Patent Description:
This disclosure relates generally to phased array antennas and more particularly to a phased array based antenna system with field-calibration capability.

A phased array antenna may include hundreds or thousands of antenna elements, each connected to a respective signal path carrying a transmitting direction signal ("transmit signal") and/or a receiving direction signal ("receive signal"). In the front ends of some "active" phased arrays, hundreds or thousands of low noise amplifiers (LNAs) and/or power amplifiers (PAs), variable phase shifters and other integrated circuit components are distributed across the antenna array in the signal paths for amplifying and phase shifting a transmit signal / receive signal routed through one or more of the antenna elements. To form accurate beams, the phase and amplitude (gain / loss) relationships between the signal paths often need to be precisely set during the antenna system manufacture and set-up. It is desirable to maintain such phase and amplitude relationships during the antenna operation in the field to ensure the antenna continues to meet any requisite performance requirements such as beam pointing accuracy and sidelobe levels.

Over time, however, degradation of LNAs, PAs and other signal path components is inevitable. Thus, antenna systems may include a built-in calibration circuit for periodically calibrating the signal paths in the field by adjusting phase shifts of the phase shifters and gains / losses of the amplifiers (and variable attenuators, if included). One type of calibration circuit only operates during predetermined maintenance periods in which the antenna system is deactivated for wireless communication with satellites or other external systems. Another type of calibration circuit enables calibration to be carried out simultaneously with such communication, but current circuits of this type are known to be highly complex.

<CIT> discloses a multi-ground station that implements a handover of a communication link from an origin first satellite to a destination second satellite. In a first phase of the handover, first and second antennas receive from and transmit to the first satellite. In a second phase, the first antenna ceases to receive from and transmit to the first satellite. In a third phase, the first antenna receives from and transmits to the second satellite, while the second antenna receives from and transmits to the first satellite. In a fourth phase, the second antenna ceases to receive from and transmit to the first satellite. In a fifth phase, the first and second antennas receive from and transmit to the second satellite.

In aspects of the present disclosure, an antenna system with a phased array is configured with control and calibration circuitry for performing a field-calibration of signal paths to antenna elements of the phased array during handover periods. As compared to current systems capable of "any time calibration", the control and calibration circuitry disclosed herein may be less complex, yet achieve the same overall objectives.

An aspect of the presently disclosed technology involves a method as defined in appended claim <NUM>.

In another aspect, an antenna system is defined in appended claim <NUM>.

The above and other aspects and features of the disclosed technology will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings in which like reference characters indicate like elements or features. Various elements of the same or similar type may be distinguished by annexing the reference label directly with a second label or with a dash and second label that distinguishes among the same / similar elements (e.g., -<NUM>, -<NUM>). However, if a given description uses only the first reference label, it is applicable to any one of the same / similar elements having the same first reference label irrespective of the second reference label. In the drawings:.

The following description, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of certain exemplary embodiments of the technology disclosed herein for illustrative purposes. The description includes various specific details to assist a person of ordinary skill the art with understanding the technology, but these details are to be regarded as merely illustrative. For the purposes of simplicity and clarity, descriptions of well-known functions and constructions may be omitted when their inclusion may obscure appreciation of the technology by a person of ordinary skill in the art.

Herein, the terms "receive" and "transmit", when used as adjectives, mean "receiving direction" and "transmitting direction", respectfully. For example, a "receive signal" is a signal propagating in the receiving direction of an antenna. Similarly, the phrase "on receive" means "during a receiving operation" and "on transmit" means "during a transmitting operation" or the like. A "beam signal" refers to a signal representing combined signal energy received from or provided to a plurality of antenna elements that collectively form an antenna beam. An "element signal" refers to a signal provided by a single antenna element on receive, or fed to a single element signal on transmit to be radiated.

<FIG> schematically illustrates example circuitry of an antenna system <NUM> in accordance with an embodiment of the present technology. Antenna system <NUM> includes an antenna array <NUM>, a controller <NUM>, a receiving cross-coupled switch (RCC) <NUM>, a transmitting cross-coupled (TCC) switch <NUM>, transmit / receive (T/R) elements <NUM>-<NUM> and <NUM>-<NUM>, variable delay lines (VDLs) <NUM>-<NUM> and <NUM>-<NUM>, a calibration circuit <NUM>, directional couplers <NUM>-<NUM> and <NUM>-<NUM>, single pole multi-throw (SPMT) switches SW1 and SW2 (discussed further below), and single pole, two throw (SPDT) switches SW3 and SW4. Antenna array <NUM> includes a first antenna <NUM>-<NUM> and a second antenna <NUM>-<NUM>, each of which may be an active phased array antenna with distributed amplifiers and phase shifters behind each antenna element <NUM> or behind small groups of antenna elements <NUM>. In various examples, antenna system <NUM> may be an antenna system at a fixed ground location; aboard a ground-based mobile vehicle or ship; or aboard an aircraft, spacecraft or satellite.

Herein, a "communication" between two entities will refer to a bidirectional communication of RF signals (data traffic and/or control signals) between the entities, using any suitable protocol. An external communication system, such as first satellite <NUM> or second satellite <NUM>, communicates with antenna system <NUM>. In other examples, the external communication system is a ground-based communication system or an aircraft-based or spacecraft-based communication system. In the following description, communication with a satellite will be described as an example.

Hereafter, a "normal communication operation" involving antenna system <NUM> will refer to a communication between antenna system <NUM> and a single satellite by means of antenna system <NUM> forming a pencil beam using first and second antennas <NUM>-<NUM> and <NUM>-<NUM>. A normal communication operation is distinguishable from a communication during a handover period, during which a communication session with antenna system <NUM> is handed over from first satellite <NUM> to second satellite <NUM>. For example, when antenna system <NUM> is coupled to end user equipment on one side of the communication session with first satellite <NUM>, a successful handover of the communication session to second satellite <NUM> dispenses with the need for the end user equipment to re-initiate the communication session by attempting to locate a suitable satellite through antenna system <NUM>. For instance, during a handover involving a voice call or a live video stream, an end user may not perceive a reduction in quality during the handover period. A handover handled by antenna system <NUM> may be referred to as a "make-before-break" handover from a first satellite to a second satellite. In such a make-before-break handover, the first and second satellites may share information about a current communication session with antenna system <NUM>. During a short handover period, e.g., about <NUM> seconds of less, both the first and second satellites may communicate the same information signals such as video or audio data, redundantly, to antenna system <NUM>, albeit using different frequencies, pseudo-random codes, modulations, or other ways to differentiate their signals. This method is sometimes referred to as "soft handover". Alternatively, the second satellite communicates just control bits, but not information signals during the handover period, and immediately after the handover period, precisely transmits information signals of the communication session intended to directly follow the information signals exchanged by the first satellite (sometimes referred to as "hard handover"). The control bits are used to manage a subsequent communication of information signals, and may convey control information such as frequencies, timing, protocol, modulation, packet structure, etc. to be used for the communication. In either case of soft or hard handover for the make-before-break handover, any discernible discontinuity in the communication session may be avoided after communication with the first satellite is dropped to complete the handover. As will be explained further below, throughout a handover period, antenna system <NUM> communicates with first satellite <NUM> using only one of the first and second antennas <NUM>-<NUM> and <NUM>-<NUM>, and communicates with second satellite <NUM> using only the other one of antennas <NUM>-<NUM> and <NUM>-<NUM>.

