Constant Absolute Bandwidth Research Articles

Design of dual‐band bandpass filter with constant absolute bandwidth

ABSTRACTA dual‐band bandpass filter using split‐ring resonators (SRRs) and defected ground structure (DGS) with constant absolute bandwidth is proposed in this article. The inner and outer SRRs are operated for respective passband. DGS is etched on the ground, which can control the coupling coefficient of the filter to maintain constant absolute bandwidth. Finally, such kind of filter with compact size and high selectivity characteristics are designed and fabricated. The simulation and measurement results are basically in good agreement. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:715–718, 2014

Tunable Band‐Pass Filters Based on Varactor‐Loaded Complementary Split‐Ring Resonators on Half‐Mode Substrate Integrated Waveguide

ABSTRACTMiniaturized band‐pass filters (BPFs) using backward wave propagation in the left‐handed (LH) band are proposed in this article. A half‐mode substrate integrated waveguide (HMSIW), complementary split‐ring resonators (CSRRs), and varactors are embedded on the same planar platform to implement the resonant‐type approach of metamaterial transmission line and tuning capability. The tuning of the passband frequency is generated by simple and single direct current (DC) voltages from 0 to 36 V, which are applied to each varactor on CSRRs. Different capacitance values and resonant frequencies are produced while maintaining a nearly constant absolute bandwidth and quality factor. About 6.5% tunability and 11.30% of 3‐dB fractional bandwidth is achieved around 2.30 GHz. The new electrically tunable BPFs are verified by a good agreement between the simulated and measured results. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2458–2460, 2013

Ultra-wideband tunable resonator based on varactor-loaded complementary split- ring resonators on a substrate-integrated waveguide for microwave sensor applications [Letters

This paper presents the modeling, design, fabrication, and measurement of an ultra-wideband tunable twoport resonator in which the substrate-integrated waveguide, complementary split-ring resonators (CSRRs), and varactors are embedded on the same planar platform. The tuning of the passband frequency is generated by a simple single dc voltage of 0 to 36 V, which is applied to each varactor on the CSRRs. Different capacitance values and resonant frequencies are produced while a nearly constant absolute bandwidth is maintained. The resonant frequency is varied between 0.83 and 1.58 GHz and has a wide tuning ratio of 90%.

Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth

In this paper, two- and three-pole microstrip LC constant fractional bandwidth (CFBW) and constant absolute bandwidth (CABW) tunable bandpass filters are proposed. The equivalent-circuit models are presented to study the tunable mechanism. The filter can be reconfigured by changing the capacitance of the LC resonators. Based on electric coupling coefficient compensation, second- and third-order tunable equivalent-circuit models with CFBW/CABW are presented. For demonstration, a semiconductor varactor diode loaded microstrip LC resonator is adopted in our work to design the second- and third-order tunable filters. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameters, group delays, and third-order intercept points for different center frequencies of the filters are presented. Each resonator requires only one varactor diode for both central frequency and resonator coupling coefficient control.

A tunable bandpass filter with constant absolute bandwidth based on one ring resonator

A miniaturized tunable bandpass filter (BPF) with constant absolute bandwidth (ABW) based on a single ring resonator is presented in this paper. The proposed BPF is composed of one ring resonator and a pair of resonators loaded with varactors. The working frequency of the BPF depends on the pair of resonators. The ring resonator is introduced to transfer energy effectively and improve the characteristics of the BPF. An experimental filter has been designed and fabricated which maintains constant ABW across the tuning range from 1.80 to 2.44 GHz. The predicted results are compared with measured data, and a good agreement is reported, which verifies the proposed method.

A Tunable Combline Bandpass Filter Loaded With Series Resonator

This paper proposes a varactor-tuned microstrip combline bandpass filter (BPF) that is loaded with lumped series resonators instead of the short-circuited end of combline. This configuration has the advantage of enhancing the tunability of the suggested BPF by varactor diodes in series resonators, which leads to a wide tuning range even with a small capacitance ratio (Cratio) of the varactor. Therefore, a low controlled bias voltage varactor-tuned BPF can be achieved. In addition, due to the controllable slope parameter of the proposed resonator, the coupling between resonators can be controlled. As a result, the proposed tunable BPF can keep nearly constant bandwidth over the wide tuning range. The insertion loss resulting from the varactors is compensated using an active capacitance circuit with negative resistance. Theoretical analysis and design approach are described. Experimental results of a demonstrative BPF show a 500-MHz tuning range (1.7-2.2 GHz) with Cratio of only 2.6 (1-5-V bias voltage) while maintaining nearly constant absolute bandwidth and low insertion loss. The measured performance of the fabricated filter shows good agreement with the simulated one.

