Reduced-range field system for measuring circularly polarized antennas

Abstract

The present invention relates to a reduced-range field system for measuring circularly polarized antennas, comprising a turntable, a feed antenna, a reflector, and a rotary motor. The turntable is used to set the circularly polarized antenna to be measured and drive the circularly polarized antenna to rotate continuously. The feed antenna is a single-polarized linearly polarized antenna, the reflector is a concave mirror, and the phase center of the feed antenna is located at the focus of the reflector. The rotary motor drives the feed antenna to rotate continuously around an axis, and this axis passes through the phase center of the reflector and the feed antenna. The present invention avoids the problem of radiation field error caused by the traditional technology requiring a larger measurement space or inaccurate measurement phase.

Description

Technical Field

[0001] The present invention relates to a measurement system, in particular to a reduced-range field system for measuring circularly polarized antennas. Background Art

[0002] refer to Figure 1 In the paper "Understanding and Measuring Circular Polarization", a system is proposed to directly measure the radiation pattern of a circularly polarized antenna using a continuously rotating linearly polarized antenna. This is done using Direct Far Field (DFF). Therefore, the distance between the linearly polarized antenna LP and the circularly polarized antenna CP must be greater than the direct far field distance 2D. 2 / λ, parameter D is the size of the larger one of the linear polarization antenna LP and the circular polarization antenna CP, λ is the wavelength corresponding to the operating frequency, so the higher the frequency and the larger the external size of the circular polarization antenna CP to be tested, the required direct far-field distance 2D 2 The larger the / λ, especially with the rise of low-orbit satellites in recent years, which operate in the Ku-band of 12-18GHz, if the corresponding wavelength λ is calculated at 12GHz, it is about 2.5cm. However, if the antenna adopts a dish antenna or a planar phased array design, the external size may be as large as 70-80cm or even larger. Therefore, the direct far-field distance is 2D. 2 / λ requires a distance of approximately 25 meters or more. A typical anechoic chamber cannot meet the measurement requirements of this type of antenna, so measurements can only be performed in an open field (open side) environment.

[0003] “Understanding and Measuring Circular Polarization,” IEEE Transactions on Education, Vol. 46, No. 3, August 2003.

[0004] Due to the aforementioned issue of excessive far-field distances due to the high antenna operating frequency, antennas operating in the Ku-band or millimeter-wave bands must be measured using optical methods using a Compact Antenna Test Range (CATR). However, using a circularly polarized antenna as the feed antenna for a CATR to measure other circularly polarized antennas has always been difficult and therefore not adopted. Physical antennas do not exhibit perfect circular polarization; in reality, they are all elliptical. Even the same antenna will have different axial ratios at different frequencies within a measurement band. Therefore, the polarization along the major axis will be overestimated, while the polarization along the minor axis will be underestimated. Furthermore, the axial ratio of a circularly polarized antenna varies with frequency, so the overestimated or underestimated polarization along the major and minor axes will vary with frequency, making correction difficult.

[0005] To avoid the aforementioned issue of using a natively polarized antenna as a reference antenna with a non-unity axial ratio, another existing technique uses a fixed dual-linearly polarized antenna (with two polarizations perpendicular to each other) to measure circularly polarized antennas using a direct far-field approach. This approach has the disadvantage of requiring both the electric field amplitude (gain) and electric field phase (phase) of the circularly polarized antenna under test to be numerically calculated to derive the circular polarization gain. However, the electric field phase (phase) is affected by the reflectors used in the reduced-range field. Therefore, this method of measuring circularly polarized antennas using a fixed dual-linearly polarized antenna and then calculating the phase cannot be integrated with the reduced-range field measurement architecture and can only be applied to a direct far-field architecture. As previously mentioned, direct far-field measurement is not suitable for indoor installations within the size of a cable, making it unsuitable for measuring low-orbit satellites above 10 GHz or 5G millimeter-wave circularly polarized antennas. Summary of the Invention

[0006] In order to solve the problems of the prior art, the present invention proposes a system that can use a reduced-range field to measure circularly polarized antennas in the Ku-band or millimeter-wave bands above 10 GHz.

