Hemispherical conformal polarization reconfigurable wearable sparse array antenna based on helmet

Abstract

The invention discloses a hemispherical conformal polarization reconfigurable wearable sparse array antenna based on a helmet, which belongs to the technical field of array antennas and comprises twelve broadband dual-circular polarization reconfigurable conformal radiation antenna elements arranged on the outer surface of a hemispherical helmet base. The three conformal radiating antenna elements are arranged at the top of the helmet and are rotationally and symmetrically arranged along the z axis of a main coordinate system, the included angle between the normal direction of each element and the + z axis is theta n, and theta n is equal to 22 degrees; the other nine elements are evenly distributed around the side bottom of the hemispherical helmet, and the normal directions of the nine elements and the Z axis form 65-degree angles. According to the invention, the gain, the coverage range and the direction flexibility of the WBAN system can be improved. Results of a verification example and an experiment example show that the conformal wearable array shows 29.6% of overlapped 3dB axial ratio bandwidth and 69.8% of-10dB impedance bandwidth in two reconfigurable CP modes of about 3GHz. The gains of the two polarization modes both exceed 7.2 dBi in a wide wave beam coverage range of 110 degrees * 360 degrees.

Description

Technical Field

[0001] The present invention relates to the technical field of array antennas, and in particular to a helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna. Background Art

[0002] In emergency rescue scenarios such as forest fires, high-speed, reliable and stable communications between rescuers in different areas are crucial to ensure the execution of various cooperative tasks, which requires wearable antennas to have wide bandwidth, reconfigurable polarization, and sufficient gain and beam coverage.

[0003] However, in complex rescue environments, severe scattering effects may cause polarization conversion of electromagnetic waves, which also requires wearable antennas to have polarization diversity or reconfigurability. At the same time, a large antenna working bandwidth is required to quickly transmit videos, images and other data during collaborative rescue operations. To this end, a hemispherical conformal polarization reconfigurable wearable sparse array antenna based on a helmet is proposed. Summary of the invention

[0004] The present invention aims to at least solve the problems of wide bandwidth, reconfigurable polarization and wide coverage faced by wearable antennas in emergency rescue scenarios in the prior art, so as to cope with one of the technical problems of electromagnetic wave polarization conversion and environmental interference. To this end, one purpose of the present invention is to propose a hemispherical conformal polarization reconfigurable wearable sparse array antenna based on a helmet.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna, comprising twelve broadband dual circular polarization reconfigurable conformal radiating antenna elements disposed on the outer surface of a hemispherical helmet base;

[0007] Among them, three conformal radiating antenna elements are arranged on the top of the helmet, rotationally symmetrically arranged along the z-axis of the principal coordinate system, and the angle between the normal direction of each element and the +z-axis is θn, θn=22;

[0008] An array of nine conformal radiating antenna elements is distributed on the side bottom of the hemispherical helmet, with their normal directions all forming an angle of 65° with the Z-axis. By electrically switching the three conformal radiating antenna elements on the top and any two adjacent conformal radiating antenna elements on the bottom, a beam scanning range of 360° in azimuth can be achieved.

[0009] As a further optimization scheme of the present invention, the three conformal radiating antenna elements on the top work simultaneously to form a fixed beam, and the beam width is optimized to 40°×40°. The two adjacent elements at the bottom of the side form a beam width of 90°×40°. The overall beam coverage range is (θ, φ) = (110°×360°).

[0010] As a further optimization scheme of the present invention, a global coordinate system is established with the center of the sphere as the origin to calculate the required phase relationship of all relevant radiating elements. The parametric equation of the position of the conformal radiating element is:

[0011]

[0012] Where rh is the radius of the hemisphere, φn and θn are the azimuth and elevation angles of the nth radiating element, respectively. Therefore, the position vector of the nth conformal radiating element is:

[0013]

[0014] As a further optimization scheme of the present invention, the normalized position vector of any far-field point P(θ, φ) in the spherical coordinate system is:

[0015]

[0016] The difference between the distance from the source point On to the field point P and the distance from the origin O to P is:

[0017] d n =O n ·r op

[0018] Therefore, the required phase compensation for the nth radiating element is:

[0019] Δθ n =-2πd n / λ.

