Antenna Systems & Technology - Spring 2016 - (Page 6)

FEATURE ARTICLE Progress Comes in All Shapes and Sizes: A Practical Guide to Selecting and Deploying Antennas in Wireless Towers By John C. Keating, P.E., VP of Professional Services | Centerline Solutions Antenna selection is an important design parameter imposed on a wireless project by the RF engineer. It's a critical decision because of the impact of this choice carries in terms of the complexity of tradeoffs, including performance, cost and time to market, to name just a few. Since the antenna selection will have far reaching impacts to the execution of the project, the RF engineer must strike the right balance between these tradeoffs and choose a compromise that best suits the objectives of the installation and its role in the overall wireless network. The compromise is generally driven by the size and/or number of antennas that can feasibly be deployed, and it compels RF engineers to make a complex, high stakes technical decision that takes into account factors such as performance gains, accommodation of multiple frequency bands and technologies, and integrated features such as remote tilt. These competing needs conspire to increase the size and complexity of the antenna, which has impacted its physical size. There is an overall perception of technology that smaller always means better and that smaller always means progress, but in the case of antennas the opposite is often true. Bigger sometimes means better with antennas. The truth is that if antenna technologies had not grown larger in a way that evolved to meet the challenges of today's wireless networks, wireless facilities would likely be a whole lot more complicated and unwieldy. There would be a lot more of them everywhere. In many wireless projects, a smaller antenna might be convenient, but a larger one often better meets the technical needs of the project. However, deploying larger antennas does create challenges. Thankfully, they are often solvable, and the goal of this article is to walk you through a number of key decisions and best practices that will help you arrive at the right decision to fit your project needs. Form Follows Function With antennas, size does matter. All other things being equal, if the engineer wants greater directivity in the antenna for increased coverage and/or interference mitigation, the length of the antennas will often be increased. With the introduction of PCS (1,900 MHz) networks in the 1990's, antenna performance gains were realized without increasing the physical size of the antenna. The wavelength of 1,900 MHz signals being less than half that of 850 MHz signals, meant that antenna gain performance was roughly double that of similarly sized 850 MHz antennas. The AWS auctions of the 2000's continued to exploit the efficiencies and packaging gains of higher frequencies. Then came 700 MHz auctions, and the tide turned back toward larger antennas to support not only the lower frequencies of 700 MHz, but also the same performance engineers had become accustomed to The upcoming 600 MHz Broadcast Incentive Auction will likely put further upward presFrequency Wavelength Wavelength sure on antenna packaging. Table 1 shows the inverse relation- (Mhz) (m) (inches) ship between frequency and wavelength. 2,125 0.14 5.51 Wavelength(m/cycle) = 300,000,000 [m/s]/Freq [cycles/s] When overlaying low-band band (700 MHz) systems, on highband systems (1,900/2,100 MHz), the optimal design often calls for the use of a physically larger antenna but the laws of physics limit the engineers' options in this particular area. 1,950 0.15 5.91 880 0.34 13.39 750 0.4 15.75 650 0.46 18.11 Table 1. More Bands, More Technologies With the first round of PCS (1,900 MHz) auctions in the 1990's also came the need for many wireless companies to accommodate more than one frequency band, and/or technology in their networks. Adding 2,100 6 Antenna Systems & Technology Spring 2016 www.AntennasOnline.com http://www.AntennasOnline.com

Table of Contents for the Digital Edition of Antenna Systems & Technology - Spring 2016

Contents
Editor’s Choice
Progress Comes in All Shapes and Sizes: A Practical Guide to Selecting and Deploying Antennas in Wireless Towers
Antennas
Components/Subsystems
Short-Range Wireless
Software / System Design
Test & Measurement
Industry News
Marketplace
Major Trends for Outdoor Cell Sites

Antenna Systems & Technology - Spring 2016