High gain printed monopole arrays for wireless applications

In this work we discuss the design of planar arrays in which N + 1 parasitic monopoles, properly placed in a linear array of N active elements, allow a broadside radiation and a gain value close to that of a standard 2N +1 active element array. Parasitic metallic strips are placed symmetrically on both sides of each microstrip monopole and, in order to achieve the correct phase lag for a broadside pattern, meandered lines are inserted between the feeding microstrips and the active monopoles. Linear arrays working in the wireless local area network (WLAN) band around 2.4 GHz and composed of 5X1 and 9X1 microstrip monopoles with their feeding network have been designed and fabricated on FR4 substrates. In order to obtain a unidirectional pattern, a metallic plane reflector is placed at a distance of about lambda/4 from the array board: predicted gain (11 dB for 5X1 array and 15 dB for 9X1 array) and bandwidth (around 600 MHz) are larger than for conventional microstrip patch arrays having similar board dimensions.