Ring Filter Research Articles

Wideband Microstrip Ring Resonator Bandpass Filters Under Multiple Resonances

A new class of wideband microstrip bandpass filters is proposed under multiple resonances of an asymmetric ring resonator. Two capacitive coupling elements are placed at two perpendicular positions of a squared ring, whereas a pair of open-circuited stubs is formed in the symmetrical plane of these two excited ports similar to a dual-mode ring filter in shape. By stretching the paired stubs close to one-eighth of a wavelength, the first two even-order resonances move down to be quasi-equally located at two sides of the first odd-order resonance, thus forming a triple-resonance ring resonator. As interdigital coupled lines are installed at two ports instead of lumped capacitors, two extra resonances can be moved into passband, thereby making up a quintuple-resonance ring resonator. To provide an insight into their operating mechanism, these ring resonators are characterized in terms of transmission line theory. Afterwards, various wideband microstrip ring resonator bandpass filters with one or two asymmetric ring resonators are optimally designed and fabricated. Simulated results are confirmed via experiment, showing good wideband filtering performance with widened/deepened upper stopband and sharpened rejection skirts outside the wide passband.

A ring filter switch for a low loss wideband and very sharp bandstop filter

AbstractA ring‐filter switch is suggested for a low loss wideband filter with on‐state and very sharp bandstop filter with off‐state. It consists of a ring filter and a switching diode. The ring filter is a wideband filter but a band‐stop filter with a certain condition. The fact can be used as a switch. To verify it, a microstrip ring‐filter switch is fabricated and measured at a center frequency of 3 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2828–2830, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22828

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.

Wastewater reclamation systems in small communities

The demands established in the rules and regulations by the administration in Catalonia seem to exclude small communities from wastewater reclamation and reuse, due to the comparatively high costs associated with the practice at small scale. In the framework of the DRAC project (Demonstration on Wastewater Reclamation and Reuse in Catalonia) two different pre-treatment systems, one extensive (infiltration-percolation) and another intensive (ring filter), each one followed by chlorine dioxide disinfection, were tested in order to be applied for small communities wastewater reclamation and reuse. The results of this study show that infiltration-percolation systems remove very efficiently physico-chemical contaminants and microorganisms. The ring filter system does not show a significant removal rate of contaminants, The use of infiltration-percolation as a pre-treatment for advanced chemical disinfection allows reducing the dose of disinfectant and the contact time needed to achieve a specific water quality, and diminishes disinfection byproducts (DBPs) generation. Therefore, this reclamation line is suitable for small communities due to its efficiency and low cost. However, further studies are needed in relation to the removal mechanisms of microorganisms, organic compounds in IP systems and the possible DBPs formation using chlorine dioxide.

Analysis of ring filter and its cascade synthesis method

AbstractA ring resonator filter with a stub (ring filter) has a band‐stop filter characteristic. The attenuation frequencies are at two symmetric locations with respect to the center frequency of the passband. If the range between these two attenuation frequencies is considered as the passband, the loss is low and the group delay is constant in the passband region. In the present paper, the condition of the ripple generation in the passband is derived for the ring filter. Further, the ripple frequencies under the ripple generation conditions are numerically obtained and compared with the measured results. Next, the passband group delay is analytically derived and compared with the measured value. Further, a method of cascading the ring filters is studied. It is found that the transfer function of the cascaded ring filter is expressed in terms of a rational function of the Richard variable $\Omega = j\tan \theta$. It is shown that a set of the characteristic impedances realizing the desired rational function can be inversely calculated. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(3): 9–16, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20298

Stabilized dual-wavelength erbium-doped dual-ring fiber laser

A stable dual-wavelength erbium-doped fiber (EDF) compound ring laser using a double-ring filter (DRF) is proposed and demonstrated experimentally. By using a ring filter incorporated within the ring cavity, the fiber laser can lase two wavelengths simultaneously. The dual-wavelength output exhibits a good performance having the optical side-mode suppression ratios (SMSRs) of 45.3 and 46.3 dB and output powers of -8.1 and -7.1 dBm, respectively. In addition, the optical output stabilities of the ring laser have been also discussed.

