Patent Description:
Phased array antennas are well known in the art for many applications, where most phased array antennas include many antenna elements, such as <NUM> elements. The phase of each of the signals from a particular source that are received by the antenna elements are selectively controlled so that all of the signals are in phase with each at a common antenna port, which allows the antenna to be narrowly directed to the source with high gain. Typically, phased array antennas include beam-forming networks that weight the individual signals so as to adjust their amplitude and phase so that they can be coherently added together in this manner. Further, at relatively high frequencies, such as <NUM> and above, beam-forming networks are not available and as such the received analog signals must be down-converted to an intermediate frequency signal before being sent to the beam-forming network, which requires significant hardware in each channel for the separate antenna elements. Also, known phased array antennas have limited flexibility because they are designed for a particular polarization. Thus, for space-borne applications, once the phased array antenna is launched on a satellite or spacecraft, it is not possible to change the polarization scheme for various types of communications signals.

Document <CIT> discloses a multibeam active discrete lens antenna comprising a plurality of primary radiating elements, each associated to a respective beam and an active radiating structure comprising a first planar array of radiating elements, a second planar array composed by a same number of radiating elements, a set of connections between each radiating element of the first planar array and one corresponding element of the second planar array, and a set of power amplifiers for amplifying signals transmitted through said connections, wherein the relative positions of the radiating elements of the first and second planar arrays and phase delays introduced by said connections are such that the radiating structure forms an active discrete converging lens and said primary radiating elements are clustered on a focal surface of said lens, facing the first planar array, characterized in that said first and second planar arrays are both aperiodic. Document <CIT> discloses an antenna unit comprising a variable power divider including a first <NUM>° phase combiner and a second <NUM>° phase combiner and a phase-amplitude adjustment block, wherein the phase-amplitude adjustment block includes, correspondingly to two-channel polarized signals, variable phase shifters for adjusting their phase amounts and variable attenuators for adjusting amplitudes (attenuation amounts). The phase amounts and the amplitudes of the two-channel polarized signals can be adjusted by an antenna control unit. Further, there are included a phase shifter and an attenuator provided on two-channel signal lines between an orthomode transducer and a first <NUM>° phase combiner and for equalizing the amplitudes and phases of the two-channel polarized signals. By this, an antenna apparatus is disclosed which uses a reflector antenna to perform transmission/reception of a signal to/from a satellite at high accuracy, and is miniaturized to be suitable for mounting on an aircraft or the like.

The subject-matter claimed is defined by independent claim <NUM>. Further embodiments are defined by dependent claims.

The following discussion of the embodiments of the invention directed to a space-fed reconfigurable phased array antenna that does not require a beam-forming network and intermediate frequency down-conversion hardware is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the phased array antenna of the invention has particular application for a spacecraft. However, as will be appreciated by those skilled in the art, the phased array antenna of the invention will have application for aircraft and ground applications.

As will be discussed in detail below, the present invention proposes a space-fed reconfigurable phased array (SRPA) antenna system that has a reduced cost and complexity over known phased array antennas because it eliminates the need for bulky, heavy and complex beam-forming networks and associated conversion electronics for converting high frequency signals to intermediate frequency signals. As will be discussed in detail below, the proposed SRPA antenna system uses a spatial signal combining technique to replace the beam-forming network that employs a combination of beams scan phase shifters and true time delay (TTD) phase shifters for beam scanning and beam shaping reconfigurablity. The spatial signal combining technique also allows use of any suitable polarization, such as vertical polarization (VP), horizontal polarization (HP), right hand circular polarization (RHCP), left hand circular polarization (LHCP), elliptical polarization, diagonal polarization, etc. The spatially combined beam is reconfigurable in beam shape and its location.

<FIG> is an isometric view of a satellite <NUM> including an SRPA antenna system <NUM> of the type referred to above showing a space-borne application of such an array antenna. The satellite <NUM> is intended to represent any airborne or space-borne platform.

<FIG> is a schematic diagram of the SRPA antenna system <NUM> separated from the satellite <NUM>. The system <NUM> will be discussed below as being in a receive mode that receives up-link signals from the ground or signals from other satellites, spacecraft or aircraft. However, those skilled in the art will understand that the system <NUM> can also be configured for transmitting signals. The antenna system <NUM> includes a front-end circuit <NUM> and a back-end circuit <NUM> separated by an open space <NUM> for the spatial combining as will become apparent from the discussion below. The front-end circuit <NUM> includes a number of antenna channels <NUM>, ten of which are shown in this non-limiting example, each including a receive antenna element <NUM> and a transmit antenna element <NUM>, where the number of the channels <NUM> in the system <NUM> is determined for a particular application based on signal gain, performance, etc., and may be upwards of <NUM> channels. The antenna elements <NUM> and <NUM> can be any suitable antenna, such as feed horns, ring-slot elements, stacked patches, flared notch elements, ridged waveguide elements, bow-tie elements, planar antenna elements, etc..

