Patent Description:
Small satellites have limited space to store electronics and an antenna, which becomes technically challenging when the electronics and associated components include radio frequency (RF) assemblies operating with a reflector and mast extending outwardly from the reflector. These components may desirably be compact when an antenna and any electronics operate at the L-band and S-band frequencies and at higher frequencies up to <NUM>. For example, an antenna that includes a small reflector and mast operable in the Ka-band may have size constraints that make it difficult to incorporate amplifiers and other components, since the antenna and its associated reflector and mast are typically reduced in size. In some designs, it may be desirable to amplify RF signals at or close to the antenna, so that the amplifiers and associated components are to be incorporated into the smaller confined spaces associated with a reflector and mast. This problem becomes even more challenging when small satellites are built as CubeSat platforms, which are becoming more commonplace as miniaturized satellites made up of multiple units with one unit being about <NUM> by <NUM> by <NUM> or roughly <NUM> inches cubed. CubeSats are advantageous for smaller satellites because they are designed to use commercial off-the-shelf (COTS) components for their major circuits and can be implemented for custom satellite operation.

In most practical small satellite applications, a number of units are combined together to form a CubeSat platform as a small satellite that is typically intended for Low Earth Orbit (LEO) and performs scientific research and explores new space technologies. CubeSats are advantageous because their use as block units to build small satellites shortens the satellite development cycle, permits greater diversity in satellite design since each small satellite can be designed for a specific function, and reduces the overall cost of satellite deployment. CubeSats and similar small satellites often are suitable for launch with multiple small satellites per payload, thus using the excess capacity of larger launch vehicles and reducing the risk to the rest of the launch vehicle and other payloads.

Typical CubeSat satellite platforms are formed from multiple, individual units combined together and include a 6U design of about <NUM> × <NUM> × <NUM> inches (about <NUM> × <NUM> × <NUM>) or a 12U design of about <NUM> × <NUM> × <NUM> inches (about <NUM> × <NUM> × <NUM>). CubeSats can be propelled by cold gas, chemical promotion, electric propulsion, or solar sails. Most CubeSats and similar small satellites have internal batteries for power, which preferably include solar cells.

Many Low Earth Orbit (LEO) small satellites, such as CubeSats, use antennas to operate in the UHF and L-band to S-band, and in the more rare deep space applications to operate in the X-band and Ka-band. These higher frequency bands allow the use of smaller antennae due to the higher frequencies, but the design constraints of small satellites, such as CubeSats, and associated smaller antenna with their smaller reflectors and masts, may make it difficult to implement workable RF assemblies with sufficient amplification at the reflector and mast to ensure there is sufficient RF signal power that reaches any electronics and RF signal processing circuits in the CubeSat.

Prior art can be found in <CIT> which generally relates to an input device of two orthogonal polarized-wave waveguide type, and radio wave receiving converter and antenna device using the input device, in <CIT> which generally relates to a scalable high compaction ratio mesh hoop column deployable reflector system, in <CIT> which generally relates to a waveguide input apparatus of wo orthogonally polarized waves including two probes attached to a common board, in <CIT> which generally relates to a multiple beam feed assembly, in <CIT> which generally relates to a feed system, in particular for receiving television or radio programming transmitted by satellite and in <CIT> which generally relates to a parabolic deployable antenna.

In general, a satellite system includes a reflector and a mast extending outwardly from the reflector. A radio frequency (RF) assembly is carried by a distal end of the mast. The RF assembly includes a conductive waveguide body having an RF cavity therein coupled with the reflector, and having a pin-receiving opening therein. An RF circuit module includes a hermetically sealed housing carried by the conductive waveguide body, RF circuitry contained within the housing, and a signal coupling pin coupled to the RF circuitry and extending through the pin-receiving opening into the RF cavity. The housing is carried by the conductive waveguide body within a planar cut-out formed at a portion of a cylindrically configured end of the conductive waveguide body.

The RF circuitry may comprise an RF signal amplifier, for example, an integrated circuit Low Noise Amplifier (LNA). In some embodiments, the RF assembly may comprise an RF cable connector carried by the conductive waveguide body and coupled to the RF circuitry. The mast may have a passageway therein and a cable may be coupled to the RF cable connector and extend through the passageway. A subreflector may be carried by a distal end of the mast and aligned between the reflector and the RF assembly. A horn may be coupled to the conductive waveguide body and directed toward the subreflector.

