Transmit/Receive Module Test System

This invention relates to an improved system for testing the transmit/receive modules of a phased-array antenna apparatus.

Phased-array antennas are used in, for example, radar systems since they can scan wide areas while remaining stationary. A phased-array antenna includes an array of antenna elements, each having its own transmit/receive module for transmitting and receiving signals via the antenna element. Each transmit/receive module includes a phase shifter. The total antenna beam is steered by controlling the phase shifts in the transmit/receive modules.

To confirm normal operation of a phased-array antenna, it is necessary to test the receive circuits of the individual transmit/receive modules. A prior scheme for such testing equips each transmit/receive module with a receive check circuit that diverts part of the unamplified transmit signal from the transmit section of the module to the receive section of the same module. During normal operation, the receive check circuit is switched off, so that the transmit signal is not diverted into the receive section. During a test, the receive check circuit is switched on and the part of the unamplified transmit signal diverted into the receive section is used as a test signal.

A problem with this scheme is that the receive check circuits themselves may malfunction. If the switch in the receive check circuit becomes stuck in the on-state, for example, then during normal operation, part of the amplified receive signal will be fed back via the receive check circuit thereby into the receive circuit, setting up an oscillation. Even one of the transmit/receive modules oscillating in this way can seriously distort the total received signal power, thereby causing the antenna array to fail as a whole.

It is accordingly an object of the present invention to provide an improved system for testing the transmit/receive modules of a phased-array antenna, in which the transmit/receive module structure is simplified and a failure in one transmit/receive module does not disable the entire array.

A transmit/receive module test system according to the present invention includes a dummy antenna element for transmitting signals to, or receiving signals from, the antenna elements of the phased-array antenna, and a dummy transmit/receive module connected to the dummy antenna element, for amplifying the signals transmitted from, or received by, the dummy antenna element. Different embodiments of this transmit/receive module test system are provided with various detectors utilized for checking the power or phase of the signals transmitted from or received by the dummy antenna element.

FIG. 1 is a block diagram of a phased-array antenna employing the transmit/receive module test system of the present invention for receive circuit checking.

FIG. 2 is a more detailed block diagram of the transmit/receive modules in FIG. 1.

FIG. 3 is a timing chart illustrating the operation of the phased-array antenna in FIGS. 1 and 2.

FIG. 4 is a block diagram of another phased-array antenna employing the transmit/receive module test system of the present invention for receive phase adjustment.

FIG. 5 is a more detailed block diagram of the transmit/receive modules in FIG. 4.

FIG. 6 is a timing chart illustrating the operation of the phased-array antenna in FIGS. 4 and 5.

FIG. 7 is a block diagram of a phased-array antenna employing the transmit/receive module test system of the present invention for transmit phase adjustment.

A first novel transmit/receive module test system according to the present invention will be described with reference to FIGS. 1 to 3. This transmit/receive module test system tests the transmit/receive modules in a phased array to ascertain whether their receive circuits are functioning normally.

FIG. 1 is a block diagram of a phased-array antenna employing the novel transmit/receive module test system. The phased-array antenna apparatus in FIG. 1 comprises a signal line 1 for input and output of an rf transmit input signal and an rf receive output signal, a branching device 2 for dividing and combining these signals, transmit/receive modules 3.sub.1 to 3.sub.n, antenna elements 4.sub.1 to 4.sub.n, a dummy module 7, a dummy transmit signal input line 7.sub.1, and a dummy antenna element 7.sub.4. The dummy module 7 will be assumed to be identical to the transmit/receive modules 3.sub.1 to 3.sub.n.

FIG. 2 is a block diagram showing the configuration of a transmit/receive module in FIG. 1. The transmit/receive module in FIG. 2 comprises a signal input/output line 31, a phase shifter 32, a circulator 33, a transmit amplifier 34, a circulator 35, an isolator 36, a limiter 37, a low-noise amplifier 38, an isolator 39, a switch 51, a transmit power detector 52, a receive power detector 53, and terminating resistors 54 to 56. It does not have a separate receive check circuit as was the case in the prior devices.