[0020] As a further optimization solution of the present invention, the conformal array achieves half-space coverage within the I MBW range of 2.6-3.4 GHz.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention arranges twelve broadband dual circularly polarized reconfigurable conformal radiating antenna elements on the outer surface of the hemispherical helmet base, wherein the three elements at the top work simultaneously to form a fixed beam with an optimized beam width of 40°×40°. Similarly, the two adjacent elements at the bottom of the side work together to increase the gain, forming a beam width of 90°×40°. Finally, by electrically switching between the three elements at the top and any two adjacent elements at the bottom of the side, an overall beam coverage range of (θ, φ) = (110°×360°) can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural diagram of the hemispherical conformal polarization reconfigurable wearable sparse array antenna of the present invention;

[0024] Figure 2 In the first example of verification of the present invention: (b)-(c) are top views of two configurations of the top three radiating elements, (a) is the coordinate system for calculating the required phase relationship of the array elements;

[0025] Figure 3 The simulated gain, AR and xz plane radiation pattern diagrams of two configurations of the top three-element subarray in the first verification example of the present invention at a frequency of 2.8 GHz;

[0026] Figure 4 Schematic diagram of the phase and angle relationship between the vector electric fields in the first verification example of the present invention, wherein (a) is a conformal radiating element, (b)-(c) are conformal top three-element subarrays configured in Case 1 and Case 2, respectively;

[0027] Figure 5 For the second verification example of the present invention: (a) simulated AR, achieved gain and (b) radiation pattern diagram of the top three-element subarray on the 2.8GHz xz plane when θn increases from 19° to 28°;

[0028] Figure 6 The simulated (a) AR, achieved gain and (b) radiation pattern diagram of the side-bottom two-element, three-element and four-element subarrays in the third verification example of the present invention in the xy plane;

[0029] Figure 7 For the third example of the present invention, (a) the simulated AR value, the achieved gain and (b) the radiation pattern diagram of the dual-element subarray at 3 GHz, including the case where there is no adjacent element and the case where there are two adjacent inactive elements;

[0030] Figure 8 The fourth example of the present invention is a graph showing the relationship between the simulated HPBW and the operating frequency on two main planes for (a) a three-element subarray and (b) a two-element subarray when operating in the LHCP mode;

[0031] Fig. 9 (a) front, (b) side, and (c) back of the conformal radiating element in Experimental Example 1 of the present invention, and (d) antenna diagram tested in an anechoic chamber;

[0032] Fig.10 Graphs showing simulation and measurement results of (a) reflection coefficient, (b) AR and achieved gain of a conformal radiating element operating in LHCP and RHCP modes in Experimental Example 1 of the present invention;

[0033] Fig.11 The simulated and measured radiation patterns of the conformal radiating element at different frequencies and different principal planes under different polarization modes in Experimental Example 1 of the present invention are as follows:

[0034] Fig.12 Experimental diagrams for characterizing the conformal wearable sparse array in Experimental Example 2 of the present invention: (a) external and (b) internal structure diagram of the fabricated conformal wearable array prototype; (c) 1:2 and 1:3 power dividers and (d) digital phase shifters; (e) power distribution phase shifting network of the top three-element subarray; (f) power distribution network of the side bottom two-element subarray;

[0035] Fig.13 Measured reflection coefficient diagrams of (a) the top three-element subarray and (b) the side bottom two-element subarray in the reconfigurable LHCP and RHCP modes in Experimental Example 2 of the present invention;

[0036] Fig.14 The simulated and measured AR values ​​and achieved gain diagrams of (a) the top three-element subarray and (b) the side bottom two-element subarray for the reconfigurable LHCP and RHCP modes in Experimental Example 2 of the present invention;

[0037] Fig.15 The simulated and measured radiation patterns of the conformal radiating element at different frequencies and different principal planes under different polarization modes in Experimental Example 2 of the present invention;

[0038] Fig.16 These are the simulated and measured radiation patterns of the conformal radiating element in Experimental Example 2 of the present invention at different frequencies, different principal planes, and different polarization modes. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention provides a technical solution: Figure 1 As shown, a helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna includes a broadband dual circular polarization reconfigurable conformal radiating antenna element arranged on the outer surface of the hemispherical helmet base.

