Three-pole Filter Research Articles

An EM-Coupled Triangular Open-Loop Filter With Transmission Zeros Very Close to Passband

This letter presents a novel EM mixed coupled triangular resonator filter with a backed aperture. Strong and controllable electric and magnetic coupling is constructed to realize transmission zeros very close to passband. Simulation and measurement results show good performances of the proposed filter such as low insertion loss, high rejection levels, as well as asymmetric characteristics. The fabricated three-pole inline filter can implement a bandwidth exceeding 6% while a very close-to-band transmission zero is simultaneously produced by the EM mixed coupling between the first and second resonators.

Compact Ultra-Wideband Microstrip/Coplanar Waveguide Bandpass Filter

A novel ultra wideband (UWB) bandpass filter is presented, using a compact coupled microstrip/coplanar waveguide (CPW) structure. The filter comprises of a single CPW quarter-wavelength resonator which is coupled to two microstrip open-circuited stubs on the other side of a common substrate. The two microstrip open-circuited stubs, which are about a quarter-wavelength long at the center frequency, can function as two resonators with associated coupling arrangement to the CPW. This forms a very compact three-pole filter. The proposed filter also exhibits a quasi-elliptic function response, with one finite-frequency transmission zero closer to each side of the passband. Thus, a high selectivity is achieved using a small number of resonators, which leads to low insertion loss and group delay across the passband. The performance is predicated using EM simulations and verified experimentally. The experimental filter shows a fractional bandwidth of 90% at a center frequency of 6.4GHz, with two observable transmission zeros (attenuation poles) at 1.95 and 10.36GHz, respectively. Furthermore, it has a very small size only amounting to 0.25 by 0.08 guided wavelength at the center frequency

Ceramic Layer-By-Layer Stereolithography for the Manufacturing of 3-D Millimeter-Wave Filters

Three-dimensional (3-D) ceramic stereolithography has been developed and used to manufacture RF devices using periodic structures. To our knowledge, it is the first time that zirconia and high-performance Ba3ZnTa2O9 ceramics are used with that process to manufacture high unloaded quality factor resonant structures and bandpass filters working in the Ka-band. A theoretical study on the performances of periodic arrangements of high-permittivity structures has been carried out and has led to the manufacture of a high unloaded quality factor cavity and narrow three-pole filter (1% bandwidth) measured at a working frequency of 33 GHz

Passive microwave filter tuning using bond wires

A practical method is proposed to tune microwave planar filters. When the circuit is fabricated, a number of additional capacitive patches and inductive lines are patterned close to the filter. These patches and lines can be connected to the filter by bond wires to tune the filter response. By replacing the traditionally used tuning screws with these bond wires, the package for a microwave filter can be much more compact, and the mechanical reliability of the tuned filters can be improved. To demonstrate the method, a three-pole microstrip filter is fabricated on a Duroid substrate. The additional capacitive patches and inductive lines are also patterned on the same substrate close to the filter. By connecting the patches and the lines to the filter with bond wires, the centre frequency of the three-pole filter is easily tuned by −7% and+7%, respectively, and can be tuned to an arbitrary value in a wider range. The return loss of the filter is tuned from 15 dB to better than 20 dB in the passband at the same time. It is also found that the bond wire has introduced negligible additional loss.

LTCC 3-D resonators applied to the design of very compact filters for Q-band applications

We propose a new low-temperature co-fired ceramic (LTCC) U-shaped resonator. The advantages of LTCC technology are employed to design this three-dimensional (3-D) lambdag/2 resonator. The latter is modeled and optimized by 3-D electromagnetic simulations and is validated by experimental results. In order to validate the coupling between these resonators, a two-pole filter, functioning around 39 GHz, has then been designed and realized with success. Finally, two very compact three-pole bandpass filters have been conceived for a Q-band duplexer design. On the one hand, a filter has been designed around 38 GHz and presents a transmission zero in the upper band. On the other hand, an other filter functioning at 40.7 GHz is presented with a transmission zero in the lower band. Experimental results are in good agreement with theoretical ones

Substrate integrated waveguide (SIW) asymmetric dual-mode filter and diplexer

Substrate integrated waveguide (SIW) can be used to implement high Q waveguide components with the same easy and low-cost fabrication process as planar circuits. In this paper two inline three-pole dual-mode filters with asymmetric transmission response based on SIW are presented. These two filters, consisting of a TE102-TE301 dual-mode SIW cavity and a TE101 mode SIW cavity, are centred at around 10 GHz with a transmission zero on the left of the passband and the right of the passband, respectively. Based on the two kinds of three-pole deal-mode filters, a diplexer with isolation better than 35 dB is developed. A linear microstrip taper is used to implement the transition between microstrip and SIW. The measured results agree with simulated results.

