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 S-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.

Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth

Two- and four-pole 0.7-1.1-GHz tunable bandpass-to-bandstop filters with bandwidth control are presented. The bandpass-to-bandstop transformation and the bandwidth control are achieved by adjusting the coupling coefficients in an asymmetrically loaded microstrip resonator. The source/load and input/output coupling coefficients are controlled using an RF microelectromechanical systems (RF MEMS) switch and a series coupling varactor, respectively. The two- and four-pole filters are built on a Duroid substrate with e r=6.15 and h=25 mil. The tuning for the center frequency and the bandwidth is done using silicon varactor diodes, and RF MEMS switches are used for the bandpass-to-bandstop transformation. In the bandpass mode of the two-pole filter, a center frequency tuning of 0.78-1.10 GHz is achieved with a tunable 1-dB bandwidth of 68-120 MHz at 0.95 GHz. The rejection level of the two-pole bandstop mode is higher than 30 dB. The bandpass mode in the four-pole filter has a center frequency tuning of 0.76-1.08 GHz and a tunable 1-dB bandwidth of 64-115 MHz at 0.94 GHz. The rejection level of the four-pole bandstop mode is larger than 40 dB. The application areas are in wideband cognitive radios under high interference environments.

Two- and Four-Pole Tunable 0.7–1.1-GHz Bandpass-to-Bandstop Filters With Bandwidth Control

Real-time behavior is specified in compliance with timeliness requirements, which in essence calls for synchronous system models. However systems often rely on unpredictable and unreliable infrastructures, that suggest the use of asynchronous models. Several models have been proposed to address this issue. We propose an architectural construct that takes a generic approach to the problem of programming in the presence of uncertain timeliness. We assume the existence of a component, capable of executing timing functions, which helps applications with varying degrees of synchrony to behave reliably despite the occurrence of timing failures. We call this component the Timely Computing Base, TCB. This paper describes the TCB architecture and model, and discusses the application programming interface for accessing the TCB services. The implementation of the TCB services uses fail-awareness techniques to increase the coverage of TCB properties.

Timely Actions in the Presence of Uncertain Timeliness

A novel compact microstrip dual-mode resonator and filter are proposed. The characteristics of the dual mode resonator are investigated. It is found that the filter response exhibits a desirable stopband response where the first spurious passband naturally occurs at 3f0. Finally, methods of miniaturizing such resonators and filters are discussed. The proposed structure was able to achieve 60% size reduction.

/pdf/compact-dual-mode-open-loop-microstrip-resonators-and-30x3odznu9.pdf

Compact Dual-Mode Open Loop Microstrip Resonators and Filters

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.

A Tunable Combline Bandpass Filter Loaded With Series Resonator

This paper presents a compact highly linear tunable second-order quasi-elliptic filter with constant 3-dB bandwidth. The proposed filter is thoroughly analyzed to clearly describe the filter equivalent circuit and the tuning mechanism involved. In addition, the tunable resonator configuration employed is shown to improve filter linearity, especially for low bias voltages where distortion is normally stronger. A quasi-elliptic tunable filter was designed, built, and tested for illustration and verification. With a 3-dB bandwidth variation of only 4.6%, the filter had a frequency coverage from 1.45 to 1.96 GHz, an insertion loss better than 2.5 dB, and measured IIP3 >; 43 dBm throughout. The experimental results are in excellent agreement to theory and simulations.

Compact Second-Order Highly Linear Varactor-Tuned Dual-Mode Filters With Constant Bandwidth

This paper presents two highly compact filter configurations using concentric open-loop resonators. A description of each filter configuration is presented, where a linkage between structural features and coupling coefficients is outlined. A third order trisection and a fourth order source-load coupled filter were designed and fabricated at 1.0 GHz, and each filter was shown to occupy an area of just 18 by 18 mm. The measured insertion loss of the third and fourth order filters was 0.83 and 1.20 dB, respectively. Moreover, these structures may also be cascaded to produce higher order compact filters.

Compact Filter Configurations Using Concentric Microstrip Open-Loop Resonators

This paper presents a novel filter design technique for the compact microstrip dual-mode filters. An equivalent circuit for the single dual-mode filter section is derived to show that a single unit behaves as a pair of coupled synchronously tuned single-mode resonators. The equivalent circuit was linked to the inverter-coupled bandpass prototype network to allow higher order filters to be realized. A complete design example (from design to realization) of a fourth-order Chebyshev bandpass filter is presented. It is shown that the dual-mode resonator may be employed to design cross-coupled filters with finite frequency zeros. Two filters are designed using optimized coupling matrix method, fabricated and tested. Experimental and simulation results are presented to validate the argument. Finally, it is shown that more compactness may be achieved with narrowband filters by employing folded resonators.

Design of Compact Dual-Mode Microstrip Filters

This paper presents the design of compact second-order

bandpass ¯lters based on dual-mode open-loop resonator. A ¯lter

design procedure is provided to facilitate the design process. The paper

also describes the nature of the inherent transmission zero associated

with the structure and presents a method of generating two additional

zeros for improving stop-band performance. Finally, a ¯lter design

example is presented to validate the argument.

/pdf/design-of-open-loop-dual-mode-microstrip-filters-5chtszx8mz.pdf

L. Athukorala

Papers

Compact Dual-Mode Open Loop Microstrip Resonators and Filters

Compact Second-Order Highly Linear Varactor-Tuned Dual-Mode Filters With Constant Bandwidth

Compact Filter Configurations Using Concentric Microstrip Open-Loop Resonators

Design of Compact Dual-Mode Microstrip Filters

Design of Open-Loop Dual-Mode Microstrip Filters