[0041] Among them, three conformal radiating antenna elements are set on the top of the helmet, and nine conformal radiating antenna element arrays are distributed on the side bottom of the hemispherical helmet, and their normal directions are all at an angle of 65° to the Z axis. By electrically switching the three elements on the top and any two adjacent elements on the bottom, a beam scanning range of 360° in azimuth can be achieved.

[0042] The three conformal radiating antenna elements at the top work simultaneously to form a fixed beam with an optimized beam width of 40°×40°. The two adjacent elements at the bottom of the side form a beam width of 90°×40°. The overall beam coverage range is (θ, φ) = (110°×360°).

[0043] Calculate the required phase relationship of all relevant radiating elements, establish a global coordinate system with the center of the sphere as the origin, and the parametric equation for the position of the conformal radiating element is:

[0044]

[0045] Where rh is the radius of the hemisphere, φn and θn are the azimuth and elevation angles of the nth radiating element, respectively. Therefore, the position vector of the nth conformal radiating element is:

[0046]

[0047] The normalized position vector of any far-field point P(θ,φ) in the spherical coordinate system is described as:

[0048]

[0049] The difference between the distance from the source point On to the field point P and the distance from the origin O to P is:

[0050] d n =O n ·r op

[0051] Therefore, the required phase compensation for the nth radiating element can be calculated as follows:

[0052] Δθ n =-2πd n / λ

[0053] Verification Example 1

[0054] According to two feasible configurations, the conformal subarray composed of the top three radiating elements is detected to achieve the best performance, which are named as Case 1 and Case 2, respectively. Figure 2 (b) and 2(c).

[0055] In the first configuration, all components are arranged rotationally symmetrically along the z-axis of the principal coordinate system, and the angle between the normal direction of each component and the +z-axis is θn. Figure 2 As shown in (a), by rotating antenna elements 2 and 3 along the z-axis of their respective local coordinate systems, we can obtain Figure 2 (c) The second configuration is shown. Regardless of the LHCP or RHCP operating mode, the structure of all radiating elements and the state of the PIN diodes are exactly the same.

[0056] In the first configuration, the separation angle of adjacent arrows is 120°, and in the second configuration, all arrows are along the -x axis. Figure 3 It can be seen that the AR bandwidth of case 1 is wider than that of case 2, and the AR value of the entire frequency band is close to zero.

[0057] like Figure 4 As shown in (a), the radiation electric field vectors of the LHCP and RHCP modes are EL and ER respectively, when they are initially along the -y axis. If the radiating element is rotated clockwise by a along the Z axis, the direction of the electric field vector will also rotate by the same angle, that is, when the values ​​of a and b are the same, the phase change or rotation angle of EL is the same, while that of ER is opposite.

[0058] According to the definition of AR, the AR value of the CP antenna should meet the following conditions:

[0059]

[0060] Among them, ARe le and ARBWe le refer to the AR value and 3 dB ARBW value of the radiating element respectively. That is, A and B represent the lowest and highest frequency points of CP radiation.

[0061] pass Figure 4 (b) shows the electric field vectors EL-case1 and ER-case1 of the top three-element subarray configured in Case 1, where the subarray is assumed to operate in LHCP mode. EL-case1 and ER-case1 are the sum of the co-polarized electric field vectors (i.e., EL1, EL2, and EL3) and the cross-polarized electric field vectors (i.e., ER1, ER2, and ER3) of the three radiating elements, respectively. Therefore, the AR and 3-dB ARBW of the top three-element subarray are:

[0062]

