Small-sized wideband CVT- and CCT-ring filters

Two types of small-sized wideband CVT- (constant VSWR impedance transformer) and CCT- (constant conductance impedance transformer) ring filters are introduced, designed, simulated and one of two, a CCT-ring filter, is tested. They consist of CVTs and CCTs, and two short stubs are connected at the 90/spl deg/ and 270/spl deg/ positions of each ring. The circumference of the ring can be reduced theoretically up to 60/spl deg/ and two of many cases having about 300/spl deg/ circumference are simulated. The simulated results show more than 100% fractional bandwidth, which can be obtained with more than 5 stages in conventional design techniques. A CCT ring filter suggested in this paper has been fabricated in microstrip technology and the measured results show good agreement with the simulated ones.