Patent Description:
Various antenna field measurement techniques use a radio-frequency source of a test bench to generate a source signal. A directional coupler obtains a reference signal from the source signal and routes the remaining source signal to a multiport switch. The multiport switch multiplexes the source signal to an antenna under test of the satellite. The antenna under test subsequently broadcasts a transmit signal to a receive antenna of the test bench. The receive antenna converts the transmit signal into a test signal. The test signal is a measurement of the field in front of the antenna under test. The measurements are repeated for each antenna of the satellite, often resulting in hundreds of cables being routed between the multiport switch and the antennas of the satellite during the tests. Installing and removing the hundreds of cables is manually intensive and time consuming.

Document by <NPL>, states a method to sample the near-field of a test antenna on a cylindrical grid. The antenna is mounted on an azimuth positioner with horizontal boresight direction. Near to the test antenna, a small probe antenna, e.g. an open waveguide, is moved verticaly while probing the near-field.

Accordingly, those skilled in the art continue with research and development efforts in the field of satellite antenna testing using simplified connections between a test bench and the antennas under test.

The presently claimed invention is defined by a method for testing a feed antenna of a.

Embodiments of the present disclosure include a system and/or a method for testing multiple feed antennas of a satellite. The feed antennas are tested one at a time using a source signal generated internal to the satellite. The system/method utilizes a stationary reference horn that samples a transmit signal spillover from a reflector on the satellite (or side lobes of the transmit signal in situations where no reflector exists). A moveable near-field probe samples the transmit signal. An intermediate reference signal from the reference horn may be mixed to an intermediate frequency in a same manner as a test signal from the probe. The intermediate reference signal is subsequently compared with the intermediate frequency test signal at a receiver to obtain an amplitude measurement and a phase measurement. Placement of the reference horn is calculated from a geometry of the feed antenna currently under test. A polarization of the reference horn may be different than a feed antenna polarization. A circularly polarized feed antenna uses a linearly polarized reference horn. A linearly polarized feed antenna uses a circularly polarized reference horn.

Referring to <FIG>, a schematic diagram of an example test system <NUM> involving a satellite <NUM> with a reflector <NUM> is shown in accordance with one or more exemplary embodiments. The test system <NUM> (e.g., a first test system 100a) includes a test bench <NUM> and the satellite <NUM> (e.g., a first satellite 140a) having the reflector <NUM>. The test bench <NUM> includes a reference horn <NUM> and a probe <NUM>. The satellite <NUM> includes a housing <NUM>, multiple transmitters <NUM> (one shown), and multiple feed antennas 154a-154n.

A power signal <NUM> is generated by the test bench <NUM> and transferred to the satellite <NUM>. The power signal <NUM> may transfer electrical power appropriate for the satellite <NUM> to be operational. The test bench <NUM> also generates a control signal <NUM> received by the satellite <NUM>. The control signal <NUM> instructs the satellite <NUM> to broadcast transmit signals <NUM> (one shown) from the feed antennas 154a-154n.

Source signals <NUM> (one shown) are generated by the transmitters <NUM> and routed to the feed antennas 154a-154n, one at a time. Selection of an antenna under test (e.g., feed antenna 154a is illustrated) is controlled by the control signal <NUM>. The antenna under test broadcasts the received source signal <NUM> as the transmit signal <NUM>. The transmit signal <NUM> conveys a carrier waveform. The transmit signal <NUM> may be reflected from the reflector <NUM> in at least two directions. In a first direction <NUM>, the reflected portion of the transmit signal <NUM> is referred to as a test portion <NUM>. The first direction <NUM> sends the test portion <NUM> to the probe <NUM>. In a second direction <NUM>, the reflected portion of the transmit signal <NUM> is referred to as a reference portion <NUM>. The second direction <NUM> sends the reference portion <NUM> to the reference horn <NUM>. The probe <NUM> implements a moveable antenna that is external to the satellite <NUM>. The probe <NUM> is operational to convert the test portion <NUM> of the transmit signal <NUM> into a test signal <NUM>. Reception of the test portion <NUM> of the transmit signal <NUM> is referred to as a first reception <NUM>. The probe <NUM> has a probe polarization <NUM>. The probe polarization <NUM> may be linear (e.g., horizontal or vertical) or circular.

