Application of Virtual Instruments to Simulate Radar Signal System

1 Introduction

Traditional radar transmitters use dedicated signal generation modules, which cannot arbitrarily set waveform forms, parameters, signal center frequency, signal power, etc. This limits the scope of application to a certain extent. Especially in the pre-research and exploration of new technologies of radar, it is necessary to conduct experiments or evaluations on 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 and high-performance commercial test instruments are integrated [1], the functions of the programming design system can be used to effectively simulate various radar signals and set the parameters of the radar signals with greater flexibility, thus overcoming the problem of poor versatility and meeting a variety of application requirements.

2 Radar signal generation system

The block diagram of the radar signal generation principle is shown in Figure 1. The baseband signal generation module uses D/A conversion to convert the digital storage waveform into I/Q two-way baseband analog signal output. The I/Q modulation module modulates the I/Q two-way signal by 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. Radar signal generation schematic.

3 Radar Signal Simulation System Based on Virtual Instrument

In the pre-research and demonstration stage of the new radar system, the radar signal generation system based on virtual instruments can meet the application requirements. Using arbitrary waveform generators, vector signal sources and pulse signal sources as hardware platforms, virtual instrument software is developed under Agilent VEE for control, realizing the simulation of a general radar signal generation system.

3.1 System hardware structure design

The structure diagram of the system is shown in Figure 2. The functions of each module are introduced below.

Figure 2. Instrument hardware connections[page]

3.1.1 Arbitrary Waveform Generator

The arbitrary waveform generator completes the output of baseband or intermediate frequency analog IQ signals 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. Playback control of the output of pulse waveform to achieve the output of single pulse waveform or pulse waveform sequence.

2. You can also set the pulse time width and the waveform parameters within the pulse (such as frequency or bandwidth, etc.).

3. Pulse time width and resampling rate can be set by software.

3.1.2 Vector signal source

The vector signal source inputs I/Q signals to complete quadrature modulation and up-conversion. The following functions can be realized through remote control:

1. The output radar signal center frequency and output power can be adjusted.

2. The amplitude and phase balance of the I/Q 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, thus achieving coherence and synchronization between various modules.

The key modules in the above system are arbitrary waveform generator and vector signal source. All major instrument manufacturers have corresponding products. In order to verify the implementation of this system, we selected Agilent's arbitrary waveform generator N6030A[2] and vector signal source E8267D[3], and selected the company's 81110A pulse generator[4] as the 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 achieve remote control of the instrument.

3.2 Virtual Instrument Software Design

The system software composition is shown in Figure 3. It adopts a modular program structure to facilitate system upgrades and expansions. The instrument driver is a collection of instrument function control functions and instrument parameter variables. The instrument control module is a subset of the instrument driver defined by the program. It extracts the instrument function functions and parameters required to build the system from the driver to meet user needs.

Figure 3. System software block diagram

3.2.1 VEE graphical development environment

Virtual instrument development environments include common application development environments such as VC++, VB, MATLAB, and graphical development environments specifically for test and measurement applications: NI LabVIEW, Agilent VEE, etc.

During the development process, Agilent VEE (Virtual Engineering Environment) development environment was selected [5]. VEE uses object-oriented programming technology and is suitable for applications such as system simulation and instrument optimization control in the test and measurement field. Its main features are: Graphical processing of programming language, using data flow chart to write code, and high programming efficiency. It provides a variety of instrument I/O drivers to realize the control of bus interfaces such as VXI, GPIB, PXI, and serial ports. It provides a large number of function libraries and can be mixed with C/C++, MATLAB, etc. [page]

3.2.2 Design of instrument control module based on driver

The instrument driver is a collection of control functions and parameters that implement instrument functions. It is the bridge between software and instruments. Instruments are shipped with corresponding drivers, and virtual instrument software is built on top of the instrument driver[6]. By receiving user-set parameters from the user operation panel, it implements a variety of signal setting functions and completes the task of automatic control. By calling the interface functions of the instrument driver[7], [8], [9], a system that meets the functional requirements can be designed.

Figure 4 illustrates the flow of the software. The functions of the software include instrument addressing, coherence setting between instruments, resampling clock setting, output power configuration for each level, trigger source selection, trigger pulse PRF value configuration, output signal center frequency configuration, signal waveform modeling, data generation and access, and waveform output playback control. The waveform playback control part is a subprocess, and its flow chart is shown in Figure 5. Its function is to control the waveform playback process of the arbitrary waveform generator by calling the function of the arbitrary waveform generator driver. The two branches realize the output of a single pulse waveform and the output of a pulse waveform sequence respectively.

Figure 4 Virtual instrument program execution flow chart

Figure 5. Waveform playback flow chart [page]

Figure 6 shows the image of the I/Q two-way linear frequency modulation baseband (-300～+300MHz) analog signal output by the arbitrary waveform generator in single waveform output mode, under the control of the trigger pulse of PRF = 2000KHz, displayed on the digital storage oscilloscope. The trigger pulse width is 300us and the pulse waveform width is 16us.

Figure 6. Linear frequency modulation signal and trigger pulse

4 Conclusion

Compared with the previous dedicated radar signal system, the radar signal simulation system based on virtual instrument has the following innovations:

1) Versatility: The waveform signal form, center frequency, power, pulse repetition frequency, etc. can be set very flexibly.

2) Software defines system functions, which facilitates system upgrades and makes it easy to integrate other instruments into the system to expand system functions.

3) Make full use of laboratory resources, reduce R&D costs and cycles, and is suitable for the R&D and experimental stages of new radar system systems.