Antenna Systems & Technology - Spring 2012 - (Page 11)

FEATURE ARTICLE Wireless Infrastructure Cable and Antenna Testing Using The Next-Generation in Handheld Measurement Tools By Jonathan Leitner, North American Product Marketing Manager for Network Analyzers • Rohde & Schwarz The deployment of advanced cellular technologies, such as LTE and LTE-Advanced, have placed greater requirements on the test and measurement industry to provide highly accurate and portable measurement tools for RF infrastructure testing. Some of the most important of these instruments are the handheld cable and antenna testers, which are actually true RF network analyzers. These analyzers have mainly been developed to measure RF cables and antennas on cell towers, but also have additional functionality for making measurements on tower mounted filters and amplifiers. Optional capabilities allow for RF spectral and power measurements as well. As cellular communications have evolved from 1G analog to today’s advanced 4G networks, there has also been a parallel development trend with handheld network analyzers focusing on the installation and maintenance of base station RF components and systems. These analyzers are based around the ability to perform highly accurate measurements using vector calibration techniques. In the past, these techniques and measurements have traditionally been relegated to more expensive and sophisticated bench top instrumentation. For simplification purposes, marketing of these instruments has deemphasized the “network analysis” terminology, and instead focuses more on using terms such as “cable and antenna analyzer.” The Rhode & Schwarz ZVH Cable and Antenna Analyzer, though capable to perform vector-corrected measurements (meaning it can measure magnitude and phase of a signal), is indeed marketed as a cable and antenna analyzer. Handheld cable and antenna analyzers have been developed to achieve the following types of measurements: • Utilize Distance-to-Fault measurements to detect compromises and breaks in RF cables from the BTS transceiver to the tower’s antenna. • Reflection and Transmission measurements on cables, filters and antennas. • Provide biasing and testing of towermounted amplifiers (TMA), which are used to improve the S/N ratio for cellular uplink signals. • Options and capabilities for RF spectral measurements, RF power sensors and vector voltmeter measurements. • One-button test sequence setup, report generation and data management. This article will present an overview on the measurement capabilities that are available with handheld network or cable and antenna analyzers, and review the applications pertaining to base station installation and maintenance. In addition to cellular base station testing, similar types of measurements can also be made on other radio and transmission systems, such as broadcast, public safety, military, etc. Since there are many component and systems commonalities between these various types of radio transmission systems. The Distance to Fault (DTF) technique is a verification measurement used by installation and maintenance personnel to determine cable and transmission line faults. Unlike older time domain reflectometry methods using a step or DC pulse, DTF makes its measurement in the frequency domain. Since all RF network analyzers/cable analyzers are frequency domain instruments at their core, they use a swept RF signal to make all measurements. The swept frequency signal incident on the transmission line (can be a coaxial cable or other type of waveguide transmission line) is reflected due to the discontinuity generated by the break or degradation in the line. This reflected wave is measured and then transformed using an iFFT (inverse Fast Fourier Transform) to obtain the time domain information. The instrument basically determines the distance to the fault, since velocity equals distance with respect to time. If we know the velocity of propagation of the cable, the computed time domain data due to the reflected wave from the fault, then it is straightforward in determining the distance to the fault. Though additional parameters like attenuation factor of the cable, or cutoff frequency if a rectangular waveguide is being measured, are also required for accurate DTF determination. The main advantage of the DTF method over traditional TDR-bases systems is the accuracy at RF frequencies. TDR’s use Distance-to-Fault Measurement: Return Loss over Distance WWW.ANTENNASONLINE.COM SPRING 2012 ANTENNA SYSTEMS & TECHNOLOGY 11 http://WWW.ANTENNASONLINE.COM

Table of Contents for the Digital Edition of Antenna Systems & Technology - Spring 2012

Antenna Systems & Technology - Spring 2012
Editor’s Choice
Next-Gen Networks Call for the Re-Architecture of Antenna Systems
Wireless Infrastructure Cable and Antenna Testing Using the Next-Generation in Handheld Measurement Tools
Antenna Upgrade Challenges in Concealed Cell Towers
Antennas
Components
Wireless Communication
Test & Measurement
Industry News
Marketplace
Efficient Design and Analysis of an Ultra Wideband Planar Antenna with Band Rejection in WLAN Frequencies

Antenna Systems & Technology - Spring 2012