Stub-loaded Ring Resonator Research Articles

Miniaturized tri-notched wideband bandpass filter with ultrawide upper stopband suppression

Stepped impedance resonator (SIR) and its derivative resonators are widely used in the design of microwave filters. However, many spurious modes will be introduced into the stopband, resulting in lower upper stopband suppression and performance degradation. Based on the principle of slit line, a method to enhance the upper stopband suppression is proposed and verified by a miniaturized tri-notched wideband bandpass filter based on stub loaded ring resonator (SLRR) and shorted-stub loaded SIR (SSLSIR). The wideband is formed by coupling SLRR and interdigital lines, which has a rectangular DGS on the back of the substrate. Three notched bands with controllable positions in the passband can be produced by inserting two different SSLSIRs inside and outside the SLRR. Four slit lines are loaded on the low impedance stub of SSLSIR to adjust the high-order modes close to the transmission zeros (TZs). The operating frequency of the filter is 2.2–7.6 GHz, and the three notched bands are located at 2.97 GHz, 5.75 GHz and 6.46 GHz, respectively. The measurement results show that the − 20 dB enhanced upper stopband of the filter can reach 32 GHz, which proves that the filter has the characteristic of ultrawide upper stopband suppression while keeping the miniaturization.

A compact wideband diplexer using stub-loaded square ring resonators

ABSTRACT In this paper, a compact wideband diplexer is designed by combining two wideband filters based on stub-loaded square ring resonator (SLSRR). By adjusting the length of the stub or square ring, the passband bandwidth can be adjusted. The first channel has a center frequency of 4.3 GHz with a fractional bandwidth (FBW) of 50%. The second channel has a center frequency of 8.75 GHz with the FBW of 51.4%. The average isolation between the two channels is averagely greater than 25 dB. The designed diplexer has the advantages of easy design of wideband, simple structure, and informal matching of impedance.

High selectivity wideband bandpass filter based on stepped impedance open stubs loaded ring resonator

A high selectivity wideband bandpass filter (BPF) is proposed based on a stepped impedance open-stub loaded ring resonator. The resonant modes can be adjusted by the parameters of the stepped impedance stubs and eventually to tune the bandwidth conveniently. The even resonant modes can be tuned lower than the first odd resonant mode that is excited by the half wavelength resonator. Due to the analysis of the electric field distributions on the resonator, three adjacent resonant modes can be employed to form a wide bandwidth by electric coupling between input/output feeding line and the resonator. In addition, by introducing two more resonant modes in the passband using the parallel-coupled feeding open stubs, the selectivity is further improved. The related coupling topology is theoretically analyzed and experimentally verified. As the design example, a wideband BPF centered at 3.24 GHz with a 3-dB fractional bandwidth of 58.3% is fabricated and measured. The experimental results fit the simulations well.

Compact tri‐notched wideband bandpass filter based on multiple resonances with wide upper stopband

AbstractIn this letter, a compact tri‐notched wideband bandpass filter based on stub‐loaded ring resonator (SLRR) and shorted stub‐loaded stepped impedance resonators (SSLSIR) with wide upper stopband is presented. The wideband characteristic is excited by coupling SLRR and SSLSIR with the arrangement of defected ground structures on the back of the substrate. By placing two sets of SSLSIRs inside and outside of the SLRR, three reflection poles can be formed in passband to introduce three notch bands with adjustable center frequencies. The quarter‐wavelength inter digital coupled lines are used to generate multiple transmission zeros to suppress high‐order harmonics to achieve a wide upper stopband characteristic. For validation, a wideband bandpass filter with a passband from 2.2 to 7.5 GHz and notch bands at 2.87, 5.69, and 6.5 GHz is fabricated. Measured results show that the 20 dB attenuation upper stopband can extend to 29 GHz.

