Research On Millimeter Wave Imaging System Based On Stepped Frequency

In a radar imaging system,the imaging resolution is mainly composed of azimuth and range resolution,and the azimuth resolution is related to the antenna size.The larger the antenna aperture,the higher the resolution;the range resolution is related to signal bandwidth.The larger the bandwidth,the higher the resolution.In traditional radars,real-aperture antennas are usually used,which are restricted by the antenna size,making it difficult to achieve high resolution in azimuth.Synthetic aperture radar synthesizes a single small aperture radar into an equivalent large-size antenna,which can obtain high resolution in azimuth.Using frequency modulated continuous wave technology or stepped-frequency continuous wave technology to transmit a wide-bandwidth millimeter wave signal,high-resolution images in the range can be obtained.This paper studies the millimeter wave synthetic aperture radar imaging system based on stepped frequency.By analyzing the principle of synthetic aperture radar and stepped frequency signal,an imaging model is established.The hardware device of the imaging system is designed and built,the function of each module in the hardware system is explained in detail,and the corresponding parameters of each module are tested and determined.The control acquisition software is written,and the overall control of the hardware system is realized through the communication with the single-chip microcomputer,stepper motor,and acquisition card.The software integrates three data acquisition modes with different functions: a single-point test mode for system debugging and troubleshooting,a system correction mode for compensating imaging data,and an imaging scan mode for imaging the target object.The realization process of data processing on the collected signals is described in detail,which lays the foundation for further imaging.For the built imaging system,system calibration and imaging experiments were carried out.The imaging effects before and after the correction are compared,which proves the necessity of the correction operation.Several experiments were designed to verify the imaging quality of the system: the imaging resolution of the system in the x,y,and z directions was measured,and they were about 8-9mm in the x direction,12 mm in the y direction,and 40 mm in the z direction.The optimal imaging distance of the system is calculated,and the results show that the target sample is placed within 5-16 cm from the transmitting and receiving antenna,and the target can be clearly imaged and the background noise of the imaged picture is small.Penetration experiments were conducted on common fabrics.The experiment found that the system can easily penetrate common fabrics and clearly image the hidden objects behind it.Even if the fabric has a certain thickness,the contour shape of the object behind can still be detected.