Using a short duty cycle, a plurality of modulation types of radar signals and critical timing pulse waveform requires high bandwidth, the measurement system is proportional to the sample rate, long memory and fast data transmission. Modular high speed digitizers are ideal for collecting and processing the radar signal, and provides several advantages to these measurements. They provide high bandwidth and long acquisition memory and a special acquisition mode in order to maximize the use of memory, these instruments provide a compact high-speed measurement and high precision analysis. This article focuses on the use of high-speed modular digitizers some advantages radar system measurements.
Pulse radar systems rely on modulated radio frequency (RF) carriers, typically including frequency, phase and complex modulation. The role of measuring instruments is based on the maximum possible fidelity obtain these pulse waveforms and measure the key parameters. As shown in a radar signal, which is a basic pulse modulation 1GHzRF carrier. 
Figure 1: Acquisition of basic pulsed RF radar signals, and perform simple RMS waveform detecting step to measure the critical timing parameter signal envelope
signal trace of FIG. 1 is a top pick-M4i.2234-x8 digitizer. This is based on a 4-channel bus 8 PCIExpress digital converter, the bandwidth of 1.5GHz, the maximum sampling rate of 5GS / s. This bandwidth and sampling rate and the IF direct capture VHF and lower UHF radar and many higher frequency radar compatible. The digitizer acquisition memory includes 4GB. A 4GB of memory data can be acquired at the maximum sampling rate of 800ms 5GS / s of. This provides good temporal resolution of the acquisition time, help to analyze phase or frequency modulated signal. In this example, the digitizer 2.5MS 500μs data acquired at the maximum sampling rate of 5GS / s used. Although this example uses only complete memory acquired five pulses, but can obtain a similar plurality of pulses 8000.
SBench6 is used to view data digitizer software. It is standard, it is a way to view and control the digitizer data, further comprising built-in tool for measuring and analyzing the acquired waveform. For example, the carrier frequency measurement for measuring signal frequency, 1.000GHz results are shown as in the left pane of FIG. There are many SBench6 numerical analysis tools, including a fast Fourier transform (FFT) and Finite Impulse Response (FIR) filter.
Pulse repetition frequency (PRF) can be estimated from the screen, but the use of the software tool to get a more accurate measurement value. The best way to accurately measure the PRF, and the duty cycle of the pulse width modulated pulse waveform are extracted envelope. Can be achieved by squaring the signal (middle trace), and then subjected to low-pass filtering (bottom trace). It is proportional to the square of the instantaneous power of the signal waveform of this operation is performed root mean square (rms) detection center of the track. If necessary power measurements, the input impedance of 50Ω divided by re-calibration data, and to complete the conversion units to watts.
After the filtering operation, the envelope of the pulse sequence shown in the bottom trace. Using the measurement tool of the software to read pulse again PRF, i.e. 10kHz, width 9.955μs, the duty cycle of 9.955%.
Pulse modulation
pulse compression is usually used to increase the range resolution of the radar. A carrier comprising a compressed modulated pulse, the pulse is different from each other every moment. It is generally used to complete the frequency or phase modulation. A radar receiver provides the necessary digital signal processing to affect pulse compression.
Scan, or changing the carrier frequency within the pulse duration is a common technique, the resulting chirp is called "chirp." FIG 2 is an example of a linear scanning radar chirp.
Modulated pulses shown in the left of the grid. During the pulse, the nominal carrier frequency varies linearly from 998MHz to 1002MHz. This FFT frequency domain to the right of the view provided by the grid is obvious. A flat top spectrum shows the frequency changes during the scan. Flat-top spectrum shows the frequency changes during scanning. Reading cursor 3.62MHz carrier frequency variation range of the spectrum. 
Figure 2: example of a linear scanning radar chirp, the pulse spectrum shows nearly linear sweep 4MHz range applied to carrier frequency.