Controller <NUM> may control overall operations of antenna system <NUM> by sending control signals over control lines CL to each of antennas <NUM>-<NUM>, <NUM>-<NUM>, calibration circuit <NUM>, RCC and TCC switches <NUM>, <NUM>, switches SW1-SW4, variable delay lines <NUM>, and in some cases, to T/R elements. The control signals output by controller <NUM> may: control switching states of switches within RCC and TCC switches <NUM>, <NUM>; control biasing and ON/OFF states of amplifiers within each of antennas <NUM>-<NUM> and <NUM>-<NUM>; control phase shifts of phase shifters within each of antennas <NUM>-<NUM>, <NUM>-<NUM> for beam steering, set variable delay paths within VDLs <NUM>-<NUM> and <NUM>-<NUM> for phase alignment between antennas <NUM>-<NUM> and <NUM>-<NUM>; and control calibration operations via control of calibration circuit <NUM> and switches SW1-SW4. For instance, during normal communication operations, controller <NUM> outputs control signals to cause first and second antennas <NUM>-<NUM>, <NUM>-<NUM> to be coupled together and collectively form a beam for communication with only one of the satellites <NUM>, <NUM>. During a first portion of a handover period, controller <NUM> may output control signals to cause only antenna <NUM>-<NUM> to communicate with satellite <NUM> by deactivating antenna <NUM>-<NUM> for any external communication, while other control signals initiate a calibration operation of antenna <NUM>-<NUM> via control of calibration circuit <NUM>. (For the calibration, controller <NUM> includes a memory <NUM> that may store phase and amplitude reference data and correction data, discussed later. ) During a second portion of a handover period, or in a different handover period, controller <NUM> may initiate calibration of antenna <NUM>-<NUM> in an analogous manner. It is noted here that the calibration of first and second antennas <NUM>-<NUM>, <NUM>-<NUM> includes a calibration of the VDLs <NUM>-<NUM>, <NUM>-<NUM>, which may be interchangeably referred to as "true time delay units" (TTDUs). VDLs <NUM>-<NUM>, <NUM>-<NUM> each include a plurality of selectable delay line sections with different lengths, and hence different insertion phases. A plurality of switches in each VDL <NUM> are controllable by controller <NUM> to select one or more of the delay lines for the signal path and thereby set a desired insertion phase through the respective VDL <NUM>. In this manner, a targeted phase relationship (typically equal insertion phases, i.e., phase alignment) between the two halves of the antenna system <NUM> may be achieved. In an alternative embodiment, one of VDLs <NUM> may be substituted with a fixed delay line and the phase relationship between the two halves is set by adjusting the other VDL <NUM>. In still other embodiments, other types of time shifters are substituted for the VDLs <NUM>. In another embodiment (discussed below in connection with <FIG>), a plurality of internal VDLs <NUM> are provided within each antenna <NUM>-<NUM>, <NUM>-<NUM>, and their delays are individually controlled by controller <NUM>.

It is noted here that controller <NUM> may output control signals on control lines CL to calibration circuit <NUM> to deactivate it for calibration operations during all periods of communication between antenna system <NUM> and any external communication system except for handover periods.

With the methods detailed below, calibration of antennas <NUM>-<NUM> and <NUM>-<NUM> is avoided during normal communication operations but is performed during handover periods. With this scheme, antenna system <NUM> may be equipped with simpler calibration circuitry to implement the calibration as would otherwise be available in conventional antenna systems configured for "any-time" on-field calibration, while achieving similar objectives. For instance, requisite tolerances in phase and amplitude alignment of signal paths throughout a certain time period of field operations with uninterrupted communications may be met by antenna system <NUM>, but conventional systems may only meet such tolerances with significantly more complex calibration circuitry.

Referring still to <FIG>, first and second antennas <NUM>-<NUM>, <NUM>-<NUM> may each be a planar phased array with N antenna elements <NUM>-<NUM> to <NUM>-N, although the number of elements may differ between the two antennas in other examples. First and second antennas <NUM>-<NUM>, <NUM>-<NUM> may each have a respective calibration element <NUM>-<NUM>, <NUM>-<NUM> located within their boundaries, typically in a central position as illustrated. Calibration elements <NUM>-<NUM>, <NUM>-<NUM> are each selectively connected to calibration circuit <NUM> through switch SW2, and may be radiating elements similar to antenna elements <NUM>. In other embodiments, only a single calibration element <NUM> is used for both antennas <NUM>-<NUM>, <NUM>-<NUM> and is mounted near the edge of one of the antennas <NUM> adjacent the other antenna <NUM>. In still other examples, each antenna <NUM>-<NUM>, <NUM>-<NUM> includes multiple calibration elements <NUM>, with each calibration element <NUM> allocated for calibration of a group of M antenna elements surrounding that calibration element within the respective antenna, where M<N.

During a normal communication operation with first satellite <NUM>, in the receive direction, a receive signal SR1 is received by each antenna <NUM>-<NUM> and <NUM>-<NUM>, which respectively derive and output "receive beam signals" SRB1 and SRB2 from the receive signal SR1. During a normal communication, "transmit beam signals" STB1 and STB2 (provided from transmitting cross-coupled switch <NUM>) are routed through T/R elements <NUM>-<NUM> and <NUM>-<NUM> to antennas <NUM>-<NUM> and <NUM>-<NUM>, respectively. Transmit/Receive (T/R) elements are elements for separating transmit signals from receive signals so as to permit both transmit and receive signals to share the same antennas and other circuit components / signal paths (e.g., the paths of a combiner / divider network within each antenna <NUM>-<NUM>, <NUM>-<NUM>). For example, T/R elements <NUM>-<NUM> and <NUM>-<NUM> may be T/R switches in the case of half-duplex communication, or diplexers in the case of full duplex communication with different frequency channels on transmit vs. receive. (Additional T/R elements may be included within each antenna <NUM>-<NUM>, <NUM>-<NUM>, discussed below. ) It is noted here that in other embodiments in which the antenna elements <NUM> are not shared between transmit and receive operations, T/R elements <NUM> can be omitted. Transmit signals STB1 and STB2 may be routed from ports p2 and p3 of T/R elements <NUM>-<NUM> and <NUM>-<NUM> to antenna array <NUM>. Concurrently or alternatingly, receive signals SRB1, SRB2 may be routed from antenna array <NUM> to ports p1 and p4, respectively, of T/R elements <NUM>-<NUM>, <NUM>-<NUM>. During a normal communication, receive signals SRB1 and SRB2 are further routed through couplers <NUM>-<NUM>, <NUM>-<NUM>; VDLs <NUM>-<NUM>, <NUM>-<NUM>; and switches SW3, SW4, respectively, to RCC switch <NUM>. RCC switch <NUM> cross-couples these signals to thereby output substantially equal amplitude output signals SOUT1 and SOUT2. Output signals SOUT1 and SOUT2 are routed to one or more demodulators, discussed later, depending on the state of antenna system <NUM>. It is noted here that in an alternative embodiment discussed later in connection with <FIG>, SPDT switches SW3 and SW4 are omitted, and inputs to SPMT switch SW1 originate from couplers within RCC switch <NUM> and TCC switch <NUM>. In this case, calibration paths on receive include paths within RCC switch <NUM>.

