Abstract: An antenna assembly comprising a radiating element which passively receives a signal fed by a vertically-stacked pair of asymmetrically-shaped, conductive cone elements mounted below the radiating element. The cone elements are centrally fed by a coaxial cable input at a common junction formed the apex of each cone element. This antenna assembly provides a low-profile antenna to transmit and receive radio frequency (RF) energy with high gain and desirable antenna patterns for data transmission in an in-building, wireless local area network. The antenna assembly can be mounted in a standard ceiling or wall-mounted enclosure, with the low-profile antenna extending beneath the surface of a conductive enclosure cover that serves as the ground plane for the antenna element. This configuration achieves high antenna gain with a downtilt-beam, omnidirectional radiation pattern, which is highly desirable in an in-building wireless local area network (WLAN) application.

Abstract: A ground-based antenna for use with a satellite communications (SATCOM) system that reduces interference from geosynchronous earth orbit (GEO) satellites. Because GEO satellites that provide coverage of the continental United States (CONUS) are uniformly separated along an equatorial arc around the earth, the GEO satellites are approximately uniformly separated in sine space when viewed from a ground terminal located within CONUS over typical communications frequency bands, such as the Ka band (29-39 GHz) and the Ku band (10-15 GHz). The invention can reduce interference by providing an uniformly illuminated rectangular aperture, in which the horizontal dimension is chosen so when the aperture is normal to a transmission axis between the antenna and the Nth satellite of a SATCOM systems, the nulls of the antenna radiation pattern align with the N±1, N±2, N±3, . . . satellites.

Abstract: A ridged feed horn antenna for use in broadband satellite communications. This multi-ridged feed horn operates in a receive band of 10-13 GHz and a transmit band of 14-15 GHz. The ridged feed horn antenna comprises excitation conductors which excite the field between each of the ridges in the feed horn antenna. The excitation conductors are connected to each of the ridges. A waveguide, terminated at the back of the horn antenna, enables the ridges to guide the energy from their respective excitation conductors toward the mouth of the feed horn antenna. A planar balun and matching circuit, located at the back of the horn antenna, may be used to feed each of the excitation conductors. Furthermore, the cross-section of each excitation conductor is chosen so as to optimize horn antenna performance. Each excitation conductor extends outwardly from the back of the horn and is parallel to the longitudinal axes of the horn waveguide.

Abstract: Methods and systems are described that may be used in the context of a Performance Enhancing Proxy architecture for Internet traffic. A method of accelerated connection opening with error handling is disclosed. Also, a method of handling the Path MTU Discovery mechanism in the context of a distributed connection splitting PEP is described. A novel packet format for a proprietary inter-PEP protocol is described which allows for low packet header overhead. A new acknowledgement scheme that adapts to packet loss conditions to minimize bandwidth consumption by selecting an acknowledgement type from several possibilities is also detailed. A method whereby potentially spurious retransmissions are minimized by timing every transmission and retransmission is also described.

Abstract: The invention provides a method and system for dealing with the flow of data between one Performance Enhancement Proxy and another in the context of split links for TCP over satellite performance improvement. The environment according to the invention may include one or more intermediate nodes experiencing variable latency and bandwidth allocations. The method and system manage the data flow to ensure bandwidth fairness between competing TCP/IP connections, prevention of PEP receiver buffer overflow and near 100% usage of the available satellite bandwidth without the need for conventional TCP/IP ACK driven probing algorithms. The near 100% usage of capacity being achieved, in part, through PEP to intermediate node message exchange.

Abstract: A method and system is presented for the bi-directional transfer of data packets over a TCP communications system that can comprise both terrestrial and satellite links, using an enhanced flight protocol that, transparently to the end users, replaces the TCP over the congested satellite link portion of the system that accelerates the data delivery between end users and improves reliability of the data packet transmission. The invention eliminates the conventional TCP 3-way handshake and other associated time-delay procedures and replaces them with an improved use of performance enhancing proxies at either end of the satellite link that use a unique acknowledgement methods, data buffer storage and packet header field arrangement among the design features of a flight protocol method and system that accelerates data packet transfer with more efficient link capacity use and greater data throughput.

Abstract: An improved multi-junction waveguide circulator that eliminates the transitions to dielectric transformers and air-filled waveguides between ferrite elements is described. The waveguide circulator in accordance with the invention can be implemented in variations from a minimum of two ferrite circulator elements held in close proximity to one another to any number of ferrite elements as required to achieve the desired isolation performance or to create a switch matrix with any combination of input and output ports. The waveguide circulator in accordance with the invention eliminates the transitions between adjacent ferrite elements and thus reduces losses, component size, and mass.

