The traditional radar transmitter adopts a dedicated signal generation module, and cannot randomly set the waveform form, parameters, signal center frequency, signal power, and the like. To a certain extent, the scope of application is limited. Especially in the stage of radar pre-research and new technology exploration, it is necessary to experiment or evaluate various radar signals. If a dedicated signal generation module is designed for each radar signal, it will be extremely costly. If virtual instrument technology is used to integrate high-performance commercial test instruments [1], the functions of the programming system can be used to simulate a variety of radar signals, and the parameters of the radar signals can be set with greater flexibility to overcome the poor versatility. The problem is to meet a wide range of application requirements. The schematic diagram of the radar signal generation principle is shown in Figure 1. The baseband signal generation module uses the D/A conversion to convert the digital storage waveform into two I/Q baseband analog signal outputs. The I/Q modulation module modulates the I/Q two-way signals with orthogonal carriers, and moves the signal center frequency to the RF or microwave frequency band. The final output of the system is the required radar signal. Figure 1. Schematic diagram of radar signal generation In the pre-research and demonstration stage of the new radar system, the radar signal generation system based on virtual instrument can meet the application requirements. Using arbitrary waveform generator, vector signal source and pulse signal source as hardware platform, virtual instrument software is developed under Agilent VEE for control, which realizes the simulation of general radar signal generation system. 3.1 System hardware structure design The structure of the system is shown in Figure 2. The functions of each module are described below. Figure 2. Hardware connection to the instrument 3.1.1 Arbitrary Waveform Generator The arbitrary waveform generator performs the output of the baseband or intermediate frequency analog IQ signal through digital storage and digital-to-analog conversion. Through software control, the arbitrary waveform generator simulates the baseband analog signal generation module to achieve the following functions: 1. Play back the output of the pulse waveform to realize the output of a single pulse waveform or pulse waveform sequence. 2. You can also set the width of the pulse time, the waveform parameters within the pulse (such as frequency or bandwidth). 3. Pulse time width, resampling rate can be set by software. 3.1.2 Vector Signal Source The vector signal source inputs the I/Q signal to perform the function of quadrature modulation and up-conversion. The following functions are realized through remote control: 1. The center frequency of the output radar signal and the output power can be adjusted. 2. The amplitude and phase balance of the I/Q two branches can be adjusted. 3.1.3 Pulse Generator The pulse generator can provide the required trigger pulse for radar pulse modulation and set the pulse repetition frequency PRF. Achieve coherence and synchronization between modules. The key modules in the above system are arbitrary waveform generators and vector signal sources. All major instrument manufacturers have corresponding products. In order to verify the implementation of the system, we chose Agilent's arbitrary waveform generator N6030A [2] and vector signal source E8267D [3], and selected the company's 81110A pulse generator [4] as a pulse source. The 81110A and E8267D are connected to the industrial computer through the GPIB bus, and the N6030A is connected to the industrial computer through the PXI bus. The industrial computer runs the virtual instrument software, and communicates with each instrument through the PXI bus and the GPIB bus to realize remote control of the instrument. 3.2 Virtual Instrument Software Design The system software is composed as shown in Figure 3. It adopts a modular program structure to facilitate system upgrade and expansion. The instrument driver is a collection of instrument function control functions and instrument parameter variables. The instrument control module is a subset of the program-defined instrument driver that extracts the instrument function functions and parameters required by the build system from the driver to suit the user's needs. Figure 3. Block diagram of the system software 3.2.1 VEE graphical development environment The virtual instrument development environment includes common application development environments such as VC++, VB, MATLAB, and graphical development environments for test and measurement applications: NI LabVIEW, Agilent VEE, and more. In the development process, the Agilent VEE (Virtual Engineering Environment) development environment [5] was selected. VEE uses object-oriented programming techniques and is suitable for applications such as system simulation and instrumentation optimization control in test and measurement. Its main features are: the graphical processing of the programming language, the use of data flow chart to write code, programming efficiency. Provides a wealth of instrument I / O drivers to achieve control of VXI, GPIB, PXI, serial and other bus interfaces. Provide a large number of function libraries, and can be mixed with C / C + +, MATLAB and other programming. 3.2.2 Driver-based instrument control module design An instrument driver is a collection of control functions and parameters that implement instrument functions. It is a bridge between software and instrument communication. The instrument is shipped with the corresponding driver, and the virtual instrument software is built on the instrument driver [6]. By receiving the user setting parameters from the user's operation panel, the rich signal setting function is realized, and the automatic function is completed. Controlled tasks. By calling the instrument driver's interface functions [7], [8], [9], you can design a system that meets the functional requirements.
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1 Introduction