Waveguide Sandwich Filters

A new class of waveguide filters is introduced, constructed from several thin plates sandwiched together. The combination of alternate plates having large and small rectangular apertures leads to a propagating structure which possesses a bandstop response and prescribed characteristic impedance. This basic element may be used as a simple compact bandstop filter, particularly where the main passband and stopband are well separated, such as in harmonic rejection. For filters with many stopbands, combinations of several waveguide sandwich filter elements are used to provide the main passband and the required attenuation characteristics in the prescribed stopbands. Although the filter is ideally suited for bandstop filtering due to its small size, low cost, low loss, and high power handling capability, additional applications to bandpass filtering and dispersive delay line operation are also cited.     

Waveguide Bandstop Elliptic Function Filters

Using the "natural prototype" for elliptic function filters, a design procedure is presented for a class of waveguide bandstop filters, which exhibit equiripple passband and stopband responses. Due to the availability of explicit formulas for element values in the natural prototype elliptic function filter, the design procedure is entirely analytic and does not require numerical synthesis techniques. The resulting physical structure is the familiar uniform guide with iris-coupled series stubs. Unlike the bandstop filters designed from maximally flat or Chebyshev prototypes, the elliptic function design results in stubs that are not exactly three-quarter-wave coupled.     

Flattened Broadband Notch Filters Using Guided-Mode Resonance Associated With Asymmetric Binary Gratings

In this letter, the broadband notch filter exhibiting a flattened bandstop spectral response is experimentally demonstrated for the first time by using the guided-mode resonance associated with the periodic subwavelength structure possessing asymmetric binary grating profiles. The proposed filter consisting of grating and waveguide structures is realized by utilizing a single-layer poly-silicon film deposited on a quartz substrate. The asymmetric grating profile is carried out by dividing the one-filling-factor binary structure into the one with two distinct filling factors within one identical period. A flat bandstop spectral response at the central wavelength of 1.22 mum is obtained under normal incidence for transverse-electric polarization. Its transmittance of bandstop spectrum can be suppressed as low as -20dB within a broad spectral range of 85 nm and its corresponding Deltalambda/lambda is larger than 6%. The spectra under oblique incidence are demonstrated to verify the proposed filter has a high immunity for the angular deviation up to 20deg     

New Narrow-Band Dual-Mode Bandstop Waveguide Filters

A complementary relation between a dual-mode bandpass and bandstop waveguide filter is found. Then a new idea for constructing a bandstop filter is developed. Two trial samples of bandstop filters are constructed to demonstrate the principle.     

All-optical tunable filters built with discontinuity-assisted ringresonators

Numerically simulated performance is presented in a new type of bandstop and bandpass filters, built with discontinuity-assisted ring resonator (DARR)-loaded couplers. The operating characteristic of the bandpass filter is similar to that of a long grating with a centered cavity or a photonic crystal with a defect. The filters are tuned by varying the refractive index or the length of the waveguide forming the ring or the cavity. Selectivity and tuning range are controlled by the coupling coefficient of the couplers, by the order of resonance in the rings, and by the reflection coefficient of the discontinuities. A design procedure and the effect of loss are also presented     

Concept of multiorder multimode resonant optical filters

The idea of implementing optical filters by coupling evanescent waves from several diffracted orders into multiple leaky waveguide modes is studied theoretically. Using a dielectric thin-film structure consisting of a coupling grating placed between adjacent waveguides, guided-mode resonance filters exhibiting multiple reflection peaks within a specified wavelength range can be obtained. These peaks originate in the resonant waveguide modes that are excited by the diffracted waves dispersed by the grating. It is shown that this device can be used to realize multiwavelength as well as wide-band spectral filters.     

A Study of the Filter Properties of Single and Parallel-Coupled Dielectric-Waveguide Gratings

Our work with gratings in dielectric image guide shows that it is distinctly advantageous to place the grating notches on the sides of the guide, or on the top of the guide, depending on the mode used. Means are discussed for modeling gratings using an equal-line-length transmission-line equivalent circuit. Excellent agreement between computed and measured bandstop frequency responses of gratings are obtained. Design relations for gratings are presented, and equations for analysis and design of parallel-coupled grating structures are derived. It is shown that a simple bandpass filter can be made from properly designed parallel-coupled gratings with distributed loads at one end. It is also shown that by use of combinations of parallel-coupled and direct-coupled gratings, multiresonator filters with Chebyshev or other characteristics can be obtained. Experimental results in agreement with computed responses are demonstrated.     

