Configurable antenna interface

Techniques for interfacing a set of active elements with an antenna array. In one exemplary embodiment, the active elements include a plurality of signal paths, each signal path including a mixer coupled to a local oscillator (LO) signal having an adjustable phase. When the active elements are to be interfaced with an unbalanced antenna, the phase of the LO signal for each signal path coupled to the unbalanced antenna may be adjusted independently of the other signal paths. When the active elements are to be interfaced with a balanced antenna, the phases of the LO signals for the two signal paths coupled to the balanced antenna are adjusted to differ by π radians from each other. The techniques may be applied in either receiver or transmitter applications to provide a flexible interface between an antenna array and an integrated circuit (IC) without the use of baluns.

BACKGROUND

The disclosure relates to the design of systems utilizing antenna arrays, and more particularly, to an interface between an antenna array and a transceiver.

Antenna arrays find application in, e.g., communications systems at radio-frequency (RF) and millimeter-wave frequencies, as well as radar systems. The multiple antenna elements provided in an array are used to compensate for communications link losses and to mitigate the effects of multipath propagation. Typically, an antenna array is coupled to a device, e.g., a radio transceiver integrated circuit (IC), containing active elements for processing the signals transmitted and received over the antenna array.

The physical interface between the antenna array and the active elements may be configured based on the type of antenna elements in the array. For example, a dipole antenna element is typically a balanced structure that includes two differential terminals. A patch antenna, on the other hand, may be an unbalanced structure that includes only one terminal referenced to a ground plane.

To properly connect the antenna elements to the active elements, a balun may be required to perform balanced-to-unbalanced or unbalanced-to-balanced transformation. The balun is usually either placed at the antenna feed, prior to interfacing with the active elements, or directly implemented as an active element. A balun generally introduces undesirable insertion losses into the system. Moreover, a balun implemented as an active element may consume significant power, and its bandwidth is limited by the cut-off frequency of the active devices.

It would be desirable to provide techniques for interfacing an antenna array with active elements that can readily accommodate either balanced or unbalanced antenna structures, without additional insertion losses or significant area requirements.

DETAILED DESCRIPTION

FIG. 1illustrates a prior art implementation of a receiver100for processing signals received over an antenna array110. InFIG. 1, the output signals of the antenna array110are coupled to a signal conditioning block120. The signal conditioning block120may perform functions such as filtering and amplification on the signals from the antenna array110. The output signals of the signal conditioning block120are coupled to a frequency conversion block130which may perform frequency conversion, e.g., frequency down-conversion of the conditioned signals. The output signals of the frequency conversion may subsequently be digitized by an analog-to-digital converter (ADC)140, and further processed by a processor150.

One of ordinary skill in the art will appreciate that the architecture of the receiver100may be adopted in receivers designed for various applications, e.g., radio-frequency (RF) communications, millimeter-wave communications, and/or radar.

NoteFIG. 1illustrates an example of a prior art system wherein the techniques of the present disclosure may be applied, and is not intended to limit the scope of the present disclosure in any way. The techniques disclosed herein may be applied to systems that omit and/or add to the functional blocks depicted inFIG. 1. For example, the ADC140may be omitted in some implementations, and processing done by the processor150may be performed directly in the analog domain.

FIG. 2illustrates a prior art interface between an antenna array having unbalanced antenna elements and a radio transceiver291in a communications system200.

InFIG. 2, an antenna array includes a plurality N of unbalanced antenna elements201.1through201.N. Each unbalanced antenna element has a single-ended terminal that functions as both the input and output of the antenna element. An example of a type of unbalanced antenna element is a patch antenna. One of ordinary skill in the art will appreciate that in the system200, a ground plane (not shown) is present that is common to all elements shown. The single terminal of the unbalanced antenna element may be referred to such a ground plane.

