Search Results (20)

This work presents a comprehensive technological study of dielectric resonator-based microstrip filters (DRMFs), encompassing the design, fabrication, and rigorous characterization of the $T{E}_{01\delta }$ mode. Through systematic coupling analysis, we demonstrate filters featuring novel input–output coupling techniques and innovative implementations of both transmission zeros (4-2-0 configuration) and equalization zeros (4-0-2 configuration), specifically designed for demanding space and radar receiver applications, while the loaded quality factor ($Q_L$) and insertion loss do not match those of dielectric resonator cavity filters (DRCFs), our solution significantly surpasses conventional microstrip filters (MFs), achieving $Q_L$> 3000 compared to typical $Q_L$≈ 200 for coupled-line MFs in X-band. The fabricated filters exhibit exceptional performance as follows: input reflection ($S_{11}$) below −18 dB (4-2-0) and −16.5 dB (4-0-2), flat transmission response ($S_{21}$), and out-of-band rejection exceeding −30 dB. Mechanical tuning enables precise control of input–output coupling, inter-resonator coupling, cross-coupling, and frequency synthesis, while equalization zeros provide tailored group delay characteristics. This study positions DRMFs as a viable intermediate technology for high-performance RF systems, bridging the gap between conventional solutions. Full article

In this paper, a compact capacitive-loaded quarter-mode substrate integrated waveguide (CL-QMSIW) resonator is proposed and analyzed. This resonator is created by loading a metal–insulator–metal (MIM) capacitor inside the QMSIW resonator. A miniaturized hybrid bandpass filter with deep stopband suppression is designed based on the CL-QMSIW resonator and the stripline resonator. The filter generates a transmission zero (TZ) that can be adjusted flexibly through cross-coupling in its lower stopband, which significantly enhances the filter’s selectivity. To verify the correctness of the proposed filter, a third-order filter was created and produced, utilizing the low-temperature co-fired ceramics (LTCC) technique. The measurement outcomes align with the results from the electromagnetic simulations. The filter is characterized by a center frequency of 7 GHz, while the core size is only $0.33{\lambda }_g\times 0.17{\lambda }_g$, and the lowest insertion loss (IL) within the band is 1.4 dB, achieving a TZ at 5.1 GHz. The proposed filter features a compact dimension, excellent selectivity, and low insertion loss. Full article

This paper presents a bandpass filter (BPF) exploiting hybrid shielded eighth-mode circular substrate-integrated waveguide (SD-EMCSIW) and complementary split ring resonator (CSRR) resonators. The proposed BPF leverages the SD-EMCSIW resonator with a 45-degree angle to create a second-order BPF with a mixed electromagnetic coupling scheme. Detailed analyses of the related electromagnetic characteristics and operating mechanisms have been performed. In order to further reduce the occupied area, the CSRR structures are embedded into the SD-EMCSIW resonators. Meanwhile, extra metallic via-holes are implemented to enhance the upper-stopband performance. A transmission zero (TZ) of the second-order BPF can be placed on either the left or right side of the passband and can be flexibly adjusted. To validate the design concept, a second-order hybrid SD-EMCSIW and CSRR BPF was designed, simulated, fabricated, and measured as a specific example. The prototype operates at a center frequency f₀ of 8.3 GHz with a 3 dB fractional bandwidth of 8.1%. Two transmission zeros are located near the right passband. The upper-stopband rejection reaches up to 15 dB at 2.85 times the center frequency f₀. Both the simulated and measured results show satisfactory agreement. Meanwhile, the overall size of the proposed hybrid SD-EMCSIW and CSRR BPF is 13.5 mm × 13.0 mm (0.37λ₀ × 0.36λ₀), featuring a compact physical dimension in the filter design. Full article

A compact high-selective band-pass frequency selective surface (FSS) with the unit cell less than λ/7 is presented. For the simulation of the structure, the multilevel Green’s function interpolation method (MLGFIM) using Floquet theory is adopted to accelerate the calculation of the complex unit cell. The radial basis function (RBF)-QR method is used in the interpolation, which makes the shape parameter in the RBF function not required to be retested for different periodicity. In this design, with an aperture coupling structure between the top and bottom layers patterned by triangular patches and meander lines, the FSS has two transmission zeros (TZs) on both sides of the pass-band and achieves a steep roll-off rate of 192 dB/GHz. Consequently, the FSS has high selectivity and out-of-band suppression, besides profiting from the low profile and symmetric geometry, this FSS exhibits good angular and polarization stabilities. The prototype of the proposed FSS is fabricated and good performance is obtained. Full article

In this study, we present a novel dual-polarized patch antenna that exhibits high isolation and two in-band transmission zeros (TZs). The design consists of a suspended metal patch, two feeding probes connected to an internal neutralization line (I-NL), and a T-shaped decoupling network (T-DN). The I-NL is responsible for generating the first TZ, and its decoupling principles are explained through an equivalent circuit model. Rigorous design formulas are also derived to aid in the construction of the feeding structure. The T-DN realizes the second TZ, resulting in further improvement of the decoupling bandwidth. Simulation and experimental results show that the proposed antenna has a wide operating bandwidth (2.5–2.7 GHz), high port isolation (>30 dB), and excellent efficiency (>85%). Full article

