Common-aperture broadband wide-angle scanning phased array antenna

Abstract

The invention discloses a common-caliber broadband wide-angle scanning phased-array antenna, which comprises a pair of inverted F-shaped antennas of an L wave band and a back cavity U-shaped slotted microstrip phased-array antenna array of an X wave band, and is characterized in that the inverted F-shaped antennas are arranged on one diagonal line of a metal plate of a regular N polygon, and N is an even number greater than or equal to 4; a dielectric layer is arranged on the metal plate, and the back cavity U-shaped slotted microstrip phased-array antenna array of the X wave band is arranged on the dielectric layer; the method can meet the development requirements of a modern SAR system.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, in particular to a common-aperture wideband wide-angle scanning phased array antenna. Background Art

[0002] Synthetic Aperture Radar (SAR) [1-4] has been widely used in the fields of electronic systems such as marine monitoring, geographical mapping, disaster warning, environmental monitoring, and target recognition due to its technical advantages of all-weather imaging and large-scale monitoring. Currently, the working frequency bands of spaceborne SAR systems mainly range from P band to X band. To achieve effective detection and classification of multiple targets, multi-band SAR technology has become an important development direction. By working in cooperation with dual frequencies or multiple frequencies, advanced SAR systems can obtain the multi-dimensional resolution characteristics, penetration characteristics, and reflection characteristics of target objects, which has made the common-aperture antenna technology increasingly attracting the attention of the academic community. However, limited by the antenna installation space of mobile platforms, the traditional scheme of using dual apertures to achieve dual-band operation is often difficult to be practically applied. Therefore, designing a single-aperture dual-band shared antenna architecture has become a more feasible technical path.

[0003] Existing common-aperture array antennas generally face two major technical bottlenecks: First, limited by the existing antenna structure, it is difficult to achieve broadband operating characteristics, such as [1] K. Naishadham, R. Li, L. Yang, T. Wu, W. Hunsicker, and M. Tentzeris, “A shared-aperture dual-band planar array with self-similar printed folded dipoles,” IEEE Trans. Antennas Propag., vol. 61, no. 2, pp. 606–613, Feb. 2013, [2] C.-X. Mao, S. Gao, Y. Wang, Q. Luo, and Q.-X. Chu, “A shared-aperture dual-band dual-polarized filtering-antenna-array with improved frequency response,” IEEE Trans. Antennas Propag., vol. 65, no. 4, pp. 1836–1844, Apr. 2017, [3] S. Zhou, P. Tan, and T. Chio, “Wideband, low profile P-and Ku-band shared aperture antenna with high isolation and low cross-polarisation,” IET Microw., Antennas Propag., vol. 7, no. 4, pp. 223–229, Mar. 2013; Second, the element spacing usually exceeds 0.6λh (λh is the wavelength of the highest frequency point), resulting in a limited grating lobe-free scanning range, such as [4] L. L. Shafai, W. A. Chamma, M. Barakat, P. C. Strickland, and G. Seguin, “Dual-band dual-polarized perforated microstrip antennas for SAR applications,” IEEE Trans. Antennas Propag., vol. 48, no. 1, pp. 58–66, Jan. 2000, [5] S.-H. Hsu, Y.-J. Ren, and K.Chang, "A dual-polarized planar-array antenna for S-band and X-band airborne applications," IEEE Antennas Propag. Mag., vol. 51, no. 4, pp. 70–78, Aug. 2009; [6] X. Qu, S. Zhong, Y. Zhang, and W. Wang, "Design of an S / X dual-band dual-polarized microstrip antenna array for SAR applications," IET Microw., Antennas Propag., vol. 1, no. 2, pp. 513–517, Apr. 2007. Summary of the Invention

[0004] To solve the problems existing in the prior art, the object of the present invention is to provide a common-aperture broadband wide-angle scanning phased array antenna, which can meet the development requirements of modern SAR systems.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a common-aperture broadband wide-angle scanning phased array antenna, comprising a pair of inverted-F antennas in the L band and a cavity-backed U-slot microstrip phased array antenna array in the X band. One of the diagonals of a regular N-sided metal plate is provided with a pair of the inverted-F antennas, where N is an even number greater than or equal to 4; a dielectric layer is provided on the metal plate, and the cavity-backed U-slot microstrip phased array antenna array in the X band is provided on the dielectric layer.