Antenna elements201.1through201.N are coupled to the “A” terminals of corresponding balun elements210.1through210.N. A balun element performs an unbalanced-to-balanced transformation from the unbalanced signal at its “A” terminal to a pair of balanced signals at its “+” and “−” terminals, i.e., a single-ended to differential transformation. The transformation is performed such that the difference between the unbalanced signal at the “A” terminal of the balun and a common mode plane is preserved as the difference between the signals at the “+” and “−” terminals of the balun. The “B” terminal in the balun may be coupled, e.g., to the common mode voltage, or directly to the ground plane (e.g., zero common mode voltage).

Each signal emerging from the balun is further coupled to a gain element221.nor222.n, wherein n is an arbitrary index from 1 to N. The signals from the “+” terminals of the baluns are coupled to corresponding gain elements221.1through221.N, while the signals from the “−” terminals of the baluns are coupled to corresponding gain elements222.1through222.N. A gain element may be, e.g., a low-noise amplifier designed to amplify a signal while introducing minimal additional noise. The gain element may also implement additional functions not explicitly shown or described, e.g., further filtering of the input signal prior to or subsequent to amplification, which functions will be clear to one of ordinary skill in the art.

Each signal emerging from a gain element is further coupled to a mixer element231.nor232.n, with the output signals from gain elements221.1through221.N being coupled to corresponding mixer elements231.1through231.N, and the signals from gain elements222.1through222.N being coupled to corresponding mixer elements232.1through232.N. The mixer elements perform frequency conversion, e.g., frequency down-conversion on the outputs of the gain elements to translate the millimeter-wavelength or radio frequency (RF) signals to an intermediate frequency (IF) or baseband frequency for further processing. The frequency conversion at each mixer is accomplished by mixing with a corresponding local oscillator (LO) signal, with the input signals to mixers231.1through231.N and232.1through232.N being mixed with corresponding LO signals generated by LO generators241.1through241.N. The outputs of the mixers231.1through231.N and232.1through232.N are combined by a combiner250.

One of ordinary skill in the art will appreciate that in a prior art technique known as “beamforming,” the phases Φ1through ΦNof the LO signals generated by the LO generators241.1through241.N may be individually adjusted to optimally combine the mixer outputs at the combiner250. For example, the signals corresponding to the antenna element201.1may be multiplied by an LO signal having a first phase Φ1, and the signals derived from the antenna element201.2may be mixed with an LO signal having a second phase Φ2, with Φ1and Φ2having a difference that accounts for, e.g., a phase difference between the signals received by the two antenna elements. Generalizations of beamforming to an arbitrary plurality N of antenna elements are well-known to one of ordinary skill in the art, and will not be further described herein.

In one implementation, the elements provided in the RF transceiver291may be denoted as “active” elements, and the RF transceiver291may be, e.g., an integrated circuit (IC). InFIG. 2, the balun elements210.1through210.N are shown as passive elements provided separately from the antenna elements and the active elements. Alternatively, the balun elements210.1through210.N may also be active elements provided on the IC.

FIG. 3illustrates a prior art interface between an antenna array having balanced antenna elements and a radio transceiver391in a communications system300.

InFIG. 3, an antenna array includes a plurality N of balanced antenna elements301.1through301.N. Each balanced antenna element has two differential terminals labeled “a” and “b”, with the signal input and output of the antenna element provided as the difference between the signals at the differential terminals. An example of a type of balanced antenna element is a dipole antenna.

InFIG. 3, the “a” terminals of the balanced antenna elements301.1through301.N are coupled to the “+” terminals of corresponding balun elements310.1through310.N, while the “b” terminals are coupled to the “−” terminals of those balun elements. Each balun element converts the difference between its “+” and “−” terminals into an unbalanced signal made available at its “A” terminal, wherein the unbalanced common mode signal may be referenced to, e.g., the ground plane at the B terminal. In this manner, the balun element performs a balanced-to-unbalanced transformation, i.e., a differential-to-single-ended transformation.

The unbalanced signals emerging from the “A” terminals of balun elements310.1through310.N are further coupled to corresponding gain elements320.1through320.N, and followed by corresponding mixer elements330.1through330.N. Mixer elements330.1through330.N perform mixing with corresponding LO signals generated by LO generators340.1through340.N. The outputs of the mixers330.1through330.N are combined by a combiner350.

