CN111125897B - Fast calculation method for noise power ratio NPR of traveling wave tube - Google Patents
Fast calculation method for noise power ratio NPR of traveling wave tube Download PDFInfo
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Abstract
The invention belongs to the technical field of traveling wave tube nonlinear distortion, and particularly relates to a method for rapidly calculating a Noise Power Ratio (NPR) of a traveling wave tube. Aiming at the difficulty in predicting the NPR (nonlinear design index) of the existing space traveling wave tube, the characteristic that the gain and the phase shift are unchanged in the calculation frequency range of the traveling wave tube is utilized, the input power is only required to be scanned once under a central frequency signal in a working bandwidth, then the output signal of the multi-frequency input signal under different input powers is rapidly solved by using a formula, the output signal is subjected to spectrum analysis, and the NPR under different input powers is obtained through calculation. The method effectively solves the problems of long calculation time and low efficiency of NPR (nonlinear programming) calculation by utilizing the injection wave interaction simulation, realizes NPR prediction in the design stage of the traveling wave tube, effectively improves the nonlinear design and inhibition efficiency of the traveling wave tube, saves the design time and reduces the development cost of the traveling wave tube.
Description
Technical Field
The invention belongs to the technical field of traveling wave tube nonlinear distortion, and particularly relates to a method for rapidly calculating a Noise Power Ratio (NPR) of a traveling wave tube.
Background
The traveling wave tube is a wide-band high-power vacuum electronic device and is widely applied to the fields of radar, communication, navigation and the like. The space traveling wave tube is widely applied to a communication satellite system by the characteristics of high power, high efficiency, ultra wide band, high reliability, long service life, radiation resistance and the like, and the space traveling wave tube is used as a final amplifier of satellite communication and plays an important role in signal amplification and transmission. In satellite communication, in order to reduce power consumption of satellite payload, under limited available frequency bandwidth, a multi-carrier working mode is used to increase system data transmission capacity, and multi-channel communication needs to be realized through a single space traveling wave tube amplifier, that is, the working bandwidth of a traveling wave tube is divided into a plurality of channels, and multiple channels of signals can be transmitted simultaneously. Due to the influence of nonlinear distortion in the traveling wave tube, the concurrence of multiple signals in the communication process can cause mutual interference among the multiple signals, and the accuracy of satellite communication and data transmission is influenced. In order to ensure the communication quality, the space traveling wave tube is required to have good linearity. In order to reduce mutual crosstalk between signals and reduce the error rate of a system, a traditional method adopts a working point power backspacing mode to reduce nonlinear distortion influence, on one hand, the signal power influence communication distance is reduced, on the other hand, the working efficiency of a traveling wave tube is also reduced, and loss is caused to a communication satellite with a tense energy source. Therefore, the noise power ratio needs to be accurately calculated and analyzed during the design of the traveling wave tube.
In order to meet the strict linearity requirement, the traditional linearity indexes such as amplitude modulation-amplitude modulation characteristics and amplitude modulation-phase modulation characteristics are not enough to accurately measure the linearity in the multi-carrier working mode of the traveling wave tube, and higher-level linearity indexes need to be specified. The Noise Power Ratio (NPR) is particularly suitable for analyzing the linearity characteristics of a traveling wave tube amplifier driven by a multi-carrier signal, and the criterion may take into account all types of interference, including noise, intermodulation, inter-channel interference and outer-channel interference. Evaluating NPR requires the input of a complex excitation signal. The signal is characterized by a white gaussian noise signal and has a portion of the spectrum removed (spectral notch). When the signal is input into the space traveling wave tube, the nonlinearity of the space traveling wave tube causes the removed specific frequency spectrum component in the input signal spectrum to appear in the output signal. The noise power ratio is defined as the ratio of the power spectral density outside the notch of the output signal frequency spectrum to the power spectral density at the notch, and the fast and accurate prediction of the noise power ratio is always an important subject for designing the high-linearity space traveling wave tube.
The core of the traveling wave tube work is the interaction process of electron beams and electromagnetic waves: in the vacuum tube shell, a beam of electron beam generated from a cathode is transmitted in the same direction with the electromagnetic wave carrying frequency signals at a certain speed, in the process, the electrons are modulated by the electromagnetic wave, the energy of the electromagnetic wave is also excited to be amplified, finally, the electromagnetic wave signals are amplified, and the rest electron beam is collected by a collector. The process of energy exchange between the whole electron beam and the electromagnetic wave is called the process of wave interaction. At present, a Lagrange frequency domain nonlinear wave-injection interaction model is generally adopted in the wave-injection interaction simulation calculation of a traveling wave tube, and the model needs to adopt a plurality of limited macro-electrons to represent electronic states of different time phases in periodic time. The model can be used for quickly and accurately carrying out simulation calculation on the wave injection interaction. Usually, the simulation calculation time of the one-shot wave interaction process of the single-frequency signal is within tens of seconds, and the convergence can be realized by adopting the macroelectrons with 32 time phases, but the calculation accuracy can be realized only by generating extremely many macroelectrons along with the increase of the number of input signals, and the calculation of NPR requires inputting dozens of or even thousands of frequency signals, so that the calculation time is too long, the software calculation is broken down, and the calculation convergence problem exists.
