Phased array antenna system

Abstract

Systems and methods are provided for implementing a phased array antenna with an optical axis direction. A scan angle within a defined scan angle range is selected for the phased array antenna such that the selected scan angle differs from a scan angle associated with the visual axis direction. An antenna port impedance associated with each of a plurality of antenna elements constituting the phased array antenna varies with the scan angle of the phased array antenna. A plurality of amplifiers are each coupled to an antenna port of one of the plurality of antenna elements. Each amplifier of the plurality of amplifiers is configured such that a maximum of performance characteristics of the plurality of amplifiers is achieved when an impedance at the antenna port corresponds to the selected scan angle.

Description

Technical Field

[0001] The present disclosure relates generally to the field of communications, and more particularly, to phased array antennas. Background Art

[0002] A phased array or electronically scanned array is an array of controlled antennas that produces a beam of radio waves that can be electronically steered to point in different directions without moving the antennas. In an array antenna, the radio frequency current from the transmitter is fed to each antenna in the correct phase relationship so that the radio waves from the individual antennas are added together to increase the radiation in the desired direction while canceling to suppress radiation in undesired directions. A directional area of ​​high gain (called a "beam") is formed by shifting the phase of the signal emitted from each radiating element to provide constructive and destructive interference, thereby steering the beam in the desired direction. The relative amplitudes of the signals radiated by the individual antennas determine the effective radiation pattern of the array. Phased arrays can be used to point a fixed radiation pattern, or for rapid scanning in azimuth or elevation. Summary of the invention

[0003] According to one example, a phased array antenna is provided, the phased array antenna comprising an antenna element array, the antenna element array comprising a beam having a visual axis direction. A plurality of phase shifters respond to a command to adjust the phase of a plurality of radio frequency (RF) signals transmitted by the antenna element array. A controller provides the command to the plurality of phase shifters. The provided command is used by the plurality of phase shifters to guide the beam within a scanning angle range relative to the visual axis direction. A plurality of amplifiers are used to amplify the plurality of signals. Each of the plurality of amplifiers is coupled to an antenna port of the antenna element array and has a performance characteristic depending on an antenna port impedance at the antenna port. The antenna impedance varies with the scanning angle of the beam within the scanning angle range, and the amplifier is configured so that the maximum value of the performance characteristic is achieved at a value of the antenna port impedance corresponding to a specific scanning angle within the scanning angle range different from the visual axis direction.

[0004] According to another example, a method for implementing a phased array antenna with a boresight direction is provided. A scanning angle within a limited scanning angle range is selected for the phased array antenna, so that the selected scanning angle is different from the scanning angle associated with the boresight direction. The antenna port impedance associated with each of the multiple antenna elements constituting the phased array antenna varies with the scanning angle of the phased array antenna. Multiple amplifiers are each coupled to the antenna port of one of the multiple antenna elements. Each of the multiple amplifiers is configured so that when the impedance at the antenna port corresponds to the selected scanning angle, a maximum value of the performance characteristics of the multiple amplifiers is achieved.

[0005] According to yet another example, a phased array antenna includes an array of antenna elements including a beam having a boresight direction. A first group of phase shifters responds to a command to adjust the phase of a radio frequency (RF) signal received at the antenna element array. A second group of phase shifters responds to a command to adjust the phase of a transmit signal for the antenna element array to transmit. A controller provides the command to the first group of phase shifters and the second group of phase shifters. The provided command is used to guide the beam within a scanning angle range relative to the boresight direction. A first group of amplifiers amplifies a signal received at the antenna element array. Each amplifier in the first group of amplifiers is coupled to an antenna port of the antenna element array and has a first performance characteristic depending on an antenna port impedance at the antenna port. The antenna impedance varies with the scanning angle of the beam within the scanning angle range, wherein a maximum value of the first performance characteristic is achieved at a first value of the antenna port impedance corresponding to a first scanning angle different from the boresight direction. A second group of amplifiers amplifies a transmit signal to be transmitted by the antenna element array. Each amplifier in the second group of amplifiers is coupled to an antenna port of the antenna element array and has a second performance characteristic that depends on an antenna port impedance at the antenna port, wherein a maximum value of the second performance characteristic is achieved at a second value of the antenna port impedance corresponding to a second scanning angle different from the line of sight direction and each of the first scanning angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The above and other features of the present invention will become apparent to those skilled in the art to which the present invention relates by reading the following description with reference to the accompanying drawings, in which:

[0007] Figure 1 is a graph showing an example of antenna gain degradation;

[0008] Figure 2 is a graph showing the performance of one example of an amplifier tuned according to the systems and methods presented herein;

