Lower Stopband Research Articles

A compact self‐packaged triple‐mode bandpass filter using dual capacitively‐loaded substrate‐integrated waveguide resonator

AbstractA compact triple‐mode (TM) bandpass filter (BPF) is designed based on the proposed dual capacitively‐loaded (DCL) substrate‐integrated waveguide (SIW) resonator. Two identical T‐shaped grounded striplines are inserted into a square SIW cavity to generate a capacitively loading effect without damaging cavity surface integrity, which contributes to maintaining EM‐shielding capability. By adjusting the size and position of the DCL structure, the first three resonant modes, including TE101, TE201, and TE301 are easily controlled to design a TM‐BPF. A transmission zero (TZ) is introduced by the grounded striplines and flexibly controlled. TZ is tuned to suppress the TE102 mode to acquire a wide upper rejection band. Furthermore, the filter design procedures are presented in the context under specified filter performance. Finally, to verify the proposed design method, an example of self‐packaged TM‐BPF at 6 GHz with a good lower stopband and a wide upper rejection band is designed, fabricated, and measured. The measured results are in good agreement with simulated ones.

Tri-Layered Stacked Substrate Integrated Waveguide Bandpass Filter Using Non-Resonant Nodes Excitation

Tri-layer stacked substrate integrated waveguide (SIW) bandpass filters (BPFs) using non-resonant nodes based on single-and dual-mode cavities are presented. Two identical single-mode (TM110) cavities in the top and bottom layer are independently coupled to a dual-mode (TM120/TM210) cavity in the middle layer by two slots. Based on carefully designed coupling topology, we can realize SIW BPFs with one or two flexible finite transmission zeros (FTZs). TM110 and TM220 modes in the dual-mode cavity are further used to excite non-resonant nodes by changing the position of slots, and additional FTZs in the upper and lower stopband can be obtained. In order to verify the proposed strategy, two samples with a center frequency of 10 GHz have been designed and manufactured.

Semi‐circular mushroom resonator loaded substrate integrated waveguide cavity based compact triple‐band bandpass filter with high selectivity

Two cascaded semi-circular mushroom resonators (ScMRs) loaded to a circular substrate integrated waveguide (CSIW) is used to implement a triple-band bandpass filter of compact size and high selectivity with six transmission zeros (TZs). The ScMRs are coupled to each other along the linear edges of the metal patches and are loaded to the CSIW cavity. A distinctive modification in the schematic and the orientation of the loaded mushroom resonators is carried out along with the introduction of radial coupling slots into the CSIW cavity to generate the three passbands. The TM101 mode is responsible for the generation of first passband. The second and third passbands are formed due to the split odd and even modes of next higher order mode (TM201). An extracted pole is formed within the second passband that splits TM201 mode into odd and even modes. TM201 odd mode (TM201odd) and TM201 even mode (TM201even) are responsible for the generation of second and third passbands, respectively. Here, source-load coupling is employed within the proposed resonator to generate one TZ each at the lower stopband and upper stopband. Two cross-couplings of different modes between two loaded ScMRs are introduced to generate four transmission zeros (TZs) additionally to achieve high selectivity. The triple bandpass filter covering a compact volume of 0.0011 λg3 is fabricated and measured to validate the filter structure. The measured result agrees decently with the simulated one where the passband center frequencies (CFs) of first, second, and third passbands are measured at 1.9, 3.5, and 4.4 GHz with measured insertion losses of 1.5, 1.87, and 1.8 dB, respectively.

Substrate-Integrated-Waveguide-Fed Wideband Filtering Antenna for Millimeter-Wave Applications

In this article, a wideband filtering antenna based on substrate integrated waveguide (SIW) structure for millimeter-wave (mm-wave) applications is proposed and studied. The proposed antenna is developed using multilayer printed circuit board (PCB) technology. It consists of an SIW feeding structure with a coupling slot, differential-fed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -shaped probes as well as radiating patches. Such architecture provides wide impedance bandwidth along with good filtering characteristic in the lower stopband. Simultaneously, by introducing a pair of open slots on the individual radiating patch as well as two shorting loops on top of the coupling slot, good filtering response in the upper stopband is obtained. The suppression level in the lower stopband is then further improved by introducing a pair of shorted stubs in the coupling slot region. The proposed filtering antenna features no extra filtering circuits, but has wide bandwidth as well as low profile. To verify the proposed structure and design philosophy, antenna array prototypes have been designed, fabricated, and measured. It achieves a 29% bandwidth from 23.5 to 31.5 GHz. Good agreement is achieved between simulated and experimental results. The proposed antenna array is particularly suitable to be applied in 5G (the fifth generation) mm-wave backhaul communications.

