JP2972682B2 - Aircraft position detection system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aircraft position detecting system, and more particularly to an aircraft position detecting system for detecting a position by selecting one of outputs of a plurality of secondary monitoring radar devices having overlapping detection ranges. About.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show a conventional example. In FIG. 5, one secondary surveillance radar device 71 has 250
The pulse-like interrogation signal I1 is transmitted in a cycle of the number of times. Also,
The other secondary monitoring radar device 72 transmits a pulse-like interrogation signal I2 at a cycle of 300 times per second. Each interrogation signal I
1 and I2 are both received by the aircraft transponder 53, and the aircraft transponder 53
The pulse-like response signal R is transmitted in synchronization with the cycle of I2. The response signal R includes information on the flight altitude of the aircraft at that time and information on the identification code (beacon code) of the aircraft, and is transmitted over a wide area by an omnidirectional antenna. The response signal R transmitted from the aircraft transponder 53 is received by each of a plurality of target detection circuits B1 to Bn (n = 2, 3, 4,...) Arranged on the ground. Since these target detection circuits B1 to Bn are installed at predetermined positions separated from each other by about several tens of kilometers,
Even if there is only one response signal R, each of the target detection circuits B1 to Bn
Received with a time difference between them. Each target detection circuit B1
Bn is 25 per second of the continuous response signal R pulses.
Only signals appearing in a repetition cycle of 0 times are detected, and the detection times are set as reception time information M1 to Mn (n =
2, 3, 4,...). The reception time information M1 to Mn output from the target detection circuits B1 to Bn are input to the position calculation circuit 55. The position calculation circuit 55 specifies the position of the aircraft based on the difference in the reception time of the response signal R in each of the target detection circuits B1 to Bn, and outputs aircraft position information.

According to FIG. 6, first, as shown in FIG.
The interrogation signal I1 is transmitted from one secondary surveillance radar device 71 at a repetition cycle of 250 times per second, as indicated by the symbol A. Further, the interrogation signal I2 is transmitted from the other secondary surveillance radar device 72 at a repetition cycle of 300 times per second, as indicated by the symbol B. Therefore, the response signal R transmitted from the aircraft transponder 53 is a signal including pulses of both repetition periods, as indicated by the symbol c. On the other hand, in each of the target detection circuits B1 to Bn, as indicated by reference numeral 2, the timing is adjusted so as to extract a pulse having a repetition cycle of 250 times per second. Therefore, in each of the target detection circuits B1 to Bn, only the pulse train having a cycle of 250 times per second is extracted as indicated by the symbol E, and the time at which this pulse is detected is used as the reception time information M1 to Mn as described above. It is input to the position calculation circuit 55. Therefore, even if an aircraft exists in an airspace where the detection ranges of the two secondary monitoring radars 71 and 72 overlap, the position of the aircraft can be accurately detected. This is generally called a synchronous interference method.

[0004]

However, in the above-mentioned conventional example, if the interrogation signal at a cycle of 250 times per second is not transmitted due to the stoppage of the operation of the secondary monitoring radar device 71 or the like, the position information of the aircraft is lost. There was an inconvenience that it could not be obtained. To avoid this,
There is a method in which the period of the pulse to be extracted by the target detection circuits B1 to Bn is changed to 300 times per second to match the other secondary monitoring radar device 72. However, each target detection circuit B
1 to Bn are separated from each other by several tens of kilometers, and there is a problem that a great deal of labor and time are required for the setting change operation, and a considerable time is required until the system is restored and the position information of the aircraft is obtained.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to improve the disadvantages of the prior art, and particularly to a system in which a specific secondary surveillance radar device cannot transmit an interrogation signal and the position of an aircraft cannot be detected. It is an object of the present invention to provide an aircraft position detection system that enables quick maintenance of a vehicle and enables quick recovery of the system.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a secondary surveillance radar device for transmitting an interrogation signal which is a pulse signal of a fixed period, and A target detection circuit that receives a pulse-like response signal returned from the aircraft transponder in synchronization with the cycle of the transmitted interrogation signal and outputs reception time information of the pulse. Further, there is provided a position calculation circuit that calculates the position of the aircraft based on the reception time information output from the target detection circuit. Among them, the secondary surveillance radar device is provided with two or more units having different interrogation signal periods. Further, the target detection circuit is configured to extract only pulses having a cycle of a specific interrogation signal selected in advance from the response signal, and to output reception time information for the extracted pulses. Then, a plurality of the target detection circuits are provided at a predetermined distance. The position calculation circuit calculates the position of the aircraft based on a time difference between pieces of reception time information output for the same reception pulse from each target detection circuit. In addition, in the present invention, on the condition that the reception time information is no longer output from the target detection circuit,
Providing a cycle changing unit that changes the cycle of the interrogation signal selected by the target detection circuit to a different interrogation signal cycle,
The configuration is adopted.