A miniaturized net-type microstrip bandpass filter using /spl lambda//8 resonators

A novel miniaturized three-pole net-type bandpass filter using /spl lambda//8 resonators has been proposed. Asymmetric frequency characteristics of this filter exhibit a single transmission zero on the lower side of the passband at finite frequency, which is attributed to multi-path effect. Full-wave simulator IE3D is used to extract the coupling coefficients and external quality factor in order to determine the physical dimensions of this filter. The measured results are in good agreement with the simulated predictions. The overall size of the filter is only about 0.22/spl lambda//sub g/ by 0.2 /spl lambda//sub g/. As a result, the filter has not only a small size but also a wider upper stopband up to 6.5 f/sub 0/.

A novel low‐pass filter using defected ground structures

AbstractIn this paper, an equivalent‐circuit model of a defected ground structure (DGS) is applied to explain the characteristics of the DGS. The parameters of the circuit model are extracted from the EM‐simulation results. A novel three‐pole lowpass filter is proposed and optimized by using the defected ground structures. It is demonstrated that the filter can provide a sharp rate of attenuation in the stop‐band, as predicted. To further verify this method, the filter with DGS is fabricated on a 30 × 30 mm2 substrate. A comparison between the simulation and the measurement confirms the effectiveness of the proposed schemes. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 17–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20888

Compact bandpass filter design using folded coupled-line resonators

In this paper, a compact bandpass filter using folded λ/4 coupled-line resonators is presented. An accurate model is made by using an efficient analytic design approach. Equations for extraction of the equivalent parallel-coupled-line structure representing the folded-line section are developed. A simple systematic design procedure is established for filter designers. Finally, a three-pole bandpass filter for the new resonators is designed. The new folded coupled-line filter exhibits a significant reduction in footprint as compared to the conventional design. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 32–35, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20714

Magnetic Tuning of Three-Pole Microstrip Bandpass Filter

Lot of work on frequency tuning in resonators and filters with magnetic biasing fields have been reported. Normally the frequency shifts are due to variation of ferrimagnetic resonance of substrate material. In the present paper we have reported the frequency tuning of three-pole microstrip bandpass filter by varying the relative permeability of the substrate material with the externally applied dc biasing magnetic field. For this a three-pole microstrip bandpass filter with a center frequency 2.8 GHz was fabricated using a thick silver film deposited on LiZnTi polycrystalline ferrite substrate. A tunability of 17 MHz in the moderate range of applied magnetic field was observed at room temperature. Fabricated device shows the negligible variation in its transmission loss in the presence of biasing field.

Miniature and tunable filters using mems capacitors

Microelectromechanical system (MEMS) bridge capacitors have been used to design miniature and tunable bandpass filters at 18-22 GHz. Using coplanar waveguide transmission lines on a quartz substrate (/spl epsiv//sub r/ = 3.8, tan/spl delta/ = 0.0002), a miniature three-pole filter was developed with 8.6% bandwidth based on high-Q MEMS bridge capacitors. The miniature filter is approximately 3.5 times smaller than the standard filter with a midband insertion loss of 2.9 dB at 21.1 GHz. The MEMS bridges in this design can also be used as varactors to tune the passband. Such a tunable filter was made on a glass substrate (/spl epsiv//sub r/ = 4.6, tan/spl delta/ = 0.006). Over a tuning range of 14% from 18.6 to 21.4 GHz, the miniature tunable filter has a fractional bandwidth of 7.5 /spl plusmn/ 0.2% and a midband insertion loss of 3.85-4.15 dB. The IIP/sub 3/ of the miniature-tunable filter is measured at 32 dBm for the difference frequency of 50 kHz. The IIP/sub 3/ increases to >50 dBm for difference frequencies greater than 150 kHz. Simple mechanical simulation with a maximum dc and ac (ramp) tuning voltages of 50 V indicates that the filter can tune at a conservative rate of 150-300 MHz//spl mu/s.

Theoretical analysis of surface mountable triple-mode ceramic cavity

A novel surface-mountable ceramic cavity has been considered. The high-permittivity ceramic filling of the basic triple-mode waveguide cavity makes the proposed structure physically small. Integrated microstrip to ceramic filled waveguide transitions provide effective coupling between ceramic cavity and planar circuit. A key point of the suggested theory consists of utilization of weighted Gegenbauer polynomials as the basis functions for the Galerkin's procedure. Such a choice of basis functions guarantees high accuracy and efficiency for the entire simulation algorithm. As an application example, a three-pole L-band filter with advanced high-quality factor is demonstrated.