Another aspect is directed to a method for making a radio frequency (RF) assembly for a satellite system that includes a reflector. The method comprises forming a conductive waveguide body having an RF cavity therein to be coupled with the reflector, and having a pin-receiving opening therein. The method includes coupling an RF circuit module to the conductive waveguide body, the RF circuit module comprising a hermetically sealed housing carried by the conductive waveguide body and RF circuitry contained within the housing. A signal coupling pin is coupled to the RF circuitry and extends through the pin-receiving opening into the RF cavity. The housing is carried by the conductive waveguide body within a planar cut-out formed at a portion of a cylindrically configured end of the conductive waveguide body.

The present description is made with reference to the accompanying drawings, in which exemplary embodiments are shown. However, many different embodiments may be used, and thus, the description should not be construed as limited to the particular embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in different embodiments.

Referring initially to <FIG>, a satellite system is illustrated generally at <NUM> that usually will orbit Earth in a Low Earth Orbit (LEO) as typical for small satellites, although any orbit altitude may be established depending on satellite functions. The satellite system <NUM> includes a satellite enclosure <NUM> that carries electronics such as a satellite transceiver and solar panels <NUM>. The satellite system <NUM> in this example is a small form factor satellite. The satellite transceiver and any associated electronic components and circuits may be formed from conventional off-the-shelf (COTS) components as is typical for those smaller satellites formed from CubeSats.

The satellite system <NUM> includes an antenna <NUM> having a reflector <NUM> carried by the satellite enclosure <NUM> and a mast <NUM> extending outwardly from the reflector as shown in the deployed condition of the antenna <NUM> in <FIG>. A radio frequency (RF) assembly <NUM> is carried by the distal end of the mast <NUM> as shown in greater detail in <FIG>, where the reflector <NUM> and mast <NUM> are shown in the stowed condition before being deployed when the satellite system <NUM> reaches the desired orbit. The RF assembly <NUM> includes a conductive waveguide body indicated generally at <NUM> that is received within the end of the mast <NUM>. In this example, the conductive waveguide body <NUM> has a substantially cylindrically configured end <NUM> that is received inside the end of the mast <NUM>, which includes a passageway <NUM> (<FIG>) therein. In this example, the mast <NUM> is hollow and has about a <NUM> inch (about <NUM>) inner diameter at its end, such that one end of the conductive waveguide body <NUM> is received within the end of the mast. This conductive waveguide body <NUM> has an RF cavity <NUM> that is best shown in the sectional view of <FIG> and a pin-receiving opening <NUM> communicating with the RF cavity. The RF cavity <NUM> is coupled with the reflector <NUM>, and in this example, designed to operate in the Ka-band, i.e., about <NUM> to <NUM>.

The RF assembly <NUM> includes an RF circuit module indicated generally at <NUM> having a housing <NUM> (<FIG>) that is hermetically sealed and carried by the conductive waveguide body <NUM> within a planar cut-out 42a formed at a portion of the cylindrically configured end <NUM> of the conductive waveguide body <NUM> (<FIG>). RF circuitry <NUM> is contained within the housing <NUM> (<FIG>, <FIG> and <FIG>) and a signal coupling pin <NUM> is coupled to the RF circuitry <NUM> and extends outwardly from the housing <NUM> and through the pin-receiving opening <NUM> into the RF cavity <NUM> to allow the RF signals to be routed from the RF cavity <NUM> into the RF circuitry when the reflector <NUM> and mast <NUM> are deployed to their fullest extent and operational. The RF circuitry <NUM> may include an RF signal amplifier <NUM> (<FIG>), which in one example, is an integrated circuit Low Noise Amplifier (LNA). An RF cable connector <NUM> is carried by the conductive waveguide body <NUM> and coupled to the RF circuitry <NUM>. A cable <NUM> is coupled to the RF cable connector <NUM> and extends through the passageway <NUM> in the mast <NUM> with the cable shown diagrammatically extending into and through the mast in <FIG>.

As best illustrated in <FIG> and <FIG>, a subreflector <NUM> is carried by the distal end of the mast <NUM> and aligned with the reflector <NUM> and RF assembly <NUM>, and in the illustrated example, is secured by three mounting spars <NUM> that are secured to both the subreflector and a first circular mounting flange <NUM> of a cylindrical horn <NUM> that is coupled to a second circular mounting flange <NUM> at the end of the conductive waveguide body <NUM>. The horn <NUM> includes a circular opening <NUM> that is directed toward the subreflector <NUM> (<FIG>).

