90results about "Radio wave reradiation/reflection" patented technology

A digital polarimeteric system employs a signal time stretching technique and digital signal processing of the time-stretched signal to accurately measure the polarization of a received RF signal with commercially available digital hardware. A superheterodyne receiver down converts received RF signal components to IF, and analog-to-digital converters sample the signal components at much lower sampling rates than would normally be required to accurately measure the signal polarization. Each signal sample is “time stretched” by storing each sample in M locations in a memory, such that N samples occupy M×N memory locations. A digital signal processor applies incremental phase shifts to the digital samples until a phase-shifted combination of the digital samples yields a minimum null output. The phase shifts producing the minimum null identify the polarization of the received signal. The stretching and digital processing yield the required number of samples per cycle of the received signal for accurate polarization measurement, thus effectively increasing the digital sampling frequency. Because each sample is stored in M memory locations, each incremental phase shift corresponds to 1 / Mth of the actual sampling interval, thereby providing the high phase resolution required to accurately measure polarization.

A radar device which is installed in a vehicle or the like needs to detect a target at a short distance from several tens of centimeters to several tens of meters and, therefore, has a problem that a reflected wave from the target may be reflected by a front case of the radar device and then reflected by the target again to be received as a secondary echo by itself. To solve this problem, it is an object of the present invention to provide a radar device again that can prevent multi-reflection to accurately measure a distance to a target in a short range. In a radar device according to the present invention, a surface of a frame body provided around a transmitting antenna and a receiving antenna is shaped so that a reflected wave from a target may not be returned in a direction in which a transmitting wave is transmitted from the transmitting antenna.

Disclosed is a method and an apparatus for channel estimation regarding electromagnetic wave multi-path characteristics between a sender and a receiver by using a chirp signal. The method includes the steps of (a) multiplying a received composite signal by a narrowband chirp-shift-keying signal or narrowband multiple center-frequency-chirp signal generated by the receiver itself and outputting a sum of individual frequency components resulting from difference in distance of multiple paths for up-chirp and down-chirp signal portions of a chirp-shift-keying signal, respectively, the received composite signal being formed by generating narrowband chirp-shift-keying signals or narrowband multiple center-frequency-chirp signals by the sender, sending the signals by a transmission antenna, receiving the signals by a reception antenna of the receiver via a multi-path channel, superimposing the signals, and adding the signals; (b) multiplying outputs of the up-chirp and down-chirp signal portions of the sum of individual frequency components and calculating a tolerance frequency output; (c) compensating for a frequency tolerance of the sum of individual frequency components by using the tolerance frequency output and generating a frequency compensation output; (d) compensating for discontinuity of chirp-shift-keying signals resulting from use of the narrowband chirp-shift-keying signals or the narrowband multiple center-frequency-chirp signals regarding the frequency compensation output and generating a discontinuity compensation output having no discontinuity; (e) decomposing the discontinuity compensation output into individual multi-path signals by using a frequency analysis method; and (f) extracting an attenuation component and a time delay component caused by the multi-path channel from the individual multi-path signals by using a size of frequency components of each frequency.

The invention discloses a terahertz active imaging radar system phase compensation method. The method comprises the following steps: S1) opening an internal calibration channel; S2) obtaining phase information of a terahertz wave echo signal of the internal calibration channel; S3) extracting phase error of the terahertz wave echo signal of the internal calibration channel; S4) through a polynomial fitting phase correction function, obtaining monomial and nonlinear term coefficient values of the phase correction function; S5) opening a reception channel; S6) obtaining an intermediate frequency echo signal of the reception channel; S7) analyzing the intermediate frequency echo signal of the reception channel to obtain target distance information; and S8) according to the target distance information and the phase correction function in the step S4), calculating compensation phase, and finishing phase compensation of intermediate frequency echo signal data of the reception channel according to the calculation result of the compensation phase. The advantages are that compared with a conventional phase compensation method, the method is high in adaptation, and can overcome the defects of a conventional terahertz active imaging radar phase compensation method.

The invention discloses an SAR data and GNSS data-based infrastructure settlement monitoring method and system. The method comprises the steps of carrying out calculation on the basis of SAR data to obtain a first deformation speed in a slope distance direction; carrying out calculation on the basis of GNSS data to obtain a second deformation speed; and carrying out calculation on the basis of thefirst deformation speed and the second deformation speed so as to obtain a third deformation speed. According to the method and system, an InSAR technology is combined with a Beidou GNSS technology,so that the settlement displacement data corresponding to a imaging period in a whole covering range can be obtained, the monitoring precision can be up to a millimeter level, and the precision requirement for squirmy disaster monitoring can be satisfied.

The invention discloses a low, slow and small target detection method based on FDA-MIMO (Multi-Input Multi-Output) radar. The detection method comprises the following steps of: constructing a multi-input multi-output frequency diversity array to transmit and receive electromagnetic wave signals under a multipath condition; performing discrete sampling on the demodulated received signals to construct an echo observation data matrix which is expressed as a vector form; then introducing a target fluctuation model, and deriving an FDA-MIMO radar low, slow and small target detector by adopting a generalized likelihood ratio test method, so that the detection probability of a target can be effectively improved under a certain false alarm probability; and finally, comparing FDA-MIMO, MIMO and FDAradar detection performances so as to simulation verify that the detection effect of the FDA-MIMO radar is more significant. Through combination of the advantages of the FDA radar and the MIMO radar,the influence of the low-altitude multipath effect on target detection can be effectively suppressed, the performance loss caused by fluctuation of a target RCS can be well overcome, and a large space diversity gain is obtained.

A digital cueing radio receiver system embodied using digital memory in lieu of analog delay lines and thereby avoiding delay line implementation difficulties. The cueing receiver system includes a wideband receiver portion providing an output signal employed for tuning a narrowband receiver portion of the system. Signal delay enabling use of the wideband receiver portion output signals for tuning the narrow band receiver portion selection frequency is provided by a digital memory circuit operating on analog-to-digital converted samples of input signal data of the receiver system. Approximated unity value related mathematical multiplication free Kernel function values are employed in the Fourier transformation. Avoidance of analog delay line-elements in embodying the system is a significant practical advantage of the invention.

A method and system for predicting a trajectory of an air-to-surface target missile is provided, including detecting a plurality of echo wave signals from the target missile through a plurality of sensors deployed at various locations relative to the target missile, extracting at least one range distance and at least one radial velocity, respectively, from the detected echo wave signals from the sensors by using a hybrid FSK / LFM unit, using a two-stage Kalman filter to filter the computed range distance and radial velocity to obtain a relative distance, a relative velocity and a relative acceleration, respectively, of the target missile, and finally applying trilateration on the relative distance, relative velocity and relative acceleration of the target missile from each two-stage Kalman filter to obtain a location, velocity and acceleration along the x, y, z directions.