[0006] As a further improvement of the present invention, the structure of the inverted-F antenna is specifically as follows:

[0007] The wire antenna is bent into an L shape, the short side is connected to the feeding port, one side of the long side is kept open at the end, and a certain point on the long side is grounded.

[0008] As a further improvement of the present invention, the dielectric layer is located between the inverted-F antenna and the feeding port.

[0009] As a further improvement of the present invention, a pair of inverted-L parasitic units are loaded on both sides of the inverted-F antenna.

[0010] As a further improvement of the present invention, between the pair of inverted-F antennas, a differential power amplifier is used to divide the signal into a pair of differential signals for feeding them.

[0011] As a further improvement of the present invention, the X-band cavity-backed U-slot microstrip phased array antenna array comprises a plurality of cavity-backed U-slot microstrip phased array antennas. Each cavity-backed U-slot microstrip phased array antenna comprises a suspended metal patch. A U-shaped slot is formed in the metal patch, and the middle of the metal patch is connected to the dielectric layer. The metal patch is surrounded by a substrate integrated rectangular cavity which is formed by a circle of metallized vias.

[0012] As a further improvement of the present invention, at least one layer of wide-angle matching layer is loaded above the cavity-backed U-slot microstrip phased array antenna to reduce the active voltage standing wave ratio during beam scanning.

[0013] The beneficial effects of the present invention are as follows:

[0014] The broadband and wide-angle scanning common aperture phased array antenna of the present invention can meet the development requirements of modern SAR systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of the L-band inverted-F antenna in the embodiment of the present invention;

[0016] Figure 2 It is a schematic structural diagram of the L-band inverted-F antenna with parasitic elements in the embodiment of the present invention; wherein, (a) is a three-dimensional view; (b) is a top view;

[0017] Figure 3 It is a schematic structural diagram of the L-band differentially-fed inverted-F antenna array with parasitic elements in the embodiment of the present invention;

[0018] Figure 4 It is a schematic structural diagram of the X-band cavity-backed U-slot microstrip phased array antenna element in the embodiment of the present invention; wherein, (a) is a three-dimensional view; (b) is a top view;

[0019] Figure 5 It is a schematic structural diagram of the X-band cavity-backed U-slot microstrip phased array antenna in the embodiment of the present invention;

[0020] Figure 6 It is a schematic diagram of the L- and X-band common aperture phased array antenna in the embodiment of the present invention;

[0021] Figure 7 It is a schematic structural diagram of the X-band cavity-backed U-slot microstrip phased array antenna loaded with a wide-angle matching layer in the embodiment of the present invention; wherein, (a) is a three-dimensional view; (b) is a top view of the wide-angle matching layer;

[0022] Figure 8 It is a schematic structural diagram of the X-band cavity-backed U-slot microstrip phased array antenna loaded with a wide-angle matching layer in the embodiment of the present invention;

[0023] Figure 9 Schematic diagram of the L- and X-band common-aperture phased array antenna including a wide-angle matching layer in an embodiment of the present invention.

[0024] Reference numerals:

[0025] 1. Inverted-F antenna, 2. Inverted-L parasitic element, 3. Metal patch, 4. Metallized via hole. Detailed implementation manners

[0026] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0027] Embodiment

[0028] A common-aperture broadband wide-angle scanning phased array antenna includes:

[0029] L-band antenna: 0.995 - 1.125 GHz

[0030] With a low operating frequency and large physical size, in order to minimize the occupied aperture as much as possible to reduce the impact on the X-band array antenna, and at the same time take into account the low profile to meet the requirements for the array size, an inverted-F antenna with a thin and short structure and a low profile is proposed as the solution, and this inverted-F antenna is located at both ends of the array.