A Novel Miniaturized Multiband Strong Coupled-FSS Structure Insensitive to Almost All Angles and All Polarizations

This article presents a novel miniaturized almost all-angle-insensitive strong coupled frequency-selective surface (SC-FSS) with all-polarization-insensitive multiband by introducing the different interlayer coupling patches. Two templates of a single passband and a dual passband with unit cell less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.03\lambda $ </tex-math></inline-formula> are adopted to bring in two stopbands on both ends of each passband. Furthermore, the corresponding equivalent circuit models are developed to explain the physical mechanism and formulate relevant design equations. Finally, a prototype of the proposed dual-passband structure is fabricated and measured to verify the results of full-wave simulation and theoretical analysis. The experiment results show that there are a lower passband working at 2 GHz and a higher passband at 5.8 GHz with a lower stopband at 4 GHz and a higher at 7.5 GHz at the ends of above passbands, respectively, which exhibits the stable performance against the variation of the incident angles (from 0° to 86°) for both TE and TM polarizations. The measurement results demonstrate that the proposed multiband SC-FSS is a good candidate for designing a high-performance antenna radome for solving electromagnetic interference (EMI) problems.

A Dual-Beam Wideband Filtering Patch Antenna With Absorptive Band-Edge Radiation Nulls

A dual-beam filtering patch antenna with two absorptive band-edge radiation nulls and four reflective stopband radiation nulls is proposed. By loading a pair of T-shaped metallic strip underneath the radiating patch, a modified TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> mode with TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> -like radiation pattern is obtained, which combines with the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode of the radiating patch, generating a wide operating band with symmetrical dual-beam radiation pattern. Two reflective radiation nulls are generated in both upper and lower stopbands for suppressing the out-of-band radiation. Through embedding two pairs of shorted small patch in the radiating patch, one absorptive radiation null combining with one absorptive resonant mode is produced at each band edge to absorb the band-edge incident energy, leading to a reduced reflection and sharp roll-off at both band edges, and therefore, the transceiver can be protected. With a total height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.038~\lambda _{0}$ </tex-math></inline-formula> , a prototype is designed, fabricated, and measured, showing a −10 dB impedance bandwidth from 4.63 to 6.10 GHz with sharp band-edge roll-off, two radiation beams directed at ±40° with an in-band gain of 6.0 dBi, and high out-of-band suppression of over 15 dB.

Designing a miniaturized microstrip lowpass-bandpass diplexer with wide stopband by examining the effects between filters

In high-frequency devices, controlling the effects of circuits on each other is especially important in compact space. In this regard, a diplexer consists of a lowpass (LP) filter and a bandpass (BP) filter has been designed, fabricated, and measured, which has appropriate responses in compact size. The BP filter is designed based on the new equivalent circuit model, which is analyzed using even–odd mode. The LP filter consists of a single-resonator suppressor and the main resonator. The effects of the filters on each other are investigated by the transmission zeros (TZs) in the output response of each filter. The measured results of the designed BP filter have a bandwidth of 0.2 GHz with a center frequency of 2.42 GHz, the lower stopband bandwidth of 2 GHz and upper stopband bandwidth of 4.68 GHz. The proposed LP filter has a wide stopband bandwidth of 7.35 GHz, from 1.75 to 9.1 GHz with a suppression level of 20 dB. The 3 dB cut-off frequency is located at 1.46 GHz with a transition band of 0.29 GHz. Finally, the proposed diplexer was fabricated and measured, and a good adaptation between simulation results and fabrication ones was observed.

