L. P. Mospan

The Simplest Notch and Bandstop Filters Based on the Slotted Strips

New configuration of the notch and bandstop filters is proposed and investigated. Here a rejection section is based on a thin slotted H-plane strip that may be considered as a limiting case of a three-slot iris. Such a section forms symmetrical frequency response with very low insertion loss out of the stopband. The results of numerical design and measurement data are given for a 3% notch filter and for 2% three-section bandstop one. In the low-power applications the proposed notch filter is probably the simplest one due to its easy fabrication and a possibility to be incorporated into a waveguide circuit by placing between the waveguide flanges.

Extracted Pole Bandpass Filters Based On The Slotted Irises

A new design of directly coupled bandpass filter that provides extracted stopband poles is presented by the example of a capacitive iris filter. The attenuation poles are introduced by cutting in iris strips additional slots parallel to the wider waveguide wall. This way of extracted poles implementation does not require spatially developed elements (in particular overmoded ones). The K-inverter corresponding the modified iris changes slightly and may be easily fine-tuned. Additional slot dimensions determine the location and Q-factor of the attenuation poles, which may be placed in the parasitic passband or on a required skirt of the main one. Numerical examples for the three-section filter in WR90 waveguide demonstrate the possibility to increase the skirt selectivity or to improve the stopband attenuation without any extension of the filter dimensions, keeping the same return loss within the passband.

A Multi-Aperture Iris in a Circular Waveguide as a Tool for the Frequency Response Control

The problem of the TE11 mode scattering by a multi-aperture resonant iris in a circular waveguide is considered. Depending on the iris layout it can lead to the transmission, reflection or hybrid response. Filter sections providing transmission or reflection of the incident modes of one or both linear polarizations at a common frequency or at different frequencies are studied. Multi-aperture irises that provide simultaneously a given reflection resonance and required transmission properties are proposed as a tool to introduce additional attenuation poles to the bandpass filter response

Numerical determination of eigenmodes of an arbitrary waveguide with coordinate boundaries in cylindrical coordinate system

Waveguide units with coordinate boundaries in the cylindrical coordinate system are widely used in microwave devices based on circular and coaxial waveguides. Besides the universal finite element methods more accurate and efficient algorithms were built for the analysis waveguides of this kind. However, all of the currently available algorithms were developed for the analysis of individual structures of interest, mainly for ridge waveguides. So far the general algorithm suitable for the analysis of any waveguide of this class has not been developed yet. In this paper we eliminate this gap by a generalization of the mode matching technique to the waveguides with coordinate boundaries in the cylindrical coordinate system taking into account field singularities. The final goal was to obtain a tool for fast calculation of the mode spectrum (up to hundreds) as it was previously built for the waveguides with piesewise Cartesian coordinate boundaries.

Spectral properties of a rectangular waveguide section with a pair of two transversal ridges

Short metal ridges in a rectangular waveguide appeared to be promising units for different microwave filters providing complicated frequency response. In particular, a waveguide containing two rectangular even (or uneven) ridges was used [1] to provide high-quality resonant reflection of the incident mode. A pair of equal height posts in a rectangular waveguide was used lately [2] in order to design a bandpass filter generating an improved response with additional attenuation poles. A quasi-elliptic filter based on a pair equal height posts was reported recently [3]. Off-centered single post and slant single ridge were used successfully in a modern filter design as well [4, 5]. Nevertheless the physical nature of the phenomenon of an attenuation pole generation provided by all the mentioned resonant sections remained unrevealed. Here we use the spectral theory of open waveguide resonators [6-8] to solve this problem. Within the frames of the spectral theory a waveguide unit is considered as open waveguide resonator loaded by semi-infinite guides. Different resonant regimes are interpreted as a response on the excitation of the natural oscillations of the resonator. Similarly to [9], we expect that understanding the physical nature of the resonant phenomena makes their conditions and limitations more clear.

Integrated software package for synthesis, analysis and optimization of frequency-selective devices of millimeter and centimeter waves

The state of the art of theory and practice of signal frequency selection in the millimeter and centimeter wave ranges can be described from one hand as going to more sophisticated schemes of filter building and from another hand, especially in millimeter waves, by extensive usage of practically non-tuning configurations. The first direction as well as the second one is based on the powerful software and on modern production processes, that provide minimal tolerances. Below is a summary of the results that have been obtained in IRE NASU regarding to one of this two sides of filter problems: the short description of the set of software packages for the synthesis and analysis of low-pass (LPF), wide-band and narrow-band band-pass (BPF), and band-stop (BSF) rejection waveguide filters.

Recent advances in computational electromagnetics for microwaves in IRE NASU

Recent advances in problem-oriented and general-purpose microwave-oriented software and applications developed in the department of computational electromagnetics are considered. Numerical-analytical automatic mode-matching based models are extended on the objects given in cylindrical coordinate system. The geometry has to be specified as the set of piece-wise coordinate fragments in Cartesian (MWD1 or MWD2 with account of edge behavior) or in Cartesian or cylindrical coordinates (MWD3) with automatic cross-section geometry recognition and subsequent formation of corresponding mode-matching technique and S-matrix based numerical algorithms. The future extension to the double-periodical screens and multilayer printed circuits (MWD4) is described moving to terahertz frequency band and “metamaterial” investigations. A set of new microwave devices is proposed which are based on the nonstandard physical principles such as the fringing field interaction, new types of eigen-oscillations of 3D open objects and artificial “optical activity”. They are the band-stop and band-pass waveguide filters, antenna-feed units, polarization rotators, twists etc.

Rotation of the polarization plane by double-layer planar-chiral structures. Review of the results of theoretical and experimental studies

This article provides examples that illustrate the search for different two-layer metamaterials that provide rotation of the polarization plane (“optical activity”). Selected objects show a twenty-year history of the search for a new principle of creation of polarization rotators based on planar metamaterials that were implemented in the form of thin-layered periodic structures. The manifestation of optical activity, presence or absence of satisfactory or perfect matching, the possibility of a multiband phenomena, the role of high spatial harmonics in “electromagnetics” of this effect are explained by the features of the eigen-oscillations that are excited in the gap of the multilayer structure.

Compact polarization rotators based on the diaphragms with several rectangular apertures

A possibility to design a compact polarization rotator based on the structures of dihedral symmetry is studied. Here, the diaphragms with several equal rectangular apertures are considered as dihedral symmetry structures. Ultimate performances of the rotators considered are obtained by using different optimization procedures. They demonstrate acceptable reflection in the predetermined frequency band The rotators that achieve the polarization plane rotation by an angle of choice are examined as well.

Compact bandpass wageguide filters based on modified split-ring resonators

Small-sized waveguide bandpass filters based on modified split-ring resonators are considered. Extremely compact dimensions are their salient features distinguishing them from known designs. The filters demonstrate enhanced out-of-band suppression in a broad frequency range. We propose a way to reduce the longitudinal dimensions of the filter, consisting in rotation of the adjacent resonators. Arrangement of adjacent sections at a right angle to each other provides a required coupling coefficient between the resonators, separated by shorter coupling guide sections.