The reference horn <NUM> implements a fixed-position antenna that is external to the satellite <NUM>. The reference horn <NUM> is operational to convert the reference portion <NUM> of the transmit signal <NUM> into a reference signal <NUM>. Reception of the reference portion <NUM> of the transmit signal <NUM> is referred to as a second reception <NUM>. The reference horn <NUM> has a horn polarization <NUM>. The horn polarization <NUM> may be linear (e.g., horizontal or vertical) or circular. In various embodiments, the horn polarization <NUM> may match the probe polarization <NUM>.

The housing <NUM> of the satellite <NUM> defines an interior <NUM> and an exterior <NUM>. The interior <NUM> of the satellite <NUM> holds the transmitters <NUM>. The feed horns are mounted on the exterior <NUM> of the satellite <NUM>. The reflector <NUM> is also mounted on the exterior <NUM> of the satellite <NUM>.

The transmitters <NUM> implement radio-frequency transmitters. The transmitters <NUM> are operational to generate the source signals <NUM>. A source signal <NUM> is presented to the antenna under test. Selection of when to generate the source signal <NUM> and which feed antenna 154a-154n receives the source signal <NUM> is governed by the control signal <NUM>.

Each feed antenna 154a-154n implements a directional radio-frequency antenna mounted on the exterior <NUM> of the satellite <NUM>. The antenna under test is operational to broadcast a source signal <NUM> as the transmit signal <NUM>. The transmit signal <NUM> is directed toward the reflector <NUM>. The satellite <NUM> may include over <NUM> to <NUM> individual feed antenna 154a-154n. The feed antennas 154a-154n have a feed polarization <NUM>. In various embodiments, the feed polarization <NUM> may be a linear polarization or a circular polarization. The feed polarization <NUM> of the feed antennas 154a-154n is generally different than the probe polarization <NUM> and the horn polarization <NUM>.

The reflector <NUM> implements a radio-frequency reflective object disposed on the exterior <NUM> of the satellite <NUM>. In various embodiments, a single reflector <NUM> extends from the housing <NUM> of the satellite <NUM>. In some embodiments, multiple reflectors <NUM> may be implemented. The reflector <NUM> is operational to redirect the transmit signal <NUM> toward the probe <NUM> and the reference horn <NUM> of the test bench <NUM>. In various embodiments, the reflector <NUM> may bounce a main lobe of the transmit signal <NUM> (the test portion <NUM>) in a first reflection <NUM> toward the probe <NUM> and bounce a side lobe of the transmit signal <NUM> (the reference portion <NUM>) in a second reflection <NUM> toward the reference horn <NUM>.

Referring to <FIG>, a schematic diagram of an example test system <NUM> involving a satellite <NUM> without a reflector <NUM> is shown in accordance with one or more exemplary embodiments. The test system <NUM> (e.g., a second test system 100b) includes the test bench <NUM> and a satellite <NUM> (e.g., a second satellite 140b) that does not implement the reflector <NUM>. The test bench <NUM> is the same as shown in <FIG>. The satellite <NUM> includes the housing <NUM> and the transmitters <NUM> (one shown).

Each feed antenna 154a-154n implements a directional radio-frequency antenna mounted on the exterior <NUM> of the satellite <NUM>. The antenna under test is operational to broadcast a source signal <NUM> as the transmit signal <NUM>. The transmit signal <NUM> is directed toward the test bench <NUM>. The satellite <NUM> may include over <NUM> to <NUM> individual feed antenna 154a-154n. The feed antennas 154a-154n have the feed polarization <NUM>. In various embodiments, the feed polarization <NUM> may be a linear polarization or a circular polarization. The feed polarization <NUM> of the feed antennas 154a-154n is generally different than the probe polarization <NUM> and the horn polarization <NUM>. While testing, the satellite <NUM> is oriented such that the main lobe (the test portion <NUM>) of the transmit signal <NUM> is directed to the probe <NUM> of the test bench <NUM>. A side lobe (the reference portion <NUM>) of the transmit signal <NUM> is directed to the reference horn <NUM>. Referring to <FIG>, a schematic diagram of an example implementation of the test bench <NUM> is shown in accordance with one or more exemplary embodiments. The test bench <NUM> generally includes the probe <NUM>, the reference horn <NUM>, a multiport switch <NUM>, a moveable platform <NUM>, a first mixer <NUM>, a second mixer <NUM>, a local oscillator (LO) source <NUM>, a distributed frequency converter (DCF) <NUM>, a receiver <NUM>, and a computer <NUM>. The test system <NUM> and the test bench <NUM> are characterized by a lack of an external radio-frequency source <NUM> that would otherwise generate a radio-frequency signal <NUM> used to create the source signal <NUM> outside the satellite <NUM>.

