Patent Application
20240275058
Embodiments of the invention relate to electronic systems, and more particularly, to antennas for radio frequency (RF) communications.
Antennas can be used in a wide variety of applications to transmit and/or receive radio frequency (RF) signals. Example applications using antennas include radar, satellite, military, and/or cellular communications.
Apparatus and methods for circularly polarized antenna arrays are disclosed. In certain embodiments, a dual-band dual-polarized antenna array is provided. The antenna array uses separate frequency bands for transmit and receive signals, and supports a right hand circular polarization (RHCP) and a left hand circular polarization (LHCP). The antenna array can be formed on a circuit board to which a beamforming integrated circuit (IC) can be attached. For example, the antennary array can formed form a low-cost printed circuit board (PCB) stack-up construction. The antenna array can provide circular polarization without needing a polarizer or coupler. Furthermore, the antenna array achieves good isolation and axial ratio under scan.
In one aspect, a circuit board includes a plurality of metal layers separated by dielectric, a first patch antenna formed in a first metal layer of the plurality of metal layers and including a first pair of signal feeds, a first delay line formed in the first metal layer and connecting the first pair of signal feeds to a first excitation via, a second patch antenna formed in a second metal layer of the plurality of metal layers and including a second pair of signal feeds, and a second delay line formed in the second metal layer and connecting the second pair of signal feeds to a second excitation via. The first patch antenna and the second patch antenna are stacked.
In another aspect, a phased array antenna system includes a circuit board including a plurality of metal layers separated by dielectric, a first patch antenna formed in a first metal layer of the plurality of metal layers and including a first pair of signal feeds, a first delay line formed in the first metal layer and connecting the first pair of signal feeds to a first excitation via, a second patch antenna formed in a second metal layer of the plurality of metal layers and including a second pair of signal feeds, and a second delay line formed in the second metal layer and connecting the second pair of signal feeds to a second excitation via. The first patch antenna and the second patch antenna are stacked. The phased array antenna system further includes a beamforming integrated circuit (IC) attached to the circuit board and having a first pin connected to the first excitation via and a second pin connected to the second excitation via.
In another aspect, a method of antenna formation is provided. The method includes forming a first patch antenna in a first metal layer of a circuit board, the first patch antenna including a first pair of signal feeds. The method further includes forming a second patch antenna in a second metal layer of the circuit board, the second patch antenna including a second pair of signal feeds, and the first patch antenna and the second patch antenna stacked and separated by dielectric. The method further includes forming a first excitation via and a second excitation via in the circuit board, and forming a first delay line in the first metal layer, the first delay line connecting the first pair of signal feeds to the first excitation via. The method further includes and forming a second delay line in the second metal layer, the second delay line connecting the second pair of signal feeds to the second excitation via.
The following detailed description of embodiments presents various descriptions of specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings.
The phased array antenna system 10 illustrates one embodiment of an electronic system that can include a circularly polarized antenna array implemented in accordance with the teachings herein. However, the circularly polarized antenna arrays disclosed herein can be used in a wide range of electronics. A phased array antenna system is also referred to herein as an active scanned electronically steered array or beamforming communication system.
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With continuing reference to
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The frequency up/down conversion circuit 8 provides frequency upshifting from baseband to RF and frequency downshifting from RF to baseband, in this embodiment. However, other implementations are possible, such as configurations in which the phased array antenna system 10 operates in part at an intermediate frequency (IF). In certain implementations, the splitting/combining circuit 7 provides splitting to one or more frequency upshifted transmit signals to generate RF signals suitable for processing by the RF front end 5 and subsequent transmission on the antennas 6a, 6b, . . . 6n. Additionally, the splitting/combining circuit 7 combines RF signals received vias the antennas 6a, 6b, . . . 6n and RF front end 5 to generate one or more baseband receive signals for the data conversion circuit 2.
The channel processing circuit 3 also includes the phase and amplitude control circuit 9 for controlling beamforming operations. For example, the phase and amplitude control circuit 9 controls the amplitudes and phases of RF signals transmitted or received via the antennas 6a, 6b, . . . 6n to provide beamforming. With respect to signal transmission, the RF signal waves radiated from the antennas 6a, 6b, . . . 6n aggregate through constructive and destructive interference to collectively generate a transmit beam having a particular direction. With respect to signal reception, the channel processing circuit 3 generates a receive beam by combining the RF signals received from the antennas 6a, 6b, . . . 6n after amplitude scaling and phase shifting.
