Too often, smart grid customers purchase the default antenna offered by the Systems Integrator without any thought or consideration as to what might be best the best antenna choice for an optimized radio link. With a little effort spent to select the perfect antenna, link data rate performance can be greatly enhanced and the link can be made more reliable. In smart grid systems, performance and reliability are critical.
There are a few simple parameters to consider regarding the best antenna selection for your installation. These include:
- Passive gain before active gain
- Power handling capacity
- Interference mitigation
- Distance between the antenna and the amplifier
- Environmental factors
We see vendors provide a generic antenna that meets the needs of most customers. However, these default antennas are rarely optimized for many standard circumstances and fail to perform as well as might be possible with just a little time spent to select the ideal antenna, and often at no extra cost to the project. So, this task is a winning strategy to perform in advance of ordering products and materials for your next smart grid project.
Default antennas try to cover many bands of frequency within one antenna. This means that the antenna is very broad in its bandwidth and this may negatively impact performance with interference problems and reduced gain. Selecting an antenna that is designed specifically for the desired frequency will save in troubleshooting and likely provide increased signal level too.
Antennas should be selected for the right beamwidth. We often use antennas that provide narrower beamwidth than may be necessary in order to reduce the impact of multipath when an antenna sees too wide of a swath of geography and therefore catches undesired signals from other radio links that harm your link. A slightly larger antenna comes with narrower beamwidth and this provides increased gain too.
“Passive gain before active gain” is an old adage from the RF industry that means buy a bigger antenna before increasing amplifier power. Gain from larger antennas is effectively a free power increase as long as it complies with regulations. It avoids increase use of electricity needed to power larger amplifiers and reduces the need for larger UPS and generators, but it can mean more tower structural loading and more tower space consumption. So, the pros and the cons need to be properly balanced.
Getting the right gain can be tricky. Regulations are always present and must be complied with in every country. There will be a need for an optimized gain to meet link requirements and to adhere to the regulators needs, but if multipath is present, and a larger antenna is used to narrow the beamwidth, then a pad may also be required to reduce gain to the desired levels. Pads are generally undesired, but may be necessary for optimization of the link.
With most smart grid installations, power levels are low. But, it is important to consider the end to end power handling needs of each device in the RF thread to ensure that it can properly handle the power levels. Selecting the right cable for the link is equally critical for success. Diligence is required to choose cables that meet the needs of the radio and the installation. It is not as rare as you might think to troubleshoot a poorly performing radio link only to find 75 ohm cable used where 50 ohm cable is required. The power losses per metre are also important to pay attention too when selecting cables. Heath and safety demands that we have a safe working environment so adherence to the applicable safety codes is mandatory to avoid unwanted radiation exposure.
Interference can be mitigated with the right antenna selection. Choosing a directional antenna may be preferred over an omnidirectional antenna to avoid undesired signals. Antenna alignment is a key factor to link performance. Misalignment can come from many sources, especially wind. So, peaking antennas as a part of the annual preventive maintenance plan is prudent.
Radios come as either one piece or two piece packages. The issue is where the amplifier is installed. Is it inside the shelter or up beside the antenna on the tower? Different cable types can minimize problems due to distance. Waveguide or cables with specialized air or foam dielectric cores can balance the problem out when amplifiers are installed indoors with long cable runs to the antenna. The goal is to deliver the power found at the output of the amplifier transparently to the connector on the rear of the antenna. AC power should not be run up the tower due to lightning concerns, so DC power is required.
Various filters can be installed with the antenna to block interference from undesired sources. Typically there are four main filter types: band-pass, band-stop, low-pass, and high-pass filters. Again, filters are not perfect so they should be used only when necessary. Sometimes, a slight mechanical misalignment of the antenna to place undesired signals in to the antenna nulls can be just as effective as a filter.
Weather can greatly impact antennas. Sea breezes and salt air can be corrosive and attack antennas and especially affect the connectors, so proper sealing of the connections is vital. Wind can cause mechanical misalignment of antennas over time so annual peaking may be necessary. Excessive rainfall over the path, as well as snow and ice formation on the antenna may impact performance at some frequencies. Rain water getting into connectors is a common problem so superior craft skills and methodologies for the installation are paramount to your success.
Mounting of the antenna away from other antennas on the same tower or nearby towers at least one half lambda away is required. Using ice guards to protect aluminum antennas from razor sharp falling ice is needed in locations where ice and snow form. The rigidity of the mount will save misalignment problems over time.
Paying attention to the details will always result in a better installation and serve to provide years of reliable performance. Antennas are often forgotten or neglected during large projects, but they can have adverse impacts on operations over time so doing a little extra effort at the start can save Utilities lots of expensive effort later.
Michael Martin has more than 35 years of experience in broadband networks, optical fibre, wireless and digital communications technologies. He is a Senior Executive Consultant with IBM’s Global Center of Excellence for Energy and Utilities. He was previously a founding partner and President of MICAN Communications and earlier was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation. He holds three Masters level degrees, in business (MBA), communication (MA), and education (MEd). As well, he has diplomas and certifications in business, computer programming, internetworking, project management, media, photography, and communication technology.