bandpass filters, and two capacitors. The transmitting array antenna and the receiving array antenna are symmetrically disposed at two opposite sides of the transceiver chip. One of the two bandpass filters is disposed between the transceiver chip and the transmitting array antenna and is connected to the transceiver chip and the transmitting array antenna. The other bandpass filter is disposed between the transceiver chip and the receiving array antenna and is connected to the transceiver chip and the receiving array antenna. One of the two capacitors is disposed between the transmitting array antenna and the corresponding bandpass filter and is connected to the transmitting array antenna and the corresponding bandpass filter. The other capacitor is disposed between the receiving array antenna and the corresponding bandpass filter and is connected to the receiving array antenna and the corresponding bandpass filter. 
     In an embodiment of the disclosure, the antenna module further includes a power divider disposed between the transceiver chip and the bandpass filter corresponding to the transmitting array antenna, and is connected to the transceiver chip and the corresponding bandpass filter. 
     In an embodiment of the disclosure, the antenna module further includes a first impedance transformer, a second impedance transformer, a first microstrip, and a second microstrip, wherein the first impedance transformer, the second impedance transformer, the first microstrip, and the second microstrip are disposed between the transceiver chip and the power divider, the first impedance transformer is connected to the transceiver chip, the first microstrip is connected to the first impedance transformer and the power divider, the second impedance transformer is connected to the transceiver chip, the second microstrip is connected to the second impedance transformer and the power divider, and a length of the first microstrip is different from a length of the second microstrip. 
     In an embodiment of the disclosure, the antenna module further includes a third impedance transformer and a third microstrip, wherein the third impedance transformer and the third microstrip are disposed between the transceiver chip and the bandpass filter corresponding to the receiving array antenna, the third impedance transformer is connected to the transceiver chip, and the third microstrip is connected to the third impedance transformer and the corresponding bandpass filter. 
     In an embodiment of the disclosure, the antenna module further includes two transmission lines, wherein one of the two transmission lines is connected to the transmitting array antenna and the corresponding bandpass filter, the other transmission line is connected to the receiving array antenna and the corresponding bandpass filter, the two capacitors are connected to the two respective transmission lines, each of the capacitors includes a first line segment connected to the corresponding transmission line, the antenna module resonates at a frequency band, and a length of the first line segment is ¼ wavelength of the frequency band. 
     In an embodiment of the disclosure, each of the capacitors further includes a second line segment connected to the first line segment, and a length of the second line segment is ¼ wavelength of the frequency band. 
     In an embodiment of the disclosure, each of the capacitors further includes a sector-shaped block connected to the first line segment. 
     In an embodiment of the disclosure, each of the transmitting array antenna and the receiving array antenna includes a main line, a plurality of symmetric branch lines extending from the main line, and a plurality of patch units connected to the branch lines, the patch units are arranged in a form of an array, the antenna module resonates at a frequency band, and a length of the main line is a wavelength of the frequency band. 
     In an embodiment of the disclosure, the patch units include feeding ends connected to the branch lines, and a distance between two adjacent feeding ends is between 0.5 to 0.7 wavelength of the frequency band. 
     In an embodiment of the disclosure, the antenna module further includes a plurality of fourth impedance transformers disposed at intersections of the main line and the branch lines. 
     Based on the above, the transmitting array antenna and the receiving array antenna of the antenna module of the disclosure are symmetrically arranged at the two opposite sides of the transceiver chip, and the design of separating the transmitting array antenna and the receiving array antenna may improve antenna efficiency. In addition, a bandpass filter is disposed between the transceiver chip and the transmitting array antenna, and another bandpass filter is disposed between the transceiver chip and the receiving array antenna. The installation of the bandpass filters may prevent the electromagnetic interference (EMI) on the transmitting array antenna, and the bandpass filters filter out unwanted frequencies for the receiving array antenna. Moreover, a capacitor is provided between the transmitting array antenna and the corresponding bandpass filter, and another capacitor is provided between the receiving array antenna and the corresponding bandpass filter. This design avoids electrostatic discharge (ESD), thus preventing excessive static electricity from damaging the transceiver chip. Furthermore, the antenna module of the disclosure has better impedance matching with the above design. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an antenna module according to an embodiment of the disclosure. 
         FIG.  2    is a block diagram of the antenna module of  FIG.  1   . 
         FIG.  3    is a schematic cross-sectional view of a circuit board with the antenna module of  FIG.  1   . 
         FIG.  4    is a plot diagram of frequency vs. reflection loss (S 11 ) of the antenna module of  FIG.  1   . 
         FIG.  5    is a plot diagram of frequency vs. isolation of the antenna module of  FIG.  1   . 
