International Telemetering Conference Proceedings / October 30-November 02, 1989 / Town & Country Hotel & Convention Center, San Diego, California / During high-power microwave (HPM) testing, where the item under test is subjected to power levels up to several thousand W/cm , the RF energy present will make typical 2 telemetry RF links useless. Therefore, other means must be used to retrieve the data during the tests. One method to accomplish data retrieval is to replace the RF data link with a fiber-optic link. This is done by replacing the transmitter with a fiber-optic transmitter on the sending end and the RF receiver with a fiber-optic receiver on the receiving end. Although this sounds simple, it is not always so. Solutions for PCM and FM-FM systems are relatively straightforward, whereas PAM systems present a unique set of problems. This paper addresses possible solutions for PCM and FM-FM and three possible solutions for PAM, one being by using a PAM-to-PCM converter.

<p dir="ltr">High-power microwave (HPM) devices are generally vacuum-based devices that transform electron beam energy into microwaves with peak powers above 100 MW from 1-300 GHz. Solid-state HPM devices provide more compactness and greater reliability while consuming less power. Nonlinear transmission lines (NLTLs) provide a solid-state alternative to HPM generation by sharpening the input pulses from a pulse forming network to create output oscillations.</p><p dir="ltr">The first section of this dissertation evaluates and explores the feasibility of using nonlinear composites containing ferroelectric (e.g., Ba_2/3Sr_1/3TiO₃, BST) and/or ferromagnetic (e.g., Ni_1/2Zn_1/2Fe₂O₄, NZF) inclusions in a linear polymer host (polydimethylsiloxane, PDMS) to tune NLTL properties for HPM applications. Appropriately modelling and designing NLTLs using nonlinear composites require accurately characterizing their linear and nonlinear electromagnetic properties. We first studied the electromagnetic properties of the composites using theoretical, numerical, and experimental approaches. Incorporating these composite models and characterizations into NLTL simulations will be discussed.</p><p dir="ltr">Vacuum-based HPM devices, such as magnetrons and crossed-field amplifiers, generally operate in the space-charge-limited region, which corresponds to the maximum current possible for insertion into the device. This motivated studying the space-charge-limited current and electron flow in a two-dimensional (2D) planar diode with various crossed-magnetic fields using particle-in-cell (PIC) simulations. For non-magnetically insulated diodes (electrons emitted from the cathode can reach the anode), analytical and/or semi-empirical solutions are derived for electrons with nonzero monoenergetic initial velocity that agree well with PIC simulations. For magnetically insulated conditions, we developed new metrics using simulations and analytic theories to assess electron cycloidal and Brillouin flow to understand the implications of increasing injection current for 2D diodes. These analyses provide details on the operation of these devices at high currents, particularly virtual cathode operation, that may elucidate behavior near their limits of operation.</p>