Patent Grant
12272866
Recently there has been interest in adoption of millimeter-wave technology for high-speed data transport to compliment current enterprise technologies, such as optical and metal-based interconnects, offering substantial advantages in bandwidth, reach, power consumption, and cost. Optical transport is well-suited for longer reaches, where power consumption due to electro-optic conversion is justified. Similarly, metal-based interconnects, such as coaxial cable or PCB traces, are ideally suited for shorter reaches. Millimeter-wave data transport based on low-cost plastic fibers fills an important gap between optical and metal-based transport, providing bandwidth and reach superior to metal with less power consumption than optical. At the appropriate frequency, low-cost plastic fibers transport electromagnetic energy with substantially lower loss than free-space, particularly at 60 GHZ, and are therefore well-suited for guided-wave gigabit data transport.
A plastic microwave fiber (PMF) guided-wave system is composed of the plastic fiber, a millimeter-wave radio, and some means of efficiently and reliably coupling energy between the radio and the fiber. Many different plastic-like compounds, such as polytetrafluoroethylene (PTFE) and polyethylene, can be used for fiber fabrication, and CMOS-based millimeter-wave single-chip radios have been developed, based on various architectures and design philosophies (References 1-6). To fully exploit the available bandwidth and reach the plastic fiber offers, it is crucial that radio-to-fiber coupling efficiency be as high as possible.
The following References are illustrative of the state of the art:
A compact millimeter-wave surface mount helix antenna for high-speed data transport over low-cost plastic fiber is described. Guided millimeter-wave technology enables gigabit transport in the centimeter to meters range, complementing current transport technologies based on optical fibers, coaxial flyover assemblies, and PCB traces. To maintain signal integrity requires an efficient launch of millimeter-waves into the plastic fiber, with low loss and minimum signal impairment. A compact helix antenna provides efficient coupling and wide bandwidth, enabling meter-range copper-grade gigabit transport.
Several approaches have adopted fiber with a rectangular cross-section, since it is polarization holding, and therefore integrates with various types of linearly polarized (LP) antennas (Reference 7). However, the unequal bend-radius is a disadvantage of this approach. Circular cross-section fiber is not LP-holding, so not only is there polarization loss between the radio and fiber, when using an LP antenna, there remains the important issue of fiber alignment to the antenna (Reference 8). Various other approaches have also been suggested for novel coupling (Reference 9).
LP polarization degeneracy of circular cross-section fiber may be neutralized by efficiently launching a circularly polarized (CP) wave into the fiber. The helix antenna is one such radiating structure that radiates CP, and in fact can be connector-less, in contrast to existing PMF coupling methods based on complicated transition structures.
Described herein is a millimeter-wave helix surface-mount antenna for high-speed data transport over low-cost plastic fiber. Guided millimeter-wave technology enables gigabit transport in the centimeter to meters range, to complement existing transport technologies based on optical fibers, flyover assemblies, and PCB traces. The electromagnetic behavior of a millimeter-wave helix surface-mount antenna optimized for launch efficiency into a circular-core plastic fiber for gigabit interconnect is described.
Millimeter-Wave Gigabit Transport
In the application of
The power necessary for electro-optic conversion generally can only be justified for +100 Gbps applications or when a +1 km reach is necessary, for example in data transport back-haul. By eliminating the need for electro-optic conversion, PMF-based data transport provides many advantages over optical and metal-based interconnects, particularly for applications involving +10 Gbps over several meters.
Table 1 provides a comparison of each technology.
Plastic Microwave Fiber Launch
Plastic fiber comes in various cross-sections and dielectric compositions. A fiber of homogeneous circular cross-section is substantially more flexible than rectangular cross-section fiber, and in contrast to hollow-core plastic fiber, is crush resistant. Indeed, these limitations of rectangular cross-section plastic fiber are frequently justified by adoption of simplified linearly-polarized coupling methods that sacrifice efficiency for overall performance.
The simplicity of the helix antenna and its efficient generation of CP waves avoids the LP mode degeneracy of circular-core fiber. This enables for example, polarization diversity for fiber-bundling many adjacent close-packed fibers to create 28 Gbps and 56 Gbps links in the meter range.
In rectangular coordinates, the horizontal and vertical LP01 eigenmodes of circular-core plastic fiber are approximated as
EH≈EoΨ(x,y)ax (1a)
EV≈EoΨ(x,y)ay (1b)
where Eo is the peak electric field and Ψ(x, y) is a mode profile function; the propagation dependence and time dependence have been suppressed for simplicity. Because the circular-core fiber is homogeneous over its cross-section, the mode profile function Ψ(x, y) applies to each of the two LP01 eigenmodes. These degenerate modes are shown in
and since the plastic fiber cross-section is axially symmetric and uniform along the propagation axis, each LP01 mode travels with identical group velocity. Uniform circular-core fiber is therefore CP mode-preserving, enabling full-duplex transmission on the same frequency due to polarization diversity. The helix antenna naturally produces CP waves and hence provides an efficient and reliable means of coupling energy between the radio and circular-core fiber. By properly forming the end section of the fiber, a connector-free transition can be established, as illustrated in
Polarization quality of a CP antenna is distinguished by the axial ratio, AR, defined as
where EH and EV are defined by Equations 1a and 1b, respectively. Note that an ideal CP antenna will exhibit an AR=1. The axial ratio of a CP antenna can be extracted from an anechoic measurement or from well-calibrated computational electromagnetic tools, such as CST.
Shown in
System-Level Performance
The performance of the helix antenna interconnect was evaluated in a Bit Error Rate Test (BERT) test-bed using an Agilent N4901B BERT system for signal quality characterization and a pair of Maja 6022 millimeter-wave fully integrated digital 60 GHz CMOS transceivers. Each transceiver comes with an integrated high-speed serial port directly interfacing with the Agilent N4901B, as shown in
A PMF system based on compact millimeter-wave surface mount helix antenna has been described, with a high coupling efficiency better than 60% (believed to be the highest reported to-date for 60 GHz applications). A comparison to existing technologies is shown in
The following is a numbered list of non-limiting illustrative embodiments of the inventive concepts disclosed herein:
| Number | Name | Date | Kind |
|---|---|---|---|
| 10819035 | Wolniansky | Oct 2020 | B2 |
| 20110248894 | Crowley | Oct 2011 | A1 |
| 20160064795 | Chang | Mar 2016 | A1 |
| 20180159235 | Wolniansky | Jun 2018 | A1 |
| 20180254127 | Dorner | Sep 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 4125152 | Feb 2023 | EP |
| Entry |
|---|
| Yanghyo Kim, et. al. “High-Speed mm-Wave Data-Link Based on Hollow Plastic Cable and CMOS Transceiver”, IEEE Microwave and Wireless Components Letters, vol. 33, No. 12, Dec. 2013 (Year: 2013). |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17066218 | Oct 2020 | US |
| Child | 17361765 | US |