A source oscillator signal <NUM> is generated by the local oscillator source <NUM> and presented to the distributed frequency converter. The distributed frequency converter <NUM> converts the source oscillator signal <NUM> to multiple copies of the local oscillator signal <NUM> that are routed to the first mixer <NUM> and the second mixer <NUM>. The local oscillator signal <NUM> carries a steady oscillating signal used to mix the test signal <NUM> and the reference signal <NUM> to an intermediate frequency. The first mixer <NUM> generates an intermediate reference signal <NUM> received by the distributed frequency converter. The second mixer <NUM> generates an intermediate test signal <NUM> received by the distributed frequency converter.

A synchronization signal is generated by the local oscillator source <NUM> and transferred to the receiver <NUM>. The synchronization signal provides a time reference for the receiver <NUM>. The receiver <NUM> receives a final test signal <NUM> and a final reference signal <NUM> from the distributed frequency converter. An amplitude <NUM> is calculated by the receiver <NUM> and presented to the computer <NUM>. The amplitude <NUM> is an amplitude of the transmit signal <NUM> presented by the feed horn (<FIG> and <FIG>). A phase <NUM> is calculated by the receiver <NUM> and provided to the computer <NUM>. The phase <NUM> is a phase of the transmit signal <NUM> presented by the feed antennas 154a-154n. The computer <NUM> generates the control signal <NUM>. Near-field pattern <NUM> information is generated by the computer <NUM>. The near-field pattern <NUM> information represents a field pattern of the transmit signal <NUM> presented by the feed horn. The control signal <NUM> is received by the moveable platform <NUM> and the satellite <NUM> (<FIG> and <FIG>).

The multiport switch <NUM> implements a single-post four-throw pin switch. The multiport switch <NUM> is operational to route the test signal <NUM> from the probe <NUM> to the second mixer <NUM>.

The first mixer <NUM> implements a frequency down converter. The first mixer <NUM> is operational to generate the intermediate reference signal <NUM> by a first mixing of the reference signal <NUM> with the local oscillator signal <NUM>. The intermediate reference signal <NUM> is presented to the distributed frequency converter.

The second mixer <NUM> implements another frequency down converter. The second mixer <NUM> is operational to generate the intermediate test signal <NUM> by a second mixing of the test signal <NUM> with the local oscillator signal <NUM>. In various embodiments, the second mixer <NUM> may be a copy of the first mixer <NUM>. The intermediate test signal <NUM> is presented to the distributed frequency converter <NUM>.

The local oscillator source <NUM> implements a radio-frequency oscillator. The local oscillator source <NUM> is operational to generate the source oscillator signal <NUM> and the synchronization signal <NUM>.

The distributed frequency converter <NUM> implements a dual down converter. The distributed frequency converter <NUM> is operational to down convert the intermediate test signal <NUM> and the intermediate reference signal <NUM> to a predetermined frequency (e.g., <NUM> megahertz). The distributed frequency converter <NUM> generally includes a local oscillator/intermediate frequency (LO/IF) unit and two mixer modules. The intermediate reference signal <NUM> is converted into the final reference signal <NUM>. The intermediate test signal <NUM> is converted into the final test signal <NUM>. The final reference signal <NUM> and the final test signal <NUM> are transferred to the receiver <NUM>.

The receiver <NUM> implements a measurement circuit. The receiver <NUM> is operational to determine the amplitude <NUM> and the phase <NUM> of the transmit signal <NUM> (<FIG> and <FIG>) based on the final test signal <NUM> relative to the final reference signal <NUM> received from the distributed frequency converter <NUM>. The amplitude <NUM> and the phase <NUM> of the transmit signal <NUM> are determined by a comparison of the final test signal <NUM> with the final reference signal <NUM>. The amplitude <NUM> and the phase <NUM> are presented to the computer <NUM>.

The computer <NUM> implements one or more processors, each of which may be embodied as a separate processor, one or more application specific integrated circuits (ASIC) or field programmable gate arrays (FPGA), and/or dedicated electronic control circuitry. The computer <NUM> is operational to generate the control signal <NUM> that instructs the satellite <NUM> when to generate the transmit signal <NUM> and from which feed antenna 154a-154n and corresponding transmitter <NUM>. The computer <NUM> is operational to control spatial movement of the probe <NUM> to multiple locations 242a-242n in front of the antenna under test. The computer <NUM> is also operational to determine the near-field pattern <NUM> information based on the amplitude <NUM> and the phase <NUM> as measured at the multiple locations 242a-242n of the probe <NUM>.

