Practical methods for submillimeter wave mixers

The demand for submillimeter wave (SMW) circuits has been steadily increasing both for the traditional science applications such as radio astronomy and atmospheric remote sensing, and also for a wide range of potential military and commercial applications such as compact range radar, ultra broad band and secure communications, remote detection of battlefield toxins and collision avoidance systems for ground vehicles and aircraft. Several approaches have been developed and many successful SMW components have been built in this frequency range in the past 20 years. However, they all suffer one or more drawbacks, such as (1) high cost, (2) low reliability and repeatability, (3) lengthy and difficult fabrication and assembly, (4) poor sensitivity, (5) narrow bandwidth, and (6) reliance on mechanical tuners. The existing problems present a clear need for an improved and more practical SMW technology base.; SMW components usually have split block waveguide housings for the nonlinear circuits. Traditionally, the blocks are fabricated by standard machining techniques, which have yielded excellent results. However, the cost can be prohibitively high, particularly for applications above 1 THz. This research has developed a micromachining method for block fabrication. It has micron-level accuracy and allows complicated patterns on the blocks. A key result is the demonstration of the first SMW micromachined mixer (at 585 GHz). It has yielded state-of-the-art performance and is easy to fabricate and assemble in large quantities. The micromachining process was then extended beyond 1 THz with the successful fabrication of a 1.6 THz waveguide housing with excellent dimensions. Furthermore, eighteen mixer housing were fabricated on a single three-inch silicon wafer with 100% yield. This level of quality and throughput cannot be matched by traditional machining.; Additional efforts have focused on understanding the new micromachined horn antennas invented through the course of this research, advancing mixer assembly techniques and determining how the integrated diode technology must be advanced in order to achieve excellent terahertz performance.; Throughout this research, we have taken advantage of the recent development of advanced and commercially available computer aided design tools that are suitable for simulating both the linear and nonlinear parts of the submillimeter-wave circuits. Also, we have benefited from the recent development of integrated Schottky diode technologies that allow greatly enhanced performance, reliability and repeatability. In combination with these developments, the new micromachining technology will make the large-scale manufacturing and rapid prototyping of terahertz circuits practical. This is a major step toward our ultimate goal of making the terahertz frequency band as useful for scientific, military and commercial applications as the microwave and infrared bands are today.