Even-mode Resonant Frequencies Research Articles

Compact tunable filtering balun with stable stopband using varactor‐loaded coupled‐line‐loaded hairpin ring resonator

A tunable filtering balun with compact size and stable stopband is proposed in this article. First, the coupled-line-loaded hairpin ring resonator (C-HRR) is introduced. Then by loading two varactors at the two null-voltage points of the C-HRR, the varactor-loaded C-HRR is designed. The odd-mode resonant frequency fo can be tuned independently without influencing the even-mode resonant frequency fe. Besides, the out-of-phase current distribution of the varactor-loaded C-HRR at fo is noticed. Finally, to validate the features of the varactor-loaded C-HRR, a tunable filtering balun is designed and fabricated. Measured results show that the filtering balun can realize a frequency tuning range from 1.9 to 2.4 GHz. In the tuning process, the amplitude and phase imbalances are less than 0.5 dB and 4° at each tuning state. The lowest spurious resulting from fe is stable and always larger than 2.33fo. The circuit size of the filtering balun is only 0.24λgh × 0.055λgh, where λgh is the guide wavelength at the highest operational frequency.

Ultra-Compact Ultra-Wideband Bandpass Filter Based on Multi Mode Resonator Concept

An ultra-compact ultra-wide band (UWB) bandpass filter (BPF) with a very sharp rejection for the high-speed wireless communication applications is proposed. The functional basis of the proposed structure is based on the multi-mode resonator (MMR) technique. The suggested ultra-wideband filter is realized by using two doublet parallel coupling lines, two symmetrical open stubs and tri-section step-impedance open stubs which are located at the center of the configuration. In order to analyze the suggested configuration, the even-mode and odd-mode methods have been utilized because of the proposed UWB BPF is a symmetrical structure. Five modes which are including three even modes and two odd modes have been placed within the UWB band. By changing the dimensions of the tri-section step-impedance open stubs and two symmetrical open stubs, the resonant modes of the constructed MMR can be tuned. These two parts have been mainly applied to adjust the resonant modes into desired passband. Changing the dimensions of the two symmetrical open stubs affects both the even and odd modes. But the tri-section step-impedance open stubs can only specially control the even-mode resonant frequencies, whereas the odd-mode ones are fixed. Consequently, the center frequency and the bandwidth of the proposed configuration can be simply adjusted. Experimental verification is provided and a reasonable agreement between simulated and measured results has been achieved. The proposed UWB BPF has a passband covers 3.55 to 10.65 GHz and the measured 3 dB fractional bandwidth (FBW) is about 100%.

A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications

This paper presents the design and implementation of a printed circuit microwave band-pass filter for 5G mid-band applications, using a Stub Loaded Multiple Mode Resonator (SL-MMR) technique. The objective of this article is to introduce a low-cost microstrip filter with improved passband and stopband characteristics, based on a mathematical analysis of stub loaded resonators. The filter cost is reduced by selecting the low-cost FR4 dielectric material as a substrate for the proposed filter. Based on the transmission line model of the filter, mathematical expressions are derived to predict the odd-mode and the even-mode resonant frequencies of the SL-MMR. The mathematical model also highlights the capability of controlling the position of the SL-MMR resonant frequencies, so that the 5G sub-band that extends along the range (3.7–4.2 GHz) can perfectly be covered with almost a flat passband. At the resonance frequency, a fractional bandwidth of 12.8% (500 MHz impedance bandwidth) has been obtained with a return loss of more than 18 dB and an insertion loss of less than 2.5 dB over the targeted bandwidth. Furthermore, a pair of parasitic elements is attached to the proposed filter to create an additional transmission zero in the lower stopband of the filter to enhance the suppression of the filter stopband. The measured and simulation results are well agreed, and both reveal the acceptable performance of the stopband and passband characteristics of the filter.

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.

Varactor Tuned Dual-Band Bandpass Filter With Independently Tunable Band Positions

A dual-band bandpass filter with different even-mode and odd-mode resonant paths is presented. The band position can be tuned independently. The basic filter structure is a stub-loaded ring resonator. A varactor diode placed in the ring controls the odd-mode resonant frequency. A second varator connects the stub to the ring and controls the even-mode resonant frequency. A transmission line-based approach is used for theoretical analysis. A prototype filter is fabricated in the microstrip technology. Measured results show that the first band is tunable over 0.69–0.88 GHz with a maximum insertion loss of 1.83 dB. The second passband can be tuned over 2.67–3.78 GHz. Maximum passband insertion loss is 2.02 dB. Use of just two tuning elements makes the structure low cost and compact.

