Design and realization of high-performance microwave and millimeter wave band-pass filters on thin polymer films

During the last decade, we observed an explosion of wireless communications and multimedia services. The rapid growth of data exchanged, through information and communication networks, requires the development of components and devices with higher performance and improved functionality, while satisfying the constraints of weight, size, power consumption and cost. Microwave filters are essential components in various electronic systems, including cellular radio, radars and satellite communications. They are indispensable to detect weak signal buried in noise and improve radar's sensitivity. They are also very useful to improve spectrum efficiency in software radio technology. In microwave communication systems, band-pass filters are usually used in both receivers and transmitters. So they are requested to meet the following electronic requirements: low insertion loss, high frequency selectivity, phase linearity and no harmonic response. Band-pass filters structures are widely reported in the literature. However these studies were conducted in the most cases on thick commercial substrates [1-3]. To date, very few studies have focused on filters on thin films whereas the low thickness of the substrate facilitates the coupling between the circuits on the surface and the lower ground plane [4] which allows having a high selectivity filter. This paper reports the design and manufacturing of microstrip band-pass filters with good performance in terms of both insertion loss and selectivity.The proof of concept is carried out on thin BCB polymer (70 μm) film very used in microelectronics thanks to its low loss tangent (tan δ = 0.0025). The studied filters are constituted of two resonators and they combine the compactness of microstrip resonators and the connection facility of coplanar pads due to microstrip-grounded coplanar waveguide transitions integrated with the filters. The filters structures, that will be presented,have the following performance:. 6% bandwidth and -1.6 dB insertion losses at central frequency of 15 GHz, 4.5% bandwidth and -1.7 dB insertion losses at central frequency of 20 GHz, 5.5% bandwidth and -1.5 dB insertion loss at central frequency of 25 GHz, 8% bandwidth and -1.1 dB insertion loss atcentral frequency of 35 GHz, 4.8% bandwidth and -1.4 dB insertion losses at central frequency of 45 GHz. The filters on thin polymer film have the advantage of being low cost and very easy to fabricate.