High-aperture-efficiency cross grid antenna and bandwidth improving method thereof

Abstract

The invention discloses a high aperture efficiency cross grid antenna and a bandwidth improving method thereof, and the cross grid antenna optimizes the current branch layout, and employs a cross configuration mode to adjust the reverse current while maintaining the same-direction radiation of the same-direction current branch part, thereby improving the bandwidth of the antenna. And the reverse current branches are introduced into the lower substrate through the metal through holes and are arranged in a staggered manner, so that the reverse current radiation is effectively counteracted, and the gain of the antenna unit is remarkably improved. Besides, on the basis of an original single-branch radiation structure, an expansion branch is added, and the length of the expansion branch is close to that of an original branch, so that a resonance point is formed in a range close to the original working frequency, and the working bandwidth of the antenna is effectively expanded. Compared with the condition that the expansion branches are not added, the working bandwidth of the antenna is improved by 9.79% after the expansion branches are added. According to the invention, the design of the broadband 28GHz frequency band cross grid antenna is realized, and the radiation bandwidth and the gain bandwidth of the antenna can be further improved on the basis of satisfying high aperture efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication antennas, and specifically, is a high aperture efficiency grid antenna based on PCB technology and a bandwidth expansion design technology thereof. Background Art

[0002] Communication antenna technology plays a vital role in modern wireless communications, radar detection, satellite communications and other fields. Especially in the 28GHz frequency band, with the rapid development of 5G and future 6G communications, this frequency band provides key support for high-speed data transmission and large-capacity communications. The 28GHz frequency band can effectively meet the needs of high-resolution imaging, precise positioning and high-speed data transmission, and will become an important part of future communication systems. However, traditional metal patch antennas have disadvantages such as low aperture efficiency and narrow bandwidth in this frequency band, resulting in poor high-frequency signal transmission performance, which makes it difficult to meet the high bandwidth and gain requirements of high-speed, large-capacity communication systems.

[0003] Prior art: China's invention patent "A Differentially Fed Asymmetric Antenna Array" (Publication No.: CN218569233U) discloses a method for constructing an asymmetric antenna array through differential feeding; the method combines a rectangular grid antenna with a patch antenna to achieve efficient asymmetric MIMO system design. By precisely designing the feed end structure, the scheme can achieve self-decoupling, and utilize differential feeding to effectively adapt the self-decoupling design to the asymmetric array, thereby significantly improving the transmit-receive isolation while maintaining a compact size, meeting the requirements of high-performance MIMO antennas.

[0004] Prior art: China's invention patent "A Grid Dielectric Resonant Antenna" (publication number: CN114336062A) discloses a grid-shaped dielectric resonant antenna; the method excites two metal patches through differential feeding, and symmetrically connects the grid-shaped dielectric block with the metal sheet, thereby achieving an organic combination of the two. The dielectric resonant antenna not only inherits the advantages of the grid antenna and the dielectric antenna, but also achieves miniaturization of the antenna size through a simplified feeding method, while effectively reducing high-frequency losses, and has high performance advantages and application value.

[0005] As contemporary communication chips are increasingly miniaturized, the requirements for antenna size are becoming more and more stringent, so high aperture efficiency has become one of the key indicators for measuring antenna performance. In the prior art, traditional rectangular grid array antennas usually use a radiation branch spacing in units of wavelength, which results in its aperture efficiency failing to reach the optimal level. On this basis, the present invention proposes a high aperture efficiency cross-grid antenna. Unlike the prior art, the cross-grid antenna uses a clever branch layout design to ensure that the reverse current can be effectively offset while significantly reducing the spacing between the radiation branches, thereby greatly improving the aperture efficiency of the antenna. In addition, on the basis of the original cross-grid antenna, the present invention further increases the extension branches and successfully broadens the working bandwidth of the antenna by introducing additional resonance points. In summary, the cross-grid antenna significantly improves the aperture efficiency and bandwidth performance of the antenna through innovative branch layout and structural optimization. Summary of the invention

[0006] The technical problem to be solved by the present invention is that existing antenna arrays have certain limitations in aperture efficiency and working bandwidth, and cannot meet the high performance requirements in high-frequency communication systems and high-speed data transmission. Especially in high-frequency bands, traditional antenna arrays usually have problems with low aperture efficiency and narrow working bandwidth, which limits their application in modern communications. The present invention proposes a high-aperture efficiency cross-grid antenna and a bandwidth enhancement method thereof, aiming to significantly improve the aperture efficiency and broaden the working bandwidth of the antenna by optimizing the antenna structure design, thereby improving the overall performance, meeting the demand for high-gain and high-bandwidth antennas, and providing a more efficient solution for future communication technologies.

