Frequency reconfigurable Yagi-like MIMO antenna system with a wideband reflector

A compact single layer frequency reconfigurable Yagi-like multiple-input multiple-output (MIMO) antenna system is presented based on a half-ring closed loop slot excitation. The traditional omnidirectional pattern of a slot antenna is made directional by using a single slot-based complementary wideband reflector (CWBR) element. The proposed CWBR is compact in size, simple in construction, and is based on a single-layer geometry unlike complex multi-layer reflectors used in the literature. It improves the front-to-back ratio between 5 and 17 dB in the entire frequency range covering 2.5–4.5 GHz. The proposed reconfigurable MIMO antenna system covers the LTE and WiMAX bands with a minimum measured bandwidth of 200 MHz per covered bands. The frequency reconfigurability is achieved by reactively loading the slot loop with varactor diodes. The overall size of the proposed antenna system is ${40}\times {100}\times {0.76}\,{\rm mm}^3$40×100×0.76mm3, making it suitable for tablet handheld devices and access points. It has a maximum measured peak gain of 5 dBi and total measured radiation efficiency of 78%. The proposed MIMO antenna system has port isolation of $\gt $>10 dB within the entire band of operation. The radiation patterns are isolated in space from each other and ensure very low envelope correlation coefficient.