ABSTRACT
During the last four decades microwave and millimeter-wave systems have been used in a wide variety
of commercial, medical, and military applications due to their advantages over other bands of the
electromagnetic spectrum (unlike infrared and optical wavelengths they have the ability to permeate fog,
dust, and smoke) and the lack of lower frequencies for new services. Some of these applications include
satellite-to-earth communication systems, plane and missile navigation, early warning radars, earth
remote sensing, short-haul line-of-sight transmission links for personal communication links (PCNs),
wireless cable, wireless radio local area networks (LANs), mobile broadband systems, automotive
anticollision radars, and hyperthermia for cancer treatment [1]. Until the early 1980s most of the
microwave/mm-wave components were built with waveguide technology (rectangular or cylindrical)
that offers low-loss and high quality factors at the price of increased size, weight, fabrication cost, and
complexity [2]. In addition, the bandwidth of those systems was limited by the bandwidth of the
employed waveguides.
