Multioctave bandwidth log-periodic microstrip antenna array

Abstract
The application of the log-periodic technique to the series-fed electromagnetically coupled overlaidpatch array allows antennas with flat conformal characteristics and wide bandwidths to be obtained. A k-β analysis of this and other microstrip array types indicate that the microstrip patch is not an optimum element for log-periodic arrays and that direct connection will result in arrays having a limited bandwidth. The addition of series capacitance to the patch equivalent circuit, implemented by electromagnetic coupling, allows an optimum to be approached. Log-periodic overlaid patch array design and measured results for an array with a 4:1 bandwidth are presented. These, together with a transmission-line analysis, indicate the array-design trade offs available and that the ultimate bandwidth is limited primarily by changes in the input return loss and radiation pattern due to the use of uniform thickness substrates.

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