JP6292758B2 - Antenna device - Google Patents

Description

  The present invention relates to a stealth technique for an antenna device.

In recent years, research and development of stealth technology that makes it difficult for a radar to detect a desired object has been actively conducted. Also in an antenna, low stealth, that is, low radar cross section (hereinafter abbreviated as RCS) is reduced. RCS is an important issue.
The RCS is a guideline indicating how much stealth the radio wave has.
The smaller this value, the shorter the distance detected by the radar.

There are monostatic radars that share one antenna for transmission / reception and bistatic radars in which the positions of the transmission antenna and reception antenna are very far apart, but most of the radars in practical use are monostatic. is there.
Therefore, reduction of RCS with respect to monostatic radar, that is, reduction of scattered waves in the direction of incoming waves is a top priority.

It is known that the RCS of an antenna greatly depends on the characteristics of an electric circuit connected to the antenna (hereinafter referred to as a termination condition).
FIG. 4 shows an example in which the authors have actually confirmed this by experimenting.
FIG. 4 shows a comparison of RCS pattern measurement results when the termination impedance of the array antenna is Z = Z1 and when Z = Z2.
The horizontal axis is the arrival direction of the incoming wave and the scattering direction of the scattered wave, and the vertical axis is the RCS.
As can be seen from the results in FIG. 4, it can be seen that the RCS pattern changes greatly due to the change in the terminal impedance of the antenna, and there is an angular range in which RCS increases and an angular range in which RCS decreases.
That is, the termination condition optimum value for minimizing the RCS is different depending on the direction.

FIG. 5 shows an antenna device disclosed in Patent Document 1 below.
In FIG. 5, time is divided into three modes, a transmission mode, a reception mode, and a standby mode (a mode in which transmission / reception is not performed), and termination conditions (impedance characteristics of the variable impedance unit) according to each mode. And the RCS characteristic of the antenna is controlled.
In this case, if the impedance characteristic of the variable impedance unit is set so that the RCS is low in the standby mode and the impedance characteristic is set so that the passage loss in the variable impedance unit is zero in the transmission and reception modes, the transmission / reception performance It is possible to reduce the RCS in the standby mode without impairing the above.
However, low RCS cannot be achieved in the transmission and reception modes.
Further, as described above, the optimum value of the termination condition for minimizing the RCS depends on the direction, but the method shown in FIG. 5 does not know the arrival direction of the incoming wave, and therefore reduces the RCS in the arrival direction. Can not do it.

US7202807B2

R. O. Schmidt, “Multiple emitter location and signal parameter estimation,” IEEE Trans.Antennas Propagat., Vol. AP-34, no. 3, pp. 276-280, Mar. 1986. R. Roy and T. Kailath, “ESPRIT−estimation of signal parameters via rotational invariance techniques,” IEEE Trans. Acoustics, Speech, and Signal Processing, vol. 37, no. 7, pp. 984-995, July 1989.

  Since the conventional antenna device is configured as described above, there is a problem that RCS in the direction of arrival of incoming waves cannot be reduced.

  An object of this invention is to provide the antenna apparatus which reduces RCS of the arrival direction of an incoming wave.

An antenna device according to the present invention includes a first impedance variable circuit connected to an antenna provided separately from an array antenna, and a transmitter / receiver connected to the first impedance variable circuit to perform transmission and / or reception. A receiver that receives an incoming wave through an array antenna, an analog / digital converter that converts an analog received signal from the receiver into a digital received signal, and estimates the frequency and direction of the incoming wave according to the digital received signal Is a database created before operation based on a known relationship between a calculation unit and a structure in which all components of the antenna and the antenna device are installed, and depending on the frequency and direction of the incoming wave, the antenna Stores the impedance value of the first impedance variable circuit that minimizes the RCS in the direction of arrival of the incoming wave at A corresponding impedance value is selected from the database according to the frequency and direction of arrival of the wave estimated by the arithmetic unit, and the first impedance variable circuit is selected with the selected impedance value. And a controller for switching the impedance value .

According to the present invention, the control unit that controls the impedance value of the first variable impedance circuit according to the estimated frequency and direction of the incoming wave is provided.
Therefore, it is possible to obtain an antenna device that reduces RCS in the direction of arrival of incoming waves.

It is a block block diagram which shows the antenna apparatus by Embodiment 1 of this invention. It is a circuit diagram which shows the detail of an impedance variable circuit. It is a block block diagram which shows the antenna apparatus by Embodiment 2 of this invention. It is explanatory drawing which shows the RCS pattern measurement result at the time of changing the termination impedance of the conventional antenna. It is a block block diagram which shows the conventional antenna apparatus.

