Microwave Engineering Europe - October 2008 - (Page 38)

38 ANTENNA TESTING The EO transducer is based on a MachZehnder interferometer on a single LithiumNiobate crystal that is an analogue optical link passing the RF signal to the detector diode. The transducer has a sub-nanosecond response time and in principle operates to 40 GHz. It has an acrylic casing of dimension of 49 mm × 12 mm × 12 mm, and the only metal part is an SMA connector that protrudes 12.5 mm from the side of the case, and two 3 mm long wires to the waveguide in the crystal. The transducer connects to an OptoElectric Field Sensor (OEFS) controller, which supplies laser power to the transducer and converts the returned RF-modulated optical signal into an RF electric signal. The controller comprises a semi-conductor laser, an optical circulator, a photo-detector and a 30 dB RF ampliﬁer. In a related Wireless Communications project, NPL has recently completed work on base-station antennas in its large antenna testing facility. This was for the development of O2’s 3G network. The mobile company used NPL’s anechoic chamber to ensure it chose the right equipment before investing in a multi-million pound infrastructure upgrade to support its 3G phone technology. 3G or “third generation” mobile phone technology allows users to send and receive large amounts of data quickly so they can stream video and access the internet from their handset. It’s a signiﬁcant step up from earlier systems, which had limited data capacity and were designed primarily for voice. To support the increased data transmission needs of 3G and meet the terms of its licence, O2 had to install a new network of antennas, capable of handling larger data volumes and higher network transmission speeds. By moving from older ﬁxed-tilt antennas to new variable tilt models, the reliability and access to the network could be improved. However there are many different antennas available and it can be difﬁcult to evaluate the best option because A more recent Anechoic Chamber at NPL, as used by O2. Courtesy of NPL © crown copyright 2005. The new state-of-theart chamber at NPL. Courtesy of NPL © crown copyright 2008. Acknowledgement to the Electronic Deptartment of the University of Birmingham for the UWB Vivaldi antenna. speciﬁcations are set by the manufacturers themselves, rather than by an independent organisation. NPL helped 02 by providing independent testing services to verify claims made by manufacturers, and ensure that they were comparable between products. NPL was able to provide full information about how the antennas could be expected to behave, including their gain and directivity. By mounting each contender in NPL’s specialised testing chambers, scientists were able to get accurate, repeatable readings, allowing comparison across the competing products. Company Information National Physical Laboratory (NPL) www.npl.co.uk MICROWAVE ENGINEERING EUROPE Free subscription at: www.mwee.com/subscribe Microwave Engineering Europe ● October 2008 ● www.mwee.com 036-038_MWEE.indd 38 3/10/08 13:21:28 http://www.npl.co.uk http://www.mwee.com/subscribe http://www.mwee.com

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Microwave Engineering Europe - October 2008 Contents Comment News Cover Feature: AWR's AXIEM Software Brings 3D Planar Electromagnetic (EM) Simulation "Up Front" RFID: Augmented Reality: Beyond RFID and QR Codes for Mobile Phone Platforms Filters & Frequency Synthesis ZigBee Goes Green with Support for Smart Energy Simplify Mobile Data Applications and Services Test Enabling the State-of-the-Art in Automatic Test Equipment National Physical Laboratory Test Facility Aids Development of Next-Generation Antennas Selecting the Synthetic Test Environment for Transmit-Receive (T-R) Modules in a Phased Array Radar System Products Calendar

Microwave Engineering Europe - October 2008

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