[0007] The technical solution adopted by the present invention is:

[0008] A high aperture efficiency cross grid antenna, in which reverse current parts are cross-arranged to achieve mutual cancellation of reverse current parts, while unidirectional current parts can be superimposed on each other to achieve improved radiation gain.

[0009] In the above technical solution, further, the cross grid antenna includes two layers of upper and lower dielectric substrates, wherein the front side of the upper dielectric substrate is provided with a top metal layer as the cross grid antenna main body, and the back side is provided with a back metal layer as a cross branch, which is the reverse current crossing part of the cross grid antenna, and the back side of the lower dielectric substrate is set as a metal ground and connected to the outer conductor of the coaxial cable, and there is no metal on its front side, and the two layers of dielectric substrates are electrically connected through metal through holes to achieve effective current coupling and signal transmission.

[0010] Furthermore, utilizing the property that electric current will flow in opposite directions when passing through half a wavelength, two antenna branches with a total length of nearly 3.5 wavelengths are constructed, wherein the branches of the current 1 in the same direction are arranged longitudinally, while the branches of the current 2 in the opposite direction are arranged in a cross form, and some branches are connected to the back side of the upper dielectric substrate through metal through holes, so that the branches of the current 1 in the same direction can radiate simultaneously, while the radiation of the branches of the current 2 in the opposite direction mostly cancels each other out.

[0011] Furthermore, the symmetrical parts of the two antenna branches are fed by differential feeding, so that the currents in the longitudinal parts of the two branches flow in the same direction, while the currents in the cross parts flow in opposite directions, thereby achieving the cancellation of reverse currents to reduce the radiation interference caused by the reverse currents.

[0012] Furthermore, the cross-grid antenna main body is composed of a number of longitudinal branches arranged symmetrically in two rows, and two adjacent longitudinal branches in opposite directions are connected by a first oblique branch, and all the first oblique branches have the same direction; the cross branches are second oblique branches symmetrical to the first oblique branches, the first oblique branches and the second oblique branches form a cross-symmetry, and both ends of the second oblique branches are connected to the cross-grid antenna main body through metal through holes, thereby forming two antenna branches as a whole.

[0013] Furthermore, a circular groove with a radius of 1.065 mm is provided at the differential feeding position, the radius of the metal through hole is 0.255 mm, and the width w of the antenna branch is 1 =0.64mm, the length of the longitudinal branch is l 1 =3.21mm, the connecting section between the first oblique branch and the longitudinal branch is horizontal, and its length is l 2 =1.35mm, the length of the first oblique branch is l 3 =2mm, the antenna operating frequency is 28GHz, and the operating bandwidth is 0.96%.

[0014] Furthermore, an additional extended branch is provided outside the longitudinal branch, and the length of the extended branch is close to that of the longitudinal branch, thereby introducing a new resonance point whose operating frequency is close to the original operating frequency, thereby achieving a widening of the operating bandwidth of the cross-grid antenna.

[0015] Furthermore, a circular groove with a radius of 1.065 mm is provided at the differential feeding position, the radius of the metal through hole is 0.255 mm, and the widths of the longitudinal branches and the cross branches are both wc 1 =0.6mm, the length of the longitudinal branch is lc 1 =3.16mm, the connecting section between the first oblique branch and the longitudinal branch is horizontal, and its length is lc 2 =1.15mm, the length of the first oblique branch is the same as the second oblique branch, which is lc 5=1.76mm, the width of the extended branch is wc 2 =0.8mm, the connecting section between the extended branch and the longitudinal branch is horizontal, and its length is lc 4 =1.7mm, the length of the extended branch is lc 3 =2.43mm, the antenna working center frequency is 26.98GHz, and the working bandwidth is 10.75%.

