Millimeter Wave Imaging System Antenna Design

Nowadays, the spread of terrorism has become one of the important issues. Theevent highlighted the current security disability when the terrorist shocked the world bylaunching “9·11” events in2001. In order to confine the increasingly flush of terrorism,governments around the world are trying to enhance the security level. The metaldetectors and X-ray detectors commonly in use at airport and train station are bothsuffering several flaws including cumbersome detecting methods(requires passengersfor taking off their metal objects when checked) and ionizing radiation, etc. By usingmillimeter-wave imaging system, we could well solve the existing problems.Millimeter-wave imaging system distinguish objects by their different scattering degree,besides, it is simple and safe, meanwhile the millimeter-wave radiation power is usuallylow, which could shield human body from the ionizing radiation damage. It is a newand potential detection system.This article describes two kinds of millimeter-wave active imaging systems. Thefirst one is called mechanically scanned millimeter-wave active imaging system, whichworks in simplex way, and it is consist of the millimeter-wave transmitting componentsand millimeter-wave receiving components. Combined with the mechanical scanningimaging device, it can detect certain areas within the millimeter wave scanning imaging.Horn antenna and lens antenna are designed for mechanically scanned millimeter-waveactive imaging system. The return loss of horn antenna is less than-25dB, the main lobebean width is less than10°, lens antenna`s return loss is less than-20dB, focal spot sizeis in1cm or so. The results of experiment indicates that the resolution of the system inabout1cm, which is quite with the antenna`s focal spot size.The second is called the holographic imaging type millimeter wave active imagingsystem. This system uses wideband millimeter wave holographic imaging form, wereason the imaging theory and give the design scheme for this system, then propose thatthe antenna portion of antenna element spacing should be less than12mm and the degree of coupling between elements should be less than-20dB. At last we give thecorresponding antenna model and simulation results.Finally, we analyze and compare the both two imaging methods, put forward theimprovement method by combining with the advantages and disadvantages of the twoimaging methods.