When a signal from a particular source (not shown) is received by the receive antenna elements <NUM> in the system <NUM> from a particular direction, they will all be out of phase with each other, and thus need to be phase shifted to be put in phase to get the desired signal gain and directivity. The signal received in each of the channels <NUM> is first amplified by a low noise amplifier (LNA) <NUM> and adjusted in phase by a beam scan phase shifter <NUM>. The phase shifters <NUM> can be, for example, modular 2π phase shifters and provide phase alignment of the signals received by the antenna elements <NUM> from the point source, such as a source on the ground. The phase shifted and amplified signal in each channel <NUM> is then attenuated by an attenuator <NUM> and sent to a TTD phase shifter <NUM>. As is well understood by those skilled in the art, a true time delay device is a signal line having a certain length, where signals propagating along the device are delayed by the length of the device. The TTD phase shifters <NUM> can be any suitable signal propagation device having the desired length on which the signal propagates so that the length of the device determines the phase of the signal at the output of the device.

The signal losses caused by the phase shifters <NUM> and <NUM> and the attenuator <NUM> can be returned to provide increased gain by an amplifier <NUM>, where the signal in each channel <NUM> is then transmitted by the transmit antenna element <NUM> into the open space <NUM> between the circuits <NUM> and <NUM>. The TTD phase shifters <NUM> provide the phase alignment of the signals transmitted by the transmitter antenna elements <NUM> across the open space <NUM>, so that they are in phase with each other when received by the circuit <NUM>. The TTD phase shifters <NUM> are necessary because a more significant degree of phase change may occur from the antenna elements <NUM> to the circuit <NUM>, which cannot be corrected by a modular 2π phase shifter, namely, the phase shifters <NUM>. Thus, the phase shifters <NUM> provide the directionality to which the antenna system <NUM> is directed to receive the signals and the TTD phase shifters <NUM> are selectively set depending on the desired wavelength of the signal being received and the distance between the front-end circuit <NUM> and the back-end circuit <NUM>. Further, by controlling the variable attenuators <NUM> in different manners for the channels <NUM>, the size of the beam can be adjusted, where some of the elements <NUM> and <NUM> may be removed from the array <NUM> based on the attenuation of the signal.

All of the signals transmitted by the transmit antenna elements <NUM> travel across the open space <NUM> and are received by an antenna horn <NUM> in the back-end circuit <NUM>. The signals from each channel <NUM> have been adjusted in phase to provide spatial signal combining such that all of the signals are in phase when they are received by the horn <NUM>. The combined in-phase signal is then sent to an ortho-mode transducer (OMT) <NUM>, whose operation is well known to those skilled in the art, that separates the signal into two separate polarizations, such as vertical polarization and horizontal polarization, which is required to create a circularly polarized signal. The two orthogonally polarized signals from the OMT <NUM> are amplified in separate lines by amplifiers <NUM> and <NUM> and are provided to a coupler <NUM> that couples the two separately polarized signals together to provide a circularly polarized signal, where the coupler <NUM> can selectively provide different power levels at its output ports. The circularly polarized signals at the output ports of the coupler <NUM> are then sent to separate phase shifters <NUM> and <NUM>, such as modular 2π phase shifters, to change the orientation of the polarization of the signals, if desired. The corrected signals from the phase shifters <NUM> and <NUM> are then provided to a second coupler <NUM> that combines the signals to provide the desired polarization at an output port <NUM>, where a second output port <NUM> of the coupler <NUM> is not used. Thus, the combination of the couplers <NUM> and <NUM> and the phase shifters <NUM> and <NUM> allow flexible polarization so that once the antenna system <NUM> has been launched on the satellite <NUM>, the polarization scheme can be changed for a different application, such as, for example, to left hand circular polarization or right hand circular polarization.