Phased array antenna systems are used in a wide variety of applications including, but not limited to, mobile communications, military and defense systems, and/or radar technology.
As shown in
The phased array antenna system 10 operates to generate a transmit beam and/or receive beam including a main lobe pointed in a desired direction of communication. The phased array antenna system 10 realizes increased signal to noise (SNR) ratio in the direction of the main lobe. The transmit and/or receive beam also includes one or more side lobes, which point in different directions than the main lobe and are undesirable.
An accuracy of beam direction of the phased array antenna system 10 is based on a precision in controlling the gain and phases of the RF signals communicated via the antennas 6a, 6b, . . . 6n. For example, when one or more of the RF signals has a large phase error, the beam can be broken and/or pointed in an incorrect direction. Furthermore, the size or magnitude of beam side lobe levels is based on an accuracy in controlling the phases and amplitudes of the RF signals.
Accordingly, it is desirable to tightly control the phase and amplitude of RF signals communicated by the antennas 6a, 6b, . . . 6n to provide robust beamforming operations.
In the illustrated embodiment, the front end system 30 is connected to an antenna array including a first receive antenna 31a, a second receive antenna 31b, a third receive antenna 31c, and a fourth receive antenna 31d, a first transmit antenna 32a, a second transmit antenna 32b, a third transmit antenna 32c, and a fourth transmit antenna 32d.
The receive antennas 31a-31d and the transmit antennas 32a-32d can be implemented on a circuit board as a dual-polarized dual-band circularly polarized antenna array in accordance with the teachings herein.
As shown in
In certain implementations, the RF receive signals have different phases, such as quadrature receive signals with a 90° phase separation. In such implementations, the first RF receive signal from the first receive antenna 31a can be referred to as a 0° RF receive signal (0°R), the second RF receive signal from the second receive antenna 31b can be referred to as a 90° RF receive signal (90°R), the third RF receive signal from the third receive antenna 31c can be referred to as a 180° RF receive signal (180°R), and the fourth RF receive signal from the fourth receive antenna 31d can be referred to as a 270° RF receive signal (270°R).
In certain implementations, the front end system 30 also generates the RF transmit signals as quadrature transmit signals with a 90 degree phase separation. Moreover, to aid in providing transmit and receive with orthogonal circular polarization, a polarity of the phase of each transmit signal can be opposite that of a corresponding receive signal. In such implementations, the first RF transmit signal to the first transmit antenna 32a can be referred to as a 0° RF transmit signal (0°T), the second RF transmit signal to the second transmit antenna 32b can be referred to as a −90° RF transmit signal (−90°T), the third RF transmit signal to the third transmit antenna 32c can be referred to as a −180° RF transmit signal (−180°T), and the fourth RF transmit signal to the fourth transmit antenna 32d can be referred to as a −270° RF transmit signal (−270°T).
With continuing reference to
Although one embodiment of a front end system 30 is shown in
In the illustrated embodiment, the car 52 transmits uplink (UL) signals to the satellite 51 over a first frequency band, and receives downlink (DL) signals from the satellite 51 over a second frequency band. Thus, the satellite communications network 50 is dual band, in this example. The satellite communications network 50 also operates with half-duplex.
The satellite communications network 50 of
A polarization of an electromagnetic wave refers to a behavior of the wave's electric field vector over time. For example, an electromagnetic wave with a linear electric field vector is referred to as a linearly-polarized wave, while an electromagnetic wave with a generally circular electric field vector is referred to as a circularly-polarized wave. Antenna elements and antenna arrays broadly fall into two categories in terms of polarization: linear and circular. Circular polarization includes a right hand circular polarization (RHCP) and a left hand circular polarization (LHCP), which are orthogonal to one another.
In certain applications, such as Satcom, it is desirable for uplink and downlink operate at orthogonal circular polarizations, for example, LHCP and RHCP, respectively, in addition to being at different frequencies. For example, communicating using antenna arrays with circular polarization provides immunity to relative rotation of the user with respect to the satellite. Furthermore, it can be desirable for both transmit and receive antenna arrays to share a common aperture, and to be implementable on a circuit board, for instance, using low cost printed circuit board (PCB) technologies. Moreover, in Satcom applications, it is desirable for the antenna array of the user terminal (for example, the car 52 of
In certain embodiments herein, a dual-band dual-polarized antenna array is provided. The antenna array uses separate frequency bands for transmit and receive signals, and supports LHCP and RHCP polarizations. The antenna array can be formed on a circuit board to which a beamforming IC can be attached. For example, the antennary array can formed form a low-cost PCB stack-up construction.
