E-Band radios, operating in the 71-76/81-86 GHz frequency range, have become the dominant wireless technology for demanding multi-gigabit per second transport applications in mobile and fixed networks. Due to their superior TCO structure, when compared to optical fiber deployments and other lower frequency microwave (MW) radio link alternatives, E-Band radios are the preferred wireless option to provide Backhaul services to 5G/ 5G Advanced systems, while the next generation of E-Band systems is planned be the foundation of wireless 6G network transport.
Hundreds of thousands of E-Band radios have already been deployed around the world, predominantly for transport links of short and medium range up to about 5 km with link availabilities of 4 9s or better. Nevertheless, long range E-Band radio links have also been deployed in many cases for longer links, up to 10 km and beyond, albeit with smaller link availabilities. Communication Service Providers (CSPs) are keen on extending the ranges for which E-Band links are applicable so that they can exploit the capacity and cost advantages of E-Band technology for longer, high availability wireless backhaul links.
One of the ways to achieve this objective is to increase the nominal diameter of the used E-Band antennas from a maximum of 60 cm (2 feet), which has been the norm so far, to 90 cm (3 feet) or even more.
A particular characteristic of E-Band antennas is that, even for a relatively small nominal diameter of 60 cm, they feature a very high gain of around 50 dB, and the beamwidth of their main radiation lobe at half of their maximum gain, sometimes referred to as Full Width Half Maximum (FWHM), is quite narrow. The metric of FWHM is used as a rule of thumb to characterize the width of antennas’ beam pattern, and for 60 cm nominal diameter E-Band antennas the FWHM is around 0.5 degrees. A nominal 90 cm diameter E-Band antenna features a beamwidth FWHM of around 0.3 degrees. For comparison, a 15 GHz antenna with a nominal diameter of 60 cm has a FWHM of around 2.5 degrees.
The small value of antenna beam FWHM imposes special attention during the phase of link alignment but also has some important implications in the alignment stability of E-Band links during operation, if the support infrastructure of the antenna does not maintain stability/geometrical invariance that is smaller than the FWHM of the antenna. There are several types of antenna support structures, such as self-supporting towers (lattice/monopole), guyed masts, pole/mast mounts on rooftops, some of which, such as monopoles and Guyed towers, have been shown to be more susceptible to deformation/instability effects than others. Deformations of properly constructed and deployed support structures are small in absolute terms, measured in terms of the angle between the deformed/non-deformed state, in general less than one degree (+/-1°). Nevertheless, they may still cause a measurable effect on an E-Band link’s alignment and performance by deflecting the very narrow E-Band antenna main radiation lobe even by few tenths of a degree (see Fig.1).
It has been observed that, in some cases, the radio/antenna mounting structure can exhibit a small tilting/bending deformation, which may vary throughout the day under the influence of direct solar radiation. This tilting/bending effect is caused by differential thermal expansion of different parts of the pole/tower structure. As the sun moves across the sky throughout the day and the thermal balance in the atmosphere changes, a slow and continually changing mounting structure deformation process occurs. The resulting link misalignment causes variation in the Received Signal Level (RSL) and Signal to Noise Ratio (SNR) of the link’s radios. Note that the larger effect impact on the link alignment due to this effect, is caused by an “up/down” movement of the main antenna radiation lobe in the elevation (vertical) plane, rather than a “left/right” movement in the Azimuth (horizontal) plane.
In other cases, under the influence of strong wind, it is possible for weaker antenna mounting structures to start swaying in both the elevation and the azimuthplanes. Such movements cause a twist of the antenna beam, misalignment of the link and detrimental effect in the link SNR and performance at a much faster rate than the sun-related warping effect.
During these misalignment incidents, the radio is adapting to the negative link SNR changes using link’s Automatic Transmit Power Control (ATPC) and/or Hitless Adaptive Modulation and Coding (HACM), which enacts automatic modulation format transitions to more robust, albeit lower capacity formats. In extreme cases large radio RSL fades can take place and the link may be cease passing traffic altogether.
