Elliptic Function Filter Research Articles

Elliptic high-pass filters with stepped impedance resonators in coplanar waveguide technology

Ultra compact elliptic-function high-pass filters (HPFs) in coplanar waveguide (CPW) technology are presented.The required shunt-connected series resonators of the elliptic-function response are implemented by means of stepped impedance resonators (SIRs), etched in the back substrate side. The accurate circuit model of the filter, including parasitic effects, is presented and used for design purposes. An order-3 prototype HPF with 0.1-dB ripple and 3-GHz cutoff frequency is designed and fabricated as proof-of-concept demonstrator. The measured filter response is in good agreement with the ideal elliptic-function in the region of interest. Filter dimensions are as small as 0.092λg × 0.185λg, λg being the guided wavelength at the cutoff frequency. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1094–1097, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26692

Pseudo-elliptic bandpass filter with subharmonic stubs

A simple bandpass filter that approximates equal ripples in both the pass band and the stopband is described. The filter comprises two stubs, resonant at one-half and one-quarter of the centre frequency, respectively, and a series overlay capacitor. The filter has a performance comparable to that of a third-order elliptic function filter and has a practical bandwidth of 16–34%.

Modified Chebyshev bandstop filter with transmission zeros at real frequencies

AbstractThe logarithmic periodic transmission line filter has been shown to be an attractive alternative to elliptic function filters when a high rate of cutoff is needed.In this article, it is shown that an improved passband and bandedge response can be obtained if impedances obtained from a Chebyshev prototype are used, and the stopband width increased by shifting the resonant frequencies of the stubs away from the centre frequency in a non‐periodic fashion. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:177–180, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25657

Double resonant stub bandstop filter with pseudo-elliptic response

A simple wideband bandstop filter that yields equal ripples in both the pass- and the stopbands is described. The filter comprises only two resonant stubs and a connecting transmission line and has a transmission response almost identical to that of a third-order elliptic function filter. The practical bandwidth is limited to 130–160%.

Inline and canonical stripline filters with ridge coupling sections for LTCC applications

Inline and canonical filters employing stripline resonators coupled by evanescent-mode ridge waveguide sections are presented. The proposed configurations are suitable choices for broadband chip filters integrated in printed circuit boards, especially for those with constraints on size and loss. Low temperature co-fired ceramic (LTCC) technology can be used to manufacture such filters. To validate the idea, prototypes of Chebyshev and elliptic function filters are designed following a systematic procedure. Stepped impedance stripline resonators are used in the Chebyshev filter to improve the spurious response. A novel canonical structure is presented for achieving high selectivity elliptic function filter responses. Rigorous mode matching method is applied to analyze and optimize all the filters, whose results are validated by commercial software. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

An Elliptic-Function Bandpass Filter Utilizing Left-Handed Operations of an Inter-Digital Coupled Line

A new elliptic-function bandpass filter (BPF) is proposed, which utilizes an inter-digital coupled line (IDCPL) as a left-handed transmission line. The IDCPL is employed in order to realize a negative coupling between non-adjacent resonators in a wideband BPF. As the authors' knowledge, the left-handed operations of the IDCPL has rarely utilized before, although the IDCPL itself has been widely used in many microwave circuits without being paid attention to the left-handed operations. Measured characteristics of two BPFs are presented in this paper, one is targeted for 3-4GHz WiMAX systems, and the other is for 3-5GHz ultra wideband communication systems (UWB).

Synthesis of Elliptic Optical Filters Using Mutually Coupled Microring Resonators

Integrated optical filters having elliptic transfer functions are proposed using two-dimensional arrays of synchronously tuned mutually coupled microring resonators. Analysis of microring filter topologies of the most general form is facilitated by the formulation of an energy-coupling matrix for the microring array. A method for synthesizing elliptic microring filter transfer functions having the prescribed transmission poles and zeros is also presented. The approach involves representing the microring filter by an equivalent electrical network of coupled LC oscillators and applying the coupling matrix technique developed for micro-wave filters to determine the coupling parameters. An example of a sixth-order elliptic function filter is presented to demonstrate the feasibility of using mutually coupled microring resonators to realize optical filters having finite transmission zeros in the transfer function

A novel microstrip lowpass filter having two transmission zeros to get sharp attenuation and wide stopband

