Abstract

Recently, millimeter wave (MMW) imaging detection systems are drawing attention for their relative safety and detection of concealed objects. Such systems use safe non-ionizing radiation and have great potential to be used in several applications such as security scanning and medical screening. Antenna probes, which enhance system performance and increase image resolution contrast, are primarily used in MMW imaging sensors. The unlicensed 60 GHz band is a promising band, due to its wide bandwidth, about 7 GHz (57 - 64 GHz), and lack of cost. However, at 60 GHz the propagation loss is relatively high, creating design challenges for operating this band in MMW screening. A high gain, low profile, affordable, and efficient probe is essential for such applications at 60 GHz.
This thesis’s focus is on design and implementation of high gain MMW probes to optimize the performance of detection/imaging systems. First, single-element broadside radiation microstrip antennas and novel probes of endfire tapered slot high efficient antennas are presented. Second, a 57-64 GHz, 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer controlled phase shifter is presented. Then, a mechanical scanner is designed specifically to test proposed antenna probes utilizing low-power 60 GHz active monostatic transceivers. The results for utilizing proposed 60 GHz probes show success in detecting and identifying concealed weapons and explosives in liquids or plastics.
As part of the first research theme, a 60 GHz circular patch-fed high gain dielectric lens antenna is presented, where the prototype’s measured impedance bandwidth reaches 3 GHz and a gain of 20 dB. A low cost, 60 GHz printed Yagi antenna array was designed, optimized, fabricated and tested. New models of the antipodal Fermi tapered slot antenna (AFTSA) with a novel sine corrugated (SC) shape are designed, and their measured results are validated with simulated ones. The AFTSA-SC produces a broadband and high efficiency pattern with the capacity for high directivity for all ISM-band. Another new contribution is a novel dual-polarized design for AFTSA-CS, using a single feed with a pair of linearly polarized antennas aligned orthogonally in a cross-shape. Furthermore, a novel 60 GHz single feed circularly polarized (CP) AFTSA-SC is modeled to radiate in the right-hand circularly polarized antenna (RHCP). A RHCP axial ratio bandwidth of < 3dB is maintained from 59 to 63 GHz. In addition, a high gain, low cost 60 GHz Multi Sin-Corrugations AFTSA loaded with a grooved spherical lens and in the form of three elements to operate as the beam steering antenna is presented. These probes show a return loss reduction and sidelobes and backlobe suppression and are optimized for a 20 dB or higher gain and radiation efficiency of ~90% at 60 GHz.
The second research theme is implementing a 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer (PET) controlled phase shifter. A power divider with a triangular feed which reduces discontinuity from feed lines corners is introduced. A 1 × 16-element array is fabricated using 60 GHz AFTSA-SC antenna elements and showed symmetric E-plane and H-plane radiation patterns. The feed network design is surrounded by electromagnetic band-gap (EBG) structures to reduce surface waves and coupling between feed lines. The design of a circularly polarized 1 × 16-element beam steering phased array with and without EBG structures also investigated.
A target detection investigation was carried out utilizing the proposed 60GHz antennas and their detection results are compared to those of V-band standard gain horn (SGH). System setup and signal pre-processing principle are introduced. The multi-corrugated MCAFTSA-SC probe is evaluated with the imaging/detection system for weapons and liquids concealed by clothing, plywood, and plastics. Results show that these items are detectable in clear 2D image resolution. It is believed that the 60 GHz imaging/detection system results using the developed probes show potential of detecting threatening objects through screening of materials and public.