[0009] Figure 3 is a graph illustrating reduced variation in antenna system performance over a range of scan angles associated with the system;

[0010] Figure 4 An example of a phased array antenna is shown;

[0011] Figure 5 shows a schematic diagram of an antenna path having an antenna element and a low noise amplifier connected through an impedance matching network;

[0012] Figure 6 It shows that Figure 2 A Smith chart of an example of an impedance transformation provided by an impedance matching network;

[0013] Figure 7 It shows that Figure 2 A Smith chart showing another example of impedance transformation provided by an impedance matching network;

[0014] Figure 8 One specific implementation of a phased array antenna utilizing amplifiers configured for maximum performance at scan angles other than boresight is shown;

[0015] Fig. 9 Another implementation of a phased array antenna utilizing an amplifier configured for maximum performance at scan angles other than boresight is shown;

[0016] Fig.10 Yet another specific implementation of a phased array antenna utilizing an amplifier configured for maximum performance at scan angles other than boresight is shown; and

[0017] Fig.11 An example of a method for implementing a phased array antenna with a boresight direction is shown. DETAILED DESCRIPTION

[0018] In a phased array antenna, the antenna gain of a beam decreases as the scan angle changes from the boresight direction, where the antenna provides maximum gain. This is called scan loss. The scan angle is in the antenna's coordinate system and can vary along multiple axes (e.g., azimuth and elevation). Figure 1 1 is a graph 10 showing one example of the reduction in antenna gain (dBi) of an array of antenna elements of a phased array antenna relative to an isotropic radiator having an angle (in this example, the elevation angle) on a vertical axis 12, the antenna gain being expressed in decibels of gain, the angle being expressed in degrees relative to a boresight direction on a horizontal axis 14. As can be seen from curve 16, as the elevation angle deviates from the boresight direction, the antenna gain drops significantly within a scan angle range 18 associated with the system.

[0019] The performance of an amplifier coupled to an array of antenna elements of a phased array antenna may also depend on the antenna impedance of the antenna elements of the array, which changes with the scanning angle. The antenna impedance may vary from implementation to implementation based on various factors, and may be determined, for example, empirically and / or analytically. Optimizing the amplifier performance for the antenna impedance in the boresight direction results in reduced amplifier performance at scanning angles away from the boresight direction. One method for alleviating the sensitivity of the amplifier to the antenna impedance is to place an isolator between them. However, in large arrays, this may be too expensive. In addition, the RF loss of the isolator affects the antenna performance.

[0020] The combination of scanning loss and reduced amplifier performance at scanning angles different from the boresight direction together leads to a significant degradation in the overall performance of the antenna system. Therefore, the system and method described herein mitigate the effect of gain loss at higher scanning angles by configuring the amplifier so that the maximum value of the performance characteristic of the amplifier corresponds to the antenna impedance at a scanning angle different from the boresight direction of the maximum antenna gain. As used herein, the maximum value of the performance characteristic represents the relative maximum value within the scanning angle range in which the phased array antenna is configured to operate via commands provided to the phase shifter. The performance characteristics may vary from implementation to implementation and may depend on whether the phased array antenna is used for transmission and / or reception. As used herein, the "performance characteristics" of an amplifier generally refers to any measure of the amplifier for which a higher value indicates better amplifier performance. In some embodiments, the maximum value of the "performance characteristics" of the amplifier is achieved by minimizing the parameter for which a lower value indicates better performance. For example, in some embodiments described herein, the maximum value of the output signal-to-noise ratio (SNR) of the amplifier to the input SNR is achieved by minimizing its noise figure, because the noise figure is the ratio of the input SNR to the output SNR in dB.

[0021] Figure 2 30 is a graph showing the performance of one example of an amplifier configured in accordance with the systems and methods presented herein. Specifically, the amplifier is configured such that the maximum value of the performance characteristic corresponds to the antenna impedance at a scan angle other than the boresight direction. The amplifier performance is represented by the vertical axis 32, where higher values ​​indicate better performance, and the elevation angle is represented on the horizontal axis 34 in degrees relative to the boresight direction. As can be seen from the curve 36, the amplifier performance reaches a maximum value 38 that is maximized at a scan angle toward the center of the scan angle range 40 associated with the system, as opposed to the boresight direction.