First the normal-mode operation of the antenna will be described. For transmission, the switch 51 in each transmit/receive module is placed in the off-state. The rf transmit signal is input via the signal line 1 to the branching device 2, which distributes it to the transmit/receive modules 3.sub.1 to 3.sub.n. In each transmit/receive module the phase shifter 32 shifts the phase of the transmit signal by a specified amount, the transmit amplifier 34 amplifies the signal, and the transmit power detector 52 checks the power level of the amplified signal. The signals that have been thus shifted, amplified, and checked are then transmitted from respective antenna elements 4.sub.1 to 4.sub.n. For reception, the switch 51 in each transmit/receive module is placed in the on-state. The signals received by the antenna elements 4.sub.1 to 4.sub.n are fed to respective transmit/receive modules 3.sub.1 to 3.sub.n, wherein each signal is limited by the limiter 37, amplified by the low-noise amplifier 38. They are then checked by the receive power detector 53, and applied through the switch 51 to the phase shifter 32. The phase shifter 32 then shifts its phase by a specified amount. The phase-shifted receive signals from the transmit/receive modules 3.sub.1 to 3.sub.n are then sent, via the signal lines 31, to the branching device 2, which combines them into a single receive output signal. In normal-mode transmit and receive operations, no signal is sent on the dummy transmit signal line 7.sub.1 and the dummy module 7 is inoperative.

Next the test-mode operation will be described. In this mode, in the transmit/receive modules 3.sub.1 to 3.sub.n, the transmit amplifiers 34 are switched off and the low-noise amplifiers 38 are switched on. Concurrently, in the dummy module 7, the transmit amplifier 34 is switched on and the low-noise amplifier 38 is switched off. A dummy transmit signal is input via the dummy transmit signal line 7.sub.1 to the dummy module 7 and transmitted from the dummy antenna element 7.sub.4. The antenna elements 4.sub.1 to 4.sub.n receive the signal radiated from the dummy antenna element 7.sub.4. In each transmit/receive module 3.sub.1 to 3.sub.n, the received signal is amplified by the low-noise amplifier 38. The receive power detector 53 checks the output of the low-noise amplifier 38 and decides whether the receive circuits are operating normally. This check is carried out in all the transmit/receive modules 3.sub.1 to 3.sub.n, without requiring a separate checking circuit in each module as in the prior devices.

The normal and test operation modes are further illustrated by the timing chart in FIG. 3. Lines (a) to (c) in FIG. 3 indicate the operation of the dummy module 7. Lines (d) to (g) indicate the operation of the transmit/receive modules 3.sub.1 to 3.sub.n. The phased-array antenna operates in the test mode during the intervals t.sub.1 to t.sub.2 and t.sub.3 to t.sub.4, and in the normal mode at other times.

The antenna elements 4.sub.1 to 4.sub.n are at various distances from the dummy antenna element 7.sub.4, so the signals they receive are not identical in power. Since the signals are all received directly from an antenna element in the same array, however, the input levels to their low-noise amplifier 38 are all more than adequate. For modules close to the dummy module 7, the receive power input to the low-noise amplifier 38, may be excessive but this excessive input power is absorbed by a dummy resistor 54 coupled to the isolator 36. All the modules in the array are thus able to check their receiving systems simultaneously.

A second novel transmit/receive module test system according to the present invention, will be described with reference to FIGS. 4 to 6. This transmit/receive module test system checks the transmission phase of the receive circuits in the transmit/receive modules of the phased array. The transmission phase tends to vary due to temperature fluctuations and aging changes. Adverse effect on reception can be prevented, however, by detecting the changes in transmission phase and adjusting the phase shifters so as to compensate.

FIG. 4 is a block diagram of a phased-array antenna employing the second novel transmit/receive module test system. The phased-array antenna in FIG. 4 is similar to that in FIG. 1, but also comprises a phase detector 8 which receives the dummy transmit signal via a dummy transmit signal input line 8.sub.1, and receives the receive signals from the transmit/receive modules 3.sub.1 to 3.sub.n via a receive signal input line 8.sub.2. FIG. 5 is a block diagram of the transmit/receive modules 3.sub.1 to 3.sub.n in FIG. 4. These are substantially identical to the transmit/receive modules in FIG. 2, but FIG. 5 also shows the driver 32.sub.1 of the phase shifter 32 and its input phase control signal line 32.sub.2, which were not provided in the module shown in FIG. 2.

