Microstrip Open-loop Resonator Research Articles

The development of a 10.7-MHz fully balanced current-tunable bandpass filter with Caprio technique

Bandpass filters are integral in modern communication systems for selecting specific frequency ranges to ensure interference-free signal transmission and reception. This paper explores various bandpass filter designs, including those using active inductors, transmission-line unit-cells, microstrip open-loop resonators, and dual-port dual-frequency integration antennas. The focus is on the 10.7-MHz bandpass filter, widely used in FM radio and television systems. The study evaluates current-controlled and balanced designs, analyzing their performance, advantages, and drawbacks. Unique trade-offs in terms of linearity, distortion, temperature sensitivity, and component variations are discussed. Additionally, advancements in filter technology and diverse design options are presented. The paper introduces a novel current-balanced, frequency-adjusted bandpass filter to address odd-order noise issues. This filter aims to achieve high linearity, harmonic distortion attenuation, and the elimination of even-order harmonics. Through synthesis, analysis, simulation, and comparison with traditional filters, the proposed design enhances signal quality and efficiency. The fully-balanced current-tunable bandpass filter with the Caprio technique at 10.7 MHz is developed, exhibiting symmetrical characteristics with lower total harmonic distortion. The circuit’s structure is simple and adaptable for integration, validated through consistent simulation results. The study concludes by emphasizing the constant sensitivity of transistor differential amplifier circuits to the center frequency and the linear relationship between center frequency and adjustable bias current. The suggested transistor and capacitor selection criteria contribute to optimizing the circuit’s performance, aligning with the Caprio technique’s recommendations. Overall, this research presents a promising solution for achieving high-quality signal transmission in contemporary communication systems

Compact and wideband microwave bandstop filter for wireless applications

Compact, tunable and wide band stop filter (BSF) for wireless application is presented. The proposed filter is composed of compact rectangular microstrip open loop resonator with stub loaded resonator as building blocks of the filter. First, two vertical lumped capacitors are inserted in the open loop resonator from top to bottom of the substrate at the place which has maximum electric field to decrease the resonance frequency which in turn miniaturize the filter size. The resonance frequency of the fundamental mode is shifted from 5.5 to 4.2 GHz when lumped capacitors of 0.2 pF are added. Second, the capacitance of the open-ended stub can be changed to control the second resonance mode of the filter. Also, by inserting another vertical capacitor at the end of the open-ended stub, the second resonance mode can be controlled and reduced. Finally, by properly selecting the capacitance of the third lumped capacitor, the second resonance mode can be designed to be close to the fundamental mode and hence wide band stop filter can be achieved. The proposed BSF has some appropriate features such as compact size (its size has more than 40% size reduction), wide stopband and most importantly tunability of stopband. The band stop filter has a center frequency of 6.2 GHz, a stop band from 3.5 to 9 GHz, insertion loss lower than − 30 dB, and a return loss higher than 0.4 dB is accomplished inside the stop band. The measured results have good matching with the simulated results.

Design of 2.4 GHz Microwave Bandpass Filter

This paper presents in detail the design of highly selective microstrip bandpass filters that consist of microstrip open-loop resonators with a cross coupling that exhibit a single pair of attenuation poles at finite frequencies. The design approach enables one to use advanced fullwave EM simulators to complete the filter design, namely, to determine the physical dimensions of the filter. The results acquired through research & development process are simulated, analyzed and verified by using parallel-coupled lines filter topology, which are later, enhanced by various value-aided software tools such as MATLAB-7.0, CorelDraw-12, Microwave Office-2012

Feasibility study of portable microwave microstrip open-loop resonator for non-invasive blood glucose level sensing: proof of concept.