[0031] X-band antenna: 8.5 - 10.5 GHz

[0032] In order to meet the requirements for the broadband width of the phased array antenna, a U-shaped slot microstrip antenna, which is a broadband antenna, is proposed as the solution, and these antennas are distributed around the inverted-F antenna below.

[0033] L-band inverted-F antenna: The antenna structure of a traditional inverted-F antenna is as Figure 1 shown. The inverted-F antenna is a wire antenna of about a quarter wavelength, bent into an L shape, with the short side connected to the feed port, one side of the long side kept open at the end, and a certain point of the long side grounded, and the resulting structure is similar to the letter F. Compared with the traditional inverted-F antenna, an additional dielectric layer is covered on the floor for the subsequent X-band antenna design.

[0034] The dielectric of the X-band antenna is located between the L-band inverted-F antenna and the feed port, which has a great impact on the impedance matching of the L-band inverted-F antenna. Therefore, the simulation and optimization of the L-band inverted-F antenna also need to load and consider the dielectric. Due to the large size of the antenna array, the domestic Wangling F4BM220 with low price and good electrical performance at 10 GHz (relative dielectric constant: 2.2, loss tangent: 0.001, thickness: 3.175 mm) is proposed to be used as the dielectric. The dielectric and the bottom metal plate are regular hexagons. The other dimensions of the antenna are: G = 115.6 mm, a2 = 3.4 mm, LIF = 49.81 mm, HIL = 25.75 mm, LFD = 8.77 mm, LFy = 128.81 mm.

[0035] The impedance bandwidth of the antenna performance is only 2.94% (1.11978 - 1.11325 GHz), which cannot meet the bandwidth requirement of 0.995 - 1.125 GHz.

[0036] The antenna structure of the inverted-F antenna with parasitic elements is as Figure 2 shown. To improve the impedance bandwidth of the inverted-F antenna 1, a pair of inverted-L parasitic elements 2 are loaded on both sides of it. The antenna dimensions are: G = 115.6 mm, a2 = 3.4 mm, LIF = 49.81 mm, HIL = 25.75 mm, LFD = 12.17 mm, LFy = 127.11 mm, LIL = 53.77 mm, Ds = 6.79 mm.

[0037] The impedance bandwidth of the antenna performance is significantly improved, meeting the bandwidth requirement of 0.995 - 1.125 GHz. However, its radiation pattern is poor, the maximum radiation direction of the E-plane pattern deviates from the normal direction, and the cross polarization of the H-plane pattern is extremely large.

[0038] The antenna structure of the differential-fed inverted-F antenna array with parasitic elements is as Figure 3 shown. To improve the radiation pattern of the inverted-F antenna with parasitic elements, it is formed into a 1×2 differential-fed array, and a differential power amplifier is used at the bottom to divide the signal into a pair of differential signals for feeding. To minimize its impact on the X-band phased array antenna, the two L-band units are respectively distributed at two corners of the hexagonal array. The antenna dimensions are: G = 115.6 mm, a2 = 2 mm, LIF = 50.23 mm, HIL = 25.97 mm, LFD = 12.27 mm, LFy = 197.82 mm, LIL = 54.22 mm, Ds = 4 mm.

[0039] In the radiation pattern of the antenna performance, the radiation pattern is greatly improved, with the pattern being symmetric and having extremely low cross-polarization. The back radiation is large because the two elements are respectively distributed at two corners of the array, resulting in the area under them not being completely covered by the ground plane. However, when combined with other modules to form the entire cylindrical + spherical cap array, these two elements will be surrounded by the ground planes of other modules, and the back radiation should be reduced, but the impedance matching should also be affected. At the same time, the impedance bandwidth is 12.78% (0.99064 - 1.12584 GHz), meeting the bandwidth requirement of 0.995 - 1.125 GHz. It is required that in the range of 0.995 - 1.125 GHz, the gain is 4.95 - 5.5 dBi. The gain is not high because the two elements are respectively distributed at two corners of the array, resulting in the area under them not being completely covered by the ground plane, leading to large back radiation. However, when combined with other modules to form the entire cylindrical + spherical cap array, these two elements will be surrounded by the ground planes of other modules, and the back radiation should be reduced and the gain should be increased.