For this reason, according to the present invention, when the secondary monitoring radar device transmitting the interrogation signal of the cycle set to the target detection circuit stops operating, the reception time information is not output from the target detection circuit. The period set in the target detection circuit is quickly switched to the period of the interrogation signal transmitted by another secondary monitoring radar device. For this reason, the output of the reception time information is restarted from the target detection circuit, and the position calculation circuit can detect the position of the aircraft, and the system is restored.

[0008] According to the second aspect of the present invention, the cycle changing unit includes:
The configuration is such that the period of the interrogation signal selected by the target detection circuit is changed on condition that the reception time information is not output from the target detection circuit for a certain period of time.

According to the present invention, for example, even if the secondary monitoring radar apparatus to be extracted by the target detection circuit fails to transmit the interrogation signal, if the interrogation signal is short and does not exceed a certain time, the secondary monitoring radar apparatus does not It is not considered that the operation of the next monitoring radar device is stopped, and the cycle changing unit does not switch the cycle of the question signal to be extracted.

[0010] In the invention according to claim 3, the cycle changing unit includes:
The configuration is such that the cycle of the interrogation signal of each secondary monitoring radar device is changed in a predetermined order.

In the present invention, for example, first to third three secondary monitoring radar devices are installed, and the period of the interrogation signal of the first secondary monitoring radar device is set in the target detection circuit. In this case, when the first secondary monitoring radar device and the second secondary monitoring radar device stop transmitting the interrogation signal at the same time, the cycle changing unit firstly changes the period of the interrogation signal of the second secondary monitoring radar device. Although it is set in the target detection circuit, since there is no output of the reception time information, the period of the interrogation signal of the third secondary monitoring radar device is set in the target detection circuit.

In the invention according to the fourth aspect, the position calculation circuit outputs an abnormality report on condition that the reception time information is no longer output from the target detection circuit, and the cycle changing unit transmits the abnormality report from the position calculation circuit. A configuration is adopted in which the period of the interrogation signal selected by the target detection circuit is changed on the condition that it is received.

According to the present invention, the cycle changing unit monitors the abnormality report output from the position calculation circuit, and when there is the report,
The cycle set in the target detection circuit is changed by the cycle changing unit.

[0014] In the invention according to claim 5, the cycle changing unit includes:
Next, a cycle selection circuit that selects a cycle of the interrogation signal to be set in the target detection circuit, and a cycle setting circuit that sets the cycle selected by the cycle selection circuit in the target detection circuit,
One cycle selection circuit is provided for a plurality of target detection circuits, and the cycle setting circuit is provided separately for each target detection circuit.

In the present invention, a cycle to be set in a plurality of target detection circuits is selected by a single cycle selection circuit.

The invention according to claim 6 employs a configuration in which a cycle setting circuit is provided adjacent to each target detection circuit, and the cycle selection circuit and the cycle setting circuit are connected by a public line. .

In the present invention, a system is configured by connecting a cycle selection circuit to a station provided at one end of a public line provided in advance and connecting a plurality of cycle setting circuits to stations nearest to the public line. You.

With these, the above-mentioned object is to be achieved.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
4 through FIG. Here, the same parts as those in the conventional example are denoted by the same reference numerals, and duplicate description will be omitted.

