JPH04307802A - Antenna system - Google Patents

Abstract

PURPOSE:To realize the antenna system having a suppression performance even to plural interference waves (undesired waves) with respect to the antenna system having a function to suppress the undesired signal made incident from a side lobe of a main beam. CONSTITUTION:The electric characteristic of a receiver connecting to an antenna of the antenna system is made equivalently identical and the dispersion in the amplitude and phase of a receiver output signal are corrected respectively by a compensation device 11 so that the reception is not equivalently modulated by noise and the result is inputted to a Fourier transformation device 10 thereby almost discriminating plural interference waves (undesired waves) by each incident direction. Thus, a weight adjusted by an adaptive filter 5 receiving an output of the Fourier transformation device is converged quickly to an optimum solution and even when the plural interference waves (undesired waves) are received, the antenna system having an interference wave suppression performance is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna device for suppressing unnecessary signals incident from side lobes of an antenna.

0002

2. Description of the Related Art FIG. 3 shows, for example, S. P. Appleb
aum: “Adaptive Arrays,” IEE
E Trans AntennaPropagate. ，
vol. AP-24, No. 5, (1976) is a configuration diagram of a sidelobe canceller, which is an antenna device that suppresses unnecessary signals incident from sidelobes. In the figure, 1 is a main antenna, 2a, 2b, 2c are auxiliary antennas, 3, 4a, 4b, 4c are receivers, 5 is an adaptive filter, and 6 is a complex subtracter. FIG. 4 shows the adaptive filter 5
It is a block diagram showing the inside of. In the figure, 7a, 7b, 7
c is a complex multiplier, 8 is a complex adder, 9 is a complex multiplier 7a
, 7b, 7c. In the figures referred to below, S is the desired wave, J0, J1
respectively indicate interference waves (unnecessary waves), d(k) is the output signal of the receiver 3 of the main antenna 1, x0(k), x1(k), x
N-1 (k) is the output signal of each receiver connected to the auxiliary antennas 2a, 2b, and 2c, y(k) is the output signal of the adaptive filter 5, and z(k) is the output signal of the complex subtracter (= output signal of the antenna device), w0(k), w1(k
), wN-1 (k) are the complex multipliers 7a, 7b, 7, respectively.
It shows the load of c. In the expressions for these signals, k is a factor representing time; when the signal is an analog signal, k is a real number; when the signal is a digital signal, k is an integer. The following explanation can be made in the same way regardless of the form of the signal, but for convenience, the case of a digital signal will be explained here. In this case, each receiver includes an A/D converter and simultaneously samples the received signals of the main antenna and each auxiliary antenna at a constant sampling period T. The sampling period T is selected so that T<(1/B), where B is the band of each receiver. Also, in order to simplify the expressions, all signals are expressed as complex signals. Each receiver internally amplifies and phase-detects the RF band reception signals received by the main antenna and each auxiliary antenna to generate a complex video signal.

Next, the operation of the sidelobe canceller shown in FIG. 3 will be explained using an example in which the sidelobe canceller receives a desired wave S and two interference waves J1 and J2. When the antenna gain of the main antenna is expressed as G(θ), d(k) can be expressed by the following equation.

0004

[Math 1]

where ωS : Angular frequency of desired wave S θS : Incident angle of desired wave S ω1 : Angular frequency of interference wave J1 θ1 : Incident angle of interference wave J1 ω2 : Angular frequency of interference wave J2 θ2 : Angular frequency of interference wave J2 Incident angle ES: Amplitude E1 of desired wave S: Amplitude E2 of interference wave J1: Amplitude n(k) of interference wave J2: Internal noise a0 of receiver 3: Gain φ0 of receiver 3: Transmission phase amount of receiver 3 Here, the desired wave S is received by the main lobe of the main antenna,
Assuming that the interference waves J1 and J2 are received by the side lobes of the main antenna, the following equation holds true.

[0006]

[Math 2]

However, the amplitude E of the interference waves J1 and J2
1, E2 is 103 to 1 compared to the amplitude ES of the desired wave S.
When it is large on the order of 0.04, the following equation is obtained.