The configuration of the couplers <NUM> and <NUM> and the phase shifters <NUM> and <NUM> in the back-end circuit <NUM> is one way to provide the flexible polarization as discussed. <FIG> is a schematic diagram of a back-end circuit <NUM> that is similar to the back-end circuit <NUM> showing another way, where like elements are identified by the same reference number. In this embodiment, the amplifiers <NUM> and <NUM> have been eliminated and one of the outputs of the OMT <NUM> includes the phase shifter <NUM> instead of the output of the coupler <NUM>. By phase shifting one of the inputs to the coupler <NUM> and one of the outputs from the coupler <NUM> in this manner, the flexible polarization can be achieved in the same manner as discussed above for the back-end circuit <NUM>.

TABLE <NUM> below provides examples of the flexible polarizations for both of the back-end circuits <NUM> and <NUM>, where Ph1 is the output phase of the phase shifter <NUM> and Ph2 is the output phase of the phase shifter <NUM>.

To further show performance of a phased array antenna as discussed above, <FIG> is a graph with degrees on the horizontal axis and gain on the vertical axis showing two beam patterns for a <NUM> element phased array antenna having a <NUM> dB amplitude taper illustrating beam scan and side-lobe reconfigurability, where plot <NUM> illustrates a <NUM>° scan and plot <NUM> illustrates a <NUM>° scan of the antenna. <FIG> is a graph with degrees on the horizontal axis and gain on the vertical axis showing two beam patterns for a <NUM> element phased array antenna having a <NUM> dB amplitude taper illustrating beam scan and side-lobe reconfigurability, where plot <NUM> illustrates a <NUM>° scan and plot <NUM> illustrates a <NUM>° scan of the antenna. The low side-lobes in the plots <NUM> and <NUM> are on the order of -30dB.

<FIG> is a graph with degrees on the horizontal axis and gain on the vertical axis showing several beam patterns depicting beam shape reconfigurability and beam broadening of a phased array antenna having a 10dB taper, where plot <NUM> illustrates a <NUM>° scan for a <NUM> element array, plot <NUM> illustrates a <NUM>° scan for a <NUM> element array, plot <NUM> illustrates a <NUM>° scan for <NUM> element array, plot <NUM> illustrates a <NUM>° scan for a <NUM> element array, plot <NUM> illustrates a <NUM>° scan for a <NUM> element array, and plot <NUM> illustrates a <NUM>° scan for a <NUM> element array. The number of elements that are switched on at any particular point in time is controlled through variable attenuators at low level.

The discussion above of the antenna system <NUM> refers to signals received from the ground or other airborne platforms. However, as will be appreciated by those skilled in the art, the antenna system <NUM> can also be used in a transmit mode where signals to be transmitted are provided on the line <NUM> and coupled into the front-end circuit <NUM> to be transmitted by the antenna elements <NUM> in phase to a specific direction. In this embodiment, the amplifiers <NUM> will likely be high power amplifiers for the transmit application.

A phased array antenna system comprises a front-end circuit including a plurality of antenna channels where each antenna channel includes a front antenna element and a rear antenna element, said front antenna element being operable to receive signals from the environment or transmit signals into the environment, each antenna channel further including a beam scan phase shifter and a true time delay (TTD) phase shifter through which the receive signals or the transmit signals propagate; and a back-end circuit spaced apart from the front-end circuit and including an antenna receiving the receive signals from the rear antenna elements or transmitting the transmit signals to the rear antenna elements, said back-end circuit further including an ortho-mode transducer that separates the transmit signal or the receive signal into orthogonally polarized signals, said back-end circuit further including a pair of couplers and a pair of polarization phase shifters that combine to adjust the polarization of the transmit signal or the receive signal.

Each antenna channel can include a variable attenuator positioned between the beam scan phase shifter and the TTD phase shifter that provides signal attenuation.

Each antenna channel can include an amplifier positioned between the beam scan phase shifter and the front antenna element that is a low noise amplifier for the receive signals from the environment or a high power amplifier for transmitting signals into the environment.

The pair of couplers can include a first coupler and a second coupler, and wherein the ortho-mode transducer can include a first output coupled to a first input of the first coupler and a second output coupled to a second input of the first coupler, and wherein a first output of the first coupler can be coupled to a first input of the second coupler and a second output of the first coupler can be coupled to a second input of the second coupler.

The pair of phase shifters can include a first phase shifter provided between the first output of the first coupler and the first input of the second coupler and a second phase shifter provided between the second output of the first coupler and the second input of the second coupler.

The pair of phase shifters can include a first phase shifter provided between the second output of the ortho-mode transducer and the second input of the first coupler and a second phase shifter provided between the second output of the first coupler and the second input of the second coupler.

