A low-profile antenna-triplexer is realized using a substrate integrated waveguide (SIW) technology for radio
altimeter/ WLAN/ISM band applications. The antenna is composed of two SIW cavity resonators where a smaller cavity is nested
inside the larger one. The larger cavity is excited by using two distinct microstrip feedlines, while the smaller one by a coax
probe. The antenna produces three distinct resonances around 4.18, 5.2, and 5.8 GHz simultaneously employing one annular
slot and two transverse slots. By exciting cavity modes (TE110/TE120) and the patch mode (TM10 ) simultaneously, an average
isolation of better than 23 dB is accomplished among three input ports. As compared to the conventional counterparts, the
proposed geometry is simple to realize in a compact space. To validate the proposed idea, the design is experimentally tested, and
the measured responses show a good agreement with the simulations. Moreover, the antenna shows a front-to-back ratio better
than 19 dB and measured gain
