Targeting the transition from a coaxial wave guide to a coplanar wave guide (CPW), a microwave and millimeter-wave wide-band coaxial-to-coplanar transition is proposed. This design connects the coaxial inner conductor to the CPW center conductor in a perpendicular manner to directly couple, on the same plane, the radial high-frequency electric field in the coax to the gap between the CPW's center conductor and ground plane. The performance of the proposed transition was compared with those of the conventional transition by experiments and electromagnetic field simulations, and it was found that the proposed method is independent of CPW shape and that it exhibits good matching performance in comparison to the conventional method especially in high-frequency bands above 15 GHz.

The design of microstrip bandpass filters using stepped-impedance resonators (SIRs) is examined. The passband center frequency for the WCDMA-FDD (uplink band) Japanese cellular system is 1950 MHz with a 60-MHz bandwidth. The SIR physical characteristic can be designed using a SIR characteristic chart based on second harmonic suppression. In our filter design, passband design charts were obtained through the design procedure. Tchebycheff and maximally flat bandpass filters of any bandwidth and any number of steps can be designed using these passband design charts. In addition, sharp skirt characteristics in the passband can be realized by having two transmission zeros at both adjacent frequency bands by using open-ended quarter-wavelength stubs at input and output ports. A new even-mode harmonics suppression technique is proposed to enable a wide rejection band having a high suppression level. The unloaded quality factor of the resonator used in the proposed filters is greater than 240.

The cutoff filter and circular window are critically important elements of circular waveguide TE11 mode transmission systems, but no detailed analysis of their characteristics has yet been undertaken. In order to gain a detailed understanding of return loss and other frequency characteristics, one must analyze the electromagnetic (E-M) fields in the waveguide cavity to the cutoff domain and higher mode oscillations. In this work we present a theoretical analysis employing a method in which E-M fields are represented in the form of transmission equations, and show that the results are in remarkably close agreement with experimental results obtained from a prototype device. It is also demonstrated that the results obtained by the proposed method are far more accurate than those obtained using conventional approximation theory.