[0022] As will be described in detail herein, this reduces the variation of antenna system performance metrics (e.g., gain to noise temperature ratio (G / T) of a received signal or equivalent isotropic radiated power (EIRP) of a transmitted signal) over scan angle, thereby providing improved performance at high scan angles. Figure 3 5 is a graph 50 showing a reduction in variation of an antenna system performance metric within a scan angle range 52 over which the phased array antenna is configured to operate. The antenna system performance metric is represented by a vertical axis 54, with higher values ​​indicating better performance, and the elevation angle is represented on a horizontal axis 56 in degrees relative to the boresight direction. A first curve 58 represents the performance of a system lacking the improvements described herein. As can be seen from curve 58, the antenna performance metric of such a system is at its maximum in the boresight direction and drops sharply as the elevation angle changes from the boresight direction.

[0023] A second curve 60 represents the performance of a system utilizing an amplifier configured as described herein, such that a maximum value of the performance characteristic of the amplifier corresponds to an antenna impedance at a scan angle different from the boresight direction (0 degrees in this example), such as Figure 2 As shown. At the boresight, the antenna gain is at a maximum value, while the amplifier performance is reduced relative to its maximum performance. Therefore, relative to the system represented in the first curve 58, the overall performance of the system in the boresight direction is slightly degraded. At larger scanning angles, the antenna gain is lower, but the amplifier performance is less degraded compared to the maximum performance corresponding to the boresight. Therefore, the antenna performance actually improves as the elevation angle deviates from the boresight direction until a point is reached where the antenna performance is maximized. It should be understood that for scanning angles between the scanning angle for which the antenna impedance has been tuned and the boresight direction, maximum performance will generally be provided. Then, as the elevation angle deviates further from the boresight, the antenna performance gradually degrades, but degrades more slowly than the system represented by the first curve 58, thereby providing excellent performance within most of the scanning angle range 52. Therefore, the antenna performance is collectively maximized within the scanning angle range 52.

[0024] Figure 4 An example of a phased array antenna 100 is shown. It should be understood that the phased array antenna 100 is a simplified representation provided for illustrative purposes, and the antenna may include additional components not shown herein. The phased array antenna includes an array of antenna elements 102 that provide a boresight direction to the beam. A plurality of phase shifters 104 respond to commands to adjust the phases of a plurality of radio frequency (RF) signals transmitted by the array of antenna elements 102. A controller 106 provides commands to the plurality of phase shifters 104. The controller 106 may be implemented in hardware, for example, as one or more application specific integrated circuits (ASICs), custom field programmable gate arrays (FPGAs) chips, in software as machine executable instructions stored on a non-transitory medium and executed by an associated processor, or as a combination of hardware and software. The provided commands are used by the plurality of phase shifters 104 to scan the beam within a scanning angle range relative to the boresight direction.

[0025] A plurality of amplifiers 108 amplify a plurality of signals. In the specific implementation shown, the amplifier 108 amplifies the received signal and can therefore be implemented as a low noise amplifier, but it should be understood that the characteristics of the amplifier can vary. Each of the plurality of amplifiers 108 is coupled to an antenna port of an array of antenna elements 102, and therefore has a performance characteristic that depends on the antenna port impedance at the antenna port. The antenna impedance varies with the scanning angle of the beam within the scanning angle range, and the amplifier 108 is configured so that the maximum value of the performance characteristic (such as the output SNR and the input SNR) is achieved at a value of the antenna port impedance corresponding to a specific scanning angle within the scanning angle range different from the visual axis direction. As described above, maximizing the output SNR and the input SNR of the amplifier 108 is equivalent to minimizing the noise figure of the amplifier 108, and therefore for convenience, minimizing the noise figure (also referred to as "noise matching") is described below. The manner in which the amplifier 108 is configured to perform noise matching with a specific antenna port impedance value corresponding to a specific scanning angle can vary between specific implementations. For example, the input matching network of the amplifier may be designed to provide an appropriate impedance transformation, the amplifier bias current may be selected to achieve noise matching, degradation may be used, or any other suitable method for selecting impedance may be employed.

[0026] Figure 5 A schematic diagram of an antenna path 150 is shown having an antenna element 152 and a low noise amplifier (LNA) 154 connected via an impedance matching network 160. The impedance matching network 160 and the LNA 154 may, for example, together implement one of an amplifier series L network having an inductor 162 in series between the antenna element 152 and the low noise amplifier 154 and a parallel capacitor 164. The inductance value of the inductor 162 and the capacitance value of the capacitor 164 may be selected to reduce the source impedance seen at the input of the low noise amplifier 154 from the impedance Z at the port of the antenna element 152 to the impedance Z at the port of the antenna element 152. A The known value of Z is adjusted to the expected value Z opt .

