Stub-loaded Stepped-impedance Resonators Research Articles

Design of microstrip quint‐band lowpass–bandpass filters with flexible passband allocation

In this paper, newly proposed microstrip quint-band lowpass–bandpass filters are presented. The lowpass filter structure comprises a meandered transmission line and modified T-shaped resonators. Based on such an lowpass filter (LPF) structure, a quad-band λ/4 inductively-coupled dual-mode stub-loaded stepped impedance resonators BPF with one pair of a coupled I/O feeding line are parallelled on both sides of LPF to construct a quint-band lowpass–bandpass filter. By incorporating the parallel I/O coupled line and utilising multiple coupling paths, four bandpass bands can be fully controlled and designed independently. Specially, two distinct types of bandpass filters with different generating mechanisms are investigated and then combined to provide the quad-band responses. To validate the design concept, two types of quint-band lowpass–bandpass filters are designed, fabricated, and tested, where simulation results agree well with measurement results.

Compact Dual-Band Bandpass Filter Based on SSL-SIR With Sharp Roll-Off

A compact dual-band bandpass filter (DB-BPF) is studied and implemented by using shorted stub-loaded stepped impedance resonator (SSL-SIR) and 0∘∘feed structure in this paper. The resonance frequencies of SSL-SIR can be analyzed and explained by odd−-even mode analysis method and it is used in the design of BPF I. Then, the BPF II is created using the theory of 0∘∘feed structure. Finally, the two structures are combined together to form a DB-BPF by reasonably adjusting the coupling between them and the position of the feed points. The simulation results suggest that the center frequencies of the two passbands are 3.45 and 5.2 GHz, respectively, which are suitable for modern wireless communication systems like 5G and WLAN. Compact size, strong passband isolation, and large stopband bandwidth are all advantages of the proposed DB-BPF filter. A prototype is created and constructed to validate this. The simulated results are in good agreement with the measured results.

A quad‐band defected microstrip structure loaded bandpass filter for standard GPS , WiFi , WLAN , and WiMAX applications

A quad-band bandpass filter is proposed using a defected microstrip structure (DMS) for GPS, WiFi, WLAN, and WiMAX applications. This filter uses a stub-loaded stepped-impedance resonator (SL-SIR). The proposed filter is fabricated on an RT/Duroid5880 substrate (εr = 2.2, h = 0.787 mm, tanδ = 0.0009). Then, the LC equivalent circuit of the proposed filter is presented. A 28th-order transfer function is obtained and approximated by 8th-order transfer functions. The results of simulation, measurements and the LC equivalent circuit are in good agreement. The proposed filter operates at 1.6, 2.48, 3.76, and 5.44 GHz. The measured insertion losses are 0.32, 027, 0.51, and 0.41 dB in the four bands, while the return losses are better than 10 dB in all frequency bands. Finally, the proposed filter is compared with other bandpass filters.

Design of a Harmonic Suppressed Dual-Band Reconfigurable Bandpass Filter for Multistandard GNSS Receivers

This paper proposes a reconfigurable dual-band bandpass filter with independently tunable center frequencies that is intended to be integrated into reconfigurable multiband global navigation satellite system receivers. The center frequencies can be adjusted within the range of 1160-1280MHz and 1530-1630MHz for the two passbands, respectively. To achieve the design goal, the input and output feed lines are shared by a pair of quarter-wave uniform impedance resonators and a stub-loaded stepped impedance resonator with terminal-loaded varactor bias circuits. The electric length of the transmission lines is changed by using bias voltage to control the varactor diodes, thereby changing the operating frequencies of the dual-band filter’s two passbands, and the independent reconfigurability of the two passbands is realized. The insertion loss is less than 1.5dB and the return loss is better than 26dB in all tuning ranges. The proposed dual-band reconfigurable filter demonstrates the flexibility of controlling the passband independently to be compatible with multistandard signals, which can accommodate the deployment of new GNSS standard specifications.

Design of Miniaturized Tri-Band Microstrip Bandpass Filter Using Meandered Stubs for WLAN and Wi-Max Band

In this paper, a miniaturized tri-band microstrip bandpass filter is designed using three sets of shorted stub-loaded stepped impedance resonators (SSLSIRs). One pair of resonators have meandered short stub-loaded resonator (MSSLSIR) to further reduce the dimensions of the whole tri-band filter. The operating frequencies of the SSLSIRs and MSSLSIR are designed for the applications in the WLAN (2.45/5.2 GHz) and Wi-MAX (3.5 GHz) systems, respectively. The proposed filter is advantageous in terms of size miniaturization up to 0.013 × 0.012 (is guide wavelength) and in terms of good control over the passbands. The simulated and measured results are both in good agreement.

