Dual-mode Stub-loaded Resonator Research Articles

Synthesis Design of Multiband Bandpass Filters Employing Multimode Bandstop Resonators With Star-Like Topology

Multimode resonators (MMRs) can be utilized to build multiband bandpass filters (MBPFs). Each individual mode serves as the operating mode for one of the passbands in a well-known coupling topology. However, several difficulties are involved with the classical design method. In this article, we present a novel star-like topology to design MBPFs based on MMRs. Differently from the classical use, in the proposed novel topology, they are so regarded as bandstop resonators and provide multiple controllable transmission zeros. To explain the proposed concept and the implementation method, two bandstop MMRs – a classical dual-mode stub loaded resonator (DSLR) and a new tri-mode dual-stub loaded resonator (TDSR) – are investigated with detailed design formulas and diagrams. Then, a tri-band MBPF with equal individual sub-bands, a quad-band and two quint-band MBPFs with unequal individual sub-bands are synthesized and designed using the proposed bandstop MMRs. Additionally, simulations and experiments are used to verify the efficiency of all prototypes. Good agreements with the theoretical calculations are observed for all the MBPFs.

Design of a dual-wideband high temperature superconducting filter

A 7-pole dual-wideband high temperature superconducting (HTS) filter based on a quarter-wavelength stub-loaded dual-mode resonator is introduced. The resonance characteristics, coupling patterns, external factor and cross coupling structure are discussed in turn. The filter is fabricated on a double side DyBa2Cu3O7 HTS thin film with a 2 inch-diameter and 0.5-mm-thick MgO substrate. The fabricated filter is measured at 77 K. The measured results show that the filter has an excellent in-band performance with center frequencies of 240 MHz, 541 MHz and passbands of 40 MHz, 140 MHz, respectively. Due to the introduction of transmission zeros, the selectivity of filter is further improved. The measured results agree with the simulated ones substantially.

Design of the quasi-0 dB backward wave-coupled line coupler using CRLH-TL based on stepped-impedance open stub-loaded dual-mode resonator

ABSTRACTThis paper demonstrates symmetric backward wave quasi-0 dB coupled line coupler (CLC) based on the globe shaped composite right/left-handed transmission line (GS-CRLH-TL). The proposed CLC shows quasi-0 dB backward wave coupling with measured maximum backward coupling level of −0.72 dB at 3.07 GHz. −3 dB bandwidth of the backward coupling region is from 2.75 GHz to 3.34 GHz, corresponding to fractional bandwidth (FBW) of 19.16%. The designed CLC shows good isolation of more than 43 dB in the backward coupling region in −3 dB frequency range from 2.75 GHz to 3.34 GHz. The measured value of return loss, at the center frequency 3.07 GHz, is more than 26.4 dB. Overall size of the fabricated CLC including 50 Ω feedline is 0.631λg × 0.455λg where λg is the guided wavelength at 3.07 GHz. Good concurrence is obtained between the simulated results, equivalent LC circuit model results and the measured results.

Design of Integrated Duplexing and Multi-Band Filtering Slot Antennas

In this paper, a duplexing antenna and two multi-band filtering antennas using resonator loaded slot are presented. The loaded slot can be flexibly designed as a dual-band or a tri-band antenna by changing the number of the loaded resonator. The operating frequencies of the slot antenna can be easily controlled through tuning the lengths and positions of the loaded elements. By integrating the multi-band antenna and the multi-mode resonator, duplexing and filtering antennas can be realized. The duplexing antenna consists of two single-mode resonators, a dual-mode stub-loaded resonator as the junction resonator and a dual-band slot antenna. The dual-band and tri-band filtering antennas each contains a dual-mode resonator or a tri-mode resonator, radiating through resonator loaded slot antenna. Since the slot is the only radiation element, all the operating bands of the three antennas show good bi-directional radiation patterns. For validation, all of the antennas are designed, manufactured and measured.

Quad-band bandpass filter based on sextuple-mode and dual-mode stub-loaded resonators

A quad-band bandpass filter (BPF) employing a sextuple-mode and a dual-mode stub loaded resonator are presented in this paper. The proposed sextuple-mode resonator generates the first, second and the fourth passband while the third passband is achieved by the dual-mode open stub-loaded resonator. The proposed sextuple-mode resonator modified from quintuple-mode resonator produces five resonant modes while the sixth-mode is generated by the coupling of the open ends of two stub resonators. Based on the odd- and even-mode analysis of the sextuple-mode resonator, the odd- and even-mode resonant frequencies can be flexibly controlled by tuning the corresponding resonator dimensions. Subsequently, the proposed sextuple resonator is combined with dual-mode open stub loaded resonator to achieve the quad-band BPF, centered at 1.75/2.45/3.50/5.25 GHz. The size of filter is about 0.13λg×0.22λg, where λg is guided wavelength on the substrate at 1.75 GHz. The measured results agree well with the simulated results.