At present, domestic fast calculation methods for space traveling wave tube noise power ratio simulation are less in research, the process of testing the noise power ratio of the space traveling wave tube is complex and takes too long, NPR of the tested traveling wave tube is tested after the traveling wave tube is manufactured, and at the moment, if the NPR does not meet the non-linear index required by a user, the traveling wave tube needs to be designed and manufactured again, so that the development cost of the traveling wave tube is greatly increased. Many domestic space traveling wave tubes cannot meet the requirements of most users because they cannot meet strict nonlinear indexes. Therefore, the NPR of the traveling wave tube cannot be predicted, the nonlinear design and the suppression of the traveling wave tube are restricted, the development cost of the traveling wave tube with high linearity is greatly increased, the development period is prolonged, and the performance of the space traveling wave tube is restricted.
Disclosure of Invention
The invention provides a fast calculation method for NPR of a traveling wave tube, aiming at the defects that the NPR of the existing nonlinear design index of the space traveling wave tube is difficult to predict and the development of the high-linearity traveling wave tube is seriously restricted. The method utilizes the characteristic that the gain and the phase shift are not changed in the frequency range calculated by the traveling wave tube, only needs to scan the input power once under the central frequency signal in the working bandwidth, then utilizes a formula to quickly solve the output signal of the multi-frequency input signal under different input powers, carries out spectrum analysis on the output signal, and calculates to obtain the NPR under different input powers.
In order to achieve the purpose, the invention adopts the technical scheme that:
the method comprises the following steps: structure of the deviceInput signal required for calculating NPR, the input signal being n f A frequency signal n f And > 10, and the frequency interval between two adjacent frequency signals is equal. The center frequency of the input signal being f 0 . Setting the amplitude of each frequency signal to accord with the Gaussian distribution with the mean value of 0 and the variance of 1, and the phase to accord with the value of [0,2 pi]Random and uniform distribution within. At a central frequency f 0 Setting the amplitude of 2-5 frequency points to 0 (frequency notch) for the center, with a given total input power P in Calculating n f The amplitude corresponding to each frequency signal. N is a f The frequency signal being characterised by a centre frequency f 0 A single frequency signal.
Step two: at a central frequency f 0 And as the input signal frequency, scanning the input power by taking the small signal power of 20-25dB of saturated input power back-off as a starting point and taking the saturated input power plus 3-5dB as an end point, and acquiring the scanned gain curve G and the phase shift curve phi data. Thereby obtaining the center frequency f 0 Complex gain curve data at different input powers of the signal.
Step three: n is f The frequency signal being regarded as the central frequency f of the amplitude variation 0 Using the single frequency signal of step two 0 And calculating the output signal of the multi-frequency input signal according to the complex gain curve data of the single-frequency signal under different input powers. And carrying out Fourier transform on the output signal to obtain an output signal frequency spectrum. Accumulating M times of input signals, averaging the frequency spectrum data of the M times of calculated output signals, and finally calculating the averaged frequency spectrum to obtain the total input power P in NPR of (ii).
Step four: varying the total input power P in And repeating the process of the third step to obtain different input powers (namely different P) in Value) NPR.
The method for rapidly calculating the NPR of the traveling wave tube effectively solves the problems of long calculation time and low efficiency of NPR calculation by utilizing the wave injection interaction simulation, solves the problem of difficulty in predicting the NPR of the traveling wave tube in the design stage, realizes NPR prediction in the design stage of the traveling wave tube, effectively improves the efficiency of nonlinear design and inhibition of the traveling wave tube, saves the design time and reduces the cost for developing the traveling wave tube.
Drawings
FIG. 1 is a spectrum of an input signal of an embodiment;
FIG. 2 is a graph of gain and phase shift for implementing a routine wave tube input power sweep;
FIG. 3 is a frequency spectrum of an input signal and an output signal of an embodiment;
FIG. 4 is a schematic illustration of an NPR of an embodiment;
FIG. 5 shows NPR calculation and test comparison of Ku band spatial traveling-wave tubes of examples.
Detailed Description
The present invention is further described in detail below with reference to mathematical model formulas and the accompanying drawings.