[0008]

[Math 3]

That is, in d(k), the component of the desired wave S is buried in the components of the interference waves J1 and J2, and as a result, it becomes very difficult to detect the desired wave S in d(k). The sidelobe canceller attempts to suppress the interference wave component incident from the sidelobe of the main antenna from d(k). First, the interference wave signal is received using the auxiliary antennas 2a, 2b, 2c provided close to the main antenna, and after being amplified and phase detected inside the receivers 4a, 4b, 4c, it is transferred to the adaptive filter 5. do. Here, the auxiliary antenna is omnidirectional, and the desired wave S and the interference wave J1
, J2 have the same antenna gain. Therefore, the component of the desired wave S included in the input signal xi (k) of the adaptive filter 5 can be ignored compared to the components of the interference waves J1 and J2, and can be expressed by the following equation.

0010

[Math 4]

Here, λ1: wavelength of interference wave J1 λ2: wavelength of interference wave J2 i: auxiliary antenna number (if i=0, auxiliary antenna 2a
) ni (k): Receiver noise αi: Receiver gain, βi: Transmission phase amount of the receiver. Further, d0 is the distance between the main antenna 1 and the auxiliary antenna 2a, and d is the distance between the auxiliary antennas. Inside the adaptive filter 5, the signal xi (k), (i=
0,...,N-1) are multiplied by the weights w i (k), (i=0,...,N-1) in the complex multipliers 7a, 7b, 7c, and then transferred to the complex adder 8 and then The signal y(k
) is generated.

0012

[Math 5]

The signal y(k) is transferred to a complex subtracter 6,
A difference signal z(k) with the output signal d(k) of the receiver 3 is generated. z(k)=d(k)−y(k)
(6
) signal z(k) can be expressed by the following equation by substituting equations 1 and 4 into equation 6.

[0014]

[Math 6]

Now, the weight w is set so that the signal y(k) takes a value as close as possible to the interference wave component contained in the signal d(k).
i (k), (i=0, ~, N-1), the signal z(k) becomes the desired signal component G(θS)ES·exp(j
It is clear from Equation 7 that the value is close to wSkTS).

[0016]

[Math 7]

[0017] If wi (k), (i=0, ~, N-1) is adjusted so that it satisfies Equations 8 and 9, the interference wave component contained in z(k) can be completely suppressed. Can be done. Formula 8
, In order to determine wi (k) according to Equation 9, it is necessary to know the incident direction and wavelength of the interference wave in advance, so in reality, wi (k) is determined by solving Equations 8 and 9. I can't. Therefore, in the sidelobe canceller, the load wi (k) is determined by the method described below. If the frequency fS of the desired wave S and the frequencies f1 and f2 of the interference waves J1 and J2 are different, the root mean square value of z(k) is expressed by the following equation.

[0018]

[Math. 8]

Here, E[f(k)] is the time average value defined by Equation 11. In addition, in deriving Equation 10, Equation 12,
The relationships shown in Equations 13, 14, and 15 were used. As is clear from Equation 10, adjusting the weight w i (k) so as to minimize the term { } on the right side of Equation 10 is E{|
Since it is equivalent to minimizing z(k) | 2 },
The interference wave component can be suppressed by adjusting the weight so as to minimize E{|z(k)|2 }. This is because when E{|z(k)|2 } is minimized, Equation 16 holds true, and considering that σn is usually very small compared to E1 and E2 and σn can be ignored in Equation 16, , Equation 16 is equivalent to Equation 8 and Equation 9.

[0020]

[Math. 9]

In this way, in the sidelobe canceller, z
The interference waves are suppressed by adjusting the weight w i (k) so as to minimize the root mean square value E{|z(k)|2 } of (k). wi (
k) is called the optimal load, which is the Wiener-Hop
It is known that it is given as a solution to the equation of f.

[0022]

[Math. 10]

Here, vector Wopt, vector R, and vector P are the optimal weight vector defined by the following equations, the covariance matrix of signal xi (k), and the mutual variance matrix of signal xi (k) and signal d(k). It is.