[0016] Furthermore, the input signal is first connected to a broadband balun, and then the output signal of the balun is connected to the corresponding feeding position of the cross grid antenna through a coaxial line, thereby realizing differential feeding of the antenna.

[0017] Furthermore, the processing plane size of the cross grid antenna unit is 16mm×24mm, and the antenna area is 7.2mm×17.3mm.

[0018] The present invention provides a high-performance cross-grid antenna design with high aperture efficiency and wide operating frequency band. The aperture efficiency of the antenna is improved by optimizing the branch arrangement. At the same time, on the basis of the original cross-grid antenna structure, the operating bandwidth of the antenna is effectively expanded by extending the branches. The radiation performance of the antenna is further improved by using differential feeding technology, thereby realizing a cross-grid antenna with excellent performance. This design not only improves the aperture efficiency of the antenna, but also broadens the operating frequency band of the antenna while ensuring efficient radiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of a three-dimensional model of a cross-grid antenna with extended branch bandwidth expansion according to the present invention;

[0020] Figure 2 is a top view of the top metal layer and the second metal layer structure of the cross grid antenna of the present invention;

[0021] Figure 3 is a top view of the cross-grid antenna structure without extended branches described in the present invention;

[0022] Figure 4 It is a current distribution diagram of the resonant frequency point of the cross-grid antenna without extended branches described in the present invention;

[0023] Figure 5 The cross grid antenna S without extended branches described in the present invention dd11 Simulation result diagram;

[0024] Figure 6 is a two-dimensional radiation pattern of the cross-grid antenna without extended branches described in the present invention;

[0025] Figure 7It is a current distribution diagram of two resonant frequency points of the cross grid antenna after adding extended branches described in the present invention;

[0026] Figure 8 The cross grid antenna S with extended branches described in the present invention is dd11 Simulation result diagram;

[0027] Fig. 9 is the simulation result of the cross grid antenna with extended branches described in the present invention, (a) is S dd11 Simulation result diagram, (b) is the two-dimensional radiation pattern of the center frequency;

[0028] Figure 1 Middle: 1. first dielectric substrate, 2. second dielectric substrate, 3. longitudinal branch, 4. first oblique branch, 5. second oblique branch, 6. extended branch, 7. metal through hole, 8. circular groove. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention; it is obvious that the described embodiments are part of the embodiments of the present invention, rather than all the design and preparation situations. Based on the embodiments of the present invention, all other embodiments obtained by researchers in this field without creative work are within the scope of protection of the present invention.

[0030] The present invention relates to a high aperture efficiency cross grid antenna and its bandwidth extension technology. The design optimizes the branch arrangement and utilizes the current reversal characteristics to achieve miniaturization of the antenna, effectively improving the aperture efficiency of the antenna. At the same time, by extending the branch length, the working bandwidth of the antenna is broadened, and the working ability of the antenna in a broadband range is improved. The antenna adopts PCB process design to ensure structural stability and high performance, and is suitable for high-speed communication systems.

[0031] The cross-grid antenna design of the present invention is composed of two layers of dielectric materials. The front of the first layer of dielectric is the main radiation part of the cross-grid antenna, and the back is the other half of the cross part, and the two layers are connected by metal through-holes. This design effectively ensures that the antenna can achieve reverse current radiation cancellation while avoiding overlapping of the cross parts, thereby ensuring the stability of the antenna structure. A metal ground plane is set on the back of the second layer of dielectric to suppress backward radiation and effectively reflect energy, thereby improving the gain of the antenna. No metal is etched on the front of this layer, and a circular groove is opened on the ground plane, and a metal through-hole is introduced in the dielectric plate. Correspondingly, a metal through-hole is also introduced at the same position of the first layer of dielectric plate to achieve direct connection between the coaxial line and the antenna part, thereby achieving differential feeding, thereby effectively improving the radiation efficiency of the antenna, reducing electromagnetic interference, and optimizing the overall signal transmission performance.