[0027] Figure 6 It shows that Figure 5 A Smith chart 180 of an example of an impedance transformation provided by an impedance matching network. In the example shown, the scan angle of the phased array is on boresight and the impedance seen at the antenna port is labeled Z A The first step in the transformation is to place the inductance from inductor 162 in series with the antenna output. This moves the impedance to the area marked Z in the Smith chart. 1 The inductance value is given by the distance from Z along the unit circle. A Move to point Z 1 The value of the required reactance is determined. The second step is to place the parallel capacitors to achieve the optimum source impedance Z optThe value of the capacitor is determined by the 1 Move to Z opt The required susceptance is determined.

[0028] Figure 7 It shows that Figure 5 Smith chart 190 of another example of impedance transformation provided by an impedance matching network. In the example shown, the scan angle of the phased array is at a scan angle different from the boresight, and the impedance seen at the antenna port is therefore different from Figure 3 The impedance depicted in . Figure 4 Examples can also be used Figure 2 The impedance matching network shown is shown, but the inductance value of inductor 162 and the capacitance value of capacitor 164 are changed to adjust the impedance change at the antenna port. Figure 4 In the specific example of Figure 3 The value used in increases.

[0029] return Figure 4 During operation, the phased array antenna 100 shown is configured to receive signals from a desired scanning angle direction relative to the boresight direction. Each antenna element in the plurality of antenna elements 102 receives an element signal (also referred to herein as a "received signal"), which is then amplified by a corresponding amplifier in the plurality of amplifiers 108. The amplified element signals are then provided to a plurality of phase shifters 104, which apply appropriate phase shifts to the element signals based on the desired scanning angle of the beam, as indicated by a control signal (also referred to herein as a "command") from a controller 106. The phase-shifted element signals are then provided to a beamforming network 110, which combines the element signals to produce a beam signal corresponding to the desired scanning angle. In the illustrated embodiment, the desired scanning angle is achieved by adjusting the phase of the element signal via the phase shifter 104. In some embodiments, the phased array antenna 100 further includes an amplitude adjustment circuit (e.g., a variable gain amplifier) ​​to further adjust the amplitude of the element signal in response to the control signal.

[0030] One parameter that determines the noise figure of a low noise amplifier is the source impedance Z presented at its input. source Ideally, Z source is a fixed value that provides the lowest noise figure (called noise match). However, in a phased array antenna, the antenna port impedance Z A (called source impedance or scan impedance) varies with the scan angle, and therefore the source impedance is not constant.

[0031] The noise optimization used in this paper can be better understood through equation (1):

[0032]

[0033] where Y s =G s +jB s is the source admittance of the active circuit presented to the amplifier, Y opt is the optimum source admittance that results in minimum noise figure, F min It is in Y s =Y opl The minimum noise figure of the active circuit of the amplifier is obtained when N is the equivalent noise resistance of the amplifier’s active circuit, G s is the real part of the source admittance, and F is the noise factor.

[0034] From equation (1), it can be seen that if the actual source admittance Y presented to the amplifier is s Equal to the optimal source impedance Y opt , then the second term in equation (1) becomes zero. In this case, the noise figure will assume the minimum achievable value. Therefore, in order to improve the overall performance of the antenna system 100 at higher scan angles at the expense of slightly lower performance at the boresight, the low noise amplifier is configured to be compatible with the antenna port impedance Z A The antenna port impedance Z may be selected for noise matching with a specific value of , which corresponds to a specific scanning angle different from the boresight direction. In the case where the antenna system is used to receive a signal having a frequency range, the antenna port impedance Z may be selected for one of the frequencies within the frequency range (including the maximum frequency, the minimum frequency, the center frequency, or other representative frequencies within the range). A a specific value.

[0035] In some implementations, a particular scan angle is selected based on the resulting value of an antenna system performance metric at one or more scan angles. Using the example of a gain to noise temperature ratio for the performance metric, it will be appreciated that the maximum gain G(θ) of the phased array antenna 100 is a function of the scan angle θ, where the maximum gain is provided at the boresight. Similarly, the noise factor, and therefore the noise temperature, is a function of the mismatch of the source admittance presented to the amplifier and the optimum source admittance of the amplifier, as discussed in Equation 1. The antenna port impedance, and therefore the admittance, varies with the scan angle θ, and therefore the noise factor F is a function of each of the scan angle and the optimum source admittance of the selected amplifier, which we denote here as opt , for that particular scan angle, the optimal source impedance matches the admittance at the antenna port.

