Not applicable.
The invention relates to satellite payloads and, in particular, is directed to a satellite feed assembly with integrated filters and test couplers.
Satellites have greatly expanded the communication capabilities available for a number of different applications. Communications satellites facilitate the transmission of voice and data over long distances. Direct broadcast satellites provide video and audio content distribution to geographical areas that greatly exceed those serviceable by conventional terrestrial distribution systems. Broadband satellites provide personal communications including data transfer among users located within a geographical region. The demand for satellites having larger capacities (e.g., 100 Gbps) to improve the broadband services is constantly increasing.
Broadband communication satellites typically are configured to use multiple beams providing forward and return communication links. In the forward link, a gateway on the ground transmits signals to a satellite. The satellite receives the signals in a receive band, down-converts the signals to a transmit band, amplifies the transmit signals using amplifiers such as traveling wave tube amplifiers (TWTAs), and transmits the amplified signals to user beams on the ground. Similarly, in the return link, a user on the ground transmits signals to the satellite. The satellite receives the signals in a receive band, down-converts the signals to a transmit band, amplifies the transmit signals using amplifiers such as TWTAs, and transmits the amplified signals to gateway beams. Forward and return communication links use separate frequencies and/or orthogonal polarizations to minimize interference between the links.
Satellite capacity can be increased by providing more user beams and gateway beams for communication links. However, the hardware required to support each beam effectively limits the number of beams a single satellite can provide. For example, the repeater payload of a communication satellite typically includes filter assemblies and test couplers in the transmit and receive signal paths of each beam. Limitations on the size and weight of the repeater payload constrain the amount of hardware that can be accommodated on the spacecraft bus and therefore the number of beams that a given satellite can support. Often times these limitations are reached well before the capacity demands of modern communication applications are met.
Accordingly, a need exists for new satellite configurations that increase communications capacity within the limitations imposed by payload size, weight and accommodation constraints.
The invention provides an improved satellite feed assembly that reduces the amount of hardware required to support each beam of a multi-beam payload. This hardware reduction is accomplished by removing filter assemblies from the satellite repeater payload and integrating filter functionality into the feed assembly itself. Additionally, test couplers also can be removed from the satellite repeater payload and integrated with the feed assembly. This high level integration at the feed level minimizes the number of RF interfaces and waveguide lengths, resulting in reduced losses and hardware reduction. The cost and weight savings achieved by removing filter assemblies and test couplers from the satellite repeater payload allow hardware for additional beams to be added to the payload, thereby increasing the communications capacity of the satellite.
According to one embodiment, a dual-band feed assembly is configured to be coupled to a satellite repeater payload. The dual-band feed assembly includes a transmit filter assembly comprising a transmit pass-band filter configured to reject frequencies close to and outside a pass-band of a transmit frequency band and a low-pass and harmonic filter configured to reject receive frequencies and harmonics of the transmit frequency band. The dual-band feed assembly further includes a receive filter assembly comprising a receive pass-band filter configured to reject frequencies close to and outside a pass-band of a receive frequency band and a high-pass filter configured to reject transmit frequencies. A multi-port junction couples the transmit and receive waveguide assemblies to a dual-band horn. The dual-band feed assembly may include integrated transmit and receive test couplers and orthogonal waveguide ports to support orthogonal polarizations (e.g., left hand circular polarization (LHCP) and right hand circular polarization (RHCP)) for both the transmit and receive bands.
The foregoing summary of the invention has been provided so that the nature of the invention can be understood quickly. A more detailed and complete understanding of the preferred embodiments of the invention can be obtained by reference to the following description of the invention together with the associated drawings.
The detailed description of the invention set forth below in connection with the associated drawings is intended as a description of various embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without all of the specific details contained herein. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the invention.
In more detail, a first station (e.g., user, gateway) transmits a signal to satellite 10. The signal is a radio frequency signal within a receive frequency band, such as the Ka band (28-30 GHz). The signal is captured by one or more input horns 11a-11n and focused into respective ones of input feed assemblies 12a-12n, which supply the signal to repeater payload 13. The number of input horns 11 and input feed assemblies 12 receiving the signal will depend on the number of beams of the satellite covering the location of the first station, where each input horn 11 and coupled input feed assembly 12 provides a single receive beam.
Repeater payload 13 down-converts the received signal to a transmit band and prepares it for transmission within a transmit frequency band via one or more output feed assemblies 14a-14n and respective output horns 15a-15n. Processing the signal typically includes amplifying the received signal, removing the signal from a first carrier frequency on which it was received, and placing it on a second carrier frequency within a transmit frequency band such as the K band (18.0-22.0 GHz) and amplifying the transmit signal using high-power TWTAs in order to meet effective isotropic radiated power (EIRP) requirements. Processing the signal also may include routing and/or distributing the received signal among the output feed assemblies. For example, a signal received via one input feed assembly 12 may be routed to a single output feed assembly 14. Alternatively, repeater payload 13 may make a determination based on the contents of the signal as to which output feed assemblies 14a-14n is to be used to transmit the signal to one or more second stations (e.g., user, gateway) located within the beams corresponding to respective output feed assemblies 14 and coupled output horns 15. The signal may be transmitted via one output feed assembly 14 or via multiple output feed assemblies 14.