In the aircraft position detecting system shown in FIG.
This is different from the conventional example in that a cycle changing unit 1 is provided. The cycle changing unit 1 changes the cycle of the interrogation signal selected by the target detection circuits B1 to Bn on condition that the reception time information M1 to Mn is no longer output from the target detection circuits B1 to Bn. It has a function to change to the cycle of the interrogation signal. In particular, the cycle changing unit 1 receives the reception time information M1 from the target detection circuits B1 to Bn over a certain period of time.
On the condition that Mn is not output, the cycle of the interrogation signal currently selected by the target detection circuits B1 to Bn is changed. Reference numeral 1a is a timer for measuring the fixed time. For this reason, in the present embodiment, the position calculation circuit 2 outputs an abnormality report via the target detection signal D on the condition that the reception time information is no longer output from the target detection circuits B1 to Bn. The period of the interrogation signal selected by the target detection circuits B1 to Bn is changed on condition that an abnormality notification is received from the position calculation circuit 2.

Here, the cycle changing unit 1 has a function of changing the cycle of the interrogation signal of each of the secondary monitoring radar devices 71 and 72 in a predetermined order. Therefore, the cycle changing unit 1 has a storage unit (not shown) in which the cycles of the interrogation signals I1 and I2 transmitted by the secondary monitoring radar devices 71 and 72 are stored in advance. For example, as in the present embodiment, when there are two secondary monitoring radar devices, the cycle changing unit 1 receives the abnormality notification from the position calculation circuit 2 every time.
The cycle of the interrogation signal set in the target detection circuits B1 to Bn is alternately switched between the cycle of the interrogation signal I1 and the cycle of the interrogation signal I2.

For this reason, the cycle changing section 1 includes a cycle selection circuit 1b for selecting a cycle of an interrogation signal to be set next time in the target detection circuits B1 to Bn, and a target setting for the cycle selected by the cycle selection circuit 1b. Cycle setting circuits S1 to Sn (n = 1, 2, 3,...) Set in the circuits B1 to Bn. Among these, one cycle selection circuit 1b is provided for each of the plurality of target detection circuits B1 to Bn, and the cycle setting circuits S1 to Sn are individually provided for each of the target setting circuits B1 to Bn. The cycle setting circuits S1 to Sn are provided adjacent to the target detection circuits B1 to Bn. The cycle selection circuit 1b and the cycle setting circuits S1 to Sn are connected by a public line.

Next, the operation of this embodiment will be described.

Now, each of the target detection circuits B1 to Bn has a first
The period of the interrogation signal transmitted from the secondary monitoring radar device 71 is set. At this time, if the operation of the first secondary surveillance radar device 71 is stopped and the transmission of the interrogation signal I1 is interrupted (A in FIG. 2), the second secondary surveillance radar device 72 continues to transmit the interrogation signal I2. However, the reception time information M1 to Mn is not output from each of the target detection circuits B1 to Bn (e in FIG. 2).
The position calculation circuit 2 always monitors whether the reception time information M1 to Mn is output from each of the target detection circuits B1 to Bn, and outputs the target time to the timer 1a of the cycle changing unit 1 during normal output. The detection signal D is output. Here, when the position calculation circuit 2 cannot obtain the reception time information M1 to Mn from all the target detection circuits B1 to Bn, the position calculation circuit 2 turns off the output of the target detection signal D and notifies the cycle changing unit 1 of an abnormality. . When the target detection signal D is turned off, the timer 1a of the cycle changing unit 1 is reset and time measurement is started. A fixed time is set in the timer 1a in advance, and when the measured time reaches the fixed time, a target absence signal N is output to the cycle selection circuit 1b (f in FIG. 2). On the other hand, when the position calculation circuit 2 receives the reception time information during the measurement of the timer 1a, the position calculation circuit 2 returns the target detection signal D to ON and cancels the abnormality notification. When the target detection signal D is turned on, the timer 1a stops measuring time. Therefore, when the output of the reception time information M1 to Mn is restarted before the time measured by the timer 1a reaches a predetermined time, the target absence signal N is not output to the cycle selection circuit 1b.

