Du Liuge

FODs detection system based on millimeter wave FMCW radar

Foreign object debris (FODs) may cause accidents or disasters. Recently, FOD detection systems have been developed and tested on airports. Most of them are based on the association of a mm-wave radar and an optical sensor. This paper describes a compact broadband (77-78 GHz) mm-wave front-end used for FOD detection application. In this paper, the foreign object detection system is introduced, then the principle and composition of the system is given. Finally, the key technologies about antenna, mm-wave RF component, signal processing, data processing etc, are given.

Effect of Probe Coupling on Near-Field Imaging Simulation

Probes coupling signal is usually ignored in traditional near-field imaging simulation, which has effect on the imaging result. This paper corrects the problem by adding coupling items in scattering equation and modifying the distance between transceiver and target. Image changing with the coupling signal and the coupling distance is investigated. Background subtraction technique is used in the simulations. It is shown that, target can be focused correctly when the distance satisfies specific conditions.

Antenna pattern correction technique for near-field RCS measurement based on image

Practically, radiation patterns of antennas are not isotropic, and the amounts of energy radiated in different directions are not the same. In the near-field measurement, the large variety of antenna pattern in amplitude and phase will lead to significant errors. Thus, the RCS measured by a near-field method is different from that measured at the far field. In this paper, we present a near-field RCS measurement method based on modifying the pattern, which can suppress the error resulted from the directive beam of antenna pattern. Microwave imaging technique is employed to extract RCS. Numerical results show that the proposed approach is effective for antenna pattern compensation in near-field RCS measurement.

A modified time-domain gating calibration method for free-space material measurement

Microwave network s-parameters calibration plays an important role in free-space material measurement. A calibration method based on time domain gating technique gives a simple way to calibrate free-space measurement system for engineers. This paper presents a modified free-space time-domain gating calibration method to increase the calibration accuracy of two-port free-space measurement systems. Based on the s-parameters calibration principle of two-port microwave network, the free-space error model is established which includes ten error terms because the isolation error terms are added into the classic calibration error model. Two simple standards measurement, which are thru and reflect, are implemented by measuring the empty sample holder and a metal plate. Then the relationship between s-parameters of standards and error terms is established. The time-domain gating technique is employed to get the directivity errors in order to obtain enough equations to solve for the error terms. After the error terms are calculated from these equations, the transmission s-parameters of the thru standard measurement are used to correct the value of error terms. Finally, the error terms are used to calculate the real s-parameters. From the testing result, it is can be seen that better calibration results are obtained by using this modified calibration method than using the classic time-domain gating based method. And the dielectric constant results agree with expected value by using the proposed method.

Study on RM and BP algorithms used for imaging with different MIMO arrays

In order to build real-time microwave imaging system, multiple-input multiple-output (MIMO) imaging method is simulated in this paper. Two types of spare MIMO array are presented using effective phase center approximate theory. Two dimensional imaging in cross-down range is simulated with range migration (RM) and back projection (BP) algorithm. Imaging results using both algorithms are analyzed. The results show that images agreed with models using BP algorithm in both arrays. However, RM algorithm is not suitable for one of the spare arrays because the actual antenna positions are different from effective element positions. A couple of antennas for an effective mono-static should be closely enough for using RM algorithm.

Ground penetrating radar imaging with a simple MIMO array

A simple Multiple-Input Multiple-Output antenna array for ground penetrating radar imaging is presented in this paper. The antenna array only consists of a linear transmit array composed of four antennas and a linear receive array composed of six antennas. The length of this array is about 90cm and the width is 12cm. An algorithm named modified Kirchhoff Migration is adopted, and 2-D and 3-D imaging simulations of three ideal scattering points ware implemented to prove its practical applicability in the end. It is shown that focused images can be obtained with the simple MIMO array for the ground penetrating radar imaging.

MIMO imaging algorithm for single-frequency data processing based on bi-static range migration

A bi-static range migration algorithm for 2-D multiple input multiple output imaging for single-frequency data processing is investigated in this paper. On the basis of considering the near field electromagnetic wave attenuation, the imaging algorithm formulae are deduced in detail by applying the Method of Stationary Phase strictly which leads to a key filter factor for 2-D single-frequency imaging algorithm as a consequence. Image can be focused or not depends on a Phase item of the filter factor while it is influenced by amplitude item slightly which can be ignored under certain conditions. In order to verify the performance of the algorithm, a simple 2-D sparse array is designed for the imaging experiments in a complex electromagnetic environment. The focusing results are excellent which shows that the MIMO imaging algorithm discussed in this paper can be used for short-range, high-resolution and real-time imaging system.

Design of modified sub-millimeter wave antenna measurement system

This paper introduces application of sub-millimeter wave antenna measurement system. Aimed at the low dynamic range in classic sub-millimeter wave antenna measurement systems, this paper presents several approach to improve system performance such as increasing local oscillator frequency, decreasing harmonic order of mixers and multi-level frequency conversion. The modified scheme is presented as well. Finally, we establish measurement system according to modified scheme and test its characteristics. The result shows that this scheme can improve dynamic range of sub-millimeter wave antenna measurement system efficiently so that it better satisfies the needs of sub-millimeter wave measurement.

Effect of probe coupling on near-field imaging

The probes coupling signal is significant in RCS (Radar Cross Section) measurement and relative near-field imaging, which has effect on imaging result. This paper presents actual near-field measurement for two dimensional imaging. And the defocusing is found with imaging algorithm based on plane-wave spectrum transforming. It is found that the coupling signal and the coupling distance are related with this phenomenon. With our testing, the target can be focused correctly when the coupling distance satisfies specific conditions.

A far-field measurement system for the multichannel phased arrays antenna

In order to accomplish measurement of an multichannel phased arrays antenna transmit and receive characteristic quickly and automatically, this paper gives the design of an far-field antenna auto test system based on LAN bus and hardware trigger signal. By studying the integrated way that equipment triggers each other, the system has achieved efficient control of AUT beam controller and other instruments.