Published Friday, January 25, 2008 | Last Update 1.28.08
Here are your replies to the January Expert Advice column

This month, Dr. Vince Rodriguez, Senior Principal Antenna Design Engineer
with the Field Generation Group of ETS-Lindgren shares some thoughts on
accurately testing today's high-frequency antenna patterns.


Comments: A helpful article. (Yes, I am lazy, too.)

James Gitre, Motorola 1/18/2008 3:07:30 PM

Reference Guide Winner

Comments: The best way to model those antennas will be to make a model of the antenna sitting on the platform (at the correct position and orientation); for example, the laptop or the mobile phone along with the correct material permittivities and permeabilities in an EM simulation software. This will give a very accurate modelling of the EM performance of the antenna without the need of having and making complex measurement test structures and also fabrication of the antenna. Depending upon the resources with the organization, this can be followed by a measurement in an anechoic chamber of the actual antenna device combination. Measuring the radiation pattern means measuring the electrical field strength of an antenna by placing another antenna at a given distance from the test antenna and revolving it around the test antenna to measure the angular variation of its electric field.

Arunabh Chattopadhyay, WINMEC
1/18/2008 3:58:59 PM

Response from the Author: Numerical Modeling is a great tool for the prediction of the behavior of Electromagnetic Systems. I totally agree with that. But we need to realize the limitations of numerical models. It will be very difficult to create a very accurate model of let's say, a wireless router. Are we going to insert all the electronic components that are inside the plastic box in our model? That will take a lot of time and conversely a lot of memory and computer resource will be needed to solve such a complex model. I am myself a Computational Electromagnetics guy, but there is no substitute for a good measurement.


Reference Guide Winner

Comments: Excellent article, thanks. It's important to point out that while Pi/8 is the correct and accepted Far Field region for EMag propagation in general, for some systems like phase tracking antennae used in phase measurement systems, you may have to adjust down the value for parallax to get the right range. Since Pi/8 is 22.5 phase degrees, if you are attempting to phase measure the wave down into single digits, then your range should be lengthened accordingly to give you that single digit value as opposed to Pi/8, right?

Joe Luker, L-3 Communications
1/18/2008 4:16:05 PM

Response from the Author: Totally agree. As I think I mentioned in my note, far field truly occurs at infinity. If measuring null depths and sidelobes is critical in your application you need to be beyond the “pi/8” boundary.


Comments: I want to get a good idea of the measured antenna patterns. Can you describe or show us what techniques required performing the uncertainty analysis of each type antenna range?

Nelson Poon, Lockheed Martin
1/19/2008 12:30:49 AM

Response from the Author: Your best bet is to search IEEE Standard ANSI/IEEE 149-1979 together with the ISO standard on uncertainty.


Comments: Besides the chamber, what microwave test equipment is typically needed for antenna measurements?

Daniel Pils, Student
1/24/2008 2:08:21 PM

Response from the Author: Well, cables, high quality cables, ideally a network analyzer, but a spectrum analyzer used as a receiver and a signal generator could be used. A positioner (to rotate the antenna under test). Reference antennas, source antennas, RF switches may be required, preamplifiers, and software to control all the equipment. There are a lot of parts in the system. It depends a lot on the quality of the measurement and what type of antenna or device you are testing. Testing cell phones adds a lot of additional equipment to communicate with the phone etc.


Comments: I enjoyed this article from start to finish. In working on two way radio while learning RF it is always a struggle to find topics of interest this day and age below 1000 MHz. While this article is mainly for GHz applications all of the theory does apply from DC to light. Looking forward to more of these topics now that I am looking for an anechoic chamber of my own to test antenna designs I am using for GHz projects.

Jason Temple, Valley Two Way
1/25/2008 4:41:42 PM


Comments: Excellent explanation of near field/far field and how to tell when you've crossed from one to the other. I've seen the final equation many times, but this was a nice clear explanation of how it is derived. Textbooks should be so clear. Thanks.

Ghery Pettit, Intel Corp.
1/25/2008 7:13:06 PM



Click here to read the full article
Click here to reply

Disclaimers:
Microwave Journal reserves the right to determine the legitimacy of all responses. The determination of the winning response is not based on any set criteria and is based only on the opinions of the editors of Microwave Journal.

Responses submitted to Expert Advice are collected for sole use by Microwave Journal and www.MWJournal.com. Names and company affiliations may be published with responses according to our editorial policies. Email addresses are collected in case we need to contact you.

Mailing address information submitted for the delivery of the Engineer's Handbook is collected solely for this purpose.

Email addresses and mailing addresses are not published and are not shared with any third party.

This form is not a magazine subscription application nor a Website registration. For magazine registration services, please click here.

Individuals may continue to respond beyond the prize limit (5 total per month) but will not be eligible for receiving the complimentary Engineer's Handbook.