Output feed assemblies 14a-14n receive one or more signals from repeater payload 13 and feed the signals to respective output horns 15a-15n. In this manner, the one or more signals are transmitted to the second station(s) located within the beams corresponding to the respective output horns 15a-15n.
Prior to being amplified and routed within repeater payload 13, the received signals must be filtered to reject frequencies outside of the receive frequency band. Similarly, the signals amplified and routed by repeater payload 13 must be filtered to reject frequencies outside of the transmit frequency band prior to transmission. As noted above, the invention removes the input/output filter assemblies that conventionally are located within repeater payload 13 in order to reduce the size and weight of the satellite repeater payload and to allow additional hardware to be included in the satellite repeater payload to support additional beams for increased communications capacity. The input/output filtering used to process the signals is integrated into the input/output feed assemblies, as described in more detail below. The dashed lines shown in
The invention is not limited to any particular number of input feed assemblies 12, with respective coupled input horns 11. Similarly, the invention is not limited to any particular number of output feed assemblies 14, with respective coupled output horns 15. Those skilled in the art will recognize that the number of feed assemblies will vary depending on the intended application and the size and weight limitations of the satellite repeater payload. Those skilled in the art will further recognize that input feed assemblies 12 may share a dual-band horn with respective output feed assemblies 14. For example, input feed assembly 12a and output feed assembly 14a may share a common dual-band horn thereby forming a single integrated dual-band feed assembly. In this manner, both forward and return communication links are implemented within a single beam, which increases the communications capacity of the satellite.
According to one embodiment, dual-band horn 21 is a high efficiency horn configured to receive signals within a receive frequency band and transmit signals within a transmit frequency band. The invention is not limited to any particular type of horn so long as the horn supports both of the transmit and receive frequency bands. Multi-port junction 22 separates the transmit and receive signals from the dual-band horn 21 and propagates them via the receive filter assembly and the transmit filter assembly to and from the repeater payload. The multi-port junction 22 provides dual-orthogonal polarizations (e.g., RHCP and LHCP) for each of the transmit and receive signals.
The transmit filter assembly includes low-pass and harmonic filter 23. Low-pass and harmonic filter 23 is configured to reject the receive frequencies and the harmonics of the transmit frequency band to prevent receive signals and transmission of the harmonic signals within the beam. In the embodiment depicted in
The transmit filter assembly further includes transmit band pass filter 25. Transmit band pass filter 25 is configured to reject frequencies close to the transmit band and outside the transmit pass band. In the embodiment depicted in
The receive filter assembly includes receive band pass filter 24. Receive band pass filter 24 is configured to reject frequencies close to the receive band and outside of the receive pass band, including the frequencies of radio astronomy bands. In the embodiment depicted in
In addition, the transmit signals are rejected using cut-off waveguide 26 arranged just after the multi-port junction 22 away from horn 21. Furthermore, two separate septum polarizers are used to generate dual-circular polarizations for the receive and transmit signals.
Turning to
The performance of the input filter assembly incorporated within a satellite feed assembly according to one embodiment of the invention is demonstrated in the graphs depicted in
The performance of the output filter assembly incorporated within a satellite feed assembly according to one embodiment of the invention is demonstrated in the graphs depicted in
The removal of the filter assemblies from the repeater payload and the integration of the filter functionality into the satellite feed assembly provides significant benefits over conventional satellite feed assemblies. For example, costs are reduced due to the reduced hardware requirements. The reduced hardware requirements translate further into a reduction of overall mass of the satellite and the size of the payload. In addition, the removal of filter assemblies from the repeater payload reduces the waveguide lengths signals must travel as well as the number of interfaces within the signal paths. This shortening of the waveguide lengths and removal of interfaces within the signal paths reduces insertion losses and improves payload performance.
In one representative example, a satellite feed assembly configured according to the embodiment depicted in
In addition to cost and weight improvements, the present invention provides improvement to the overall performance of the satellite feed assembly and input/output filter assemblies. By integrating the input and output filter assemblies into the satellite feed assembly, the total waveguide length and the number of waveguide junctions traveled by transmit and receive signals is reduced. This has resulted in approximately 0.4 dB improvement in RF performance, which translates into about 10% improvement in both EIRP and G/T in RF performance.
The foregoing description is provided to enable one skilled in the art to practice the various embodiments of the invention described herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, the following claims are not intended to be limited to the embodiments of the invention shown and described herein, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.