Dual-feed Cassegrain Antenna For Millimeter Wave Imaging

Since several years the use of passive(radiometer)mm Wave remote sensing is considered as an appropriate tool for a lot of security related applications.Those are personnel screening for concealed object detection under clothing,or enhanced vision for vehicles or aircraft,just to mention example.Radiometers,having only a receiver to record natural thermal radiation power,provide typically emission and reflection properties of a scene using the environment and the cosmic background radiation as a natural illumination source.The passive signature of a scene and its objects is quite different depending on the target and its scattering characteristics,and the actual illumination properties.An example is considered radiometric discriminator device for comparing the radiometric brightness temperature of two following spots of antenna beam on the observed remote scene.In this case,the real signal from discriminator can be similar to the radar imaging in form of the bright points based on the difference between the metal object and the background of an absorbing or semi-absorbing environment.To realize the function of finding objects,the scanning antenna is symmetrically decided into two parts.This signal arises only when the two parts generate different levels of brightness temperatures because of a target captured in alternative pixel scanning along the observed scene.This survey consists of several parts,thus there could be distinguished three main research directions.These are: existing passive millimeter wave imaging technology,proposal and prototype of millimeter-wave imaging system and two channels passive millimeter wave discriminator system.First and foremost,a comprehensive survey of passive millimeter wave imaging technology.Initially,a sample of a two-mirror antenna of the Cassegrain type is presented,with the calculated parameters of the antenna gain coefficient,and calculations of the antenna directivity diagram are provided.Consequently,investigations on design of Cassegrain dual mirror passive 8 mmwave antenna have been performed.First experimental results are shown and discussed.This survey consists of several parts,thus there could be distinguished three main research directions.These are: comprehensive proposal and prototype of millimeterwave imaging systems,the directional pattern of the horn in the plane E and H,calculate the amplitude distributions in the antenna array corresponding to the radiation pattern of the irradiator in the E and H plane,the principle of operation of the discriminator is explained,the calculation of radiation temperatures of materials and possible distances is considered.Finally,it would be demonstrated results are received to validate the analytical results.A design goal for this part of paper is design of Cassegrain dual mirror passive 8 mm-wave antenna.