Abstract: Various sensors, systems, and methods for monitoring environmental conditions are provided. In one embodiment, among others, a passive sensor includes an antenna; a modulating circuit coupled to the antenna by a microstrip transmission line, the modulating circuit capable of modulating a backscattered signal; a sensing material disposed between the microstrip transmission line and a ground plane of the passive sensor, where an electrical property of at least a portion of the sensing material varies with the environmental condition; and where the modulated backscattered signal includes at least one of phase and amplitude information corresponding to the electrical property of the portion of the sensing material.

Abstract: Various sensors, systems, and methods for monitoring environmental conditions are provided. In one embodiment, among others, a passive sensor includes an antenna; a modulating circuit coupled to the antenna by a microstrip transmission line, the modulating circuit capable of modulating a backscattered signal; a sensing material disposed between the microstrip transmission line and a ground plane of the passive sensor, where an electrical property of at least a portion of the sensing material varies with the environmental condition; and where the modulated backscattered signal includes at least one of phase and amplitude information corresponding to the electrical property of the portion of the sensing material.

Abstract: A low cost, compact, electronically scanned millimeter wave (MMW) lens enables the projection of a highly directional beam of Ka band millimeter wave (MMW) electromagnetic energy, while eliminating the need for mechanical movement of the lens. The present invention allows for the economical production and operation of the lens in the Ka and higher frequency ranges by exploiting waveguide technology. The waveguides of the present invention are tapered longitudinally resulting in a wider portion of the waveguide in electromagnetic communication with an interior cavity of the lens. The waveguide taper improves impedance matching between the waveguides and the lens cavity. The waveguides also include symmetric power dividers, located longitudinally within the waveguide aperture, ensuring port widths below .lambda..sub.g /2, thus, reducing or eliminating unwanted mode components which reduces sidelobe energy. This results in a low loss, low sidelobe steerable beam of MMW energy.