Abstract: An exemplary radio-frequency (RF)-based navigation reference system uses one or more non-collocated and time-synchronized direction-finding transmitters to enable a client receiver to estimate its own 3-D position, velocity and time (PVT) using direction-finding (DF) waveforms obtained from said reference transmitters. At least one reference transmitter is sufficient for obtaining a 3-D PVT solution provided the client receiver is equipped with an accurate (low-drift) local clock such as a chip-scale atomic clock (CSAC). All other client receivers require at least two reference transmitters to estimate their 3-D PVT.

Abstract: An improved implementation of a 2×4 divider formed from a bridge junction is described. The bridge junction uses parallel and series connections of coaxial lines to eliminate impedance transformers that are normally required in a 2×4 power divider. In a preferred embodiment, the bridge junction is comprised of UT-085 coax transmission lines, 20 gauge twin lead wire and SB-805-61 ferrite beads with ½ turn windings to provide a wide bandwidth, compact, high power and rugged arrangement.

Abstract: A radio-based navigation system uses a small multi-mode direction-finding antenna and a direction-finding receiver to determine platform position, velocity, attitude and time while simultaneously providing protection against narrowband and broadband sources of interference. Global Navigation Satellite System (GNSS) signals such as those from a Global Positioning System (GPS) provide attitude measurements with a compact multi-mode direction-finding antenna (e.g., a small two-arm spiral with improved angle-of-arrival performance over the entire hemisphere enhanced through use of a conductive vertical extension of the antenna ground plane about the antenna perimeter and/or conductive posts placed evenly around the antenna perimeter) that provides protection against jammers. The multi-mode spiral may be treated as an array of rotationally-symmetric antenna elements.

Abstract: An exemplary radio-based navigation system uses a small multimode direction-finding antenna and a direction-finding receiver capable of determining platform position, velocity, attitude, and time while simultaneously providing protection against narrowband and broadband sources of interference. Global Navigation Satellite System (GNSS) signals such as those from the Global Positioning System (GPS) provide attitude measurements with a compact multimode direction-finding antenna (e.g., a small two-arm spiral with improved angle-of-arrival performance over the entire hemisphere enhanced through the use of a conductive vertical extension of the antenna ground plane about the antenna perimeter and/or conductive posts placed evenly around the antenna perimeter) which provides simultaneous protection against jammers. The multimode spiral may be treated as an array of rotationally-symmetric antenna elements.

Abstract: An improved implementation of a 2×4 divider formed from a bridge junction is described. The bridge junction uses parallel and series connections of coaxial lines to eliminate impedance transformers that are normally required in a 2×4 power divider. In a preferred embodiment, the bridge junction is comprised of UT-085 coax transmission lines, 20 gauge twin lead wire and SB-805-61 ferrite beads with ½ turn windings to provide a wide bandwidth, compact, high power and rugged arrangement.

Abstract: A radio-based navigation system uses a small multi-mode direction-finding antenna and a direction-finding receiver to determine platform position, velocity, attitude and time while simultaneously providing protection against narrowband and broadband sources of interference. Global Navigation Satellite System (GNSS) signals such as those from a Global Positioning System (GPS) provide attitude measurements with a compact multi-mode direction-finding antenna (e.g., a small two-arm spiral with improved angle-of-arrival performance over the entire hemisphere enhanced through use of a conductive vertical extension of the antenna ground plane about the antenna perimeter and/or conductive posts placed evenly around the antenna perimeter) that provides protection against jammers. The multi-mode spiral may be treated as an array of rotationally-symmetric antenna elements.

Abstract: Controlled phase shift in the operation of an RF antenna element is achieved by selectively choosing between different modes of antenna element resonance. Additional phase control resolution is achieved by combining this with other types of phase shifters. Such phase shifters are especially useful within a phased array of RF antenna radiator elements.

Abstract: An exemplary radio-based navigation system uses a small multimode direction-finding antenna and a direction-finding receiver capable of determining platform position, velocity, attitude, and time while simultaneously providing protection against narrowband and broadband sources of interference. Global Navigation Satellite System (GNSS) signals such as those from the Global Positioning System (GPS) provide attitude measurements with a compact multimode direction-finding antenna (e.g., a small two-arm spiral with improved angle-of-arrival performance over the entire hemisphere enhanced through the use of a conductive vertical extension of the antenna ground plane about the antenna perimeter and/or conductive posts placed evenly around the antenna perimeter) which provides simultaneous protection against jammers. The multimode spiral may be treated as an array of rotationally-symmetric antenna elements.