Dual-Band Differential Bandpass Filters Using Quadruple-Mode Stubs-Loaded Ring Resonator With Intrinsic Common-Mode Suppression for 5G

A novel quadruple-mode stubs-loaded ring resonator (SLRR) is presented in this letter, which can achieve compact dual-band differential bandpass filters (BPFs) with intrinsic common-mode suppression. The differential-mode (DM) equivalent circuit and common-mode (CM) equivalent circuit of the SLRR are given and investigated by using the even-/odd-mode theory. Two DM resonances of the SLRR can be adjusted independently and are used to construct two DM passbands. Due to the magnetic-dominated coupling between two SLRRs, the intrinsic CM suppression characteristics are achieved in the differential passbands without using any additionally loaded elements. And by loading the different short-circuited coupled lines (SCCLs) at the parallel-coupled feed-line of differential BPF separately, two transmission zeros (TZs) are introduced on both sides of the DM passbands, which improves the selectivity of dual differential passbands. Furthermore, to realize the desired external Q values for two DM passbands, hybrid feeding line structure including tapped and coupled-line feeding structures is used to produce the valid excitation for the differential BPF. At the same time, the open stubs are attached to the inside of the ring resonator to reduce the filter size. Finally, two dual-band differential BPFs with central frequencies of 3.5 GHz and 4.9 GHz are designed and fabricated for fifth generation of mobile communications (5G). The measured minimum CM suppression of the two DM passbands are 31.0 dB and 34.8 dB.

Compact Dual-Band HTS Bandpass Filter Using Coplanar Waveguide Short-Circuited Stub-Loaded Ring Resonator

A compact coplanar waveguide (CPW) dual-band high-temperature superconducting (HTS) bandpass filter using a short-circuited stub-loaded ring resonator (SC-SLRR) is introduced in this paper. The equivalent circuit of the SC-SLRR is built and its resonant formulas are presented. The relationship between the parameters of electrical length and resonant performances are deduced. Resonant modes of the proposed resonators can be simultaneously excited and easily tuned for a dual-band application. To verify this methodology, a second-order CPW HTS dual-band bandpass filter operating at 2.36/4.93 GHz is designed. This filter is implemented on a 0.5-mm thick MgO wafer with a one-sided YBa 2 Cu 3 O 7 film, and it has the compact size of 0.146λg × 0.083λg. Measured results agree well with the simulated ones, which show that the minimum insertion losses of both bands are less than 0.15 dB.

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.

Theoretical Based Design of Ultra-Wideband Filter with Dual Band-Notch

In this paper, a compact ultra-wideband microstrip band-pass filter with single/dual-notched bands is proposed. The filter is theoretically designed based on a multiple-mode resonator which consists of a short circuit stub loaded-ring resonator. A multi stepped impedance resonator is also applied to reject unwanted in-band frequencies and extend the upper-stopband. The proposed filter is analyzed by utilizing graphs according to odd- and even-mode method. The resonant modes are allocated between 3.1 GHz to 10.6 GHz and transmission zeros are adjusted at upper stopband to create a sharp roll-off and suppress the spurious harmonics, as well as a compact physical size. Full-wave simulations are performed for three types of filters, with and without notch-bands, to verify theoretical results. The measurement results demonstrate that not only − 3 dB fractional bandwidth is more than 120% and but also at least − 20 dB suppression can be achieved at upper-stopband.

A compact trisection microstrip bandpass filter with frequency-dependent cross-coupling

ABSTRACTA compact microstrip bandpass filter using stub loaded ring resonators and double-loop ring resonators in an embedded triplet configuration with frequency-dependent cross-coupling is proposed in this article. The embedded triplet configuration is realized by putting the loops of the double-loop ring resonator into the circles of the stub loaded ring resonators. The frequency-dependent cross-coupling has been introduced to the filter by a manner of separate electric- and magnetic-coupling path. Three transmission zeros are obtained to enhance the frequency selectivity and stopband performance. Among them, two are achieved by the frequency-dependent cross-coupling, the other one is created by the harmonic effect of the transmission lines. The filter is designed for 2.4 GHz Wireless Local Area Networks application with 20.8% fractional bandwidth. The measured results show reasonable agreement with the simulated ones.