[0032] The cross-grid antenna of the present invention has a structure similar to that of a traditional rectangular grid array antenna and a half-wave dipole antenna, and both achieve radiation through half-wavelength current distribution. In the traditional rectangular grid array antenna design, the length of the long side is one wavelength of the corresponding operating frequency, and the length of the short side is half a wavelength of the corresponding operating frequency. Since the current on the long side reverses direction every time it passes half a wavelength, the radiation on the long side cancels each other out; and the current on the short side has the same direction, so that the short side branches can radiate together. In terms of arrangement, the long side boundary points of each row are located at the midpoint of the adjacent long sides, thereby ensuring that the short sides can radiate together, and the short side spacing is one wavelength of the corresponding operating frequency.

[0033] Unlike traditional rectangular grid antennas, the cross-grid antenna of the present invention achieves an increase in radiation gain through staggered branches. Specifically, the cross-grid antenna uses a design in which two branches are staggered to ensure that the branches of the same-direction current are arranged longitudinally, while the branches of the opposite current are cross-arranged to achieve mutual cancellation of current radiation. Compared with traditional rectangular grid antennas, this structure has a more compact arrangement, and the spacing between radiating branches is less than half a wavelength. The present invention significantly improves the aperture efficiency of the grid antenna and effectively reduces the interference between radiating branches. In addition, the cross-grid antenna adopts a differential feeding method, which effectively enhances the stability of the antenna structure and further improves the overall performance.

[0034] On the basis of achieving effective radiation of the cross-grid antenna, the present invention further improves the working bandwidth of the antenna by adding extended branches. Since the antenna operating frequency is closely related to the length of the branches, the longer the branch length, the lower the antenna operating frequency, and each branch length corresponds to a specific resonant frequency point. Therefore, the above-mentioned cross-grid antenna usually has only one resonance point, resulting in a relatively limited working bandwidth. In order to solve this problem, the present invention symmetrically adds extended branches to the longitudinally arranged radiation branches. The extended branches are similar in length to the longitudinal branches, so that the operating frequency of the extended branches is close to the original operating frequency, generating a new resonance point. This design enables the antenna to achieve a wider operating frequency band while increasing the resonance point. Since the extended branches are the same as the longitudinal branches, the current can be in the same direction at the operating frequency, and the extended branches can also effectively radiate, thereby further enhancing the performance of the antenna. Although the addition of extended branches will cause a slight decrease in the antenna gain, the overall gain remains at a high level, fully ensuring the high performance of the antenna and successfully achieving a significant expansion of the working bandwidth.

[0035] According to a specific embodiment of the present invention, this embodiment discloses a design technology of a high aperture efficiency cross-grid antenna with bandwidth extension, wherein the antenna is composed of two layers of Rogers 6002 dielectric material (each dielectric substrate has a thickness of 0.254 mm) and three layers of metal layers (each metal layer has a thickness of 0.018 mm). The specific structure includes a bottom metal stratum, a second metal cross-branch portion, and a top metal cross-grid antenna main body portion.

[0036] The design and modeling process of the antenna was completed in the HFSS software environment. To facilitate analysis, the transparency of the upper material was set in the software so that the three-dimensional structure of the antenna can be clearly displayed. Figure 1 shown. Figure 2 It shows a detailed view of the top layer cross grid antenna and the second layer cross branches.

[0037] Specifically, the cross-grid antenna in this embodiment is composed of three parts: the bottom metal ground (i.e., the first layer of dielectric substrate), the second layer of cross-branch parts, and the top layer of cross-grid antenna main body (i.e., the second layer of dielectric substrate). Among them, the bottom metal ground is provided with a circular groove with a radius of 1.065mm at the differential feeding position, and a metal through-hole with a radius of 0.255mm is introduced at the corresponding position of the two layers of dielectric substrate to realize coaxial differential feeding. At the same time, the second layer of dielectric substrate also needs to introduce a metal through-hole with a radius of 0.255mm at the connection part of the cross-branch to ensure the electrical connection between the upper and lower branch parts.

[0038] The cross grid antenna is prepared by using the gold immersion process. Each branch is periodically designed with longitudinal branches and cross branches to form four longitudinal branches and three cross branches. Then, two branches of the same length are symmetrically cross-arranged, and the second oblique branch is connected to the back of the upper dielectric board through a metal through-hole.

