Millimeter-Wave Dual-Band Filtering Patch Antenna and MIMO Array Using Multinull Resonator

A compact millimeter-wave (mm-wave) dual-band filtering patch antenna is presented. It is fed by a new multinull resonator, composed of a single-layer substrate integrated waveguide (SIW) cavity-backed slot. This multinull resonator can produce two resonant modes and three radiation nulls. With the load of a radiating patch, another radiation null can be generated between the two operating bands. In addition, the radiating patch produces two patch modes by introducing an H-shaped slot and four shorting pins. Therefore, a second-order bandpass filtering response is obtained for each operating band. Owing to this new multinull resonator, two controllable radiation nulls are realized beside each band, showing high-frequency selectivity and an out-of-band suppression level of more than 18 dB. The antenna prototype, with only two substrate layers, has antenna gains of 8 and 7.5 dBi in the 28- and 39-GHz bands. Furthermore, the dual-band filtering patch antenna is extended to a
$2\times 2$
multiple input/multiple output (MIMO) antenna. With the aid of
$\pi $
-/L-shaped parasitic strips, the isolation of the E-plane MIMO is enhanced by 5 dB. The isolations between any two-antenna elements are higher than 20 dB for the two passbands.