Such effects have, so far, restricted the size of deployed E-Band antennas to a maximum of 60 cm, thus influencing, among other factors, the useful range of E-Band links. Additionally to the discussed dynamic effects, there is also an initial alignment precision issue for 90cm nominal diameter E-Band antennas, which may cause the link gain achievable in the field to be lower than the value one would expect from the antenna specifications, thus lowering the practical benefit of using such antennas. While the stability problem caused by wind gusts can be greatly mitigated by employing suitably rigid and stable support structures, the issue caused by thermal expansion/contraction may affect even robust support structures and is more difficult to solve with passive means.. A solution is to introduce an antenna design that can actively respond to the discussed link alignment deviations to restore the link alignment to as close an optimized state as possible.
Since 2016 Intracom Telecom has been designing, developing, and manufacturing high RF performance E-Band radios, featuring market leading spectral efficiency and range. Furthermore, Intracom Telecom’s antenna manufacturer subsidiary Faini Telecommunication Systems, designs and manufactures high performance Microwave (MW), E-Band and Dual Band antennas. Responding to CSP’s requirements for longer and more stable E-Band-based multi-gigabit per second links, Intracom Telecom and Faini proceeded to the co-development of an E-Band Automatic Beam Stabilizing Antenna (ABSA). This type of antenna is appropriate for use cases where the support structure of the antenna/radio system undergoes thermal expansion/contraction related deformations, affecting the orientation of the antenna radiation beam, causing link misalignment, performance degradation or even outages. The E-Band ABSA system has been designed to provide antenna beam stabilization in two-dimensions (2-D), i.e. in both the Elevation and Azimuth planes, and is applicable to both 60 cm and 90 cm nominal diameter antennas. A unique feature of the Intracom Telecom/Faini 2-D ABSA is that it has been designed from the start to be a Dual Band antenna that is capable of combining E-Band and MW radios through a single dish (see Fig.2).
The E-Band ABSA system is composed of a control module, placed in an outdoor enclosure that is externally attached to the antenna mount, and a specially designed configurable subreflector / dipole mechanism integrated inside the antenna reflector drum. The control module provides the controlling signal for the movement of the antenna subreflector, while at the same time it serves as a management interface for the antenna stabilization mechanism. The control module interfaces on the one side with the active antenna subreflector / dipole mechanism and on the other side with the E-Band radio, other external networking devices and the antenna power supply feed. It can establish secure IP-based communication with network management systems and provide full management visibility via detailed monitoring information regarding the status of the antenna functions, such as current and “historical” antenna adjustment angle.
The development of such a system poses engineering challenges, as it requires a reliable, high sensitivity and accuracy mechanism that is able to provide effective stabilization to very small alignment deviations below +/-1 degrees, while the accuracy of compensation needs to be much better than the FWHM of the E-Band antenna beamwidth. To achieve this difficult task, the beam compensation mechanism of the antenna processes sensor data from embedded high accuracy accelerometers and gyroscopes. These detect movements and deviations of the radio/antenna system from an initial reference orientation and provide input to an algorithm that controls the adjustment of the antenna active sub-reflector positioning. The Intracom Telecom ABSA system also receives feedback from the RSL indication of the attached radio to calibrate and optimize the stabilization efficiency, accuracy, and reliability. The result is that the radiation beams of the antennas on both sides of the link can effectively maintain their original orientation, set at the time of initial link alignment (see Fig.3). The 2-D ABSA mechanism is integrated with a standard antenna reflector and mounting bracket structure and can compensate maximum alignment deviations between +/-1.5 degrees (assuming the initial aligned position is a zero-degree deviation), while maintaining an ETSI EN 302 217 Class 3 antenna radiation pattern performance.
In conclusion, the use of the Intracom Telecom ABSA system improves the average link capacity and link availability when the antenna installation structure suffers from thermal expansion/contraction related tilting. The Intracom Telecom ABSA enables the more widespread deployment of 90 cm l diameter antennas, enhancing the link gain by about 5 dB compared to 60 cm diameter antennas, contributing to the possible extension of the range of high availability E-Band multi-Gbit/s radio links by up to 20%. The misalignment correction mechanism ensures that the link alignment is optimal from the installation phase, which it helps to conclude faster and with higher precision, and onwards throughout the lifetime of the link.
The, currently unique, Dual Band capability of the Intracom Telecom ABSA system can enhance the range extension benefit derived from the use of 90 cm diameter antennas by multiplying it with the range extension benefit of the Dual Band technique. Combining this innovative antenna with Intracom Telecom’s long range UltraLink™ E-Band radios enables CSPs to deploy E-Band technology in their networks for significantly larger than before link ranges.