JPH04286978A - Front end for radar - Google Patents

Abstract

PURPOSE:To enable withstand power of a variable attenuator which is used for protecting against leaked power to a reception system at the time of transmission to be improved at a front end for radar. CONSTITUTION:A variable attenuator is provided with two 3dB hybrid circuits of input/output, PIN diodes being added in parallel at a tip of 1/4 wavelength line at both sides, and a T branch where one output is terminated and the other is connected to an output side 3dB hybrid circuit as well as a controller which outputs a forward-bias voltage and a backward-bias voltage at the PIN diode at the T branch output side which is connected to the termination so that the PIN diode of the T branch output side which is connected to the output side 3dB hybrid circuit becomes a minimum series resistance at the time of transmission.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar front end installed in a receiving system immediately after an antenna of a radar device.

0002

[Prior Art] FIG. 3 is a configuration diagram of a conventional radar front end. In the figure, 1 is a transmitter connection terminal, 2
is a circulator for switching between transmission and reception, 3 is an antenna connection terminal, 4 is a variable attenuator connected to the circulator 2,
5 is a low noise amplifier connected to this variable attenuator 4, 6 is a mixer connected to this low noise amplifier 5, 7 is a local signal input terminal, 8 is an IF signal output terminal, and 9 is a controller that drives the variable attenuator 4. , 10 are control signal input terminals of this controller. FIG. 4 is a block diagram of the variable attenuation 4, and in the figure, 12a and 12b are 3dB hybrid circuits,
13 is an input terminal, 15 is a DC cut capacitor, 16
a, 16b are quarter wavelength lines, 17a, 17b, 17
18a and 18b are terminals, 19 is a ground, 20 is an output terminal, 21 is a bias terminal, and 22 is a bias line. FIG. 5 shows the forward current of the PIN diodes 17a, 17b, 17c, and 17d.
It is a graph of series resistance characteristics, where 23 is a forward current-series resistance characteristic curve, 24 is a forward current axis, and 25 is a series resistance axis.

Next, the operation will be explained. When sending,
A transmission signal is input from a transmitter connection terminal 1, is outputted from an antenna connection terminal 3 by a transmission/reception switching circulator 2. Further, at the time of reception, the received signal is inputted from the antenna connection terminal 3 and inputted to the variable attenuator 4 by the transmission/reception switching circulator 2. The variable attenuator 4 receives a drive voltage from the controller 9 according to the control signal input to the control signal input terminal 10, and when the received signal is below a predetermined level, it enters a passing state, and when it is above a predetermined level, the variable attenuator 4 enters a passing state. is in a predetermined attenuation state so that the low-noise amplifier 5 at the subsequent stage is not saturated. The received signal output from the variable attenuator 4 enters the low noise amplifier 5, is amplified, and is then input to the mixer 6. A local signal is input to the mixer 6 from a local signal input terminal 7, and the received signal input to the mixer 6 is output from an IF signal output terminal 8 as an intermediate frequency (IF) signal. Furthermore, when sending
Because the transmitted signal leaks from the transmit/receive switching circulator 2 and is reflected at the antenna connection terminal 3, it leaks into the low noise amplifier 5 of the receiving system. Therefore, in order to prevent damage, the variable attenuator 4 is It is controlled to the same predetermined damping state.

Next, the operation of the variable attenuator 4 will be explained using FIG. 4. During reception, the received signal input from the input terminal 13 is divided into two parts by the 3 dB hybrid circuit 12a and outputted to two output terminals, respectively. At this time, when setting the pass state, a reverse bias voltage is applied from the controller 9 to the bias terminal 21, and the four PIN diodes 17a, 17b, 17c, and 17d enter a high impedance state of several MΩ, and the received signal ,D
C-cut capacitor 15, quarter wavelength line 16a,
16b, input to the 3 dB hybrid circuit 12b on the output side, synthesized, and output from the output terminal 20. Further, when setting the attenuation state during reception and transmission, the controller 9 applies a forward bias voltage corresponding to the same attenuation amount to the bias terminal 21 during both transmission and reception,
Through the bias line 22, a forward current i1 shown in FIG.
are four PIN diodes 17a, 17b, 17c, 1
7d, the series resistor r1 enters a low impedance state, and the signal flows through the PIN diodes 17a and 17.
b, 17c, and 17d are added in parallel. Due to mismatch, most of it is reflected to the input side, and some of it is connected to the PIN.
It is absorbed by the diodes 17a, 17b, 17c, and 17d, and the remainder is input to the 3 dB hybrid circuit 12b on the output side, synthesized, and output from the output terminal 20. At this time, the signal reflected to the input side enters the 3 dB hybrid circuit 12a again, is combined, and is absorbed by the terminal end 18a.

[0005]

[Problem to be Solved by the Invention] Since the conventional radar front end is configured as described above, it has a high resistance to power leakage to the receiving system during transmission.
There was a problem in that the power resistance could not be sufficiently improved due to the limitations of heat loss in the series resistance of the N diode and heat loss at the termination of the 3 dB hybrid circuit on the input side.

