Figure 4 Performance of the microstrip open-loop resonators. Details of Ža. simulated and Žb. measured spurious responses

4. CONCLUSIONS

We have proposed two types of microstrip open-loop resonators, and have investigated the effect of the variation in the width of one of the longer strips of the open loop on their resonance characteristics. For estimation of the fundamental resonance frequency, we have derived simple empirical expressions as a function of the variable strip width and the fundamental resonance frequency of the associated resonator. Moreover, it has been shown that the ŽVG. MOLR can support a wider upper stopband, including the first spurious resonance frequency, by suppressing the spurious passband at the first spurious resonance frequency for planar bandpass filters. So, these structures can be more flexible for constructing a variety of planar filters with a wider upper

Figure 5 Comparison of measured Q-factors of conventional halfwavelength microstrip resonator and novel microstrip open-loop resonators for r 2.33 and h 1.575 mm

stopband. The resonance characteristics of the ŽVG. MOLR are also different from those of the ŽFG. MOLR. As a result, microstrip open-loop resonators are not only much simpler in structure, but also have a larger slow-wave effect as compared to conventional half-wavelength microstrip and standard microstrip loop resonators.

REFERENCES

1.J.S. Hong and M.J. Lancaster, Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters, IEEE Trans Microwave Theory Tech 44 Ž1996., 2099 2109.

2.J.S. Hong and M.J. Lancaster, Theory and experiment of novel microstrip slow-wave open-loop resonator filters, IEEE Trans Microwave Theory Tech 45 Ž1997., 2358 2365.

3.C.C. Yu and K. Chang, Novel compact elliptic-function narrowband bandpass filters using microstrip open-loop resonators with coupled and crossing lines, IEEE Trans Microwave Theory Tech 46 Ž1998., 952 958.

4.EM user’s manual, Sonnet Software, Inc., version 6.0, Liverpool, NY, 1999.

2001 John Wiley & Sons, Inc.

LEAKY-WAVE RADIATION FROM A GROUNDED DIELECTRIC WAVEGUIDE WITH FINITE PERIODIC GROOVES ON A CONDUCTING PLANE

Cheol Hoon Lee1 and Young Ki Cho1

1 Electronic and Electrical Engineering

Kyungpook National University

Taegu 702-701, Korea

Recei ed 7 May 2001

ABSTRACT: The leaky-wa e radiation problem from a grounded dielec- tric wa eguide with finite conducting periodic groo es of an arbitrary profile is considered. To check the alidity of the results for the finite periodic case, an analysis method for the infinite periodic case is also considered for comparison. The analysis method for the finite periodic case is based on a combined FEM (finite-element method) MoM (method of moments) procedure, whereas a full MoM procedure is used for the infinite periodic case. 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 180 185, 2001.

Key words: leaky wa e; periodic structure; gratings

I. INTRODUCTION

Grating structures have found many applications in the areas of optics plus microwave and millimeter-wave engineering. Some important applications include beam couplers for the optical range and leaky-wave radiators and band-reject filters for the microwave and millimeter range. As a result, much research concerning periodic loading problems in various waveguides has been conducted in such areas.

Among prior work with a direct bearing on the current study, Park and Seshadri 1 2 analyzed dielectric-slab waveguide geometry grounded by a sinusoidally corrugated conducting surface using a perturbation procedure for a grating Žbeam. coupler application. Other researchers have focused on the surface-wave scattering problem or leaky-wave radiation problem due to finite periodic rectangular notches in a ground plane using a spectral-domain analysis 3 , along with a sampling theorem or equivalent-circuit approach 4 . In