In recent years, Split-Ring Resonators (SRRs) and Complementary Split-Ring Resonators (CSRRs) have gained significant attention for their unique electromagnetic properties, such as negative permeability and negative permittivity, making them promising candidates for advanced microwave devices. This paper presents the design and analysis of a substrate-integrated waveguide (SIW) filter using CSRR structures for miniaturization. The improved CSRR unit can be easily integrated on the surface of the SIW, making it an ideal candidate for the design of compact SIW filters. In this paper, an improved CSRR-loaded SIW filter is designed and analyzed based on its equivalent lumped parameter model. A filter with a center frequency at 22.6 GHz is designed. Several transmission zeros (TZs) are also realized to improve the skirt selectivity of the filter. The design process involves theoretical analysis and electromagnetic simulations to optimize the dimensions of the CSRR resonators to achieve the desired filter characteristics. The measured and simulated results show good agreement, confirming the effectiveness of the proposed improved CSRR-loaded SIW filter. The successful implementation of the improved CSRR-loaded SIW filter demonstrates its potential for achieving miniaturization and enhanced performance in advanced microwave applications. Full article

In this paper, a wideband absorptive filtering power divider (AFPD) which features the characteristics of high selectivity and flat output distributions is proposed. It is composed of one unequal width three-coupled line (TCL), two coupled lines (CLs), two stepped open-circuited stubs, two kinds of isolation resistors, and two types of absorptive branches. The design equations of the proposed AFPD are derived using an even-odd decomposition method, and parametric investigations are also performed. It is found that the passband bandwidth can be adjusted by the stepped open-circuited stub which generates two transmission zeros (TZs). By combining the TCL with the CLs, the passband bandwidth is effectively enlarged. In addition, two isolated resistors are utilized for achieving good isolation and output-port matching performance. Without affecting the passband responses, the input port absorptive feature within the whole frequency band can be obtained by loading the absorptive branches both on the input and output ports. For validation, an example operating at the center frequency of 2 GHz was modeled and tested. Results exhibit that the passband FBW reaches 72% under 1 dB criterion, which illustrates flat output port distributions. In addition, for 10 dB return loss, the input and output impedance matching bandwidths are 250% and 78%, respectively. The features of good filtering responses are demonstrated by realizing the rectangle coefficient of 1.24 and the out-of-band suppression of more than 20 dB. Full article

A balanced bandpass filter (BPF) with a wide differential mode (DM) bandwidth and steep DM passband selectivity and high common-mode (CM) block based on slotline stub-loaded resonators (SSLRs) is designed in this brief. The proposed SSLR, which is composed of a half-wavelength slotline resonator and a shorted slot stub loaded at the symmetrical plane, is applied to achieve a broad DM passband with a center frequency at 5.1 GHz and a 3 dB bandwidth of 92%. Meanwhile, two transmission zeros (TZs) are introduced to realize a steep DM passband selectivity. The center frequency and bandwidth of the DM passband can be adjusted by changing the dimensions of SSLRs and the gaps between them. Meanwhile, one narrow notched band with a 3 dB bandwidth of 4.9% is realized by employing one coupled quarter-wavelength short-circuited stub at the input ports. In addition, the DM stopband with a rejection level of 10 dB can be extended to 20 GHz. The designed balanced broadband filter is stimulated by a U-shaped microstrip line to slotline transition structure, which can realize wideband a CM block with a high suppression level without influencing the DM one, and this can reduce the design complexity. In order to prove the idea, a balanced broadband filter is designed and measured. The predicted results of S parameters are compared with the measured ones, and a good agreement is achieved. Full article

In this paper, a compact high-selectivity frequency tunable bandpass filter (BPF) with constant absolute bandwidth (ABW) based on varactor-loaded step-impedance resonators (SIRs) is presented. By introducing cross coupling between resonators, a pair of transmission zeros (TZs) close to the passband are produced and the selectivity of the filter is enhanced significantly. Another pair of TZs are generated to improve the out-of-band rejection by using source-load coupling. The varactor-loaded SIRs are utilized to design the compact fourth-order tunable BPF in order to realize wide tuning range and compact size. In addition, the frequency-dependent coupling feeding structures are employed instead of lumped capacitors used in conventional feeding structures, as a result, the insertion-loss performance is improved. The simulated and measured results are presented and show good agreement. The measured results exhibit a tuning range from 0.8 to 1.14 GHz with a 3 dB constant ABW of about 47 ± 5 MHz, the return loss of the filter is greater than 13.9 dB, and the insertion loss is about 2.7–3.1 dB. Moreover, four TZs are generated, and the proposed tunable filter shows high selectivity with a rectangular coefficient of 2.3–3.1. Full article

