Abstract: An anechoic test chamber for testing an electromagnetic loss characteristic of a material specimen has first and second opposed and tapered conical sections. The chamber has an anechoic material covering its inside surface. Feed and receive antennas are disposed on the ends of the conical sections. An aperture plate is disposed between the first and second sections. The aperture plate electromagnetically isolates the first and second conical sections except for the aperture itself. A method of determining an electromagnetic loss characteristic of a material specimen utilizes a dual tapered conical chamber for processing S-parameter measurements to determine impedance, complex permittivity, or complex permeability of the specimen.

Abstract: An anechoic test chamber for testing an electromagnetic loss characteristic of a material specimen has first and second opposed and tapered conical sections. The chamber has an anechoic material covering its inside surface. Feed and receive antennas are disposed on the ends of the conical sections. An aperture plate is disposed between the first and second sections. The aperture plate electromagnetically isolates the first and second conical sections except for the aperture itself. A method of determining an electromagnetic loss characteristic of a material specimen utilizes a dual tapered conical chamber for processing S-parameter measurements to determine impedance, complex permittivity, or complex permeability of the specimen.

Abstract: A conformable, integrated antenna assembly providing three or more radiating apertures in a single antenna structure is provided. The antenna assembly is adapted to mount flush with the fuselage or other surface of an aircraft or other structure. A range of antenna services, including communications, navigation and IFF (CNI) services, may thus be provided while simultaneously minimizing aerodynamic drag and reducing size, weight and cost.

Abstract: A radome structure has an outer first layer of a fiber-reinforced composite material of quartz fibers in a noncrystalline cured oligomeric cyanate ester pre-polymer. A second layer of a syntactic foam underlies and is bonded to the first layer. A third layer of the same fiber-reinforced composite material (although possibly of different thickness) underlies and is bonded to the second layer. A fourth layer of the syntactic foam underlies and is bonded to the third layer. A fifth layer of the same fiber-reinforced composite material (preferably of the same thickness as the first layer) underlies and is bonded to the fourth layer. The structure is formed by layup of the first layer inside a female mold, and successively shaping the remaining layers and tacking them to each preceding layer. The shell produced in this manner can be joined to conforming shells.

Abstract: A radome structure has an outer first layer of a fiber-reinforced composite material of quartz fibers in a noncrystalline cured oligomeric cyanate ester pre-polymer. A second layer of a syntactic foam underlies and is bonded to the first layer. A third layer of the same fiber-reinforced composite material (although possibly of different thickness) underlies and is bonded to the second layer. A fourth layer of the syntactic foam underlies and is bonded to the third layer. A fifth layer of the same fiber-reinforced composite material (preferably of the same thickness as the first layer) underlies and is bonded to the fourth layer. The structure is formed by layup of the first layer inside a female mold, and successively shaping the remaining layers and tacking them to each preceding layer. The shell produced in this manner can be joined to conforming shells.

Abstract: A notch antenna (10) has a metallic notch element (20) deposited on a dielectric substrate (12), which element has a smooth continuously curved edge located adjacent a substrate edge (18). A metallic ground plane (28) is located adjacent the substrate edge (18) spaced very closely to element 20 at one end and at a gradually increased spacing moving away from the one end. An electromagnetic field transmitting coaxial cable (30) with ferrite beads (44) received over its outer conductor for reducing spurious radiation is located on the opposite side of substrate (12,14). The cable center conductor (34) is connected to a metallic strip (38) that is located on the same side of substrate (12,14) as the coaxial cable and tracks the same path as the notch element (20) on the opposite side of substrate (12). The antenna (10) is fed by electromagnetic energy at the closely spaced region of the element (20) and ground plane (28).

Abstract: A method of testing the reflectivity of RF absorber materials utilizes an elongated chamber lined with RF absorber material and having a source antenna at one end, with the other end terminating in either a "short circuit", or a piece of RF absorber material which is to be tested. A probe antenna is moved along the axis of the chamber and the standing wave created by the source antenna and the reflection from the other end is recorded, first with the short circuit condition, and then with the test sample in place, and the results are compared to yield a figure for the reflectivity of the test sample.

Abstract: A structure for attenuating the passage of electromagnetic energy includes at least two panels made of electromagnetic energy-attenuating material having adjacent edges thereof either abutting or overlapping one another to form a portion of an enclosure. A shielding tape defining transverse waveguide channels either straddles the seam between the two panels in the abutting mode, or is sandwiched between the overlapping edges of the panels in the overlapping mode. In either mode, the shielding tape operates not to create complete conductive continuity between the two panels at every point, as do previous tapes and techniques, but rather to define a multiplicity of small waveguides which are operating beyond cutoff, and are of such an impedance relative to the impedance of the incoming electromagnetic energy that in the frequency range in question, the energy is attenuated by the channel waveguides to levels 50 dB to greater than 100 dB.

Abstract: A structure for attenuating the passage of electromagnetic energy includes at least two panels made of electromagnetic energy attenuating material having adjacent edges thereof disposed in near abutment to form at least a portion of an enclosure. Electromagnetic energy attenuating strips are disposed astraddle and lengthwise of the adjacent edges of the panels on opposed faces thereof, with the strips being in intimate, face-to-face contact with the panels. Fastening means are employed to connect and compress strips and panels together in a sandwich seam and in a manner that doubles the length of travel for any radiated energy attempting to travel between the strips and panels. The attenuation effected by the seam is enhanced by placing a thin layer or coating of lossy material between at least one of the strips and abutting panels.

Abstract: An anechoic chamber utilizes an expanded central area resembling two flared horns with their rims fastened together, with the general vertex area of one of the horns forming the source area of the chamber and the other end the test or receiver end, there being adequate room beneath the two ends to include as part of the chamber rooms outside the chamber shell for housing the transmitter and receiver equipment. The purpose of the flare is to reduce shallow angle incidence on the walls of the chamber to improve performance by decreasing reflectivity.

Abstract: A microwave absorber is provided for use as lining in an anechoic chamber for positioning on the sides of the chamber, especially in the area about midway between the source and receiver, the absorber element being designed to augment chamber performance by effectively increasing the angle of incidence of radiation at the absorber, yielding an improved performance.

Abstract: Various aspects of electro-magnetic testing are facilitated by inserting a foamed plastic dielectric lens at a particular position between a particular radiating source and the test aperture. The lens is constructed according to electro-optic formulae and the radiation wavelength to produce a plane wave of uniform phase. To control extraneous energy contributed by reflections from the flat face of the lens, this surface is provided with two layers of high-performance absorber material. The amplitude characteristics in the test region are controlled by appropriate selection of the source antenna. Radiation-absorbent material is also provided to eliminate amplitude distortion. This makes possible testing under far-field conditions in test cells of modest size, which has heretofore been possible only with elaborate parabolic reflectors. Weather restrictions on use of free-space ranges, the sheer size of such ranges, and security problems attendant on their use, are all thus avoided.