A Low-Profile, Wideband, Filtering-Response, Omnidirectional Dielectric Resonator Antenna Without Enlarged Size and Extra Feeding Circuit

A low-profile omnidirectional dielectric resonator antenna (DRA) with wide-bandwidth and high-selectivity filtering response is proposed. Initially, the traditional low-profile DRA has no filtering response. Then, an array of four shorting pins1 is loaded inside the DRA. It proves that the nonradiative pins1 mode could be excited and the radiation-gain null1 in the upper stopband is produced due to the canceled electric fields. Then, the shorting pins2 is loaded to reallocate these modes closely to each other. After that, the additional shorting pins3 is embedded to resonate the nonradiative pins3 mode, thus forming up the radiation-gain null2 in the lower stopband. Finally, the proposed DRA is fabricated and measured. The antenna has simultaneously acquired wide bandwidth (41.2%) and stable omnidirectional patterns in the range of 1.85-2.81 GHz. Besides, the filtering response is generated with a 14 dB out-of-band suppression level. Particularly, it maintains the primary property of the traditional DRA without extra feeding circuit, such as single layer, compact volume, and low profile (0.12 free-space wavelength).

Magnetoelectric Dipole Filtering Antenna Based on CSRR With Third Harmonic Suppression

In this letter, a high selectivity filtering magnetoelectric (ME) dipole antenna with harmonic suppression is investigated. By etching a complementary split resonant ring (CSRR) on shorted wall of ME dipole, a radiation null at upper passband edge can be obtained. The intrinsic radiation null at lower passband edge of ME dipole is utilized, together with the radiation null generated by CSRR, to obtain high selectivity. In addition, to suppress the third harmonic of the antenna, a stepped impedance resonator is loaded on the Г-shaped feeding structure. For verifying, a prototype operating from 1.44–2.79 GHz is designed, fabricated, and measured. Compared with the traditional ME dipole antenna, the proposed filtering antenna shows upper and lower stopband rejection levels as high as 16.61 and 17.84 dB, respectively. Furthermore, a third harmonic suppression level of 12.78 dB is obtained. Good agreement can be observed between the simulation and measurement.

Flexible design of W‐band bandpass filter with multiple transmission zeros

AbstractIn this paper, a novel E‐plane waveguide bandpass filter with multiple transmission zeros is proposed in W‐band. The center frequency and bandwidth of this filter can be flexibly designed. Stripe line resonators and L‐shaped resonators are used in the filter. The filter contains four resonators, two of which are used to generate transmission zeros in the upper stopband, and the other two are used to generate transmission zeros in the lower stopband. These transmission zeros can enhance the out‐of‐band suppression and selectivity of the filter. And the position of the transmission zeroes can be flexibly changed as required. One sample is fabricated and measured to verify the proposed filter. The minimum insertion loss in passband is 0.6 dB. Good agreements between the simulated and measured results are achieved.

HTS Wideband Bandpass Filter Based on Ladder Topology Circuit and Microstrip Transformation

This article presents a novel high-temperature superconducting ultra-wideband filter with a 108% fractional bandwidth. A high-order ladder topology circuit is utilized in the proposed filter to ensure a deep out-of-band rejection. Superconducting quasi-lumped elements are applied to reduce the insertion loss brought by the high-order circuit. The proposed filter derives from a low-pass filter (LPF) with a cut-off frequency at 2.7 GHz. Microstrip transformation is adopted in this LPF to achieve a lower stopband at 0.8 GHz. The proposed transformation provides a possibility to separately tune the lower and upper cut-off frequency in a microstrip filter. The measured results demonstrate a good agreement with circuit analysis and EM simulations, and show an excellent performance.

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.

High selectivity and wideband bandpass filtering impedance transformer

An impedance transformer (IT) with wideband and high selectivity is presented in this paper. Three transmission poles were obtained within the passband and provides a wide passband response. Moreover, there are two transmission zeros (TZs) close to the passband that were achieved by a shunt parallel coupled line and provide high selectivity. For validation of proposed circuit, the ITs were designed at a center frequency (f0) of 3.5 GHz using an impedance-transforming ratio (r) of 5 and 10. For r = 5, |S21| and |S11| are 0.36 dB and 28 dB at f0, respectively. Within the passband, |S21| and |S11| are better than 0.65 dB and 18 dB, respectively. The TZs at 2.65 GHz (0.76f0) and 1.22f0, close to the passband, were measured with attenuation better than 37 dB. The out-of-band attenuations are higher than 20 dB from DC to 2.77 GHz of the lower stopband and from 4.16 GHz to 9.73 GHz of the higher stopband. For r = 10, |S21| = −1.4 dB and |S11| = −23 dB were measured at f0. An 18 dB return loss was obtained from 3.415 GHz to 3.694 GHz (FBW = 7.96%).