The antenna array can provide circular polarization without needing a polarizer or coupler. Furthermore, the antenna array achieves good isolation and axial ratio under scan.
In the illustrated embodiment, the metal layer MC has been patterned to form various conductive structures which include a first transmit patch antenna 101, a second transmit patch antenna 102, a third transmit patch antenna 103, and a fourth transmit patch antenna 104, which have been arranged in a two by two (2×2) array, in this embodiment.
The first transmit patch antenna 101 is fed by a first signal feed 141a and a second signal feed 141b, which are formed in the metal layer MC and are capacitively coupled to the first transmit patch antenna 101. Likewise, the second transmit patch antenna 102 is fed by a first signal feed 142a and a second signal feed 142b, the third transmit patch antenna 103 is fed by a first signal feed 143a and a second signal feed 143b, and the fourth transmit patch antenna 104 is fed by a first signal feed 144a and a second signal feed 144b.
Accordingly, each of the transmit patch antennas 101-104 includes a pair of signal feeds, which can be associated with a vertical (V) excitation and a horizontal (H) excitation of the patch. Thus, the pair of signal feeds can be referred to as having a V signal feed and an H signal feed. With respect to a center point of a given transmit patch antenna, the first signal feed and the second signal feed are at about equal distance (for example, within 10%) from the center point of the patch, but angularly separated by about 90° (for example, 90°+/−10%). Thus, the first signal feed and the signal feed of a given transmit patch antenna can be placed about 90 degree apart from one another along a circumference of a circle that is centered at the center point of the transmit patch antenna. In this example, each signal feed is capacitively coupled to the patch, and includes a conductive stub to aid in providing impedance matching. The transmit patch antennas are octagonal, in this embodiment. However, other shapes (including, but not limited to, square) are also possible.
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Furthermore, a common signal via is connected to the delay line associated with a particular transmit patch antenna. For example, a first transmit signal via 121 is connected to the delay line 111a/111b for the first transmit patch antenna 101, a second transmit signal via 122 is connected to the delay line 112a/112b for the second transmit patch antenna 102, a third transmit signal via 123 is connected to the delay line 113a/113b for the third transmit patch antenna 103, and a fourth transmit signal via 124 is connected to the delay line 114a/114b for the fourth transmit patch antenna 104.
In certain implementations, each transmit signal via is connected to a corresponding pin or pad of a beamforming IC that is attached to a side of the circuit board 150 opposite the circularly polarized patch antenna array. Additionally or alternatively, the transmit signal vias 121-124 can be driven by quadrature transmit signals, for example, a 0° RF transmit signal (0°T), a −90° RF transmit signal (−90°T), a −180° RF transmit signal (−180°T), and a −270° RF transmit signal (−270°T), respectively.
Although the signal feeds for a given transmit patch antenna are driven by a common signal via (which in turn, can be connected to a pin of a beamforming IC), the delay lines provide a length difference to the first signal feed and the second signal feed of a given transmit patch antenna. In certain implementations, the length difference is λTX/4, corresponding to a quarter of the wavelength of the transmit signal that is transmitted on the transmit patch antennas. Implementing the signal feeds in this manner aids in exciting circular polarization by introducing a 90° delay between the V and H feed points.
Furthermore, by forming the delay lines on the same metal layer as the transmit patch antennas, no vias go directly to the patches. Rather, excitation vias excite the delay lines and do not directly excite the antennas. By implementing antenna excitation in this manner, undesirable coupling to other metal layers (for instance, to the receive patch antennas discussed below) is avoided.
The metal layer MC has also been patterned to form various parasitic metallization 130 to aid in directing transmit and receive beams communicated using the antenna array. For example, inclusion of the parasitic metallization 130 improves the beam shape affected by having two radiating overlapped patches.
With continuing reference to
By implementing the circuit board 150 with decoupled stacked patch antennas, the transmit patch antennas 101-104 serve as reflectors for the receive patch antennas 105-108, and vice versa. Thus, a compact form factor is achieved while appropriate electromagnetic reflections are provided.