Self-management of blood glucose level is part and parcel of diabetes treatment, which involves invasive, painful, and uncomfortable methods. A proper non-invasive blood glucose monitor (NIBGM) is therefore desirable to deal better with it. Microwave resonators can potentially be used for such a purpose. Following the positive results from an in vitro previous work, a portable device based upon a microwave resonator was developed and assessed in a multicenter proof of concept. Its electrical response was analyzed when an individual's tongue was placed onto it. The study was performed with 352 individuals during their oral glucose tolerance tests, having four measurements per individual. The findings revealed that the accuracy must be improved before the diabetes community can make real use of the device. However, the relationship between the measuring parameter and the individual's blood glucose level is coherent with that from previous works, although with higher data dispersion. This is reflected in correlation coefficients between glycemia and the measuring magnitude consistently negative, although small, for the different datasets analyzed. Further research is proposed, focused on system improvements, individual calibration, and multitechnology approach. The study of the influence of other blood components different to glucose is also advised. Graphical abstract.

Design of Chipless RFID Tag by Using Miniaturized Open-Loop Resonators

In this paper, an open-loop resonator with fragment-loading structure is used for the first time in the design of radar cross section-based chipless radio-frequency identification (RFID) tag. By optimizing the distribution of fragment patches in an open loop, a microstrip open-loop resonator can be miniaturized so that the data capacity of the chipless RFID tag designed using such a miniaturized loop resonator can be significantly increased. Moreover, the resonant frequency of the fragment-loaded resonator can be adjusted conveniently by removing or disconnecting some fragment patches, which provides great flexibility for data encoding of the chipless RFID tag. The proposed chipless RFID tag with miniaturized open-loop resonators is designed and tested and can acquire 3.56 bits per resonator and a coding density of approximately $745.1~\text {bits}/\lambda _{g}^{2}$ . Several experimental results validate the proposed design as well as its implementation in a realistic environment.

Design of compact size and tunable band pass filter for WLAN applications

Compact size and tunable band pass filter based on open-loop resonators is proposed. The proposed structure consists of dual-armed microstrip open-loop resonators. A second armed open-loop resonator, which acts as band rejection resonator, is connected directly to the input and output ports to achieve the desired band pass behaviour. The open-loop microstrip resonators are combined with four lumped capacitors to reduce the overall size of the proposed filter. The capacitors are inserted at places where maximum electric field is occurred in order to increase the effective capacitance and reduce the resonant frequency as well. The resonance frequency is translated from 6.75 to 5.3 GHz for WLAN applications. Consequently, the filter size will be more compact and the filter performance will be improved by enhancing the energy stored in the resonator. The proposed design using lumped capacitors represents a reduction in size of more than 35% when compared with conventional filter without using lumped capacitors. A good consistency is achieved between simulated and measured results.

Design of Narrowband Band Pass Filter using Open-loop Square Resonators with Loading Element

Objectives: In this paper we propose to design a compact, sharp-rejection narrowband BandPass Filter (BPF). Methods/Statistical Analysis: The behavior of the microstrip open-loop resonator is observed using full-wave electromagnetic simulations. By adding a loading element at the center of the open loop square resonator we are achieving two operating modes (even and odd modes) exist within a single resonator. Variation of parameters of the loading element leads to asymmetric frequency response used for filter design. The simulated results met all the design specifications of the given band pass filter. Findings: In the dual-mode open loop resonator the even and odd modes (currents are mutually exclusive in nature) do not couple each other and leads to a rejection point in the frequency, which is associated with the even mode. Multiple sections of resonator give the sharp rejection (high dynamic range) after the passband. Application/Improvements: The proposed band pass filter can be widely used in communication system and space technology, especially mobile and satellite communication due to its better performance and compactness.

A Label-Free Biosensing Platform Using a PLL Circuit and Biotin-Streptavidin Binding System.

This paper proposes a novel RF biosensor that utilizes a frequency synthesizer associated with a microstrip open-loop resonator for label-free biomolecular detection. The RF biosensor consists mainly of a resonance-assisted transducer and a phase locked loop (PLL) circuit. In this work, the performance of the RF biosensor is validated using the well-known biotin-streptavidin binding system. When biotin is bound to streptavidin, the input impedance of the resonator is varied, resulting in a change in the oscillation frequency. The concentration of the streptavidin is ultimately detected by a voltage signal of the PLL's loop filter with simple measurement equipment. According to the experimental results, the RF biosensor has revealed excellent sensitivity ( ~ 61 kHz/ngml(-1)) and a low detection limit ( ~ 1 ng/ml), as well as a rapid response. These results demonstrate that the RF biosensor can be an effective sensing platform for label-free detection in a biomolecular binding system.

