Electronic Military & Defense Annual Resource

5th Edition

Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.

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Techniques Pushing The Boundaries Of Radar Test And Measurement The development of increasingly powerful, complex radar systems requires an evolution in the tools and techniques used to test them. By Chris Loberg D esigners of modern electronic warfare (EW) and radar systems face significant challenges in devel- oping systems with the flexibility and adaptability required for next-generation threat detection and avoidance. Capable tools for generation and analysis of extremely complex pulse patterns are required to validate designs with advanced scanning methodologies — tools that can handle complex radar baseband, IF and RF signals, as well as identify multi-system interference. Another important trend is the growth of high-speed private satellite (K-band) communication networks in EW, which adds visibility testing needs. With today's rapid advances in radar technology, devel- oping and manufacturing highly specialized and innovative electronic products to detect radar signals takes leading- edge technology and tools. The good news is that the tools needed to manage the requirements of modern radar applications now are arriving on the market. These include high-performance arbitrary waveform generators, advanced real-time spectrum analyzers, and ultra-high-bandwidth oscilloscopes. Real-time visibility of advanced pulse com- pression systems, and the generation and analysis of all digital dynamic signal types, are vital to enabling designers to create highly reliable, cutting-edge defense and electronic warfare systems. Modern Radar Challenges When measuring and testing a pulsed radar transmitter, it used to be that the signal tested was likely a staid, steady stream of pulses. Today, it's a whole different story, with radar engineers creating designs that serve up pulses in all kinds of innovative ways. For instance, pulsed RF radars use variable transmitting frequencies that take the form of frequency hopping patterns. These patterns are complex, unpredictable, and typically non-repeating (or repeating over extremely long periods of time). Carrier frequency can even change for each transmitted pulse. Pulse compression techniques are used to increase range by transmitting longer pulses (so average power is increased for a given peak power), while echo processing at the receiver can result in a much better spatial resolution by "compressing" the pulse through correlation or dispersion processing. Also, an important issue for some radar systems is carrier phase coherence. For example, in higher-performance coherent MTI (Moving Target Indicator) architecture, phase coherence must be preserved between consecutive pulses. Returning echoes, no matter the phase characteristics of the transmitted pulse, will consist of a superposition of sig- nals with a variety of relative phases. There will be multiple target echoes with arbitrary delays, multiple echoes from the same target with different times of arrival due to multi-path, all kinds of clutter, and frequency shifts. The instantaneous amplitude and phase for a given echo also will be controlled by the target shape and size. In short, no matter the complex- ity of the transmitted signal, the reflected signal will be much more complex. Generating radar signals is one of the most challeng- ing tasks for a signal generator. The signals' combination of carrier frequency, modulation bandwidth, and, in most cases, their pulsed nature, creates a series of requirements that are difficult to match with existing instrumentation. The increasing complexity of radar systems, the growing use of complex modulation techniques such as OFDM (orthogonal frequency-division multiplexing) or UWB (ultra wideband), and the signal quality requirements for a successful test impose severe constraints on the stimulus equipment used in radar testing. Furthermore, the need to emulate multi-antenna radar systems based on phased-array antennas or, more recently, MIMO (multiple-input, multiple-output) architectures makes it necessary to generate multiple signals with tightly con- trolled timing and phase alignments. Traditionally, radar signal generation has been implemented with a baseband signal generator and an RF/µW modulator, often integrated as one piece of equipment. With up to 50 GS/s sampling rate at 10 bits vertical resolution, the latest generation of arbitrary waveform generators can effectively be used to test these architectures, with performance allowing the direct genera- tion of radar signals with carriers up to 20GHz (beyond the Ku band). This solution offers much higher signal quality, cost-effectiveness, and repeatability than traditional solutions. Radar Measurement Considerations The selection of optimum equipment for measuring radar pulses depends on the nature of the pulses and on capabil- ity differences among the available types of test equipment. Other considerations for determining appropriate equipment include the parameters that need to be measured and the range of values expected for the results. Pulse RF carrier frequency is a basic consideration. If the available equipment does not cover the frequencies involved, then a frequency conversion device will be required in Electronic Military & Defense Annual Resource, 5th Edition 32

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