AbstractThis paper proposes a novel microstrip four‐pole lowpass filter with compact size and excellent frequency property. Two transmission zeros are introduced in its stopband. The first transmission zero is produced nearby the passband and makes a sharp rate of attenuation. The second transmission zero is introduced to increase significantly the stopband width. The positions of the two transmission zeros can be adjusted easily. Although it has a smaller number of circuit elements and a lower insertion loss, the filter shows a frequency response better than that of a five‐pole elliptic function filter. The measured filtering characteristics of the filter agree excellently with the simulated results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2253–2256, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21902

Novel waveguide filters with multiple attenuation poles using dual-behavior resonance of frequency-selective surfaces

This paper develops novel waveguide filters consisting of frequency-selective surfaces (FSSs) in order to realize both the drastic size reduction and multiple attenuation poles in stopbands at both sides of passband. The FSS provides not only a passband but also attenuation-pole frequencies in stopbands since the FSS has both the aperture-element and the patch-element behaviors. In the present design method, the shape of each FSS is designed by a genetic algorithm so that the resonant curve of FSS can be fitted to that obtained from an equivalent-circuit approach. By using such FSSs and quarter-wavelength waveguides, a bandpass filter with six attenuation poles like an elliptic-function filter has been constructed. Furthermore, a technique of the size reduction by controlling adequately the resonant response of each FSS is presented. In this filter, the FSSs are closely located at the interval of the length much shorter than a quarter wavelength. It is shown from the design example that the half longitudinal length of the former example can be obtained, keeping both the passband response and attenuation poles in stopbands. The effectiveness of the waveguide filters with FSSs is validated by good agreement between the calculated and the measured results.

Design of novel cross-coupling elliptic function filters with the miniaturized edge-coupled split ring resonators

In this paper, a new class of cross-coupled planar microwave filters using the microstrip edge-coupled split-ring resonator (EC-SRR) is introduced and its simple equivalent circuit is proposed. The utilization of the microstrip split-ring resonators not only makes the filters compact, but also allows either positive or negative cross coupling to be realized. Also, three-pole and four-pole cross-coupled microstrip elliptic function bandpass filters using the EC-SRR are presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 495–499, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20862

Canonical ridge waveguide filters in LTCC or metallic resonators

A new physical realization of an elliptic function filter response is proposed for achieving compact size, wide bandwidth, wide spurious free stopband and high-selectivity performance. The filter configuration can be implemented in conventional waveguide technology or embedded in a multilayer low-temperature co-fired ceramic structure for integration with other circuitry in a chip module. The filter is analyzed using rigorous mode matching. To validate the concept, prototypes of four- and six-cavity elliptic filters are designed following a systematic procedure. Approximate synthesis is used to obtain initial dimensions of the filter and the desired optimum response is obtained by means of a final full-wave optimization. The results are verified with other numerical methods and with the measurements of a fourth-order waveguide filter.

Realization of a dual-mode bandpass filter exhibiting either a Chebyshev or an elliptic characteristic by changing perturbation's size

A dual-mode resonator with square patches attached to inner corners of a conventional microstrip loop resonator is proposed. The two types of coupling between the degenerate modes are described by changing the perturbation's size for realization of either a Chebyshev or an elliptic function filter. A novel type of dual-mode microstrip bandpass filter using degenerate modes of this type of dual-mode resonators is developed. It is shown that the perturbation's size determines the filter characteristic, whether it is Chebyshev characteristic or elliptic characteristic.

A Robust Fuzzy-Logic Technique for Computer-Aided Diagnosis of Microwave Filters

This paper introduces an improved algorithm based on fuzzy logic for tuning microwave filters. The approach is demonstrated by considering slightly detuned and highly detuned eight-pole elliptic function filters with tuned resonators and four-pole Chebyshev filter with mistuned resonators. Employing Sugeno-type fuzzy-logic system (FLS) along with fuzzy subtractive clustering results in much fewer fuzzy rules. The parameters of the fuzzy system are methodically adjusted to provide an optimized system. Unlike previous published method, only one FLS is adequate to deal with both cases of slightly detuned and highly detuned filters. The achieved results demonstrate the validity of the proposed approach in identifying the filter elements that cause the detuning.

