Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2000-03-09
2001-10-16
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping a forming surface
C164S340000, C164S369000
Reexamination Certificate
active
06302184
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to frequency-selective antenna equipment and associated methods of manufacture for simultaneously transmitting and receiving microwave frequency signals through free space, especially to and from a satellite.
BACKGROUND OF THE INVENTION
Satellite communications (satcom) systems operating at microwave carrier frequencies (between 3 GHz and 300 GHz) typically employ parabolic reflector antennas through which signals from the satellite (downlink signals) are received while signals to the satellite (uplink signals) are simultaneously transmitted. The parabolic reflector is typically illuminated for both the uplink and the downlink by a single feed horn that supports all signal polarizations. In most satcom systems, the uplink signal frequency is somewhat higher than the downlink signal frequency. In typical Ku-band systems, for example, the uplink frequency is commonly in the range 14.0 GHz-14.5 GHz while the downlink frequency is commonly in the range 10.95 GHz-12.75 GHz.
In most satcom systems, the uplink signal polarization is specified by the communications system to be orthogonal to the polarization of the downlink signal in order to minimize cross-talk between the uplink and downlink signals. In these cross-polarized systems, the circular waveguide feed horn is connected to an orthomode transducer (OMT) to separate the orthogonally polarized uplink and downlink signals. The OMT may also include a transmit frequency band reject filter in the receive arm of the OMT. Each of the orthogonal arms of the OMT is in turn connected to an associated filter and to separate receiver and transmitter hardware in rectangular waveguide.
Some satcom systems are designed so that the uplink and downlink signals have the same polarization (i.e. they are co-polarized), even though associated signal cross-talk problems may thus be encountered. In one approach to antenna hardware for such a co-polarized system, the set of feed horn, OMT and filter hardware used for the more common cross-polarized systems may be easily adapted by inserting a co-polarization (co-pol) adapter (such as Prodelin TD0362 Co-Pol is Adapter) between the feed horn and the OMT. The co-polarization adapter comprises a
90
degree waveguide twist and orthogonal waveguide filter arms that force the uplink and downlink signals to appear at the OMT to be orthogonally polarized signals. While this approach takes advantage of common waveguide components from the more-common cross-polarized system, the co-pol adapter adds considerable cost, weight, insertion loss and size to the feed assembly.
In a simpler alternative approach, a single-piece co-polarized diplexer (such as Prodelin TD0361 Co-Pol Diplexer) connected between the feed horn and the transmitter and receiver hardware is used to frequency-select the uplink and downlink signals and to connect to separate transmitter and receiver hardware. A co-pol diplexer uses waveguide filters and a waveguide junction to separate the (co-polarized) uplink and downlink signals presented to the co-pol diplexer in square waveguide and to feed separate transmitter and receiver hardware in rectangular waveguide. While the co-pol diplexer provides a fairly simple solution to the problem of uplink and downlink separation in a co-polarized satcom system, electrical performance requirements have dictated that known co-pol diplexer designs be manufactured using expensive electroforming or machining techniques because of the complex geometry required.
While known co-pol diplexers offer advantages relative to other techniques used for uplink and downlink signal separation in a co-polarized satcom system, significant cost is incurred to electroform or machine the co-pol diplexers of known designs. In many very small aperture terminal (VSAT) and other satcom terminal applications, the cost of a complex electroformed or machined part may be a significant proportion of overall satcom terminal cost. Therefore, while a single-piece co-pol diplexer has been developed, it is still desirable to develop an improved co-pol diplexer that does not suffer from the inherent limitations imposed by prior co-pol diplexer designs, such as disproportionate cost. Because large numbers of co-pol diplexers are needed in order to meet the needs of the global satcom market, there is a strong need for a co-pol diplexer that can be manufactured at a reduced cost.
SUMMARY OF THE INVENTION
An apparatus for coupling a receiver and a transmitter to a single antenna so as to allow for the simultaneous transmission and reception of co-polarized signals is provided. The apparatus comprises a waveguiding structure defining a junction for separating a first signal having a first frequency and a second signal having a second frequency in the waveguiding structure. The first and second signals are co-polarized and the first frequency is different from the second frequency. The apparatus further comprises a first filter, connected to the waveguiding structure, for filtering the first signal, and a second filter, connected to the waveguiding structure, for filtering the second signal. So that the apparatus may be manufactured using low-cost reusable-mandrel casting techniques, all internal surfaces of the apparatus are visible from some point external to the apparatus.
A method for manufacturing a co-polarized diplexer is also provided. The method comprises positioning within a casting mold at least one mandrel configured to form a mold cavity defining a waveguiding structure, the waveguiding structure including a junction for separating first and second co-polarized signals at different frequencies. The method further comprises filling the mold cavity of the casting mold with a hardenable casting composition to form the co-polarized diplexer about the at least one mandrel, and slideably removing the at least one mandrel from the waveguiding structure after the hardenable casting composition has hardened.
The co-pol diplexer of the present invention improves significantly upon the design and fabrication methods for existing co-pol diplexers because all internal surfaces of the co-pol diplexer of the present invention are visible from some point external to the co-pol diplexer. The co-pol diplexer of the present invention thus may be manufactured by low-cost reusable-mandrel casting techniques rather than the expensive electroforming or machined assembly techniques required to fabricate conventional co-pol diplexers.
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Moheb Hamid
Robinson Colin Michael
Alston & Bird LLP
Elve M. Alexandra
Kerns Kevin P.
Prodelin Corporation
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