[0036] In one example, a particular scan angle may be selected to provide a predetermined minimum value of the antenna system performance metric within a maximum possible range of scan angles. It should be appreciated that as the particular scan angle varies away from the boresight direction, the impedance mismatch at angles away from the boresight direction will decrease. Thus, in one specific implementation, the particular scan angle may vary within a range of scan angles away from the boresight direction until the antenna system performance metric drops below a predetermined minimum value for at least one scan angle within the range, wherein the maximum deviation of the particular scan angle from the boresight direction maintains minimum performance within the selected predetermined range.

[0037] In another specific implementation, the value of a particular scan angle is selected to maximize the minimum value of the gain to noise temperature ratio within a predetermined scan angle range. In this case, the optimization problem is to select a source admittance for the amplifier that maximizes the value:

[0038]

[0039] where θ i In the limited scanning angle range [θ i ,θ N ] changes within, and T 0 It is 273K.

[0040] It should be understood that the variation of gain with scan angle and the variation of noise angle with scan angle can be modeled based on the design of the phased array antenna 100, and thus θ can be determined via an appropriate optimization algorithm (such as a gradient search). opt Alternatively, a “brute force” approach can be employed, where a particular scan angle θ is evaluated. opt Each of multiple pre-selected values ​​and select the maximum value.

[0041] In one implementation consistent with this example, the scan angle is selected to maintain at least a minimum value of the antenna performance metric at the maximum scan angle of the operating range of the scan angle, so that the defined scan angle range covers the entire operating range of the phased antenna array 100. Alternatively, a particular scan angle may be selected to provide a predetermined minimum value of the antenna system performance metric over an appropriate subset of the selected scan angles within the scan angle range. It should be understood that the selected subset of scan angles may exclude the boresight direction.

[0042] In another specific implementation, a particular scan angle is selected based on the maximum scan angle such that the selected scan angle is at a predetermined position between the boresight direction and the maximum scan angle, such as midway between the boresight direction and the maximum scan angle. For example, if the maximum scan angle is a sixty degree elevation angle from the boresight direction, the amplifier 108 may be noise matched to an antenna port impedance corresponding to a thirty degree elevation angle.

[0043] In another example, a particular scan angle is selected such that the sum of the performance metric over all scan angles within the scan angle range or a suitable subset of the scan angle range is maximized. Again using the gain to noise temperature ratio, the optimization problem can be expressed as selecting the defined scan angle range [θ i ,θ N ] is the specific scanning angle θ that maximizes this value opt :

[0044]

[0045] Figure 8 A specific implementation of a phased array antenna 200 using an amplifier configured to achieve maximum performance at a scanning angle other than the boresight direction is shown. In the specific implementation shown, the phased array antenna 200 is configured to transmit a signal in a desired scanning angle direction relative to the boresight direction. The beamforming network 202 receives a beam signal intended to be transmitted in the desired scanning angle direction. The beamforming network 202 divides the beam signal into element signals (also referred to as "transmit signals" in this article), which are provided to a plurality of phase shifters 204. Each phase shifter in the plurality of phase shifters 204 responds to a control signal from a controller 206 to provide an appropriate phase shift to the signal based on the desired scanning angle of the beam. The phase-shifted signal is then amplified by a plurality of power amplifiers 208 and provided to an antenna element 210 for transmission, thereby generating a transmit beam in the desired scanning angle direction. In the embodiment shown, the desired scanning angle is achieved by adjusting the phase of the element signal via the phase shifter 204. In some embodiments, the phased array antenna 100 also includes an amplitude adjustment circuit (eg, a variable gain amplifier) ​​to further adjust the amplitude of the element signal in response to the control signal.

[0046] A power amplifier is designed for a given output power level. One parameter that determines the output power level is the load impedance Z presented at its output. Load Ideally, Z Load is a fixed value that allows the power amplifier to produce a given output power level. However, in a phased array antenna, the antenna port impedance Z A varies with the scan angle, and therefore the load impedance Z Load To improve antenna performance metrics (such as the antenna's equivalent radiated power or equivalent isotropic radiated power) at higher scan angles at the expense of slightly lower performance at boresight, the power amplifier 208 is configured to operate at an antenna port impedance Z AThe impedance matching network 212 is a network that provides maximum output power at a specific value of that corresponds to a specific scan angle different from the boresight direction. In the illustrated implementation, multiple impedance matching networks 212 are implemented between the antenna 210 and the amplifier 208. The impedance matching network 212 adjusts the antenna impedance to the desired load impedance. In one implementation including an integrated circuit design, the impedance matching network can be designed using lumped components such as inductors and capacitors.