[0007] The invention discloses a reduced-range field system for measuring circularly polarized antennas, comprising a darkroom, a reflector, a turntable, a feed antenna, a rotating motor, a fixing fixture, a signal transceiver, and a control operation unit.

[0008] The darkroom is a rectangular parallelepiped, comprising a bottom plate parallel to the ground, a top plate spaced parallel to the bottom plate, and first, second, third, and fourth side plates surrounding and connecting the top and bottom plates. The first and third side plates have the same area, the second and fourth side plates have the same area, and the area of ​​the first side plate is smaller than the area of ​​the second side plate.

[0009] The reflector is a concave mirror and is placed in the dark room and arranged adjacent to the first side plate, with the concave surface of the reflector facing the third side plate.

[0010] The turntable is arranged in the darkroom and adjacent to the third side plate. The turntable is used to arrange the circularly polarized antenna to be tested, and the turntable drives the circularly polarized antenna to rotate continuously.

[0011] The feed antenna is a single linearly polarized antenna with its phase center located at the reflector's focal point. Driven by a rotary motor, the feed antenna continuously rotates about an axis that passes through the reflector and the feed antenna's phase center. The rotary motor drives the feed antenna for more than 30 revolutions during the time it takes the turntable to drive the circularly polarized antenna one revolution.

[0012] The fixing fixture is used to fix the rotating motor and the feed antenna, and the fixing fixture includes a vertical rod, a height adjustment unit and a motor locking unit.

[0013] The upright pole is arranged perpendicular to the base plate. The height adjustment unit includes a sleeve portion and a first connecting portion extending outward from the sleeve portion. The sleeve portion is encircled and sleeved around the upright pole, movable along the upright pole, and can be fixed at any position on the upright pole. The motor locking unit includes a motor fixing portion and a second connecting portion. The motor fixing portion and the second connecting portion are connected in an L-shape. The motor fixing portion includes a through hole. The rotary motor is fixed to the through hole. The feed antenna is locked to the rotary motor. A coaxial transmission line for connecting the feed antenna extends through the through hole. The second connecting portion of the motor locking unit is connected to the first connecting portion of the height adjustment unit, and the second connecting portion is rotatable relative to the first connecting portion.

[0014] Preferably, the height of the feed antenna from the bottom plate is h1, the height of the lower edge of the reflector from the bottom plate is h2, the height of the upper edge of the reflector from the bottom plate is h3, and h1 <h2<h3。

[0015] Preferably, the height of the phase center of the feed antenna from the bottom plate is h1, the height of the lower edge of the reflector from the bottom plate is h2, and the height of the upper edge of the reflector from the bottom plate is h3, and h1 = (h2 + h3) / 2.

[0016] Preferably, the linear distance from the phase center of the feed antenna to the geometric center of the reflector is D1, and the linear distance from the geometric center of the reflector to the origin of the rotation coordinate of the turntable is D2, S = D2 / D1, 1.4 <S<1.42。

[0017] Preferably, the straight-line distance D1 is 3.4 meters, the straight-line distance D2 is 4.8 meters, and the size of the reflector is 1.2x1.2m 2 .

[0018] The signal transceiver includes a signal generator and a signal analyzer. The signal generator and the signal analyzer are electrically connected to the circularly polarized antenna to be tested and the feed antenna, respectively. The signal analyzer outputs an electric field strength signal value corresponding to the received radio frequency signal.

[0019] The control operation unit is electrically connected to the turntable, the rotation motor, and the signal transceiver, and the control operation unit plots a plurality of electric field strength signal values ​​corresponding to a plurality of angles of the turntable to obtain a rotation linear radiation pattern.