The first receive patch antenna 105 is fed by a first signal feed 145a and a second signal feed 145b, which are formed in the metal layer MB and are capacitively coupled to the first receive patch antenna 105. Likewise, the second receive patch antenna 106 is fed by a first signal feed 146a and a second signal feed 146b, the third receive patch antenna 107 is fed by a first signal feed 147a and a second signal feed 147b, and the fourth receive patch antenna 108 is fed by a first signal feed 148a and a second signal feed 148b.
Accordingly, each of the receive patch antennas 105-108 includes a pair of signal feeds (a first signal feed and a second signal feed), which can be associated with a V excitation and an H excitation of the patch. With respect to a center point of a given receive patch antenna, the first signal feed and the second signal feed are at about equal distance from the center point but angularly separated by about 90°. In this example, each signal feed is capacitively coupled to the patch, and includes a conductive stub to aid in providing impedance matching.
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Although the signal feeds for a given receive patch antenna are connected to a common signal via (which in turn, can be connected to a pin of a beamforming IC), the delay lines provide a length difference to the first signal feed and the second signal feed of a given receive patch antenna. In certain implementations, the length difference is λRX/4, corresponding to a quarter of the wavelength of the receive signal that is received by the receive patch antennas.
In certain implementations, the receive signal vias 125-128 are associated with quadrature receive signals, for example, a 0° RF receive signal (0°R), a 90° RF receive signal (90°R), a 180° RF receive signal (180°R), and a 270° RF receive signal (270°R), respectively.
In the illustrated embodiment, the receive patch antennas 105-108 are wider than the transmit patch antennas 101-104 to achieve a difference in operating frequency between the receive patch antennas 105-108 and the transmit patch antennas 101-104.
In one example, the receive patch width is about 6 mm to achieve mid-band operation at about 11.7 GHz, while the transmit patch width is about 5.5 mm to achieve mid-band operation at about 14.25 GHz. The pitch of the receive patch antenna and the transmit patch antennas can be equal, for instance, about 10.5 mm in one example. Although example dimensions and operating frequencies have been described, other dimensions and frequencies are possible.
With respect to transmission on the transmit patch antennas 101-104, when the upper transmit patch radiates, the lower receive patch acts as a parasitic metallization that increases the effective permittivity. This can lead to a size of the top patch being close to a size of the receive patch despite working at a significantly higher frequency band. When the lower receive patch radiates, the upper transmit patch acts as a parasitic radiating element.
With continuing reference to
The circuit board 150 includes parasitic vias to restore symmetry that would otherwise be lost due to the presence of excitation vias that are connected to the delay lines. For example, with respect to the transmit signal via 121, parasitic vias 131, 132, and 133 have been included. Additionally, with respect to the receive signal via 125, parasitic vias 135, 136, and 137 have been included. With respect to a given patch antenna, the parasitic vias and the excitation vias are mirrored. Moreover, in the illustrated embodiment, the parasitic vias and the excitation vias are about equidistant from a center point of a corresponding patch antenna.
Moreover, the excitation vias for transmit and receive have been placed near a diagonal of the patch antenna, with the transmit excitation via opposite the receive excitation via. Positioning the excitation vias in this manner aids in providing enhanced transmit and receive isolation.
Although not depicted in
Such a beamforming IC can include transmit channels used to provide RF transmit signals that are phase delayed relative to one another to the excitation vias associated with the transmit patch antennas. For example, in one embodiment, the beamforming IC provides quadrature phase RF transmit signals 0°T, −90°T, −180°T, and −270°T to the excitation vias 121-124, respectively. Additionally, the beamforming IC can include receive channels for processing quadrature phase RF receive signals 0°R, 90°R, 180°R, and 270°R from the excitation vias 125-128, respectively.
The RF transmit signals and the RF receive signals have phase delays that are equal in magnitude but opposite in polarity to aid the antenna array in operating with orthogonal circular polarization. For example, implementing the antenna array with the phase delays shown in
Thus, the circuit board 150 of
In the illustrated embodiment, the circuit board 250 includes eight metal layers 201-208, respectively (also referred to as Sig 1, Sig 2, Sig 3, Sig 4, Sig 5, Sig 6, Sig 7, and Sig 8), and nine dielectric layers 211-219, respectively. Various example vias are depicted, including a via 221 from Sig 1 to Sig 6, a via 222 from Sig 1 to Sig 8, a back-drilled via 223 (which in this example is back-drilled to Sig 7), a via 224 from Sig 1 to Sig 2, and a via 225 from Sig 2 to Sig 3.