In an example, the cylindrically configured end <NUM> of the conductive waveguide body <NUM> includes a flattened side 42b (<FIG>) opposite the planar cut-out 42a, helping to reduce unnecessary weight and facilitating insertion of the conductive waveguide body into the end opening of the mast <NUM>. The conductive waveguide body <NUM> may be formed from a low expansion and strong metallic material, such as Kovar, i.e., a nickel-cobalt ferrous alloy having a similar coefficient of thermal expansion (CTE) characteristic as borosilicate glass. Kovar is advantageous because the RF circuit module <NUM> may include a multilayer, low temperature co-fired ceramic (LTCC) substrate <NUM> (<FIG>), for example, formed from nine different tape layers about <NUM> inches (about <NUM>) thick. An example LTCC substrate <NUM> is GreenTape™ 9K7 LTCC as a low loss ceramic dielectric tape from Dupont. This LTCC substrate <NUM> may have a coefficient of thermal expansion ratio to make it operable with the Kovar material, which is advantageous in deep space applications where sunlight may warm up materials and later deep cold space itself will cool the heated material, thus creating extreme temperature variations and changes in dimensions of the different components because of the extreme swings in temperature.

In an example, the subreflector <NUM> is circular configured as illustrated in <FIG> and formed of a metallic material, such as 6AL-4V Titanium Tiodized, Type II material. The mounting spars <NUM> are formed of a similar coated Titanium material as the subreflector <NUM> and connected to the subreflector by cruciform screws <NUM> that pass through the subreflector and into the end of the spars and are bent inward to attach to the smaller diameter first mounting flange <NUM> on the circular horn <NUM> forming an aperture and attached by cruciform screws <NUM> that pass through the first and second circular mounting flanges <NUM>,<NUM> and into the end of the mounting spars <NUM>. The horn <NUM> may also be formed of similar material such as 6AL-4V Titanium Tiodized, Type II material. This material is a coated titanium using an electrolytic process in an alkaline bath and provides a better surface for space applications as in satellites. Each spar <NUM> in an example could be formed from the <NUM> inch (about <NUM>) diameter rod material, imparting sufficient mounting strength for the subreflector <NUM>.

The conductive waveguide body <NUM> includes its second circular mounting flange <NUM> having a substantially similar diameter as the first circular mounting flange <NUM> on the circular horn <NUM> and both mounting flanges are secured to each other by the cruciform screws <NUM> (<FIG>), e.g., Number <NUM>-<NUM> NAS 1101E00, as a non-limiting example. The circular horn <NUM> may include a cylindrically configured meander line polarizer <NUM> received within the circular horn opening <NUM> that may operate as a passive broadband polarizing device to convert polarization properties of RF wave and permit, for example, a linear polarized antenna to propagate circular polarization without variations in pattern performance. In an example, the polarizer <NUM> may be formed from several printed circuit sheets with etched-copper meander lines with sheets spaced about one-quarter wavelength apart to effect conversion between linear and circular polarization. The second circular mounting flange <NUM> of the conductive waveguide body <NUM> is connected onto a third circular mounting flange <NUM> positioned at the end of the mast <NUM> (<FIG>) and retained by appropriate fasteners, such as offset cruciform screws <NUM> similar used for securing together first and second circular mounting flanges <NUM>,<NUM>.

Referring now to <FIG>, there are illustrated further details of the RF assembly <NUM> that includes the conductive waveguide body <NUM> supporting the RF circuit module <NUM>. As noted before, the RF circuit module <NUM> includes RF circuitry <NUM> contained within its housing <NUM>, and the signal coupling pin <NUM> is coupled to the RF circuitry and extends outwardly from the housing and through the pin-receiving opening <NUM> into the RF cavity <NUM> as best shown in <FIG>. The signal coupling pin <NUM>, in an example, is formed as a <NUM> inch (about <NUM>) diameter Kovar waveguide pin that is received into the pin receiving opening <NUM>, which in an example, is about a <NUM> inch (about <NUM>) diameter hole (<FIG>) extending from the planar cut-out 42a into the RF cavity <NUM>. The conductive waveguide body <NUM> has its RF cavity <NUM> coupled with the reflector <NUM>, and the conductive waveguide body may include a vent hole <NUM> that is about <NUM> inches (about <NUM>) diameter as a non-limiting example.