Design of Dielectric Waveguide Bandpass Filters Using Parallel-Coupled Gratings

Techniques for the design of narrow-band (of the order of a percent or so), bandpass filters using dielectric waveguide gratings are presented. These filters use both single, uncoupled gratings and parallel-coupled configurations of gratings to form multiresonator bandpass filter structures. Transmission-line equivalent circuits are used to model the dielectric waveguide gratings. Using this model, it is then shown how direct-coupled-resonator theory can be applied to such filter structures to synthesize a prescribed passband having Chebyshev or maximally flat characteristic. On the other hand, the parallel-coupled gratings give these filters broad and strong, absorptive stopbands, as is explained. Experimental results are presented which show good agreement between theoretical and measured results.     

Simulation Study of Electronically Scannable Antennas and Tunable Filters Integrated in a Quasi-Planar Dielectric Waveguide

Preliminary studies on electronically scannable leaky-wave antennas integrated in a dielectric waveguide are reported. Electronic scan is simulated by a small mechanical motion from which the relation between the scan angle and the necessary change in the dielectric constant can be derived. The work is also applicable to electronically tunable bandstop filters.     

共面波导结构MEMS滤波器的设计

设计了一种基于共面波导结构的 MEMS 带阻滤波器。利用计算机软件 HFSS 模拟出滤波器的带阻中心频率约为 22 GHz、损耗 19.86 dB、阻带宽度为 5 GHz,而设计大小仅为 1 000 μm×1 100 μm×400 μm。只需改变设计参数,即可获取其它频段的带阻滤波器。该滤波器具有阻带高、插入损耗低、尺寸微小、加工容易等特点。在微尺寸条件下分析了滤波器结构的热应力特性,利用大型有限元软件 ANSYS 模拟表明在–50~+80℃的温度范围内,结构不会产生变形,表明了器件有良好的可靠性。     

Ultrathin wideband slot and patch FSS elements with sharp band edge characteristics

ABSTRACT

Two diverse applications of FSS as bandpass and bandstop filters with wideband and sharp band edge characteristics are investigated in this paper. The proposed design comprised of a tapered tripole element in aperture and patch type printed on either side of a dielectric material to act as bandpass and bandstop filters respectively. The structures are ultrathin in design; structures comprise two metallic layers, isolated by single thin substrates with a thickness of 0.027λ. In the case of bandpass, the structure shows a relative bandwidth (?1 dB) of 8.87% with insertion loss better than 0.2 dB at normal incidence. Whereas, in the case of bandstop, it shows 24.36% (?10 dB). Further, the parametric analysis is performed for obtaining optimal performance. Both structures in the proposed form have spectacular application in bandpass filtering (slot FSS) and electromagnetic shielding (patch FSS). Further, two design techniques are presented namely dielectric encapsulation and substrate integrated waveguide (SIW) based FSS structures to develop a periodic structure to cater the high power handling in microwave sources. Finally, a fabricated prototype along with experimental verification proves the validity of simulated results.     

Selective Digital Filters with Linear Phase

A method for synthesis of digital bandpass and bandstop filters obtained by parallel connection of two allpass networks, is considered. A procedure is based on allpass network linear phase approximation at three levels in mini-max sense, which enables obtaining of selectivedigital filters in form of elliptic filters with linear phase in both passband and stopband.     

Dual-Mode Dielectric Resonator Loaded Cavity Filters

A new miniature realization of dust-mode filters is presented. As a basic building element of the filter, the dielectric resonator axially mounted in a waveguide below cutoff and resonating in a hybrid, degenerate mode is used. A dramatic reduction in size and weight, and excellent temperature performance with minimum degradation of resonator Q was achieved. Dust-mode configuration, preferred in satellite applications, allows simple realization of high-performance elliptic function filters. Experimental results are presented and demonstrate excellent agreement with the theory. Bandpass filter configuration is discussed however, realizations of bandstop, directional, etc., filters are also possible.     

