30 GHz Printed Ridge Gap Components and Antennas for Imaging Systems

Working at millimeter waves (MMW) has gained massive attention for wireless communications and imaging systems. For imaging systems, MMW can be used for security to provide good resolution images and detect concealed weapons as it can penetrate common clothes and reflect from the human body and metal objects. Moreover, MMW is safe for human health, contrary to conventional X-ray imaging, which uses an ionized wave. Thus, it has a harmful effect on human health. This research is focusing on building an active wide-view angle millimeter-wave imaging system with a small area of mechanical movement to reduce the data collection time. The imaging system is composed of three main parts: 1) the millimeter-wave components and antennas, 2) the mechanical part for moving the antennas and performing the scan of the imaging area, and 3) the imaging reconstruction algorithm. In order to have an efficient imaging system, the printed ridge gap technology (PRGW) is used to build the imaging system components and antennas. High efficiency coaxial to PRGW transition with a fractional bandwidth of 59.22% at 32.25 GHz is designed to feed the system components. For the transmitting part of the imaging system, a moderate gain PRGW differential feeding planar aperture antenna and a wideband rat-race coupler are designed. The antenna, the rat-race, and the coaxial transition are combined to form the transmitting part, then fabricated and measured. The resulted bandwidth is from 25.62 to 34.34 GHz with a return loss better than 10 dB, a maximum gain of 12.28 dBi, and 3-dB gain bandwidth from 25.62 to 33.77 GHz. For the receiving antenna, a PRGW Butler matrix and its components (directional couplers, 45◦ phase shifters, and crossovers) are designed. A semi-log periodic antenna fed by the PRGW is designed as the radiating element. The PRGW components, the coaxial transition, and the antennas are combined to form the receiving part of the imaging system, which is fabricated and measured. The resulting beam directions are at ±13◦ and ±36◦, at the center frequency (30 GHz). The return loss and the isolations are better than 10 dB over the frequency range from 26.1 to 33.5 GHz. For the imaging reconstruction algorithm, a synthetic aperture radar algorithm is used. Two tests are carried out, one uses CST simulation results, and the other uses measured data from the Concordia antenna chamber lab. The results show an output resolution of 0.6 λ. Finally, the whole imaging system is built with the designed differential feeding antenna as the transmitter, the designed Butler matrix as the receiver, and the synthetic aperture algorithm as the image reconstruction algorithm. The performance network analyzer (PNA) is used to collect the data (s-parameters) required to reconstruct the image, and the antenna range controller system (NSI 5913) is used to mechanically scan the imaging area. The imaging system is used to scan a mannequin carrying an object shaped like a pistol and a knife. The results show that the two objects are detected