Embodiment 1 FIG.
The first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an antenna apparatus according to Embodiment 1 of the present invention.
In FIG. 1, 1 is an incoming wave, 2 is an antenna, 3 is an impedance variable circuit, and 4 is a transmitter / receiver that performs transmission and / or reception.

11 is an array antenna having two or more antenna elements, 12 is a receiver, and 13 is an A / D converter that converts an analog reception signal into a digital reception signal.
Reference numeral 14 denotes an arithmetic unit that performs digital signal processing on the digital reception signal and estimates the frequency and direction of arrival wave 1.
A control unit 21 controls the impedance value of the impedance variable circuit 3 in accordance with the estimated frequency and direction of arrival waves.
31 is a transmission signal according to the frequency of the incoming wave 1, 32 is a transmission signal according to the direction of arrival of the incoming wave 1, and 33 is a control signal for controlling the impedance value.
Reference numeral 41 denotes a structure in which all components are installed.

  In the example of FIG. 1, the impedance variable circuit 3, the transmitter / receiver 4, the receiver 12, the A / D converter 13, the calculation unit 14, and the control unit 21 that are components of the antenna device are, for example, a microcomputer It is assumed that it is configured by hardware such as a semiconductor circuit board on which is mounted.

Next, the operation will be described.
The array antenna 11 that has received the incoming wave 1 transmits the received signal to the receiver 12 via the transmission line.
The received signal is transmitted from the receiver 12 to the A / D converter 13.
The A / D converter 13 converts the received signal from an analog signal to a digital signal.
The received signal converted into the digital signal is input to the calculation unit 14.

The calculation unit 14 performs fast Fourier transform (FFT) on the digital received signal, analyzes the frequency spectrum of the incoming wave 1, and estimates the frequency of the incoming wave 1.
In addition, the calculation unit 14 processes the digital reception signal according to a predetermined algorithm and estimates the arrival direction of the incoming wave 1.
As an algorithm for estimating the arrival direction, for example, the MUSIC method proposed in Non-Patent Document 1 or the ESPRIT method proposed in Non-Patent Document 2 can be used.
The frequency and direction of arrival wave 1 estimated by calculation unit 14 are transmitted to control unit 21 by transmission signals 31 and 32.

The control unit 21 includes a memory (database) that stores the set impedance value of the impedance variable circuit 3 that reduces the RCS of the antenna 2 including the structure 41 most according to the frequency and the arrival direction.
In FIG. 1, the database is divided into N (1, 2, 3) when the elevation angle (θ) direction is divided into three ranges θ1 to θ3 and the azimuth angle (φ) direction is divided into three ranges φ1 to φ3. ..., N) set values in the frequency band (Band).
A to I represent control signal types, for example, control voltage values.

Since the antenna 2 and the structure 41 are known, the relationship between the termination condition of the antenna and the RCS pattern can be known by performing measurement and / or electromagnetic field analysis before operation, and based on this, the database Can be created.

Based on the frequency and direction of arrival transmitted from the calculation unit 14, the control unit 21 selects a corresponding set impedance value from the database, and applies a control signal 33 corresponding thereto to the impedance variable circuit 3.
As a result, the impedance value of the impedance variable circuit 3 is switched to a value that minimizes the RCS in the direction of arrival.

As a configuration of the variable impedance circuit 3, for example, the configuration shown in FIG.
FIG. 2A shows a π-type impedance variable circuit using three impedance variable circuit elements Z.
As the variable impedance circuit element Z, a variable inductor, a variable capacitance diode (varactor), or the like can be used.

The arrangement of the three impedance variable circuit elements Z is not limited to the π-type, and the same effect can be obtained even in the T-type as shown in FIG.
With this configuration, the impedance value of the variable impedance circuit 3 can be freely controlled, so that the amplitude and phase of the re-radiated wave from the antenna 2 can be freely controlled. It is possible to minimize the scattered wave in the direction.

When the variable impedance circuit 3 is configured using the variable impedance circuit element Z as described above, the variable impedance range may be limited depending on the performance of the variable impedance circuit element Z.
In addition, the frequency range where the effect is exhibited may be limited.
As another configuration of the impedance variable circuit 3 for improving this, for example, the configuration shown in FIG.
This configuration is provided at both ends of a plurality of transmission lines Zn each having a different characteristic impedance, with phase shifters P / Sn (1, 2,..., N) inserted in the middle, and a plurality of transmission lines Zn. , And a switch SPnT that switches and selects one of the plurality of transmission lines Zn.
By adopting this configuration, the applicable impedance range and frequency range can be expanded.