Quad-mode dual-band bandpass filter based on a stub-loaded circular resonator

In this paper, a quad-mode dual-band bandpass filter (BPF) only using a stub-loaded circular resonator is presented. The odd- and even-mode resonant frequencies can be easily computed and flexibly controlled by the radius of the circle and the two sets of stubs, as all odd- and even-mode equivalent circuits are half-wavelength resonators (double-ended short-circuited uniform transmission line resonator). Introducing the resonator makes the filter be analyzed and designed easily. To further improve the isolation between the two passbands, a dual-band BPF is designed by introducing the source-load coupling technique; the simulation and test S-parameter curves show that the designed BPF has four controllable transmission zeros. The good agreement of measured data with simulation results verifies the proposed design.

Design of compact multi-mode microstrip resonator filters for dual-band application

<span>This paper presents the design of compact multi-mode microstrip resonator filters for dual-band application. The design is simulated using Advanced Design System (ADS) 2016 software. The benefit of the proposed filter is found to have a dual-mode frequency, where the odd-mode resonant frequency is the fundamental frequency represented by the length of the resonator while the even-mode resonant frequency is represented by the length of the stub. To validate the design, a prototype is fabricated on Rogers RO4003C substrate and measured using PNA Network Analyzer.</span>

Open Loop Resonator-Based Triple Passband Filter for 1.5 GHz, 2.45 GHz and 3.65 GHz Applications

In this paper, a dual mode mixed open loop resonator (OLR)-based metamaterial antenna is introduced for the design of a triple-passband filter for GPS, WLAN and WiMAX applications. The antenna is embedded into a 50-Ω microstrip framework. The Rogers RT-5880, which has a succinct structure, is used as the substrate in the proposed passband filter design, where the attainment of the antenna is explored both integrally and experimentally. A partial ground system is applied in the ground layer and stepwise analysis is performed on the proposed resonator, which can pursue the fundamental even-mode resonant frequency. Based on the proposed resonator, a bandpass filter is designed and fabricated to justify the perception, focusing on 1.5 GHz, 2.45 GHz, and 3.65 GHz. In addition, the filter is evaluated using the Nicolson–Ross–Weir approach at the filtering frequency. The effective electromagnetic parameters retrieved from the simulation of the S-parameters imply that the OLR metamaterial antenna exhibits negative refraction bands. With a favorable design and double-negative characteristics, this structure is suitable for a triple passband filter, particularly at 1.5 GHz, 2.45 GHz and 3.65 GHz, which cover GPS, WLAN, and WiMAX, respectively.

Independent Control Function for Concurrent Dual-Band VCO

This letter presents a concurrent dual-band voltage-controlled oscillator (VCO) with independent control of the two oscillation frequencies based on a common dual-band bandpass filter (BPF). The odd- and even-mode resonant frequencies of the BPF can be independently tuned to realize the concurrent dual-band VCO. Based on the principle of the flexible tuning characteristics, analytical equations are obtained to introduce a method for circuit size reduction and tuning range extension. The measured results show that the two oscillation frequencies cover a tuning range of 1.59–1.802 and 3.314–3.42 GHz, respectively.

Independently Tunable Concurrent Dual-Band VCO Using Square Open-Loop Resonator

A concurrent dual-band voltage-controlled oscillator (VCO) with independently tunable dual oscillation frequencies is proposed. A shared square open-loop dual-mode resonator and two varactor diodes are the basic units offering flexible tuning for the dual-band operation. A back-to-back varactor diode between the split of the resonator controls the odd-mode resonant frequency, and a single varactor diode is placed at the center of the resonator to adjust the even-mode resonant frequency. By combining the other four resonators with the shared dual-mode resonator, two distinct three-pole tunable bandpass filters (BPF) are designed as two frequency selective elements. Based on the two elements, a parallel-feedback concurrent dual-band VCO is fabricated with independently-tuned dual oscillation frequencies. Moreover, the mathematical deductions are analyzed to optimize the tuning ranges of the dual-oscillation frequencies and the circuit sizes. The measured results show that the two oscillation frequencies cover a tuning range of 5.114–5.28 GHz and 7.61–7.97 GHz, respectively.