The processors may be implemented in hardware, software executing on hardware, or a combination of both. The computer <NUM> include tangible, non-transitory memory (e.g., read-only memory in the form of optical, magnetic, and/or flash memory). For example, the computer <NUM> may include application-suitable amounts of random-access memory, read-only memory, flash memory and other types of electrically erasable programmable read-only memory, as well as accompanying hardware in the form of a high-speed clock or timer, analog-to-digital and digital-to-analog circuitry, and input/output circuitry and devices, as well as appropriate signal conditioning and buffer circuitry.

Computer-readable and executable instructions embodying the present method may be recorded (or stored) in the memory and executed as set forth herein. The executable instructions may be a series of instructions employed to run applications on the computer <NUM> (either in the foreground or background). The computer <NUM> may receive commands and information, in the form of one or more input signals from the receiver <NUM> and the moveable platform <NUM>. The computer <NUM> may also communicate instructions to the satellite <NUM>.

Referring to <FIG>, a schematic diagram of an example probe movement is shown in accordance with one or more exemplary embodiments. The antenna under test (e.g., feed antenna 154a is illustrated) generate the transmit signal <NUM>. The transmit signal <NUM> has a near-field pattern <NUM>. A main lobe <NUM> of the near-field pattern <NUM> may be aligned with the feed antenna 154a. Multiple side lobes 236a-236n of the near-field pattern <NUM> may be spatially spread from the main lobe <NUM> in one or more directions.

The probe <NUM> measures the transmit signal <NUM> at the multiple locations 242a-242n in a scan plane <NUM>, one location at a time. The probe <NUM> is moved spatially in the scan plane <NUM> from one location to another to measure the near-field pattern <NUM> from different points of view. Some of the measurements are of the main lobe <NUM>. Other measurements capture the side lobes 236a-236n. The resulting test signals <NUM> may be transferred to the computer <NUM> via the second mixer <NUM>, the distributed frequency converter <NUM> and the receiver <NUM>. The computer <NUM> uses the resulting amplitude <NUM> and phase <NUM> information to reconstruct the near-field pattern <NUM> of the feed antenna 154a.

Referring to <FIG>, a flow diagram of an example method <NUM> for testing a satellite <NUM> is shown in accordance with one or more embodiments. The method (or process) <NUM> is implemented by the test bench <NUM> and a satellite <NUM>. The method <NUM> generally includes steps <NUM> to <NUM>, as illustrated. The sequence of steps is shown as a representative example. Other step orders may be implemented to meet the criteria of a particular application.

In the step <NUM>, electrical power is applied to the satellite <NUM>. The computer <NUM> commands the satellite <NUM> via the control signal <NUM> to transmit from one of the feed antennas 154a-154n in the step <NUM>. The satellite <NUM> generates the source signal <NUM> internally in the step <NUM> and presents the source signal <NUM> to a feed antenna 154a. The feed antenna 154a generates the transmit signal <NUM> in the step <NUM> by broadcasting the source signal <NUM> external to the satellite <NUM>.

In the step <NUM>, the test portion <NUM> of the transmit signal <NUM> is generated by a first reflection <NUM> of the transmit signal <NUM> from the reflector <NUM> in the first direction <NUM> toward the probe <NUM>. The probe <NUM> converts the test portion <NUM> of the transmit signal <NUM> into the test signal <NUM> in the step <NUM>. In the step <NUM>, the reference portion <NUM> of the transmit signal <NUM> is generated by a second reflection <NUM> of the transmit signal <NUM> from the reflector <NUM> in a second direction <NUM> toward the reference horn <NUM>. The reference horn <NUM> converts the reference portion <NUM> of the transmit signal <NUM> into the reference signal <NUM> in the step <NUM>.

In the step <NUM>, the first mixer <NUM> generates an intermediate reference signal <NUM> by a first mixing of the reference signal <NUM> to an intermediate frequency. In the step <NUM>, the second mixer <NUM> generates an intermediate test signal <NUM> by a second mixing of the test signal <NUM> to the intermediate frequency. The distributed frequency converter <NUM> converts the intermediate test signal <NUM> and the intermediate reference signal <NUM> to the final test signal <NUM> and the final reference signal <NUM> in the step <NUM>.

