Abstract: A structure which exhibits magnetic properties when it receives electromagnetic radiation is formed from an array of capacitive elements each of which is smaller, and preferably much smaller, than the wavelength of the radiation. Each capacitive element has a low resistance conducting path associated with it and is such that a magnetic component of the received electromagnetic radiation induces an electrical current to flow around the path and through the associated element. The creation of internal magnetic fields generated by the flow of the induced electrical current gives rise to the structure's magnetic properties.

Abstract: An optical modulator includes an optical input; an optical output; at least one optical path connecting the optical input and output; and an electrode structure for selectively changing the optical characteristic of a part of the at least one optical path in response to a control signal such as to modulate light passing along the optical path. The optical path further includes a structure which slows the passage of light along the part of the optical path to enhance the modulation effect of the modulator for a given length of optical path. Preferably the structure comprises a sequence of coupled resonator structures in which each resonator structure is defined by a pair of partially reflecting planes which define an optical resonator cavity within the optical parts.

Abstract: The performance of a microwave antenna is improved by incorporating a fine wire dielectric material which has a dielectric constant ∈ of less than unity at microwave frequencies. The effect of the dielectric material is to refract microwaves so that the antenna appears to have a larger aperture than that of its physical size. Furthermore, by selecting the transmission cut off frequency of the dielectric material, two antenna elements which are intended to operate within different frequency bands can be mounted one behind the other.

Abstract: A reflector circuit is provided which responds to illuminating radiation with corresponding output radiation of increased magnitude relative to the illuminating radiation, while also providing a frequency selective limiting characteristic. The circuit comprises an antenna for receiving the illuminating radiation and emitting the corresponding output radiation, a delay line providing a frequency selective limiting and signal storage characteristic and an amplifier assembly. The antenna provides an input signal upon receipt of the illuminating radiation, a portion of which is amplified, frequency selectively filtered and then stored for a period after which it is emitted as the output radiation from the circuit. Switches are incorporated and are operable to counteract spontaneous oscillation within the circuit.

Abstract: A reflector circuit is provided which responds to illuminating radiation with corresponding output radiation of increased magnitude relative to the illuminating radiation. The circuit comprises an antenna for receiving the illuminating radiation and emitting corresponding output radiation, a delay line providing a frequency selective limiting and signal storage characteristic and an amplifier assembly incorporating a reflection amplifier for providing signal amplification. The reflection amplifier is capable of providing high gains approaching +30 dB at relatively low current consumption, for example, tens of microamperes. The antenna provides an input signal upon receipt of the illuminating radiation, a portion of which is amplified, frequency selectively filtered, and then stored for a period after which it is emitted as the output radiation from the circuit. Switches may be incorporated and are operable to counteract spontaneous oscillation within the circuit.