Cryogenic devices

Details Cryogenic devices Cryogenic devices

2002-07-02

2004-03-30

Jones, Melvin (Department: 3744)

Refrigeration

Structural installation

With electrical component cooling

Reexamination Certificate

active

06711912

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to cryogenic front-end receivers and, more particularly, to cryogenic front-end receivers of minimal size based on super-conducting elements, low thermal transmission interconnects, self-resonating filters and low dissipated power profile.
2. Description of the Related Art
Until the late 1980s, the phenomenon of superconductivity found very little practical application due to the need to operate at temperatures in the range of liquid helium. In the late 1980s ceramic metal oxide compounds containing rare earth elements began to radically alter this situation. Prominent examples of such materials include YBCO (yttrium-barium-copper oxides, see WO88/05029 and EP-A-0281753), TBCCO (thallium-barium-calcium-copper oxides, see U.S. Pat. No. 4,962,083) and TPSCCO (thallium-lead-strontium-calcium-copper oxides, see U.S. Pat. No. 5,017,554). All of the above publications are incorporated by reference for all purposes as if fully set forth herein.
These compounds, referred to as HTS (high temperature superconductor) materials, exhibit superconductive properties at temperatures sufficiently high enough to permit the use of liquid nitrogen as a coolant. Because liquid nitrogen at 77K (196° C./321° F.) cools twenty times more effectively than liquid helium and is ten times less expensive, a wide variety of potential applications began to hold the promise of economic feasibility. For example, HTS materials have been used in applications ranging from diagnostic medical equipment to particle accelerators.
Currently one of the fastest growing applications for superconductivity lies in the area of electronics and associated microwave engineering, due to the astronomical growth in the telecommunications industry and the increased use of consumer electronics by the general population. In spite of the recent advances in superconductivity, however, size, cost and power requirements have limited the commercial use of this promising technology in all but high-end applications such as space instrumentation and military applications.
An essential component of many electronic devices, and particularly in the communications field, is the filter element. HTS filters have significant advantages in extremely low in-band insertion loss, high off-band rejection and steep skirts due to the extremely low radio frequency (RF) loss in the HTS materials.
However, the conventional transmission line HTS filters, having conventional HTS resonators (such as strip line resonators) as building blocks, require a large substrate area due to the area requirement that at least one dimension of the resonator be equal to approximately half a wavelength (i.e. &lgr;/2). See, for example, U.S. Pat. No. 5,616,538 (incorporated by reference for all purposes as if fully set forth herein). Thus, in conventional low frequency HTS filters having multiple poles and coupled with conventional semiconductor electronic components, such as gallium arsenide (GaAs) amplifiers, the cryogenic coolers required to cool the HTS materials to below their critical temperature (T
c
) are relatively large and require heat lifts of at least 6 watts at 80K at an ambient temperature of 20° C.
FIG. 1
is a perspective view of such a conventional prior art cryogenic receiver. The overall integrated package consists of several distinct elements. The connectors
110
are used for bringing power and RF signals in and out of the cryoelectronic section, which consists of a dewar assembly
120
containing cryoelectronic components
130
such as RF filters and amplifiers. The dewar assembly
120
is the vacuum cavity necessary to reduce convective heat loading to the cryoelectronic components from molecules within the dewar assembly
120
. A cryogenic source, in this case a cooler
140
, provides the cooling for the cryoelectronic section. The enclosure
150
is an outer package containing the previously described elements as well as circuit boards
160
which provide control functions for the cooler and other error or failure detection and alarms, and a fan
170
for cooling the circuit boards
160
.
The size of a conventional unit, as illustrated in
FIG. 1
, is typically on the order of at least about 15 inches wide×20 inches long×10 inches deep (about 38.1×50.8×25.4 cm). The large size and weight of these conventional units stems predominately from the cooling required due to the physical size of the cryoelectronic section, the power required for the amplifiers, and additional convective heat flow from the RF transitions (normally coaxial cables with connectors), from ambient conditions into the dewar assembly
120
. The physical size, weight and total operating power supplied to the unit is thus dominated by the cooler
140
and dewar assembly
120
. For the conventional unit, the cooling lift required per channel is about 1W when operated at 20° C., thus the total operational power needed for the cooler
140
alone is >125W.
Examples of conventional units are the Superfilter™ Systems available from Superconductor Technologies Inc., Santa Barbara, Calif. (see www.suptech.com for more information), and the ClearSite™ systems available from Conductus Inc., Sunnyvale, Calif. USA (see www.conductus.com for more information).
The large size and weight of these conventional units substantially limits the application of this technology. One such application is a tower top application in which a receiver front-end is mounted onto an antenna of a cellular or similar base station, such as those disclosed in U.S. Pat. No. 6,104,934 (incorporated by reference for all purposes as if fully set forth herein). The size and cooling requirements of the disclosed receiver are such that the cooling unit must be placed somewhere adjacent the antenna, and is not combinable with the electronics into an integrated unit.
For miniaturization purposes, the components comprising the greatest real estate needed are the cooler
140
, cryoelectronic components
130
and dewar assembly
120
.
One way to reduce the real estate requirements of a cryoelectronic front-end receiver is to employ lumped element architecture based on conventional HTS filters. These filters can be made to operate at frequencies below 5 GHz with a somewhat more compact physical size; however, filter performance of these conventional lumped element HTS filters is generally limited by intermodulation products and insertion loss.
The use of devices containing HTS filters presents other design problems. For example, the interconnects typically utilized to connect the cryogenic portion of the device (usually a dewar containing the HTS filter under vacuum) to other electronic components are long coaxial cables. These long cables, because of their length, exhibit low thermal transmission, which is highly desirable in a cryogenic system where keeping components cold is critical. However, these long cable lines also exhibit RF losses, thus contributing to degradation in RF performance (i.e. an increase in the signal-to-noise ratio). To compound problems even further, the long cables also require the dewar of the cryogenic portion of the device to be larger in volume, which requires a design capable of maintaining the vacuum necessary over the life of the unit, which is more difficult to achieve.
There has been a long felt need, as well as numerous attempts by persons of ordinary skill in the art, to reduce the size of filter elements constructed of HTS materials. U.S. Pat. No. 6,108,569, incorporated by reference herein for all purposes as if fully set forth, discloses the use of self-resonant spiral resonators to reduce the size of HTS material filters and concurrently solves cross-talk and connection problems. In spite of the great potential for miniaturization afforded by significant recent technological advances, the problems of vacuum degradation, high thermal transmission, and high dissipated power semiconductor devices, have resulted in less than optimum performance and yielded increased cooling costs.
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