[0006] The present invention was made to solve the above problems, and provides a variable attenuator that can improve power resistance against heat loss at the terminal that absorbs the series resistance of the PIN diode and the reflected power. The purpose is to obtain a front end for radar equipped with.

[0007]

[Means for Solving the Problems] A radar front end according to the present invention has variable attenuators for input and output.
It consists of a B hybrid circuit and two T branches with PIN diodes added in parallel to the tips of the quarter wavelength lines on both sides, and the input terminal of the T branch is connected to the two output terminals of the 3 dB hybrid circuit on the input side. each connected to two T
One output terminal of the branch is connected to the two input terminals of the 3 dB hybrid circuit on the output side, and a termination is connected to the other output terminal of the two T branches. The controller that drives the variable attenuator controls the variable attenuator using a control signal that controls settings during reception and a transmission trigger that controls transmission and reception.

[0008]

[Operation] During transmission, the radar front end configured as described above applies a reverse bias voltage to the PIN diode on the terminal side of the output line of the T-branch of the variable attenuator, and enters the passing state. A forward current is passed through the PIN diode on the 3 dB hybrid side of the output line of the T-branch so that it has the minimum series resistance, and it is set to be in a cutoff state, and the leakage power of the transmission signal is absorbed at the end of the Also, during reception, a forward current is passed through the PIN diode at the terminal end of the T-branch output line of the variable attenuator so as to have the minimum series resistance.
It is set to be in a cutoff state, and the received signal is output to the other output terminal of the T branch. At this time, in the pass state, a reverse bias voltage is applied to the PIN diode, which enters a high impedance state and is input to the 3 dB hybrid circuit on the output side without attenuation. In addition, in the attenuation state, a forward bias current corresponding to the amount of attenuation is passed through the PIN diode, the PIN diode becomes a low impedance, and a part of the received signal is reflected to the input side due to mismatch. It enters the 3dB hybrid circuit on the input side again, is combined, and is absorbed at the terminal. On the other hand, PIN
The remaining received signal attenuated by the diode section enters the 3 dB hybrid circuit on the output side, is combined, and is output.

[0009]

[Example] Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a radar front end, and in the figure, numerals 1 to 10 are the same as the conventional radar front end. 11 is a transmission trigger signal input terminal. FIG. 2 is a block diagram of the variable attenuator 4, and in the figure, 12 to 13 and 15 to 22 are the same as the conventional variable attenuator. 14a and 14b are T branches.

Next, the operation will be explained. When sending,
A transmission signal is input from a transmitter connection terminal 1, is outputted from an antenna connection terminal 3 by a transmission/reception switching circulator 2. Further, at the time of reception, the received signal is inputted from the antenna connection terminal 3, and inputted to the variable attenuator 4 by the transmission/reception switching circulator 2. The variable attenuator 4 receives a drive voltage from the controller 9 in accordance with the control signal input to the control signal input terminal 10. When the received signal is below a predetermined level, the variable attenuator 4 enters a communication state, and when the received signal is above a predetermined level, the variable attenuator 4 enters a communication state. is in a predetermined attenuation state so that the low-noise amplifier 5 at the subsequent stage is not saturated. The received signal output from the variable attenuator 4 enters the low noise amplifier 5, is amplified, and is then input to the mixer 6. A local signal is input to the mixer 6 from the local signal input terminal 7, and the received signal input to the mixer 6 is output from the IF signal output terminal 8 as an intermediate frequency signal. Furthermore, during transmission, the transmitted signal leaks from the transmission/reception switching circulator 2 and is reflected at the antenna connection terminal 3, causing the transmission signal to pass through the low-noise amplifier 5 of the receiving system.
To prevent damage, the variable attenuator 4 is
According to the transmission trigger signal input to the transmission trigger signal input terminal 11, a drive voltage is applied from the controller 9, and the circuit is controlled to be in a cut-off state.