OTA-C Filters with Finite Zeros

In this paper we present a novel technique for OTA-C filter realizations with finite zeros based on doubly loaded passive ladder networks. Only grounded capacitors are needed; all floating capacitors are replaced with active simulations eliminating bottom-plate parasitic capacitors and non-observable poles. Bandpass, highpass and bandstop filters are easily obtained from a lowpass OTA-C prototype applying standard frequency transformations that preserve the active simulation of floating capacitors, i.e. the finite zeros realization. Also, we address the high frequency stability problem of highpass and bandstop OTA-C filters simulating doubly loaded passive ladder networks. These filters usually have floating nodes where the OTA excess-phase acting over the nodal parasitic capacitance can introduce unstable poles at high frequencies. The stability problem is fairly the same for highpass and bandstop OTA-C filters based on approximations with and without finite zeros; only the most complex case (filters with finite zeros) will be addressed here.     

A Theoretical Investigation of Slot Waveguide Bragg Gratings

Bragg grating, structures based on dielectric slot waveguide, are investigated theoretically for potential applications as optical resonators and filters. Important device performance parameters, such as the reflection spectrum, the peak reflectivity, and the field confinement factor, are examined as functions of key waveguide and grating design parameters.     

微带型回音壁模介质谐振器带阻方向滤波器

本文报道了使用新型平面回音壁模介质谐振器的微带型毫米波带阻、方向滤波器。全文用行波环谐振器的方法进行分析,并给出了Ka波段带阻、方向滤波器的实验研究,其结果表明,该谐振器特别适用于毫米波微带集成电路。     

High-performance microwave coplanar bandpass and bandstop filters on Si substrates

High-performance bandpass and bandstop microwave coplanar filters, which operate from 22 to 91 GHz, have been fabricated on Si substrates. This was achieved using an optimized proton implantation process that converts the standard low-resistivity (/spl sim/10 /spl Omega//spl middot/cm) Si to a semi-insulating state. The bandpass filters consist of coupled lines to form a series resonator, while the bandstop filter was designed in a double-folded short-end stub structure. For the bandpass filters at 40 and 91 GHz, low insertion loss was measured, close to electromagnetic simulation values. We also fabricated excellent bandstop filters with very low transmission loss of /spl sim/1 dB and deep band rejection at both 22 and 50 GHz. The good filter performance was confirmed by the higher substrate impedance to ground, which was extracted from the well-matched S-parameter equivalent-circuit data.     

Bandstop filter for the H10 mode in a rectangular waveguide

A bandstop filter for the H10 mode in a rectangular waveguide is established by a stub in the E-plane. The enlargement of the bandwdth of this filter by a stepped pattern of the stub or by cascading of stub filters is outlined.     

Narrow-band microstrip bandpass filters with low radiation lossesfor millimeter-wave applications

Microstrip lines are attractive for the lower millimeter-wave ranges, but use of relatively thick substrates would be desirable in order to minimize losses. On such substrates the usual types of microstrip narrowband bandpass filters (formed from, e.g. coupled line segments with open ends) tend to radiate strongly giving very poor performance. It has been found that a grating technique initially developed for use with dielectric waveguides can be adapted for microstrips to obtain narrowband millimeter-wave microstrip filters with little radiation and strong filter characteristics. The stopbands are broad, the second passband occurring at three times the frequency of the first passband. These filters use parallel-coupled gratings with a single grating in cascade at each end. The modifications to the dielectric waveguide filter theory that are necessary for use with microstrips are detailed. Experimental results from microstrip realizations, which demonstrate their potential for millimeter-wave microstrip applications, are also presented     

Scattering by a lossy dielectric cylinder in a rectangularwaveguide

Electromagnetic fields in a rectangular waveguide containing a lossy dielectric cylinder are investigated by means of the orthogonal expansion method. The calculated results are provided by measurement. Resonance effects become visible through the frequency responses of the scattering parameters and understandable by patterns due to magnetic fields and Poynting vectors. The lowest resonance is nonsymmetric and can be used to realize tunable bandstop filters with a relative 3-dB bandwidth of about 0.04 and an attenuation of more than 40 dB