[0024]

[Math. 11]

Here, T represents transpose, and * represents complex conjugate. In this way, the optimal weight of the sidelobe canceller can be determined by Equation 17 if the covariance matrix of the auxiliary antenna output signal and the mutual variance matrix of the main antenna output signal and the auxiliary antenna output signal are known. However, in reality, vector R and vector P are not known, and even if they were known, using Equation 17 would require calculating the inverse matrix for vector R, ensuring real-time processing of load calculation. In order to do this, use the load calculator 9's H/
The amount of W increases. For this reason, Equation 17 is inappropriate as a method for calculating the load, and in normal sidelobe cancellers, the method of determining the optimal load sequentially from the signals xi (k) and d(k) is Be taken. A typical method is the well-known LMS (Least
Mean Square) algorithm is often used.

[0026]

[Math. 12]

μ is a constant that defines the magnitude of load correction, and is a parameter that controls the speed and stability with which wi(k) converges to the optimal solution of Equation 17.

Now, FIGS. 5 and 6 show the results of an antenna pattern derived by simulation when the conventional sidelobe canceller described above receives one interference wave (J1). FIG. 5 shows the antenna pattern before load adjustment, and FIG. 6 shows the antenna pattern after load adjustment. As shown in Figure 6, after the load adjustment, the antenna gain in the incident direction (12°) of the interference wave J1 is lower (-20°).
dB or less), it can be seen that the sidelobe canceller suppresses the interference wave J1. Next, FIG. 7 shows the results of a simulation of an antenna pattern when a conventional sidelobe canceller receives two interference waves (J1, J2). When two interference waves are received as shown in Figure 7, the antenna gain in the direction of incidence of interference wave J1 (12 degrees) is -10 dB, and the gain in the direction of incidence of interference wave J2 (6 degrees) is -10 dB.
It can be seen that the antenna gain of ゜) is 0 dB, and the sidelobe canceller does not suppress the interference waves as compared to the case where one interference wave is received. This is because the load adjusted by the sequential algorithm shown in Equation 21 has not converged to the optimal solution shown in Equation 17. Furthermore, as shown in FIG. 7, in the conventional sidelobe canceller, when two interference waves are received, the sidelobe levels in directions other than the direction in which the interference waves are incident become extremely high.

[0029]

[Problem to be Solved by the Invention] A conventional antenna device having the function of suppressing unnecessary signals incident from the sidelobes of the main beam is configured as described above, and a plurality of interference waves (unnecessary waves) are received. In this case, there was a problem that the interference wave suppression performance deteriorated and the sidelobe level in directions other than the incident direction of the interference wave increased. This invention was made to solve the above problems, and has interference wave suppression performance even when multiple interference waves (unnecessary waves) are received.
It is an object of the present invention to obtain an antenna device that can avoid an increase in the sidelobe level in directions other than the incident direction of interference waves.

[0030]

Means for Solving the Problems In order to achieve the above object, a sidelobe canceller according to the first aspect of the invention includes the following elements. Compensation means for equivalently correcting the electrical characteristics of (a) the main antenna and a plurality of auxiliary antennas, (b) a receiver connected to each of the above antennas, and (c) a receiver connected to each of the above auxiliary antennas. ,(d)
Fourier transform means that inputs the output signal of the compensation means and performs Fourier transform; (e) an adaptive filter that inputs the output signal of the Fourier transform means; (g) a receiver output signal connected to the main antenna and the adaptive filter; Subtraction means for calculating the difference between the output signal and the output signal. The active antenna having a sidelobe canceller function according to the second invention includes the following elements. (a) a plurality of antenna elements arranged at predetermined distance intervals; (b)
) a receiver connected to the antenna element; (c) compensation means for equivalently correcting the electrical characteristics of each of the receivers; (d
) Beam forming means that receives part or all of the output signal of the compensation means and forms a beam in a predetermined direction; (
e) Fourier transform means that inputs part or all of the output signal of the compensation means and performs Fourier transform, (f) an adaptive filter that receives the output signal of the Fourier transform means as input, (g) the output signal of the beam forming means. and a subtraction means for calculating the difference between the output signal of the adaptive filter and the output signal of the adaptive filter.