Microwave filters with improved spurious performance based on sandwiched conductor dielectric resonators

Microwave filters based on a novel resonator comprised of a sandwiched conductor dielectric resonator (SCDR) loaded in a cylindrical cavity are analyzed in this paper. The SCDR is a compact resonator that exhibits good spurious performance. Resonant frequencies of the lower order modes are analyzed, and mode charts, unloaded Q, slot coupling, and screw coupling graphs are presented. S-parameters are computed using the finite-difference time-domain (FDTD) method for one- and four-pole SCDR filters and compared with measured results. The measured spurious performance for the four-pole elliptic function filter shows a large improvement over conventional dielectric-resonator filters. The measured results agree closely with predicted values obtained using the FDTD method.

Dual-mode elliptic-function bandpass filter usingone single patchresonator without coupling gaps

A novel dual-mode, compact, and simple elliptic-function bandpass filter structure without coupling gaps is proposed. This filter has insertion loss < 1.5 dB and return loss > 10 dB within 2.3–2.375 GHz. Without coupling gaps between the feed lines and the patch resonator, the new filter can provide a low insertion loss and reduce uncertainty in fabrication.

A microstrip elliptic function filter with compact miniaturized hairpin resonators

A four-pole elliptic function bandpass filter is designed using compact miniaturized microstrip hairpin resonators. It is shown that the filter occupies a very small area. The full-wave simulator IE3D is used to design the resonator and to calculate the coupling coefficients of the three basic coupling structures. Measurement results are compared with the computed responses.

Synthesis of lossy reflection-mode prototype networks with symmetrical and asymmetrical characteristics

A modified synthesis procedure for lossy reflection-mode prototype networks is presented. The resultant one-port filters are composed of a cascade of Brune or Triplet sections realising symmetrical and asymmetrical transfer functions, respectively. The Brune sections of symmetrical reflection functions have progressively decreasing resonator Q and the prototypes are suitable for dual-mode realisation. Tables of element values are provided for elliptic function filters up to degree six. Numerical examples are also presented for both types of transfer function.

Novel compact elliptic-function narrow-band bandpass filters using microstrip open-loop resonators with coupled and crossing lines

Novel compact elliptic-function narrow-band bandpass filters have been designed and fabricated. This new configuration consists of two identical microstrip open-loop resonators with coupled and crossing lines. A theoretical investigation has confirmed that this novel configuration is capable of providing elliptic-function filtering. Furthermore, the feasibility of this filter is verified experimentally. Centered at 2.039 GHz, the fabricated microstrip bandpass filter shows a measured 3-dB bandwidth of 2% and two deep notches in its stopband. In addition, the main circuit of this filter occupies only 2.5 cm/spl times/1.5 cm using a substrate with dielectric constant of 10.5, making it very attractive for applications in the mobile and personal communication systems (PCS's).

High-Q TE01 mode DR filters for PCS wireless base stations

This paper presents the state of the art of high-Q TE01 mode DR cavity filters for PCS wireless base station applications. In order to have TE01 mode filter to be competitive with other high-Q cavity technologies, employment of nonadjacent coupling to implement advanced filter features and easy filter machining and integration are essential. The quadruplet and trisections are regarded as basic blocks to implement symmetric and asymmetric transmission zeros in filter stop band. The relative alignment of the magnetic mode field across the coupled adjacent cavities is analyzed to identify the sign of nonadjacent coupling. A direct cascading of a wide band combine filter to a TE01 mode dielectric resonator (DR) filter is proposed to suppress the spurious response of the DR cavity filter. This approach simplifies the integration between the DR filter and the spurious suppression device and has been proved to be very cost effective. Experimental eight- and six-pole quasi-elliptic function filters show the typical performances. To take advantage of the special property of magnetic mode field alignment across the adjacent cavities, a five-pole canonical asymmetric filter with three transmission zeros in low side is implemented. We believe this filter is a new design for high-Q cavity filter, while a three-pole elliptic function filter is new for DR filter technology.

Modeling of conductor-loaded resonators and filters in rectangular enclosures

Full-wave modeling of conductor-loaded resonators in rectangular enclosures and the associated coupling structure is presented. The modeling yields generalized scattering matrices of the cylindrical conductor-loaded resonators in rectangular waveguides. By applying short and open conditions and cascading procedure, resonant frequencies, field distributions of the resonator, and coupling coefficients between two cavities through an iris are obtained. The computed results are compared with the measured data and both are in good agreement. A four-and an eight-pole dual-mode elliptic-function filter were designed, constructed, and tested. Measured frequency responses of the filters verify the theory.