Here, when the target absence signal N is input to the cycle selection circuit 1b, the cycle selection circuit 1b performs another operation different from the cycle of the interrogation signal currently set in each of the target detection circuits B1 to Bn. The period of the interrogation signal is selected and output to each of the period setting circuits S1 to Sn. In the example of FIG. 1, since there are two secondary surveillance radar devices, the first secondary surveillance radar device 7
When the target absence signal N is input to the period selection circuit 1b in a state where the period of the first interrogation signal I1 is set in each of the target detection circuits B1 to Bn, the period selection circuit 1b performs the second secondary monitoring. The period of the interrogation signal I2 of the radar device 72 is selected. Therefore, the cycle selection circuit 1b includes a memory (not shown) for storing the currently set surroundings in each of the target detection circuits B1 to Bn. Thereafter, each time the target absence signal N is input, the cycle selection circuit 1b alternately selects the cycle of the first secondary monitoring radar device 71 and the cycle of the second secondary monitoring radar device 72. If there are three secondary surveillance radar devices A, B, and C, the cycle selection circuit 1b repeats the cycles of A, B, and C in order each time the target absence signal N is input. To select.

When selecting a new cycle, the cycle selecting circuit 1b puts the information on the cycle switching signal C and inputs it to each of the cycle setting circuits S1 to Sn via the public line (g in FIG. 2).
The cycle setting circuits S1 to Sn receiving the cycle switching signal C set the cycle of the interrogation signal selected by the cycle selection circuit 1b to each of the target detection circuits B1 to Bn. Thereby, for example, even if the first secondary monitoring radar device 71 stops operating in FIG. 1, each of the target detection circuits B1 to Bn responds to the interrogation signal I2 of the second secondary monitoring radar device 72. Signal R
, The position of the aircraft can be continuously detected.

[0027]

Next, a more specific example of the above embodiment will be described in detail with reference to FIGS.

In FIG. 3, the dotted arc V1 is the effective range of the interrogation signal of the secondary surveillance radar device 71. Also,
Reference symbol V2 is the effective range of the interrogation signal of the secondary monitoring radar device 72. Now, the range surrounded by the arc V1 and the arc V2,
That is, two aircraft transponders 53 exist in a region where both types of interrogation signals I1 and I2 are effectively transmitted. Here, the secondary surveillance radar device 71 has a query repetition cycle of 250 times per second, and the time for the antenna to make one revolution is 10 seconds. Secondary surveillance radar device 72
Has a query repetition cycle of 300 times per second, and the time required for the antenna to make one revolution is 10 seconds. Also, a dotted circle V
A is an effective range of the response signal R returned from the aircraft transponder 53, and within the range, the receiving site SI
TE1 to SITE3 are installed.

FIG. 4 shows the configuration of each of the receiving sites SITE1 to SITE3. In FIG. 4, the antenna An (n = 1,
The response signal R received in 2, 3) is received by the receiving circuit RXn
(N = 1, 2, 3), the above-described target detection circuit Bn
(N = 1, 2, 3). Here, only pulses having a preset period of the interrogation signal are extracted, and information Mn (n = 1, 2, 3) of the reception time of the pulse is supplied to the data processing circuit DPn (n = 1, 2, 3, 3). ) Is output to the outside. In the target detection circuit Bn, the period setting circuit Sn (n = 1, 2, 3) provided therewith has a period switching signal C
Is input, the cycle of the currently set interrogation signal can be switched to a different interrogation signal cycle.

The position calculating circuit 2 and the timer 1a and the cycle selecting circuit 1b included in the cycle changing section 1 are provided in one place. A single cycle selection circuit 1b and a position calculation circuit 2, and a cycle setting circuit S and a target detection circuit Bn provided at the reception sites SITE1 to SITE3, respectively.
It is desirable to be connected by a public line because it is several tens km away. In the cycle selection circuit 1b, as the cycle of the interrogation signal set in each target detection circuit Bn, 25
Zero times is currently selected. Further, the cycle selection circuit 1b
Is 250 m / s each time the target absence signal N is input.
Cycle and a cycle of 300 times per second are alternately selected. The timer 1a is set so as to output the target non-existence signal N 60 seconds (six antenna rotations) after the input of the target detection signal D is stopped.

