Inverted defected ground structure for microstrip line filters reducing packaging complexity

A new defected ground structure for microstrip line circuits was introduced by keeping the ground plane of the circuit fully metallized and etching the slots on the superstrate, which is directly lain on the top of the substrate. The metal of the superstrate is connected by via holes to the ground plane. The structure has the great advantage in reducing the packaging complexity, since it can be directly based on the carrier block without the need of machining a recessed region in it. Moreover, a higher Q-factor is obtained for this kind of structures. The low-pass filter based on this structure was designed, fabricated and measured. The DGS structure located on the superstrate provides the transmission zeros improving the steepness of the transmission characteristic and the attenuation in the stop-band. The filter insertion losses are better than 0.4 dB. The measured data fit well the results of MoM simulation.