Coplanar Waveguide Filter Research Articles

Global modeling of a periodic coplanar waveguide structure for filter applications using an efficient iterative procedure

AbstractA global modelizing of periodic structures for coplanar waveguide filter is presented. These structures offer a very low insertion loss; thus, they can be exploited to achieve a high performance in miniature microwave filters. The analysis is achieved by using a new iterative method based on the wave concept. In this method, a recursive relationship between a given source and reflected waves from the circuit plane is generated. The good agreement between simulated and experimental published data justifies the design procedure. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 157–160, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20406

Investigation on Asymmetric Parallel-coupled CPW for .LAMBDA./4 Bandpass Filters with Broad Rejection Band

Asymmetric parallel-coupled coplanar waveguide (CPW) is originally characterized here as an equivalent unified K-inverter network. On a basis of our developed self-calibrated method of moments (MoM), the relevant network parameters are extracted to explicitly demonstrate the frequency-dependent coupling behavior with the 1st zero coupling at the λ/2 length of overlapped section. By differentiating the coupled spaces and overlapped lengths, the two CPW coupling structures are dissimilarly constructed and utilized as the input/output excitation of a λ/4 CPW bandpass filter. Through allocating the two unequal zeros towards the spurious harmonic around 3λ/4, an improved two-stage λ/4 CPW filter is designed at 5.0GHz. Optimized results achieve broad rejection band, ranging from 5.8GHz beyond 18.0GHz, as verified by the ADS simulation.

Compact superconducting coplanar meander line filters

Novel slow-wave coplanar waveguide (CPW) filters using high temperature superconductor (HTS) films are presented. Both half-wavelength and quarter-wavelength resonators are used in the filter topology. The miniaturisation is achieved using meander structure and interdigital grounding lines. A 3-pole Chebyshev bandpass filter has been designed, fabricated and studied. The untuned experimental results are in very good agreement with the simulated responses.

Design and Development of Ferroelectric Tunable Coplanar Waveguide Components for Ku- and K-Band Applications

In the past several years, we have demonstrated electrically tunable microstrip components such as resonators, filters, diplexers, and couplers based on conductor/ferroelectrics/dielectric two-layered structure. Recently, we are focusing our efforts on tunable coplanar waveguide (CPW) components in collaboration with NASA Glenn Research Center, Cleveland, OH. The advantages of CPW components include higher dielectric tunability compared to microstrip structure, ease of shunt connections, and ease of testing. To date, we have modeled several CPW structures with ferroelectric thin-film to study the effect of inserting the ferroelectric thin-film on electric tunability, attenuation and dispersion. Also, we have designed and fabricated devices such as resonators, and filters. The ferroelectric tunable CPW filters were tunable by more than 3% at bias voltage levels of - 100V. The BSTO based CPW filters offer higher sensitivity parameter as well as lower loss parameter compared to BSTO tunable 2-pole microstrip filters.

Ferroelectric Thin-Film-Based Electrically Tunable Bandpass Filters

We report on gold/Ba 0 . 5 Sr 0 . 5 TiO 3 (BST) ferroelectric thin film C-band tunable bandpass filters (BPFs) designed and fabricated on magnesium oxide substrates using three different structures: microstrip, coplanar waveguide (CPW), and conductor backed coplanar waveguide (CBCPW). The two-pole filters were designed for a center frequency of 5.89, 5.88, or 5.69 GHz with bandwidths of 3, 9, or 7%, respectively. The BST-based CPW filter offers a higher sensitivity parameter as well as a lower loss parameter compared to the BST tunable two-pole microstrip filter and CBCPW filter. With an applied voltage of 40 V, the tuning range for the BPF with CPW structure was determined to be 170 MHz.

Compact low-loss monolithic CPW filters using air-gap overlay structures

In this letter, two types of compact low-loss monolithic coplanar waveguide (CPW) filters using air-gap overlay structures are presented. Vertical stacking in overlay structures offers size reduction. Furthermore, air-gap overlay structures do not require additional dielectric process and are free from dielectric losses. An X-band bandpass filter using air-gap overlaid artificial transmission lines showed 67% size reduction. A stepped-impedance low-pass filter using highly separated metal-air-metal (MAM) capacitors as low-impedance lines achieved not only size but also loss reduction. Small size, low loss, and simple process steps make the air-gap overlay structures very promising for monolithic CPW passive devices such as filters.