In the transmit direction, only one of the signals SIN1 or SIN2 may be input during a normal communication in which only one of transmit signals ST1 and ST2 is transmitted to first satellite <NUM> or second satellite <NUM>. In this case, transmit beam signals STB1 and STB2 are derived from the inputted one of the signals SIN1 and SIN2. Both signals SIN1 and SIN2 may be input during a portion of a handover period in which signals ST1 and ST2 are transmitted simultaneously to first and second satellites <NUM> and <NUM>, respectively.

During the normal communication operation with first satellite <NUM>, antenna system <NUM> may not process any signals transmitted from second satellite <NUM>, and vice versa during normal communication with second satellite <NUM>. For instance, first satellite <NUM> may transmit / receive over a first frequency channel(s) while second satellite <NUM> transmits / receives over a second frequency channel(s) that differs from the first frequency channel, and antenna system <NUM> may filter out signals outside the first frequency channel when communicating normally with first satellite <NUM>. In the same manner as that described above for the normal communication with first satellite <NUM>, antenna system <NUM> may, in a post-handover period, communicate normally with second satellite <NUM> by receiving / transmitting signals SR2 / ST2 transmitted from / to second satellite <NUM> using both antennas <NUM>-<NUM> and <NUM>-<NUM>, and not process signals from / to first satellite <NUM>. In this post-handover period, one of signals SIN1, SIN2, derived from a single modulator, may be inputted to antenna system <NUM>; and both signals SOUT1 and SOUT2 are outputted from antenna system <NUM> in an analogous manner as described above.

During the handover period, a coupled path output terminal of one or both couplers <NUM>-<NUM>, <NUM>-<NUM> is selectively connected to calibration circuit <NUM> through switch SW2, but the coupled signal through the coupled paths may not be used during normal communication operation. Briefly, in a receive path calibration according to an embodiment, one of 2N possible receive paths at a time is calibrated, and a plurality of such receive paths are calibrated sequentially. At any given time, a receive signal path is calibrated from a selected one of the antenna elements <NUM>-i (i = any one of <NUM> to N) to a reference point. In one example, if sufficient time is available during the handover period, all of N receive paths from antenna <NUM>-<NUM> to the reference point may be calibrated in one portion of the handover period. If further sufficient time is available, some or all of N receive paths from antenna <NUM>-<NUM> may be calibrated. An example calibration operation will be described below.

<FIG> schematically illustrates additional example circuitry and connection paths of antenna system <NUM>. In particular, example circuit elements coupled between transmitting cross-coupled (TCC) switch <NUM>, antenna array <NUM> and calibration circuit <NUM> are depicted. A first transmit signal path between TTC switch <NUM> and first antenna <NUM>-<NUM> includes a series connection of a SPDT switch SW3', a coupler <NUM>-<NUM>', and T/R element <NUM>-<NUM> (note that transmit signal STB1 is applied to port p2). A second transmit signal path between TTC switch <NUM> and second antenna <NUM>-<NUM> includes a series connection of a SPDT switch SW4', a coupler <NUM>-<NUM>', and T/R element <NUM>-<NUM> (where transmit signal STB2 is applied to port p3). Thus, in this example, the transmit signal paths between TTC switch <NUM> and antenna array <NUM> omit VDLs. In alternative configurations, one or more VDLs are included. It is noted here that SPMT switch SW1 has an input port h and four output ports f, g (seen in <FIG>), f' and g', and SPMT switch SW2 has an input port a and six output ports b, c, d, e (<FIG>), d' and e'. During calibration, transmit calibration paths differ from the receive calibration paths of <FIG> by selective routing through ports d' and e' of switch SW2 and ports f' and g' of switch SW1, as illustrated in <FIG>. In an alternative configuration to that shown in <FIG>, if it is desired to include transmit paths within TCC switch <NUM> in calibration measurements, SPDT switches SW3' and SW4' may be omitted, and transmit path calibration inputs to SPMT switch SW1 may originate from couplers within TCC switch <NUM>.

<FIG> schematically illustrates example additional transmit and receive circuitry of the antenna system of <FIG>. Antenna system <NUM> may further include first and second low noise blocks (LNBs) <NUM>-<NUM>, <NUM>-<NUM>, first and second demodulators <NUM>-<NUM>, <NUM>-<NUM>, first and second modulators <NUM>-<NUM>, <NUM>-<NUM>, and a signal processor <NUM>. First and second low noise blocks <NUM>-<NUM> and <NUM>-<NUM> each provide additional low noise amplification of receive signals.

During a portion of the handover period in which the cross-coupling of RCC switch <NUM> is intentionally broken (discussed later in connection with <FIG>), first and second demodulators <NUM>-<NUM> and <NUM>-<NUM> receive and demodulate signals SOUT1 and SOUT2, respectively. The demodulated outputs are provided to signal processor <NUM> for further processing. For instance, signal processor <NUM> may be connected to an I/O interface (not shown) and may output end-user data, e.g., audio / video data derived from the demodulated signals. During a soft handover as mentioned above, signal processor <NUM> may recover redundant information signals from signals SOUT1 and SOUT2 that originated from receive signals SR1, SR2 from the different satellites <NUM> and <NUM>. Signal processor <NUM> may output a single audio / video output data stream to the I/O interface based on the redundant information signals.

First and second modulators <NUM>-<NUM> and <NUM>-<NUM> receive input signals to be modulated from signal processor <NUM>. For instance, only one of the modulators <NUM>-<NUM> and <NUM>-2may be selected as a single modulator to output modulated signals which modulate a data stream received from signal processor <NUM>. During normal communication, the modulated signal is split by TCC switch 41to generate transmission signal ST1 or ST2 to satellite <NUM> or <NUM>, respectively, via antenna array <NUM>. During a portion of a handover period in which the cross-coupling of TCC switch <NUM> is broken, both first and second modulators <NUM>-<NUM> and <NUM>-<NUM> individually modulate signals for transmission to first satellite <NUM> and second satellite <NUM>, respectively, in an analogous manner to the handover operations described herein for the receiving direction.

<FIG> schematically depicts an exemplary antenna array <NUM> of antenna system <NUM>. Antenna array <NUM> may include side by side antennas <NUM>-<NUM> and <NUM>-<NUM>, each of which may be phased arrays including a plurality N of antenna elements <NUM>-<NUM> to <NUM>-N conformally arranged with respect to a common surface F, e.g., a top surface of a dielectric substrate. Each of antenna elements <NUM> may be a printed patch antenna on surface F. Alternatively, antenna elements <NUM> are dipoles, monopoles or other antenna types uniformly spaced from surface F. In any case, one or more calibration elements <NUM> may be similarly mounted or printed within the aperture perimeter of each antenna <NUM>-<NUM>, <NUM>-<NUM>. A convenient location for a calibration element <NUM> is a central location with respect to the group of antenna elements <NUM> designated to be calibrated by through use of that calibration element <NUM>. Each calibration element <NUM> is a radiating element that may be directly connected to calibration circuit <NUM> via a respective signal line <NUM>-<NUM> or <NUM>-<NUM> and a switching path within switch SW2. Each antenna <NUM>-<NUM> and <NUM>-<NUM> may further include an N:<NUM> combiner / divider <NUM> and N RF Integrated Circuits (RFICs) <NUM> respectively connected between the N antenna elements <NUM>-<NUM> to <NUM>-N and the N:<NUM> combiner / divider <NUM>. Each of the antenna elements <NUM> may be used for both transmit and receive operations. In other embodiments, the antenna elements <NUM> are not shared for transmit and receive operations. Instead, a plurality K < N of the antenna elements <NUM> in each antenna <NUM> are dedicated for transmitting signals from antenna system <NUM>, and a remaining plurality P = N-<NUM> antenna elements are dedicated for receiving signals transmitted from satellites to antenna system <NUM>. The K elements may be interspersed with the P antenna elements such that each of the K and P antenna elements may be defined by a common form factor and have the same effective aperture. Alternatively, a subarray of K transmitting antenna elements <NUM> may reside adjacent to a subarray of P receiving antenna elements <NUM>. In any of the above schemes, each antenna <NUM> may employ a single combiner / divider network <NUM> for both combining all of the receive signals into a combined receive beam signal and dividing an input transmit beam signal into N or K divided transmit signals that are output to N or K antenna elements <NUM>, as the case may be. In another example, a separate divider network is used for the transmit signals.

