High-order UWB bandpass filter using cascaded E-shape microstrip structure

One type of E-shape microstrip structure is composed of λ_g/2 hairpin resonator loaded by a grounded stub at its middle. For the first time, using an equivalent circuit for this structure, high-order UWB bandpass filter design technique is presented based on cascading E-shape microstrip structures. Two third-order UWB bandpass filters are designed, simulated, fabricated and measured. These filters are compact and have dimensions smaller than 3.5 mm × 3.2 mm × 0.4 mm. The theoretical and measured results show excellent agreement. It is observed that UWB bandpass filters with the E-shape microstrip structure are capable of offering compact circuit size, flat group delay, good selectivity, excellent wideband rejection and low insertion loss.