A tunable planar bandpass filter based on a technique that utilizes a half mode substrate integrated waveguide (HMSIW) and novel inter-resonator coupling is presented. The tunable HMSIW based bandpass filter is implemented using two half triangle shaped cavities coupled together through inter-resonator coupling forming half mode bowtie shaped structure. The bowtie-shaped filter exhibits similar performance as found in rectangle- and circle-shaped SIW based bandpass filters. This concept reduces the circuit foot print, and miniaturization high quality factor is maintained by the structure. The tunable filter utilizes packaged RF MEMS switches; switching between different configurations of switches achieves four distinctive frequency states between 4.8�5.3 GHz. The filter maintains a constant absolute 1 dB bandwidth of 100 ± 10 MHz for all frequency states. © 2015, Electromagnetics Academy. All rights reserved.