The principle described above makes it possible to minimize the RCS in the direction of arrival.
Further, even if the arrival direction of the incoming wave changes with time, it is possible to always keep the RCS in the arrival direction to the minimum by following the change.
In FIG. 1, the antenna 2 is illustrated as having one element, but the same effect can be obtained even with an array antenna having a plurality of elements.

As described above, according to the first embodiment, the control unit 21 that controls the impedance value of the impedance variable circuit 3 is provided according to the estimated frequency and direction of the incoming wave 1.
Therefore, control by the control unit 21 reduces the RCS in the arrival direction of the incoming wave 1 by controlling the impedance value of the impedance variable circuit 3 so that the RCS in the arrival direction of the incoming wave 1 is minimized in the antenna 2. An antenna device can be obtained.

Further, according to the first embodiment, the impedance variable circuit 3 is configured by a π-type circuit.
Therefore, since the impedance value of the impedance variable circuit 3 can be freely controlled, the amplitude and phase of the re-radiated wave from the antenna 2 can be freely controlled. As a result, the scattered wave in the arrival direction can be controlled. Can be minimized.

Furthermore, according to the first embodiment, the impedance variable circuit 3 is configured by a T-type circuit.
Therefore, since the impedance value of the impedance variable circuit 3 can be freely controlled, the amplitude and phase of the re-radiated wave from the antenna 2 can be freely controlled. As a result, the scattered wave in the arrival direction can be controlled. Can be minimized.

Furthermore, according to the first embodiment, the impedance variable circuit 3 includes a plurality of transmission lines having different characteristic impedances, each having a phase shifter P / Sn (1, 2,..., N) inserted in the middle. Zn and a switch SPnT that is provided at both ends of the plurality of transmission lines Zn and switches and selects one of the plurality of transmission lines Zn.
Therefore, the applicable impedance range and frequency range can be expanded.

Embodiment 2. FIG.
FIG. 3 is a block diagram showing an antenna apparatus according to Embodiment 2 of the present invention. The same components as those described above are denoted by the same reference numerals as those described above, and detailed description thereof is omitted.
In FIG. 3, 51 a to 51 n are n impedance variable circuits inserted in n transmission lines that connect the n antenna elements constituting the array antenna 11 and the receiver 12.
A control unit 22 controls the impedance values of the impedance variable circuits 51 a to 51 n in addition to the impedance value of the impedance variable circuit 3 in accordance with the frequency and direction of arrival waves estimated by the calculation unit 14.
Reference numeral 34 denotes a control signal applied from the control unit 22 to the impedance variable circuits 51a to 51n.

Next, the operation will be described.
In the first embodiment described above, the RCS of the antenna 2 with respect to the incoming radio wave direction can be minimized, but the RCS of the array antenna 11 for detecting the incoming direction cannot be reduced.
Therefore, the same measures as those for the antenna 2 are taken for the array antenna 11.

That is, the impedance variable circuits 51a to 51n are inserted between the array antenna 11 and the receiver 12, and the impedance that minimizes the RCS of the array antenna 11 according to the frequency and direction of arrival is stored in the database of the control unit 22. The set impedance values of the variable circuits 51a to 51n are stored.
And the control signal 34 corresponding to the transmission signal 31 of the frequency of the incoming wave 1 estimated by the calculating part 14 and the transmission signal 32 of the arrival direction is applied to the impedance variable circuits 51a-51n.
By doing so, the RCS of the array antenna 11 can also be controlled to be minimum with respect to the arrival direction.

  2A to 2C is applied as a specific example of the impedance variable circuit 3, the specific examples of the impedance variable circuits 51a to 51n are illustrated in FIGS. The configuration shown in (c) may be applied.

As described above, according to the second embodiment, the impedance values of the impedance variable circuits 51a to 51n are controlled in addition to the impedance value of the impedance variable circuit 3 in accordance with the estimated frequency and direction of arrival wave 1. A control unit 22 is provided.
Therefore, the control by the control unit 22 is performed by controlling the impedance values of the impedance variable circuit 3 and the impedance variable circuits 51a to 51n so that the RCS in the arrival direction of the incoming wave 1 is minimized in the antenna 2 and the array antenna 11. An antenna device that reduces the RCS in the direction of arrival of the incoming wave 1 at the antenna 2 and the array antenna 11 can be obtained.