Ultracompact microstrip dual‐ and triple‐band bandpass filters with a common resonator feeding structure

Microstrip dual- and triple-band bandpass filters (BPFs) exhibiting an ultracompact size and high frequency selectivity are proposed in this study. A common resonator feeding technique is proposed and was applied to design the multiband BPFs. In the design, the first and last resonators are realised using stepped-impedance resonators and are used to form a passband that has lower operating frequencies than the passband(s) of other resonator(s). Moreover, the first and last resonators serve as the input-output feeding structure and provide a source-load coupling for the passband(s) operating at higher frequencies. Thus, finite transmission zeros can be formed over the stopband. Hence, size miniaturisation and high frequency selectivity can be achieved simultaneously. The higher operating passband(s) is (are) formed by the dual-mode stub-loaded resonator(s) to reduce the number of resonators and the overall size of a filter. To verify the design approach, a dual-band BPF centred at 1.3 and 2.58 GHz with an ultracompact circuit size of 0.048 λ g × 0.088 λ g ( λ g : guided wavelength at the central frequency of the lower passband) and a triple-band BPF centred at 1.24, 2.5, and 3.5 GHz with an ultracompact circuit size of 0.15 λ g × 0.12 λ g were designed and fabricated. The measurement and electromagnetic simulation results were in good agreement.

Compact dual-band bandpass filter and diplexer using hybrid resonant structure with independently controllable dual passbands

In this article, a compact dual-band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub-loaded dual-mode resonator and a slotline stub-loaded dual-mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual-band BPF. Multiple TZs are generated by introducing a source-load coupling, thus improving the selectivity of the passbands. Then, the dual-band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual-band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45 GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method.

Compact microstrip eight‐channel multiplexer with independently switchable passbands

A compact eight-channel multiplexer with independently switchable passbands has been presented and investigated. The use of the dual-mode stub-loaded resonators can lead to significant size reduction for the multiplexer, this is because the required resonator number is reduced. In addition, the multiplexer is designed based on the distributed coupling technique, so that each passband can be designed individually due to the loading effect is small. Moreover, the complicated nine-port matching network at the input is not required. Besides, since the p-i-n diodes are connected to the output resonators for each channel, all passbands of the multiplexer can be independently switched on and off when the diode is in the reverse-biased and forward-biased states, respectively. Therefore, the proposed multiplexer can arbitrarily transfer to a single-band bandpass filter, a diplexer, a triplexer, a quadruplexer, a quinqueplexer, a sexaplexer, a septiplexer, and an octoplexer. For a demonstration, an eight-channel multiplexer with the second-order bandpass response have been designed and fabricated with microstrip in printed circuit board. The measured results are in good agreement with the full-wave simulation results.

Compact microstrip balanced-to-balanced diplexer using stub-loaded dual-mode resonators

Compact microstrip balanced-to-balanced diplexer using stub-loaded dual-mode resonators

Design of a Dual-Mode Balun Bandpass Filter With High Selectivity

In this letter, a new dual-mode balun bandpass filter (BPF) with high selectivity is proposed. The balun BPF is mainly composed of two different types of microstrip-to-slotline transition structures, two identical dual-mode stub-loaded resonators, and a pair of balanced outputs. First, to convert unbalanced signals from port 1 into balanced signals between port 2 and port 3, two different types of microstrip-to-slotline transition structures are utilized. Afterward, two identical stub-loaded resonators are embedded in the circuit for realizing the dual-mode bandpass response. Furthermore, four transmission zeros generated outside the passband are wisely introduced and well elucidated, thus ensuring high selectivity performance. For demonstration, a sample of balun BPF centered at 2.78 GHz ( $f_{0})$ with 0.5-dB magnitude imbalance and 5° phase imbalance is designed, fabricated, and measured. Both simulation and measurement are in good agreements.

Design of a filtering power divider with microstrip‐to‐slotline transition structures

A filtering power divider (FPD) with high selectivity is presented. Initially, by elaborately introducing two different types of microstrip-to-slotline transition structures and a pair of dual-mode stub-loaded resonators, dual-mode bandpass response is attained in this design. Afterwards, the resistor R is utilised to achieve high in-band isolation between two output ports of the FPD. Moreover, four transmission zeros are generated outside the passband for high selectivity performance. To validate the feasibility of the new approach, a prototype FPD operating at 3.62 GHz (f 0) is designed, fabricated and measured. Both simulated and measured results are provided in good agreement indicating that the proposed FPD exhibits a better than 20 dB isolation inside the passband and extended upper stopband up to 10 GHz.