In the following discussion, it will be assumed for simplicity of explanation that each of the antenna elements <NUM> is used for both transmit and receive operations. To this end, on transmit, N:<NUM> combiner / divider <NUM> of antenna <NUM>-<NUM>, when operating as a divider, divides a "transmit beam signal" STB1 received at a port <NUM>-<NUM> of antenna <NUM>-<NUM> into N "transmit element signals" STE-<NUM> to STE-N. The latter signals are respectively adjusted by RFICs <NUM> and radiated by antenna elements <NUM>-<NUM> to <NUM>-N of antenna <NUM>-<NUM> to form at least part of a transmit antenna beam generated by antenna array <NUM>. Likewise, an input transmit beam signal STB2 at port <NUM>-<NUM> of antenna <NUM>-<NUM> is divided and transmitted by antenna <NUM>-<NUM> through its antenna elements <NUM>. In the receive direction, signals received by antenna elements <NUM>-<NUM> to <NUM>-N of antenna <NUM>-<NUM> are adjusted by respective RFICs <NUM> to generate "receive element signals" SRE-<NUM> to SRE-N that are applied to N respective input ports of N:<NUM> combiner/divider <NUM> operating as a combiner. These signals are combined to generate receive beam signal SRB1. Similar operations are performed by antenna <NUM>-<NUM> to generate receive beam signal SRB2.

<FIG> shows an example configuration of an RFIC <NUM> for transmitting / receiving signals to/from any given antenna element <NUM>-i. RFIC <NUM> may include receive circuitry ("receive chain") <NUM> and transmit circuitry ("transmit chain") <NUM>, each connected between T/R elements <NUM> and <NUM>, which may be T/R switches or diplexers. T/R element <NUM> has an input port at node <NUM> connected to antenna element <NUM>-i, a first output port connected to one end of receive chain <NUM> and a second output port connected to one end of transmit chain <NUM>. The other ends of receive chain <NUM> and transmit chain <NUM> are connected to respective first and second output ports of T/R element <NUM>, where an input port of T/R element <NUM> connects to one of the N output ports of N:<NUM> combiner/divider <NUM>. If T/R elements <NUM> and <NUM> are T/R switches, they may provide separate routes for transmit and receive signals during different time slots in a half-duplex operation. If different frequency channels are used on transmit and receive, T/R elements may be diplexers and prevent the transmit signals from interfering with the receive chain <NUM> by removing unwanted frequencies, and vice versa.

Receive chain <NUM> may include a series connection of an amplitude adjuster <NUM>, a phase shifter <NUM> and a bandpass filter (BPF) <NUM>. The order of the shown series connection may differ in other examples. Each amplitude adjuster <NUM> may be comprised of just a low noise amplifier (LNA) <NUM>, or an LNA <NUM> in series with a variable attenuator <NUM>. Transmit chain <NUM> may include a series connection of a phase shifter <NUM>, a BPF <NUM> and an amplitude adjuster <NUM>, where the latter may be comprised of just a power amplifier (PA) <NUM> or a PA <NUM> in series with a variable attenuator <NUM>. Each of amplitude adjusters <NUM>, <NUM>, phase shifters <NUM>, <NUM> and BPFs <NUM> within antenna array <NUM> may be individually controlled by a respective or grouped control signal generated by controller <NUM> and sent over a respective control line CL or a shared control line CL. A control signal sent to a phase shifter <NUM> or <NUM> sets the insertion phase of that phase shifter. A first control signal sent to an amplitude adjuster <NUM> or <NUM> may control a bias voltage for the LNA <NUM> or PA <NUM> therein and thereby control its gain, or the first control signal may carry the bias voltage itself. A first control signal to an LNA or PA within amplitude adjuster <NUM> or <NUM> may also set an ON-OFF state of that LNA of PA. A second control signal output to a variable attenuator <NUM> or <NUM> within amplitude adjuster <NUM> or <NUM> sets the variable attenuator's insertion loss. A control signal output to a BPF <NUM> or <NUM> may set a passband for that BPF.

For antenna array <NUM> to form a desired antenna beam in the transmit direction, the amplitudes and phases of transmit signals at feed points <NUM> of each antenna element <NUM> may generally need to be within a certain range of predetermined values. Thus, for each antenna <NUM>-<NUM>, <NUM>-<NUM>, the insertion phase and insertion loss (the latter often called path gain or forward voltage gain S21) of the signal paths between the port <NUM> (or other reference point within antenna system <NUM>) and a feed point <NUM> of each antenna element <NUM> should be within predefined tolerances of values determined when antenna system <NUM> was set-up during manufacture. Such tolerances should be met for the vast majority of the signal paths to generate a transmit antenna beam with requisite characteristics, e.g., beam pointing accuracy, beamwidth, antenna gain, sidelobes, etc. The same holds true for the receive paths. During the manufacturing process, a calibration procedure to ensure that such tolerances are met for a super majority of the signal paths (e.g., over <NUM>% or over <NUM>%) may have been performed using calibration circuit <NUM> and calibration elements <NUM>. Once antenna system <NUM> has been field-operated, however, the signal path characteristics may have changed due to a variety of factors, and calibration circuit <NUM> may be used to periodically re-calibrate the signal paths.

<FIG> schematically illustrates an alternative configuration for the antenna array <NUM> of antenna system <NUM>. Antenna array 21a includes first antenna 20a-<NUM> and second antenna 20a-<NUM>, each including a plurality of variable delay lines (VDLs), each for providing selectable variable delays, controlled by controller <NUM>, to groups of antenna elements <NUM> within each antenna. Thus, instead of including a single N:<NUM> combiner / divider, each antenna 20a includes a plurality (N/K) VDLs <NUM>-<NUM> or <NUM>-<NUM>, coupled between a plurality of K:<NUM> combiner / dividers <NUM> and an (N/K):<NUM> combiner / divider. Accordingly, signal paths associated with (N/K) groups of K antenna elements <NUM> may each be effectively phase shifted by a respective VDL <NUM>-<NUM> or <NUM>-<NUM> as part of a calibration procedure. For example, signals paths associated with a first group of K antenna elements <NUM>-<NUM> to <NUM>-K are delayed by a first VDL <NUM>-<NUM> controlled to have a first delay whereas signal paths associated with a second group of K antenna elements <NUM>-(N+<NUM>-K) to <NUM>-N are delayed by a different VDL <NUM>-<NUM> controlled to have a second delay.