[0031]

[Operation] In the antenna device configured as described above, the electrical characteristics of the receiver connected to the antenna element are equivalently the same, and the receiver output signal is By correcting variations in amplitude and phase using compensation means, and then inputting them to Fourier transform means, it is possible to roughly discriminate between multiple interference waves (unwanted waves) according to the direction of incidence, and thereby the output of Fourier transform means is input to Fourier transform means. The weight adjusted in the input adaptive filter quickly converges to the optimal solution, and even if a plurality of interference waves (unnecessary waves) are received, these can be suppressed.

[0032]

[Embodiment] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the first invention. In this embodiment, compared to the conventional configuration of the sidelobe canceller shown in FIG. 3, the gain and transmission phase amount of the electrical characteristics of each receiver newly connected to each auxiliary antenna are made equivalently the same. 1, and a Fourier transformer which inputs the output signal of the compensator 11 and discriminates a plurality of interference waves according to the direction of incidence. Output signal of each receiver xi (k), (i=,1,...,N-1
), the output signal of the compensator 11 is vi (k), (i=0,
1,...,N-1), and the output signal of the Fourier transformer 10 is um(k), (m=0,1,...,M-1),
The operation of the new components of the sidelobe canceller shown in FIG. 1 will be described below. In equation 4, αi, βi
, (i=0,...,N-1)
The gains and transmission phase amounts of b, 4c, and 4d take different values for each receiver. It is generally difficult to align the electrical characteristics of receivers so that these quantities take the same value, and adjustment requires time. The compensator 11 compensates for such variations in the electrical characteristics of the receivers by the calculation shown in the following equation, and makes the characteristics of the receivers 4a, 4b, and 4c equivalently the same.

[0033]

[Math. 13]

[0034] Here, C and Γc are the gain and transmission phase amount which serve as reference values for compensation. The gain compensation amount C/αi and the phase compensation amount Γc−βi are stored in the memory inside the compensator 11, and the calculation of Equation 22a is executed by a microcomputer, etc., thereby making it easy to compensate for the electrical characteristics of the receiver. It can be implemented. The above αi and βi can be obtained by measuring the characteristics of the receiver in advance. In the present invention, the spatial spectrum of the interference wave is obtained using Fourier transform, which will be described next, and the interference wave is discriminated from the difference in the spatial spectrum, so compensation for the electrical characteristics of the receiver is important. The above-described variation in the characteristics of the receiver is equivalent to modulating the received signal with noise, and has the effect of spreading the spatial spectrum of the interference wave. Therefore, unless variations in receiver characteristics are compensated for, interference waves cannot be discriminated by Fourier transform, and the effect of suppressing multiple interference waves, which is the objective of the present invention, cannot be expected. In general, it is known that the variation in receiver characteristics is dominated by that in the amount of transmitted phase, and that the variation in the amount of transmitted phase is uniformly distributed in the range [0, 2π]. On the other hand, the variation in gain is small, and the following equation holds true through simple adjustment. α0=α1=…=αN-1
(22
b) Hereinafter, for ease of explanation, it is assumed that Equation 22b holds true and Equation 22c holds true. C=1, Γc=0
(22
c)

After inputting the output signals vi (k), (i=0,...,N-1) of the compensator 11, the Fourier transformer 10 internally performs the Fourier transform operation shown in the following equation to obtain um ( k), (m=0,...,M-1) and transfer it to the adaptive filter 5.

[0036]

[Math. 14]

Here, the coefficient 1/2 of sin θm is s
This is for normalizing so that the range of inθm/2 is (-0.5, 0.5). θm is a predetermined constant, and is appropriately determined within the range where the interference wave is incident. In particular, with M=N, sin θm /2=m/N,
(m=0, 1, ~, N-1) (24) If θm is chosen so that it becomes, Equation 23 becomes equivalent to the discrete Fourier transform (hereinafter referred to as DFT) shown in the following equation.