[0063] AR case1 (dB)=20log 10 AR case1 =0

[0064] Here, ARcase1 and ARBWcase1 refer to the AR and 3-dB ARBW of the three-element subarray, respectively. Figure 4 As shown in (b), the amplitudes and phases of the field vectors EL1, EL2, and EL3 are exactly the same, while the amplitudes of the vectors ER1, ER2, and ER3 are the same, but the phase relationship is different, and the value of |ER-case1| is zero. Therefore, ARcase1 is calculated to be 1 (or 0dB), while ARBWcase1 is infinite. Figure 4(c) shows that when the top three radiating elements are configured as case 2 and the subarray is still assumed to operate in LHCP mode. In this case, the calculation formulas for ARcase2 and ARBWcase2 are:

[0065]

[0066] The ARBW of the subarray operating in Case 2 is the same as the ARBW of the radiating elements. Among the first three different configurations of radiating elements, the conformal subarray in Case 1 shows the best AR performance.

[0067] Verification Example 2

[0068] Verify the effect of θn on the AR, achieved gain and radiation pattern in the xz plane at 2.8 GHz for the top three-element subarray.

[0069] pass Figure 5 It can be seen that the AR value remains basically unchanged, while the gain value decreases as θn increases. Figure 5 As shown in (b), as θn increases, the main lobe gain decreases, while the side lobe level increases. The separation angle between the normal directions of the conformal radiating elements increases, resulting in a decrease in the radiation contribution to the desired +z axis direction. By comparison, it can be seen that when θn = 19°, the actual gain of the subarray is higher. However, the distance between the three antenna elements is very close, resulting in bottom overlap. Considering the gain and production complexity, the actual gain of the subarray is higher when θn = 22°.

[0070] Verification Example 3

[0071] Nine conformal radiating antenna element arrays are distributed on the side bottom of the hemispherical helmet, and their normal directions are all at an angle of 65° to the Z axis. Figure 6 As shown in Figure 1, the half-power beamwidth (HPBW) of the three-element and four-element subarrays in the xy plane is less than 40°, and the HPBW of the two-element subarray in the two main planes is about 90°×40°. Therefore, through beam switching between nine elements, the overall beam steering coverage is 90°×360°. Figure 7 As shown, the adjacent inactive elements have little impact on the radiation performance of the dual-element subarray.

[0072] Verification Example 4

[0073] Verify the effect of operating frequency change on the HPBW of the top three-element subarray and the side bottom two-element subarray.

[0074] like Figure 8 As shown in (a), under the I MBW of 2.4-3.4 GHz, the HPBW of the three-element conformal array located on the top of the hemisphere is greater than 40° in both the xz plane and the yz plane. Figure 8(b) It can be seen that in the I MBW range of 2.6-3.4 GHz, the HPBW minimum values ​​of the 2-element conformal array in the xz plane and yz plane are 93° and 39°, respectively. Therefore, both proposed subarrays have good axial ratio performance within their coverage range. The conformal array combining the two subarrays can achieve half-space coverage within the I MBW range of 2.6-3.4 GHz.

[0075] Experimental Example 1

[0076] Figure 17 shows a broadband unidirectional dual-CPs reconfigurable conformal radiating element, the total size of which is π×332×12 mm3. Fig. 9 As shown in (d), the DUT is mounted on an ABS hemispherical structure with a radius of 120 mm and a thickness of 12 mm. A RI GOL DP832 DC power supply is used to provide the required bias voltage for the PI N diode. When the bias voltage is set to 0.9 V and -0.9 V, the conformal radiating element can operate in LHCP and RHCP modes, respectively. In the far-field anechoic chamber of Beijing Institute of Technology, the radiation performance of the two polarization modes, including reflection coefficient, AR, achieved gain and radiation pattern, was measured using a vector network analyzer and a standard horn antenna.

[0077] Simulated and measured reflection coefficient, AR and achieved gain of conformal radiating elements in two polarization modes Fig.10 As shown. Fig.10 As shown in (a), when S11 is less than -10 dB, the measured overlap I MBW of the LHCP and RHCP working modes is 40.3% (i.e., 2.31 to 3.48 GHz), which is close to the simulation result of 40.6% (i.e., 2.24 to 3.42 GHz). Fig.10 (b) shows that the measured overlapped 3-dB ARBW for both modes is 33% (i.e., 2.52 to 3.51 GHz), which is consistent with the simulated 32% (2.5 to 3.45 GHz). Within the operating band, the measured gain is between 4.7 and 5.58 dBi, while the simulated gain is between 5.1 and 6 dBi (for both polarization modes).