High Selectivity Wideband Bandpass Filter Using Stub Loaded Resonator

AbstractThis article presents a high selectivity wideband bandpass filter (BPF) adopting stub loaded resonator. Hereinto, aim passband is determined by BPF without stub embedded, which is only composed of four half-wavelength open-loop resonators. Based on typical tapped-line coupling, two same stubs are located at physical middle points of two resonators connected with I/O feed lines, respectively. Due to embedded point at middle of loaded resonator, the stub with two open-end branches has no influence on original half-wavelength resonant frequency, and aim passband keeps unchanged. Because of different even-mode resonant frequencies between loaded and unloaded resonators, no new passband is constructed. With the help of embedded stubs, original transmission zero (TZ) near low-edge of aim passband is shifted towards passband, and a new TZ is introduced near high-edge. High selectivity and good passband characteristics are obtained optimizing sizes of stubs, I/O tapped position and top open-end length of loaded resonator.

Compact Tunable Balanced Bandpass Filter With Novel Multi-Mode Resonator

A novel multi-mode resonator is presented to design compact tunable balanced bandpass filters (BPFs). From the theoretical analysis, the common-mode (CM) resonant frequencies are different from that of the differential-mode (DM) response, so the CM suppression can be achieved without adding any extra lumped elements. For the DM response, the modal frequencies of odd and even modes can be adjusted simultaneously by varying the varactors. This helps to design the DM response with tunable passband center frequency. Moreover, the even-mode resonant frequency can be tuned independently, leading to controllable passband bandwidth of the DM. To verify the design method, a compact tunable balanced BPF is developed, fabricated and measured. Good agreement can be attained between the measurement and simulation.

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.

Novel Frequency-Agile Bandpass Filter With Wide Tuning Range and Spurious Suppression

A new frequency-agile scheme for the loaded stepped-impedance resonator (SIR) is introduced, which can be employed for designing a wideband tunable bandpass filter (BPF). Two identical capacitors are added to the two open ends, and a capacitor is added to the center of the SIR. By properly controlling their respective values, the even-mode resonant frequency $(f_\mathrm{even})$ can be bidirectionally tuned, resulting in a wideband tuning range (approximately double those of the traditional tunable resonators). However, in such frequency range, the odd-mode resonant frequency $(f_\mathrm{odd})$ functions as a spurious resonance would appear. To overcome this, the feed line is attached to the center of the SIR where it is always short-circuited for $f_\mathrm{odd}$ and its odd-order harmonics, which cannot be excited accordingly. Thus, the wideband tuning range of the passband $(f_\mathrm{even})$ in the proposed BPF is validated to be meaningful, and the selectivity of the passband is improved due to the suppression of odd-mode spurious near the passband. For demonstration, a wideband tunable BPF is designed, and the simulated and measured results are presented, showing good agreement. The results showcase that the tuning range of passband reaches 84.4%, i.e., from 0.77 to 1.42 GHz with insertion loss from 3.1 to 1 dB.

Tri-band filter with multiple transmission zeros and controllable bandwidths

This paper presents a compact microstrip tri-band bandpass filter (BPF) using two multimode stepped-impedance resonators (SIRs) with a 0° feed structure. The fundamental odd-mode and even-mode resonant frequencies and the third resonant frequency are utilized to determine the center frequencies of the tri-band filter. The mode-splitting technique is used by combining two SIRs with electrical coupling. Therefore, two modes generate one passband and the bandwidths can be controlled by the electrical coupling strength. The 0° feed network is applied to create one pair of transmission zeros at each side of all the triple passbands, resulting in high selectivity. Finally, a tri-band BPF with the central frequencies of 1.8, 2.4, and 5.8 GHz, and respective fractional bandwidths of 8.9, 12.5, and 5.3% are designed and fabricated. The simulated and measured results show a good agreement.