Description of the first step:
constructing an input signal required for calculating the NPR, the input signal being n f (more than 10) frequency signals, and the frequency interval between two adjacent frequency signals is equal. The center frequency of the input signal is f 0 . Setting the amplitude of each frequency signal to accord with the Gaussian distribution with the mean value of 0 and the variance of 1, and the phase to accord with the value of [0,2 pi]Random and uniform distribution within. At a central frequency f 0 Setting the amplitude of 2-5 frequency points to 0 (frequency notch) for the center, with a given total input power P in Calculating n f The amplitude corresponding to each frequency signal. N is a f The frequency signal being characterised by an intermediate frequency f 0 A single frequency signal.
The input signal required for calculating NPR is constructed, as shown in equation (1), input signal U in Is n f A frequency signal with a minimum frequency of f min Maximum frequency of f max Frequency spacing between two adjacent frequency signals
Are equal. Calculated center frequency f 0 ＝(f min +f max )/2，U k Is the amplitude of the k-th frequency signal,
for the k-th frequency signalThe initial phase. t is time. Setting the amplitude of each frequency component of the input signal to conform to a Gaussian distribution with a mean of 0 and a variance of 1 to generate M × n f A random number P of Gaussian distribution k (k＝1,2,...,n f ). The phase is coincident with [0,2 pi ]]Random uniform distribution of inner, generating Mxn f Uniformly distributed random numbers
At a central frequency f 0 The 3 frequency points are set to the center with an amplitude of 0 (frequency notch), as shown in FIG. 1 (center frequency f) 0 ＝1.5GHz，n f =13 frequency signals, P in = 5.5 dB) spectrum has a frequency bin signal power of 0 around the center frequency, as shown by the frequency notch around the center frequency in the input spectrum in fig. 1.
Setting a shape factor s k (k＝1,2,...,n f ) Generating pits in the middle of the pass band and pits at the bottom s k =0, at the pit edge
Providing s outside the pit k At f =1 max And f min Setting s k ＝0。
Calculating n f Total input power of frequency signal is P in As shown in equation (2). According to n f Total input power P of individual frequency signals in The amplitude U corresponding to each frequency signal can be calculated k As shown in equation (3).
e.g. calculated at frequency f 0 =1.5GHz as center frequency, n f =13 frequency signals, total input power P in The spectrum of the input signal at = -5.5dB is shown in fig. 1.
The input signal needs to be calculated for many times, the amplitude of each frequency of the input signal is a random number conforming to Gaussian distribution each time, and the phase is a random number conforming to uniform distribution. The input signal is different for each calculation. Calculating the input signal M times, so it is necessary to generate M × n f A random number of amplitude and phase.
N is a f The individual frequency signals are characterized as center frequency single frequency signals, as shown in equation (4).
Wherein t is time, f 0 Is the center frequency, omega 0 ＝2πf 0 Is the center angular frequency, f k For the frequency corresponding to the kth frequency signal, Δ ω k ＝2π(f k -f 0 ) Is the difference, U, of the kth frequency signal and the central angular frequency signal k Is the amplitude of the k-th signal,
is the initial phase of the kth signal.
The second step is explained as follows:
with n f Center frequency f of frequency signal 0 And as the input signal frequency, scanning the input power by taking the small signal power of 20-25dB of saturated input power back-off as a starting point and taking the saturated input power plus 3-5dB as an end point, and acquiring the scanned gain curve G and the phase shift curve phi data. Thereby obtaining the center frequency f 0 Complex gain data at different input powers of the signal.
For example, input n f A frequency signal, lowest frequency f min =1.494GHz, maximum frequency f max =1.506GHz, the center frequency is f 0 =1.5GHz. And the saturated input power is-2.5 dBm, the small signal power after 20dB backoff is-22.5 dBm, and a gain curve G (a gain curve in fig. 2) and a phase shift curve Φ (a phase shift curve in fig. 2) are obtained.
Complex gain g (P) in ) Denoted by G and φ as:
G(P in ) For an input power of P in Gain of time, [ phi ] (P) in ) For an input power of P in Phase shift of time, j being the unit of imaginary number, g (P) in ) Representing input power as P in The complex gain of time.
The third step is explained as follows:
n f the frequency signal being regarded as the central frequency f of the amplitude variation 0 Using the center frequency f obtained in step two 0 The output signal of the multi-frequency signal can be calculated according to the complex gain curve data of the signal under different input powers. And carrying out Fourier transform on the output signal to obtain an output signal frequency spectrum. Accumulating and calculating M times of input signals, averaging the frequency spectrum data of the output signals calculated by M times, and finally calculating the averaged frequency spectrum to obtain the total input power P in NPR of (ii).
