A miniaturized bandstop filter (BSF) is introduced in this paper. The filter consists of one meander spurline and a pair of capacitively loaded stubs. The meander spurline with low resonant frequency and improved slow‐wave factor exhibits excellent resonant bandgap characteristics which can be modeled by a longitudinally coupled resonator. The design of the proposed microstrip BSF is presented, and its performance is measured. Measurements show that there is a stopband from 2.3 to 5.6 GHz with S21 less than –20 dB. The total length of this BSF equals 23 mm.
Finite-thickness photonic crystals (PC's) with periodically corrugated interfaces are suggested to realize some unusual features in the behavior of transmitted Bragg beams (diffraction orders). The scattering of s -polarized plane waves by such structures is studied. It follows from the numerical results that rather thin corrugated PC's borrow their basic properties from both conventional PC's and gratings, leading to some new effects. In particular, a shift of the actual cutoff frequencies towards larger values than those of the Rayleigh cutoff frequencies can be obtained due to the ordinary opaque range in transmission, within which all propagative orders vanish. This effect can even be enhanced due to the nonordinary behavior arising at the edges of the ordinary opaque range, which manifests itself in that some but not all propagative orders in transmission are suppressed. Hence the opaque ranges for individual orders are wider than the corresponding ordinary range. Besides, frequency ranges exist which are not connected with the edge of the ordinary opaque range, where a similar nonordinary effect does appear. As a result, each propagative order in transmission generally has its own set of opaque ranges. Only a single order can be contributive while several others are formally propagative, too. The corrugations have to be located at the upper interface in order to realize these nonordinary effects. Moving the corrugation from the upper to the lower interface leads to a disappearance of the observed effects, so that their nature cannot be explained exclusively in terms of matching the wave vectors of the diffraction orders and the Floquet-Bloch waves. The conventional sequence of cutoffs for different diffraction orders with respect to each other can be changed for certain structures if the rods of a PC are made of Drude metal. Hence, transmission regimes can be realized which are beyond the classical theory of gratings. Several effects arising when varying the angle of incidence are demonstrated and briefly discussed. The detected effects can be used for controlling the number of actually contributive beams and for obtaining alternating ranges of single-beam and multibeam operation, which should lead to extending the potentials of optical and microwave technologies based on the use of single-beam and multibeam regimes.
Scattering of s-polarized plane waves by finite-thickness periodic structures is studied, which contain components made of ultralow-permittivity metamaterial ͑ULPM͒, and therefore exhibit intermediate properties between those made of pure metals and of pure dielectrics. The numerical results presented demonstrate basic frequency-and angular-selectivity-concerned effects arising in the structures with sinusoidal corrugations, which are made of ULPM, and for a stack of two such periodic structures, in which one of them is made of ULPM and the other one of a dielectric. The results presented are mostly related to the zero-permittivity case, when there is no wave propagating in the transverse direction within the metamaterial. The field inside ULPM is either close to or exactly the static one. For the structures of the first type, this can lead to a straightening of the field lines at the lower ͑noncorrugated͒ interface and, in turn, to a suppressing of higher modes ͑Bragg beams͒ in the transmitted field, which are allowed to propagate. The known property of a zero-permittivity noncorrugated slab, i.e., the cutoff-type frequency dependence of the transmittance, appears also for corrugated periodic structures studied in both single-and multimode regimes. In our study, a similar behavior vs the angle of incidence is demonstrated and a condition for its appearance is given. For the structures of the second type, it is shown that these effects can be combined with those, which are typical for dielectric gratings and usually associated with bulk and surface modes. Stacking ULPM and dielectric layers can also lead to an enhancement of some effects, which are inherent to each of the layers, as well as to several abnormal effects. The effects found promise to be useful for controlling and, in particular, for splitting/combining of light and microwave radiation.
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