         FIG.  6    is a plot diagram of radiation angle vs. antenna gain of the antenna module of  FIG.  1   . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG.  1    is a schematic diagram of an antenna module according to an embodiment of the disclosure. Referring to  FIG.  1   , an antenna module  100  of the present embodiment includes a transceiver chip  110 , a transmitting array antenna  140 , a receiving array antenna  140   a , two bandpass filters  120 , and two capacitors  123 . The antenna module  100  may be used as a radar to detect and transmit signals at the same time. In the present embodiment, the antenna module  100  is a millimeter wave antenna with a central frequency point at 24 GHz, and the transceiver chip  110  is a 24 GHz transceiver single-chip, microwave integrated circuit (transceiver MMIC), but the type of the transceiver chip  110  and the antenna frequency band are not limited thereto. 
     Since the transmitting end and the receiving end of the antenna module  100  perform wireless transmission at the same frequency at the same time, in the present embodiment, the transmitting end and the receiving end are divided into two portions. That is, the transmitting array antenna  140  and the receiving array antenna  140   a  may have better performance.  FIG.  1    shows the transmitting array antenna  140  and the receiving array antenna  140   a  are symmetrically disposed at the two opposite sides of the chip  110 . 
     A distance L 1  between the transmitting array antenna  140  and the receiving array antenna  140   a  is about 30 mm. A distance L 2  from the transceiver chip  110  to the right end of the circuit board installed in the antenna module  100  is about 27 mm. A distance L 3  from the transceiver chip  110  to the left end of the circuit board installed in the antenna module  100  is about 24 mm. A width L 4  of the transceiver chip  110  is about 6.5 mm. The length of the circuit board is about 57.5 mm, and a width L 5  of the circuit board is about 16 mm. 
     One of the two bandpass filters  120  (the bandpass filter  120  on the right of  FIG.  1   ) is disposed between the transceiver chip  110  and the transmitting array antenna  140  and is connected to the transceiver chip  110  and the transmitting array antenna  140 . The transmitting array antenna  140  is connected with the bandpass filter  120  in series to prevent the electrostatic interference (EMI). 
     The other bandpass filter  120  (the bandpass filter  120  on the left of  FIG.  1   ) is disposed between the transceiver chip  110  and the receiving array antenna  140   a  and is connected to the transceiver chip  110  and the receiving array antenna  140   a . The receiving array antenna  140   a  is connected with the bandpass filter  120  in series, and may filter out unwanted frequencies. 
     In the present embodiment, the bandpass filter  120  is, for example, a combination of two capacitors at positions B 1  and B 2  and an inductance between the positions B 1  and B 2 . These two capacitors may be grounded. Of course, the type of the bandpass filter  120  is not limited thereto. 
     Moreover, in the present embodiment, the antenna module  100  further includes a power divider  116  disposed between the transceiver chip  110  and the bandpass filter  120  (the bandpass filter  120  on the right in  FIG.  1   ) corresponding to the transmitting array antenna  140 , and the power divider  116  is connected to the transceiver chip  110  and the bandpass filter  120 . The power divider  116  is, for example, a Wilkinson power divider  116 , but the type of the power divider  116  is not limited thereto. 
     The antenna module  100  further includes a first impedance transformer  111 , a second impedance transformer  112 , a first microstrip  114 , and a second microstrip  115 . The first impedance transformer  111 , the second impedance transformer  112 , the first microstrip  114 , and the second microstrip  115  are disposed between the transceiver chip  110  and the power divider  116 . 
     Specifically, the first impedance transformer  111  and the second impedance transformer  112  are disposed at positions A 4  and A 5 . The first impedance transformer  111  is connected to the transceiver chip  110 , and the first microstrip  114  is connected to the first impedance transformer  111  and the power divider  116 . The second impedance transformer  112  is connected to the transceiver chip  110 , and the second microstrip  115  is connected to the second impedance transformer  112  and the power divider  116 . 
     In the present embodiment, the length of the first microstrip  114  is different from the length of the second microstrip  115 . In the present embodiment, the length of the first microstrip  114  is slightly longer than the length of the second microstrip  115  to compensate the phase difference. In addition, the transmitting end of the transceiver chip  110  is differential, so the first impedance transformer  111  and the second impedance transformer  112  located at the positions A 4  and A 5  are connected to the Wilkinson power divider  116 . The power divider  116  converts the signals transmitted by the first microstrip  114  and the second microstrip  115  to be in the same phase. 
