Passive millimeter-wave imaging based on subharmonic self-oscillating mixing

The broad topic of the presented Ph.D. thesis consists in the research on novel methods in the field of microwave imaging, in particular the so-called passive millimetre-wave imaging, which is also referred to as radiometric imaging. This latter technique is used to form an image of a particular scene by means of sensing the natural electromagnetic radiation emitted by any object at microwave / millimetre-wave wavelengths, similar to the way in which a photograph is captured by sensing the radiation occurring at optical wavelengths.;Present and future applications consist in both military and commercial infrastructure fields such as in surveillance, navigation, and automotive technology, as well as aircraft landing or highway traffic monitoring in fog. Moreover, the ever increasing demand for security screening systems at airports and other public environments creates a growing need for health-hazardless automated real-time scanners with minimized false alarms, and millimetre-wave imaging offering the ability to detect concealed weapons or hazardous objects through clothing material represents an excellent choice for this purpose. Furthermore, millimetre-wave imaging is applied to biomedical imaging such as the location of hot spots, tumours, or other anomalies in the body. Additional applications consist in non-destructive material testing and geological examinations such as the sensing of the Earth's atmosphere, oil spill detection, research on volcano activity, or meteorology.;However, present state-of-the-art systems almost always require a trade-off between a cost-intensive real-time FPA imager and lower-cost bulkier and slower mechanical scanning systems. Currently, a number of technological limitations are encountered in the design of receivers operating at millimetre frequencies. Low-noise amplifiers (LNA) at millimetre-wave frequencies are cost-intensive and subject to high power consumption due to their low efficiency, which results in a heat dissipation problem especially for compact-size high-density FPAs with a large number of parallel receiver channels. Avoiding this problem by using a heterodyne receiver requires the use of external local oscillators (LO) with adequate power, which, once again, introduces a difficult and cost-intensive design at high frequencies and moreover increases circuit size as an external LO has to be implemented on each receiver element.;In this way, the limitations of current FPA systems may be overcome, as on one hand, a more efficient heterodyne receiver can be used with the external LO being integrated in the mixer, which simultaneously solves the previously mentioned heat dissipation and circuit size problem. On the other hand, adequate LO power can be generated by employing subharmonic operation, thus generating the LO signal at a frequency of only a fraction of the RF input, where its generation is much less problematic.;In this project, a complete passive millimetre-wave imager at 35 GHz based on the previously described subharmonic SOM technique is proposed. The research work in this Ph.D. thesis focuses in particular on the design, implementation, and experimental testing of subharmonic SOMs. The final 35 GHz SOM circuit is eventually implemented into a straight-forward mechanical raster scanning imaging system based on a single-element receiver in order to prove functionality of the SOM technique in the framework of millimetre-wave imaging systems. This first millimetre-wave imaging test-bed serves as the base for future research in the field. Future work includes the parallelization of these receivers in the form of an FPA system, and also the task of pushing the design toward higher frequencies, in particular 94 GHz, for achieving higher image resolutions and more compact-sized imagers.;The presented work has been carried out in three major design steps with 1) the extensive research on SOMs and their subharmonic implementation using a low-frequency prototype at 5.8 GHz as a means of design optimization and verification and its subsequent scaling to the final design frequency of 35 GHz, 2) the development of a single-element receiver based on the successfully implemented subharmonic SOM design, and 3) the integration of the receiver into a complete mechanical scanning imaging system at 35 GHz. (Abstract shortened by UMI.)...