RF Tunable Bandstop Filters With Constant Bandwidth Based on a Doublet Configuration

This paper presents a novel approach to design RF tunable bandstop filters with constant absolute bandwidth. The filters are based on a doublet configuration which is attractive for high-order filter designs. In the doublet, two varactor-tuned resonators, arranged in a mirror-symmetrical manner, are coupled to a main transmission line. A novel coupling scheme is utilized between the resonators and the main line. Theoretical analysis indicates that, as the resonant frequency varies, the coupling coefficient within the fixed coupling region can be inherently changed to desirable values to meet the requirement of constant absolute bandwidth. Using the coupling scheme, constant absolute bandwidth can be obtained without extra circuits to control the coupling strengths. For demonstration, first-order and high-order filters are designed. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

FREQUENCY-TUNABLE BANDPASS FILTERS WITH CONSTANT ABSOLUTE BANDWIDTH AND IMPROVED LINEARITY

This paper presents a frequency-tunable bandpass fllter with constant absolute bandwidth and improved linearity. The proposed resonator is composed of an open-ended transmission line with back-to-back varactor diodes loaded at one end. The back-to-back varactor diodes are used to enhance the linearity of the fllter, which is better than that of the single varactor counterparts. A mixed electric and magnetic coupling scheme is utilized to control the overall coupling coe-cients so that the absolute bandwidth can be kept constant when the frequency is tuned. For validation, two frequency-tuning fllters with 30-MHz and 44-MHz absolute bandwidth are implemented. The experimental and simulated results are presented to verify the proposed design.

Tunable Balanced Bandpass Filter With Constant Bandwidth and High Common-Mode Suppression

This paper presents tunable balanced bandpass filters with constant fractional bandwidth (FBW) and constant absolute bandwidth (ABW), respectively. The equivalent differential- and common-mode circuits of the proposed filters are analyzed. The differential-mode bandwidths can be maintained constant when the frequency is tuned by selecting proper coupling regions and controlling the external quality factor Qe. To suppress the common-mode response, different elements are loaded in the middle of the resonators to misalign common-mode resonant frequencies. The common-mode response can be suppressed without degrading the differential-mode performance. For demonstration, two tunable balanced filters with constant FBW and ABW are implemented, respectively. Comparisons of the calculated, simulated, and measured results are presented to verify the theoretical predications.

A Tunable Bandpass Filter with Constant Absolute Bandwidth

A novel tunable bandpass filter with constant absolute bandwidth is presented in this paper. Introducing a mixed electric and magnetic coupling structure and a new external coupling scheme, nearly constant absolute bandwidth is maintained across the tuning range. Theoretical analysis and design approach are demonstrated. The proposed filter is designed with a frequency coverage of 0.78–1.08 GHz and constant 3-dB bandwidth of 50 MHz over the tuning range. The experimental results show good performance of the filter and validate the design concept.

Varactor-Tuned Dual-Mode Bandpass Filters

This paper presents a new type of varactor-tuned dual-mode bandpass filter. Since the two operating modes (i.e., the odd and even modes) in a dual-mode microstrip open-loop resonator do not couple to each other, the tuning of the passband frequency becomes simple with a single dc-bias circuit while keeping nearly constant absolute bandwidth. Design equations and procedures are derived, and two two-pole tunable bandpass filters of this type are demonstrated experimentally.

Low-Loss Frequency-Agile Bandpass Filters With Controllable Bandwidth and Suppressed Second Harmonic

This paper presents a novel approach to design frequency-agile bandpass filters with constant absolute bandwidth and passband shape, as well as a suppressed second harmonic. A novel mixed electric and magnetic coupling scheme is proposed to control the coupling coefficient variation. Theoretical analysis indicates that it is able to achieve desired coupling coefficients between the proposed resonators at various frequencies so as to obtain constant absolute bandwidth. Moreover, this half-wavelength resonator has a Q higher than the quarter- and half-wavelength counterparts, thus resulting in low insertion loss. A filter of this type is designed to validate the proposed idea. To remove the spurious responses of the filter, a method is then introduced to suppress the second harmonic without degrading the passband performance. For demonstration, two frequency-agile filters with 60- and 80-MHz constant absolute bandwidth are implemented with the frequency tuning range from 680 to 1000 MHz. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

