A bandpass filter (BPF) with shielded inverted microstrip lines (SIMSL), previously demonstrated by the author, has shown the nontrivial asymmetry of filter responses in spite of adopting a conventional filter synthesis procedure. This paper will reveal the mechanism of the asymmetry and propose prescriptions for recovering the defect, in addition to observing the wave propagation property of SIMSL. Firstly, the behavior of phase constants or effective dielectric constants for various modes propagating on single SIMSL are indicated in terms of the line configuration, and the dispersion characteristics of the quasi-TEM mode are interpreted from the point of mode coupling between the pure TEM mode and dielectric slab modes. Then it is shown that the asymmetry is dependent only on the transmission characteristics of SIMSL parallel-coupled lines involved in the filter circuits. Theoretical considerations reveal that the asymmetry is due to the fact that SIMSL has quite different phase constants for the even- and odd-mode. On the basis of these results, the optimized BPF is designed and it is experimentally demonstrated that the symmetry of its responses is notably recovered. Furthermore, this optimization is still quite efficient for achieving high attenuation properties at its harmonics.

This paper describes a 2.4-GHz downconverter that runs on a 1-V supply. The downconverter integrates an LNA, a quadrature mixer, a complex channel-select band-pass filter (BPF), a limiting amplifier, and a frequency doubler using 0.2-µm CMOS/SOI technology. The frequency doubler doubles the frequency deviation of FM signals as well as the frequency itself, which in turn doubles the modulation index. This improves the sensitivity of FM demodulation. The power consumption of the downconverter is 23 mW with a 1-V power supply. A bit-error-rate (BER) measurement using the downconverter and a demodulation IC shows -76.5-dBm sensitivity at a 0.1% BER.

The present study introduces the adaptive BPF to the BPSK coherent detection system and the characteristic of the resulting system is investigated.

A two stage Combline Bandpass Filter (C-BPF) of the Vertically Installed Planar (VIP) structure has been investigated, which is essentially composed of a strongly coupled microstrip lines terminated with a planar fin and through-hole combined with the tapping feed approach. The principle and performance of this filter is studied approximately by an equivalent circuit model and also by the normalized 3D-FDTD method more exactly. The time domain iteration in the FDTD analysis is performed in an expanded time dimension resulting in a reduced CPU time. Some of the obtained numerical results are compared well with the measured ones. A modified VIP combline BPF has the advantages of simple structure, easy tuning, low cost, versatile bandwidth control and good skirt characteristics brought about by two attenuation poles.