[0020] The present invention provides the advantage of using a single linearly polarized antenna to continuously rotate to measure the circularly polarized antenna's gain, requiring only the electric field amplitude (Gain). This avoids the problem of using a fixed dual linearly polarized antenna to measure the circularly polarized antenna's gain in the prior art, which requires the additional electric field phase (Phase). This phase is often inaccurate due to the influence of reflectors. This allows the use of a reduced-range-range-reflection (CATR) technique, which requires relatively little anechoic chamber space, instead of a direct far-field (DFF) technique. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of an existing circularly polarized antenna measurement system.

[0022] Figure 2 It is a schematic diagram of a preferred embodiment of the present invention.

[0023] Figure 3 Schematic diagram of a fixing fixture according to a preferred embodiment of the present invention.

[0024] Figure 4 It is a 2D slice rotation linear radiation pattern. DETAILED DESCRIPTION

[0025] See Figure 2 A preferred embodiment of the reduced-range field measurement system for circularly polarized antennas of the present invention includes a darkroom 1, a reflector 2, a turntable 3, a feed antenna 4, a rotating motor 5, a fixing fixture 6, a signal transceiver 7, and a control operation unit 8.

[0026] The darkroom 1 is a rectangular parallelepiped, comprising a bottom plate 11 parallel to the ground, a top plate 12 spaced apart and parallel to the bottom plate 11, a first side plate 13 surrounding and connecting the top plate 12 and the bottom plate 11, a second side plate 14, a third side plate 15, and a fourth side plate 16. The first side plate 13 and the third side plate 15 have the same area, the second side plate 14 and the fourth side plate 16 have the same area, and the area of ​​the first side plate 13 is smaller than that of the second side plate 14.

[0027] The reflector 2 is a concave mirror and is placed in the darkroom 1 and disposed adjacent to the first side plate 13 , with the concave surface of the reflector 2 facing the third side plate 15 .

[0028] The turntable 3 is disposed in the darkroom 1 and adjacent to the third side plate 15 . The turntable 3 is used to place the circularly polarized antenna 9 to be tested and drive the circularly polarized antenna 9 to rotate continuously.

[0029] Feed antenna 4 is a single linearly polarized antenna, with its phase center 41 located at the focal point of reflector 2. Driven by a rotary motor 5, feed antenna 4 rotates continuously about an axis 43, with axis 43 passing through reflector 2 and the phase center 41 of feed antenna 4. For every rotation of circularly polarized antenna 9 by turntable 3, rotary motor 5 causes feed antenna 4 to rotate more than 30 times. In the preferred embodiment, rotary motor 5 is a stepper motor, and for every rotation of circularly polarized antenna 9 by turntable 3, rotary motor 5 causes feed antenna 4 to rotate 35 times.

[0030] See Figure 2 and Figure 3 The fixing fixture 6 is used to fix the rotating motor 5 and the feed antenna 4. The fixing fixture 6 includes a vertical rod 61, a height adjustment unit 62 and a motor locking unit 63.

[0031] The upright pole 61 is arranged perpendicular to the base plate 11. The height adjustment unit 62 includes a sleeve portion 621 and a first connecting portion 622 extending outward from the sleeve portion 621. The sleeve portion 621 is sleeved around the upright pole 61 and can move along the upright pole 61 and can be fixed at any position on the upright pole 61. The motor locking unit 63 includes a motor fixing portion 631 and a second connecting portion 632. The motor fixing portion 631 and the second connecting portion 632 are connected to form an L shape. The motor fixing portion 631 includes a through hole 6311. The rotary motor 5 is fixed to the through hole 6311. The feed antenna 4 is locked to the rotary motor 5 and is used to connect the coaxial transmission line 42 ( Figure 2 ) extends through the through hole 6311. The second linking portion 632 of the motor locking unit 63 is connected to the first linking portion 622 of the height adjustment unit 62, and the second linking portion 632 can rotate relative to the first linking portion 622.