<FIG> illustrates example receive path calibration loops and calibration circuitry in antenna system <NUM>. <FIG> illustrates example transmit path calibration loops and calibration circuitry in antenna system <NUM>. For example, referring collectively to <FIG>, in accordance with embodiments herein, during a portion of a handover period, antenna <NUM>-<NUM> communicates with a satellite while a calibration operation is performed on antenna <NUM>-<NUM>. As shown in <FIG>, to field-calibrate receive paths between individual antenna elements <NUM> of antenna <NUM>-<NUM> and reference point <NUM>-<NUM>, a reference path measurement may first be taken. Receive path measurements may thereafter be made with respect to the reference path measurement. In the reference path measurement, all the LNAs <NUM> of antenna <NUM>-<NUM> are first turned OFF to limit noise in the measurement. Switch SW2 is controlled to connect input port "a" with output port d, where port d connects to a coupling port of coupler <NUM>-<NUM>. A test signal TSOUT is then routed through a series path comprising switch SW2, coupler <NUM>-<NUM>, VDL <NUM>-<NUM>, switch SW3 (with its switch path controlled to close towards switch SW1), and switch SW1 (with its switch path closed between input port h and output port g as seen in <FIG>). Thus, a return signal TSIN at port p5 of calibration circuit <NUM> represents the fed back portion of test signal TSOUT in the reference path. Calibration circuit <NUM> may then measure the relative amplitude and phase of TSIN vs. TSOUT to arrive at a reference path measurement (e.g. insertion loss and insertion phase for the reference path). Measurements of receive paths including antenna elements <NUM> may then be initiated.

For instance, to measure a receive path between antenna element <NUM>-<NUM> and reference point <NUM>-<NUM>(under the assumption that the paths within T/R element <NUM>-<NUM> and coupler <NUM>-<NUM> remain constant throughout the measurement), the LNA <NUM> connected to antenna element <NUM>-<NUM> may be switched ON while the remaining LNAs of antenna <NUM>-<NUM> remain OFF. Concurrently, a control signal may set the switching path of switch SW2 to signal line <NUM>-<NUM> (path a-c is closed), while calibration circuit <NUM> outputs the same test signal TSOUT. Note that the frequency of test signal TSOUT may differ from the frequency or frequencies used for the current normal communication between antenna <NUM>-<NUM> and the satellite. Test signal TSOUT is routed to calibration element <NUM>-<NUM>, which radiates the same. The radiated signal is captured by antenna element <NUM>-<NUM> of antenna <NUM>-<NUM> and routed through the receive path of RFIC <NUM> connected to antenna element <NUM>-<NUM>, and then through N:<NUM> combiner / divider <NUM> of antenna <NUM>-<NUM> and the remaining receive path chain to port p5 of calibration circuit <NUM>, i.e., T/R element <NUM>-<NUM>, coupler <NUM>-<NUM>, VDL <NUM>-<NUM> and switches SW3 and SW1. Thus, the near field signal TSOUT received by antenna element <NUM>-<NUM> is fed back to calibration circuit <NUM> through switch SW1 as another instance of input signal TSIN. Calibration circuit <NUM> may then again measure the relative amplitudes and phases of TSIN vs. TSOUT to arrive at a test path measurement, and compare the test path measurement to the reference path measurement to arrive at a final receive path measurement.

Calibration circuit <NUM> may then report the measurement result to controller <NUM> on a data line <NUM>. Controller <NUM> may then compare the measurement result to an expected result, e.g., a result of the same measurement taken during manufacturing set up of antenna system <NUM> and stored in memory <NUM>. In some examples, controller <NUM> or a controller of calibration circuit <NUM> just compares relative phases and relative amplitudes of the measured results to one another, e.g., by using one of the results as a reference and comparing the other results to the reference. In either case, if the comparison indicates that amplitude and/or phase of the overall signal path has changed beyond a threshold, or is different from that of the reference result by more than a threshold, controller <NUM> may implement an adjustment. The adjustment may involve adjusting a phase offset of phase shifter <NUM> and/or the gain of LNA <NUM> and/or the loss of attenuator <NUM> within the receive path <NUM> connected to the antenna element <NUM>-i that was just measured. After the adjustment, the calibration test may be repeated to ensure that the adjustment was successful. This process may then be sequentially repeated for the remaining antenna elements (<NUM>-<NUM> through <NUM>-N if antenna element <NUM>-<NUM> was measured first) if time permits during the handover period. In another portion of the handover period, or in a next handover period, an analogous calibration process may be performed to calibrate the receive paths of antenna <NUM>-<NUM> while antenna <NUM>-<NUM> communicates with a satellite.

It is noted here that a phase alignment between first antenna <NUM>-<NUM> and second antenna <NUM>-<NUM> may be implemented by first comparing the reference path measurements in the calibrations of the two antennas to each other, and then reporting the results to controller <NUM>. Controller <NUM> can then make a delay adjustment in one or both of the VDLs <NUM>-<NUM>, <NUM>-<NUM> to align the phases of the receive paths leading to the two antennas <NUM>-<NUM>, <NUM>-<NUM>. A delay adjustment to one or more VDLs <NUM> in the configuration of <FIG> may also be made after measurements are made in signal paths connected to different VDLs <NUM>. In another example sequence, VDLs <NUM> in any of the above configurations may be calibrated prior to a calibration of the phase shifters and/or amplifiers in the RFICs <NUM>.

<FIG> illustrates that an analogous calibration procedure may be performed to calibrate transmit paths within each antenna <NUM>-<NUM> and <NUM>-<NUM>. In a transmit path calibration for antenna <NUM>-<NUM>, for instance, all the power amplifiers <NUM> of antenna <NUM>-<NUM> may be initially turned OFF so that antenna <NUM>-<NUM> is deactivated for communication with any satellite. A reference path measurement may be made by outputting a test signal TSOUT from port p5 of calibration circuit <NUM> while the signal paths of switches SW1 and SW3' are controlled to route signal TSOUT to coupler <NUM>-<NUM>', and the signal path of switch SW2 is connected from port a to port d'. This allows the test signal TSOUT to propagate through back to port p6 of calibration circuit <NUM> as a return signal TSIN. Signals TSIN and TSOUT are then compared to obtain a reference path "S21" S-parameter measurement (insertion loss and phase) measurement. Transmit path measurements to the antenna elements <NUM> may then be initiated by turning on one PA <NUM> at a time. To measure a transmit path to antenna element <NUM>-<NUM>, for example, test signal TSOUT is routed to antenna element <NUM>-<NUM> through the transmit path chain from port p5 through the connected RFIC <NUM>. Antenna element <NUM>-<NUM> radiates the test signal, which is received by calibration element <NUM>-<NUM> and routed back to calibration circuit <NUM> as a return signal TSIN. TSIN is then compared to TSOUT in an analogous manner as was done for the reference path measurement to arrive at a test path measurement, which is compared to the reference path measurement to arrive at a transmit path measurement. The measurement result may be sent to controller <NUM>, which may then make analogous adjustments to amplitude and phase of the transmit path elements as was done for the receive path case, thereby completing the transmit path calibration. The process may then be repeated for antenna elements <NUM>-<NUM> to <NUM>-N. Although no VDL is shown in <FIG>, it is understood that time shifting (provided by means of VDLs) may be used on transmit in addition to phase shifting (provided by means of RFIC phase shifters <NUM>.

