Introduction and Overview of the Book

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High-power microwaves (HPMs), or directed energy RF, is an evolution of vacuum electron devices (VEDs) that seeks to generate the highest peak power levels in the frequency range of 100 s MHz through 100 GHz (and even higher frequencies) in short pulses (10–100 s ns in duration) that can be repetitively pulsed [1, 2]. They came onto the scene in the late 1960s following the advent of pulsed power drivers that not only provided high-energy electron beams (in the order of a MeV and higher), but concomitantly provided high currents as well (1–10’s kA) [3]. Similar to VEDs, the electron beam is the power source from which the microwaves grow. Unlike VEDs, HPM sources have much less-stringent vacuum and material requirements since their applications tend to be limited in scope with short mission times.
The state-of-the-art in the practice of HPM sources has been led by intense beam-driven oscillators whose output scale as Pf 2, where P is the peak output microwave power and f is the operating frequency [2, 4]. This is the Figure-of-Merit (FOM) for HPM oscillators. The equivalent FOM for HPM amplifiers is PfΔf whereΔf is the bandwidth (BW). Until recently, conventional wisdom suggested that for emerging defense applications, the highest power on target (highest intensity field) was of greatest utility. However, recent advances in the understanding of the interaction of intense microwave fields with components and circuits argue that a tailored waveform synthesized at low power and amplified to very high power, might provide even superior capabilities. This is termed waveform diversity. Consider a comparison of the state-of-the-art oscillator and amplifier in terms of the FOM: (i) the ITER/DIII-D’s plasma-heating gyrotron oscillator at 110 GHz, 1MW(10 s pulse), 1.1MHz BW, has a FOM 1.2 × 1012 W-GHz2 and essentially no BW. (ii) Haystack radar’s gyrotron amplifier at 94 GHz, 55kW output power (5.5kW average), 1600MHz BW yields a FOM 8.3 × 106 W-GHz2. Thus, there is a 2 order-of-magnitude opportunity to advance the FOM in high-power amplifiers with considerable BW. Interest in metamaterials (MTMs) grew rapidly following the publication of Pendry [5] and its practical implementation by Smith afterwards [6]. As discussed in this chapter, the history of MTMs dates back to the nineteenth century with numerous contributors, many of whom have only
recently been rediscovered. This history has been reviewed in several books [7, 8] and continues to be unraveled.
While numerous books have been written on the EM properties of MTMs, all of the applications that have been described in these books to-date are at low-power levels. In this book, we bring together advances that have been made in studying MTMs as slow-wave structures (SWSs)for active electron beam-driven HPM devices. We discuss structures that satisfy Wasler’s definition of a MTM(see Section 1.2), and we also describe periodic SWSs with degenerate band edges (DBEs) that do not satisfy this definition, yet do offer novel engineered dispersion relations that are relevant to our overall goal-seeking to discover novel beam/wave interactions that can be exploited for new HPM amplifiers.
Original languageEnglish
Title of host publicationHigh Power Microwave Sources and Technologies Using Metamaterials
EditorsJohn Luginsland, Jason Marshall, Arje Nachman, Edl Schamiloglu
PublisherJohn Wiley & Sons, Ltd
Number of pages16
ISBN (Electronic)9781119384465, 9781119384472, 9781119384458
ISBN (Print)9781119384441
Publication statusPublished - 1 Dec 2021


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