Abstract: An antenna array of parabolic rectangular reflectors for use in satellite communications. The antenna comprises two parabolic reflectors disposed contiguously on a common outer surface. The common surface forms a continuous antenna aperture. The parabolic reflectors have rectangular side edges which permit the adjacent edges of the parabolic reflectors to be spaced closely. The mouth of each parabolic reflector is focussed on a separate feed. The focus of the feed is not located at the center of the reflector but rather offset. The antenna feeds and the reflector foci are displaced toward the center of the array such that the spacing between the antenna feeds is less than half the length of the antenna. The present invention provides the displacement of each reflector focal point and each antenna feed toward the center of the array.

Abstract: A phase shifter adjusts the phase between two segments of an RF feed line that are fed with the phase shifter. Specifically, the phase shifter adjusts the phase between two signals in RF feed line segments by changing the electrical path lengths that RF energy travels down in each respective RF feed line. The phase shifter includes a coupling arm, a key, a spring, and a support architecture that fastens the phase shifter to a substantially planar surface. The support architecture is rotated manually or with a machine such as a motor. The coupling arm can include a coupling ring, a wiper element, a support trace, and a dielectric spacer. The phase shifting system is a relatively compact structure having a predetermined value of capacitance maintained between a coupling ring disposed on the coupling arm and a coupling ring disposed on a planar surface.

Abstract: A phased-array antenna whose main beam can be positioned (scanned) substantially anywhere within a full hemispherical coverage. The phased-array antenna consists of a plurality of radiating multi-filar helix antenna elements, each of which is independently rotatable on its helix axis relative to the antenna base plane. The rotation of each radiating element substantially decreases the noise temperature, the passive intermodulation of signals, and the sidelobe levels relative to an antenna which uses PIN diode phase shifters. A change in the radiated signal phase of each element in the antenna array is achieved by the mechanical rotation of the multi-filar helical antenna element on its axis. Mechanical rotation is provided by a drive system or multiple drive systems coupled to at least one radiating antenna element. The drive system rotates the at least one radiating element on its axis by various amounts.

Abstract: An antenna system can generate RF radiation fields having dual simultaneous polarization states and having substantially rotationally symmetric radiation patterns. The antenna system generates RF radiation patterns where the beamwidths of respective RF fields for respective radiating elements are substantially equal and are relatively large despite the compact, physical size of the antenna system. The antenna system can include one or more patch radiators and a non-resonant patch separated from each other by an air dielectric and by relatively small spacer elements. The patch radiators and non-resonant patch can have predefined shapes for increasing polarization discrimination. The lower patch radiators can be mounted to a printed circuit board that can include an RF feed network and a ground plane which defines a plurality of symmetrically, shaped slots. The slots within the ground plane of the printed circuit board can be excited by stubs that are part of the feed network of the printed circuit board.

Abstract: One or more feedback elements generate a feedback signal in response to a transmitted signal outputted by each radiator of the antenna system. This feedback signal is received by each radiator, also described as a radiating element, and combined with any leakage signal present at the port of the antenna. Because the feedback signal and the leakage signal are set to the same frequency and are approximately 180 degrees out of phase, this signal summing operation serves to cancel both signals at the output port, thereby improving the port-to-port isolation characteristic of the antenna. Each feedback element can include a photo-etched planar metal strip supported by a planar dielectric card made from printed circuit board material. Such feedback elements can provide a high degree of repeatability and reliability in that the manufacturing of such feedback elements can be precisely controlled.

Abstract: A filter network demultiplexes a frequency division multiplexed input signal which involves a reduced number of multiplier or multiplying steps. The filter network comprises L−1 Z−N shift registers in series receiving the multiplexed input signal Y(n) to produce L−1 corresponding shifted signals, pairs of which are added. The filter network further comprises a set of q multiplier sections including p first multiplier sections each being coupled to the added signals for combining each output of a corresponding set of N transformed filter coefficients gi. There are provided a set of N second adder sections each being coupled to distinct outputs of the multiplier sections for producing a corresponding set of N transformed signals, and a set of t third adders each receiving a distinct pair of signals {CT(n),CT′(n)} from the transformed signals Ck(n) for producing a first filtered signal Ao(n) and a set of N−1 filtered signals Ak(n+k), with k=1, . . .