<FIG> is a block diagram of a calibration circuit 50a, which is an example of calibration circuit <NUM> of antenna system <NUM>. Calibration circuit 50a includes SPDT switches SW7 and SW8, an RF source <NUM>, a controller <NUM>, an RF receiver <NUM> and an I/O interface <NUM>. During a receive path calibration measurement as described above, RF source <NUM> generates test signal TSOUT while switch SW7 is controlled by controller <NUM> (which in turn receives commands from controller <NUM> for the calibration procedure) to set its switching state to position "A", thereby routing signal TSOUT to port p6. Switch SW8 is likewise controlled to its position "A" to receive the return signal TSIN at port p5 and route it to receiver <NUM>. Controller <NUM> and receiver <NUM> may together or individually perform the comparisons noted above between signals TSOUT and TSIN and between the reference path and test path signals and send the measurement results to controller <NUM> on data line <NUM> through I/O interface <NUM>. During a transmit path calibration measurement as described above, the same or similar operations are performed with the switch positions of switches SW7 and SW8 each switched to position "B". In this manner, the test signal TSOUT is routed to port p5 while the return signal TSIN is received at port p6.

<FIG> schematically illustrates another example of a calibration circuit within the antenna system. An advantage of this architecture is that it may reduce or minimize low frequency noise. Calibration circuit 50b includes an RF source 51a, an RF receiver 53a and a controller 55a, and may further include switches SW7, SW8 and an I/O interface <NUM> (both not shown in <FIG>) controlled in the same manner described above. RF source <NUM> includes a first local oscillator (LO) <NUM>, an RF power divider <NUM>, an upconverter <NUM> and a second local oscillator <NUM>. In an example, second LO <NUM> is a lower noise generating LO than first LO <NUM>. Receiver 53a includes an RF power divider <NUM>, a peak detector <NUM>, a downconverter <NUM> and a phase detector <NUM>. Controller 55a includes first and second analog to digital converters (ADCs) <NUM>-<NUM>, <NUM>-<NUM> and a digital signal analyzer <NUM>.

To implement a receive path or a transmit path calibration measurement, first LO <NUM> generates a relatively low frequency RF signal, which is split by divider <NUM> into first and second divided LO signals. The first divided LO signal is upconverted by upconverter <NUM> using a second LO signal generated by second LO <NUM>, and the upconverted signal is output as test signal TSOUT. The return signal TSIN is divided by divider <NUM> into a first divided return signal which is applied to peak detector <NUM>, and a second divided return signal applied to downconverter <NUM>. Peak detector <NUM> detects peak amplitudes of signal the first divided return signal and outputs an envelope signal to ADC <NUM>-<NUM>, which generates digital samples of the envelope signal. The digital samples are analyzed by analyzer <NUM>, which generates therefrom first and second amplitude result signals A1, A2. Result signal A1 represents a mean µ of the samples whereas result signal A2 represents a standard deviation ∂<NUM> of the samples, which is indicative of amplitude noise. Result signals A1 and A2 are output to controller <NUM> over a data line <NUM>. Controller <NUM> uses the result signals to make a determination on adjusting amplitude in the associated receive or transmit paths that were measured.

Downconverter <NUM> receives and downconverts the second divided return signal using a first reference signal REF1, which is the first divided LO signal output from divider <NUM>. The downconverted output signal of downconverter <NUM> is applied to phase detector <NUM> which detects the signal's phase using a second reference signal REF2 (the second LO signal). Phase detector <NUM> outputs a phase signal indicative of the detected phase, and the phase signal is digitized by ADC <NUM>-<NUM> to provide a stream of phase samples. The phase samples are analyzed by analyzer <NUM>, which generates therefrom a first phase result signal representing a mean µ of the phase samples and a second phase result signal H2 representing a standard deviation (SD) ∂<NUM> of the phase samples. These result signals H1, H2 are likewise output to controller <NUM> over a data line <NUM>. Controller <NUM> uses the result signals to make a determination for adjusting phase in the associated receive or transmit paths that were measured.

<FIG> schematically illustrates a further example of a calibration circuit within the antenna system. An advantage of this architecture is that it may reduce or minimize both cost and space occupation. Calibration circuit 50c includes a controller 55b, an RF source 51b and an RF receiver 53b. Controller 55b includes first and second ADCs <NUM>-<NUM>, <NUM>-<NUM> and an analyzer <NUM>. RF source 51b includes a single LO <NUM> and a divider <NUM> that divides an LO signal from LO <NUM> into a first divided output signal as test signal TSOUT, and a second divided LO signal. Receiver 53b includes a hybrid coupler <NUM> and an In-phase / Quadrature phase (I/Q) demodulator <NUM>. Hybrid coupler <NUM> divides the return signal TSIN into first and second output signals offset in phase from each other by <NUM>°. I/Q demodulator demodulates these output signals into I and Q output signals. ADC <NUM>-<NUM> samples the I signal while ADC <NUM>-<NUM> samples Q signal. Analyzer <NUM> analyzes the I and Q samples to generate therefrom third and fourth amplitude result signals A3, A4 representing mean and SD, respectively, of the insertion loss (S21 amplitude) in the measured path. Analyzer <NUM> further analyzes the I and Q samples to generate therefrom phase result signals H3, H4 representing mean and SD, respectively, of the insertion phase in the measured path. These result signals A3, A4, H3, H4 are output to controller <NUM> over data lines <NUM>. Controller <NUM> uses the result signals to make determinations for adjusting amplitude and phase in the associated receive or transmit paths that were measured.

<FIG> is a flowchart of an example method <NUM> of operating and calibrating the antenna system <NUM> in the field. <FIG> is a timing diagram illustrating exemplary timing of beam forming and calibration operations during method <NUM>. <FIG> illustrates example first and second beams that may be formed by antenna system <NUM> during a first portion of a handover period designated by method <NUM>. <FIG> shows example third and fourth beams formed by antenna system <NUM> during and after a second portion of the handover period, respectively. Only the main beams (and not the sidelobes) are shown in <FIG> for simplicity, and while the antenna patterns thereof are illustrated in a single plane, the beams may be pencil beams with approximately equal characteristics in all planes.

Referring generally to <FIG>, with method <NUM>, prior to the handover period, a first beam B1 is formed (S502) for normal communication with first satellite <NUM> through antenna array <NUM>. In this state, which occurs prior to a time t0 of <FIG>, controller <NUM> may turn on all the amplifiers within antennas <NUM>-<NUM> and <NUM>-<NUM> of antenna array <NUM> such that both antennas are fully activated for the communication. Thus, antenna array <NUM> has an effective aperture with 2N antenna elements spanning a two-dimensional plane combining the N antenna elements of each antenna <NUM>-<NUM>, <NUM>-<NUM>, and a first pencil beam B1 is thereby formed at a high gain G1. The phases of phase shifters <NUM> are controlled to produce either a uniform phase, or a phase gradient, if needed, across the effective aperture of antenna array <NUM>. In this manner, the peak of first beam B1 points at a scan angle θ<NUM> as seen in <FIG>, towards satellite <NUM>. The scan angle θ<NUM> is an angle with respect to a predetermined reference axis, e.g., a normal to the planar surface F of antenna array <NUM>.

When a handover for handing over the communication with antenna system <NUM> from first satellite <NUM> to second satellite <NUM> is imminent, a handover period beginning at time t0 is set up by controller <NUM> or an external system. During a first portion of the handover period (operations S504) from time t0 to time t1, a second beam B2 is formed for communication with first satellite <NUM> using first antenna <NUM>-<NUM> without any contribution from second antenna <NUM>-<NUM>. To form second beam B2, controller <NUM> deactivates second antenna <NUM>-<NUM> for external communication by turning off all its amplifiers (except one at a time may be turned on during a calibration procedure as explained earlier). With antenna <NUM>-<NUM> thus deactivated, a calibration procedure is performed between times t0 and t1 using calibration circuit <NUM> as described above. Since second beam B2 is formed with just the antenna elements of antenna <NUM>-<NUM>, the effective aperture of antenna array <NUM> is reduced by half, and the resultant beam B2 is wider than beam B2 and has a lower gain G2.

