An Improved Design of Equal-Split Filtering Divider with Integrated Coupled-Line Band-Pass Filter
Keywords:
Band-pass filter, coupled line filter,, equal split, filtering dividerAbstract
A novel methodology is proposed for achieving good output port isolation and return loss in a micro-strip filtering divider design with integrated coupled-line (CPL) band-pass filter (BPF). The designed filtering divider shows improved performance parameters as compared to previously reported work. It is proposed that by incorporating an extended transmission line (TL) and a conventional resistor as isolation elements, in addition to good even mode response (i.e., insertion loss IL, and input port return loss RL), the odd mode response (i.e., output port RL and isolation) can simultaneously be improved. In addition, two transmission zeros are realized in the vicinity of the pass band providing a reasonable skirt. Firstly, the coupled-line filter (CPLF) is matched to 70.7 omega and subsequently integrated in place of conventional quarter wavelength transformers in a Wilkinson Power Divider (WPD) for equal division. Under these matched conditions, it is shown that a TL section and isolation resistor sufficed to achieve a reasonable output port return loss (RL) and isolation in the resulting filtering divider. Experimental validation of the proposed methodology comes from the measurements results of the fabricated CPL filtering divider designed at 3 GHz conforming reasonably to the simulated ones. For instance, 1 dB fractional bandwidth of 15.3%, port isolation of better than 31 dB and good out-of-band performance up to 2.67f0 were experimentally achieved.
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