[0078] Fig.11 The simulated and measured normalized radiation patterns of the conformal radiating element in two reconfigurable CP operating modes at 2.6, 3, and 3.4 GHz are shown.

[0079] Among them, (a) xz plane and (b) yz plane at 2.6 GHz for LHCP operation;

[0080] (c) xz plane and (d) yz plane at 2.6 GHz for RHCP operation;

[0081] (e) xz plane and (f) yz plane at 3 GHz for LHCP operation;

[0082] (g) xz plane and (h) yz plane at 2.6 GHz for RHCP operation.

[0083] (c) xz plane at 2.6 GHz and (d) yz plane at 2.6 GHz;

[0084] (e) xz plane at 3 GHz and (f) yz plane at 3 GHz;

[0085] (g) xz plane at 3 GHz and (h) yz plane at 3 GHz;

[0086] (i) xz plane at 3.4 GHz and (j) yz plane at 3.4 GHz;

[0087] (k) xz plane at 3.4 GHz and (l) yz plane at 3.4 GHz.

[0088] The results show that the higher the operating frequency, the narrower the HPBW on the two main planes. Fig.11 As shown, the HPBW of the proposed conformal antenna in the xz plane is 100°, 90° and 88° at the three frequencies of the two working modes. Similarly, the HPBW in the yz plane is 98°, 90° and 84° at different frequencies. Due to the structural symmetry of the conformal element, the radiation patterns of the LHCP and RHCP modes are basically the same. In addition, for the two CP states, the cross-polarization levels in the broadside direction are lower than -16.7, -17.2 and -16.4 dB at the frequencies of 2.6, 3 and 3.4 GHz, respectively. In the two CP working modes, the front-to-back ratio (FBR) of the radiation pattern is greater than 25, 17 and 15 dB at the three frequencies, respectively.

[0089] Experimental Example 2

[0090] To identify the radiative performance of a hemispherical conformal dual CPs reconfigurable wearable sparse array, e.g. Fig.12 As shown in Figure 1, a hemispherical conformal array prototype with a total size of 2π / 3×1203mm3 was fabricated and tested. Fig.12 As shown in (c) and (d), 1:2 and 1:3 power dividers and three digital phase shifters are used to perform phase compensation for 2-element and 3-element array antennas. Fig.12 (e)(f) show the power distribution and phase shifting networks for 2-element and 3-element array antennas.

[0091] Fig.13The measured reflection coefficients of the top three-element subarray and the side bottom two-element subarray in LHCP and RHCP operating modes are shown, and these subarrays are integrated with the corresponding power distribution networks. Fig.13 As shown in (a), in both CP working modes, the ultra-wide overlap I MBW (when S11 is less than -10dB) generated by the two-element conformal subarray in the range of 1.8 to 4.5GHz is 85.7%. Fig.13 (b) It can be seen that in LHCP and RHCP modes, the measured overlapping I MBW is 69.8% (i.e., 2.03 to 4.21 GHz). The measured I MBW of these two conformal sub-arrays is much wider than that of the conformal radiating element.

[0092] Fig.14 The simulated and measured results of AR and achieved gain for the top three-element subarray and the side bottom two-element subarray in two reconfigurable polarization modes are shown. Fig.14 As shown in (a), the ultra-wide overlap 3dB ARBW measured in the 2 to 4 GHz range is 64.5% in the LHCP and RHCP operating modes. Compared with the simulation results, the measured AR value is slightly higher. Fig.14 (b) shows that the measured overlapped 3-dB ARBW of the two-element subarrays in the two reconfigurable CP modes is 29.6% (i.e., 2.56 to 3.45 GHz), and the frequency range is shifted up by about 40 MHz compared with the simulation results. Fig.14 As shown in (a), in the LHCP and RHCP working modes, the measured peak gains of the three-element conformal subarray are 9.38 and 9.55 dBi, respectively, which are slightly lower than the simulated results of 10.5 and 10.4 dBi. Fig.14 (b) It can be seen that the measured peak gains of the dual-element subarray in the two polarization modes are 8.1 and 8.15 dBi, respectively, while the simulated results are 8.65 and 8.67 dBi, respectively.

