Significant progress has been made in the research of Laser Detection and Ranging (LADAR) systems, also known as Light Detection and Ranging (LIDAR). These research results are widely applied to target imaging and tracking. LADAR has a significant advantage over traditional RFRADAR in terms of image resolution because it uses much shorter wavelengths of the electromagnetic spectrum (especially in ultraviolet, visible, or near-infrared light). Since image resolution depends on the wavelength of the electromagnetic radiation used, shorter wavelengths provide greater resolution for different surfaces of the target. These shorter wavelengths range from approximately 10 micrometers to UV (ca. 250 nm). MIT Lincoln Laboratory has developed a system that employs a Doppler-based LADAR system for accurately tracking moving aircraft. This system uses a Kalman filter target tracker to accurately assess the aircraft's position and velocity. A Kalman filter is a set of mathematical equations that estimate the state of a process. Thus, the Kalman filter can be used to determine the aircraft's position and velocity. The LADAR system requires two 40 GHz microwave synthesizers. One synthesizer is used to simulate the Doppler displacement of the object by transmitting a varying frequency signal to the receiver. Another synthesizer is used to track Doppler analog frequency changes of the target. In addition to the requirement for wideband generation, the synthesizer must be able to respond quickly to changes detected by the Doppler tracking Kalman filter at the center of the LADAR system. At its fastest, the synthesizer must be able to perform frequency sweeps at a maximum rate of 500 MHz per second, with single frequency changes occurring as quickly as 2 ms. The Gigatronics Model 2400B series microwave synthesizers provide wideband frequency synthesis and the fast frequency switching required to meet these needs. The 2400B series offers a list mode with frequency switching speeds up to 160 μs. In this mode, the 2400B is also pre-programmed to jump to predefined frequency points. Clearly, 160 μs provides excellent frequency switching time. However, reprogramming the list takes time and cannot respond quickly to changes detected by the Doppler tracking Kalman filter. The synthesizer must respond to single frequency change commands within microseconds of receiving remotely controlled commands. Traditional ASCII-based General Purpose Instrument Bus (GPIB) processing would take 20 ms. List mode and traditional GPIB communication prohibit such applications. To meet the 2ms frequency switching requirement, the 2400B series synthesizers rely on Automation Xpress software. This software includes an application programming interface (API) in dynamic link library (DLL) format. An API is a set of routines, protocols, and tools for building software applications. Using the API, editors can independently instruct frequency changes, leveraging the 2400B's fast frequency switching architecture. Automation Xpress significantly reduces the 2400B's processor load by offloading instrument status processing to a PC. After the instrument status calculations for frequency generation are executed, the primary time required for frequency switching is the time it takes for data to be transferred from the controller to the 2400B. Automation Xpress's switching time specification is 1.0ms, including the configuration of the modem processor and memory (as shown in the figure). When using the GPIB EndorIdentify signal as the starting point for determining the switching time to the Lock/Level signal, the typical frequency switching time (excluding additional controller processor overhead) is approximately 1ms. This signal indicates that the frequency change has been completed. Operating system requirements must be met to provide the fast switching capabilities of Automation Xpress. The LADAR system developed at MIT uses the Linux Fedora Core4 operating system. Conversely, Automation Xpress is designed for Windows 2000 and XP operating systems. Therefore, Gigatronics engineers had to convert the Automation Xpress API to a Linux-based shared function library. The 2400B series synthesizers have been successfully integrated into a Doppler tracking Kalman filter LADAR system designed at MIT. This system is currently undergoing testing. Editor: He Shiping