Abstract: A sensor is provided for detecting the presence of dielectric media, e.g., ice. The sensor includes a plurality of microstrip resonators which are positioned for electromagnetic coupling with a microstrip transmission line. The resonators produce amplitude minima in a radio-frequency signal that is carried over the transmission line. The resonance of the resonators changes in response to the addition of a dielectric coating. Each resonator can be configured with a different resonant frequency which serves as a signature that identifies the respective resonator's position. The sensor has a thin aerodynamic profile, can conform to nonplanar surfaces and its installation requires no intrusion into an aircraft skin.

Abstract: Microwave amplifiers are disclosed having a hollow helix slow-wave structure coupled directly to input and output waveguides. This helix-waveguide coupling structure couples the TEM mode of the helix to the TE10 mode of the rectangular waveguides and also defines ports communicating with the helix interior. Heating of the helix during high-power operation can be removed by cooling liquid pumped through the helix via these ports. The helix is surrounded by a cylindrical housing containing a low-pressure ionizable gas which forms a plasma channel that focuses the electron beam without the need for surrounding magnetic structures. A plasma cathode electron gun is arranged to inject an electron beam through the helix. Backflowing ions from the housing are harmlessly absorbed into the face of the plasma cathode. The microwave amplifier is converted to a backward wave oscillator by coupling a load to one of the waveguides.

Abstract: A dielectric-loaded, microwave sensor which can detect dielectric coatings, e.g., air, water and ice, on a road surface. The sensor includes an antenna having an aperture and also includes a dielectric member with a lower surface and an upper surface. The dielectric member is arranged with its lower surface across the antenna aperture and the sensor is embedded in a road with the dielectric member's upper surface coplanar with the road's surface. An antenna beam, which is incident upon the dielectric member, generates a return microwave signal which is the composite of microwave reflections from the dielectric member's inner and outer surfaces. Air, water and ice can be uniquely identified by the absence or presence of an amplitude minimum at predetermined frequencies of the return microwave signal. The thickness of an ice coating is determined by observation of the frequency of the amplitude minimum.

Abstract: Multiple radio frequency (RF) outlet ports are provided along the side of a slow wave tube to establish a distributed RF output in response to the transmission of an e.sup.- beam through the tube. The tube has a periodically rippled inner surface, and the outlet ports are spaced along the tube by substantially integral numbers of ripple periods. When implemented as a backward wave oscillator, RF power is extracted during a single pass through the tube; a travelling wave tube amplifier implementation is also possible. The separation of the RF extraction from the absorption of the e.sup.- beam at the end of the tube eliminates RF reflections and permits water cooling of the e.sup.- beam absorber. The RF extraction ports are also preferably configured as built-in mode converters from a TM.sub.01 cylindrical tube mode to a TE.sub.10 rectangular extraction mode, with four symmetrically arranged rectangular extraction waveguides at each extraction location combining their energies into a single TE.sub.10 output.

Abstract: Plasma wave tubes are disclosed having waveguide injection systems configured for injection of an RF signal to prebunch the electron beam of the tube and thereby control the frequency of an RF output signal. Preferred embodiments of the injection system include a plurality of rectangular waveguides arranged radially about a cylindrical waveguide member and joined to it for communication with its interior. Plasma wave tubes (140) are also disclosed that utilize the injection system as a collector (44C) to couple an RF output signal from the tube.

Abstract: A surface condition sensing system includes a frequency controlled source of electromagnetic power adapted to produce a band of selected frequencies which are directed to a surface under examination. A monitoring circuit compares transmitted and reflected electromagnetic power as a function of frequency from the surface, and generates a plurality of absorption signals representing the difference between the amplitude of the transmitted signal with the corresponding amplitude of the reflected signal. An evaluator circuit generates a surface condition signal representing the results of a comparison between the plurality of absorption signals with known surface models. A control circuit generates a status signal representative of the surface condition. The system can be configured as a road condition sensor or as an aircraft ice detection sensor.