During a second portion of the handover period (operations S506) from time t1 to time t2, beam B2 continues to be formed by antenna <NUM>-<NUM> for communication with first satellite <NUM>, while second antenna <NUM>-<NUM> is re-activated for communication with second satellite <NUM> to initiate a seamless handover of the communication from first satellite <NUM> to second satellite <NUM>. When second antenna <NUM>-<NUM> is re-activated, it forms a third beam B3 which has approximately the same gain G2 as the second beam B2. Thus, during this time period, antennas <NUM>-<NUM> and <NUM>-<NUM> are operated independently and transmit / receive independent signals. For instance, antenna <NUM>-<NUM> communicates with second satellite <NUM> with signals at different frequencies and/or protocols than those used by satellite <NUM>, whereby interference in each communication is minimized. If second satellite <NUM> is located in a different direction with respect to the reference axis of antenna array <NUM>, third beam B3 is formed pointing in the different direction of second satellite <NUM>. This scenario is depicted in <FIG>, which shows the peak of third beam B3 pointing at a scan angle θ<NUM>, which is offset from angle θ<NUM> and may correspond to a line of sight direction to second satellite <NUM>. To re-point third beam B3 to scan angle θ<NUM>, controller <NUM> applies control signals to phase shifters <NUM> of antenna <NUM>-<NUM> to set their phases so that a phase gradient is generated across its effective aperture. Additionally, amplitudes of the signal paths connected to each antenna element <NUM> may be individually controlled to fine tune the beam characteristics, by controlling the gains of the LNAs and PAs and the losses of the variable attenuators. The process of setting phases and adjusting amplitudes in this manner may be referred to as adjusting the beam weights of the antenna elements <NUM>.

If sufficient time is still available in the handover period according to predefined operating requirements, a third portion of the handover period, between time t2 and time t3 in <FIG>, may be allocated for operations S508. During this period, first antenna <NUM>-<NUM> is deactivated for any external communication by turning OFF all its amplifiers (except one or more amplifiers connected to an antenna element <NUM> to be initially calibrated). This deactivation terminates the communication with first satellite <NUM>. Meanwhile, second antenna <NUM>-<NUM> continues to communicate with second satellite <NUM>. While first antenna <NUM>-<NUM> is deactivated, an analogous calibration procedure as was used to calibrate second antenna <NUM>-<NUM> during the first portion of the handover period is used to calibrate first antenna <NUM>-<NUM>.

On the other hand, if insufficient time remains in the handover period for completing calibration of all signal paths to all of the antenna elements <NUM> within antenna array <NUM>, the calibration of the remaining antenna elements <NUM> may be performed during the next handover period.

After the handover period (subsequent to time t3 in <FIG>), a fourth beam B4 is formed for the communication with second satellite <NUM> using both first and second antennas <NUM>-<NUM>, <NUM>-<NUM> (S510). To form fourth beam B4, the phase shifters <NUM> of antenna <NUM>-<NUM> may be controlled to form the same phase gradient as for second antenna <NUM>-<NUM>, whereby fourth beam B4 is formed as shown in <FIG> to point at angle θ<NUM> and to have about the same gain G1 as the first beam B1.

<FIG> illustrates a functional block diagram of a receive cross-coupled (RCC) switch 40a, shown in relation to other components of antenna system <NUM>. RCC switch 40a is an embodiment of RCC switch <NUM> described above. <FIG> also illustrates a state of antenna system <NUM> during a normal communication with first satellite <NUM>, e.g., prior to time t0 of <FIG>. Cross-coupled switch 40a includes first, second, third and fourth 3dB hybrid couplers <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>; single pole, double throw (SPDT) switches SW11, SW12, SW13 and SW14; cross-coupled signal lines <NUM> and <NUM>; and straight-path signal lines <NUM> and <NUM>, a plurality of terminations R connected to various ports of the couplers <NUM> and switches SW11-SW14. Other shown exemplary components of antenna system <NUM> include antenna array <NUM>, calibration chains (CC) <NUM>-<NUM> and <NUM>-<NUM>; first and second low noise blocks (LNBs) <NUM>-<NUM>, <NUM>-<NUM>; first and second demodulators <NUM>-<NUM>, <NUM>-<NUM>; and signal processor <NUM>. The switching states of switches SW11-SW14 are controlled by controller <NUM> (not shown in <FIG>) via control signals on control lines CL. Calibration chain <NUM>-<NUM> includes T/R element <NUM>-<NUM>, coupler <NUM>-<NUM>, VDL <NUM>-<NUM> and switch SW3 as shown in <FIG>. CC <NUM>-<NUM> includes T/R element <NUM>-<NUM>, coupler <NUM>-<NUM>, VDL <NUM>-<NUM> and switch SW4.

For each 3dB hybrid coupler <NUM>, a signal applied to any port a, b, c or d is equally divided but quadrature phase shifted among the opposite facing output ports. Thus, a signal applied to port "a" is equally divided into a signal at port b and a signal at port c that lags the signal at port b by <NUM>°, but reflected power at ports b and c mostly appears at port d, and is terminated there is a termination R is connected. Other types of 3dB couplers, such as hybrid ring ("rat race") couplers or Wilkinson power dividers, may be substituted in other embodiments.

During the normal communication with satellite <NUM>, all the amplifiers of first and second antennas <NUM>-<NUM>, <NUM>-<NUM> may be turned ON, and switching states of switches SW11-SW14 are controlled to cross-couple first and second receive beam signals SRB1 and SRB2 output by first and second antennas <NUM>-<NUM> and <NUM>-<NUM>, respectively. By phase balancing the two halves of RCC switch 40a and the two signal paths connecting first and second antennas <NUM>-<NUM>, <NUM>-<NUM> to RCC switch 40a, substantially of the receive signal energy appears as equal amplitude, phase balanced signals SOUT1 and SOUT2. The electrical lengths of signal lines <NUM>, <NUM>, <NUM> and <NUM>, as well as the electrical lengths in the couplers <NUM>-<NUM> to <NUM>-<NUM> and switches SW11-SW14 may all have been precisely calibrated during the manufacture and initial set-up of antenna system <NUM>. For instance, a first electrical length of a signal path from port "a" of coupler <NUM>-<NUM> to port "a" of coupler <NUM>-<NUM> may have been set equal to a second electrical length of a signal path from port "a" of coupler <NUM>-<NUM> to port "a" of coupler <NUM>-<NUM>. However, the electrical length from port a of coupler <NUM>-<NUM> to port d of coupler <NUM>-<NUM> may have been set to "phase lead" the first electrical length by <NUM>°. In this manner, the signal energy of two input signals, kSRB1 and kSRB2 (where k ≈ <NUM>) appearing at ports "a" and d of coupler <NUM>-<NUM> may constructively add, such that substantially all the signal energy of these signals appears at port c of coupler <NUM>-<NUM> as signal SOUT1. An analogous constructive addition of signal energy is applicable at coupler <NUM>-<NUM> to generate output signal SOUT2. Accordingly, beam B1 is formed for normal communication with first satellite <NUM>. An analogous configuration for transmit cross-coupler <NUM> can be implemented to generate substantially the same antenna pattern for beam B1 on transmit.