High-Performance 1.5–2.5-GHz RF-MEMS Tunable Filters for Wireless Applications

This paper presents high-performance RF microelectromechanical systems (RF MEMS) tunable filters with constant absolute bandwidth for the 1.5-2.5-GHz wireless band. The filter design is based on corrugated coupled lines and ceramic substrates (er=9.9) for miniaturization, and the 3-bit tuning network is fabricated using a digital/analog RF-MEMS device so as to provide a large capacitance ratio and continuous frequency coverage. Narrowband (72 ± 3 MHz) and wideband (115 ± 10 MHz) 1-dB bandwidth two-pole filters result in a measured insertion loss of 1.9-2.2 dB at 1.5-2.5 GHz with a power handling of 25 dBm and an IIP3 >> 33 dBm. The filters also showed no distortion when tested under wideband CDMA waveforms up to 24.8 dBm. The designs can be scaled to higher dielectric-constant substrates to result in smaller filters. To our knowledge, these filters represent the state-of-the-art at this frequency range using any planar tuning technology.

Corrugated Microstrip Coupled Lines for Constant Absolute Bandwidth Tunable Filters

This paper presents corrugated coupled lines for miniaturized fixed and tunable microstrip bandpass filters. The novel approach uses microstrip corrugated coupled-line concept to synthesize a coupling coefficient, which maintains a nearly constant absolute bandwidth across the tuning range. A miniaturized two-pole varactor tuned filter is demonstrated with a frequency coverage of 1.32-1.89 GHz and an insertion loss < 3 dB with a constant 1-dB bandwidth of 70 ± 4 MHz across the tuning range. In addition, a three-pole comb-line 4.7% fixed filter at 1.94 GHz shows a 3:1 resonator spacing reduction over the conventional approach with an insertion loss of only 1.1 dB. This technique will allow the design of miniaturized small bandwidth fixed and tunable microstrip filters.

Electronically Tunable Filters

In this article, a brief introduction to the development of tunable filters was given. A classical design technique based on a combline filter approach was shown, where minimum degradation in passband performance could be obtained across a broad-tuning range. The fundamental disadvantages associated with the conventional resonator tuning approaches were also discussed, recognizing the importance of developing new techniques for realizing tunable microwave filters. It was shown that there is a possibility in realizing an electronically reconfigurable microwave filter based on parallel- coupled switched-delay lines, which possesses the important property of maintaining constant absolute bandwidth over almost an octave of tuning bandwidth. Furthermore, the filter has the ability to incorporate active switching elements in the filter circuit, without sacrificing its loss and linearity performance. With the exceptional linearity performance and power handling capability, the filter is readily adapted to poor environments. Although the use of p-i-n diodes as switching elements would result in large dc consumption, the approach could also be readily adapted for use with any switches, such as pHEMT or RF MEMS switches, to achieve extremely low power consumption. The integration of switchable couplings to enable both bandwidth and center frequency to be reconfigurable would be an enhancement.

Cochlea-Based RF Channelizing Filters

A new type of contiguous-channel RF multiplexing filter has been developed. The filter topology is derived from an electrical-mechanical analogy of the mammalian cochlea, and this channelizer retains the desirable features of the cochlea including multiple-octave frequency coverage, a large number of output channels, and an enhanced high-order upper stop-band response. Results of two 20-channel, 20-90-MHz channelizer prototypes, one with constant fractional bandwidth channels and another with constant absolute bandwidth channels, are presented and agree well with theory.

Efficient design methodology for microwave frequency multiplexers using infinite-array prototype circuits

Frequency multiplexers of the manifold type, in which individual channel filters connect to a main trunk line without the use of isolating directional circuit components, are noted for their compactness, achieved through controlled signal interactions among channel circuits. A major drawback often associated with manifold designs is the potentially large number of network variables that must be handled simultaneously. The new multiplexer design approach being presented utilizes infinite-array prototype circuits based on logarithmic-periodic principles which, in turn, allow a significant reduction in the simultaneous-variable count. The technique is not confined to manifold architectures and can accommodate both contiguous and noncontiguous channels with a wide variety of frequency band allocations. The versatility of the approach is illustrated by two experimental contiguous-band five-channel multiplexer circuits that operate at C- and X-band frequencies, with one circuit designed for equal fractional bandwidths of 20%, and the other for constant absolute bandwidths of 800 MHz. These examples are believed to represent the first practical and successful utilizations of logarithmic periodicity in microwave multiport network design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>