相位调制也可以实现脉冲压缩。相位调制技术将脉冲分成多个段，每个段都以特定的相移传输。这些段的长度相等，相移的选择由代码确定。通用代码是二进制的，其中代码值根据代码序列在+1和-1之间切换，对应于0°和180°的相移。最常用的代码序列是巴克码，它与其他序列的自相关性较低，并且产生的旁瓣较低。
图3：使用长度为13的巴克码的调相脉冲，作为波形中的陷波，相位反转很明显
图3是使用长度为13的巴克码的调相脉冲的示例，最好在主机中对调相脉冲进行解调，这样可以进行更复杂的数据分析，可以使用第三方软件，如MATLAB或LabVIEW，甚至可以用C，C++或Python进行自定义编程。这些第三方程序提供了快速解调这些信号的功能。可以根据应用程序进行定制，它们提供了极大的灵活性，支持进行更复杂的分析。
M4i.2234-x8数字化仪的PCIex8 Gen2接口增强了在数字化仪外部进行处理的能力。使用Spectrum的驱动程序，该接口可以在合适的主机上实现大于3.4GB/s的数据传输速率。这种传输速率在处理高速信号采集是非常重要的，它可以采集多达4GB的数据，因为它可以将数据快速传输到主机。
对于那些中级编程技能的人来说，并行处理的SpectrumCUDA访问选项（SCAPP）提供了更大的处理能力，该选项允许数字化仪与基于CUDA的图形处理单元(GPU)直接连接，这使GPU的多处理核心和超大内存可用于高级高速信号处理。在此应用程序中，它可以提供更快的计算时间。
图4：使用在主机上运行的专有程序进行相位解调，解调后的波形仅在存在载波的情况下才有效。
图4显示了使用专有解调程序获取调相脉冲的结果。解调波形仅在信号载波存在时有效，它显示了巴克码序列值，可以看到13位的巴克码（+1+1+1+1+1-1-1+1+1-1+1+1-1+1），+1代表0°，-1代表180°。这是最长的巴克码序列。该代码的频谱旁瓣电平为-22.3db。
第三方软件包如LabVIEW和MATLAB提供了专门为雷达分析设计的应用程序包。MathWorks在MATLAB相控阵系统工具箱中包含RadarWaveformAnalyzer应用程序就是一个很好的例子。Spectrum提供驱动程序和示例程序，以将这些程序与其数字化仪连接起来。
该模块数字化仪还提供多种采集模式，旨在有效地使用采集内存，减少采集之间的死区时间，尤其是对于信号（如雷达应用中的信号）而言，它们的占空比很低。
图5：通过在多路采集模式下采集波形，可以更有效地使用采集内存，此模式可获取多个波形，每个波形均位于其自己的段中，这消除了重大事件之间的停滞时间，时间戳记记录每次触发的时间。
如图5a所示，多重记录或分段模式允许以极短的重新布防时间(在5GS/s采样率下约6.5ns)记录多个触发事件。采集存储器被分成若干大小相等的段。每个触发事件填充一个段。在段触发事件之间停止采集，以节省可用内存。用户可以在段内对触发前和触发后的时间间隔进行编程。所获取的段数仅受所使用内存的限制，在使用先进先出(FIFO)获取模式时不受限制。与多个触发器关联的重要数据存储在连续段的采集内存中。不记录与事件之间的死区时间相关的数据。每个触发器事件都有时间戳，因此可以知道每个触发器的精确位置。图5b显示了“多重记录”模式的时间戳操作的图形视图。时间戳存储在卡上硬件的额外FIFO内存中。如果需要，可将其读出。
多重采集模式通过不记录死区时间来节省存储空间。这在可用的采集存储器中提供了更多重要事件。图1中的脉冲宽度约为10µs，死区时间为90µs，因此在多重采集模式下，将不会记录90µs，并且可以采集并存储另外9个脉冲。这种模式在研究雷达操作中脉冲之间的变化时非常有用。还有其他几种采集模式，可以更有效地控制数字化仪，优化数据采集过程。
Radar signals are difficult to measure, but is very suitable for modular digitizer acquisition and analysis of these signals. Digitizer provides excellent signal integrity, and provides a variety of tools to analyze the acquired waveforms. Fast data transfer to the host the ability to make more extensive analysis tools are available, resulting in a very flexible radar measurement system.