A Low-Profile Dual-Band Filtering Hybrid Antenna With Broadside Radiation Based on Patch and SIW Resonators

This paper presents a differentially fed dual-band hybrid antenna with broadside radiation, enhanced bandwidth, and high selectivity. The proposed antenna is constructed using a single-layer substrate based on rectangular patch resonator and substrate integrated waveguide (SIW) cavity. Herein, TM10 and TM12 modes of the rectangular patch resonator, together with TE21 and TE23 modes of the rectangular SIW cavity, are selected for resonances in the concerned dual-band radiation. Among them, TM10 and TE21 are employed for the lower passband, while TM12 and TE23 for the higher passband. Besides, for achieving broadside radiation performances in both bands, two arrays of shorting pins are loaded in the rectangular patch resonator and the constituted electric wall surround the rectangular SIW cavity is properly truncated to reshape the radiation patterns of TM12 and TE23, respectively. Notably, the resonant and radiation properties of all the involved modes are obtained with theoretical deduction. Furthermore, the cascaded trisection composed of the SIW cavity, the patch resonator, and the radiation impedance creates two radiation nulls in each upper stopband of both passbands and the mixed coupling between two resonators generates another radiation null to be located in the lower stopband of the higher passband. For demonstration, a prototype antenna with the dual bands at 3.5 and 5.8 GHz is fabricated and tested. The measured results show that the antenna has achieved an improved bandwidth (|Sdd11| < -10 dB) from 3.26 to 3.58 GHz and 5.60 to 5.90 GHz, respectively, with stable broadside gains of around 8.5 dBi. In addition, in the stopband, three radiation nulls are created at 3.71, 5.32, and 6.12 GHz for effective enhancement of dual-band frequency selectivity.

Hybrid Absorptive-Diffusive Frequency Selective Radome

This article proposes a hybrid absorptive–diffusive frequency-selective radome (AD-FSR) that has a broadband transmission window with wide absorption and diffusion bands located at two sidebands, respectively. The proposed hybrid AD-FSR consists of a resistive sheet and a bandpass frequency-selective surface (FSS) integrated with a coding metasurface separated by a certain distance. The wide absorption band is realized by the combined effect of the resistive sheet and the FSS integrated with a metasurface as a reflector in its lower stopband, while a broad passband is obtained when the electromagnetic (EM) wave penetrates through the resistive sheet in the passband of the FSS. In the upper side of the passband, the EM wave is diffused to reduce the radar cross section (RCS) of the surface by arranging the unit cell of the AD-FSR and its mirror based on the phase cancellation theory. Equivalent circuit and relevant theoretical formulas are utilized to better comprehend the physical mechanism of the proposed hybrid AD-FSR. A design example is then fabricated and measured, and the experimental results show that a broad transmission band is achieved from 6.92 to 13.12 GHz with a minimum insertion loss of 0.43 dB in a wide low reflectivity ( $\pmb {|S_{11} |} dB) band from 2.24 to 18 GHz.

Compact UWB Half-Mode SIW Bandpass Filter With Fully Reconfigurable Single and Dual Notched Bands

Compact ultra-wideband (UWB) bandpass filters based on the half-mode substrate integrated waveguide (SIW) with fully reconfigurable single and dual notched bands are proposed in this article. The lower stopband of the UWB bandpass filter is formed by the intrinsic cutoff frequency of the half-mode SIW, and transmission zeros in the upper stopband are created by utilizing three U-shaped slot resonators. Coupling microstrip resonators loaded by varactor diodes are placed along the open side of the half-mode SIW and microstrip feeding line to construct the in-band notches. By controlling the bias voltages and the size of resonators, fully reconfigurable single and dual notched bands can be obtained. Moreover, the frequency and bandwidth of each notched band can be controlled independently. To demonstrate the proposed technique, five and seven distributed coupling microstrip resonators are first applied to obtain the fully reconfigurable single notched band with the suppression level of 30 and 36 dB, respectively. Then, reconfigurable dual notched bands are demonstrated by changing the bias voltages using the same prototype with seven resonators. At last, nine resonant cells with two sets of different sizes are shown to design reconfigurable dual notched bands with frequency tuning range covering almost the full UWB passband.