Compact dual‐band bandpass filter with flexible passband frequencies and sharp skirt using cross coupling and mixed magnetic and electric coupling

This paper presents the design of a compact dual-band bandpass filter (DB-BPF) with flexible passband frequencies and sharp skirt. A pair of stub loaded stepped-impedance resonators (SL-SIRs) together with two different tri-section stepped-impedance resonators (TS-SIRs) constitute this DB-BPF. The low impedance sections of two SL-SIRs and one TS-SIR are realized by ring structure, on the one hand to acquire two independent resonant modes of SL-SIRs, and on the other hand to let the harmonic mode of TS-SIR be away from the upper passband. The cross coupling, the canceling effect of mixed electric and magnetic coupling (MEMC), and the virtual ground introduce the TZs, resulting in the sharp skirt property of proposed DB-BPF. Step-to-step design process is given to guide the DB-BPF design. As an example, a 0.9 / 1.8 GHz DB-BPF is designed and fabricated. The fabricated sharp skirts DB-BPF has a compact size of 0.079λg × 0.193λg, low passband loss of 0.84 / 0.98 dB and high band-to-band rejection of better than 40.6 dB.

High Selectivity Single Wideband and Quad-Band HTS Filters Using Novel Quad-Mode Resonators With Self-Coupled Structure

This paper presents improved quad-mode resonators based on the open/short-end load of the center stub, which introduces the self-coupled structure. Compared with the traditional stub-loaded stepped impedance resonator (SLSIR), the proposed quad-mode resonators can significantly reduce the circuit size and further increase the design freedom. First of all, a comprehensive theoretical analysis is performed to infer the resonant characteristics of the proposed resonator. Then, two design prototypes based on different center loads of the resonator were demonstrated to verify the feasibility of the design method. First, a prototype of a wideband high temperature superconducting (HTS) filter with an FBW of 89% is proposed, whose center frequency (CF) can be flexibly controlled. Next, a quad-band HTS filter using different central stub load is proposed, which centered at 1.20, 2.52, 3.51, 4.44 GHz with the 3-dB FBW of 4.8%, 3.96%, 3.97% and 2.2%, respectively. The internal and external coupling mechanisms are also carefully studied to meet the specified requirements. The two prototypes proposed in this paper both have the advantages of compact size, ultra-low insertion loss and steep suppressed skirts. In addition, the measured results are in good agreement with the EM full-wave simulated results.

Design of Dualband Bandpass High-Temperature Superconducting Filter With Group Delay Equalization

A novel dualband high-temperature superconducting (HTS) bandpass filter is proposed with group delay equalization for 5G emergency communication receivers with N41 and N79 bands in this paper. The dual-folded stub-loaded stepped impedance resonator (DSLSIR) is applied to realize dualband performance. The proposed DSLSIR has miniaturized circuit size and more design freedom to independently adjust the two designed center frequencies, comparing with other reported DSLSIRs. Two cross-coupling transmission lines are added at the top and bottom parts of the cascaded sixth-order filter with DSLSIRs to flatten the group delay of the passband at both bands. A dualband bandpass HTS filter etched on the YBCO superconducting material is fabricated to verify the proposed design method. The measurement is actualized at the temperature of 77 K to make YBCO microstrip lines perform superconducting features. The results show that the first center frequency is 2.595 GHz with 6.2% bandwidth for N41 band and 0.3 dB insertion loss while the second center frequency is 4.85 GHz with 2% bandwidth for N79 band and 0.4 dB insertion loss. Meanwhile, the group delays at the N41 and N79 bands keep 2 ns fluctuations in the 60% passband. The agreement between the measured and simulated results indicates that the proposed dualband bandpass HTS filter with low insertion loss, sharp roll-off skirt and flat group delay is a promising candidate for emergency communication receiver.

Dual‐wideband differential bandpass filter with intrinsic common‐mode suppression based on hybrid transmission structure

Based on the microstrip-line/slot-line hybrid transmission structure, a novel method of realizing dual-wideband differential bandpass filter (DDBPF) is proposed and demonstrated in this paper. By virtue of hybrid transmission structure, the proposed DDBPF has intrinsic common mode (CM) rejection. Moreover, the dual-wideband transmission performance of differential mode (DM) signal can be approached by using two dual-mode stub-loaded stepped-impedance resonators. The two passbands of the proposed DDBPF are respectively centered at 2.76 GHz and 4.12 GHz which fractional bandwidths are 20.7% and 11.4%. The DM harmonic suppression can extend to 43.5 GHz with rejection level of 13 dB. The CM attenuation of DDBPF can reach 60 dB within DM passband. Furthermore, the CM suppression with attenuation level of 20 dB is ranging from 0.5 GHz to 43.5 GHz. The measurement results are in good agreement with the simulation results, which validates the effectiveness of proposed design methodology.