The RF circuit module <NUM> supports RF circuitry <NUM> having an RF signal amplifier <NUM> as an integrated circuit Low Noise Amplifier (LNA) and mounted on the LTCC substrate <NUM>, forming an LNA hybrid. As best shown in <FIG>, the signal coupling pin <NUM> in an example is brazed by <NUM> Au-20Sn gold-tin solder to the back side of the LTCC substrate <NUM>. The signal coupling pin <NUM> in an example is about <NUM> inch (about <NUM>) diameter and about <NUM> inches (about <NUM>) long, and configured to extend into the RF cavity <NUM> and operate in Ka-band. The signal coupling pin <NUM> extends from the rear or bottom side of the LTCC substrate <NUM> and extends through the pin-receiving opening <NUM> into the RF cavity <NUM> a substantial amount without touching the bottom side of the RF cavity.

The RF circuit module <NUM> includes a Kovar seal ring <NUM> (<FIG>) received on an <NUM> Au-20Sn gold-tin preform <NUM> that is about <NUM> inches (about <NUM>) thick, in one example. The RF module is closed and hermetically sealed by a Kovar lid <NUM>. The Kovar seal ring <NUM> includes a central dividing wall forming first and second substrate cavities <NUM>,<NUM> (<FIG>), with the first cavity including the Low Noise Amplifier <NUM> mounted on the LTCC substrate <NUM> and connected to circuit traces formed on the LTCC substrate. The signal coupling pin <NUM> is connected to the Low Noise Amplifier <NUM> via the circuitry formed in the different tape layers of the LTCC substrate and extends from the rear side of the LTCC substrate <NUM>. The first cavity <NUM> includes DC bias capacitors <NUM> (<FIG>) and the second cavity <NUM> may include a printed bias T-circuit <NUM> that operates as a diplexer, in an example, and may help set the bias and aid in passing RF signals, but blocking bias levels. As best shown in the exploded isometric view in <FIG>, the first cavity <NUM> may also include an RF absorber <NUM> to absorb extraneous RF waves, and one or both substrate cavities <NUM>,<NUM> may include a particle getter <NUM> that operates as a reactive material inside the hermetically sealed housing <NUM> to help maintain vacuum and react with any foreign particles that might remain inside the RF circuit module <NUM> during manufacturing. One or more of the substrate cavities <NUM>,<NUM> may also include a hydrogen getter <NUM>, for example, to control and reduce residual amounts of hydrogen and gas inside the sealed RF circuit module <NUM> if any gaseous particles are left over from manufacturing or somehow leak into the RF circuit module.

The low temperature co-fired ceramic (LTCC) substrate <NUM> is received on the planar cut-out 42a formed on the conductive waveguide body <NUM>. In an example, the circuitry on the LTCC substrate <NUM> connects to a quartz launch substrate <NUM> (<FIG>) that is about <NUM> inches (about <NUM>) thick. In an example, a flea clip <NUM> (<FIG>) attaches to the RF cable connector <NUM>, which in this example, could include a brazed-in feedthrough <NUM> and a smooth bore threaded shroud <NUM> configured to connect to the RF cable <NUM>. An example of the threaded shroud <NUM> is a cylindrical smooth bore threaded shroud, such as part number MSSS-<NUM> manufactured by Micro-Mode as a micro cable connector.

The RF assembly <NUM> forms a Ka-band feed assembly and is operative as a waveguide fed hybrid microcircuit. The signal coupling pin <NUM> is operative to transition a waveguide fed signal to a microstrip launch as part of the LTCC substrate <NUM> and the quartz launch substrate <NUM> connected to the RF circuit module <NUM>. The mechanical form factor and micro interconnect, e.g., the RF cable connector <NUM>, allows the conductive waveguide body <NUM> to fit inside the end opening of the small, deployable composite mast <NUM>, which in an example, is about <NUM> inches (about <NUM>) in diameter. The radio frequency and amplifier bias voltage may be routed to different feed electronics contained within the satellite system <NUM> on one <NUM> inch (about <NUM>) diameter coaxial cable <NUM> with the aid of the printed bias T-circuit <NUM> (<FIG> and <FIG>), which minimizes the quantity and diameter of cables that have to be deployed within the mast <NUM>. Multiple hybrid circuit designs can be used for different customer applications with no change necessary to the mast or waveguide structure such as the reflector <NUM>, mast <NUM>, horn <NUM>, or subreflector <NUM>.

The satellite system <NUM> that includes the reflector <NUM>, mast <NUM>, and RF assembly <NUM> as described provides a competitive advantage in the small satellite market of CubeSats and enables wideband communications in smaller volume packages that are inexpensive to launch and may be used with different deployable antennas. The satellite system <NUM> may be used in remote sensing applications similar to Hawkeye <NUM> systems and in voice, machine-to-machine, and high data rate communications.