A novel superconducting CPW slow‐wave bandpass filter

AbstractA novel slow‐wave half‐wavelength coplanar waveguide (CPW) resonator using high‐Tc superconducting (HTS) films has been studied and used in a new filter topology. The slow‐wave effect is achieved by the capacitively loaded structure with a symmetrical interdigital line loaded on both sides of the central line. The velocity reduction (Vp/c0) of the resonator is about 0.050. A three‐pole Butterworth bandpass filter has been designed and fabricated with the use of the resonator. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 255–259, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10431

Triple-mode asymmetric filters in a rectangular waveguide

This paper describes cavity structure which can be used to implement triple-mode filters in a rectangular waveguide with asymmetric transmission zeros. The structure described is very simple to manufacture, and is therefore particularly suitable for diplexer applications in the Ka-band and above. As an application example, a three-pole filter is demonstrated, thereby fully validating the proposed triple-mode configuration. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 228–231, 2001.

RF applications of high temperature superconductors in MHz range

High quality, low noise RF devices (resonators and filters) in MHz range have been designed, fabricated, and tested. The devices were designed using either interdigital capacitor or spiral structures and made from two inch HTS wafers. Applications of these devices to magnetic resonance imaging (MRI) and RF communication are reviewed. Substantial gain in signal-to-noise ratio (SNR) using HTS coils for both proton and sodium MRI on animals and humans at field strength of 0.5 T-3 T are demonstrated. HTS single-pole and three-pole bandpass filters operated at 77 K are built. Multi-pole bandpass filters in MHz range are successfully made on two-inch, single layer HTS wafer. A three-pole filter with a center frequency of 18 MHz has shown a low insertion loss of 0.7 dB at 77 K.

Design and implementation of a lumped-element multipole HTS filter at 15 MHz

We have designed a three-pole bandpass filter operating at 15 MHz. The parameters of the filter include high Q, narrow band, low insertion loss and a return loss of 20 dB. The filter was fabricated from double-sided YBCO thin film on a two inch LAO substrate. The design utilizes individual HTS lumped elements (interdigital capacitors and meander line inductors) to realise the poles of the filter. The design and modeling of the filter are discussed in detail. Experimental results from the S-parameter measurements will be presented. Good agreement has been found between the simulation results and experimental data.

Bandpass filter on parallel array of high-Tc superconductor coupled coplanar waveguides

A novel bandpass filter using a parallel array of the high-temperature superconductor coplanar lines on an LaAlO3 substrate is developed. The simulation procedure based on quasi-TEM analysis is briefly discussed. A coplanar waveguide three-pole Chebyshev bandpass filter with 14% equal-ripple bandwidth at 1.775 GHz and 0.6 dB insertion loss at T = 78 K was designed, fabricated, and measured. Good agreement between measured and simulated data was observed.

CAD of triple-mode cavities in rectangular waveguide

In this paper describe a very simple cavity structure which can be used as the basic building block for the computer-aided design (CAD) of triple-mode filters in rectangular waveguide. The input output ports are standard rectangular waveguides with a common longitudinal axis. The proposed configuration is geometrically simple and exhibits the very important feature of being amenable to a rigorous electromagnetic simulation. As an application example, a three-pole filter is demonstrated thereby fully validating the configuration proposed.

Highly miniaturised superconducting lumped-element bandpass filter

Experimental results for a novel three-pole HTS lumped-element bandpass filter for 2 GHz and 2% fractional bandwidth with elliptic response are reported. Despite extremely high miniaturisation, this filter has a low insertion loss of 0.1 dB. Measurement and simulation results are compared and are in good agreement.

Waveguide filters with planar circuit inserts suitable for integration of active devices

This paper presents a class of waveguide bandpass filters with conformal iris patterns made of planar circuits suitable for integration of active devices. Multiple planar inserts are located along the propagation path with specially designated spacing between two adjacent planar inserts on which the iris patterns are etched. The electrical performance of such novel filters with the enclosure of a circular waveguide is demonstrated by the field-theoretical design and experimental characterization of a three-pole Tschebyscheff-type filter. Results of this type of planar-insert-based waveguide filter is compared with its conventional all-metallic iris counterpart designed at the same center frequency, showing nearly an identical frequency response between the two different topologies. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 77–80, 1997.