A Shared-Aperture Dual-Band Dual-Polarized Filtering-Antenna-Array With Improved Frequency Response

In this paper, a novel dual-band dual-polarized array antenna with low frequency ratio and integrated filtering characteristics is proposed. By employing a dual-mode stub-loaded resonator (SLR) to feed and tune with two patches, the two feed networks for each polarization can be combined, resulting in the reduction of the feed networks and the input ports. In addition, owing to the native dual resonant features of the SLR, the proposed antenna exhibits second-order filtering characteristics with improved bandwidth and out-of-band rejections. The antenna is synthesized and the design methodology is explained. The coupling coefficients between the SLR and the patches are investigated. To verify the design concept, a C-/X-band element and a $2 \times 2$ array are optimized and prototyped. Measured results agree well with the simulations, showing good performance in terms of bandwidth, filtering, harmonic suppression, and radiation at both bands. Such an integrated array design can be used to simplify the feed of a reflector antenna. To prove the concept, a paraboloid reflector fed by the proposed array is conceived and measured directivities of 24.6 dBi (24.7 dBi) and 28.6 dBi (29.2 dBi) for the X-polarization (Y-polarization) are obtained for the low- and high-band operations, respectively.

Interview

Dr Jianpeng Wang, from the Nanjing University of Science and Technology in China, talks about the work reported in their Letter ‘Compact microstrip balun diplexer using stub-loaded dual-mode resonators’, page 1994. Dr Jianpeng Wang As is well known, dual-band operation is frequently demanded in transceiver modules of modern wireless microwave communication systems. Rather than arranging two separated frequency-selective radio frequency (RF) circuits in the systems, many researchers choose an independent device, i.e., the diplexer, to support such systems. This is a useful component for reducing the overall size of RF transceiver applications. Microstrip diplexers are a three-port passive devices, which have the capability to split common input signals into two individual output streams operating in different frequency bands with high port-to-port isolation. The involved stub-loaded resonators in our design are the typical form of the dual-mode resonator. Their resonant properties have been characterised by using the even-odd mode analysis method. Through this method, we can examine how, by properly adjusting the length of the loaded stub, the even-mode resonant frequency of the dual-mode resonator can be tuned, while keeping the odd-mode resonant frequency almost unchanged. In this context, two resonant frequencies generated by the employed stub-loaded resonator can be flexibly controlled to realise a dual-mode response, which will substantially decrease the size of the balun diplexer, making it preferable to single mode resonators. In general, the utilised resonators play an important role in the implementation of compact balun diplexers with a certain bandwidth and two transmission poles in each operating band. What makes our work unique is the implementation of a typical multi-function integrated component, which effectively simplifies the circuit design, and reduces the overall size of radio frequency (RF) transceiver front-end systems. During the design phase, each balun filter channel in the diplexer can be independently controlled without effecting others, thus showing greater flexibility. Furthermore, no additional T-junction or matching networks are demanded at the common input port in our balun diplexer design. In our Electronics Letters paper, we introduced a new microstrip unbalanced-to-balanced (balun) diplexer, which utilises the stub-loaded dual-mode resonators. The proposed diplexer consists primarily of two balun filter channels. Meanwhile, these two balun filter channels are directly connected through a common open-circuited half-wavelength transmission line without any additional matching network. This unique property will reduce the overall size compared with other diplexer circuits using T-junction for the purpose of impedance matching. By adopting this method, we can create a compact, high performance balun diplexer with a remarkably simple structure. These changes are meaningful for RF engineers who design multi-function embedded unbalanced-to-balanced feeding networks in modern dual-band wireless communication systems. The presented design concept is a worthy guideline for the implementation of multi-function embedded passive components. In short, compared with the current approaches, it is more desirable to develop multi-function embedded components based on the viewpoints of explicit operation principles, simple structures, and high performances. In this way, these components can really facilitate and simplify RF transceiver front-end systems. It is our belief that components or systems using these techniques will prove more valuable to the engineering community.

Compact microstrip balun diplexer using stub‐loaded dual‐mode resonators

A new microstrip unbalanced-to-balanced (balun) diplexer based on stub-loaded dual-mode resonators is presented. The proposed balun diplexer primarily consists of two balun filter channels, and both channels are entirely independently designable, thus bringing great flexibility in the balun diplexer design. Besides, owing to the direct connection of two dual-mode balun filters, no additional matching networks are demanded at the common input port, leading to a significant size reduction. For demonstration, a prototype balun diplexer operating at 2.30 and 2.72 GHz is implemented. Both simulated and experimental results are provided in good agreement.

