A novel wideband bandpass filter based on CSRR‐loaded substrate integrated folded waveguide

A novel wideband bandpass filter based on folded substrate integrated waveguide (FSIW) is presented in the article. Five square complementary split‐ring resonators (CSRRs) are etched in the middle layer of the FSIW. By adjusting the physical size of the CSRR structure, the resonant frequency of the CSRRs can be tuned at the same time and the stopband performance can be changed. As transverse electromagnetic (TEM) mode can be transmitted in the stripline, FSIW excited by stripline shows wider passband than that excited by microstrip line directly. To achieve perfect impedance matching, two microstrip lines to stripline transitions are added in two ports of the filter. The proposed bandpass filter exhibits compact size, high selectivity, good stopband rejection, lower radiation loss, and wideband performances. The measured results show that the fractional bandwidth of the filter is about 35.5%. The measured return loss is better than 15 dB from 4.84 GHz to 6.90 GHz, and the insertion loss is less than 1.2 dB. The comparison between the simulated results and the measured ones validate the possibility of the technology that combines the FSIW and CSRR.     

Design of a compact dual‐band folded‐waveguide bandpass filter using multilayer waveguide resonators

A novel compact dual‐band bandpass filter based on multilayer folded‐waveguide (FWG) structure is presented in this article.In this design, slots are used to realize direct coupling between adjacent resonators and apertures are adopted to implement cross coupling between non‐adjacent resonators.A new technique of external quality factor of FWG resonator and coupling coefficients between different resonators are studied using full‐wave simulator. In order to demonstrate the proposed technique, a four‐pole dual‐band bandpass filter is designed, fabricated and measured using vector network analyzer. Measurement results which are well agreed with simulation results are presented. Moreover, four‐pole substrate integrated folded waveguide SIFW dual‐band bandpass filter, using two layers of slotted folded waveguide resonators, is demonstrated. The proposed filter has a compact size and it is excellent candidate for the application of wireless communication systems. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:780–788, 2015.     

Compact bandpass filter using CMRC‐based dual‐behavior resonator

This article presents a novel bandpass filter (BPF) using two proximity‐coupled dual‐behavior resonators (DBRs). The employed DBR is implemented by a single shunt stub with the compact microstrip resonator cell at its open end instead of the traditional dual stubs in cross‐shape. Due to the adoptions of the proposed DBR and proximity‐coupling scheme, both the transverse and longitudinal dimensions of the proposed BPF are reduced significantly. To verify the proposed idea, a demonstration microstrip BPF is designed and fabricated, and good agreement between the simulated and measured results can be observed, showing low loss and high selectivity due to four transmission zeroes in the stopband.     

Design of dual‐mode dual‐band rectangular waveguide filtering antenna

A dual‐mode dual‐band rectangular waveguide filtering antenna with fourth‐order Chebyshev response is presented. First, design equations and processes of filtering networks are presented. Then, filtering antenna is constructed through cross‐shaped slot for radiation instead of the output port of filtering networks. A pair of degenerated modes are exploited in waveguide resonator design to miniaturize the whole size and form two passbands. In addition, the bandwidth can be adjusted flexibly in proper range. A prototype at C‐band is fabricated and measured, showing two operation channels of 5 to 5.05 GHz and 5.1 to 5.15 GHz with high rejection between two bands. Good agreement is achieved between the simulations and measurements, showing excellent performance in terms of filtering, out‐of‐band rejection, and gain in bands.     

A balanced dual‐band bandpass filter with independently tunable differential‐mode frequencies

A balanced dual‐band bandpass filter (BPF) with independently tunable differential‐mode (DM) frequencies is proposed in this letter. The proposed BPF is composed of complementary split‐ring resonators (CSRRs) etched on the ground and varactors loaded on the resonators. A balanced stepped‐impedance microstrip‐slotline transition structure is introduced to transfer the DM signals successfully and block the common‐mode (CM) signals transmission. Good DM transmission and CM suppression can be achieved. Moreover, by changing the reverse bias voltages of the varactors loaded on coupling CSRRs, two DM resonant frequencies of the proposed balanced BPF can be tuned independently. To verify the feasibility of the design method, a balanced BPF with DM frequency ranging from 0.80 GHz to 1.12 GHz and 1.55 GHz to 2.05 GHz is fabricated and measured. Good agreement between the simulation and measurement results demonstrate the validity of the design.     

A bandpass filter using modified half mode substrate integrated waveguide technique

This article reports a novel bandpass filter using modified half mode substrate integrated waveguide technique. The via‐fences are deployed as impedance inverters for the proposed filter to reduce its footprints, which are extracted by using a full‐wave electromagnetic simulator HFSS for the filter design. Detailed design procedure is discussed. A bandpass filter having a center frequency of 10.03 GHz and a pass band from 9.78 to 10.3 GHz is designed for demonstration, and experiments are carried out for the validation. Good agreements between experiment and simulated results are obtained, which show that the proposed filter has a compact size, a low insertion loss, and a high selectivity. It is attractive for the radio communication system. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:277–281, 2015.     