A balanced bandpass filter (BPF) with an improved frequency selectivity for differential-mode (DM) excitation and high rejection for common-mode (CM) excitation is proposed in this paper. Two half-wavelength stepped impedance resonators (SIRs) are employed based on mixed electric and magnetic couplings to realize a DM passband centered at 2.48 GHz. The center frequency and bandwidth can be easily controlled by optimizing the dimensions of SIRs and the coupling between them, respectively. Meanwhile, two transmission zeros (TZs) are generated based on the mixed electric and magnetic couplings and are independently controlled by tuning the coupling strength. Moreover, a wide DM stopband can be realized by optimizing the SIRs. The proposed balanced BPF is fed by balanced U-type microstrip–slotline transition structures, which can achieve high wideband CM rejection without influencing the DM responses, and the design complexity can be clearly reduced. Finally, a balanced BPF is fabricated, and a good agreement between the simulation and the measurement is observed, which verifies the design method. Full article

The development of mobile 5G technology poses new challenges for high-frequency and high-performance filters. However, current commercial acoustic wave filters mainly focus on 4G LTE, which operates below 3 GHz. It is necessary to accelerate research on high-frequency acoustic wave filters. A high-selectivity film bulk acoustic resonator (FBAR) filter chip for the 3.4–3.6 GHz range was designed and fabricated in this paper. The design procedure includes FBAR parameter fitting, filter schematic analysis, and the generation principle of transmission zeros (TZs). The measured results show that the filter chip is of high roll-off and stopband suppression. Most of the stopband suppression is better than 35 dB. Finally, error analysis was conducted, and FBAR parameters were modified after testing for future filter design work. Full article

Reconfigurable filters are one of the key components in microwave communication systems. This letter presents a 4th-order low-temperature cofired ceramic (LTCC) bandpass filter with both a tunable center frequency and bandwidth. This filter has four resonators, and each resonator consists of a circular patch, a center-through via, and two varactors. The varactors are placed on the top and bottom layers of the ceramic medium, which can effectively reduce the size of the 4th-order tunable filter. Three transmission zeros (TZs) are introduced to improve the upper stopband rejection. This filter demonstrates a 3-dB bandwidth (BW) range of 170–220 MHz around 2.86 GHz and a 3-dB BW range of 190–320 MHz around 3.2 GHz with a 13 dB minimum return loss. Insertion loss ranging from 3.5 dB to 6.85 dB has been obtained. The overall circuit size, including the package, is 11 mm × 6 mm × 1.6 mm. Full article

This paper presents a tunable bandpass filter (BPF) with constant absolute bandwidth (CABW) and switchable properties. The BPF is performed by using a tri-mode cross-shape resonator (CSR) loaded with varactors. The CABW and switchable ability are achieved by adjusting the resonant frequencies. Meanwhile, the two transmission zeros (TZs) produced by center-loaded stubs strengthen the skirt selectivity in the on-state and the isolation in the off-state. For demonstration, a tri-pole switchable BPF with three control voltages is implemented and verified, and the control mechanism is simple. In the on-state, it exhibits a 120 MHz, 3 dB CABW with the measured insertion loss (IL) of 2.2–2.5 dB in the tuning range of 0.816–1.188 GHz. In the off-state, the measured isolation is better than 27 dB. Full article

In this paper, an electrically small tunable microstrip bandpass filter with two concurrently tuned transmission zeros (TZs) is presented. The filter consists of two coupled resonators and varactors as tuning elements. An application of a multipath coupling network results in TZs on both sides of the passband. The filter controlled by a single voltage has a wide tuning range from 370 MHz to 800 MHz and a low insertion loss ranging from 1.9 dB to 3.4 dB. To achieve high attenuation in the stopband, two sections of the designed filter were cascaded. Both one-section and two-section filters were validated by measurements. The obtained results are in a very good agreement with simulations. Full article

In this paper, a balanced-to-balanced filtering directional coupler (FDC) that can realize a 3 dB coupling degree directional coupler with high isolation and directivity is proposed. The design of the proposed FDC is primarily based on microstrip/slotline transition structures, resonance structures, and odd–even mode phase velocity compensation structures. A U-type microstrip feed line integrated with a stepped-impedance slotline resonator is adopted at the input and output ports, which makes the differential-mode (DM) responses independent of the common-mode (CM) ones, and brings superior DM transmission and CM suppression. In addition, by loading the microstrip stub-loaded resonators (SLRs), a DM passband with sharp filtering performance is realized, and transmission zeros (TZs) can be added into the design, which makes it more selective. Moreover, phase compensating slotlines are added into the coupling structure to enhance the isolation. In order to verify the feasibility of the proposed design method, an FDC prototype circuit was made and tested. The simulation results are in good agreement with the measured results. The designed coupler’s DM operating band covers 2.65 GHz to 3 GHz (FBW = 12.4%), and the insertion and return losses are 4.6 dB and 20 dB, respectively. The isolation degree is better than 15 dB, and the CM suppression is more than 55 dB. The total coupler size is about 67.7 mm × 63.8 mm. The designed balanced-to-balanced FDC can be widely used in S-band wireless communication systems. Full article