Compact UWB Antenna With Tunable Band-Notched Characteristic Based on Microstrip Open-Loop Resonator

A compact ultrawideband (UWB) antenna with an electronically tunable notched band is proposed for UWB communication applications. The proposed antenna utilized a C-shaped ground to realize miniaturization and a pair of open-loop resonators (OLRs) to create notched band. The center frequency of the notched band can be electronically tuned by changing the effective electrical length of the OLRs, which is achieved by employing varactor diodes. A prototype with an overall size of 24 × 28 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was constructed, and good agreement has been obtained between simulation and measurement. The experimental results show that, for a varactor diode capacitance approximately ranging from 0.63-2.67 pF, a continuous tuning notched band range from 5.1 to 5.9 GHz is achieved.

A novel ultra‐wide band bandpass filter with notched band using slotline and microstrip resonators

AbstractA novel ultra‐wide band bandpass filter with notched band is presented.Multi‐mode resonator is realized using a stepped‐impedance slotline. The resonator is orthogonally coupled to the microstrip feed lines, and ultra‐wide passband is obtained. Microstrip open loop resonators are loaded on the slotline, and notched band from 5.1 to 5.3 GHz is achieved. The filter is designed, fabricated, and measured. Good agreement is achieved between measured and predicted results. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2949–2951, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26430

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.

Integrated narrow/band-notched UWB antenna

An ultra-wideband disk monopole antenna incorporating a band-notch function is presented. A narrowband slot antenna has also been integrated into the upper portion of the disk. The slot antenna is fed via a microstrip line, printed onto the reverse side of the substrate. A microstrip open-loop resonator (OLR) was used to generate a stop-band (or band-notch) within the return loss curve for the UWB antenna. The OLR uses the disk monopole as a ground plane. The new integrated wide/narrowband antenna can easily be redesigned and provides a notch band having a high quality factor.

A Dual Passband Filter using Hybrid Microstrip Open Loop Resonators and Coplanar Waveguide Slotline Resonators

A novel dual passband filter using hybrid microstrip open loop resonators and coplanar waveguide (CPW) slotline resonators is proposed. With the CPW feeding structure, the center frequencies and 3-dB fractional bandwidth (FBW) can be achieved relatively independently. The external quality factor and coupling coefficient of the resonators are obtained. The proposed dual passband filter has center frequencies of 2.44 GHz and 3.5 GHz, which could be appropriately used for wireless local area networks (WLAN) and WiMax. Good agreement between simulated and measured results is demonstrated.

An Improved Microstrip Open-Loop Resonator Bandpass Filter with DGSS for WLAN Application

This paper presents a novel harmonic-suppressed microstrip open-loop resonator bandpass filter with the different transmission line characteristic impedance of the feed line and open-loop resonator for wireless local area network (WLAN) application. To improve the stopband rejection of the filter, the dumbbell-shape defected ground structure (DGS) are applied under the feed lines to suppress the harmonics and the equivalent parameters extraction formulations of double-dumbell-shaped DGSs are the first to proposed. The bandpass filter with center frequency of 2.44 GHz were designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. Measurement results show the filter has a wide stopband characteristic with 30 dB attenuation up to 7.5 GHz and only has an –1.23 dB insertion loss while it is a little larger than the conventional one. The measured results are in good agreement with the simulated results. It can be widely used for WLAN application.