     In addition, the antenna module  100  further includes a third impedance transformer  113  and a third microstrip  118 . The third impedance transformer  113  and the third microstrip  118  are disposed between the transceiver chip  110  and the bandpass filter  120  corresponding to the receiving array antenna  140   a . Specifically, the third impedance transformer  113  is disposed at the position A 1 . The third impedance transformer  113  is connected to the transceiver chip  110 , and the third microstrip  118  is connected to the third impedance transformer  113  and the bandpass  120 . 
     In the present embodiment, the path among the first impedance transformer  111 , the second impedance transformer  112 , and the corresponding bandpass filter  120  meets the impedance matching of 50 ohms. The path between the third impedance transformer  113  and the corresponding bandpass filter  120  meets the impedance matching of 50 ohms. 
     It should be mentioned that since the transceiver chip  110  transmits signals to the transmitting array antenna  140  via the first microstrip  114  and the second microstrip  115 , the power divider  116  is disposed between the transceiver chip  110  and the bandpass filter  120  corresponding to the transmitting array antenna  140  to obtain the signals in the same phase. On the other hand, since the signals is transmitted via a single third microstrip  118  between the transceiver chip  110  and the receiving array antenna  140   a , the power divider  116  is not needed. 
     In addition to the above differences, the configuration of components from the bandpass filter  120  to the transmitting array antenna  140  is the same as the configuration of components from the bandpass filter  120  to the receiving array antenna  140   a.    
     Specifically, the antenna module  100  further includes two transmission lines  122 . One of the two transmission lines  122  (the transmission line  122  on the right) is connected to the transmitting array antenna  140  and the corresponding bandpass filter  120 . The other transmission line  122  (the transmission line  122  on the left) is connected to the receiving array antenna  140  and the corresponding bandpass filter  120 . 
     One of the two capacitors  123  (the capacitor  123  on the right) is disposed between the transmitting array antenna  140  and the corresponding bandpass filter  120  (the bandpass filter  120  on the right) and is connected to the transmission line  122  (the transmission line  122  on the right) between the transmitting array antenna  140  and the corresponding bandpass filter  120 . The length of each of the transmission lines  122  may meet the impedance matching of 50 ohms. 
     The other capacitor  123  (the capacitor  123  on the left) is disposed between the receiving array antenna  140   a  and the corresponding bandpass filter  120  (the bandpass filter  120  on the left) and is connected to the transmission line  122  (the transmission line  122  on the left) between the receiving array antenna  140  and the corresponding bandpass filter  120 . 
     The installation of the capacitor  123  may avoid electrostatic discharge (ESD) and prevent excessive electrostatic current from passing through the transmitting array antenna  140  or the receiving array antenna  140   a  to damage the transceiver chip  110 . 
     In the present embodiment, each of the capacitors  123  includes a first line segment  124  (at positions C 1  and C 2 ) connected to the corresponding transmission line  122 , a second line segment  128  (at positions C 2  and C 4 ) connected to the first line segment  124  by bending, and a sector-shaped block  126  (at positions C 2  and C 3 ) connected to the first line segment  124 . The antenna module  100  resonates at a frequency band, the length of the first line segment  124  is ¼ wavelength of the frequency band, and the length of the second line segment  128  is ¼ wavelength of the frequency band, so as to have better impedance matching. 
     In the present embodiment, the antenna module  100  is a millimeter-wave antenna and has higher frequency. Therefore, through the adjustments of the first impedance transformer  111 , the third impedance transformer  113 , the two bandpass filters  120 , and the two sector-shaped capacitors  123 , better impedance matching between the transceiver chip  110  and the transmitting array antenna  140  and the receiving array antenna  140   a  may be achieved. 
     Moreover, each of the transmitting array antenna  140  and the receiving array antenna  140   a  includes a main line  143 , a plurality of symmetric branch lines  141 ,  142 ,  144 , and  145  extending from the main line  143 , and a plurality of patch units  131 ,  132 ,  133 , and  134  connected to these branch lines  141 ,  142 ,  144 , and  145 . 
     These patch units  131 ,  132 ,  133 , and  134  are arranged in an array. In the present embodiment, each of the transmitting array antenna  140  and the receiving array antenna  140   a  has four patch units  131 ,  132 ,  133 , and  134  presented in a 2×2 array. However, the number of the patch units  131 ,  132 ,  133 , and  134  and the dimension of the matrix are not limited thereto. The length and width of the patch units  131 ,  132 ,  133 , and  134  are about 3.1 mm and 3.1 mm, but not limited thereto. 
