Abstract: A method for simulating a Doppler signal under stationary conditions is described. The method includes sampling a radar return signal at an integer multiple of the return signal frequency plus a fraction of the return signal period and generating a base band signal from the samples.

Abstract: A radar altimeter is described which includes a transmitter for transmitting a radar signal, a receiver for receiving the reflected radar signal, and at least one antenna coupled to one or both of the transmitter and receiver. The altimeter also includes a forward facing millimeter wave (MMW) antenna configured to move in a scanning motion and a frequency up/down converter coupled to the MMW antenna, the transmitter, and the receiver, and a radar signal processor. The converter up converts a frequency received from the transmitter to a MMW frequency for transmission through the MMW antenna, and down converts frequencies received to a radar frequency which are output to the receiver. The radar signal processor controls scanning motion of the MMW antenna, processes signals received at the antenna for a portion of the scanning motion, and processes signals received at the MMW antenna for other portions of the scanning motion.

Abstract: A method of determining a target location from a vehicle is described. The method includes identifying the target utilizing a video system, determining an angular location vector to the target with respect to the vehicle, determining a position of the vehicle utilizing a digital terrain elevation map and precision radar altimeter, calculating a location where the angular location vector would intersect with the digital terrain elevation map, and generating a target position based on vehicle position and the location of the intersection of the angular location vector and digital terrain elevation map.

Abstract: A method for testing a radar system utilizing flight test radar data is described. The method includes time synchronizing measured radar data with a GPS based time marker, storing at least a portion of the time synchronized radar data, storing the GPS data, processing the stored GPS data to correspond with a physical position of an antenna which received the radar data, providing a radar model, and comparing the processed radar model data to the stored radar data.

Abstract: A method for reducing effects of terrain return fading due to summation of out of phase radar returns in determining locations of radar targets is described. The method comprises determining an interferometric angle, &PHgr;, to a radar target based on at least one radar return and filtering the interferometric angle, &PHgr;, by adjusting an effect of terrain features contributing to the interferometric angle, &PHgr;, proportionally to a degree of radar return fading resulting from the terrain features of the radar targets. A corrected interferometric angle, &PHgr;out., is then provided, based at least in part on the filtering.

Abstract: An in-phase/quadrature component (IQ) mixer is configured to reject returns from a negative doppler shift swath in order to mitigate corruption of returns of a positive doppler shift swath. The mixer includes a sample delay element which produces a quadrature component from the in-phase component of an input signal. Further included are a plurality of mixer elements, a plurality of low pass filters, a plurality of decimators, and a plurality of all pass filters which act upon both the in-phase and quadrature components of the input signal. Also, a subtraction element is included which is configured to subtract the filtered and down sampled quadrature component from the filtered and down sampled in-phase component.

Abstract: A method for suppressing ground return radar fading in a radar altimeter is described. The method includes providing a radar gate width which corresponds to an area that is smaller than an antenna illumination area being impinged by transmissions of the radar altimeter, dithering the radar gate viewing area within the antenna illumination area being impinged by transmissions of the radar altimeter, and taking radar return samples with the radar altimeter.

Abstract: An apparatus for calibrating a radar altimeter is described. The altimeter provides an angle to a target based on radar energy received at right, left, and ambiguous antennas. The apparatus comprises a turntable on which the radar is mounted, a turntable controller which controls positioning of the radar altimeter, a radar energy source receiving transmit signals from the radar altimeter, a reflector, and a calibration unit. The reflector reflects and collimates radar energy from the radar source towards the radar altimeter. The calibration unit receives an angle from the controller indicative of a position of the radar altimeter with respect to the collimated radar energy and a measured angle from the radar altimeter. The calibration unit calculates a correction based on differences between the angle received from the turntable and the measured angle received from the altimeter and provides the calibration correction to the altimeter.

Abstract: A phase processor is disclosed which is configured to receive processed radar return data from a left radar channel, a right radar channel, and an ambiguous radar channel. The phase processor comprises a plurality of phase detectors each with an input and a reference input. The phase detectors are configured to determine a phase difference between radar return data received at the input and radar return data received at the reference input.

Abstract: A filter, includes a first order band pass filter configured to process non-zero amplitude gated radar return samples and process a portion of received zero amplitude return samples. The filter also calculates past filter outputs based on filter outputs generated during previous non-zero gated radar return samples.