Independently controllable dual‐band microstrip bandpass filter using quadruple‐mode stub‐loaded resonator

In this article, a quadruple‐mode stub‐loaded resonator (QM‐SLR) is introduced and its four modes are excited using a simple approach, which can provide a dual‐band behavior. By changing the length of the loaded stubs, independently tunable transmission characteristics of the proposed quadruple‐mode stub‐loaded resonator were extensively described for filter design. Moreover, microwave varactors were adopted to represent the length variation of the loaded stubs for the dual‐band tunability. The equivalent circuit modeling of the open stub with microwave varactor was given and discussed. Then, adopting the compact quadruple‐mode stub‐loaded resonator with three varactors, an independently controllable dual‐band bandpass filter (BPF) was designed, analyzed, and fabricated. Its separated bandwidths and transmission zeros can be tuned independently by changing the applying voltage of the microwave varactors. A good agreement between simulated and measured results verified the design methodology. The proposed filter possesses compact size, simple structure, and excellent dual‐band performances. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:602–608, 2016.     

Widely separated dual‐band half‐mode SIW bandpass filter

A novel half‐mode substrate integrated waveguide (HMSIW) based dual‐band bandpass filter (DBBPF) is proposed. Back to back connected two defected ground structure (DGS) resonators on the top layer of HMSIW cavity constitute the passband with two transmission zeros (TZs) at a lower frequency. The higher modes TE₃₀₁ and TE₃₀₂ of HMSIW cavity give the passband response at higher frequency using the mode shifting technique with slot perturbation. The source‐load coupling has been used to create finite frequency TZs to improve the selectivity of the second passband. Therefore, the proposed filter gives two widely separated passbands, center frequencies (CFs) at 5.83 and 18.1 GHz with an attenuation of greater than 10 dB between the passbands. The synthesized filter is fabricated using a low‐cost single layer PCB process, and the measured S‐parameters are almost mimic the EM‐simulation results.     

Half mode substrate‐integrated waveguide‐loaded evanescent‐mode bandpass filter

In this article, a filter size reduction of 46% is achieved by reducing a substrate‐integrated waveguide (SIW)‐loaded evanescent‐mode bandpass filter to a half‐mode SIW (HMSIW) structure. SIW and HMSIW filters with 1.7 GHz center frequency and 0.2 GHz bandwidth were designed and implemented. Simulation and measurements of the proposed filters utilizing combline resonators have served to prove the underlying principles. SIW and HMSIW filter cavity areas are 11.4 and 6.2 cm², respectively. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Compact differential dual‐band bandpass filter using single quad‐mode metal‐loaded dielectric resonator

This letter presents a novel miniaturized differential dual‐band bandpass filter (BPF) using a single quad‐mode metal‐loaded dielectric resonator (DR). The differential dual‐band BPF is designed in a single‐cavity configuration with one quad‐mode DR and four feeding probes, featuring compact size. The rectangular DR is directly mounted on the bottom of the metal cavity and covered by a metal plate on the top surface. It allows two pairs of orthogonal modes (LSE₁₀ and LSM₁₀), which can be differentially excited and coupled by introducing proper perturbation for constructing dual‐band differential‐mode frequency response. To validate the proposed idea, a compact differential BPF with good performance using a quad‐mode DR cavity is designed, fabricated, and measured. The simulated and measured results with good agreement are presented.     

A tunable third‐order bandpass filter based on combining dual‐mode square‐shaped substrate integrated waveguide resonator with triangular‐shaped resonator

A frequency reconfigurable third‐order bandpass filter based on two substrate integrated waveguide (SIW) cavities is presented in this article. The purposed filter consists of a dual‐mode square‐shaped resonator and a triangular‐shaped resonator. In the square‐shaped cavity, four lumped capacitors are loaded as electrical tuning elements in the area where the electric fields of diagonal TE₂₀₁ and TE₁₀₂ modes are strongest. And an another capacitor is loaded at the suitable region of the triangular‐shaped cavity. Square‐shaped cavity introduces two transmission zeros and the triangular‐shaped cavity can suppress out‐of‐band spurious modes. The method that combines the resonators with different shapes and multiple modes into an organic whole cannot only achieve synchronous tuning but also have complementary advantages and improve out‐of‐band rejection. To verify its practicality, a SIW reconfigurable bandpass filter is simulated when the capacitance value varies from 0 to 1.4 pF and measured at 0.7, 0.8, and 0.9 pF, respectively. Measured results show that when the center frequency is tuned from 3.42 to 3.52 GHz, the proposed filter exhibits good tuning performance with insertion loss of less than 2.5 dB and return loss of better than 10 dB, which is suitable for fifth‐generation communication system.     

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual‐band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U‐shape half‐wavelength resonator, a folded stub‐loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential‐mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common‐mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual‐band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.     

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.     

