Digital Array Antenna Test Based on Virtual Instrument

0 Introduction

LabVIEW is the abbreviation of laboratory virtual instrument engineering workbench. It is an innovative software product of NI Corporation in the United States. It is also the most widely used, fastest growing and most powerful graphical software integrated development environment. As a software instrument, LabVIEW has powerful functions in data acquisition and control, data analysis and display. It supports a variety of signal interface cards. Users can quickly and easily set and debug various input data parameters in real time, and the program running results are also very intuitive. Digital antenna array is the product of the combination of antenna and digital signal processing technology. It has many advantages such as flexible working mode, excellent anti-interference performance and super angular resolution. Therefore, it has been widely used in military and civilian fields. Generally, array antenna correction and lobe measurement require the collection of a large amount of data and multiple cycles of calculation. The work efficiency is low and many instruments and equipment are used.

Therefore, in the digital array antenna test, the advantages of LabVIEW are very obvious. It can realize the simultaneous acquisition, real-time monitoring and analysis of a large number of channel signals, which not only saves resources, but also simplifies the test process and improves work efficiency.

1 System Introduction

At the receiving end of the system, each unit channel of the receiving antenna amplifies the received signal through the receiving front end and directly sends it to the digital receiver and acquisition computer. The data acquisition card collects and controls the I/Q signal output by the receiver, mechanical parameters such as antenna azimuth, and trigger signal, and finally calculates the antenna lobe diagram on the terminal control processing computer. The system working process is shown in Figure 1.

System Diagram

During the test, we used LabVIEW to design the user graphical interface, which is responsible for channel monitoring and data acquisition. The data acquisition system in LabVIEW consists of acquisition hardware, hardware drivers, and data acquisition functions. The installed hardware driver contains the operation commands that the hardware can accept. Before using these hardware, the hardware and software settings are performed as needed to meet the requirements of sampling frequency and other aspects. In this system, we use NI's PCI-6534 acquisition card. LabVIEW controls the data acquisition card to collect the IQ signal output by the receiver and other mechanical parameters. After completing the settings of the acquisition card, we can perform acquisition and channel monitoring.

Figure 2: Front Panel of the Channel Monitor VI

2 Channel Monitor

Since the whole system is composed of multiple channels, in order to ensure that each channel is in normal working state during the calibration process, we need to check the channels before the calibration begins. At the same time, since the operating frequency band of this system is within the civilian communication frequency band, in order to avoid the influence of civilian communication signals on the calibration process, we also need to monitor the external electromagnetic signals. Therefore, channel monitoring is an important part to ensure the smooth progress of the calibration. Figure 2 is the front panel interface of the channel monitoring VI, and Figure 3 is the block diagram of the channel monitoring VI. The Dialog Tab Control control is used in the front panel (Figure 2), so that we can switch between multi-channel simultaneous monitoring and single-channel observation. In this VI, in addition to being able to intuitively monitor whether each channel is working properly, we can also measure and compare the differences in the power gain of each channel and complete the monitoring of information such as the channel time domain signal amplitude and IQ signal orthogonality.

Figure 3: Block diagram of the channel monitoring VI

In the block diagram of channel monitoring VI (Figure 3), we call MATLAB mathematical processing software in the background through the COM component method. Its main task is to group the multiple channel serial data streams output by the acquisition card by channel, and perform number system conversion and data analysis as needed. These functions speed up the program running speed and improve the ability and flexibility of the VI data processing.

3. External Calibration Data Collection

After making sure that all channels are in normal working condition and there is no external electromagnetic interference, you can start external calibration.

3.1 Serial Data Acquisition Sub-VI

In order to complete the external correction, the azimuth of the antenna's mechanical rotation must be obtained in real time during the data collection process. Here we use the serial port to collect the code disk value of the antenna's mechanical rotation to obtain the antenna's real-time rotation azimuth.

The serial port uses RS232, D-type port, which uses pins 2, 3 and 5, one for sending, one for receiving and one for grounding. Visa is used in Labview. First, set the serial port, set the serial port number and baud rate. Pay special attention to installing the visa driver package. Only after installing this driver package can the serial port be selected.

Figures 4 and 5 are the serial data acquisition subVI and its block diagram (serial acquisition part). With the measurement results of the north-fixing instrument, through this subVI we can obtain the real-time code disk value of the antenna mechanical rotation, antenna azimuth and normal azimuth.

3.2 Data Acquisition VIs

Data acquisition is the most basic and important part of the test process. Its front panel is shown in Figure 6. In data acquisition VI, we can not only control the start and end of acquisition, but also control the length of acquired data by modifying parameters on the front panel, and continuous acquisition can be achieved from tens of kilobytes to tens of megabytes.

Data Acquisition VIs

3.3 External Calibration Data Acquisition VI

With the serial port data acquisition subVI, combined with the data acquisition VI, by reasonably controlling the data acquisition length, we can finally complete the external correction data acquisition. Figure 7 is the front panel of the external correction data acquisition VI, where we can specify the frequency of the external correction test and the data storage path, and can monitor the code disk value of the antenna mechanical rotation and the normal direction of the antenna in real time, and stop data acquisition at any time according to actual needs. Figure 8 is the block diagram of the external correction data acquisition VI.

4 Conclusion

Through the above main programs and some other auxiliary programs, we have completed a complete process from channel monitoring to external correction data acquisition during antenna testing. This system fully utilizes the advantages of LabVIEW in software measurement programming and data acquisition, improves work efficiency, shortens work time, and has been verified in practice.