Separately-designable diplexer with multiple transmission zeroes using common stub-loaded SIR

AbstractA separately-designable diplexer with multiple transmission zeroes (TZs) using common stub-loaded stepped impedance resonator (SIR) is proposed. The common stub-loaded SIR operating in third harmonic (f3) and fifth harmonic (f5) is used for designing the two diplexer channels. The stub is loaded at the voltage-null point of f3 of the SIR. It can separately control f5 but has no effect on f3 so that the two channels can be separately designed. Meanwhile, the input port is tap-connected to the common stub-loaded SIR, which necessarily produces a TZ between f3 and f5, existing in both channel filtering responses. By properly choosing coupling schemes of the two channels, more TZs are realized at the desired locations. Thanks to the generation of the multiple TZs, both passband selectivity and isolation between the two channels are improved significantly. For demonstration, a diplexer operating at 2.22 and 2.95 GHz is designed, fabricated, and measured. The simulated and measured results are presented, showing good agreement.

Compact four‐pole wideband bandpass filter with mixed electric and magnetic coupling

AbstractA wideband bandpass filter (BPF) based on two dual‐mode stub‐loaded stepped‐impedance resonators (SLSIRs) with mixed electric and magnetic coupling (MEMC) is proposed. Magnetic coupling is realized by using a transmission line, open end‐coupling and inter‐digital‐coupling provide a weak and a strong electric coupling, respectively. Due to the canceling effect of MEMCs, together with its harmonic effect, four transmission zeros (TZs) aside the passband are created and the selectivity of the filter is therefore highly improved. To verify the proposed design, a four‐pole wideband BPF operating at 3.35 GHz with 3 dB fractional bandwidth (FBW) of 32.96% is designed, fabricated, and measured. The measured minimum insertion loss is 0.95 dB, and the passband return loss is better than 11 dB.

Compact DGS quad band filter for multi-service wireless communication systems using stub loaded stepped impedance resonators

This paper presents a compact dual-mode quad band micro-strip band-pass (BPF) and low pass (LPF) filter by using a stub-loaded stepped-impedance resonator (SIR) and a short-circuited stub-loaded uniform impedance resonator. Also, ring SIR geometry is introduced to miniature the size of this filter while maintaining excellent performance. The use of a stub resonator at the central point of the ring SIR can generate two resonant modes in two pass bands. For demonstration purposes, a quad-band filter for the applications of the WLAN/WiMAX/WLAN/UWB at 1.7/3.8/6.91/10.10, Worldwide Interoperability for Microwave Access at 3.8 GHz and wireless local area networks at 6.91 GHz and 10.10 GHz is designed, and fabricated.

Compact Ultra-Wideband Bandpass Filters Achieved by Using a Stub-Loaded Stepped Impedance Resonator

In this paper, we develop a bandpass filter using a stub-loaded stepped impedance resonator (SLSIR) and calculate the even and odd resonant modes of this type of resonator using the input impedance/admittance analysis. In this study, two impedance ratios and two length ratios are operated as the design parameters for controlling the resonant modes of the SLSIR. Several resonant mode variation curves operating three resonant modes with different impedance ratios and two length ratios are developed. By tuning the desired impedance ratios and length ratios of the SLSIRs, compact ultra-wideband (UWB) bandpass filters (BPFs) can be achieved. Two examples of the UWB BPFs are designed in this study. The first example is UWB filter with a wide stopband and the second one is dual UWB BPF, namely, with UWB performance and a notch band. The first filter is designed for a UWB response from 3.1 to 5.26 GHz having a stopband from 5.3 to 11 GHz, with an attenuation level better than 18 dB. The second filter example is a dual UWB BPF with the frequency range from 3.1 to 5 GHz and 6 to 10.1 GHz using two sets of the proposed SLSIR. The measured results have insertion loss of less than 1 dB, and return loss greater than 10 dB. Furthermore, the coupling structures and open stub of the SLSIR also provide several transmission zeros at the skirt of the passbands for improving the passband selectivity.