Then, the two secondary monitoring radar devices 7
When the interrogation signals I1 and I2 having different cycles are transmitted from the airplane transponder 53 and the airplane transponder 53,
Response signal R containing 250 pulses per second and 300 pulses per second
Send This response signal R is transmitted to the reception site SITE1
~ SITE3 with a time difference due to the respective positional relationships. Antenna An is the aircraft transponder 5
3 and receives the response signal R from the receiving device RXn. The receiving device RXn detects the detected video signal VDn.
(N = 1, 2, 3) is output. The target detection circuit Bn
From the video signal VDn, only pulses appearing in the same cycle as the interrogation signal I1 of the first secondary surveillance radar device 71 are extracted. Then, the reception time is measured and the beacon code is decoded from the information carried on the extracted pulse signal.
The data processing circuits DP1 to DP3 convert the aircraft address data including the beacon code and the reception time into a transmittable data format, and output the data as reception time information M1 to M3. The reception time information M1 to M3 are input to the position calculation circuit 2, and the position of the aircraft is calculated. Target detection circuit B1
When there is an input of the reception time information M1 to M3 from any one of B1 to B3, the position calculation circuit 2 continues to output the target detection signal D.

Here, the first secondary surveillance radar device 71
Is stopped, the interrogation signal I1 is not transmitted.
250 response signals are not output per second. As a result, in the selection processing in the target detection circuits B1 to B3, since all the response signals are rejected, none of the reception time information M1 to M3 is output. Therefore, the target detection signal D is not output, and the timer 1a starts operating. If this state continues for 60 seconds, the timer 1a outputs the target non-existence signal C, and the cycle selection circuit 1b outputs the cycle switching signal C instructing a cycle of 300 times per second. The cycle setting circuits S1 to S3 that have received the cycle switching signal C set the repetition cycle of the pulses extracted by the target detection circuits B1 to B3 to 300 times per second. Therefore, the repetition cycle selected and processed by the target detection circuits B1 to B3 is changed to the query repetition cycle of the second secondary monitoring radar device 72 (300 times per second).
The response signal to the second secondary surveillance radar device 72 is to be selected. As a result, the operation of the aircraft address monitoring system can be continued using the response signal R corresponding to the interrogation signal of the second secondary monitoring radar device 72.

Here, three reception sites have been described as an example, but the same operation is performed with four or more reception sites. Also, the present invention
The present invention is not limited to the above embodiment and examples. The public line is not required as long as the position calculating circuit 2 and the cycle selecting circuit 1b are connected to the target detecting circuit Bn and the cycle setting circuit Sn by a communicable line. The cycle selection circuit 1b may be provided for each target detection circuit Bn. Period change unit 1
May directly monitor the reception time information Mn output from each target detection circuit Bn and activate the timer 1a when the reception time information Mn is no longer output. The method of selecting the next cycle to be set in the cycle changing unit 1 may be any method.
The timing of changing the cycle set in the target detection circuit Bn does not have to be determined to be a certain time after the reception time information is no longer output.

[0034]

According to the present invention, the interrogation signal is no longer transmitted from the specific secondary surveillance radar device and is received from the target detection circuit. When the time information is no longer output, the cycle change unit changes the cycle of the interrogation signal set in the target detection circuit and synchronizes it with another secondary monitoring radar device, so that it reaches a remote location where the target detection circuit is installed. The system can continue to detect the position of the aircraft without the need for a worker to go and change the settings, and the system can operate stably.

According to the second aspect of the present invention, a fixed grace period is given to the determination as to whether or not the reception time information is no longer output. It is possible to prevent a situation in which the period of the target interrogation signal is easily switched due to an inconvenience or the like, and a stable switching operation can be realized.

According to the third aspect of the present invention, the cycle changing unit includes:
Since the cycle of the interrogation signal different for each secondary monitoring radar device is sequentially switched, for example, A,
Even if two of the secondary surveillance radar devices of B and C have stopped operating, the cycle changing unit selects the cycle of A, then selects the cycle of B, and then selects the cycle of A again. The inconvenience of selecting the period can be prevented, and the period of the effective interrogation signal of the secondary monitoring radar device can be reliably selected.

According to the fourth aspect of the present invention, the cycle changing unit includes:
Since the switching timing of the interrogation signal cycle can be measured by monitoring the abnormality notification notified from the position calculation circuit, it is not necessary to connect the cycle change unit and the plurality of target detection circuits with a large number of signal lines. In addition, it is possible to simplify the connection configuration of the system, thereby suppressing occurrence of troubles in the signal lines.

