《2.4GHz 天线设计》.pdfVIP

WHITE PAPER /4 printed monopole antenna for 2.45GHz 1. Preface Taking the demand for small size, easy fabrication and low cost into account in the development of low-power radio devices for short-range 2.4GHz applications, a quarter wavelength monopole antenna implemented on the same printed circuit board as the radio module is a good solution. A printed quarter wavelength monopole antenna is very easy to design and can be tuned simply by slight changes in length. This article presents basic guidelines on how to design such an antenna for use together with the 2.4GHz transceiver and transmitter devices from Nordic Semiconductor. The described antenna should be fabricated on standard 1.6mm, low cost FR4 printed circuit board (PCB). 2. Basic properties of a quarterwave monopole antenna A quarterwave monopole is a ground plane dependent antenna that must be fed single-ended. The antenna must have a ground plane to be efficient, and ideally the ground plane should spread out at least a quarter wavelength, or more, around the feed-point of the antenna. The size of the ground plane influences the gain, resonance frequency and impedance of the antenna. The length of the monopole PCB trace mainly determines the resonant frequency of the antenna, but because of the very wide gain bandwidth of a quarterwave monopole, the antenna length is not too critical. But like any other antenna types, the gain of a quarterwave monopole will vary if parameters in the surroundings , such as case/box materials, distance to the ground plane, size of the ground plane, width and thickness of the PCB trace are varied. If any of these parameters are changed, a retuning of the monopole PCB trace length may be necessary for optimum performance in each application. 3. Determining the length of the printed monopole antenna The antenna is fabricated on a standard 1.6mm FR4 substrate material with a typical dielectric constant of 4.4 at 2.45GHz.