Researchers have now demonstrated a variety of superconductive microwave devices. A survey of the published work in the United States and Japan indicates that a substantially more diverse set of prototype devices have been addressed in the United States. Table 4.3 shows a representative listing.
|Filters with low loss||Y||Y|
|Filters for high power||Y||Y|
|Tunable filter prototypes||Y||N|
|Compact delay lines||Y||Y|
|Electrically small antennas with matching elements||Y||N|
|Patch antenna arrays||Y||N|
|Integrated JJ mixer/antennas||Y||Y|
The first three entries in Table 4.3 relate to filters with properties that are particularly relevant to wireless applications. The earlier and more competitive drive toward wireless in the United States is evidenced by the range of types of filter structures investigated, including aspects of tunability. The wider diversity of nonfilter devices in the United States is a reflection of the Department of Defense support beyond telecommunications applications.
More important than the diversity of device types is the fact that underlying the device development in the United States is a substantially more robust technology infrastructure for design, manufacturing, and packaging than exists today in Japan. Table 4.4 summarizes the substantial differences that exist. The disparity is most notable in the two areas of high-power/low-distortion and tuning. U.S. researchers have driven much more aggressively to extract from the wireless hardware community the specifications for competitive HTS filter subsystems, and these researchers have consequently identified the need for both very low distortion and precise frequency setting. In these critical areas, plus that of cryopackaging, this WTEC panel judged that the United States has approximately a 2-year lead.
|HTS films with low loss||Y||Y|
|High power and low distortion phenomenology||Y||N|
|Large-area HTS films and low-defect, low-loss substrates||Y||N|
|Filter topology variants (lumped, transmission line, disk, etc.)||Y||N|
|Structures and algorithms for tuning||Y||N|
|Cryopackaging and thermal management||Y||N|