Spurious Stopband Research Articles

Synthesis of One Dimensional Electromagnetic Bandgap Structures with Fully Controlled Parameters

In this paper, we propose a novel synthesis strategy for the design of one dimensional electromagnetic bandgap (1-D-EBG) structures where all the performance parameters of these devices can fully be controlled, i.e., the central frequency of the forbidden band, its attenuation level and bandwidth, and the ripple level at the passbands. The novel synthesis strategy employs a new inverse-scattering technique to accurately synthesize the 1-D-EBG structure, targeting a properly interpolated version of a classical periodic filter fulfilling the required frequency specifications. The new inverse-scattering technique follows a continuous layer peeling approach and relies on the coupled-mode theory to precisely model the microwave structures. Telecommunication and radar systems, as well as material characterization devices, will be profited by this proposal with which enhanced filters, sensors, power dividers, couplers, mixers, oscillators, and amplifiers can be designed in many different technologies. As a proof of concept, a 1-D-EBG structure in microstrip technology with a single forbidden band (free of spurious stopband replicas), with attenuation level of 30 dB, fractional bandwidth larger than 100%, and return loss level at the passbands of 20 dB, has been designed and fabricated. The measurements obtained are in very good agreement with the simulations and target specifications, being free of spurious replicas up to the 15th harmonic, showing the robustness and very good performance of the novel design strategy proposed.

Band-stop filter with suppression of requested number of spurious stopbands

Design method for band-stop filters (BSFs) that suppress a requested number of spurious bandstops and reduce ripples in the passbands below ~1 dB is proposed. BSF is designed in a form of a cascade of cells, each consisting of steps of equal electrical length, where the number of steps is used to control the number of suppressed spurious bandstops. Analytical formulas are developed that enable initial design of BSF for a given central frequency, depth, and bandwidth of the stopband. Varying the minimum characteristic impedances of initial cells, through an optimization using circuit simulation, the ripples in passbands are reduced below ~1 dB. Using the proposed theory, three filters in microstrip technology, with suppression of 3, 5, and 7 spurious stopbands respectively, were designed, fabricated, and measured. Good agreement between simulated and measured results has been observed. The proposed design can be recommended for filters having broad stop bandwidths, between 40 and 100%.

A Novel Bandpass Filter Using Asymmetric Open Stub-Loaded SIRs

A novel microstrip bandpass filter using stepped impedance resonators (SIRs) with asymmetric open stub-loaded is proposed in this paper. The filter uses asymmetric open stubs as capacitive loads, resulting in higher-order spurious frequencies suppression and wider upper stopband. Compared with the traditional filter based on stepped impedance resonators at the same design frequency of 2.4 GHz, the proposed filter can significantly reduce the circuit size of 45 %. By changing the geometric dimensions of the asymmetric open stub-loaded SIRs, which can achieve single-band bandpass filter at the centre frequency of 3.5 GHz and dual-band bandpass filter at the centre frequency of 2.4/3.5 GHz.

Two Novel Classes of Band-Reject Filters Realizing Broad Upper Pass Bandwidth—Synthesis and Design

The synthesis and design of two novel classes of band-reject filters capable of realizing broad upper pass bandwidth is presented in this paper. The proposed filters comprise novel coupled-line network sections whose equivalent distributed circuits are also derived in this work for the first time. By virtue of the circuit-oriented synthesis approach pursued in this study, the new filters comprise asymmetrically coupled stepped-impedance resonators. Numerical examples are presented demonstrating the step-by step synthesis and design of the two new classes of band-reject filters performing a particular electrical specification. Finally, one of the two synthesized band-reject filters is fabricated and characterized leading to a measured frequency performance exhibiting a first spurious stopband centered at five times the center frequency of the fundamental stopband.

Analysis of Planar Ultrawideband Antennas With On-Ground Slot Band-Notched Structures

Planar ultrawideband (UWB) antennas with on-ground band-notched structures are studied in this paper. Two different slot resonators, which feature quarter-wavelength and half-wavelength configurations, are embedded into the arc shaped ground plane of the circular disk patch antennas in order to obtain the desired band-rejection around 5.8 GHz. Their principles and characteristics are analyzed and compared in detail providing designers with in-depth understanding and useful design information. By choosing the quarter-wavelength slot resonator, the first spurious stopband can be pushed up to 3 f 0 (f 0 stands for the center frequency of the notch) and this antenna retains a super wide working band which spans from 1.62 GHz to 17.43 GHz. Performance in both the frequency domain and time domain for this antenna has been investigated carefully. The transmission response of a transceiving antenna system and their corresponding transient analysis are discussed at the end of this paper.