[0038]

[Math. 15]

The calculation of Equation 25 is performed using fast Fourier transform (hereinafter referred to as
By using an algorithm (called FFT), high-speed execution is possible. Since um (k) generated according to Equation 23 or Equation 25 is input to the adaptive filter 5, the load calculator 9 adjusts the load wi (k) by a sequential algorithm shown in the following equation. wi(k+1)=wi(k)+2
μz(k)u*i(k) (26)

(i=0,~,M-1)

FIG. 8 shows an example of an antenna pattern derived by simulation when the sidelobe canceller according to the present invention configured as described above receives two interference waves. As shown in Fig. 8, the incident direction (12°) of the interference wave J1 and the interference wave J2
The antenna gain in the direction of incidence (6 degrees) is approximately -20 dB, and the same suppression performance as in the case of one interference wave shown in FIG. 6 is obtained. Furthermore, compared to FIG. 5, it can be seen that the side lobe levels in directions other than the direction in which the interference waves are incident are maintained at the same level as when no interference waves are received.

Although the case where the calculation method for load adjustment executed inside the load calculator 9 is the LSM algorithm has been described here, the present invention is not limited to this, and the invention is not limited to this, and the present invention is also applicable to other algorithms such as the learning identification algorithm shown in equation 27. ,
A similar effect can be obtained by using the probability approximation algorithm shown in Equation 28.

[0042]

[Math. 16]

Furthermore, although the case where the auxiliary antennas are arranged one-dimensionally has been explained here, the present invention is not limited to this, and the same effect can be obtained even when the auxiliary antennas are arranged two-dimensionally on a plane. have

An embodiment of the second invention will be described below. FIG. 2 is a configuration diagram showing an embodiment of the present invention 2,
It is an active antenna with a sidelobe canceller function. In this example, N
In order to equivalently equalize the gain and transmission phase amount of the electrical characteristics of each of the N+1 receivers connected to the +1 antenna element, a compensator 11 and the output signal of the compensator 11 are input. It is constructed with a Fourier transformer for discriminating a plurality of interference waves according to their incident directions, and a beamformer 13 that receives the output signal of the compensator 11 and performs directional synthesis to form a main beam. The output signal of each receiver xi (k), (i=0,1,...,N-1), the output signal of the compensator 11 is vi (k), (i=0,1,...,N
-1), and the output signal of the Fourier transformer 10 is um (
k), (m=0, 1,...,M-1), the function of the sidelobe canceller of the active antenna in FIG. 2 is equivalent to the function of the sidelobe canceller in FIG. a sidelobe canceller compensator 11,
The content of invention 1 achieved by the combination of the Fourier transformer 10 and the adaptive filter 5, and the content of invention 2 achieved by the combination of the active antenna compensator 11, the Fourier transformer 10, and the adaptive filter 5 in FIG. 2 are as follows: , operation, and effect are the same, so redundant explanation will be omitted, and the different configurations and operations will be explained below. Here, N is the total number of antenna elements, and M is the number of output channels of the Fourier transformer 10. In FIG. 2, parts having the same or equivalent functions as those of the conventional example are given the same reference numerals. Desired wave S and interference waves J1 and J2 arriving from external space are received by antenna elements 12a, 12b, 12c and 12d, respectively.
After being amplified, phase detected, and sampled within the receivers 4a, 4b, 4c, and 4d, the signals are transferred to the Fourier transformer 10 and beamformer 13. Output signal xi (k) of each receiver
can be expressed by the following equation, assuming that each antenna element is non-directional.

[0045]

[Math. 17]

Here, ωS : Angular frequency of desired wave S λS : Wavelength of desired wave S θS : Incident angle of desired wave S ES : Amplitude of desired wave S ω1 : Angular frequency of interference wave J1 λ1 : Wavelength of interference wave J1 θ1: Incident angle of interference wave J1 E1: Amplitude of interference wave J1 ω2: Angular frequency of interference wave J2 λ2: Wavelength of interference wave J2 θ2: Incident angle of interference wave J2 E2: Amplitude of interference wave J2 α: Antenna element spacing ni (k): Receiver noise αi: Gain βi of receiver i: Transmission phase amount of receiver i. The beamformer 13 has a function equivalent to that of the main antenna 1 shown in the conventional example shown in FIG. 3, and forms a beam in the incident direction of the desired wave S by performing directional synthesis using the integral calculation shown in the following equation.