The test-mode operation of this phased-array antenna is similar to that described in FIGS. 1 to 3, except that it tests the phase of the receive signals. The phase detector 8 detects the phase of the signals on the dummy module transmit signal input line 8.sub.1 and the receive signal input line 8.sub.2 and generates a signal indicating their phase difference on the phase difference output line 8.sub.3. The change in the phase difference is calculated by a phase difference change calculator 9 and supplied to the driver 32.sub.1 of the phase shifter 32 in the corresponding module, where it is added to or substracted from the phase control signal 32.sub.2 supplied to the driver 32.sub.1. The phase shifter 32 thus compensates for changes in the transmission phase of the receive system.

A timing chart of the phase check operation is shown in FIG. 6. If the phase difference detected in the interval t.sub.1 -t.sub.2 and the phase difference detected in the interval t.sub.3 -t.sub.4 are different as shown in line (d) of FIG. 6, the difference is added to, or substracted from, the phase control signal 32.sub.2 to correct the phase of the receiving system.

The transmission phase of the receive circuits in each transmit/receive module is checked separately in this way. A module control signal as shown in FIG. 4 can be used to select the transmit/receive module to be tested and disable the other transmit/receive modules. The receive circuits in the transmit/receive module can also be tested by checking the receive power as in FIGS. 1 to 3, and this test can be performed on all transmit/receive modules simultaneously.

This invention can also provide a system for checking the transmission phase of the transmit circuits, as will be described with reference to FIG. 7. The novel transmit/receive module test system in FIG. 7 differs from those in FIGS. 4 to 6 in that the dummy module 7, instead of transmitting a test signal to the other modules, receives a sequence of test signals transmitted from the other modules in turn. The phase detector 8, for detecting the phase difference between the transmit and receive signals, is similar to that in FIG. 4 and is connected by similar signal lines 8.sub.1, 8.sub.2, and 8.sub.3 ; further description will be omitted. The system illustrated in FIG. 7 can also be used to ascertain whether the transmitting circuits in the transmit/receive modules 3.sub.1 to 3.sub.n are operating normally by checking the power received at the dummy antenna element 7.sub.4.

By using a single dummy module and antenna element for the entire antenna array, instead of a receive check circuit in every transmit/receive module, the novel transmit/receive module test systems described above simplify the structure of the transmit/receive modules of the phased-array antenna and thereby improve their reliability to a substantial degree. In the simplified transmit/receive modules, the danger of feedback from the receive check circuit to the receive section is avoided, so that while failure of a single transmit/receive module may slightly degrade the performance of the phased-array antenna, it cannot produce disabling oscillations as was the case in the prior devices. A further advantage of the novel test systems is that they also provide means of checking the transmission phase of the transmit and receive circuits in the array and adjusting the phase shifters to compensate for variations, thus improving the accuracy of the phased-array antenna.

The scope of this invention is not limited to the embodiments illustrated in the drawings, but includes many modifications which will be obvious to one skilled in the art. For example, the timing sequences shown in FIG. 3 and FIG. 6 can be modified, and the operations described above can be combined in various ways. It is not necessary for the receive systems of the transmit/receive modules to be checked simultaneously; it is also possible to check them one by one. Also, it is not necessary for the dummy module to be identical to the other modules; unused functions can be eliminated from the dummy module. In the system in FIGS. 1 to 3, for example, the low-noise amplifier function can be removed from the dummy module. The internal configuration of the transmit/receive modules can also be altered by adding or deleting functional elements as necessary. It is furthermore not necessary for the dummy module to be physically installed in the array; it can be located elsewhere with only its dummy antenna element present in the array. The dummy antenna element also need not be part of the array, but can be installed at another nearby location.

It is also possible to provide a plurality of dummy modules and dummy antenna elements in a single array so as to reduce the difference between the distances from the dummy antenna element to the antenna elements for the respective transmit/receive modules.

The apparatus in FIG. 4 and FIG. 6 detected the phase changes of the transmit/receive modules individually and corrected their operation individually, but it is also possible to apply a correction to eliminate the phase differences between all the transmit/receive modules.