[0093] Fig.15The simulated and measured normalized radiation patterns of the top three-element conformal subarray in two reconfigurable CP operating modes at 2.6, 3, and 3.4 GHz are shown. The HPBW measured for the array antenna in the xz plane are 57°, 48°, and 47° in the LHCP and RHCP operating modes, respectively. Similarly, the HPBW measured in the yz plane are 56°, 47°, and 46°, respectively. Clearly, the radiation patterns of the LHCP and RHCP modes are almost identical. In addition, the cross-polarization levels in the broadside direction are lower than -15.9, -20.1, and -14 dB at 2.6, 3, and 3.4 GHz, respectively, for both CP states. The measured FBR of the radiation pattern is higher than 12.9, 12.2, and 10 dB at the three frequencies for both polarization modes, respectively. The measured and simulated radiation patterns are in good agreement.

[0094] Fig.16 The simulated and measured normalized radiation patterns of the side-bottom dual-element conformal subarray in two CP operating modes at 2.6, 3, and 3.4 GHz are shown. The HPBW measured for the proposed array antenna in the xz plane is 94°, 95°, and 93° for both operating modes at three frequencies. Similarly, the HPBW measured in the yz plane is 43°, 41°, and 39°. In addition, the cross-polarization levels are lower than -14.1, -12.2, and -12.5 dB at 2.6, 3, and 3.4 GHz for both CP states. The measured FBR of the radiation pattern is higher than 15.3, 11.6, and 13.1 dB at three frequencies for both CP operating modes.

[0095] Parts not involved in the present invention are the same as the prior art or can be implemented by the prior art. Although the embodiments of the present invention have been shown and described, it is understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hemispherical conformal polarization reconfigurable wearable sparse array antenna based on a helmet, characterized in that: The invention comprises twelve broadband dual circularly polarized reconfigurable conformal radiating antenna elements arranged on the outer surface of a hemispherical helmet base; Among them, three conformal radiating antenna elements are arranged on the top of the helmet, rotationally symmetrically along the z-axis of the principal coordinate system, and the angle between the normal direction of each element and the +z-axis is θn, θn=22; by setting the feeding phases of the three top radiating elements to -120°, 0° and 120° respectively, an axial ratio performance close to 0dB is achieved. An array of nine conformal radiating antenna elements is distributed on the side bottom of the hemispherical helmet, with their normal directions all forming an angle of 65° with the Z-axis. By performing beam switching on the three conformal radiating antenna elements on the top and any two adjacent conformal radiating antenna elements on the bottom, a beam scanning range of 360° in azimuth can be achieved.

2. The helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna according to claim 1, characterized in that: The three conformal radiating antenna elements at the top work simultaneously to form a fixed beam with an optimized beam width of 40°×40°. The two adjacent elements at the bottom of the side form a beam width of 90°×40°. The overall beam coverage range is (θ, φ) = (110°×360°).

3. The helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna according to claim 1, characterized in that: A global coordinate system is established with the center of the sphere as the origin, and the required phase relationship of all relevant radiating elements is calculated. The parametric equation for the position of the conformal radiating element is: Where rh is the radius of the hemisphere, φn and θn are the azimuth and elevation angles of the nth radiating element, respectively. Therefore, the position vector of the nth conformal radiating element is:

4. The helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna according to claim 1, characterized in that: The normalized position vector of any far-field point P(θ,φ) in the spherical coordinate system is: The difference between the distance from the source point On to the field point P and the distance from the origin O to P is: d n =OO n ·r op Therefore, the required phase compensation for the nth radiating element is: Dth n =-2πd n / min.

5. The helmet-based hemispherical conformal polarization reconfigurable wearable sparse array antenna according to claim 1, characterized in that: The conformal array achieves half-space coverage in the IMBW range of 2.6-3.4 GHz.

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