Telecommunications – Wireless distribution system
Reexamination Certificate
2000-11-29
2003-10-28
Maung, Nay (Department: 2684)
Telecommunications
Wireless distribution system
C455S076000, C455S081000, C361S688000, C361S704000
Reexamination Certificate
active
06640084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microwave radio transmitters and receivers, and particularly to a transceiver which constitutes a complete outdoor radio unit for the Local Multipoint Distribution Service (LMDS).
2. Description of the Related Art
The Local Multipoint Distribution Service (LMDS) is a wireless, broadband technology which is expected to provide a variety of communications services, including video distribution, high speed Internet access, real-time multimedia file transfer, video conferencing, and telecommunications, both for residential and commercial applications. LMDS systems use very high frequencies, the actual spectrum allocation varying from country to country. In the United States, the FCC auctioned licenses for the LMDS in 1998 for two blocks of frequencies located in the 28 GHz band and the 31 GHz band of the spectrum. The short wavelength at such frequencies means that communications in the LMDS is line of sight. Prototype systems use hubs or base stations mounted on towers spaced apart every few kilometers (4-5 kilometers, or about 2.5-3.1 miles apart) to repeat signals and to serve as the centers of cells which service several thousand subscribers, including residences and businesses by transmission to small rooftop antennas. LMDS may be integrated with conventional data transmission techniques, such as twisted pair or fiber optic cables, in a hybrid system. The transmission to subscribers could be by fiber optic cable, but a more likely scenario may be transmission by fiber optic cable to the base unit and retransmission to subscriber units by radio wave, as the advantage offered by LMDS lies partly in the elimination of hardwiring each subscriber unit, and partly in the increased speed of transmission and larger bandwidths by radio wave as opposed to transmission by modem over telephone lines.
Nevertheless, many LMDS systems remain at the prototype level due to technical problems with transceiver equipment and with systems integration. Several problems exist with conventional LMDS transmitter and receiver equipment.
Conventional LMDS transmitter and receiver equipment uses a plurality of discrete modules or components, increasing system costs and entailing loss of efficiency. A conventional transmitter may have a plurality of modules built in separate packages which are connected together. For example, a high power amplifier module may be connected to an upconverter and then attached to a connectorized filter and finally to the antenna feed. This construction approach requires developing techniques for matching the separate modules, and increases costs by the separate packaging of the modules, as well as the loss of transmitter power from coupling the components, with consequent decrease in transmitter power efficiency. Therefore, there is a need for an LMDS transceiver which reduces the number of separate modules in an LMDS transmitter-receiver system.
A further problem with microwave transceiver design is the multiplication of components and internal layout of the transceiver within the housing. Modern microwave transmitter and receiver designs typically use frequency synthesizers having phase lock loop circuitry under the direction of a microprocessor. Such a system is outlined in U.S. Pat. No. 5,844,939, issued Dec. 1, 1998 to Scherer et al. Further, a Product Data Book from Qualcomm Incorporated, CDMA Technologies, of San Diego, Calif. describes the Qualcomm® CDMA Technologies Phase-Locked Frequency Synthesizer integrated circuit Q3236® at pages 126-168, and a method of hardwiring the frequency synthesizer to operate at a single frequency without the requirement of a microprocessor at pages 126, 131. Further, connections between circuit boards frequently require a plurality of cables, some being used for high frequency signals and others being used to transfer DC voltages between circuit boards. It would therefore be desirable to reduce the number of discrete components and improve the internal architecture of a transceiver for the LMDS by providing better matching sections.
Another problem encountered in transceivers for LMDS operation is efficient heat transfer. Many transceivers rely upon air convection for the cooling of electronic components, and require a fan to force air flow through the housing. While effective, this design approach increases transceiver size and cost. Further, printed circuit boards in conventional microwave transceivers usually use silver, copper molybdenum, and copper tungsten as carrier material for attachment by conventional solder connections. Such carrier materials are not as efficient heat conductors as copper, and traditional solder connections are not flexible, causing attached components to break during expansion and contraction of the printed circuit boards. Consequently, it is desirable to have a transceiver for LMDS operation with improved heat transfer properties in order to house the transceiver in a smaller package.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a complete outdoor radio unit for lmds solving the aforementioned problems is desired.
SUMMARY OF THE INVENTION
The complete outdoor radio unit for LMDS is a light weight, compact transceiver featuring planar circuitry. The transceiver uses cross polarization through an orthomodal transducer to provide isolation between the transmitter and receiver. The transceiver includes three printed circuit boards directly attached by thermally conductive epoxy to a heat sink which forms part of the antenna dish/transceiver housing for effective heat transfer. One of the three circuit boards is a millimeter wave circuit board, which is attached to the heat sink by a millimeter ground plane. The millimeter ground plane has a plurality of cavities defined therein which form the lower portion of waveguide assemblies. Two of the waveguides are used as receiver and transmitter transmission lines into the orthomodal transducer, and two of the waveguides are used as bandpass filters. The waveguides interface with the millimeter wave board through microstrips. The millimeter wave board is connected to the other circuit boards by a flex cable using thin film conductive strips to accommodate both high frequency and DC voltages. The transceiver also includes a DC—DC converter in the power supply which is modified to connect the base plate to the heat sink for compactness and improved heat transfer, and a frequency synthesizer with a phase locked loop hardwired to a single reference frequency for compact size. Optionally, the transceiver may be equipped with a five-pole edge coupled bandpass filter constructed from thin film rather than lumped components.
The transceiver includes three printed circuit boards, including a power supply board, an L-band microwave circuit board, and a millimeter wave printed circuit board. The power supply board and the L-band microwave circuit board are directly adhered to a planar ground plane/heat sink which forms part of the antenna housing by a thermally conductive epoxy, and hence are coplanar. The millimeter wave printed circuit board is adhered to a second ground plane by thermally conductive epoxy, the second ground plane being attached directly to the heat sink so that the second ground plane is coplanar with the first two printed circuit boards, giving the transceiver a planar configuration with all three circuit boards attached to the heat sink for effective heat transfer.
Connections between circuit boards are facilitated by a novel flex cable fabricated using thin film techniques and which allows both microwave frequency signals and DC signals to be transferred using the same cable. Optionally, an edge coupled five pole bandpass filter including a dielectric substrate having thin film strips arranged in a precise pattern and a metallic lid placed 50-60 mils from the filter may be provided for rejection of image frequencies and for filtering the local oscillator frequencies fr
Bawangaonwala Ali I.
Funk Eric
Nagabhushana Sunil M.
Nguyen Tho
Pande Krishna
Lele Tanmay
Litman Richard C.
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