A compensated compact microstrip resonant cell with photonic band-gap performance

A compensated compact microstrip resonant cell (C-CMRC) with photonic band-gap (PBG) performance is presented in this paper. Two open microstrip stub-lines are added at the center of the compact microstrip resonant cell ( CMRC) to compensate for the unbalanced change of inductance and capacitance in low pass band. It can significantly improve the return loss and insertion loss. Furthermore, the C-CMRC with capacitive loading leads to a stronger slow-wave and enlarged stop-band bandwidth. A low pass filter with 3 C- CMRC resonators in series has been designed according to the PBG performance. The period is only 0.15 lambda(g) due to the slow-wave effect. Comparison with the general PBG period of 0.5 lambda(g), the circuit size is reduced effectively. The original CMRC and the C-CMRC with open stub lines are designed, fabricated and measured to validate the improved performance. A low pass filter with 3 C- CMRC resonators is also designed with 1.26 dB insertion loss below 1.8 GHz and more than 25 dB stop-band from 2.6 to 9 GHz.