Design of compact dual‐band bandpass filter using dual‐mode stepped‐impedance stub resonators

A dual-band bandpass filter (BPF) using a novel stepped-impedance stub resonator (SISR) is presented. The proposed SISR is found to have the advantage that the even-mode resonant frequencies can be flexibly controlled, whereas the odd-mode resonant frequencies are fixed. Based on the proposed SISR, a dual-band filter is implemented by tuning its geometric parameters. To improve the selectivity, a filter with four transmission zeros on either side of both passbands is designed by introducing a 0° feeding structure. A prototype of a dual-band BPF centred at 1.84 and 2.65 GHz has been designed and fabricated. The measured results validate the full-wave EM simulated results.

DUAL-BAND BANDPASS FILTER WITH INDEPENDENTLY TUNABLE PASSBANDS AND WIDE STOPBAND

This paper presents a dual-mode stub loaded ring resonator (SLRR) to design a tunable dual-band bandpass filter (BPF) with two independently controllable passbands. The proposed resonator principally comprises a stepped-impedance ring resonator (SIRR) loaded with three stubs and two varactor diodes. Two independently tunable passbands are implemented by employing two varactors to control the dominant even-mode resonant frequency and odd-mode resonant frequency, respectively. Moreover, a new stub loaded double-ring resonator (SLDRR) is proposed to design the second tunable dual-band filter by shorting two stubs of the SLRR. With the same tuning method, the second filter can achieve two independently controllable passbands. In order to suppress the harmonics, defected ground structures (DGSs) are introduced at input and output feeding lines without degrading the passbands characteristics. The measured results are in good agreement with the simulated ones.

Compact and High Selectivity Tri-Band Bandpass Filter Using Multimode Stepped-Impedance Resonator

In this letter, a miniaturized tri-band bandpass filter (BPF) using a multimode stepped-impedance resonator (SIR) with a 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> tapped-feed structure is presented. The odd- and even-mode fundamental resonant frequencies and the first high-order resonant frequencies of the SIR are utilized to generate dual-mode dual-band response and the tapped side-coupled feed-lines construct an additional passband avoiding occupying extra size. Owing to the 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> tapped-feed structure and the intrinsic characteristics of the SIR, multiple transmission zeros are created to improve the selectivity of the filter. The bands of the designed tri-band BPF are located at 1.57 GHz (GPS application), 3.5 GHz (WiMAX application) and 5.8 GHz (WLAN application). Good agreement between the simulated and the measured results is observed.

Tunable Bandpass Filter With Independently Controllable Dual Passbands

This paper presents a two-pole dual-band tunable bandpass filter (BPF) with independently controllable dual passbands based on a novel tunable dual-mode resonator. This resonator principally comprises a λ/2 resonator and two varactor diodes. One varactor is placed at the center of the resonator to determine the dominant even-mode resonant frequency; the other is installed between two ends of the resonator to control the dominant odd-mode resonant frequency. These two distinct odd- and even-mode resonances can be independently generated, and they are used to realize the two separated passbands as desired. Detailed discussion is carried on to provide a set of closed-form design equations for determination of all of the elements involved in this tunable filter, inclusive of capacitively loaded quarter-wavelength or λ/2 resonators, external quality factor, and coupling coefficient. Finally, a prototype tunable dual-band filter is fabricated and measured. Measured and simulated results are found in good agreement with each other. The results show that the first passband can be tuned in a frequency range from 0.77 to 1.00 GHz with the 3-dB fractional-bandwidth of 20.3%-24.7%, whereas the second passband varies from 1.57 to 2.00 GHz with the 3-dB absolute-bandwidth of 120 ± 8 MHz.

A 60/77 GHz dual-band bandpass filter with MMIC technology

This paper presents a novel dual-band bandpass filter with two sets of stub-loaded open-loop resonator, using stepped-impedance, which results in a reduction in size. Two sets of resonators are synthesized using a doublet coupling scheme for 60/77 GHz resonance. The two passbands are flexible due to implement with two parallel transmission paths and tuning each bandwidth independently by changing even-mode resonant frequency. The fractional 3-dB bandwidths at 60 and 77 GHz are 11.4 and 8.3%, respectively. The values at 60 and 77 GHz are −2.26 and −2.63 dB and the values at 60 and 77 GHz are −24.8 and −18.5 dB, respectively. Between the two passbands, the transmission zero at 67 GHz gives nearly 22.6 dB isolation. Good performance makes this system attractive for wireless communications.