     The length of the main line  143  (positions A 2  and A 3 ) is a wavelength of the frequency band at which the antenna module  100  resonates, and may meet the impedance matching of 50 ohms. The patch units  131 ,  132 ,  133 , and  134  include respective feeding ends  131   a ,  132   a ,  133   a , and  134   a  connected to the respective branch lines  141 ,  142 ,  144 , and  145 . A distance D between two adjacent feeding ends is between 0.5 to 0.7 wavelength of the frequency band, for example, 0.6 wavelength, 7.48 mm, and may meet the impedance matching of 80 ohms. In addition, the lengths of the branch lines  141 ,  142 ,  144 , and  145  may also meet the impedance matching of 80 ohms. 
     Moreover, the antenna module  100  further includes fourth impedance transformers  147  and  148  disposed at the intersections of the main line  143  and the branch lines  141 ,  142 ,  144 , and  145  (the positions A 2  and A 3 ) to match the impedance. 
       FIG.  2    is a block diagram of the antenna module of  FIG.  1   . Please refer to  FIG.  2   .  FIG.  2    shows the antenna module  100  when signals are received and transmitted. The signals received by the receiving array antenna  140   a  are transmitted to the transceiver chip  110  via the capacitors  123 , the bandpass filters  120 , and the third impedance transformer  113 . The signals from the transceiver chip  110  are transmitted to the transmitting array antenna  140  via the first impedance transformer  111  and the second impedance transformer  112 , the power divider  116 , the bandpass filters  120 , and the capacitors  123 . 
     The transmitting array antenna  140  and the receiving array antenna  140   a  may operate synchronously. The antenna module  100  may detect the speed and the distance (scalar) of an object approaching or moving away with 1 transmit 1 receive (1T1R). When the antenna module  100  is operated with 1 transmit 2 receive (1T2R), it may be used to detect the features of objects in different orientations (i.e., vectors on a 2D plane). 
     It is worth mentioning that the antenna structure for 24 GHz radar detection currently on the market is configured on two independent circuit boards, and then the signals from the two circuit boards that are disposed one above another are connected in series. The antenna module  100  of the present embodiment is located on the same layer on the circuit board. 
       FIG.  3    is a schematic cross-sectional view of a circuit board with the antenna module of  FIG.  1   . Referring to  FIG.  3   , in the present embodiment, the circuit board  10  where the antenna module  100  is disposed includes, for example, a special board  12  (Ro4350B board) uppermost, the antenna module  100  (the transmitting array antenna  140 , the receiving array antenna  140   a , and a microstrip passive circuit disposed on the upper surface of the special board  12 ), and then four layers of regular boards  14 ,  16 ,  18 ,  20  (FR4 board) below. The special board  12  is pressed with the regular boards  14 ,  16 ,  18 , and  20 , so that there is no gap between the special plate  12  and the regular board  14 . Such a design enables the antenna module  100  to have good quality for 24 GHz at both the transmitting end and the receiving end, and compared with conventional design, the structure of the present embodiment has the advantage of cost saving. 
       FIG.  4    is a plot diagram of frequency vs. return loss (S 11 ) of the antenna module of  FIG.  1   . Referring to  FIG.  4   , in the present embodiment, the return loss of the transmitting array antenna  140  and the receiving array antenna  140   a  in the range of 24.05 GHz to 24.25 GHz may be at −10 dB or less, therefore achieving good performance. 
       FIG.  5    is a plot diagram of frequency vs. isolation of the antenna module of  FIG.  1   . Referring to  FIG.  4   , in the present embodiment, the distance L 1  ( FIG.  1   ) between the transmitting array antenna  140  and the receiving array antenna  140   a  is 30 mm, the isolation is −30 dB or less, and therefore the performance is good. 
       FIG.  6    is a plot diagram of radiation angle vs. antenna gain of the antenna module of  FIG.  1   . Referring to  FIG.  6   , in the present embodiment, the radiation angles of the main beams of the transmitting array antenna  140  and the receiving array antenna  140   a  may both be greater than 0 dBi from −40 degrees to +40 degrees, which achieves good performance. 
     Based on the above, the transmitting array antenna and the receiving array antenna of the antenna module of the disclosure are symmetrically arranged at two opposite sides of the transceiver chip, and the design of separating the transmitting array antenna and the receiving array antenna may improve antenna efficiency. In addition, a bandpass filter is provided between the transceiver chip and the transmitting array antenna, and another bandpass filter is provided between the transceiver chip and the receiving array antenna. The installation of the bandpass filters may prevent the electromagnetic interference (EMI) on the transmitting array antenna, and the bandpass filters filter out unwanted frequencies for the receiving array antenna. Moreover, a capacitor is provided between the transmitting array antenna and the corresponding bandpass filter, and another capacitor is provided between the receiving array antenna and the corresponding bandpass filter. This design avoids electrostatic discharge (ESD), preventing excessive static electricity from damaging the transceiver chip. Furthermore, the antenna module of the disclosure has better impedance matching with the above design.