[0040] The antenna structure of the antenna element of the X-band cavity-backed U-slot microstrip phased array antenna is as Figure 4 shown. A U-shaped slot is opened on the metal patch 3 of the microstrip antenna, and it is surrounded by a substrate-integrated rectangular cavity, which is formed by a circle of metallized vias 4.

[0041] Due to the large size of the antenna array, the dielectric is proposed to use domestic Wangling F4BM220, which is cheap and has good electrical performance at 10 GHz (relative dielectric constant: 2.2, loss tangent: 0.001, thickness: 3.175 mm). The antenna dimensions are respectively: hs = 3 mm, dx = 15.24 mm, dy = 17.6 mm, Wp = 9.2 mm, Lp = 7.8 mm, W1 = 0.8 mm, L1 = 7.4 mm, W2 = 1.2 mm, L2 = 5 mm, Rv = 0.7 mm, D1 = 0.2 mm, D2 = 5 mm.

[0042] In the antenna performance, the impedance bandwidth (VSWR ≤ 3.6) meets the scanning range of ±60° within 8.5 - 10.5 GHz, and the gain is 4.94 - 6.2 dBi.

[0043] The antenna structure of the antenna array is as Figure 5 shown. The X-band array is an equilateral hexagon, with a total of 125 array elements, arranged in an equilateral triangular grid covering the entire hexagonal array, and positions are left at two corners for placing two L-band antennas.

[0044] In terms of antenna performance, the impedance bandwidth (VSWR < 2) covers 8.5 - 10.5 GHz. In the range of 8.5 - 10.5 GHz, the gain is 25.4 - 27.5 dBi. Within the scanning range (-60° to 60°), the active VSWR of the central unit is < 5. At the same time, the radiation pattern shows good performance. Radiation direction: when φ = 0°, θ = 0°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 1.8. The gain of the X-band phased array antenna in the normal direction is about 26.3 dBi, and the maximum sidelobe is about 16 dB smaller than the main lobe. Radiation direction: when φ = 0°, θ = 30°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 2.18. The gain of the X-band phased array antenna in the direction of φ = 0°, θ = 30° is about 25.8 dBi, and the maximum sidelobe is about 17.3 dB smaller than the main lobe. Radiation direction: when φ = 0°, θ = 45°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 3. The gain of the X-band phased array antenna in the direction of φ = 0°, θ = 45° is about 24 dBi, and the maximum sidelobe is about 16 dB smaller than the main lobe. Radiation direction: when φ = 0°, θ = 60°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 2.75. The gain of the X-band phased array antenna in the direction of φ = 0°, θ = 60° is about 22.5 dBi, and the maximum sidelobe is about 15.5 dB smaller than the main lobe. Radiation direction: when φ = 90°, θ = 30°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 2.25. The gain of the X-band phased array antenna in the direction of φ = 90°, θ = 30° is about 25.5 dBi, and the maximum sidelobe is about 15 dB smaller than the main lobe. Radiation direction: when φ = 90°, θ = 45°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 2.75. The gain of the X-band phased array antenna in the direction of φ = 90°, θ = 45° is about 24 dBi, and the maximum sidelobe is about 14 dB smaller than the main lobe. Radiation direction: when φ = 90°, θ = 60°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 5. The gain of the X-band phased array antenna in the direction of φ = 90°, θ = 60° is about 21 dBi, and the maximum sidelobe is about 12 dB smaller than the main lobe.

[0045] The antenna structure of the L- and X-band common-aperture phased array antenna is as Figure 6 shown. The X-band array is an equilateral hexagon with a total of 125 array elements, arranged in an equilateral triangular grid covering the entire hexagonal array, and positions are left at 2 corners for placing 2 L-band antennas.

