Guided‐wave characteristics of periodic microstrip lines with inductive loading: Slow‐wave and bandstop behaviors

Characterization of periodic microstrip‐line EBG structures with improved bandstop behaviors

“…Firstly, all the results show a deep and wide stop-band with the minimum S 21 lower than nearly Ϫ35 dB with the number of unit cell of N ϭ 3, as compared with Ϫ17 dB of the three-cell EBG (Fig. 2) and Ϫ35 dB of the five-cell EBG reported in [5], thereby implying its promising application in the low-pass filter with miniaturized size. Secondly, as L 1 is reduced from 1.8 to 1.2 mm, as shown in Figure 4(a), the stop-band becomes wider and deeper, the cutoff frequency is almost kept as an unchanged value of about 4.3 GHz, and the 1 st harmonic passband is raised from 12.2 to 15.2 GHz.…”

“…In recent years, as photonic bandgap (PBG) material was invented in the optical field, much effort has been made in the microwave field to develop a variety of planar electromagnetic band-gap (EBG) structures [2,3] that are intuitively viewed as periodic transmission lines [4,5] with inductive loading in series. By etching out a certain portion of metallic ground underneath the strip conductor in periodical intervals, the so-called microstrip-line EBG structure with circular and rectangular aperture configurations were constructed in [2] and [3], respectively.…”

“…Meanwhile, the wide strip section with width W can be considered as a shunt capacitor due to its low characteristic impedance or tightened coupling between the wide strip and ground plane. In addition, our previous study [5] showed that the increase in the number of unit cells can help to realize the good low-pass filtering behavior with a widened and deepened stop-band of band-pass filters. During this investigation, our focus is to demonstrate that the strip/aperture widths and length can be optimally designed in order to achieve a deep and wide stop-band without enlarging the size of the whole EBG circuit under the fixed cell number N ϭ 3.…”

“…Each unit cell is comprised of one backside-apertureloaded narrow strip conductor with length L 2 at the center and two widened strip conductors with the identical lengths L 1 . Following the statement in [1,5], the narrow strip section with backside aperture can be equivalently perceived as an enhanced series inductance at low frequencies, due to its high characteristic impedance or weakened coupling between the narrow strip and ground. Meanwhile, the wide strip section with width W can be considered as a shunt capacitor due to its low characteristic impedance or tightened coupling between the wide strip and ground plane.…”

“…By etching out a certain portion of metallic ground underneath the strip conductor in periodical intervals, the so-called microstrip-line EBG structure with circular and rectangular aperture configurations were constructed in [2] and [3], respectively. Their electrical performances have been theoretically and experimentally characterized in terms of the S-parameters of an EBG device [2,3] and unit-length transmission parameters of an EBG media [5].Based upon our previous work in the design of lowpass filters [6], an improved microstrip-line EBG structure is constructed by widening the strip width of a low-impedance section and formulating the backside aperture underneath the narrow strip of a high-impedance section, as illustrated in Figure 1. In order to characterize it in theory, a numerical finite-difference time-domain (FDTD) method [7] is developed with the use of Mur's absorbing boundary conditions (ABCs).…”