According to the fifth aspect of the present invention, since only one cycle selection circuit is provided for the plurality of target detection circuits and the cycle setting circuit, the system is compared with a case where the cycle selection circuits are individually provided for each target detection circuit. The configuration can be simplified, and the system cost can be reduced and troubles can be suppressed.

In the invention according to claim 6, an existing public line is used at least for the connection between the cycle setting circuit and the cycle selection circuit, so that the construction work of the system can be easily performed and the use of the line can be performed. Considering the frequency, it is possible to provide an unprecedented superior aircraft position detection system in which the cost for system construction and operation can be reduced at a lower cost than when a dedicated line is provided.

[Brief description of the drawings]

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

FIG. 2 is a time chart for explaining the operation of the system shown in FIG. 1;

FIG. 3 is a schematic configuration diagram showing an example based on the embodiment of FIG. 1;

FIG. 4 is a block diagram of a reception site shown in FIG. 3;

FIG. 5 is a system configuration diagram of a conventional example.

FIG. 6 is a time chart for explaining the operation of the conventional system shown in FIG. 5;

[Explanation of symbols]

 Reference Signs List 1 cycle changing unit 1a timer 1b cycle selection circuit 2 position calculation circuit 53 aircraft transponder 71, 72 secondary surveillance radar device B1 to Bn target detection circuit C cycle switching signal D target detection signal I1, I2 interrogation signal M1 to Mn reception time information N target absence signal R response signal S1-Sn cycle setting circuit

Continuation of the front page (56) References JP-A-11-133149 (JP, A) JP-A-62-298084 (JP, A) JP-A-60-222782 (JP, A) JP-A-63-266381 (JP) JP-A-8-105966 (JP, A) JP-A-6-3422061 (JP, A) JP-A-5-506951 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) G01S 7/00-7/42 G01S 13/00-13/95 G08G 5/00

Claims (6)

(57) [Claims] 1. A secondary surveillance radar device for transmitting an interrogation signal which is a pulse signal of a fixed period, and a pulse-like signal returned from an aircraft transponder in synchronization with a period of the interrogation signal transmitted from the secondary surveillance radar device A target detection circuit that receives a response signal and outputs reception time information of the pulse, and a position calculation circuit that calculates the position of the aircraft based on the reception time information output from the target detection circuit, The surveillance radar device is provided with two or more units having different periods of the interrogation signal to be transmitted, and the target detection circuit extracts only the pulse having the period of the specific interrogation signal selected in advance from the response signal. A configuration in which the reception time information is output for a pulse, a plurality of the target detection circuits are provided at a predetermined distance, and the position calculation circuit includes: In an aircraft position detection system that calculates the position of the aircraft based on a time difference between reception time information output for the same reception pulse from each of the target detection circuits, the reception time information is no longer output from the target detection circuit An aircraft position detection system provided with a period changing unit that changes a period of the interrogation signal selected by the target detection circuit to a period of a different interrogation signal under the condition. 2. The cycle changing unit changes a cycle of an interrogation signal selected by the target detection circuit on condition that the reception time information has not been output from the target detection circuit for a certain period of time. The aircraft position detection system according to claim 1, wherein: 3. The aircraft position detection system according to claim 1, wherein the cycle changing unit changes the cycle of the interrogation signal of each of the secondary monitoring radar devices according to a predetermined order. 4. The position calculation circuit outputs an abnormality notification on condition that reception time information is no longer output from the target detection circuit, and the cycle changing unit receives the abnormality notification from the position calculation circuit. 2. The aircraft position detection system according to claim 1, wherein a period of the interrogation signal selected by the target detection circuit is changed on the condition that the interrogation signal is selected. 5. A cycle selection circuit, wherein the cycle changing unit selects a cycle of an interrogation signal to be set next in the target detection circuit;
A cycle setting circuit for setting the cycle selected by the cycle selection circuit in the target detection circuit, wherein the cycle selection circuit is provided for each of the plurality of target detection circuits, and the cycle setting circuit is 2. The aircraft position detecting system according to claim 1, wherein the target position detecting circuit is provided individually for each of the target detecting circuits. 6. The cycle setting circuit according to claim 5, wherein said cycle setting circuit is provided adjacent to each of said target detection circuits, and said cycle selecting circuit and said cycle setting circuit are connected by a public line. Aircraft position detection system.