[0032] The height of the feed antenna 4 from the bottom plate 11 is h1, the height of the lower edge of the reflector 2 from the bottom plate 11 is h2, the height of the upper edge of the reflector 2 from the bottom plate 11 is h3, and h1 <h2<h3。

[0033] Preferably, the linear distance between the phase center 41 of the feed antenna 4 and the geometric center 21 of the concave surface of the reflector 2 is D1, and the linear distance between the geometric center 21 of the reflector 2 and the origin 31 of the rotation coordinate of the turntable 3 is D2, S = D2 / D1, 1.4 <S<1.42。

[0034] In this preferred embodiment, the height of the phase center 41 of the feed antenna 4 from the bottom plate 11 is h1, the height of the lower edge of the reflector 2 from the bottom plate 11 is h2, and the height of the upper edge of the reflector 2 from the bottom plate 11 is h3, h1 = (h2 + h3) / 2, the straight-line distance D1 is 3.4 meters, the straight-line distance D2 is 4.8 meters, and the size of the reflector 2 is 1.2x1.2m 2 .

[0035] The signal transceiver 7 includes a signal generator 71 and a signal analyzer 72. The signal generator 71 and the signal analyzer 72 are electrically connected to the circularly polarized antenna 9 and the feed antenna 4 to be tested, respectively. The signal analyzer 72 outputs an electric field strength signal value according to the received radio frequency signal.

[0036] The control operation unit 8 is electrically connected to the turntable 3, the rotation motor 5, and the signal transceiver 7, and the control operation unit 8 plots the multiple electric field strength signal values ​​corresponding to the multiple angles of the turntable 3 to obtain the following: Figure 4 The rotating linear radiation pattern shown.

[0037] The present invention has the advantage of using a single linearly polarized antenna as the feed antenna 4 to continuously rotate and measure the circularly polarized gain of the circularly polarized antenna 9 to be measured. Only the electric field amplitude (Gain) needs to be used, thereby avoiding the problem described in the background art of using a fixed dual linearly polarized antenna to measure the gain of the circularly polarized antenna 9, which also requires the electric field phase (Phase). The electric field phase (Phase) is inaccurate due to the influence of the reflector 2. Therefore, this embodiment can use a shortened range distance (CATR) instead of a direct far field (DFF), which has relatively small space requirements for the darkroom 1.

[0038] The above descriptions are merely embodiments of the present invention and are not intended to limit the scope of the present invention.

[0039] Reference numerals

[0040] CP Circularly Polarized Antenna

[0041] LP linearly polarized antenna

[0042] 1 Darkroom

[0043] 11 bottom plate

[0044] 12 Top Plate

[0045] 13 First side panel

[0046] 14 Second side panel

[0047] 15 Third side panel

[0048] 16 Fourth side panel

[0049] 2 reflectors

[0050] 21 Geometric center of the reflector

[0051] 3 Turntable

[0052] 31 origin

[0053] 4 Feed antenna

[0054] 41 Phase Center

[0055] 42 coaxial transmission line

[0056] 43 Axis

[0057] 5 Rotary motor

[0058] 6 fixed fixture

[0059] 61 upright pole

[0060] 62 Height adjustment unit

[0061] 621 Sleeve Department

[0062] 622 First connection

[0063] 63 Motor locking unit

[0064] 631 Motor fixing part

[0065] 6311 Through Hole

[0066] 632 Second connection

[0067] 7 Signal transceiver

[0068] 71 Signal Generator

[0069] 72 Signal Analyzer

[0070] 8 Control computing unit

[0071] 9 Circularly polarized antenna

[0072] D1, D2 height

[0073] h1, h2, h3 straight-line distance

Claims

1. A reduced-range field measurement system for a circularly polarized antenna, comprising: A turntable for placing a circularly polarized antenna to be tested, and the turntable drives the circularly polarized antenna to rotate continuously; a reflecting mirror, wherein the reflecting mirror is a concave mirror; a feed antenna, wherein the feed antenna is a single linear polarization antenna, and a phase center of the feed antenna is located at a focus of the reflector; and A rotary motor is driven by the rotary motor to continuously rotate the feed antenna around an axis, and the axis passes through the phase center of the reflector and the feed antenna.

