Abstract: A high-gain digitally tuned antenna system comprises a modified swept-back fractal (MSBF) radiator element, with the fractal preferably being a Sierpinski carpet fractal based on a parallelogram. A digital tuning circuit coupled to the radiator comprises an array of inductors which can be selectively connected to form a network which tunes the antenna system to a selected tuning frequency. The system is preferably arranged to selectively connect the inductors in series such that the combined inductances substantially cancel the capacitance of the radiator at a selected tuning frequency. The antenna system is preferably arranged to operate over the 30-88 MHz, 108-174 MHz, and 225-600 MHz bands, with a radiator height of 15? or less.

Abstract: Antenna system embodiments are illustrated that include a planar, top-loaded dipole antenna and a planar elliptical dipole antenna arranged substantially coplanar and within the top-loaded dipole antenna. These antenna structures facilitate their combination with tuning coil chains, baluns and impedance matching circuits to operate over multiple frequency bands. System embodiments exhibit high gain and selectivity and may be digitally tuned over wide frequency bands (e.g., 30-600 MHz). The embodiments may be digitally tuned to support operational modes such as frequency hopping to thereby realize a secure communication system. Because these embodiments are configured to operate in the absence of a ground plane, they are especially suited for mounting on various portions of an aircraft's structure. For example, they may be configured as winglets and situated far out on wingtips to thus free the remainder of an aircraft's structure for other operational systems.

Abstract: Antenna embodiments are illustrated that are particularly suited for use in aircraft navigation, identification and collision avoidance systems. An exemplary antenna embodiment operates about a center wavelength and in association with a ground plane and comprises first and second grounded, shortened, and top loaded monopoles. These monopoles are spaced apart above a ground plane and each of them includes a feed post, a shorted post, and a top load wherein the shorted post is spaced from the feed post, is coupled to the ground plane, and has a length less than one fourth of the center wavelength. In addition, the top load is coupled to the feed post and the shorted post and is configured along orthogonal minor and major axes of the top load to have a width along the minor axis and a length along the major axis that exceeds the width.

Abstract: Compact top-loaded, fractal monopole antenna system embodiments are provided for multi-band airborne operation over ultrabroadband ranges (e.g., 30 to 2000 MHz). These multi-band embodiments are self-contained, aerodynamic and compact (e.g., blade height less than 9.5 inches) and are power efficient with a low return loss (e.g., less than ?7 dB). System embodiments include a set of impedance-matching circuits configured to substantially match an antenna impedance to a predetermined system impedance over a set of predetermined frequency bands. In an embodiment, at least one impedance-matching circuit includes a chain of selectable air-core inductors which are novelly arranged to improve radiation efficiency and prevent damage to support substrates. In an embodiment, a lowest-frequency one of the impedance-matching circuits is configured to process signals having a maximum wavelength ?max wherein a fractal member is configured with a length that does not exceed ?max/40.

Abstract: Antenna system embodiments are shown which are especially suited for mounting on aircraft and for operation across widely-spaced frequency bands. Embodiments include blade members positioned in a ring arrangement and tuning circuits that are each coupled between a respective pair of the blade members and configured to successively remove blade members from operation as the operational frequency increases.

Abstract: The present invention is directed to multi-element antennas that include, for each adjacent pair of antenna elements, at least one switch arranged to selectively connect that pair to thereby selectively alter an antenna dimension. Accordingly, a multi-element antenna can be configured to enhance its gain at different operational frequencies while a corresponding impedance matching network can enhance the impedance match (i.e., reduce reflected signal energy) between the antenna and a corresponding system (e.g., a transceiver system). The antenna and system can thus be effectively tuned across a wide operational band. The antenna and impedance matching network are configured with switch command signals and match command signals that are provided in response to each of a plurality of frequency codes.

Abstract: Single-port weighting systems are shown for applying phase and/or amplitude weights to received signals. One system embodiment includes an array of antenna elements, a microwave power combiner, a plurality of microwave structures and a single microwave downconverter that is coupled to the power combiner and has a single output port for access to the received signals. Each of the microwave structures couple first and second signal paths between a respective one of the antenna elements and the power combiner, insert a phase shift in one of the first and second signal paths and insert first and second mixers respectively in the first and second signal paths wherein the mixers each have an input port for application of the weights.

Abstract: Methods are disclosed for receiving GPS signals in the presence of multiple interference signals. The methods feature the orthogonal projection of sub-optimal weight vectors onto sets of orthonormal basis vectors. They facilitate the use of single-port reception techniques in which power is monitored only at a single GPS array output port regardless of the number of array elements. The methods do not require prior knowledge of interference signal structure and their use of uncoupled orthonormal basis vectors facilitates the simultaneous adjustment of array weights and rapid convergence to an optimal set of weights.

Abstract: A Tee slot blade antenna for aircraft and other high speed vehicles has a pair of dielectric sections, one section extending longitudinally along the blade and the other extending transversely from an intermediate location along the longitudinal section. The resonant frequency of the antenna is determined by the length of each section and the position of the transverse section along the longitudinal one, while the characteristic impedance is a function of the width of each section. The Tee slot antenna is capable of operating over a wide bandwidth on a smaller blade than prior single slot antennas. A Tee slot antenna designed for one frequency range can be combined with either a single slot antenna or another Tee slot antenna designed for another frequency range on the same antenna blade, without impairing the bandwidth of either antenna.

Abstract: A microstrip antenna which includes a ground member, a dielectric element mounted on the ground member and a radiating element on the dielectric element, has been improved by means of a distinct grounding ring of conductive material which is spaced apart from and extends around the radiating element. The grounding ring is connected to a ground member, thereby laterally isolating the antenna and permitting a closer spacing with adjacent antennas. The gap between the radiating element and the grounding ring is different in different directions.