Design of tri-layer tri-band microstrip band pass filter using hairpin and spiral resonators

This paper presents the design of tri-band hairpin filter using tri-layer structure to achieve miniaturization. Five miniaturization methods are utilized for the proposed filter to achieve excellent size reduction. The tri-band hairpin filter is designed at the centre frequencies of 2.4, 3.5 and 5.2 GHz respectively. The filter consists of a pair of quarter wavelength spiral and hairpin resonators and they are connected to the common via which provides the ground connection for the resonators. A pair of uniform impedance resonators are implemented on top layer which corresponds to the centre frequency of 3.5 GHz. The spiral resonators correspond to the centre frequencies of 2.4 and 5.2 GHz are added on middle and bottom layers respectively. The pass band frequencies can be tuned independently for desired values by adjusting the geometric parameters of the resonators. The resonators are arranged in tri-layer structure to reduce the size of the filter. The filter is designed on a substrate of neltek with the dielectric constant of 3.2 and thickness of 0.9 mm. The optimization of tri band filter is achieved by the software ADS 2009. The overall size of the filter is 7 × 8 mm².