The antenna system can be configured to be provided on a spacecraft or an aircraft.

The front antenna elements and the rear antenna elements can be selected from the group consisting of antenna horns, ring-slot elements, stacked patch elements, flared notch elements, ridged waveguide elements and bow-tie elements.

The beam scan phase shifters and the polarization phase shifters can be modular 2π phase shifters.

The antenna in the back-end circuit can be a feed horn.

A phased array antenna system for a space-borne platform comprises a front-end circuit including a plurality of antenna channels where each antenna channel includes a front antenna element and a rear antenna element, said front antenna element being operable to receive signals from the environment or transmit signals into the environment, each antenna channel further including a beam scan phase shifter and a true time delay (TTD) phase shifter through which the receive signals or the transmit signals propagate; and a back-end circuit spaced apart from the front-end circuit and including a fed horn receiving the receive signals from the rear antenna elements or transmitting the transmit signals to the rear antenna elements, said back-end circuit further including an ortho-mode transducer that separates the transmit signal or the receive signal into orthogonally polarized signals, and a first coupler and a second coupler, wherein the ortho-mode transducer includes a first output coupled to a first input of the first coupler and a second output coupled to a second input of the first coupler, and wherein a first output of the first coupler is coupled to a first input of the second coupler and a second output of the first coupler is coupled to a second input of the second coupler, said back-end circuit further including a first polarization phase shifter provided between the first output of the first coupler and the first input of the second coupler and a second polarization phase shifter provided between the second output of the first coupler and the second input of the second coupler, where the signals are reconfigurable in beam shape and location.

A phased array antenna system for a space-borne platform comprises a front-end circuit including a plurality of antenna channels where each antenna channel includes a front antenna element and a rear antenna element, said front antenna element being operable to receive signals from the environment or transmit signals into the environment, each antenna channel further including a beam scan phase shifter and a true time delay (TTD) phase shifter through which the receive signals or the transmit signals propagate; and a back-end circuit spaced apart from the front-end circuit and including a fed horn receiving the receive signals from the rear antenna elements or transmitting the transmit signals to the rear antenna elements, said back-end circuit further including an ortho-mode transducer that separates the transmit signal or the receive signal into orthogonally polarized signals, and a first coupler and a second coupler, wherein the ortho-mode transducer includes a first output coupled to a first input of the first coupler and a second output coupled to a second input of the first coupler, and wherein a first output of the first coupler is coupled to a first input of the second coupler and a second output of the first coupler is coupled to a second input of the second coupler, said back-end circuit further including a first polarization phase shifter provided between the second output of the ortho-mode transducer and the second input of the first coupler and a second polarization phase shifter provided between the second output of the first coupler and the second input of the second coupler.

Claim 1:
A phased array antenna system (<NUM>) for a space-borne platform, said system comprising:
a front-end circuit (<NUM>) including a plurality of antenna channels (<NUM>) where each antenna channel includes a front antenna element (<NUM>) and a rear antenna element (<NUM>), said front antenna element being operable to receive signals from the environment or transmit signals into the environment, each antenna channel further including a beam scan phase shifter (<NUM>) and a true time delay, TTD, phase shifter through which the receive signals or the transmit signals propagate;
a variable attenuator (<NUM>) positioned between the beam scan phase shifter (<NUM>) and the TTD phase shifter (<NUM>) that provides signal attenuation, and
an amplifier (<NUM>) positioned between the beam scan phase shifter (<NUM>) and the front antenna element (<NUM>) that is a low noise amplifier for the receive signals from the environment or a high power amplifier for transmitting signals into the environment; and
a back-end circuit (<NUM>) spaced apart from the front-end circuit and including a single feed horn (<NUM>) receiving the receive signals from the rear antenna elements or transmitting the transmit signals to all of the rear antenna elements, said back-end circuit further including an ortho-mode transducer (<NUM>) that separates the transmit signals or the receive signals into orthogonally polarized signals, and a first coupler(<NUM>) and a second coupler (<NUM>), wherein the ortho-mode transducer (<NUM>) includes a first output coupled to a first input of the first coupler and a second output coupled to a second input of the first coupler, and wherein a first output of the first coupler is coupled to a first input of the second coupler and a second output of the first coupler is coupled to a second input of the second coupler, said back-end circuit further including a first polarization phase shifter (<NUM>) provided between the second output of the ortho-mode transducer (<NUM>) and the second input of the first coupler and a second polarization phase shifter (<NUM>) provided between the second output of the first coupler and the second input of the second coupler.