[0039] Preferably, the cross-grid antenna is fed by a lumped port. In this embodiment, the two lumped ports are respectively set to 1W power and the input phases are respectively set to 0 degrees and 180 degrees to realize differential feeding. The impedance of the port is set to 50Ω. In the simulation design, the antenna is judged whether it is working properly by observing the current distribution characteristics of the antenna. Specifically, the current direction of the longitudinal branch part should be the same to achieve radiation enhancement; and in the cross branch part, the current direction should be opposite to achieve the effect of radiation cancellation.

[0040] The structure of the cross grid antenna without extended branches is as follows: Figure 3 Considering that the antenna adopts differential feeding, the S parameter is S dd11 To characterize, S dd11 The calculation formula is as follows:

[0041] Sdd11 = 0.5×(S 11 + S 22 -S 21 -S 12 ) (1)

[0042] Among them, S 11 and S 22 Represent the reflection coefficients of the input port and output port respectively; S 21 represents the transmission coefficient of the signal from the input port to the output port through the network; and S 12 is the reverse transmission coefficient,

[0043] By optimizing the longitudinal branch length, the cross-branch length, and the overall branch width of the antenna, the optimization target is set to S dd11 The lowest value is less than -20dB in 27.5GHz-28.5GHz. The optimized parameters are: w 1 =0.64mm, l 1 =3.21mm, l 2 =1.35mm, l 3 =2mm.

[0044] Antenna S dd11 The simulation results are as follows Figure 4 As shown in Figure 2. According to the simulation results, the antenna operating frequency is 28 GHz and the operating bandwidth is 0.96% (27.86 to 28.13 GHz). In addition, the antenna radiation pattern is shown in Figure 2. Figure 5 As shown, the maximum gain is 11.3dBi and the sidelobe level is less than -11dBi.

[0045] After the length of the branch of the cross grid antenna is determined, the antenna operating frequency is determined accordingly. There is only one resonance point in the operating frequency band, so the bandwidth is narrow. In order to increase the bandwidth, the present invention adds an extended branch to the longitudinal branch of the cross grid antenna. Specifically, the extended branch increases the distance between the original longitudinal branch and the newly added longitudinal branch by adding a small section of transverse branch, and at the same time makes the length of the extended branch slightly longer than the original longitudinal branch, so that the operating frequency of the extended branch is slightly lower than the operating frequency of the original branch.

[0046] After the introduction of the extended branch, the antenna operating frequency can be expanded from the original one resonance point to two resonance points, significantly improving the antenna operating bandwidth. Although the antenna gain is lower than before the addition of the extended branch, the gain still remains at a high level within the operating bandwidth.

[0047] Since the operating frequency of the extended branch is different from that of the original branch, the width of the extended branch needs to be different from that of the original branch to achieve better matching. By optimizing the length and width of the original branch and the horizontal and vertical lengths of the extended branch, the S near the two operating frequencies is finally dd11 All are lower than -10dB, ensuring good performance. The simulation results are as follows Figure 6 As shown in the figure, it can be seen that the center frequency of the antenna is 26.98GHz and the working bandwidth is 10.75%, which is 9.79% higher than the bandwidth before the expansion branch is added. The radiation pattern of the antenna at the two resonant points is shown in Figure 7 As shown in the figure, the gains are 9.5dBi and 12.1dBi respectively, which is lower than before the expansion branch is added. The gain curve within the working bandwidth is as follows Figure 8 As shown, it can be seen that the antenna gain is greater than 6dBi within the bandwidth. The optimized parameters are: wc 1 =0.6mm, wc 2 =0.8mm, lc 1 =3.16mm, lc 2 =1.15mm, lc 3 =2.43mm, lc 4 =1.7mm, lc 5 =1.76mm.

[0048] The antenna of the present invention can achieve a bandwidth of about 10% in the 28 GHz frequency band, and most of the in-band gains are above 8 dBi, the maximum gain reaches 11.2 dBi, and the aperture efficiency reaches 62%.

[0049] The above describes the specific examples of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make different changes or modifications within the scope of the claims without affecting the essential content of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

Claims

1. A high aperture efficiency cross grid antenna, characterized in that: In the cross-grid antenna, the reverse current parts are cross-arranged to achieve mutual cancellation of the reverse current parts, while the same-direction current parts can be superimposed on each other to achieve the improvement of radiation gain.