It will be appreciated that in an implementation of beamforming using the system300, the phases Φ1through ΦNof the LO signals may be adjusted independently to optimally combine the mixer outputs at the combiner350.

It will be appreciated from the above descriptions ofFIGS. 2 and 3that the connectivity between the antenna elements and the active elements, i.e., through the balun elements210.1through210.N or310.1through310.N shown, depends on whether the particular antenna elements of the antenna array are unbalanced or balanced. Thus, a radio transceiver architecture that is designed to support one type of antenna element may not be flexible enough to support a different type of antenna element. Furthermore, one of ordinary skill in the art will appreciate that implementing the balun elements shown may undesirably introduce losses into the system, and that implementing the balun elements as active elements in the radio transceiver291or391may additionally consume significant die area in an IC. It would be desirable to provide techniques to interface the antenna elements with the active elements in a readily configurable manner that can accommodate either balanced or unbalanced antenna elements. It would be further desirable to minimize insertion losses and die area consumed using such techniques.

FIG. 4illustrates an exemplary embodiment of an interface between multiple unbalanced antenna elements and active elements491in a receiver400for a communications system.

InFIG. 4, unbalanced antenna elements201.1through201.N are coupled to a set of active elements491. The active elements491of the receiver400include gain elements420.1through420.N, followed by corresponding mixer elements430.1through430.N that mix the outputs of the gain elements with corresponding LO signals generated by LO generators440.1through440.N. The outputs of the mixers430.1through430.N are combined by a combiner450. Each combination of a gain element420.n, mixer element430.n, and LO generator440.nmakes up a signal path405.n, with the receiver400including N distinct signal paths405.1through405.N.

InFIG. 4, the phase Φnof each LO signal generated by LO generators440.1through440.N may be adjusted independently of the phase of the other LO signals. In an exemplary embodiment, the phase Φnof each LO signal may be digitally programmed into the corresponding LO generator. For example, each of the LO generators440.1through440.N may be provided with a register (not shown) specifying a phase of the LO signal to be generated. In an exemplary embodiment, the phase may be digitally specified using five bits that completely span a full cycle of 2π radians.

FIG. 4Aillustrates an exemplary embodiment of an interface between multiple balanced antenna elements and active elements491in a receiver400A. The active elements491may correspond to the same active elements491used in the receiver400shown inFIG. 4, with differing values provided for the LO phases Φ1through ΦNas further described hereinbelow.

InFIG. 4A, balanced antenna elements301.1through301.(N/2) are coupled to the active elements. Each of the “a” and “b” terminals of each balanced antenna element is coupled to a corresponding one of the signal paths405.1through405.N, with the two terminals of a single balanced antenna coupled to two signal paths, as shown. Furthermore, for the two signal paths corresponding to a single balanced antenna, the LO phases are adjusted to differ by exactly it radians. One of ordinary skill in the art will appreciate that this effectively introduces a phase inversion between the outputs of the two signal paths corresponding to a single balanced antenna. Thus by appropriately adjusting the phases Φ1through ΦN/2of the LO generators440.1through440.N, the same set of active elements491may be configured to accommodate either unbalanced or balanced antenna elements without any hardware modification, and without the need for any baluns. This advantageously avoids the possible losses and area trade-offs associated with the use of baluns.

It will be appreciated that the techniques of the present disclosure may be especially suitable for use in millimeter-wave based communications systems. In such systems, the bandwidths of a typical communications channel may be on the order of GHz, and thus the active elements in the signal paths may already be designed to accommodate signal bandwidths on the order of GHz. To accommodate such bandwidths using prior art techniques such as passive baluns may undesirably consume excessive area and/or cost, since passive baluns generally have limited bandwidth, and may require the provisioning of multiple sections at the expense of area and cost.

A further advantage of the techniques of the present disclosure is that the active elements in the signal paths, e.g., the gain elements or mixer elements, may be configurable to be well-matched to each other, such that the overall system exhibits good broadband common-mode rejection characteristics.