Abstract: A compact, non-phased-array, electronically reconfigurable antenna (ERA) system with at least two operational modes has a first operational objective that is polarization-sensitive null steering (PSNS) and a second operational objective that is direction-finding (DF). The system can rapidly switch between two operational states. In the first state, the system behaves like a polarization filter (PF) and operates as a controlled reception pattern antenna (CRPA), while in the second state the system behaves as an angle-of-arrival (AOA) sensor and operates as a fixed reception pattern antenna (FRPA). The system may include a spiral-mode antenna with both feed and load ports; a mode-forming network; an electronics package; and feedback control electronics. Radio frequency (RF) interference rejection and RF direction-finding may be performed as well as reduction and/or elimination of multiple jamming signals that are intentionally or unintentionally directed at a Global Positioning System (GPS).

Abstract: Reconfiguration of parasitically controlled elements in a phased array is used to expand the range of operational functions. Embedded array elements can be frequency tuned, and bandwidth can be improved by using reconfiguration to broaden the bandwidth of the embedded elements. For high gain arrays, beam squint can be a limiting factor on instantaneous bandwidth. Reconfiguration can alleviate this problem by providing control of the element phase centers. Scan coverage can be improved and scan blindness alleviated by controlling the embedded antenna patterns of the elements as well as by providing control of the active impedance as the beam is scanned. Applying limited phase control to the elements themselves can alleviate some of the complexity of the feed manifold. A presently preferred method of designing reconfigurable antennas is to selectively place controlled parasitic elements in the aperture of each of the antenna elements in the phased array.

Abstract: A compact, non-phased-array, electronically reconfigurable antenna (ERA) system with at least two operational modes has a first operational objective that is polarization-sensitive null steering (PSNS) and a second operational objective that is direction-finding (DF). The system can rapidly switch between two operational states. In the first state, the system behaves like a polarization filter (PF) and operates as a controlled reception pattern antenna (CRPA), while in the second state the system behaves as an angle-of-arrival (AOA) sensor and operates as a fixed reception pattern antenna (FRPA). The system may include a spiral-mode antenna with both feed and load ports; a mode-forming network; an electronics package; and feedback control electronics. Radio frequency (RF) interference rejection and RF direction-finding may be performed as well as reduction and/or elimination of multiple jamming signals that are intentionally or unintentionally directed at a Global Positioning System (GPS).

Abstract: A large aperture lightweight antenna uses an inflatable spherical surface deployed within a lighter than air platform. Beam steering is accomplished by moving the RF feedpoint(s) with respect to the reflector. The antenna can use an inflatable collapsible transreflector.

Abstract: Reconfiguration of parasitically controlled elements in a phased array is used to expand the range of operational functions. Embedded array elements can be frequency tuned, and bandwidth can be improved by using reconfiguration to broaden the bandwidth of the embedded elements. For high gain arrays, beam squint can be a limiting factor on instantaneous bandwidth. Reconfiguration can alleviate this problem by providing control of the element phase centers. Scan coverage can be improved and scan blindness alleviated by controlling the embedded antenna patterns of the elements as well as by providing control of the active impedance as the beam is scanned. Applying limited phase control to the elements themselves can alleviate some of the complexity of the feed manifold. A presently preferred method of designing reconfigurable antennas is to selectively place controlled parasitic elements in the aperture of each of the antenna elements in the phased array.

Abstract: Controlled phase shift in the operation of an RF antenna element is achieved by selectively choosing between different modes of antenna element resonance. Additional phase control resolution is achieved by combining this with other types of phase shifters. Such phase shifters are especially useful within a phased array of RF antenna radiator elements.

Abstract: The invention relates to a small (0.5 wavelength or less) adaptable antenna system. In particular it relates to the use of loaded parasitic components in the antenna aperture for the purpose of controlling the RF properties of the antenna. Such an antenna system is here referred to as a controlled parasitic antenna (CPA). Parasitic elements within the radiating aperture are terminated by active (controllable) impedance devices. A feedback and control subsystem periodically adjusts the impedance characteristics of these devices based on some observed metric of the received waveform. Such antenna systems can provide multifunctionality within a single aperture and/or mitigate problems associated with the reception of an interfering signal (or signals) or multi-path effects. Such antenna systems are particularly suitable to a situation where an aperture size is desired that is too small for the use of an adaptive phased array.