Modeling and Susceptibility Study of Ring Resonator Bandpass Filter for Wireless Applications

This article presents a T-type stub loaded ring resonator bandpass filter with defected ground structure (DGS) for applications in wireless communication systems. Two H-shaped DGS have been used at the ground plane to suppress spurious frequency response above the passband. Parametric analysis of the proposed filter has been done using IE3D 15.2. Measured result shows a fractional bandwidth of 13.8%, centered at 3.3 GHz, and sharpness factor of 160 dB/GHz. Better than 20 dB out-of-band rejection level has been achieved from 3.64 to 7 GHz. A susceptibility test has been performed to check whether the filter will be able to operate satisfactorily in the presence of interfering signals. To validate the simulated results it is fabricated and tested. The simulated data show a good agreement with measured data.

Ultra-Wideband Filter with Dual Notch Bands Based on Ring Resonator

ABSTRACTAs the ultra-wideband system is easy to be interfered by narrow-band signals, an Ultra-wideband (UWB) bandpass filter for the rejection of wireless local area network and satellite communication signals is proposed. The main resonant structure was composed of an open stubs loaded ring resonator. The cascaded open stubs increased a resonant frequency and improved the selectivity of the filter. Two notch bands were realized by coupling W-shaped short stub loaded resonators and etching complementary split rings resonators. The notch frequencies could be obtained by adjusting the size of two band-stop resonators. The UWB bandpass filter was then simulated, fabricated, and tested. Simulation results are in sound agreement with measured results. Both show that the filter has a compact size with a wide upper stopband, and dual notch bands are centered at 5.8 and 8.0 GHz, respectively, which suppressed the interference from a wireless local area network and satellite communication signals in the UWB passband.

High selectivity wideband filtering crossovers using stub-loaded ring resonators

Two high selectivity wideband filtering crossovers using stub-loaded ring resonators are proposed in this paper. Cascaded coupled lines and open stubs are used to generate two/four transmission zeros each near the crossover passbands. In addition, patterned grounded conductor in the ground plane can enlarge the coupling coefficient for the coupled lines with increasing the even-mode characteristic impedance, and the isolated conductor placed inside the slot can decrease the odd-mode characteristic impedance. Two filtering crossovers operated at 2.2 GHz with bandwidths of 27.5% from 1.945 to 2.55 GHz are designed and fabricated. They show good return loss more than 20 dB and nice insertion loss less than 1.7 dB in passband.

Compact Multi-Band Bandpass Filters With Mixed Electric and Magnetic Coupling Using Multiple-Mode Resonator

In this paper, a multiple stubs loaded ring resonator (MSLRR) is proposed to design directly coupled multi-band bandpass filters (BPFs) with mixed electric and magnetic coupling (MEMC). The proposed MSLRR exhibits multiple-mode resonant behavior. The increased number of loaded stubs excite many more useful resonant modes, but these resonant modes can be still independently controlled. As examples, a dual-band BPF, a tri-band BPF, a quad-band BPF, and a quint-band BPF using different types of MSLRRs are designed and fabricated. The passband frequencies and return losses (RLs) of these multi-band BPFs can be independently controlled. A dual-mode open loop resonator is then introduced in the quint-band BPF to enhance the sixth resonant mode of the MSLRR to produce the sixth passband so that a sext-band BPF is also presented. Multiple transmission zeros due to the cancelling effect of MEMC and virtual grounds in the MSLRR can be observed around the passbands resulting in sharp passband selectivity and high band-to-band isolation. Moreover, all of the fabricated multi-band BPFs have compact sizes, good RLs, and low insertion losses. Good agreements are observed between the simulated and measured results.

Compact Dual-Band Bandpass Filter Using Stubs Loaded Ring Resonator

AbstractThis paper presents a novel second-order dual-band bandpass filter (BPF) by using proposed stubs loaded ring resonator. The resonant behavior of proposed stubs loaded ring resonator is analyzed by even-/odd-mode method, which shows its multiple-mode resonant characteristic. Parameters sweep is done so as to give the design guidelines. As an example, a second-order dual-band BPF operating at 1.8/5.2 GHz for GSM and WLAN applications is designed, fabricated and measured. The fabricated filter has a very compact size of 0.05λg×0.15λg. Measured results also show that the proposed dual-band BPF has a better than 20 dB rejection upper stopband from 5.47 GHz to 12.56 GHz. Good agreement is shown between the simulated and measured results.