2. The reduced-range field measurement system for circularly polarized antennas according to claim 1, wherein: Also includes: a signal transceiver device, comprising a signal generator and a signal analyzer, the signal generator and the signal analyzer being electrically connected to the circularly polarized antenna to be tested and the feed antenna, respectively, the signal analyzer outputting an electric field strength signal value corresponding to a received radio frequency signal; and A control operation unit is electrically connected to the turntable, the rotation motor, and the signal transceiver, and the control operation unit obtains a rotation linear radiation field pattern after plotting the multiple electric field strength signal values ​​corresponding to the multiple angles of the turntable.

3. The reduced-range field measurement system for circularly polarized antennas according to claim 1, wherein: During the time that the turntable drives the circular polarization antenna to rotate once, the rotary motor drives the feed antenna to rotate more than 30 times.

4. The system for measuring a circularly polarized antenna with a reduced-range field as claimed in claim 1, wherein: Also includes: A fixing fixture is used to fix the rotary motor and the feed antenna. The fixing fixture includes a vertical pole, a height adjustment unit and a motor locking unit. The upright pole is arranged perpendicular to a bottom plate, and the bottom plate is arranged parallel to the ground. The height adjustment unit includes a sleeve portion and a first connecting portion extending outward from the sleeve portion. The sleeve portion is sleeved around the upright rod and can move along the upright rod and can be fixed at any position on the upright rod. The motor locking unit includes a motor fixing portion and a second connecting portion, and the motor fixing portion and the second connecting portion are connected in an L shape. The motor fixing portion includes a through hole, and the rotary motor is fixed to the through hole. The feed antenna is locked to the rotary motor. The second connecting portion of the motor locking unit is connected to the first connecting portion of the height adjustment unit, and the second connecting portion can rotate relative to the first connecting portion.

5. The reduced-range field measurement system for circularly polarized antennas according to claim 1, wherein: Also includes: A darkroom is in the shape of a rectangular parallelepiped, comprising a bottom plate arranged parallel to the ground, a top plate spaced apart and parallel to the bottom plate, a first side plate, a second side plate, a third side plate and a fourth side plate surrounding and connecting the top plate and the bottom plate, wherein the first side plate and the third side plate have the same area, the second side plate and the fourth side plate have the same area, the area of ​​the first side plate is smaller than the area of ​​the second side plate, the reflector is arranged adjacent to the first side plate, and the concave surface of the reflector faces the third side plate, and the turntable is arranged adjacent to the third side plate.

6. The reduced-range field measurement system for circularly polarized antennas according to claim 5, wherein: The height of the feed antenna from the bottom plate is h1, the height of the lower edge of the reflector from the bottom plate is h2, and the height of the upper edge of the reflector from the bottom plate is h3. <h2<h3。 7. The reduced-range field measurement system for circularly polarized antennas according to claim 6, wherein: The height between the phase center of the feed antenna and the base plate is h1, the height between the lower edge of the reflector and the base plate is h2, and the height between the upper edge of the reflector and the base plate is h3, where h1=(h2+h3) / 2.

8. The reduced-range field measurement system for circularly polarized antennas according to claim 1, wherein: The linear distance between the phase center of the feed antenna and a geometric center of the concave surface of the reflector is D1, and the linear distance between the geometric center of the reflector and the origin of the rotation coordinate of the turntable is D2, S = D2 / D1, 1.4 <S<1.42。 9. The system for measuring a circularly polarized antenna with a reduced-range field as claimed in claim 8, wherein: The straight-line distance D1 is 3.4 meters, and the straight-line distance D2 is 4.8 meters.

10. The reduced-range field measurement system for circularly polarized antennas according to claim 9, wherein: The size of the reflector is 1.2 x 1.2m 2 .

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