A miniaturized double-surface CPW bandpass filter improved spurious responses

A novel miniaturized double-surface coplanar waveguide (CPW) filter has been developed. The filter is constructed by an electrode pattern of half-wavelength resonators on a double-sided circuit board with a high dielectric constant. A miniaturized pattern can be obtained by optimization of the electrode layout without any deterioration in unloaded Q. We use a particular pattern of via holes to reduce spurious responses. The filter is 38% smaller in size than the conventional /spl lambda//4 CPW filter. Spurious responses up to the third harmonic are suppressed by 13 dB, and satisfy the performance level required for industrial-scientific-medical band equipment. The measurement results agree well with the results of simulation.

A new micromachined overlay CPW structure with low attenuation over wide impedance ranges and its application to low-pass filters

In this paper, a new micromachined overlay-coplanar-waveguide (OCPW) structure has been developed and its characteristics are studied in detail as a function of the line parameters. In OCPW, the edges of the center conductors are lifted by micromachining techniques and partially overlapped with the ground plane to facilitate low-impedance lines. The elevated center conductors help to reduce the conductor loss by redistributing the current over a broad area. Comparative experiments on low-loss and lossy substrates also confirm the screening effect from the substrate losses by confining the electric field in the air between the overlapped conductor plates. Compared with the coplanar-waveguide (CPW) lines, the OCPW lines show wider impedance range (25-80 /spl Omega/) and lower loss (<0.95 dB/cm at 50 GHz). The advantages of OCPW for low-Z/sub 0/ lines are utilized to realize a high-performance stepped-impedance low-pass filter at X-band. The OCPW filter shows distinct advantages over the conventional CPW filter in terms of size, loss, skirt, and stopband characteristics.

Design and performance of miniaturized HTS coplanar waveguide meanderline bandpass filters

The design and performance of coplanar waveguide (CPW) microwave bandpass filters (BPFs) using high T c superconducting (HTS) films have been studied. We designed BPFs for mobile at f 0=2GHz and satellite at f 0=10GHz telecommunications, respectively ( f 0: central frequency). BPFs were designed by using the transmission-line model (equivalent circuit model). We obtained different properties from straight and meanderline BPFs. So, we arranged by considering transmission meanderline model. It is shown that the size of the filters can be greatly reduced by introducing CPW with meanderline geometry. Experiment of a prototype miniaturized CPW filter will be presented.

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.

Coplanar waveguide filters with floating strips

Coplanar waveguide edge-coupled filters with floating conductor strips directly below the coupled-line sections are investigated. It is demonstrated that tight coupling can easily be implemented in this way. A 50% bandpass filter with centre frequency at 3 GHz was studied. The filter used four coupled-line sections. The floating conductor strips were incorporated into the design and the authors have been able to achieve very similar even and odd mode phase velocities, so that the filter is spurious-free at twice the basic passband range. The measured passband insertion loss is &lt; 1 dB. It also has a very good stopband performance.

Design and performance of miniaturized superconducting coplanar waveguide filters

Design and performance of coplanar waveguide (CPW) microwave filters using high Tc superconducting films have been studied. The bandpass filter made of CPW requires the coating of only one side of the substrate with a superconductor, and the width of the CPW filter can be uniformly reduced in scale without changing its characteristic impedance, leading to a miniaturized filter by adopting the meanderline geometry. In order to realize the miniaturized filter we investigate the interdigital gap with strong coupling and the modeling of the corner bend. It is shown that the size of the filter can be greatly reduced by introducing CPW with a meanderline geometry. Experiments of a prototype miniaturized CPW filter with its computer-simulated performance have been presented.

Computations for radiation and surface-wave losses in coplanar waveguide bandpass filters

A new approach is developed to simulate both radiation and surface-wave losses in general coplanar waveguide (CPW) discontinuity structures. The newly derived formulas are concise, simple, and efficient for computation. Full-wave characterization of CPW filter structures are first accomplished by the mixed-potential integral equation and the method of moments. Given equivalent magnetic-current distributions on the apertures of a CPW, the matrix pencil approach is applied to extract the scattering parameters and the new formulas are employed to obtain the losses and far-field patterns of the space-wave radiation and surface wave. Simulation of the calculated radiation and surface-wave losses by field theory is found to be consistent to the total power loss determined from the scattering parameters by circuit theory, which verifies the correctness of our new expressions.