Next, regarding the operation of the variable attenuator 4,
This will be explained using FIGS. 2 and 5. When receiving, input terminal 1
The received signal input from 3 is sent to the 3dB hybrid circuit 1.
2a, the signal is divided into two parts and outputted to two output terminals, respectively. At this time, when setting the pass state, a reverse bias voltage is applied from the controller 9 to the bias terminal 21b, and the four PIN diodes 17c, 17d, 17e,
17f is in a high impedance state of several MΩ, and a forward bias voltage is applied to the bias terminal 21a, and the forward current i2 shown in FIG. , respectively, resulting in a low impedance state with a minimum series resistance r2. Therefore, from the T-branches 14a, 14b to the terminal 1
When looking at the sides of 8a and 18b, the quarter wavelength line 16a
, 16b are in an open state, and the received signal passes through the T-branches 14a and 14b, the DC cut capacitor 15, the quarter wavelength lines 16c, 16e, 16d, and 16f, and is sent to the 3dB hybrid circuit 12b on the output side. The signals are input, synthesized, and output from the output terminal 20. Further, when setting the attenuation state during reception, the voltage applied to the bias terminal 21a is the same as that in the pass state, and the controller 9 applies a forward bias voltage corresponding to the amount of attenuation to the bias terminal 21b, and the bias line 22b The forward current i1 shown in FIG. 5 flows through the four PIN diodes 17c, 17d, 1
7e and 17f, the series resistor r1 enters a low impedance state, and the signal passes through the PIN diode 17c.
, 17d, 17e, and 17f are added in parallel, and due to mismatch, most of it is reflected to the input side, a part is absorbed by the PIN diodes 17c, 17d, 17e, and 17f, and the rest is reflected to the output side. 3dB hybrid circuit 12b
The signals are inputted to the input terminal 20, synthesized, and outputted from the output terminal 20. At this time, the signal reflected to the input side enters the 3 dB hybrid circuit 12a again and is combined, and is absorbed at the terminal 18c. During transmission, the leakage power of the transmission signal input from the input terminal 13 is divided into two by the 3 dB hybrid circuit 12a and output to two output terminals, respectively. At this time,
A reverse bias voltage is applied to the bias terminal 21a by the controller 9, and the two PIN diodes 17a, 17
b becomes a high impedance 2 state of several MΩ, and
A forward bias voltage is applied to the bias terminal 21b, and a forward current i2 shown in FIG. 5 flows through the bias line 22b to the four PIN diodes 17c, 17d, 1.
7e and 17f, respectively, resulting in a low impedance state with minimum series resistance r2. Therefore, T branch 14a, 1
When looking at the 3 dB hybrid circuit 12b on the output side from 4b, the quarter wavelength lines 16c and 16d are in an open state, and the leakage power enters the terminals 18a and 18b from the T branches 14a and 14b and is absorbed. Ru.

0012

As described above, according to the present invention, a variable attenuator is connected to two 3dB hybrid circuits for input and output, and PIN diodes are added in parallel to the tips of the quarter-wavelength lines on both sides between them. However, one output is terminated and the other is configured with a T-branch connected to the output side 3dB hybrid circuit, and at the time of transmission, the PIN diode on the T-branch output side connected to the output side 3dB hybrid circuit is connected in minimum series. Apply a forward bias voltage so that it becomes a resistance,
The PIN diode on the T-branch output side connected to the termination is
Since a reverse bias voltage was applied and the leakage power of the transmitted signal was absorbed at the termination, the heat loss at the series resistance part of the PIN diode to which the forward bias voltage was applied and at the termination per diode was reduced. This has the effect of reducing the size and improving power resistance.

[Brief explanation of the drawing]

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

FIG. 2 is a configuration diagram of a variable attenuator in a radar front end showing an embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional radar front end.

FIG. 4 is a block diagram of a variable attenuator in a conventional radar front end.

FIG. 5 is a graph of forward current-series resistance characteristics of a PIN diode used in a variable attenuator.

[Explanation of symbols]

1 Transmitter connection terminal 2 Transmission/reception switching circulator 3 Antenna connection terminal 4 Variable attenuator 5 Low noise amplifier 6 Mixer 7 Local signal input terminal 8 IF signal output terminal 9 Controller 10 Control signal input terminal 11 Transmission trigger signal input terminal 12 3 dB Hybrid circuit 13 Input terminal 14 T-branch 15 DC cut capacitor 16 Quarter wavelength line 17 PIN diode 18 Termination 19 Ground 20 Output terminal 21 Bias terminal 22 Bias line 23 Forward current-series resistance characteristic curve 24 Forward current axis 25 Series resistance axis

Claims (1)

[Claims] [Claim 1] Consisting of a circulator for switching between transmission and reception, a variable attenuator connected to this circulator, a low-noise amplifier connected to the output of this variable attenuator, a mixer connected to this low-noise amplifier, and a controller that drives the variable attenuator. A front end for a radar, characterized in that the variable attenuator is constituted by a microwave integrated circuit or the like, and the radar front end is characterized in that the variable attenuator is constituted by a microwave integrated circuit or the like, and is provided with the following features. stomach. Two 3dB hybrid circuits installed for input and output. B. Two T-branches are provided at the two output ends of the 3dB hybrid circuit on the input side. A DC cut capacitor connected to one terminal of the above two T-branches, a quarter connected to this capacitor
Wavelength line, PIN diode provided in parallel between the line and ground on the output side of this quarter wavelength line, 4 above.
A DC cut capacitor connected in series to the output side of the 1/2 wavelength line, and a terminal terminal connected to this. A DC provided between the other terminal of the two T-branches and the two input terminals of the 3dB hybrid circuit on the output side.
A cutting capacitor, two quarter-wavelength lines each connected in series to this capacitor, and two quarter-wavelength lines each connected in series to this capacitor.
Two PINs are installed in parallel between the line and ground in the middle of the wavelength line and on the output side of the second quarter-wavelength line.
A diode, a DC cut capacitor installed in series between the second 1/4 wavelength line and the input terminal of the 3dB hybrid on the output side. Ho. P connected to each two output terminals of the above T branch
Two bias lines conveying control signals to the IN diodes.