A novel multilayer super-compact inharmonic photonic band-gap (PBG) structure for microstrip applications

A novel two-layer biperiodic PBG microstrip structure, characterized by periods in an inharmonic ratio and by the use of highly reactive elements (printed inductors/capacitors), is proposed. The inharmonicity of the periods (a and 2a/3) ratio gives rise to a resulting configuration of larger period (2a) which, in conjunction with the loading effect of the reactive elements, leads to an extremely low cutoff frequency and makes therefore the structure super-compact. Moreover, the existence of three different effective periods, each controlling a different frequency range, yields a huge photonic band-gap. Two different configurations of this novel PBG, including inductor and capacitor elements in the intermediate PBG plate, respectively, are presented. It is shown from simulation and measurement results that these structures exhibit a low-pass filter behavior with a cut-off frequency corresponding to a≈λ/8 and a gap of width exceeding 150% with excellent transmission in the pass-band.