2. The high aperture efficiency cross-grid antenna according to claim 1, characterized in that: The cross grid antenna comprises an upper and lower dielectric substrate, wherein the front side of the upper dielectric substrate is provided with a top metal layer as the cross grid antenna body, and the back side is provided with a back metal layer as a cross branch, which is the reverse current crossing part of the cross grid antenna; the back side of the lower dielectric substrate is set as a metal ground and connected to the outer conductor of the coaxial line, and there is no metal on the front side; the two dielectric substrates are electrically connected through metal through holes to achieve effective current coupling and signal transmission.

3. The high aperture efficiency cross-grid antenna according to claim 2, characterized in that: Taking advantage of the property that electric current will flow in opposite directions when passing half a wavelength, two antenna branches with a total length of nearly 3.5 wavelengths are constructed, in which the branches of the current in the same direction are arranged longitudinally, while the branches of the current in the opposite direction are arranged in a cross form. Some branches are connected to the back side of the upper dielectric substrate through metal through holes, so that the branches of the current in the same direction can radiate simultaneously, while the radiation of the branches of the opposite current part mostly cancels each other out.

4. The high aperture efficiency cross-grid antenna according to claim 3, characterized in that: The symmetrical parts of the two antenna branches are fed by differential feeding, so that the currents in the longitudinal parts of the two branches flow in the same direction, while the currents in the cross parts flow in the opposite direction, thereby achieving the cancellation of reverse currents to reduce the radiation interference caused by the reverse currents.

5. The high aperture efficiency cross-grid antenna according to claim 3, characterized in that: The main body of the cross-grid antenna is composed of a number of longitudinal branches arranged symmetrically in two rows, and at the same time, two adjacent longitudinal branches in opposite directions are connected by a first oblique branch, and all the first oblique branches have the same direction; the cross branches are second oblique branches symmetrical to the first oblique branches, the first oblique branches and the second oblique branches form a cross symmetry, and the two ends of the second oblique branches are connected to the cross-grid antenna main body through metal through holes, thereby forming two antenna branches as a whole.

6. The high aperture efficiency cross-grid antenna according to claim 5, characterized in that: A circular groove with a radius of 1.065mm is provided at the differential feeding position, the radius of the metal through hole is 0.255mm, the width of the antenna branch w1=0.64mm, the length of the longitudinal branch is l1=3.21mm, the connecting section of the first oblique branch and the longitudinal branch is horizontal, and its length is l2=1.35mm, the length of the first oblique branch is l3=2mm, the antenna operating frequency is 28GHz, and the operating bandwidth is 0.96%.

7. The high aperture efficiency cross-grid antenna according to claim 5, characterized in that: An additional extended branch is arranged outside the longitudinal branch, and the length of the extended branch is close to that of the longitudinal branch, thereby introducing a new resonance point whose operating frequency is close to the original operating frequency, thereby achieving the expansion of the working bandwidth of the cross grid antenna.

8. The high aperture efficiency cross-grid antenna according to claim 7, characterized in that: A circular groove with a radius of 1.065mm is provided at the differential feeding position, the radius of the metal through hole is 0.255mm, the width of the longitudinal branches and the cross branches are both wc1=0.6mm, the length of the longitudinal branches is lc1=3.16mm, the connecting section between the first oblique branch and the longitudinal branch is horizontal, and its length is lc2=1.15mm, the first oblique branch and the second oblique branch have the same length, which is lc5=1.76mm, the width of the extended branch is wc2=0.8mm, the connecting section between the extended branch and the longitudinal branch is horizontal, and its length is lc4=1.7mm, the length of the extended branch is lc3=2.43mm, the working center frequency of the antenna is 26.98GHz, and the working bandwidth is 10.75%.

9. The high aperture efficiency cross-grid antenna according to claim 7, characterized in that: The input signal is first connected to a broadband balun, and then the output signal of the balun is connected to the corresponding feeding position of the cross-grid antenna through a coaxial cable, thereby realizing differential feeding of the antenna.

10. The high aperture efficiency cross-grid antenna according to claim 7, characterized in that: The cross-grid antenna unit has a processing plane size of 16 mm×24 mm, and an antenna area of ​​7.2 mm×17.3 mm.

Images