Balanced Bandpass Filter Using Stub-Loaded Ring Resonator and Loaded Coupled Feed-Line

A balanced bandpass filter is proposed based on stub-loaded ring resonators (SLRRs) and loaded coupled feed-lines (CFLs) with high selectivity and common-mode (CM) rejection. By controlling the coupling coefficient of the CFLs, three transmission poles within the differential passband are achieved. The CFLs are loaded with open- and short-circuited stubs at the end of the traditional parallel-coupled feed-lines, which resulting in multiple transmission zeros (TZs) in differential mode (DM) and CM to improve the passband selectivity and CM suppression, simultaneously. Finally, the proposed filter is designed and fabricated, the simulated and measured results are in good agreement. The filter shows low insertion loss, multiple transmission zeros, high selectivity and enhanced CM rejection.

Design of a Stub-Loaded Ring-Resonator Slot for Antenna Applications

A T-shaped stub-loaded ring-resonator (SLRR) slot etched on the ground plane or on the radiating patch has been designed and analyzed for antenna applications. Compared with the conventional ring slot, the two resonant frequencies of the proposed SLRR-slot can be lowered, and can also be tunable by varying the parameters of the four T-shaped stubs. To validate the design concept, a tri-band printed antenna and a dual band-notched ultra-wideband (UWB) antenna using the SLRR-slot on the ground plane and radiating patch, respectively, are presented. For the tri-band antenna, a simple U-shaped slot etched on the microstrip feeding line is used to excite a third upper-frequency band independently without increasing the overall size of the antenna and without affecting the lower two bands. The proposed tri-band antenna has three frequency bands of 2.4, 3.5, and 5.8 GHz, and the dual band-notched UWB antenna can guarantee a very wide bandwidth from 3.0 to 12.0 GHz with dual undesired bands successfully. The experimental results including radiation patterns, peak gains and efficiencies of both antennas are presented.

A DUAL-BAND BANDPASS FILTER FOR 2.4 GHZ BLUETOOTH AND 5.2 GHZ WLAN APPLICATIONS

In this paper a dual-band bandpass filter, using stub loaded ring resonator and etched nested C-shape defected ground structure (DGS), is reported. The operating frequencies of the bandpass filter conform to the Bluetooth (2.4 GHz-2.484 GHz) and WLAN (5.15 GHz-5.35 GHz) systems. Due to its applications in WLAN and Bluetooth systems, the filter will be subjected to high EM radiation from the antenna and nearby sources. Therefore, susceptibility study of such filter is very important. The susceptibility study of the filter has been carried out by subjecting the structure to an interference source. Experimental results are presented and analyzed.

DUAL-BAND BANDPASS FILTERS USING A NOVEL QUAD-MODE STUB-LOADED RING RESONATOR

This paper presents two dual-band bandpass filters with controllable passband frequencies and bandwidths. The filters are realized utilizing a novel quad-mode stub-loaded ring resonator. All the four mode equivalent circuits of the resonator are quarter-wavelength resonators, and their fundamental resonance frequencies are used to form the passbands. So the designed filters have a compact circuit size and relatively wide upper stopband. For validation, two experimental filters operating at 1.5/2.4 GHz and 1.5/3.5 GHz are designed. In the design of the second filter, hook-shape feed-lines and source-load coupling are applied to generate more transmission zeros, which greatly improve the selectivity of the filter. Finally, the filters are fabricated, and measured. The measured results have good agreement with the simulated ones.

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.

Ultra-Wideband Bandpass Filter With a Notch-Band Using Stub-Loaded Ring Resonator

A quadruple-mode ultra-wideband (UWB) bandpass filter with a notch-band and wide upper stopband is presented in this letter. The UWB filter is realized using a ring resonator which is loaded with two sets of stubs, i.e., one is loaded in the center and two little stubs at the symmetrical side locations. The loaded stubs are used to create transmission zeros in upper stopband thus high modes are suppressed greatly. Moreover, two identical via-loaded ring resonators are inserted within the stub-loaded ring resonator, to create a notch-band around 5-6 GHz to avoid WLAN signals. Two reflection poles appear in the notch-band, resulting in a switchable bandwidth of the notch-band. Finally, a UWB filter with a notch-band is simulated and fabricated, and measured results provide an experimental validation of predicted performance of the filter.