This study reveals a miniaturized high efficiencyantenna for 802.11 ac WLAN applications for UNII-1, UNII-2 and UNII-3 bands operating between 5.18 GHz and 5.8 GHz. Designed antenna can be used in industrial WLAN 802.11 ac applications because of having a relatively omnidirectional radiation pattern and high total efficiency within a small form factor where high isolation required for a MIMO system. Conventional printed Inverted-F antennas are widely used in industry because of their small form factor and wide band characteristics in the desired frequency range. In addition, PIFAs generally tend to have high directivity radiation pattern whose maximum directivity may reach to 5-6 dBi at 5 GHz band. In this study, proximity feeding was used instead of generic micro strip feeding in order to shrink size of the antenna. Also, proximity feeding could be a candidate to feed antennas in the multilayer FR-4 based boards widely used in industrial applications. Presented proximity feed antenna has smaller form factor compared to generic PIFAs and has a more desired omnidirectional pattern with maximum directivity of 2.8 dBi for whole band. This leads us to design an electrically small antenna which has an optimal radiation pattern for indoor Wi-Fi applications with high efficiency of up to 85% at whole band.