UMTS diplexer design using dual‐mode ring resonators

AbstractIn this letter, we propose a novel design of a UMTS diplexer using dual‐mode rectangular ring‐resonators. The diplexer is composed of two rectangular rings, which termed as the Tx‐ and Rx‐ring, with each ring its input and output ports separated from each other by a quarter‐wavelength to create the degenerate‐mode resonance. The ratio of the long‐ and short‐side dimension of rectangular ring can be used to fine tune the passband's bandwidth and the ratio is properly chosen to achieve sufficient bandwidth required by the UMTS diplexer applications. An enhanced parallel‐coupled structure is introduced in the circuit to replace the conventional end‐gap coupling for reducing the insertion losses in the passband. The effect of the coupling‐line length is also simulated and the resulting data are used to precisely tune the positions of the zeros. In the zero assignment, one of the zeros possessed by each ring filter is managed to be implanted in the passband of its counterpart filter for increasing the isolation between the Rx‐ and Tx‐port. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 63–65, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22030

Periodic stepped-impedance ring resonator (PSIRR) bandpass filter with a miniaturized area and desirable upper stopband characteristics

A periodic stepped-impedance ring resonator (PSIRR) is proposed to design dual-mode bandpass filters with a miniaturized area and desirable upper stopband characteristics. Design parameters of a PSIRR include impedance ratio R of the hi-Z to low-Z sections, their lengths, and number of impedance steps 2N. The resonant characteristics of PSIRRs with various N and R values are investigated by both the transmission-line theory and electromagnetic simulation. Proper choice of the above parameters leads to an optimal reduction of circuit area and extension of upper rejection bandwidth. Two extra transmission zeros exist in the upper stopband and are tunable via changing the arm lengths of the line-to-ring coupling structure. Realized by the standard microstrip technology, the dual-mode PSIRR bandpass filter has not only the first spurious response at higher than 3.7/spl times/ the passband frequency, but also an area reduction of better than 60% against a conventional ring filter. Experimental results of several fabricated circuits validate the analysis and theoretical prediction.

New design concept of dual‐mode bandpass filter by using nonorthogonal input and output ports for wireless application

AbstractIn this paper, new design concept of nonorthogonal input and output (I/O) ports applied to optimize dual‐mode bandpass ring filter is proposed. Compared to conventional dual‐mode filters, the proposed filter with nonorthogonal I/O could not only support two degenerate modes operation, but also increase design flexibility. Moreover, the design of dual‐mode filters would not have an I/O geometry limitation, corresponding to high integration. Finally, a simple structure and high selectivity for the dual‐mode bandpass filters were obtained. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 639–641, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21431

An analysis of miniaturized dual-mode bandpass filter structure using shunt-capacitance perturbation

A dual-mode bandpass ring filter using two pairs of shunt capacitances has been analyzed and designed. The size of the ring resonator can be reduced significantly by increasing the shunt capacitances. Since the resonator size is not an integer multiple of operating frequency, harmonic suppression is easily achieved. Analysis shows that the two pairs of shunt capacitances independently control the even- and odd-mode resonant frequency of the ring resonator. Moreover, the shunt capacitance also allows easier biasing, making tunable filters using varactors realizable. Various configurations of dual-mode bandpass filters have been reported, and the advantages and disadvantages of each structure are discussed. Several filters of various capacitances have been designed and tested at 1.8 GHz, and show significant size reduction of over 67%. A varactor-tuned filter has also been designed, and demonstrated a measured tunable center frequency of 20%. This study is a solution to the miniaturization of ring filters, and allows performance tuning, making ring filters more attractive in monolithic microwave integrated circuits and system-on-chip applications.

Ring filters and their application to new measurement technique on inherent-ring-resonance frequency

A ring filter is proposed as a wide-banded filter. It consists of a ring and two short stubs that are connected at the 90/spl deg/ and 270/spl deg/ points of the ring. Since the characteristic impedances of all the transmission line sections have an effect on the bandwidths of the ring filters, their relations are studied. On the basis of the study, one having more than 100% fractional bandwidth is selected and tested. The measured results are in good agreement with the simulated ones. As an application of the ring filter, a new and simple method to determine an inherent-ring-resonance frequency is introduced. The ring filter may be seen in such a way that two filters are connected in parallel. Therefore, if the two powers of the two filters are out of phase at the output, the excited power cannot be delivered. That can be used for determining the inherent-ring-resonance frequency and its condition is derived. Also, an effective loss tangent at a frequency of interest may be obtained correctly using the method suggested. To verify the method, two ring filters have been fabricated in microstrip lines and the measured results also show good agreement with the predicted ones.

Circuit-oriented modelling of ring-resonators

In this work we propose a circuit-based analysis of both a ring phase shifter and a single ring filter, taking into account the effects of imperfections in the directional couplers and polarization conversion in bent waveguides. New models for the directional coupler and for the bent waveguide are proposed and used to find an analytical expression of the transfer functions of ring based devices. The numerical results obtained with the new models show that defects in directional couplers and polarization conversion in bent waveguides are responsible of spectral impairments often observed experimentally, confirming the validity of the model.