Embodiment 3 FIG.
In the first embodiment and the second embodiment, the arrival direction of the incoming wave 1 is one direction.
When the incoming wave 1 arrives from a plurality of directions, an impedance value that averagely reduces the RCS with respect to the plurality of arrival directions may be stored in the memories of the control units 21 and 22.
By doing so, it is possible to reduce the RCS even for a plurality of directions of arrival.

As described above, according to the third embodiment, when the incoming wave 1 arrives from a plurality of directions, the control units 21 and 22 average the plurality of directions of arrival in the antenna 2 and the array antenna 11. Therefore, the impedance values of the variable impedance circuits 3, 51a to 51n are controlled so as to reduce the RCS.
Therefore, even when the incoming wave 1 arrives from a plurality of directions, the RCS can be reduced with respect to the plurality of arrival directions.

Embodiment 4 FIG.
In the third embodiment, there is a problem that the memory capacity of the impedance value stored in the memories of the control units 21 and 22 becomes enormous when dealing with many directions of incoming waves.
There are infinite combinations of directions of incoming waves.
Therefore, in practice, the RCS can only be reduced for some limited incoming wave directions.

Therefore, the RCS reduction impedance value corresponding to each estimated direction of arrival is switched sequentially in time.
By doing so, it becomes possible to reduce the RCS on a time average basis for a plurality of directions of incoming waves.

As described above, according to the fourth embodiment, when the incoming wave 1 arrives from a plurality of directions, the control units 21 and 22 determine the arrival direction of each incoming wave at the antenna 2 and the array antenna 11. The impedance values of the impedance variable circuits 3, 51a to 51n are controlled to be switched over time so that the RCS is reduced.
Therefore, even when the incoming wave 1 arrives from a plurality of directions, the RCS can be reduced with respect to the plurality of arrival directions.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Arrival wave, 2 antenna, 3, 51a-51n Impedance variable circuit, 4 transmitter / receiver, 11 array antenna, 12 receiver, 13 A / D converter, 14 calculating part, 21,22 control part, 31, 32 Transmission signal, 33, 34 Control signal, 41 Structure.

Claims (9)

A first variable impedance circuit connected to an antenna provided separately from the array antenna;
A transmitter / receiver connected to the first variable impedance circuit for transmitting and / or receiving;
A receiver for receiving an incoming wave through the array antenna;
An analog / digital converter for converting an analog reception signal by the receiver into a digital reception signal;
In accordance with the digital received signal, a calculation unit that estimates the frequency and direction of arrival waves,
A database created prior to operation based on a known relationship between the antenna and a structure in which all components of the antenna device are installed, and the incoming wave at the antenna according to the frequency and direction of the incoming wave A database that stores the impedance value of the first variable impedance circuit that minimizes the RCS in the direction of arrival of the data, and the database according to the frequency and direction of arrival of the wave estimated by the computing unit A control unit that selects a corresponding impedance value from among the selected impedance values and switches the impedance value of the first impedance variable circuit with the selected impedance value . A second impedance variable circuit connected to each of the array antennas;
The receiver
Connected to the second variable impedance circuit to receive an incoming wave;
The controller is
The impedance value of the second variable impedance circuit is controlled in addition to the control of the impedance value of the first variable impedance circuit according to the estimated frequency and direction of arrival of the incoming wave. 1. The antenna device according to 1. The controller is
3. The antenna apparatus according to claim 1, wherein the antenna device controls an impedance value of the first impedance variable circuit so that an RCS in an arrival direction of an incoming wave is minimized. The controller is
The antenna apparatus according to claim 2, wherein, in the array antenna, an impedance value of the second impedance variable circuit is controlled so that an RCS in an arrival direction of an incoming wave is minimized. The controller is
When the incoming wave arrives from a plurality of directions, the antenna controls the impedance value of the first impedance variable circuit so that RCS is reduced on average in the plurality of directions of arrival. The antenna device according to claim 1 or 2. The controller is
When the incoming wave arrives from a plurality of directions, the antenna is configured to switch the impedance value of the first impedance variable circuit over time so that the RCS of the incoming direction of each incoming wave is reduced. The antenna device according to claim 1 or 2, characterized in that The first impedance variable circuit includes:
3. The antenna device according to claim 1, wherein the three impedance variable circuit elements are π-type circuits connected in a π-type. The first impedance variable circuit includes:
3. The antenna apparatus according to claim 1, wherein the three impedance variable circuit elements are T-type circuits connected in a T-type. The first impedance variable circuit includes:
A plurality of transmission lines each having a different characteristic impedance with a phase shifter inserted in the middle,
The antenna device according to claim 1, further comprising: a switch provided at both ends of the plurality of transmission lines and configured to switch and select one of the plurality of transmission lines.

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