Although one example of a circuit board 250 is depicted, a circularly polarized antenna array can be formed using a wide variety of circuit board processes, including circuit boards with other numbers and/or types of layer stack ups and/or vias.
With continuing reference to
In one embodiment, the metal layers 201-208 are copper metal layers, the dielectric layers 211, 212, 214, 215, 216, and 218 are prepreg dielectric layers, and the dielectric layers 213, 217, and 219 are core dielectric layers with a dielectric constant higher than that of the prepreg dielectric layers. However, other implementations are possible.
Persons of ordinary skill in the art will appreciate various materials and thicknesses suitable for implementing the depicted layers and vias.
For example, a first receive line 331 connects a first receive pin of the IC 301 to the receive excitation via 311 (0°R), a second receive line 332 connects a first second pin of the IC 301 to the receive excitation via 312 (90°R), a third receive line 333 connects a third receive pin of the IC 301 to the receive excitation via 313 (180°R), and a fourth receive line 334 connects a fourth receive pin of the IC 301 to the receive excitation via 314 (270°R). Additionally, a first transmit line 341 connects a first transmit pin of the IC 301 to the transmit excitation via 321 (0°T), a second transmit line 342 connects a second transmit pin of the IC 301 to the transmit excitation via 322 (−90°T), a third transmit line 343 connects a third transmit pin of the IC 301 to the transmit excitation via 323 (−180°T), and a fourth transmit line 344 connects a fourth transmit pin of the IC 301 to the transmit excitation via 324 (−270°T).
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The routing layer 370 of
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Imperfections in the intended polarization of an antenna system can be quantified by the cross-polarization gain (X-POL) and co-polarized gain (CO-POL).
In
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Axial ratio (AR) is a measure of imperfection of a circularly polarized antenna. An ideal circularly polarized antenna has AR=1 (0 dB), with AR less than 4 dB over a scanning range of +/−60° being good axial range.
In
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Devices employing the above described schemes can be implemented into various electronic devices. Examples of electronic devices include, but are not limited to, RF communication systems, consumer electronic products, electronic test equipment, communication infrastructure, etc. For instance, one or more circularly polarized antenna arrays can be included in a wide range of RF communication systems, including, but not limited to, radar systems, base stations, mobile devices (for instance, smartphones or handsets), phased array antenna systems, laptop computers, tablets, and/or wearable electronics.
The teachings herein are applicable to RF communication systems operating over a wide range of frequencies, including not only RF signals between 100 MHz and 7 GHz, but also to higher frequencies, such as those in the X band (about 7 GHz to 12 GHz), the Ku band (about 12 GHz to 18 GHz), the K band (about 18 GHz to 27 GHz), the Ka band (about 27 GHz to 40 GHz), the V band (about 40 GHz to 75 GHz), and/or the W band (about 75 GHz to 110 GHz). Accordingly, the teachings herein are applicable to a wide variety of RF communication systems, including microwave communication systems.
The RF signals wirelessly communicated by the circularly polarized antenna arrays herein can be associated with a variety of communication standards, including, but not limited to, Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Code Division Multiple Access (CDMA), wideband CDMA (W-CDMA), 3G, Long Term Evolution (LTE), 4G, and/or 5G, as well as other proprietary and non-proprietary communications standards.
The foregoing description may refer to elements or features as being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/feature is directly or indirectly connected to another element/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/feature is directly or indirectly coupled to another element/feature, and not necessarily mechanically. Thus, although the various schematics shown in the figures depict example arrangements of elements and components, additional intervening elements, devices, features, or components may be present in an actual embodiment (assuming that the functionality of the depicted circuits is not adversely affected).
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while the disclosed embodiments are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and/or circuit topologies, and some elements may be deleted, moved, added, subdivided, combined, and/or modified. Each of these elements may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments. Accordingly, the scope of the present invention is defined only by reference to the appended claims.
Although the claims presented here are in single dependency format for filing at the USPTO, it is to be understood that any claim may depend on any preceding claim of the same type except when that is clearly not technically feasible.