In the step <NUM>, the receiver <NUM> determining an amplitude <NUM> and a phase <NUM> of the transmit signal <NUM> based on the final test signal <NUM> relative to the final reference signal <NUM>. The amplitude <NUM> and the phase <NUM> of the transmit signal <NUM> are determined by comparing the final test signal <NUM> with the final reference signal <NUM>. The method <NUM> is repeated per the step <NUM> for a next feed antenna (e.g., 154b) until the feed antennas 154a-154n have been processed.

Referring to <FIG>, a flow diagram of an example method <NUM> for determining the near-field pattern <NUM> of a feed antenna 154a is shown in accordance with one or more embodiments. The method (or process) is implemented by the test bench <NUM> and a satellite <NUM>. The method <NUM> generally includes steps <NUM> to <NUM>, as illustrated. The sequence of steps is shown as a representative example. Other step orders may be implemented to meet the criteria of a particular application.

In the step <NUM>, the probe <NUM> is placed at an initial location 242a-242n in the scan plane <NUM> (<FIG>). The amplitude <NUM> and the phase <NUM> of the transmit signal <NUM> is determined in the step <NUM> at the initial location 242a-242n. The probe <NUM> is moved to a next location 242a-242n in the step <NUM>. The test bench <NUM> repeats the determination of the amplitude <NUM> and the phase <NUM> at the next location 242a-242n in the step <NUM>. If the transmit signal <NUM> is untested at one or more locations 242a-242n per the step <NUM>, the method <NUM> return to the step <NUM> and moves the probe <NUM> to an untested location. Once the amplitude <NUM> and the phase <NUM> have been determined at each location 242a-242n, the computer <NUM> generates the near-field pattern <NUM> in the step <NUM>.

The test bench <NUM> makes use of a stationary probe <NUM> while transmitters <NUM> in the satellite <NUM> is used to generate the source signals <NUM>, instead of the external radio-frequency source <NUM>, for near-field antenna measurements. Use of the satellite <NUM> transmitters <NUM> eliminates the usage of multiple couplers and radio-frequency cables thereby reducing a weight and a cost of the testing. Embodiments of the disclosure generally eliminate the implementation of test couplers, multiple radio-frequency cables, and multiple port radio-frequency switches.

This disclosure is susceptible of embodiments in many different forms. Representative embodiments of the disclosure are shown in the drawings and are herein described in detail with the understanding that these embodiments are provided as an exemplification of the disclosed principles, not limitations of the broad aspects of the disclosure. To that extent, elements and limitations that are described, for example, in the Abstract, Background, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference or otherwise.

For purposes of the present detailed description, unless specifically disclaimed, the singular includes the plural and vice versa. The words "and" and "or" shall be both conjunctive and disjunctive. The words "any" and "all" shall both mean "any and all", and the words "including," "containing," "comprising," "having," and the like shall each mean "including without limitation. " Moreover, words of approximation such as "about," "almost," "substantially," "approximately," and "generally," may be used herein in the sense of "at, near, or nearly at," or "within <NUM>-<NUM>% of," or "within acceptable manufacturing tolerances," or other logical combinations thereof. Referring to the drawings, wherein like reference numbers refer to like components.

Claim 1:
A method (<NUM>) for testing a feed antenna (154a) of a satellite (<NUM>) comprising:
generating (<NUM>) a source signal (<NUM>) internal to the satellite (<NUM>), wherein the satellite (<NUM>) includes the feed antenna (154a) disposed on an exterior (<NUM>) of the satellite (<NUM>);
generating (<NUM>) a transmit signal (<NUM>) external to the satellite (<NUM>) by a broadcast of the source signal (<NUM>) with the feed antenna (154a);
generating (<NUM>) a test signal (<NUM>) with a probe (<NUM>) in response to a first reception (<NUM>) of a test portion (<NUM>) of the transmit signal (<NUM>), wherein the probe (<NUM>) is external to the satellite (<NUM>);
generating (<NUM>) a reference signal (<NUM>) with a reference horn (<NUM>) in response to a second reception (<NUM>) of a reference portion (<NUM>) of the transmit signal (<NUM>), wherein the reference horn (<NUM>) is external to the satellite (<NUM>), wherein the second reception (<NUM>) made by the reference horn (<NUM>) is receiving a side lobe (236a) of the transmit signal (<NUM>); and
determining (<NUM>) an amplitude (<NUM>) and a phase (<NUM>) of the transmit signal (<NUM>) based on the test signal (<NUM>) relative to the reference signal (<NUM>).