[0047]

[Math. 18]

Here, θ is a parameter that controls the direction in which the beam is formed, and usually θ=θs. P indicates the number of integrals, and the following formula must hold true. P≦N

(32) When P=N, a beam is formed using all of the receiver output signal xi, that is, vi (k) corrected by the compensator, and when P<N, the receiver output signal vi( k) will be used to form a beam. In general, the larger P is, the sharper it is (the narrower the half width)
It is possible to form a beam, but the calculation time is longer. By substituting equation 30 into equation 31, the following equation is obtained as the output signal of the beam former 13.

[0049]

[Math. 19]

Here, Equation 34, Equation 35, Equation 36, Equation 37
It can be seen that Equation 33 is equivalent to Equation 1, and that the beam former 13 has the same function as the main antenna 1 of FIGS. 1 and 3. Next, after inputting the output signal vi (k) of the compensator 11, the Fourier transformer 10 internally performs the Fourier transform operation shown in the following equation to convert um (k)
is generated and transferred to the adaptive filter 5.

[0051]

[Math. 20]

Here, Q is a parameter that controls the number of integrals, and must have the following relationship. Q≦N

(39) When Q=N, all of vi (k) is used for Fourier transformation, and when Q<N, vi
A portion of (k) will be used for Fourier transformation. Generally, increasing Q improves the ability to discriminate interference wave signals, but increases calculation time.

[0053]

As described above, according to the present invention, the electrical characteristics of the receiver connected to the antenna element are equivalently the same, and the receiver output is adjusted so that the received signal is not equivalently modulated by noise. By inputting the signals to the Fourier transform means after each signal is corrected by the compensation means, it is possible to roughly discriminate between multiple interference waves (unwanted waves) according to the direction of incidence, thereby creating an adaptive filter that receives the output of the Fourier transform means as input. The loads adjusted in will now converge to the optimal solution quickly,
An antenna device can be obtained that has interference wave suppression performance even when a plurality of interference waves (unnecessary waves) are received, and can also avoid an increase in side lobe levels in directions other than the incident direction of interference waves.

[0054]

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of the second invention.

FIG. 3 is a configuration diagram showing a conventional sidelobe canceller.

FIG. 4 is an internal configuration diagram of an adaptive filter according to the first invention, the second invention, and a conventional example.

FIG. 5 is a diagram showing an antenna pattern when a conventional sidelobe canceller receives one interference wave. (Before load adjustment)

FIG. 6 is a diagram showing an antenna pattern when a conventional sidelobe canceller receives one interference wave. (After load adjustment)

FIG. 7 is a diagram showing an antenna pattern when a conventional sidelobe canceller receives two interference waves.

FIG. 8 is a diagram showing an antenna pattern when the antenna devices of the first and second inventions receive two interference waves.

[Explanation of symbols]

1 Main antennas 2a, 2b, 2c Auxiliary antenna 3 Receivers 4a, 4b, 4c, 4d Receiver 5 Adaptive filter 6 Complex subtracters 7a, 7b, 7c Complex multiplier 8 Complex adder 9 Load calculator 10 Fourier transformer 11 Compensation antenna element 13
beam former

Claims (2)

[Claims] Claim: 1. An antenna device having the following elements: Compensation for equivalently correcting the electrical characteristics of (a) the main antenna and the plurality of auxiliary antennas, (b) the receiver connected to each of the above antennas, and (c) each receiver connected to each of the above auxiliary antennas. means, (d) Fourier transform means for inputting and Fourier transforming the output signal of the compensation means; (e) an adaptive filter inputting the output signal of the Fourier transform means;
g) subtraction means for calculating the difference between the receiver output signal connected to the main antenna and the output signal of the adaptive filter; 2. An antenna device having the following elements. (a) a plurality of antenna elements arranged at predetermined distance intervals; (b) a receiver connected to the antenna elements; and (c) compensation for equivalently correcting the electrical characteristics of each of the receivers. (d) beam forming means for forming a beam in a predetermined direction using part or all of the output signal of the compensation means as input; (e) Fourier transformation using part or all of the output signal of the compensation means as input; (f) an adaptive filter inputting the output signal of the Fourier transform means; (g) subtraction means for calculating the difference between the output signal of the beam forming means and the output signal of the adaptive filter.