Microstrip switchable diplexer based on dual‐mode stub‐loaded stepped‐impedance resonators with three operating states

A new three-state switchable diplexer based on dual-mode stub-loaded stepped-impedance resonators (SL-SIRs) has been proposed. The three-state diplexer comprised six SL-SIRs with a distributed coupling structure. By appropriately adjusting the structural parameters of the SL-SIRs, a two-pole filtering response can be implemented at each channel passband. In addition, three p-i-n diodes, which were connected to the T-junction of the input coupled-line, were used to control the switching between the three operating states. Moreover, each operating state can be switched independently. For the purpose of demonstration, a three-state switchable diplexer was designed and fabricated using microstrip technology. The simulated results were consistent with the measured results, which indicate that the proposed switchable diplexer not only has a good in-band performance but also provides good isolation of better than 25 dB between output channels.

Millimetre‐wave low‐temperature co‐fired ceramic bandpass filter with independently controllable dual passbands

This study presents a detailed investigation on the frequency properties of the stub-loaded stepped-impedance resonator (SIR). For the first time, the frequency controllability of the third and fifth harmonic resonant frequencies (f3 and f5) of the SIR under different ratios of impedance and electric length is subjected to a complete theoretical analysis. It can be found that there is a length ratio which makes f3 and the voltage-null point at f3 never be affected by the change of the impedance ratio. Furthermore, the stub loaded at this voltage-null point also has no effect on f3. These features are successfully applicable to realise independent frequency control for dual-band bandpass filters (BPFs). In this situation, a new coupling path through the loaded stub can be constructed only for f5, and the coupling coefficients for the two bands can be individually varied. Accordingly, both the operational frequencies and bandwidths of the two bands can be separately adjusted. For demonstration, an independently controllable dual-band BPF operating at 27.5/33 GHz is designed and fabricated for millimetre-wave wireless applications. Good accordance is achieved between the simulated and measured results.

Dual-Band Bandpass Filter with Reduce Center Isolation Using Stub Loaded-Stepped Impedance Resonator

Dual-Band Bandpass Filter with Reduce Center Isolation Using Stub Loaded-Stepped Impedance Resonator

Compact tri-band bandpass filter using asymmetric stub-loaded stepped-impedance resonator with multiple transmission zeros

In this paper, a tri-band bandpass filter (BPF) using asymmetric stub-loaded stepped-impedance resonator (SL-SIR) is presented. The asymmetric characteristic of SL-SIR broadens degrees of freedom for three controllable modes design. Also, the coupling coefficients (Mij) and the external quality factors (Qei) at each passband of the filter can be independently adjusted by the proposed mixed-type feedline structure. Besides, multi-transmission zeros are produced to improve the isolation and selectivity of the passbands. Finally, a tri-band BPF is operated at 1.9 GHz (time division long term evolution – TD-LTE band), 3.2 GHz (worldwide interoperability for microwave access – WiMAX band), and 5.8 GHz (wireless local area networks – WLAN band) and their insertion loss are 1.03, 0.94, and 1.27 dB, respectively. The measured results of the fabricated tri-band BPF exhibit good agreement with simulated results.

Tri-band bandpass filter using modified tri-section and stub-loaded stepped impedance resonators

Tri-band bandpass filter using modified tri-section and stub-loaded stepped impedance resonators

Compact Multi-band Power Dividers Based on Stub Loaded Stepped-Impedance Resonators with Defected Microstrip Structure (SL-SIR-DMS)

Abstract Based on conventional Wilkinson power divider, two compact multi-band equal power dividers (PDs) employing stub loaded stepped-impedance resonators with defected microstrip structure (SL-SIR-DMS) is proposed in this paper. The proposed SL-SIR-DMS is analyzed by even/odd mode method. It is found that different defected structures can lead to different frequency responses. In addition, by using DMS, tri-band and even quad-band responses can be easily achieved without increasing the resonator size. As verification, one tri-band equal PD and one quad-band one are fabricated. The predicted results on S parameters are compared with the measured ones and good agreement is found.

Compact dual-band bandpass filter using open stub-loaded stepped impedance resonator with cross-slots

A compact dual-band bandpass filter using stub-loaded stepped impedance resonator (SLSIR) with cross-slots is presented. The symmetric SLSIR is analyzed using even- and odd-mode techniques. Design equations are derived and they are used to guide the design of the circuits. Two passbands can be easily tuned by cross-slots and open stubs. Transmission zeros among each passbands are created, resulting in high isolation and frequency selectivity. An experimental circuit is fabricated and evaluated to validate the design concept. The fabricated filter is compact with 19.76 × 12.7 mm2. The measurement results are in good agreement with the full-wave simulation results.