Abstract: A steerable antenna system for transmitting and/or receiving an electromagnetic signal to a relatively moving target includes a hyperbolic subreflector secured to a frame rotatably mounted on a support structure via a first motor and a feed source located at a first focus of the subreflector for illuminating the same. The source, fixed to the structure, has a source axis pointing at the subreflector. A parabolic reflector having a focus in common with the second focus of the subreflector to transfer the signal between the same and a planar reflector is secured to the frame and has a beam axis. The planar reflector having a normal axis intersecting the beam axis with an angle is rotatably mounted on the frame via a second motor to transfer the signal between the parabolic reflector and the target. The system may include a controller connected to the motors to control the system to steer at the target anywhere within a full spherical angular range.

Abstract: A compact antenna system can generate RF radiation fields having increased beamwidths and bandwidths. The antenna system can include one or more patch radiators separated from each other by an air dielectric and by relatively small spacer elements. The lower patch radiators can be mounted to a printed circuit board that can include an RF feed network and a ground plane which defines a plurality of symmetrically, shaped slots. The slots within the ground plane of the printed circuit board can be excited by stubs that are part of the feed network of the printed circuit board. The slots, in turn, can establish a transverse magnetic mode of RF radiation in a cavity which is disposed adjacent to the ground plane of the printed circuit board and a ground plane of the antenna system. The feed network of the printed circuit board can be aligned with portions of the cavity such that the portions of the cavity function as a heat sink for absorbing or receiving thermal energy produced by the feed network.

Abstract: An antenna system can generate RF radiation fields having dual simultaneous polarization states and having substantially rotationally symmetric radiation patterns. The antenna system generates RF radiation patterns where the beamwidths of respective RF fields for respective radiating elements are substantially equal and are relatively large despite the compact, physical size of the antenna system. The antenna system can include one or more patch radiators and a non-resonant patch separated from each other by an air dielectric and by relatively small spacer elements. The patch radiators and non-resonant patch can have predefined shapes for increasing polarization discrimination. The lower patch radiators can be mounted to a printed circuit board that can include an RF feed network and a ground plane which defines a plurality of symmetrically, shaped slots. The slots within the ground plane of the printed circuit board can be excited by stubs that are part of the feed network of the printed circuit board.

Abstract: A congestion avoidance scheme for ABR services in an ATM satellite system is described. The scheme relies on the broadcast nature of a satellite system to control the rates at which user terminals can send their requests for capacity. The scheme is integrated with the uplink scheduler mechanisms and therefore it is capable of achieving high bandwidth efficiency. It also achieves fairness in satellite resource utilization, while guaranteeing low cell loss ratio with rather modest buffer size.

Abstract: Using a method and apparatus for connecting an electrical cable to a circuit board. The connector is largely semi-circular in shape and generally comprises four prongs for attaching the connector to the edge of a circuit board. The connector is particularly useful for attaching a coaxial cable to a circuit board where the coaxial cable is not very flexible. The coaxial cable can be easily placed onto the connector. Once the coaxial cable is placed on the connector, the outer conductor can be attached to the connector and the inner conductor can be attached to the circuit board.

Abstract: One or more feedback elements generate a feedback signal in response to a transmitted signal outputted by each radiator of the antenna system. This feedback signal is received by each radiator, also described as a radiating element, and combined with any leakage signal present at the port of the antenna. Because the feedback signal and the leakage signal are set to the same frequency and are approximately 180 degrees out of phase, this signal summing operation serves to cancel both signals at the output port, thereby improving the port-to-port isolation characteristic of the antenna. Each feedback element can include a photo-etched planar metal strip supported by a planar dielectric card made from printed circuit board material. Such feedback elements can provide a high degree of repeatability and reliability in that the manufacturing of such feedback elements can be precisely controlled.

Abstract: A drive mechanism for an antenna array mounted on a moving vehicle. The antenna array is mounted on a disc having two motors which, cooperatively, rotate the disc and rotate a number of antenna elements mounted on the disc. By rotating the antenna elements, the main lobe of the array may be scanned towards a satellite in the elevation plane. To track a moving source from a moving vehicle, one of the motors rotates the disc as a whole, thereby scanning the beam in the azimuth plane. Each antenna element is at an angle to the vertical so that, by rotating the disc to face the direction of the signal source, such as a satellite, a better signal can be obtained.