Novel Dual-band Bandpass Filter Design Using Microstrip Open-loop Resonators

This paper presents a novel dual-band banpass filter using microstrip open-loop resonators. A new microstrip unit of dual-band bandpass filter is introduced, which can be used as unit element of duan-band filter design. The two open-loop resonators are treated as passband resonator and stopband resonator in analysis, respectively. A five-pole C-band dual-band bandpsss filter has been designed and fabricated. The measured results show a good agreement with the simulated results.

RF CIRCUIT DESIGN INTEGRATED WITH MICROSTRIP DGS

This paper presents microstrip transmission lines for designing a microstrip open loop resonator bandpass filter and a novel dual band transmitter. Microstrip open loop resonator bandpass filter with the dumbbell DGS under feed lines enhances the harmonic suppressed at the center frequency of 2.44 GHz. An asymmetric dumbbell DGS-integrated microstrip line is applied to the dual band transmitter which performs as a frequency doubler at 6.8 GHz or a power amplifier at 2.4 GHz. For the proposed bandpass filter, it has a wide stopband characteristic with attenuation −25 dB up to 8 GHz and has an −1.25 dB insertion loss by using two dumbbell DGS. Measurements of the dual band transmitter show that in frequency double mode, fundamental suppression and maximum output are −41 dBc and 7.8 dBm. And in amplifier mode, second harmonic suppression, P1 dB and gain achieve −52.6 dBc, 13.7 dBm and 16.5 dB, respectively.

Microstrip Open Loop Resonator Bandpass Filter with DGS for WLAN Application

This paper presents a novel harmonic-suppressed microstrip open loop resonator bandpass filter with defected ground structure (DGS) for wireless local area network (WLAN) application. To improve the stopband rejection of the filter, DGSs are applied under the feed lines to suppress the harmonics. The bandpass filter with center frequency of 2.44 GHz is designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. By using two dumbbell-shape DGSs the filter has a wide stopband characteristic with attenuation −25 dB up to 8 GHz and has an −1.25 dB insertion loss while it demonstrates a little larger than the conventional one. The measured results agree well with the simulation results. The proposed filter is found to possess low in-band insertion loss and high out-band suppression, making it suitable in WLAN application.

A Compact Open-Loop Filter With Mixed Electric and Magnetic Coupling

A novel cascaded microstrip open-loop resonator filter with controllable electric and magnetic mixed coupling is presented to have one or more transmission zeros. For two coupled resonators, the coupled sides with the maximum magnetic field are combined with their open gaps with the maximum electric field, creating the electric and magnetic mixed coupling. By adjusting the distances between resonators and the positions of open gaps in a mixed coupled filter, the coupling coefficients can be changed, and controllable transmission zeros can be produced in the lower stopband, upper stopband, or both. Design and fabrication of the proposed second-and fourth-order filters show the advantages: such as a smaller number of resonators, higher rejection level, as well as asymmetrical response; moreover, the location of the transmission zeros can be precisely controlled.

Dual-Mode Microstrip Open-Loop Resonators and Filters

A miniature dual-mode microstrip open-loop resonator is proposed. Distinct characteristics of this new type of dual-mode resonator are investigated using full-wave electromagnetic simulations. It is shown that the two operating modes, i.e., the even and odd modes, within a single dual-mode resonator of this type do not couple. It is also found that there is a finite-frequency transmission zero inherently associated with the even mode. Two two-pole filters using this type of dual-mode resonator are demonstrated with opposite asymmetric responses, which result from different locations of the transmission zero. Higher order filters of this type are also investigated. Both simulated and measured results are presented.

Novel bandpass filter with size reduction and harmonic suppression

AbstractA novel microstrip bandpass filter with size reduction and harmonic suppression is proposed in this article. The filter is based on microstrip open loop resonators with coupled open stubs. By adding coupled open stubs to open loop resonator, extra controllable transmission zero can be obtained. The extra transmission zero can be tuned at the second harmonic frequency to suppress spurious response. When compared with the conventional microstrip open‐loop bandpass filter, this filter could achieve size reduction and spurious responses suppression simultaneously. A demonstration filter was designed, fabricated, and measured. Theoretical and experimental results are presented and show good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 914–916, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22323