[0047] Using the example of effective isotropic radiated power (EIRP) for the performance metric, it will be appreciated that the maximum power G(θ) of the phased array antenna 100 is a function of the scan angle θ, where maximum gain is provided at the boresight. Some power may be lost due to a mismatch in impedance at the power amplifier and the impedance at the antenna port. The antenna port impedance, and therefore admittance, varies with the scan angle θ, and therefore the reflected power R is a function of each of the scan angle and the optimal source impedance of the selected amplifier, which we denote here as for a particular scan angle θ opt , for that particular scan angle, the optimal source impedance matches the admittance at the antenna port.

[0048] In one example, a particular scan angle may be selected to provide a predetermined minimum value of the antenna system performance metric within a maximum possible range of scan angles. It should be appreciated that as the particular scan angle varies away from the boresight direction, the impedance mismatch at angles away from the boresight angle will decrease. Thus, in one specific implementation, the particular scan angle may vary within a range of scan angles away from the boresight direction until the antenna system performance metric drops below a predetermined minimum value for at least one scan angle within the range, wherein the maximum deviation of the particular scan angle from the boresight direction maintains minimum performance within the selected predetermined range.

[0049] In another specific implementation, the value of a particular scan angle is selected to maximize the minimum value of ERIP within a predetermined scan angle range. In this case, the optimization problem is to select the source admittance for the amplifier that maximizes the value:

[0050]

[0051] where θ i In the limited scanning angle range [θ 1 ,θ N ] change within, P in is the power input to the system, and I iso is the power radiated by a hypothetical lossless isotropic antenna in the direction of the scan angle.

[0052] It should be understood that the variation of gain with scan angle and the variation of reflected power with scan angle can be modeled based on the design of the phased array antenna 100, and thus θ can be determined via an appropriate optimization algorithm (such as a gradient search). opt Alternatively, a “brute force” approach can be employed, where a particular scan angle θ is evaluated. opt Each of multiple pre-selected values ​​and select the maximum value.

[0053] In one implementation consistent with this example, the scan angle is selected to maintain at least a minimum value of EIRP at a maximum scan angle of the operating range of the scan angles, so that the defined scan angle range covers the entire operating range of the phased antenna array 100. Alternatively, a particular scan angle may be selected to provide a predetermined minimum value of EIRP or other performance metric over a suitable subset of the selected scan angles within the scan angle range. It should be understood that the selected subset of scan angles may exclude the boresight angle.

[0054] In another specific implementation, a specific scan angle is selected based on the maximum scan angle such that the selected scan angle is at a predetermined position between the boresight direction and the maximum scan angle, such as midway between the boresight direction and the maximum scan angle. For example, if the maximum scan angle is a sixty degree elevation angle from the boresight direction, the power amplifier 208 may be noise matched to an antenna port impedance corresponding to a thirty degree elevation angle.

[0055] In another example, a particular scan angle is selected such that the sum of the EIRP or other performance metric over all scan angles within the scan angle range or a suitable subset of the scan angle range is maximized. The optimization problem can be expressed as selecting the defined scan angle range [θ 1 ,θ N ] is the specific scanning angle θ that maximizes this value opt :

[0056]

[0057] Fig. 9Another specific implementation of a phased array antenna 300 using an amplifier configured to achieve maximum performance at a scanning angle other than the boresight direction is shown. In the specific implementation shown, the phased array antenna 300 is configured in a half-duplex arrangement to transmit and receive radio frequency signals in a desired scanning angle direction relative to the boresight direction. In the half-duplex arrangement, two sets of transmit / receive (Tx-Rx) switches 302 and 303 are used to switch the antenna 300 between the transmit path and the receive path of each antenna element in a plurality of antenna elements 304. During transmission, a beamforming network 306 receives a beam signal intended to be transmitted in the desired scanning angle direction. The beamforming network 306 divides the beam signal into element signals, which are provided to a plurality of phase shifters 308. Each of the plurality of phase shifters 308 responds to a control signal from a controller 309 to provide an appropriate phase shift to the signal based on the desired scanning angle of the beam. The phase shifted signals are then amplified by a plurality of power amplifiers (PAs) 310-312 and provided to antenna elements 304 for transmission, thereby generating a transmit beam in the desired scan angle direction.

[0058] During reception, each of the plurality of antenna elements 304 receives an element signal, which is then amplified by a corresponding one of the plurality of low noise amplifiers (LNAs) 314-316. The amplified signals are then provided to a plurality of phase shifters 308, which apply appropriate phase shifts to the signals based on the desired scan angle of the beam, as provided by a controller 309. The phase shifted signals are then provided to a beamforming network 306, which combines the signals to produce a beam signal corresponding to the desired scan angle.