[0046] In the antenna performance of the L-band antenna in the common-aperture antenna, the difference from when there is no X-band phased array antenna is small, indicating that the influence of the X-band antenna is not significant. The impedance bandwidth covers 0.995 - 1.125 GHz. The small difference from when there is no X-band phased array antenna indicates that the X-band antenna has little influence on it. In the range of 0.995 - 1.125 GHz, the gain is 3.09 - 4.01 dBi. The small difference from when there is no X-band phased array antenna indicates that the X-band antenna has little influence on it. The gain is not high, but because the two elements are respectively distributed at two corners of the array, the area under them is not completely covered by the ground plane, resulting in large backward radiation. However, when combined with other modules to form the entire cylindrical + spherical cap array, these two elements will be surrounded by the ground planes of other modules, and the backward radiation should be reduced and the gain should be increased. The radiation pattern has a small difference from when there is no X-band phased array antenna, indicating that the X-band antenna has little influence on it. The backward radiation is large because the two elements are respectively distributed at two corners of the array, resulting in the area under them not being completely covered by the ground plane. However, when combined with other modules to form the entire cylindrical + spherical cap array, these two elements will be surrounded by the ground planes of other modules, and the backward radiation should be reduced, but the impedance matching should also be affected.

[0047] In the antenna performance of the X-band phased array antenna in the common-aperture antenna, the impedance bandwidth (VSWR < 2) covers 8.5 - 10.5 GHz. The difference from when there is no L-band antenna is small, indicating that the L-band antenna has little influence on it. In the range of 8.5 - 10.5 GHz, the gain is 25.3 - 27.5 dBi. The difference from when there is no L-band antenna is small, indicating that the shielding effect of the L-band antenna is not significant and the L-band antenna solution is okay.

[0048] Within the scanning range (-60° to 60°), the active VSWR is < 5. At the same time, the radiation pattern has a small difference from when there is no L-band antenna, indicating that the shielding effect of the L-band antenna is not significant and the L-band antenna solution is okay. Radiation direction: When φ = 0° and θ = 0°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central element is less than 1.7. The difference from when there is no L-band antenna is small, indicating that the L-band antenna has little influence on it and the L-band antenna solution is okay.

[0049] The antenna structure of the X-band loaded wide-angle matching layer back-cavity U-slot microstrip phased array antenna is as Figure 7 shown. Two additional layers of wide-angle matching layers are loaded above the microstrip antenna to reduce the active VSWR during beam scanning. The dielectric is still the domestic Wangling F4BM220 used for the microstrip antenna (relative dielectric constant: 2.2, loss tangent: 0.001, thickness: 0.25 mm). The dimensions of the wide-angle matching layers are respectively: dx = 15.24 mm, dy = 17.6 mm, MPdx = 3.08 mm, MPdy = 2.4 mm, MPLx = 2 mm, MPLy = 2 mm.

[0050] In the antenna performance, the impedance bandwidth (VSWR ≤ 2.3) satisfies a scanning range covering ±60° within 8.5 - 10.5 GHz. From this, it can be obtained that the wide-angle matching layer improves the impedance matching of the phased array antenna during scanning. In the range of 8.5 - 10.5 GHz, the gain is 4.68 - 5.83 dBi.

[0051] The antenna structure of the antenna array is as Figure 8 shown. The X-band array is an equilateral hexagon with a total of 125 array elements, arranged in an equilateral triangular grid covering the entire hexagonal array, and positions are left at 2 corners for placing 2 L-band antennas.

[0052] In the antenna performance, the impedance bandwidth (VSWR < 1.9) covers 8.5 - 10.5 GHz. Within the scanning range (-60° to 60°), the active VSWR is all < 3.3. At the same time, the radiation pattern performs well. From this, it can be obtained that the wide-angle matching layer improves the impedance matching of the phased array antenna during scanning. Radiation direction: when φ = 0° and θ = 0°, within the range of 8.5 - 10.5 GHz, the simulated active VSWR of the central unit is less than 2.92.

[0053] The antenna of the L- and X-band common aperture phased array antenna includes a structure with a wide-angle matching layer as Figure 9 shown. The X-band array is an equilateral hexagon with a total of 125 array elements, arranged in an equilateral triangular grid covering the entire hexagonal array, and positions are left at 2 corners for placing 2 L-band antennas.

[0054] In the antenna performance of the L-band antenna in the common aperture antenna, the difference from when there is no X-band phased array antenna is small, indicating that the influence of the X-band antenna is not significant.