A Novel CSRRs DGS as Lowpass Filter

A novel complementary split-ring resonators (CSRRs) DGS has been investigated theoretically and experimentally. The proposed DGS provides excellent performance in terms of double resonant property, ripple in the pass band, sharp selectivity at the cut-off frequency and spurious free wide stop band. A LPF using the proposed DGS unit is fabricated and three cascaded DGSs are employed in another LPF to obtain very wide reject band. The measured results illustrated the excellent performance.

Miniaturized Dual-Mode Ring Bandpass Filters With Patterned Ground Plane

Miniaturized dual-mode ring bandpass filters with a patterned ground plane are proposed. By loading the resonator periodically with the butterfly radial slot cells on the ground plane, the size of a ring filter is reduced along with an extended upper stopband. Based on the equivalent circuits, the mode-splitting characteristics and impact of the patterned ground plane on the electrical performances of the filter are investigated. A slotline ring filter with a patterned ground plane is also proposed. The miniaturization is achieved by loading the periphery of the slotline ring with the butterfly radial stubs at the backside. The filter has a higher first spurious response and deeper stopband rejection than a conventional microstrip ring filter. Measured results validate the analysis and theoretical prediction with good agreement.

Design of bandstop filters utilising circuit prototypes

A systematic circuit-oriented approach to the design of bandstop filters with pre-defined upper passband characteristics is presented. An experimental filter is built with a fundamental stopband centred at 1.085 GHz and a first spurious stopband centred at 5.4 GHz.

The design of novel multilayer slow-wave aperture-coupled microstrip bandpass filters

New multilayer aperture-coupling microstrip slow-wave bandpass filters using an open-loop resonator loaded with interdigital capacitive fingers is proposed. The new filter configuration consists of two arrays of microstrip open-loop resonators loaded with four fingers and eight fingers that can be coupled through the apertures on the common ground plane. The filter is not only compact in size, but also exhibits spurious stopband rejection. Filters of this type with elliptic function and Chebyshev response are demonstrated. There is good agreement between the measured and simulated results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1633–1639, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21715

On the design of novel compact broad-band planar filters

On the basis of impedance steps and coupled-line sections as inverter circuits, novel wide-band and very compact filters are presented. The application of alternately high- and low-impedance lines presented to the connected transmission-line resonators partly reduces their lengths to a quarter-wavelength only. In addition, effective techniques are demonstrated to reduce spurious stopband resonance resulting from a remaining half-wavelength resonator. Both suspended stripline (SSL) and microstrip filters were designed, fabricated, and tested, proving this concept in an excellent way. For the prototype filters, center frequencies around 6 GHz were selected. Bandwidths are between 2.5-3.25 GHz, and insertion-loss amounts to around 0.25 dB for the microstrip filters and 0.5 dB (including the transitions to coaxial line) for the SSL filters, respectively. For the selected center frequency and on a substrate with a dielectric constant of 10.8, the smallest microstrip filter is only 15 mm/spl times/5 mm in size.

Spectral approach to the synthesis of bandstop filters

A nontraditional approach to the synthesis of bandstop filters (BSF) based on the analysis of the spectrum of complex eigenfrequencies of multimode resonators forming a filter is described. Two types of BSF resonators, which are formed by cross-section enlargements of a finite length of a rectangular waveguide in E- or H-plane, are considered. It was shown that a BSF of the first type had no spurious stopbands and practically did not introduce a loss in the passband. The high accuracy of the filter design is confirmed by the experimental data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Note Concerning Modes in Dielectric Waveguide Gratings for Filter Applications

Peng and Oliner, and others have shown that TM-to-TE or TE-to-TM mode conversions occur when a single, lowest order surface wave is incident obliquely onto a wide dielectric grating and that the lowest order converted modes of this sort can cause spurious stopbands which are especially troublesome because they are so close to the desired stopband, In this note it is observed that the spurious response situation is not as bad in the case of a grating cut into a dielectric waveguide (which can be thought of as having two, obliquely incident waves present). In this latter case, the fields have even or odd symmetry which eliminates part of the mode couplings includhrg the lowest order TM-to-TE or TE-to-TM couplings. Experimental and theoretical results indicate that gratings can be made to be free from spurious responses or appreciable radiation over sizeable bands so that they can be useful in at least some kinds of dielectric waveguide filter structures.