Different RF frequencies may be applied with some change to the waveguide structure geometry and the signal coupling pin <NUM>', for example, shown in a second embodiment of <FIG>, where the RF circuitry <NUM>' is formed of an RF signal limiter and some modifications are made for operation in the high-power X-band of about <NUM> to <NUM>. In this second embodiment illustrated in <FIG>, prime notation is used throughout the description and common components between the first embodiment shown in <FIG> are given the same reference numeral but in prime notation.

As illustrated, an RF assembly <NUM>' includes its conductive waveguide body <NUM>' having an RF cavity <NUM>' (<FIG>) that is coupled with a reflector (not shown) and having a pin-receiving opening <NUM>' therein. The RF circuit module <NUM>' has a different configuration with RF circuitry <NUM>' operative in the X-band at <NUM> to <NUM>. The conductive waveguide body <NUM>' includes an integral waveguide flange <NUM>' corresponding to the second circular mounting flange <NUM> of the first embodiment. The signal coupling pin <NUM>' in this second embodiment is also formed from Kovar and is about <NUM> inches (about <NUM>) in diameter to operate in the X-band. The RF cable connector <NUM>' in this example may be formed as an SMA connector and the conductive waveguide body <NUM>' may be formed from copper-molybdenum (Cu-Mo) material. The conductive waveguide body <NUM>' may include a rectangular configured end <NUM>' forming part of the RF circuit module <NUM>' as a housing <NUM>' and carries the RF cable connector <NUM>' and a Kovar seal ring <NUM>' and Kovar cover as a lid <NUM>' that may be connected by fasteners such as screws 102a'. In an example, the RF circuitry <NUM>' is operatively connected to a brazed-in probe substrate <NUM>' that receives the signal coupling pin <NUM>'.

The lower portion of the conductive waveguide body <NUM>' may include a closeout cover <NUM>' as an electromagnetic interference (EMI) shield secured by screws <NUM>' that also protects a DC circuit card assembly (CCA) <NUM>' to form a dual sided conductive waveguide body having RF and DC sides. The RF side containing the RF circuity <NUM>' may be hermetically sealed for use with an open die as an example and the DC side may contain all necessary DC power and control functionality via the attached circuit card assembly <NUM>' and cable connector <NUM>'.

The waveguide mounting flange <NUM>' is integrated with the conductive waveguide body <NUM>' and allows for direct interconnection to waveguide components without the requirement for a waveguide coaxial transition or connectorized cable. The integrated waveguide flange <NUM>' also allows for high-power applications where loss due to connectors and cables cannot be tolerated and it also provides a resilient and compact interface. The RF assembly <NUM>' is formed of high conductivity, low CTE material to provide thermal management and mounting of high-power dissipating components as used in many high RF power applications. The RF circuit <NUM>' may include amplifiers and similar components as in the first embodiment.

Different manufacturing techniques may be used and in an example shown in the high-level flowchart of <FIG>, a method for making the RF assembly for the satellite system with the reflector is illustrated generally at <NUM>. The process starts (Block <NUM>) and a conductive waveguide body <NUM> is formed (Block <NUM>). The RF circuit module <NUM> having the signal coupling pin <NUM> is formed (Block <NUM>). The RF circuit module <NUM> is assembled with the conductive waveguide body <NUM> to form the RF assembly <NUM> (Block <NUM>). The RF assembly <NUM> is assembled to the mast <NUM> carried by the reflector <NUM> (Block <NUM>). The process ends (Block <NUM>).

Claim 1:
A satellite system (<NUM>) comprising:
a reflector (<NUM>);
a mast (<NUM>) extending outwardly from the reflector (<NUM>); and
a radio frequency, RF, assembly (<NUM>) carried by a distal end of the mast (<NUM>),
the satellite system (<NUM>) being characterized in that the RF assembly (<NUM>) comprises:
a conductive waveguide body (<NUM>) having an RF cavity (<NUM>) therein coupled with the reflector (<NUM>), and having a pin-receiving opening (<NUM>) therein, and
an RF circuit module (<NUM>) comprising a housing (<NUM>) carried by the conductive waveguide body (<NUM>), RF circuitry (<NUM>) contained within the housing (<NUM>), and a signal coupling pin (<NUM>) coupled to the RF circuitry (<NUM>) and extending through the pin-receiving opening (<NUM>) into the RF cavity (<NUM>), wherein the housing (<NUM>) comprises a hermetically sealed housing, and wherein the housing (<NUM>) is carried by the conductive waveguide body (<NUM>) within a planar cut-out (42a) formed at a portion of a cylindrically configured end (<NUM>) of the conductive waveguide body (<NUM>).