Patent Application
20160126629
1. Field
This invention relates generally to a scanning array antenna and, more particularly, to a hybrid scanning array antenna that electrically scans in elevation and mechanically scans in azimuth, where the antenna is compact to be suitable for airborne platform applications.
2. Discussion
There is a constellation of stationary geosynchronous communications satellites in orbit around the earth that are used for both commercial and military purposes. Adjacent satellites in the constellation are required to be some minimal distance or number of degrees apart so that uplink signals transmitted to a particular satellite in the constellation from ground stations or airborne platforms are not received and do not interfere with the adjacent satellites. In order to accomplish this, the transmission antennas that transmit the uplink signals need to have a beam width on the order of a few degrees and have high gain.
Active phased array narrow beam width antennas that are able to electronically scan in both the azimuth and elevation directions are available in the art for this purpose. Active phased array antennas have good antenna and radar cross-section (RCS) performance, but they are expensive. Further, the cost of active phased array antennas increases proportionally with the aperture size of the antenna. Generally, BLOS or SATCOM antennas require large aperture areas, which result in array antennas with thousands of individually phased-weighted and amplified antenna elements, which significantly increases the cost of the antenna.
For airborne platform satellite communications applications, it is known in the art to provide an antenna dish that is mechanically scanned in both the azimuth and elevation directions using a two-dimensional gimbal. Such dish antennas are typically large in size and are mounted under a radome extending from the aircraft skin. Because the radome extends from the aircraft it creates drag, which reduces fuel efficiency and reduces mission time on station. Additionally, the radome increases the aircraft's RCS, which causes the aircraft to become more visible on radar. Further, dish antennas often have poor aperture efficiency and high side-lobe levels for antennas designed to operate over wide instantaneous bandwidths. Transmit versions of dish antennas often require a high power traveling wave tube amplifier (TWTA) to amplify the transmit signal.
The following discussion of the embodiments of the invention directed to a hybrid electronic/mechanical scanning array antenna is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the discussion below describes the antenna as having particular application for transmission purposes for an airborne platform. However, as will be appreciated by those skilled in the art, the antenna of the invention may have other applications.
The antenna 10 includes an outer housing 12 having an upper cylindrical side wall 14, a lower cylindrical side wall 32, a top cover 16 and a closeout bottom cover 18 mounted together in any suitable manner, such as with glue, snap-fit assembly, etc. A circular bearing ring assembly 20 is mounted within the housing 12 and provides the bearings on which the antenna aperture is mechanically rotated in azimuth. A waveguide aperture 24 is positioned within the cover 16 and includes a waveguide fed slot array 22 having antenna slot antenna elements 26, where the waveguide aperture 24 is shown separated from the antenna 10 in
The waveguide aperture 24 is mounted to a top surface of a circular heat sink mounting cold plate 30 positioned within the housing 12. As will be discussed in further detail below, the mounting plate 30 includes a configuration of flow channels therein that accept a cooling fluid, such as water, to cool the antenna electronics. A multi-layer circuit board 38 is mounted to an underside of the mounting plate 30 opposite to the waveguide aperture 24. A series of ring frame GaN solid state power amplifier (SSPA) modules 40 are fastened with electrical interconnects passing to and from the circuit board 38 opposite to the mounting plate 30. Each module 40 is associated with one of the slot elements 26 in the aperture 24 and defines one of the antenna elements that can be electronically steered through phase weighting. The circuit board 38 and the ring frame modules 40 are designed and integrated with the slot array 22 in such a way as to form a radiation pattern that can be scanned in elevation. In this non-limiting embodiment, there are sixty-four of the slot elements 26 and the modules 40 for a particular application. The discussion below of the other elements of the antenna 10 will directed to this number of antenna elements with the understanding that other applications may employ other numbers of antenna elements.
Four sixteen element SiGe beam forming network (BFN) circuits 54 are mounted to the circuit board 38 that provide the variable phase shifting for the phase weighting of the electronic scanning, as will be discussed in detail below. Further, a field programmable gate array (FPGA) circuit (not shown in
The antenna 10 includes a cylindrical fluid RF DC rotary joint 60 including a rotor 62 that rotates and a stator 64 that does not rotate, where the stator 64 and the rotor 62 are generally concentric with each other in a stacked configuration and where the rotor 62 is coupled to the mounting plate 30. The rotary joint 60 allows RF, DC and digital signals to pass through, and also passes the cooling fluid that removes waste heat from the cold plate 30. An RF input connector 76 is located on the stator 64, on-axis with the rotary joint 60, and is accessible through an opening 78 in the closeout cover 18, where the RF signals provided to the connector 76 pass through the rotary joint 60 and feed the circuit board 38. A DC electrical harness 66 and a digital harness 68 extend through the housing wall 32 and are coupled to the stator 64. DC slip joints internal to the rotary joint 60 allow the electrical harnesses 66 and 68 to exit the rotor 62, pass through the mounting plate 30, and feed the circuit board 38 on the aperture side. Cooling fluid hoses 70 and 72 extend through the housing wall 32 and are coupled to the stator 64. The hose 72 receives the cooling fluid from, for example, a chiller (not shown), and directs the cooling fluid into the rotary joint 60 from the stator 64 to the rotor 62 and then to flow channels in the mounting plate 30. The heated cooling fluid flows from the flow channels within the mounting plate 30 to the rotor 62 and out of the rotary joint 60 through the hose 70. An azimuth drive motor actuator and encoder 74 rotates the cold plate 30 for the azimuth scanning and provides measurements as to how much rotation has occurred for accurate scanning. The rotating assembly is actuated by a spur gear connected to the motor actuator 74, however, can be replaced with a belt drive motor or by moving the ring frame modules 40 to be between the slot array 22 and the cold plate 30. Position and velocity telemetry is provided by an inertial measurement unit (IMU) 58 having GPS capability that is mounted to the housing 12.
The RF signal on the line 110 is divided four times in the power divider and RF distribution layer 94 and each divided RF signal is sent to one of the four sixteen element BFN circuit 114. The signal sent to each BFN circuit 114 is power divided sixteen times by a power divider 124 and sent to sixteen separate channels 122 each including a variable phase shifter 126, a variable attenuator 128 and an amplifier 130. The phase shifter 126 provides the phase shift of the signals for the electronic beam steering in elevation and the amplifier 130 generally recovers the signal loss provided by the phase shifter 126 and the attenuator 128. The operation and control of the phase shifters in phased antenna arrays for electronic beam steering is well understood by those skilled in the art. Each of the sixteen signals from each of the BFN circuit 122 is routed back through the power divider and RF distribution layer 94 to be sent to one of the sixty-four ring frame modules 112 on line 132 representing the electrical connector 50. The modules 112 include a driver amplifier 136, such as a 0.2 W GaAs SSDA chip, and a high power amplifier 138, such as a 2-8 W GaN SSDA chip. A DC bias signal for the amplifiers 136 and 138 is provided on line 134 from the DC power distribution layer 90, and represents the electrical connector 52. The amplified RF signal is then sent through a waveguide channel 140 representing the signal channel 48 to be radiated by the slot 88. The FPGA circuit 116 receives a control signal from the DC power distribution layer 90 on line 142.
The foregoing discussion disclosed and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
