Patch Driven Yagi Antenna ... This information was found on the internet and I have lost the link to the original source so I reproduced it here. The reference at the end of the document provides some information concerning the author. I thought the information was very interesting and needed to easy for me to find so I placed it here. Description of Antenna This antenna design yagi-style directors to enhance the performance of a standard patch. The configuration is shown below in the diagram. Design Curves The design curves included here enable the dimensions of the patch and the director boom to be obtained as a function of gain and bandwidth. FIGURE 1 Gain vs Boom Length This figure shows the gain obtained for specific boom lengths of between 1.2 lambda and 15 lambda, for a patch width of 0.45 lambda. Patch height is between . Director spacing is 0.3 lambda. The optimum director length for the range of boomlengths (all dimesions in wavelengths) is shown in the table below: Boom Length 1.2 2.4 4.2 8.4 12 15 Director Length 0.445 0.442 0.431 0.422 0.419 0.412 FIGURE 2 Bandwidth vs Patch Width Once the boom length is known the bandwidth can be adjusted by varying the patch width. The patch height is 0.037 lambda and the gain is not significantly affected by varying the patch width. FIGURE 3 Bandwidth Multipication Factor vs Patch Width If an even further increase in bandwidth is needed then the patch height may be increased resulting in the bandwidth being multiplied by a factor determined from above figure. Finally the patch length may be obtained from the equation 1, the discreet values for the patch heights of 0.0876 lambda, 0.07586 lambda, 0.06353 lambda are 0.3371 lambda, 0.3448 lambda, 0.3529 lambda respectively. Patch Length = -0.658425(Patch Height) + 0.39475....1 Example An antenna of the following specification is required: maximum boomlength of 8.4 lambda mimimum bandwidth of 40% maximum possible gain. From figure 1 the gain for this antenna will be approximately 16.5 dBi. The directors will have a length of 0.422 lambda (from table) which are spaced 0.3 lambda apart. The maximum bandwidth (with a patch width of 0.8 lambda) is approximately 23.5% (from figure 2). This can be further increased to 42.3% (from figure 3) by increasing the patch height to 0.0876 lambda. The corresponding patch length is then 0.3371 lambda. The final characteristics of the antenna are therefore as follows: total boomlength of 8.4 lambda bandwith of 42.3% directors of 0.422 lambda long and 0.3 lambda apart from each other patch of 0.8 lambda wide, 0.3371 lambda long and 0.0876 lambda high NOTE: These design curves provide only a rough estimate of a particular antenna's dimensions and performance. In order to fully specify the antenna it should be simulated, using the values obtained from the curves if so desired. Reference: Fourth Year Design Report, "Investigate the Design of a Patch Driven Yagi Antenna" prepared by Tobin Devasia for the School of Electrical and Information Engineering, University of the Witwatersrand, August 2003.

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