Ultra‐wideband bandpass filter on coplanar waveguide: Proposal and implementation

In this paper, a novel ultra‐wideband (UWB: 3.1 ～ 10.6 GHz) bandpass filter on coplanar waveguide (CPW) is presented, designed and implemented. At first, an open‐ended nonuniform or multiple‐mode resonator with three distinctive sections is constructed and investigated toward generating the first three resonant modes occurring around the lower‐end, center, and higher‐end of the UWB band. Then, a CPW interdigital capacitor element with enlarged ground‐to‐ground distance is characterized to excite two additional resonant poles below and above the UWB's center. As a result, a five‐pole UWB bandpass filter with only one full‐wavelength is constituted. Its performance is studied on the basis of a simple cascaded transmission‐line network, whose parameters are extracted from our self‐calibrated method of moments. After the optimized results are confirmed by full‐wave simulation over the filter layout, a UWB filter sample is fabricated to demonstrate the actual UWB passband behavior with the 2.8–10.2 GHz bandwidth, where the insertion loss is less than 1.5 dB and variation in group delay is less than 0.33 ns. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Design of wideband bandpass filter using short‐circuited circular patch resonator loaded with slots

This paper presents a wideband bandpass filter design based on a short‐circuited circular patch resonator with inductively loaded slots. The cavity model method is used to analyze the excited resonances of the resonator. According to the illustration of the cavity model, the TM₀₁₀ mode is excited as the fundamental mode, the resonant frequency of which is much lower than that of the TM₁₁₀ mode and can be further lowered by the loaded arc‐oriented slots. Therefore, the proposed resonator can be used to design a filter with compact size. In addition, one of the two orthogonal degenerate TM₁₁₀ modes can be independently tuned by the slot along the symmetric plane without affecting the TM₀₁₀ mode. Since the resonant frequency of each mode can be tuned independently by the parameters of the slots, and the coupling between resonant modes of the resonator and source/load can be adjusted by the feeding angle and the capacitive loaded stubs on the feeding lines, the center frequencies and bandwidths of the designed bandpass filters can be tuned easily. The analysis is theoretically and experimentally verified by two examples with good agreement between the simulated and measured results.     

A novel E‐plane substrate inserted bandpass filter with high selectivity and compact size

In this article, a novel E‐plane substrate inserted waveguide bandpass filter with high selectivity and compact size is proposed in Ka‐band. By integrating an extra resonator between two metal septa, the E‐plane waveguide filter is achieved with two transmission zeros at both sides of the passband which contribute to the high‐skirt selectivity. One sample is fabricated, whose total length is just 5 mm, namely, less than 0.5 and the minimum insertion loss is only about 0.3 dB. Good agreements between simulated and measured results are obtained. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:451–456, 2014.     

Compact dual‐ and triband bandpass filter using frequency selecting coupling structure loaded stepped‐impedance resonator

This article presents two novel resonators, that is, frequency selecting coupling structure loaded stepped‐impedance resonator (FSCSLSIR) and π‐section loaded FSCSLSIR. The resonator behaviors and guidelines are given to design FSCSLSIR dual‐band bandpass filter (BPF) and π‐section loaded FSCSLSIR triband BPF. The proposed dual‐ and triband BPF have very compact sizes of 0.13 λ_gd × 0.06 λ_gd and 0.115 λ_gt × 0.074 λ_gt, respectively. Moreover, good return loss, low insertion loss, and high band‐to‐band isolation can be observed, and the proposed FSCSLSIR dual‐band BPF has an ultrawide stopband from 5.79 to 36 GHz. The experimental results are in good agreement with the simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:427–435, 2015.     

Independently controllable dual‐band filter using single quad‐mode silver‐loaded dielectric resonator

This article proposes a novel bandpass filter with two controllable passbands using a single quad‐mode silver‐loaded dielectric resonator (DR). The silver plane is inserted in the middle of the cubic DR and two degenerate pairs are used to build the two passbands. Because of the distinct E‐field distributions, the silver plane has significant effect on the degenerate pair (TE^x₁₁₂ and TE^y₁₁₂), whereas another one (TE^x₁₁₁ and TE^y₁₁₁) remains unchanged. With the aid of the silver plane, both center frequencies and bandwidths of the two bands can be controlled independently. To verify the proposed idea, a prototype dual‐band BPF is designed and fabricated. Good agreement between simulated and measured results can be observed.     

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.     

Electromagnetic design of folded‐waveguide resonator filter with single finite‐frequency transmission zero

This article presents electromagnetic (EM) design of a new folded‐waveguide resonator filter that uses an advanced coupling scheme to achieve the desired asymmetric frequency response with an attenuation pole of finite frequency on the high side of the passband. A filter of this type with a fraction bandwidth about 5% at a center frequency of 4.45 GHz has been successfully designed using a commercially available electromagnetic simulator. The designed filter has been fabricated and tested. Simulations and experimental results are presented to validate the design and to show the advantages of this type of filter. This filter also provides a compact size compared with conventional cavity resonator filters. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.