P11342: Table Top Shielded Antenna Anechoic Chamber for Bluetooth Applications

2010-2 / 2010-3 Daniel Pulito (EE) Jason Blackman (EE) Customer/Sponsor Mark Hinman, KODAK Mission Statement To design, construct and calibrate a table top shielded anechoic chamber that will minimize reflections of the source antenna, Project Guide shield the test antenna from spurious electromagnetic radiation George Slack and be capable of making automated measurements of the antenna gain and radiation pattern in the frequency range 1 GHz to 3 GHz. Faculty Advisor Dr. Jayanti Venkataraman

For additional information, visit https://edge.rit.edu/content/P11342/public/Home

Background With the increase in wireless technology at frequencies in the low gigahertz region, the assessment of an antenna’s design and performance has become very challenging. Creating a noise free environment allows accurate measurements to be taken.

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-40.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Freq [GHz] Design of Broadband Antenna In order to increase the versatility of the chamber and allow it to operate at a wide range of frequencies, a broadband antenna was designed. A Patch Antenna with A return loss of -15 dB from2 to 5 GHz was Designed Details about the Chamber The chamber is made of 1/16” thick aluminum and has dimensions 37” by 27” with a height of 9”. The box was provided by Kodak and was being used for a slightly different setup that included a PC inside the box. As a result, there are many unnecessary holes that fit connectors that are no longer needed. Making improvements to the aluminum box to convert it into a fully shielded anechoic chamber was the first step of the project.

Absorbent Foam The box is lined with ¾” thick foam that absorbs RF power. This helps reduce reflections inside the chamber that lead to false measurements.

Testing Isolation Isolation between the inside of the chamber and the outside world is an important figure of merit for an anechoic chamber. The isolation will be different depending on what frequency is used. The isolation measurements done so far have been using 2.412GHz, which is Bluetooth and Wi-Fi. The broadband antenna wasn’t manufactured in time to make measurements with, so a 2.4GHz patch antenna is used instead. A USB Wi-Fi module is used to output a single tone which can be accurately measured using a Spectrum Analyzer. The module is placed a fixed distance from the patch antenna with a direct path, then the power measurement is taken. The module is then placed inside the chamber and the antenna on the outside, the same distance away as before. The power measurement is subtracted from the previous measurement to find the isolation.

Measuring Radiation Pattern and Gain A LabVIEW program controls the motor to rotate in 0.5 degree steps and takes a reading from the spectrum analyzer at each location. Once a full revolution is complete, the radiation pattern is plotted. An antenna with known gain is used as reference to calibrate the gain of each antenna tested.

Acknowledgements Special Thanks to: Mark Hinman & Kodak George Slack Dave Hathaway and the Machine Shop Personnel Vincent Baier