Dual-Band Patch Antenna With Filtering Performance and Harmonic Suppression

A novel design of a dual-band antenna with integrated filtering performance is proposed. A low-profile aperture-coupled U-slot patch antenna is employed for the dual-band operation with a uniform polarization, which is fed by a dual-mode stub-loaded resonator (SLR). The U-slot patch works as a dual-mode resonator of the dual-band filter as well as the radiation element. The odd- and even-modes of the SLR are coupled and tuned with the U-slot patch, generating two second-order operation bands at 3.6 and 5.2 GHz. Compared with the traditional patch antenna, the proposed antenna exhibits improved bandwidth and frequency selectivity. In addition, the bandwidths can be controlled by adjusting the coupling strength between the SLR and the patch. Furthermore, the higher order harmonics can be suppressed over a broadband without increasing the footprint of the design. The measured and simulated results agree well with each other, showing excellent performance in terms of impedance matching, bandwidths, second-order filtering, out-of-band rejection, cross-polarization discrimination, and gains at both the bands.

Compact Microstrip Dual-Band Quadrature Coupler Based on Coupled-Resonator Technique

A compact dual-band coupled-resonator quadrature (90°) coupler with flexible passband allocation has been presented. By introducing the dual coupling paths between input and output ports, the design flexibility is increased, and thus, a dual-band response can be realized. For demonstration, a dual-band 90° coupler operating at 1.6 and 2.1 GHz has been designed and fabricated with microstrip technology. The 90° coupler is formed by only four dual-mode stub-loaded resonators, leading to a compact size, i.e., about 0.27 $\lambda_{{g}}$ by 0.27 $\lambda_{{g}}$ . A good agreement is achieved between simulation and measurement.

Compact Highly Integrated Planar Duplex Antenna for Wireless Communications

This paper proposes a novel concept of an integrated duplex antenna for realizing a compact multifunction RF front end by integrating a duplexer and a dual-band patch antenna. First, an all-resonator-based duplexer is designed. It is composed of two sets of split-ring resonators as channel filters, which are joined by a dual-mode stub-loaded resonator as the junction resonator. Then, a novel dual-band patch antenna is achieved by coupling a patch with a hairpin resonator through a slot in the ground. Uniform radiation characteristics have been achieved across the two bands. Finally, the duplexer is integrated with the dual-band patch antenna to form a highly integrated duplex antenna by coupling the hairpin resonator to the junction resonator of the duplexer directly. In this process, the 50- $\Omega $ interface and matching network between them are removed, contributing to a compact footprint. The details of codesign approach have been discussed in this paper. Compared with the traditional cascaded duplexer and antennas, this paper is much more compact and integrated but with an improved frequency response. A prototype of an integrated duplex antenna at S-band is fabricated and measured, showing two operation channels of 2.52–2.65 GHz for transmitting and 2.82–2.94 GHz for receiving with an isolation of over 32 dB. The measured results agree well with the simulation results.

Microstrip dual‐mode bandpass filter design using pie‐section truncated semi‐circle and quarter‐circle resonators

New dual-mode microstrip bandpass filters (BPFs) using pie-section truncated semi-circle and/or quarter-circle resonators are presented. The even-mode and odd-mode frequency responses of these two resonators are investigated. Compared to the four-parameter optimisation of the conventional stub-loaded dual-mode resonator, only three parameters need to be adjusted and optimised for the proposed resonators. Based on these two novel resonators, three BPF examples are designed, fabricated and tested. In addition, the technique of source-load cross coupling to improve performance of the filters is adopted. The good agreement between simulated and measured results validates the design concept.

Frequency-reconfigurable microstrip filter with dual-mode resonators using RF PIN diodes and DGS

This work presents a novel frequency miniaturized reconfigurable dual-mode stub-loaded resonator switchable from bandpass filter to single/double-notched bandnotch filter. The proposed filter topology employs RF PIN diodes as the switching device. Based on the odd- and even-mode equivalent circuits, the resonant characteristics of the proposed microstrip resonator are investigated. The defected ground structure pattern enhanced the performance; the 3-dB bandwidth reached 63%, with insertion loss of −0.5 dB. There was great sharpness of 55 dB in the low-frequency edge (from 1.7982 to 1.8466 GHz) and 33 dB in the high-frequency edge (from 3.4329 to 3.4995 GHz). The frequency-reconfigurable microstrip filter has been designed, fabricated, and measured for application in narrow band and ultra-wideband.

Compact and High-Isolation Diplexer Using Dual-Mode Stub-Loaded Resonators

A novel compact microstrip diplexer for UMTS and WCDMA system is proposed in this letter. The diplexer is mainly composed of three dual-mode stub-loaded microstrip resonators. Two resonant modes of a stub-loaded resonator work together with one mode produced by the common stub-loaded resonator to form a passband or operating band of the proposed diplexer. Extensive study is then conducted on coupling scheme involved in various parts of the diplexer. In particular, the resonance of a resonator is employed to create a desired transmission zero in the stopband, thus improving the isolation between two passbands. The proposed diplexer is in final fabricated and measured. A good agreement between EM simulated and measured results evidently validates the proposed methodology.