A class of novel uniplanar series resonators and their implementation in original applications

A class of novel millimetric uniplanar series resonators are presented, which can be used in monolithic and hybrid uniplanar microwave integrated circuits (MIC's). The proposed structures are able to demonstrate low radiation and compactness characteristics, which are attractive for passive and active monolithic and hybrid integrated circuits. A principle of achieving these high-quality circuits is described and also confirmed by experimental and theoretical results, which are in good agreement up to 50 GHz. To illustrate the features of the proposed series resonators and demonstrate their effectiveness, two classes of miniature coplanar waveguide (CPW) filters (namely, low-pass and bandpass) are designed using these resonators. The developed low-pass filter has some important advantages such as low insertion loss in passband, very wide stopband, high cutoff rates, small size, low number of elements, and an effective control of spurious signals. On the other hand, the newly developed bandpass filter provides an alternative, yet compact, structure to classical filters. Obviously, many other classes of filters or passive components can also be designed.

Tunable and adaptive bandpass filter using a nonlinear dielectric thin film of SrTiO3

We have prepared an electrically tunable and adaptive 3-pole half-wave bandpass coplanar waveguide filter incorporating a 1.2-μm-thick paraelectric SrTiO3 bottom layer and a 0.4-μm-thick superconducting YBa2Cu3O7−x top electrode layer on a LaAlO3 substrate. By applying a separate bias voltage on each pole and also on each coupling capacitance of the device at 4 and 76 K, the filter response is not only fine tuned to achieve symmetric and optimized filter characteristics with less than 2% bandwidth centered around 2.5 GHz, but also broadband tuned to shift the passband by more than 15%.

Coplanar waveguide with top and bottom shields in place of air-bridges

A convenient technique for the elimination of the coupled slot-line mode in coplanar waveguide (CPW) nonsymmetric circuits is proposed. This technique simply uses top and/or bottom ground plane shields and avoids the more costly airbridges. These shields are easy to fabricate; however, they may slightly affect the propagation of the CPW mode in the form of power leakage into the parallel plate TEM mode. This effect can be avoided by restricting operation to lower frequencies. Numerical comparisons between the effect of the shields and the airbridges on a CPW filter are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A solution of coplanar waveguide with air-bridges using complex images

A method for solving general CPW circuits including air bridges is proposed. The method generalizes the integral equation technique to nonplanar structures containing hybrid electric and magnetic currents. It also exploits the full-wave complex image technique to calculate the Green's functions of this structure efficiently. The method, therefore, offers a substantial reduction in computer time and memory over many other full-wave methods. The accuracy of the method is checked by comparing the results with available FDTD-theoretical and experimental results for a coplanar-waveguide band-reject filter. Using only 92 matching points, the method gave very good agreement. >

High-T/sub c/ superconducting coplanar waveguide filter

Coplanar waveguide (CPW) low-pass filters made of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) on LaAlO/sub 3/ substrates, with dimensions suited for integrated circuits, were fabricated and packaged. A complete filter gives a true idea of the advantages and difficulties in replacing thin-film metal with a high-temperature superconductor in a practical circuit. Measured insertion losses in liquid nitrogen were superior to the loss of a similar thin-film copper filter throughout the 0- to 9.5-GHz passband. These results demonstrate the performance of fully patterned YBCO in a practical CPW structure after sealing in a hermetic package. >

Design and performance of a high-T/sub c/ superconductor coplanar waveguide filter

The design of a coplanar waveguide low-pass filter made of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) on an LaAlO/sub 3/ substrate is described. Measurements were incorporated into simple models for microwave CAD analysis to develop a final design. The patterned and packaged coplanar waveguide low-pass filter of YBCO, with dimensions suited for integrated circuits, exhibited measured insertion losses when cooled in liquid nitrogen superior to those of a similarly cooled thin-film copper filter throughout the 0 to 9.5 GHz passband. Coplanar waveguide models for use with thin-film normal metal (with thickness either greater or less than the skin depth) and YBCO are discussed and used to compare the losses of the measured YBCO and copper circuits.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A planar subharmonically-pumped 71 GHz receiver with integral feed antenna

A planar, subharmonically-pumped, hybrid millimeter-wave receiver with integral antenna is described. Coplanar waveguide filters are used to isolate the ports and provide image enhancement. The integral planar antenna has 12 dB gain and is suited for use as a feed. The main lobe is normal to the substrate surface. The receiver is designed for an instantaneous bandwidth of 10 GHz. Experiments at 71 GHz indicate single-sideband mixer conversion loss of 6.5 dB. We believe that this represents the highest level of integration yet demonstrated in this frequency range.