[0055] The impedance bandwidth covers 0.995 - 1.125 GHz. The difference from when there is no X-band phased array antenna is small, indicating that the influence of the X-band antenna on it is not significant. In the range of 0.995 - 1.125 GHz, the gain is 3.09 - 4.01 dBi. The difference from when there is no X-band phased array antenna is small, indicating that the influence of the X-band antenna on it is not significant. The gain is not high, but because the 2 units are respectively distributed at two corners of the array, the area under them is not completely covered by the ground plane, resulting in large backward radiation. However, when combined with other modules to form the entire cylindrical + spherical cap array, these 2 units will be surrounded by the ground planes of other modules, and the backward radiation should be reduced and the gain should be increased. The radiation pattern has little difference from when there is no X-band phased array antenna, indicating that the influence of the X-band antenna on it is not significant. The large backward radiation is because the 2 units are respectively distributed at two corners of the array, resulting in the area under them not being completely covered by the ground plane. However, when combined with other modules to form the entire cylindrical + spherical cap array, these 2 units will be surrounded by the ground planes of other modules, and the backward radiation should be reduced, but the impedance matching should also be affected.

[0056] In the antenna performance of the X-band phased array antenna in the common-aperture antenna, the impedance bandwidth (VSWR < 1.9) covers 8.5 - 10.5 GHz. The difference from the case without the L-band antenna is small, indicating that the L-band antenna has little impact on it. In the range of 8.5 - 10.5 GHz, the gain is 25.3 - 27.5 dBi. The difference from the case without the L-band antenna is small, indicating that the shielding effect of the L-band antenna is not significant and the design of the L-band antenna is not a problem. Within the scanning range (-60° to 60°), the active VSWR is all < 3.5. At the same time, the radiation pattern has little difference from the case without the L-band antenna, indicating that the shielding effect of the L-band antenna is not significant and the design of the L-band antenna is not a problem.

[0057] The above-described embodiments merely represent specific implementation manners of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A common-aperture wideband wide-angle scanning phased array antenna, characterized in that, It includes a pair of L-band inverted-F antennas and an X-band cavity-backed U-slot microstrip phased array antenna array. A pair of the inverted-F antennas are arranged on one diagonal of a regular N-sided metal plate, where N is an even number greater than or equal to 4; a dielectric layer is provided on the metal plate, and the X-band cavity-backed U-slot microstrip phased array antenna array is arranged on the dielectric layer.

2. The co-aperture wideband wide-angle scanning phased array antenna according to claim 1, wherein The structure of the inverted-F antenna is specifically as follows: The wire antenna is bent into an L shape, with the short side connected to the feeding port, one side of the long side kept open at the end, and a certain point of the long side grounded.

3. The co-aperture wideband wide-angle scanning phased array antenna according to claim 2, wherein The dielectric layer is located between the inverted-F antenna and the feeding port.

4. The co-aperture wideband wide-angle scanning phased array antenna according to claim 2, characterized in that, A pair of inverted-L parasitic elements are loaded on both sides of the inverted-F antenna.

5. The co-aperture wideband wide-angle scanning phased array antenna according to claim 4, wherein Between a pair of the inverted-F antennas, a differential power amplifier is used to divide the signal into a pair of differential signals for feeding.

6. The co-aperture wideband wide-angle scanning phased array antenna according to claim 1, wherein The X-band cavity-backed U-slot microstrip phased array antenna array includes multiple cavity-backed U-slot microstrip phased array antennas. Each cavity-backed U-slot microstrip phased array antenna includes a suspended metal patch. A U-shaped slot is opened on the metal patch, and the middle of the metal patch is connected to the dielectric layer. The metal patch is surrounded by a substrate-integrated rectangular cavity, and the rectangular cavity is composed of a circle of metallized vias.

7. The co-aperture wideband wide-angle scanning phased array antenna according to claim 6, characterized in that, At least one layer of wide-angle matching layer is loaded above the cavity-backed U-slot microstrip phased array antenna to reduce the active standing wave ratio during beam scanning.

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