Sadahiko Yamashita

Geometrical structures and fundamental characteristics of microwave stepped-impedance resonators

/spl lambda//sub g//4-,/spl lambda//sub g//2-, and /spl lambda//sub g/-type transmission-line stepped-impedance resonators (SIRs) have been proposed and various practical applications have been reported on the basis of the analysis related to each resonator. This paper standardizes these three types of SIRs and systematically summarizes their fundamental characteristics, such as resonance conditions, resonator length, spurious (higher order) responses, and equivalent circuits. Practical applications which employ features of three types of SIRs are investigated with demonstrations of specific structures. Original design formulas with respect to /spl lambda//sub g/-type dual-mode resonators are analytically derived. Advanced SIRs using composite material and multisteps are also introduced and their availability is discussed.

Bandpass Filters Using Parallel Coupled Strip-Line Stepped Impedance Resonators

Approximate design formulas for bandpass filters using parallel coupled stripling stepped impedance resonators (SIR) are derived. The formulas take into account the arbitrary coupling length as well as quarter-wavelength coupling. Some advantages of this filter are its abilities to control spurious response and insertion loss by changing the structure of the resonator. Using the design formulas two experimental filters were designed and fabricated and their performances closely matched design data.

Compact bandpass filters using stepped impedance resonators

This paper presents a theoretical analysis of, and experimental results given by, stepped impedance (SI) resonators constructed and used as high-Q resonators in the UHF band. These results made it clear that the Q-factor is higher than conventional capacitor-loaded resonators. Three types of bandpass filters were designed and fabricated using the SI resonators. The filters mentioned in this paper show that excellent performance has been obtained.

A Design Method of Bandpass Filters Using Dielectric-Filled Coaxial Resonators (Short Papers)

Design formulas for capacitively coupled bandpass filters using dielectric-filled coaxial resonators are derived and experimentally verified. The most important advantage of this filter is its ability to provide wide stopband characteristics for harmonics suppression. Its features can be obtained from the configuration using both quarter-wavelength uniform impedance resonators (UIRs) and stepped impedance resonators (SIRs).

Basic Structure and Characteristics of SIR

Transmission-line resonators are most frequently used in frequency regions above the VHF band, yet, as described in the previous chapter, most applications employ structures with uniform characteristic impedance. Transmission-line resonators possessing a stepped-impedance structure (SIR) have long been known as an available resonator structure, and are often used to experimentally examine the effect of discontinuity in the impedance step of a transmission line [1]. However, this stepped impedance structure was hardly ever used for practical circuits, with the exception of impedance transformers.

Half-Wavelength-Type SIR

The basic structure, electrical characteristics, and application examples of a λg/2 type SIR are discussed in this chapter. Although the λg/4 type SIR is proven to be the most suitable structure for miniaturization, in practical application the λg/2 type SIR realizes far more RF devices than does the λg/4 type SIR. This is due to the fact that the λg/2 type SIR is usually composed of a stripline configuration, thus allowing a wide range of geometrical structures while possessing good affinity with active devices.

Quarter-Wavelength-Type SIR

The basic characteristics and practical applications of a λg/4-type SIR are described in this chapter. From an application-oriented viewpoint, the λg/4type SIR is the most attractive among various types of SIR, and numerous R and D results have been reported on this type. The main reason for such interest is that the λg/4-type SIR has an essential availability for resonator miniaturization [1]. As discussed in Chap. 2, one of the main features of the) λg/4-type SIR is the capability of reducing resonator size, while another is the capability of controlling spurious frequencies by design. These two properties make the λg/4-type SIR an extremely suitable resonator element for mobile communication filters. A coaxial structure is most frequently adopted for practical application of λg/4-type SIR to filters. Coaxial type resonators have the following advantages.

Expanded Concept and Technological Trends in SIR

In the previous parts we considered the SIR as a distributed transmission-line resonator possessing a step-junction structure. When focusing on broad electrical characteristics to classify single-dimensional transmission-line resonators into homogeneous and inhomogeneous impedance resonators, the SIR can be categorized as an inhomogeneous impedance resonator. Thus, by expanding the basic concept of the SIR defined in the previous chapters, an expanded analysis method can be applied to inhomogeneous impedance resonators, such as tapered-line resonators possessing a continuous change in characteristic impedance. Although in the former discussions the step change in characteristic impedance is realized by a geometrical change in the structure of the transmission line, an equivalent impedance step can be achieved by altering the material applied to the transmission line, or by a combination of both structural and material changes.

One-Wavelength-Type SIR

A one-wavelength resonator formed by a stripline, micro-stripline, or slotline structure features low radiation-loss characteristics, and a structural advantage enabling the elimination of parasitic components which are usually induced at the open- and short-circuited ends of conventional half- or quarterwavelength resonators. These features account for their frequent application to standard resonators for measuring stripline characteristics and dielectric substrate properties. However, when considering their practical application as single mode resonators, the overall size of the λg(one-wavelength) resonator becomes a large handicap as compared to the other candidates.

Compact TV Channel Filters in the UHF Band

This paper describes the design and fabrication of compact bandpass filters for UHF TV channels using Stepped Impedance Resonators (S.I.R.). The fabricated channel filter shows an insertion loss of below 3.0 dB with 6 MHz passband at a center frequency of 690 MHz. The center frequency can be changed ±50 MHz.