Abstract: A method for calculating a center frequency and a bandwidth for a radar doppler filter is herein described. The center frequency and bandwidth are calculated to provide radar performance over varying terrain and aircraft altitude, pitch, and roll. The method includes receiving an antenna mounting angle, a slant range, and velocity vectors in body coordinates, calculating a range swath doppler velocity, a track and phase swath bandwidth, and a phase swath doppler velocity. The method continues by calculating a range swath center frequency based on the range swath doppler velocity, calculating a phase swath center frequency based on the phase swath doppler velocity, and calculating a level and verify swath bandwidth based upon the track and phase swath bandwidth.

Abstract: A method for resolving radar range ambiguities is disclosed, where the radar is modulated with a phase code which comprises a number of chips. The method includes acquiring a radar return within a verify gate, the verify gate being aligned with one chip of the phase code, determining an amplitude of the return, stepping the gate outbound to a next chip of the code, acquiring a return, and determining if the return has an amplitude greater than a threshold based on the original return. The verify gate is repeatedly stepped outbound to determine if a chip can be found which has an amplitude in excess of the threshold or until returns from all chips within the phase code have been acquired. If such a position is found, search logic of the radar is moved outbound to the chip position which had the highest amplitude return, if not the original chip position and the entire process begins again.

Abstract: A method for testing radar system performance is disclosed which utilizes radar data test points in a radar data file. The method includes interpolating GPS data from a flight test to provide a GPS data point for every radar data test point, generating body coordinate values for every point in a corresponding digital elevation map (DEM) file using the interpolated GPS data, and applying a bounding function around at least a portion of the body coordinate values generated from the DEM file at a given time. The method also includes determining which body coordinate value generated from the DEM file is closest a current GPS data point for the given time and comparing the determined body coordinate value to the radar data test points at the given time.

Abstract: A method for processing radar return data to determine a physical angle, in aircraft body coordinates to a target, is disclosed. The radar return data includes a phase difference between radar return data received at an ambiguous radar channel and a left radar channel, a phase difference between radar return data received at a right radar channel and an ambiguous radar channel, and a phase difference between radar return data received at a right radar channel and a left radar channel. The method includes adjusting a phase bias for the three phase differences, resolving phase ambiguities between the three phase differences to provide a signal, and filtering the signal to provide a physical angle to the target in aircraft body coordinates.

Abstract: A filter, includes a first order band pass filter configured to process non-zero amplitude gated radar return samples and process a portion of received zero amplitude return samples. The filter also calculates past filter outputs based on filter outputs generated during previous non-zero gated radar return samples.

Abstract: A method for testing a radar system utilizing flight test radar data is described. The method includes time synchronizing measured radar data with a GPS based time marker, storing at least a portion of the time synchronized radar data, storing the GPS data, processing the stored GPS data to correspond with a physical position of an antenna which received the radar data, providing a radar model, and comparing the processed radar model data to the stored radar data.

Abstract: A phase processor is disclosed which is configured to receive processed radar return data from a left radar channel, a right radar channel, and an ambiguous radar channel. The phase processor comprises a plurality of phase detectors each with an input and a reference input. The phase detectors are configured to determine a phase difference between radar return data received at the input and radar return data received at the reference input.

Abstract: An antenna is described which includes first, second, and third conductive layers and a first and second laminate to separate the layers. The laminates are configured with plated through holes to provide contact between the first and third layers, the holes defining antenna cavities, the second conductive layers being the antenna. A plurality of slots in the first conductive layer align within the defined antenna cavities, further defining the antenna cavities for the second conductive layer.

Abstract: An in-phase/quadrature component (IQ) mixer is configured to reject returns from a negative doppler shift swath in order to mitigate corruption of returns of a positive doppler shift swath. The mixer includes a sample delay element which produces a quadrature component from the in-phase component of an input signal. Further included are a plurality of mixer elements, a plurality of low pass filters, a plurality of decimators, and a plurality of all pass filters which act upon both the in-phase and quadrature components of the input signal. Also, a subtraction element is included which is configured to subtract the filtered and down sampled quadrature component from the filtered and down sampled in-phase component.

Abstract: A method for determining a position of a doppler radar target in aircraft body coordinates is described. The method includes calculating values for doppler circle equations, in doppler coordinates, based upon a range to the target, a vehicle velocity, and a center frequency and bandwidth of a doppler swath filter. Further, an interferometric circle in body coordinates is calculated based upon a range to the target, and an interferometric angle. The doppler circle equations are transformed into body coordinates utilizing received pitch, roll and yaw information. Finally, an intersection of the interferometric circle equations with the transformed doppler circle equations is calculated, the intersection being the position of the target in body coordinates.