I’ve been fascinated with antennas since I got my amateur radio license in high school. Just the idea of a hunk of metal on a pole that allowed radio conversations locally, internationally, and even interplanetary seemed like black magic to me. Honestly, some aspects still do!
I learned the mathematics in engineering school, which unraveled some of the mystery, but probably heightened the fascination. In my ham radio days, I built antennas from formulas and tested them with an SWR meter and a transmitter. It was crude, but with patience and a good pair of wire cutters, I frequently made antennas that brought gushing signal reports.
Later, when I had access to more sophisticated tools, such as a network analyzer, my learning went into high gear. Now, I could see the performance of the antenna from a much more detailed view and effects of things I never even thought of became apparent — presence of nearby metal structures and dielectrics, performance of different materials, and even how some insulating materials at lower frequencies absorb a great deal of energy at higher frequencies.
When the subject of passive RFID tags is discussed (see my article in WDD), the antenna is virtually the system. The design of the antenna, including accounting for all possible external influences on performance, is the difference between a tag meeting design goals and not working at all. And, at the upper UHF frequencies we’re talking about, these possible influences as well as critical dimensions can be quite subtle.
For this reason, simulation is something that has become a necessity. Today’s simulation tools not only allow antennas to be quickly designed, but many “what ifs” answered in a reasonable amount of time and without actually building any hardware. Any external influence on the system can be analyzed if it can be mathematically modeled. Worst-case conditions can be predicted to ensure that all products meet specifications even in the most compromising RF environments. In addition, measurements from the actual hardware can be used to troubleshoot, optimize, and verify performance.
Yes, it’s a lot different today than the days when I used “468/f” to determine the length of a half-wave dipole, but the stakes are so much higher as well. RFID tags and Readers must perform in all kinds of conditions and locations to be viable in the marketplace. Plus, the micro-price points of the devices add quantum levels of complexity as well. Superior simulation that is fast is cornerstone to producing market-ready products at competitive prices.
Read Mark's article "The Effects of Meandering in RFID Tag Design at: http://www.wirelessdesignmag.com/ShowPR.aspx?PUBCODE=055&ACCT=0027977&ISSUE=1101&RELTYPE=wtf&PRODCODE=X0160&PRODLETT=A&CommonCount=0 
Mark Forbes is Content Manager for Mentor Graphics Corporation with 31 years in electronic design, antenna design, product marketing, and documentation. Mark has patents in antenna design and digital communications, and is inventor of the Ventenna, a concealed antenna system. He has a BSEE from Bradley University in Peoria, Illinois.