EBG-based dual mode resonator filter

Periodic etched pattern on the ground plane underneath the ring resonator are incorporated to realize a miniaturized ring filter with stronger rejection of higher harmonic passbands. Two square microstrip ring filters, with and without periodic etched pattern on the ground plane, were designed with a bandwidth of 135 MHz centered at 2.4 GHz and 3 GHz respectively. A rejection of at least 25 dB of the second harmonic passband has been achieved for the filter with periodic etched pattern.

A new measurement technique on inherent-ring-resonance frequency using ring filters

As an application of the ring filters, a new and simple method to determine an inherent-ring-resonance frequency and an effective loss tangent at a frequency of interest is introduced. When a certain condition is satisfied in the ring filters, a frequency, where all the excited power is reflected, exists. That is the inherent-ring-resonance frequency and the effective loss tangent from its reflection coefficient may be obtained correctly. To verify the method, two ring filters have been fabricated in microstrip lines and the measured results show good agreement with the predicted ones.

Comparison of different advanced disinfection systems for wastewater reclamation

Several lines of reclamation have been tested in the Palamós/Vall-Llobrega (Girona, Spain) wastewater treatment plant. Each line consists of a filtration treatment (infiltration-percolation, sand filter, ring filter and physico-chemical treatment) plus a disinfection system (UV, peracetic acid, chlorine dioxide and ozonation). Every combination has been evaluated and compared with the other possibilities. This combination of filtration and disinfection allows the use of lower doses of disinfectants, thus minimising the negative impacts of the whole process and improving the reliability of the reclamation facilities.

Slow-wave bandpass filters using ring or stepped-impedance hairpin resonators

This paper proposes a new class of slow-wave bandpass filters that uses a microstrip line periodically loaded with microstrip ring or stepped-impedance hairpin resonators. The new slow-wave periodic structures utilize the parallel and series resonance characteristics of the resonators to construct a bandpass filter. Unlike conventional slow-wave filters, the proposed bandpass filters are designed to produce a narrow passband at the fundamental mode of the resonators. The new filters provide lower insertion loss than that of parallel- or cross-coupled ring and stepped-impedance hairpin bandpass filters. The calculated frequency responses of the filters agree well with experiments.

Ring filter to locate external boundaries in SPECT using scatteredradiation

A novel form of filter for SPECT is described, in which,after back projection and summation, the reconstructed signal is a measureof the total activity within a ring of specified radius, centre and width.The filter is applied to the problem of using Compton scatteredradiation to locate external boundaries.In the simple case of the determination of the radius ofa circular scattering body of known centre, the filter output would identifya transition region and define an appropriate threshold as the boundarywas crossed. However it can alsobe applied to locate the boundaries seen in individual SPECT projectionsand hence trace out the envelope of the scattering body.Monte Carlo simulation based on 99mTc is used to testthe performance of the filter in a range of situations, with encouragingresults.

High-temperature superconducting passive microwave devices, filters and antennas

High-temperature superconducting (HTS) passive microwave devices, such as filters and antennas, are promising devices. In particular, HTS filters may be successfully marketed in the near future. Cross-coupled filters, ring filters, and coplanar waveguide filters are good options to reduce filter size. On the other hand, HTS patch antennas which can be cooled by a cryo-cooler are also promising devices as well, since they show higher efficiency than normal antennas. This paper examines the design process and filter properties of HTS filters as well as the gains, directivity, and cooling system of HTS patch antennas.

Cryogenic millimeter-wave ring filter for space application

A tunerless cryogenic millimeter-wave ring filter has been designed for a space application. Detuning of the center frequency caused by thermal deformations has been compensated by a novel mechanism based on the use of two materials with different temperature expansion coefficients. An improvement of 1:8 in the detuning of the center frequency, compared to an uncompensated ring filter, is reported. By applying the new design, external tuning aids can be avoided even in applications where a wide operational temperature range is of interest. Thus, the new ring filter is especially advantageous in space-borne millimeter-wave receivers.

SAW ring filters with insertion loss of 1 dB

This paper presents low loss ring SAW filters on 49/spl deg/YX, 64/spl deg/YX, 128/spl deg/YX LiNbO/sub 3/ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per /spl lambda/ (/spl lambda/ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128/spl deg/YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at /spl plusmn/25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at /spl plusmn/25 MHz, offset from the center frequency. The chip size is 5/spl times/4/spl times/0.7 mm.