Meander Line Anteena
Fundamental Dimension Limits of Antennas
Ensuring Proper Antenna Dimensions in Mobile Device Designs
Randy Bancroft Centurion Wireless Technologies Westminster, Colorado
Abstract–The electronics industry has historically decreased the physical dimensions of their product offerings. In the age of wireless products this drive to miniaturize continues. Antennas are critical devices that enable wireless products. Unfortunately, system designers often choose antenna dimensions in an ad hoc manner. Many times the choice of antenna dimensions is driven by convenience rather than through the examination of fundamental electrical limitations of an antenna. In this presentation the fundamental limits and the trade-offs between the physical size of an antenna and its gain, efficiency and bandwidth are examined. Finally, we examine the difficulty experienced in determining the physical dimensions of an antenna when “non-antenna” sections of a device’s structure may be radiating.
“It was the IRE (IEEE) that embraced the new field of wireless and radio, which became the fertile field for electronics and later the computer age. But antennas and propagation will always retain their identity, being immune to miniaturization or digitization.” – Harold A. Wheeler
Electrically Small Antennas
Many customers often budget the amount of antenna volume for a given application on an ad hoc basis rather than through the use of electromagnetic analysis. Frequently the volume is driven by customer convenience and is small enough that performance trade-offs are inherent in the antenna solution. Many times the volume allotted may be such that only an electrically small antenna can be used in the application. Early in a design cycle it is important to determine if the physical volume specified is, in theory, large enough electrically to allow the design of any antenna which can meet the impedance bandwidth requirements specified. There is a fundamental theoretical limit to the bandwidth and
Ensuring Proper Antenna Dimensions in Mobile Device Designs
Randy Bancroft Centurion Wireless Technologies Westminster, Colorado
Abstract–The electronics industry has historically decreased the physical dimensions of their product offerings. In the age of wireless products this drive to miniaturize continues. Antennas are critical devices that enable wireless products. Unfortunately, system designers often choose antenna dimensions in an ad hoc manner. Many times the choice of antenna dimensions is driven by convenience rather than through the examination of fundamental electrical limitations of an antenna. In this presentation the fundamental limits and the trade-offs between the physical size of an antenna and its gain, efficiency and bandwidth are examined. Finally, we examine the difficulty experienced in determining the physical dimensions of an antenna when “non-antenna” sections of a device’s structure may be radiating.
“It was the IRE (IEEE) that embraced the new field of wireless and radio, which became the fertile field for electronics and later the computer age. But antennas and propagation will always retain their identity, being immune to miniaturization or digitization.” – Harold A. Wheeler
Electrically Small Antennas
Many customers often budget the amount of antenna volume for a given application on an ad hoc basis rather than through the use of electromagnetic analysis. Frequently the volume is driven by customer convenience and is small enough that performance trade-offs are inherent in the antenna solution. Many times the volume allotted may be such that only an electrically small antenna can be used in the application. Early in a design cycle it is important to determine if the physical volume specified is, in theory, large enough electrically to allow the design of any antenna which can meet the impedance bandwidth requirements specified. There is a fundamental theoretical limit to the bandwidth and
References: [1] H.A. Wheeler,“Fundamental Limits of Small Antennas,” Proceedings of The I.R.E. (IEEE), December 1947, pg. 1479-1484 [2] K. Fujimoto, A. Henderson, K. Hirasawa and J.R. James, Small Antennas, John Wiley & Sons Inc. 1987 [3] H.A. Wheeler,“The Radiansphere Around a Small Antenna,” Proceedings of The I.R.E. (IEEE), August 1959, Vol. 47 [4] James S. McLean, “A Re-Examination of the Fundamental Limits on The Radiation Q of Electrically Small Antennas,” IEEE Transactions on Antennas and Propagation Vol 44, NO. 5, May 1996, pg. 672-675 [5] Johan C.—E. Sten, Arto Hujanen, and P¨ivi K. Koivisto, “Quality Factor of an Electrically Small Antenna a Radiating Close to a Conducting Plane,” IEEE Transactions on Antennas and Propagation, VOL. 49, NO. 5 May 2001, pp. 829—837 [6] Gary A. Thiele, Phil L. Detweiler, and Robert P. Penno, “On the Lower Bound of the Radiation Q for Electrically Small Antennas,” IEEE Transactions on Antennas and Propagation, VOL. 51, NO. 6 June 2003, pp. 1263—1268 [7] Roger F. Harrington, “Effect of Antenna Size on Gain, Bandwidth, and Efficiency,” Journal of Research of the National Bureau of Standards—D, Radio Propagation VOL. 64D, No. 1, January-February 1960, pp. 1—12 [8] O. Staub, J.F. Z¨rcher, and A. Skrivervlk, “Some Considerations on the Correct Measurement of the Gain u and Bandwidth of Electrically Small Antennas,” Microwave and Optical Technology Letters, VOL. 17, NO. 3 February 20, 1998, pp. 156—160