Electrically Coupled Folded Arm Resonators with the Feedline Patch Antenna for Spurious Harmonic Suppression and Bandwidth Improvement

This paper presents a new design of the filtering antenna with a quasi-elliptic function response. The basic structure of the proposed filtering antenna is consists of a four-folded arms open-loop resonator (OLR). The proposed filtering antenna is simulated, improved and, analyzed by using 3D Computer Simulation Technology (CST) electromagnetic simulator software. The design has good spurious harmonic suppression in the upper and lower stopbands. The Insertion Loss of the proposed filtering antenna IL=0.2 dB and the Return Loss RL= -25.788 dB at the center frequency fo=5.75 GHz. The passband bandwidth which is relatively wide, and equal to 0.793 GHz. The microstrip filtering antenna circuit shows good design results compared to the conventional microstrip patch antenna. The filtering antenna design circuit with etched ground plane structure also has good design results compared to the filtering antenna design which has a complete ground plane structure.

High selectivity wideband BPF with very wide stopband characteristic

This paper describes the design and evaluation of a highly selective wideband microstrip bandpass filter with a near brick-shaped transmission response and a very wide stopband characteristic. The proposed filter structure excites multimode resonances that combine to realize a wideband filter response and excited too are transmission zeros that create a highly selective filter with wideband suppression in the upper and lower stopbands. The filter configuration comprises electromagnetically coupled resonators that are stub loaded. The input and output feedlines are interdigitally coupled to the resonators. Measured results confirm the low-loss and via-free wideband filter exhibits an elliptical response with a wide stopband with a rejection greater than 30 dB. The selectivity factor and stopband performance of the proposed filter is better than that obtained with the high-temperature superconductor (HTS) filters. Design of the filter is relatively simple and easy to manufacture using standard PCB technology. There is good correlation between the simulation and measured results. The proposed wideband bandpass filter is suitable for applications in high interference environments and cognitive radio systems.

Wideband microstrip‐to‐air‐filled substrate integrated waveguide transition with controllable band‐pass performance

AbstractA novel wideband back‐to‐back microstrip‐to‐air‐filled substrate integrated waveguide (AFSIW) transition with controllable band‐pass performance is presented. The wideband transition is constructed by a gradient microstrip and a section of widened partially dielectric‐filled AFSIW. The sharp rejection performance above the pass band is achieved by taking advantage of the notch characteristics of the widened partially dielectric‐filled AFSIW section. The lower stop band is determined by the cut‐off characteristic of the intermediate AFSIW between the back‐to‐back transitions. The relationship between the band‐pass response and the dimensional parameters of the transition is investigated. A prototype is designed, manufactured and measured. The measured fractional bandwidth (FBW) is 57.63% centered at 14.75 GHz. The suppression over 20 ~ 25 GHz is better than 25 dB, and a transmission zero with a suppression of 51.7 dB is introduced at 1 GHz away from the upper‐edge frequency of the pass band.

An inline pseudoelliptic self‐packaging substrate integrated suspended line filter with mixed electric and magnetic coupling

A novel compact and self-packaging inline pseudoelliptic filter is proposed. The proposed filter exploits controllable mixed electric and magnetic coupling using substrate integrated suspended line (SISL) technology. Based on a synchronously tuned coupled resonator circuit with parallel LC resonant tank and admittance inverters, general formulas for extracting electric and magnetic coupling coefficients are derived. Meanwhile, a basic mixed coupled SISL resonator pair is investigated and a systematic design procedure of a second-order mixed coupled SISL filter is also given. Two prototypes of the second-order filter with one transmission zero (TZ) at either upper or lower stopband are designed, which is corresponding to either magnetic or electric coupling dominant case. Furthermore, for asynchronously tuned coupled resonator cases, an inline third-order pseudoelliptic SISL filter characterized by symmetric TZs is designed, fabricated, and measured for validation. The simulated and measured results show a good agreement with the synthesized ones.