<FIG> illustrates an operation state of antenna system <NUM> with receive cross-coupled switch 40a during the above-described first portion of the handover period between times t0 and t1 of <FIG>. In this state, the second antenna <NUM>-<NUM> is deactivated by turning OFF all its amplifiers (LNAs and PAs). (Such turning OFF of the amplifiers may have been implemented in a ramping down fashion. ) Hence, no satellite signal is transmitted / received on lines <NUM> and <NUM>. Accordingly, first antenna <NUM>-<NUM> generates second beam B2 without any contribution from first antenna <NUM>-<NUM>. Demodulator <NUM>-<NUM> demodulates output signal SOUT1 to provide a demodulated signal SOUT1'. The two halves of RCC switch 40a may remain cross-coupled through signal lines <NUM> and <NUM> by maintaining the previous switching states of switches SW11-SW14 as illustrated.

<FIG> illustrates an operation state of antenna system <NUM> with RCC switch 40a during the first portion of the handover period, subsequent to the time of the operational state of <FIG>. In the state of <FIG>, all the amplifiers within second antenna <NUM>-<NUM> remain turned OFF and the cross-coupling within RCC switch 40a is broken by swapping the switching positions in each of switches SW11-SW14, as illustrated. With the cross-coupling broken, second antenna <NUM>-<NUM> may be calibrated in the manner described above while first antenna <NUM>-<NUM> continues to communicate with first satellite <NUM> by forming second beam B2.

<FIG> illustrates an operation state of antenna system <NUM> with RCC switch 40a during the second portion of a handover period, between times t1 and t2 discussed above. In this state, the amplifiers within second antenna <NUM>-<NUM> are turned back ON such that second antenna <NUM>-<NUM> is re-activated. In addition, controller <NUM> adjusts the phases of the phase shifters within second antenna <NUM>-<NUM> to cause it to form third beam B3 with its main lobe pointing at satellite <NUM>. Meanwhile, the cross-coupling in RCC switch 40a remains broken, such that first and second antennas <NUM>-<NUM> and <NUM>-<NUM> individually communicate with first and second satellites <NUM> and <NUM>, respectively. Accordingly, first demodulator <NUM>-<NUM> outputs a first demodulated signal SOUT1' to signal processor <NUM>, representing a demodulated receive signal from satellite <NUM>, and second demodulator <NUM>-<NUM> outputs a second demodulated signal SOUT2' representing a demodulated receive signal from satellite <NUM>.

<FIG> illustrates an operation state of antenna system <NUM> with RCC switch 40a during the third portion of the handover period, between times t2 and t3 of <FIG>. In this state, first antenna <NUM>-<NUM> is deactivated by having its amplifiers turned OFF, thereby ceasing the communication with first satellite <NUM>. Meanwhile, the cross-coupling state of RCC switch 40a remains disconnected and second antenna <NUM>-<NUM> continues to form beam B3 for communication with second satellite <NUM>. As a result, the demodulated output signal to signal processor <NUM> is just signal SOUT2' output by second demodulator <NUM>-<NUM>, which is derived from the receive signal SR2 of the second satellite <NUM>. Thus, the handover of the communication session with antenna system <NUM> is effectively handed over to second satellite <NUM>. In this state, the above-described calibration of first antenna <NUM>-<NUM> may be performed, if time is still available in a requisite handover period.

<FIG> illustrates an operation state of antenna system <NUM> with RCC switch 40a during the third portion of the handover period, following the calibration of first antenna <NUM>-<NUM> as in <FIG>. <FIG> shows that the cross-coupling of RCC switch 40a is reconnected by changing the switching states of switches SW11-SW14. This occurs while first antenna <NUM>-<NUM> remains deactivated and second antenna is in communication with satellite <NUM> by forming beam B3.

<FIG> illustrates an exemplary operational state of antenna system <NUM> with RCC switch 40a just after the handover period. In this state, first antenna <NUM>-<NUM> is reactivated and its phase shifters <NUM> have been adjusted to continue the phase gradient of second antenna <NUM>-<NUM> across the effective aperture of first antenna <NUM>-<NUM>, such that the resulting beam B4 continues to point towards second satellite <NUM> and a normal communication operation is again performed.

<FIG> schematically illustrates an alternative embodiment of an antenna system including field-calibration circuitry. Antenna system 10a differs from antenna system <NUM> by providing means for including the cross-coupled switches in the calibration paths. Thus, antenna system 10a omits SPDT switches SW3, SW3', SW4 and SW4' of <FIG> (and thus calibration chains <NUM>-<NUM> and <NUM>-<NUM> differ from chains <NUM> accordingly). Receiving cross-coupled (RCC) switch 40b differs from RCC switch 40a by connecting ports b of couplers <NUM>-<NUM> and <NUM>-<NUM> to different input ports of switch SW1, and omitting the terminations. An analogous connection is made in a transmitting cross-coupled switch (not shown). Accordingly, calibration paths on receive include paths within RCC switch 40b and calibration paths on transmit would include analogous calibration paths in a transmitting cross-coupled switch.

Accordingly, antenna system 10a includes single pole multi-throw (SPMT) switch SW1 having an output port coupled to the input port p5 of calibration circuit <NUM>, and having a plurality of input ports. An output port of coupler <NUM>-<NUM> is coupled to a first input port of SPMT switch SW1, and an output port of the coupler <NUM>-<NUM> is coupled to a second input port of the switch SW1; and controller <NUM> controls the switch SW1 to close a first switching path between the first input port and the output port thereof to calibrate the first antenna <NUM>-<NUM>, and to close a second switching path between the first input port and the output port thereof to calibrate the second antenna <NUM>-<NUM> on receive. Analogous operations are implemented for calibrating the transmit paths.

As used herein, a "controller" is a device that may include a processor and a memory. A controller may be embodied with processing circuitry, which may be in the form of a general or specific-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof to perform its operations described herein. For instance, controller <NUM> or controller <NUM> may read and execute instructions read from a memory therein to perform its operations. The memory can be any suitable non-transitory computer-readable storage medium. The term "processor" as used herein is intended to include any processing device, such as, for example, one that includes a central processing unit (CPU) and/or other processing circuitry. Moreover, a "processor" includes computational hardware and may refer to a multi-core processor that contains multiple processing cores in a computing device. Various elements associated with a processing device may be shared by other processing devices.

Claim 1:
A method (<NUM>) of calibrating an antenna system (<NUM>) comprising an antenna array (<NUM>) of at least first and second antennas (<NUM>-<NUM>, <NUM>-<NUM>), the method comprising:
prior to a handover period in which communication with the antenna system is handed over from a first communication system (<NUM>) to a second communication system (<NUM>), forming (<NUM>) a first beam for the communication with the first communication system through the first and second antennas;
during a first portion of the handover period: forming (<NUM>) a second beam for the communication with the first communication system using the first antenna while deactivating the second antenna for external communication, and calibrating the second antenna while the second antenna is deactivated for external communication;
during a second portion of the handover period: activating (<NUM>) the second antenna for a handed over communication with the second communication system by forming a third beam using the second antenna while the first antenna maintains its communication with the first communication system via the second beam; and
after the handover period, forming (<NUM>) a fourth beam for the communication with the second communication system through both the first and second antennas.