In a further exemplary embodiment of the present disclosure, the flexibility of the architecture described hereinabove allows the design of systems that may simultaneously accommodate both unbalanced and balanced antenna elements.FIG. 4Billustrates an exemplary embodiment of an interface between an antenna array and active elements in a receiver400B, with the antenna array including at least one unbalanced antenna and at least one balanced antenna.

InFIG. 4B, unbalanced antenna elements201.1and201.2are coupled to signal paths405.1and405.2, respectively. The phases Φ1and Φ2the LO generators440.1and440.2may be independently adjusted in accordance with the principles of the present disclosure to accommodate the unbalanced antenna elements. Furthermore, terminals “a” and “b” of a balanced antenna element301.M are coupled to signal paths405.(N−1) and405.N, respectively. As shown inFIG. 4B, the phases of the LO generators440.(N−1) and440.N are adjusted to vary in one degree of freedom ΦM, and to differ from each other by π radians.

It will be appreciated that while exemplary embodiments of the present disclosure have been described with reference to processing of the signals from an antenna array at a receiver, the techniques herein may also be readily applied to the interface between a transmitter and an antenna array. For example, the phase of an LO signal used for upconverting a baseband signal in a TX signal path may also be made adjustable, and unbalanced and/or balanced antenna elements may be accommodated by appropriately selecting the phases of the LO signals used for upconversion.

FIGS. 5 and 5Aillustrate exemplary embodiments of an interface between multiple antenna elements and active elements591in a transmitter for a communications system.

InFIG. 5, unbalanced antenna elements201.1through201.N are coupled to a set of active elements591. The active elements591include a processor550for generating a plurality of baseband signals550.1through550.N coupled to a plurality of corresponding mixers530.1through530.N. The mixers530.1through530.N perform upconversion of the baseband signals by mixing with corresponding LO signals generated by LO generators540.1through540.N. As earlier described herein, the LO signals are adjustable with corresponding phase offsets Φ1through ΦN. The outputs of the mixers are coupled to corresponding gain elements520.1through520.N, which may perform amplification of the mixer output prior to coupling with the plurality of antenna elements201.1through201.N.

InFIG. 5A, balanced antenna elements301.1through301.N are coupled to a set of active elements591. The active elements591may be identical to those shown inFIG. 5. The outputs gain elements520.1through520.N are coupled to differential terminals a and b of balanced antenna elements301.1through301.(N/2). As earlier described with reference to the receiver architecture inFIG. 4A, the phases of the two LO signals in the signal paths provided to the same balanced antenna element301.nmay be adjusted to vary in one degree of freedom ΦM, and to differ from each other by π radians.

One of ordinary skill in the art will appreciate that the active elements591may also be configured to accommodate mixed sets of balanced and unbalanced antenna elements for transmission over an antenna array, as described inFIG. 4Bin the context of reception. It will further be appreciated that in alternative exemplary embodiments (not shown), a single set of active elements may simultaneously accommodate both transmit and receive signal paths to a plurality of antenna elements by using, e.g., a duplexer or other means known to one of ordinary skill in the art. Such alternative exemplary embodiments are contemplated to be within the scope of the present disclosure.

FIG. 6illustrates an exemplary embodiment of a method600according to the present disclosure. Note the method is shown for illustrative purposes only, and is not meant to limit the scope of the present disclosure to any particular method described. The method shown is for interfacing a plurality of signal paths with an antenna array.

At block610, the phase of a first LO signal of a first signal path is adjusted independently of the phase of a second LO signal of a second signal path when the first and second signal paths are coupled to first and second unbalanced antenna elements, respectively, of the antenna array, the first local oscillator (LO) signal being mixed with a signal in the first signal path, the second local oscillator (LO) signal being mixed with a signal in the second signal path.

At block620, the phase of the first LO signal is adjusted to differ by π radians from the phase of the second LO signal when the first and second signal paths are coupled to first and second balanced nodes, respectively, of a balanced antenna element of the antenna array.