As can be seen from equation (4), the multi-frequency input signal can be regarded as the intermediate frequency f with amplitude variation 0 The input signal is subjected to wave injection interaction amplification through a traveling wave tubeIs large. Using the center frequency f obtained in step two 0 The complex gain curve data under different input power of the signal can be used for obtaining the output signal U of the multi-frequency input signal by using the formula (6) out (t) of (d). To output signal U out (t) performing Fourier transform to obtain an output signal spectrum. Accumulating and calculating M times of input signals, averaging the frequency spectrum data of the output signals calculated by M times, and finally calculating the averaged frequency spectrum to obtain the input power P in NPR of (ii).
U out (t)＝g(|C(t)| 2 )C(t)cos(2πf 0 t-φ(t)) (6)
C (t) in the formula (6) is characterized as a center frequency f for an input multi-frequency signal 0 The amplitude after the signal. I C (t) 2 I is characterized as a center frequency f by an input multi-frequency signal 0 Instantaneous power after the signal. g (| C (t) & gtY 2 ) For a central frequency signal with input power | C (t) 2 Complex gain function at l.
For example, by using measured gain and phase shift data of a certain Ku band space traveling wave tube, the number of input frequencies is set as follows: n is f =27, adjacent frequencies are equally spaced by 1MHz, and the total input power is-3 dB relative to the saturated input power. The input signal is calculated M =1000 times, the output signal is subjected to spectral analysis, the spectral data is averaged, the obtained input signal and output signal spectra are shown in fig. 3, and the calculated NPR is shown in fig. 4.
Step four is explained as follows:
varying the total input power P in And repeating the process of the third step to obtain the NPR under different input powers.
FIG. 5 is a comparison between NPR calculation and test of a Ku-band space traveling wave tube, which verifies the accuracy of the calculation method of the invention, and the error between the calculation and the test data is within 1.1 dB.
In conclusion, the method effectively solves the problems of long calculation time and low efficiency of NPR (nonlinear numerical control) calculated by utilizing the wave injection interaction simulation; the method is applied to the traveling wave tube design stage to predict the noise power ratio of the traveling wave tube, solves the problem that the NPR of the traveling wave tube is difficult to predict in the design stage, realizes the NPR prediction in the design stage of the traveling wave tube, effectively improves the efficiency of nonlinear design and suppression of the traveling wave tube, saves the design time, and reduces the cost of developing the traveling wave tube.
Claims (2)
1. A fast calculation method for an NPR of a traveling wave tube comprises the following specific steps:
the method comprises the following steps: the input signals required for calculating the NPR are constructed:
input signal is n f Frequency signals, the frequency interval between two adjacent frequency signals is equal, the center frequency of the input signal is f 0 Setting the amplitude of each frequency signal to accord with the Gaussian distribution with the mean value of 0 and the variance of 1, and the phase to accord with the value of [0,2 pi]Random uniform distribution of inner, n f Is more than 10; at a central frequency f 0 Setting the amplitude of 2-5 frequency points as 0, i.e. frequency notch, for the center, by a given total input power P in Calculating n f Amplitude corresponding to frequency signal, n f The frequency signal being characterised by a centre frequency f 0 A single frequency signal;
step two: at a central frequency f 0 As the input signal frequency, the input power scanning is carried out by taking the small signal power of 20-25dB of saturated input power back-off as a starting point and taking the saturated input power plus 3-5dB as an end point, and the data of a scanned gain curve G and a phase shift curve phi are obtained, so that the central frequency f is obtained 0 Complex gain curve data at different input powers of the signal;
step three: using f obtained in step two 0 Calculating the output signal of the multi-frequency input signal by using complex gain curve data of the single-frequency signal under different input powers, and performing Fourier transform on the output signal to obtain an output signal frequency spectrum; accumulating M times of input signals, averaging the frequency spectrum data of the M times of calculated output signals, and finally calculating the averaged frequency spectrum to obtain the total input power P in NPR of (g);
step four: varying the total input power P in And repeating the process of the third step to obtain different input powers, namely different P in NPR at value.
2. The method for rapidly calculating the NPR of the traveling wave tube according to claim 1, applied to a traveling wave tube design stage to predict the noise power ratio of the traveling wave tube.
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| CN105335585A (en) * | 2015-12-07 | 2016-02-17 | 电子科技大学 | Fast three-order intermodulation calculation method of traveling-wave tube |
| CN109740225A (en) * | 2018-12-25 | 2019-05-10 | 电子科技大学 | A method of it calculates and assesses for broad-band TWT |
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| CN105335585A (en) * | 2015-12-07 | 2016-02-17 | 电子科技大学 | Fast three-order intermodulation calculation method of traveling-wave tube |
| CN109740225A (en) * | 2018-12-25 | 2019-05-10 | 电子科技大学 | A method of it calculates and assesses for broad-band TWT |
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