[0059] Due to reciprocity, assuming the same frequency is used, the antenna port impedance Z of the antenna element A The scanning angle is the same for transmission and reception. However, the performance change of the low noise amplifier with the change of antenna port impedance may be different from the performance change of the power amplifier for the changing antenna port impedance. These differences in amplifier performance changes may result in selecting different antenna port impedance values ​​for the low noise amplifiers 314-316 and the power amplifiers 310-312, respectively, and thus selecting different specific scanning angles. The reception performance metric for reception (such as gain to noise temperature ratio) may depend on the performance change of the low noise amplifiers 314-316 in a manner different from the manner in which the performance metric for transmission (such as equivalent isotropic radiated power) depends on the performance change of the power amplifiers 310-312. Therefore, in some specific implementations, the low noise amplifier is configured to perform noise matching at a first value of the antenna port impedance corresponding to a first scanning angle, and the power amplifier is configured to obtain maximum output power at a second value of the antenna port impedance corresponding to a second scanning angle different from the first scanning angle.

[0060] Fig.10 Another specific implementation of a phased array antenna 400 using an amplifier configured to achieve maximum performance at a scanning angle other than the boresight direction is shown. In the specific implementation shown, the phased array antenna 400 is configured as a frequency division duplex arrangement to transmit and receive radio frequency signals in the desired scanning angle direction relative to the boresight direction. In the frequency division duplex arrangement, two sets of duplexers 402-404 and 406-408 allow multiple antenna elements 410 to be used for both transmission and reception. During transmission, a beam forming network 412 receives a beam signal intended to be transmitted in the desired scanning angle direction. The beam forming network 412 divides the beam signal into element signals, which are provided to multiple phase shifters 414. Each phase shifter in the multiple phase shifters 414 responds to a control signal from a controller 416 to provide an appropriate phase shift to the signal based on the desired scanning angle of the beam. The phase-shifted signals are then amplified by a plurality of power amplifiers (PAs) 420-422 and provided to the antenna element 410 for transmission, thereby generating a transmit beam in the desired scan angle direction.

[0061] During reception, each of the plurality of antenna elements 410 receives an element signal, which is then amplified by a corresponding one of the plurality of low noise amplifiers (LNAs) 424-426. The amplified signals are then provided to a plurality of phase shifters 414, which apply appropriate phase shifts to the signals based on the desired scan angle of the beam, as provided by a controller 416. The phase shifted signals are then provided to a beamforming network 412, which combines the signals to produce a beam signal corresponding to the desired scan angle.

[0062] Since different frequencies are used for transmission and reception, the change in the antenna port impedance of the antenna element over the scan angle may be different for transmission and reception. Therefore, different values ​​of the antenna port impedance may be selected for the low noise amplifier and the power amplifier, respectively. Therefore, in some specific implementations, the low noise amplifier is configured to perform noise matching at a first value of the antenna port impedance corresponding to a first scan angle, and the power amplifier is configured to obtain maximum output power at a second value of the antenna port impedance corresponding to a second scan angle different from the first scan angle.

[0063] In view of the above structural and functional characteristics, reference Fig.11 To better understand the exemplary method. Although for the purpose of simplicity of explanation, Fig.11The exemplary method of the present invention is shown and described as being performed sequentially, but it should be understood and appreciated that the present example is not limited to the order shown, because some actions may occur multiple times and / or simultaneously in other examples in a different order than shown and described herein. In addition, it is not necessary to perform all the described actions to implement the method.

[0064] Fig.11 An example of a method 500 for implementing a phased array antenna having a boresight direction is shown. At 502, a scan angle within a defined scan angle range of the phased array antenna is selected so that the selected scan angle is different from a scan angle associated with the boresight direction. At 504, a plurality of amplifiers (each coupled to an antenna port of an antenna element of a plurality of antenna elements) are configured so that a maximum value of a performance characteristic of the plurality of amplifiers is achieved when an impedance at the antenna port corresponds to the selected scan angle. In one specific implementation, the amplifiers are configured by providing an impedance matching network for each of the plurality of amplifiers to adjust the impedance at the antenna port to which the amplifier is connected.

[0065] It should be understood that the scanning angle can be selected to maximize the performance metric of the phased array antenna within a scanning angle range, which scanning angle range may include all scanning angles in the operating range of the phased array antenna or a suitable subset of the operating range. Suitable performance metrics of the phased array antenna may include, for example, gain to noise temperature ratio, effective radiated power, and effective isotropic radiated power. In a specific implementation, the scanning angle is selected to provide an extreme value of a function of the performance metric of the phased array antenna at all scanning angles within the defined range or a subset. For example, the scanning angle can be selected to maximize the sum of the performance metric at all scanning angles within the defined range or a subset. Alternatively, the scanning angle can be selected to maximize the minimum value of the performance metric at all scanning angles within the defined range or a subset.

[0066] The desired characteristics of the antenna array may be different for reception and transmission of the antenna. Therefore, in one specific implementation, each of a first scanning angle different from the scanning angle associated with the boresight direction and a second scanning angle different from both the scanning angle associated with the boresight direction and the first scanning angle may be selected. A first group of amplifiers (such as low noise amplifiers) that amplify the received signal may be configured so that a maximum value of a first performance characteristic is achieved when the impedance at the antenna port corresponds to the first scanning angle, and a second group of amplifiers (such as power amplifiers) that amplify the transmitted signal may be configured so that a maximum value of a second performance characteristic is achieved when the impedance at the antenna port corresponds to the second scanning angle. Therefore, the antenna array can be optimized for both its transmit and receive functions.

[0067] What has been described above is an example. Of course, it is impossible to describe every conceivable combination of parts or methods, but those of ordinary skill in the art will recognize that many other combinations and arrangements are possible. Therefore, the present disclosure is intended to cover all such changes, modifications and variations that fall within the scope of the present application (including the appended claims). As used herein, the term "includes" means including but not limited to, and the term "comprising" means including but not limited to. The term "based on" means at least partially based on. In addition, in the case where the present disclosure or claims state "one", "a kind of", "first" or "another" element or its equivalent, it should be interpreted as including one or more than one such element, neither requiring nor excluding two or more such elements.

Claims

1. A phased array antenna, comprising: an array of antenna elements, the array of antenna elements comprising a beam having a boresight direction; a plurality of phase shifters responsive to commands to adjust phases of a plurality of signals transmitted through the array of antenna elements; a controller for providing the commands to the plurality of phase shifters, wherein the provided commands are used by the plurality of phase shifters to steer the beam within a range of scan angles relative to the boresight direction; as well as a plurality of amplifiers for amplifying the plurality of signals, wherein each of the plurality of amplifiers is coupled to an antenna port of the antenna element array and has a performance characteristic that depends on an antenna port impedance at the antenna port, wherein the antenna impedance varies with a scanning angle of the beam within the scanning angle range, and a maximum value of the performance characteristic is achieved at a value of the antenna port impedance corresponding to a specific scanning angle within the scanning angle range different from the boresight direction.

2. The phased array antenna according to claim 1, wherein each of the plurality of antenna elements has a corresponding impedance matching network to adjust the impedance at the antenna port so that the maximum value of the performance characteristic is achieved when the antenna port impedance corresponds to the selected scanning angle.

3. The phased array antenna according to any one of claims 1 to 2, wherein the specific scanning angle within the scanning angle range is selected to maximize a performance metric of the phased array antenna.

4. The phased array antenna of claim 3, wherein the plurality of amplifiers comprises a first plurality of amplifiers, each of the first plurality of amplifiers being configured to amplify one of the plurality of signals received at an associated antenna element, and the performance metric comprising a gain to noise temperature ratio of the phased array antenna.

5. The phased array antenna of claim 4, wherein the performance metric is a first performance characteristic and the specific scanning angle is a first specific scanning angle, the plurality of amplifiers include a second plurality of amplifiers, each of the second plurality of amplifiers being configured to amplify a signal of the plurality of signals for transmission at an associated antenna element, so that when the antenna port impedance corresponds to a second specific scanning angle different from the line of sight direction and the first specific scanning angle, a maximum value of a second performance metric of the phased array antenna is achieved, the second performance metric including one of an effective radiated power of the phased array antenna and an effective isotropic radiated power of the phased array antenna.

6. A phased array antenna according to claim 3, wherein the plurality of amplifiers are each configured to amplify a signal among the plurality of signals for transmission at an associated antenna element, and the performance metric comprises one of an effective radiated power of the phased array antenna and an effective isotropic radiated power of the phased array antenna.

7. The phased array antenna of claim 3, wherein the specific scanning angle is selected so that a minimum value of the performance metric over all scanning angles within the scanning angle range is maximized.

8. The phased array antenna of claim 3, wherein the particular scan angle is selected so that a sum of the performance metric over all scan angles within the scan angle range is maximized.

9. The phased array antenna of claim 3, wherein the scan angle range defines a maximum scan angle, and the specific scan angle is selected to be midway between the boresight direction and the maximum scan angle.

10. The phased array antenna of claim 3, wherein the particular scan angle is selected to maximize the function of the performance metric over all scan angles within a suitable subset of a defined scan angle range.

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