Inductive Stubs Research Articles

A new technique for improving performance of conventional CRLH resonators using IDC/UISs with enhanced harmonic suppression in balanced dual-band BPFs

Abstract The design of balanced filters based on composite right/left hand (CRLH) structure is well developed. Among those, few designs exist which although they provide some good responses, suffer from narrow stopbands and interdependent passbands. This paper proposes a new technique for improving the characteristics of dual-band balanced bandpass filters (B-BPFs) based on planar CRLH. Using unequal inductive stubs (UISs) attached to the interdigital capacitor (IDC) unit cell, we were able to achieve outstanding harmonic suppression and passband controllability. This structure offers higher degrees of freedom compared to conventional designs and provides better control over the filter specifications. Mathematical modeling, analysis, simulation, fabrication, and performance measurement of the proposed technique in a dual-band B-BPF are also provided. Our work resulted in an independent and controllable dual-band B-BPF with ultra-wide upper differential-mode (DM) stopband of 5.9f 1 and common-mode (CM) suppression of 40.4 and 32.6 dB for the first and second bands, respectively.

Asymmetrical CPW-Fed Circularly Polarized Two-Port MIMO Antenna for Satellite and Wi-Fi 6E Communication

A circularly polarized compact two-port MIMO antenna is presented along with asymmetrical CPW feed and a novel decoupling structure. The asymmetric CPW feed of the antenna is improving the impedance matching significantly and shifting the operating band towards the lower frequency. The novel inverted Z-shaped decoupling is used to enhance the isolation which mitigates the surface wave effectively between two antennas. The triangular-shaped inductive stubs are unified in the inverted Z-shaped decoupling structure which is used to perturb the surface wave movement and to influence the circular polarization (CP) behaviour in the two-port antenna. MIMO antenna obtains the 10 dB impedance bandwidth (IBW) from 6.38 GHz to 6.84 GHz along with minimum port isolation of 30 dB. The 3-dB axial ratio (AR) is obtained from 6.59 to 6.84 GHz frequency which is 52.1% of the total 10 dB IBW of the antenna. The proposed work can be prominent for super-extended C-band of satellite communication and Wi-Fi 6E U-NII6 and U-NII7 communication.

A Zeroth-Order Slot-Loaded Cap-Shaped Patch Antenna With Omnidirectional Radiation Characteristic for UHF RFID Tag Design

The zeroth-order resonance of a compact patch structure is explored for designing a metal-mountable tag antenna in the United States (US) ultrahigh-frequency (UHF) radio frequency identification (RFID) passband. This zeroth-order resonator (ZOR) structure comprises a cap-shaped patch loaded with two L-shaped slots. Also, the patch is coupled to the ground through two inductive stubs which provide enough parasitic reactance to support the zeroth-order resonance. The proposed single-element ZOR can generate sufficient antenna impedance for achieving a conjugate match with the RFID chip impedance. Good omnidirectional radiation characteristic with vertically polarized fields can be attained in the azimuth plane when the tag antenna is placed on a metallic surface. The proposed tag antenna’s realized gain at 915 MHz is −1.382 dB [effective isotropic radiated power (EIRP) 4 W]. A stable read distance of ~15 m is obtainable with even spatial coverage in the entire azimuth plane. The resonance frequency of the proposed tag does not vary much with the object being tagged.

A microstrip quasi-elliptic bandpass filter implemented using stub loaded resonators

A highly selective microstrip bandpass filter consists of electromagnetically coupled U-shaped open ring resonators is presented in this paper. The resonators are directly loaded with open-circuited inductive stubs and the feed-lines are interdigital coupled to the resonators. The proposed filter structure provides sufficient degree of freedom to control the centre frequency, fractional bandwidth and transmission zeros. It is shown that the fractional bandwidth of this filter can be adjusted from 15.3 to 9.8% and center frequency from 3.3-3.8 GHz with negligible effect on the stopband characteristics. In addition, the transmission zero f tz2 can be relocated from 3.8 to 4.4 GHz and f tz1 from 3.1 to 2.7 GHz independently. Filter structure is simple, easy and economical to manufacture as fabricated on a conventional dielectric substrate using standard PCB technology. It is found that the simulation and measured results are in good correlation. The sharp selectivity, low losses and wide stop band characteristics make the proposed filter applicable in cognitive radio systems and in high interference environments.

Slotted E-Shaped Meta-Material Decoupling Slab for Densely Packed MIMO Antenna Arrays.

In contemporary wireless communication systems, the multiple-input and multiple-output systems are extensively utilized due to their enhanced spectral efficiency and diversity. Densely packed antenna arrays play an important role in such systems to enhance their spatial diversity, array gain, and beam scanning capabilities. In this article, a slotted meta-material decoupling slab (S-MTM-DS) with dual reflexes slotted E-shapes and an inductive stub is proposed. Its function was validated when located between two microstrip patch antenna elements to reduce the inter-element spacing, the mutual coupling, the return losses, and manufacturing costs due to size reduction. A prototype is simply fabricated in a volume of 67.41 × 33.49 × 1.6 mm3 and frequency-span measured from 8.4:11 GHz. At 9.4 GHz frequency, the spaces between the transmitting elements are decreased to 0.57 of the free space wavelength. When the proposed isolation S-MTM-DS is applied, the average isolation among them is measured to be −36 dB, the operational bandwidth is enhanced to be 1.512 GHz, the fractional bandwidth improved to be 16.04%, and the return losses are decreased to be −26.5 dB at 9.4 GHz center frequency. Consequently, the proposed design has the potential to be implemented simply in wireless contemporary communication schemes.

Compact polarisation insensitive wide angular stable triple band absorber for RF energy harvesting, RCS reduction, and sensor applications

This paper presents a new compact ultra-thin triple-band absorber which shows near-unity absorption in C, X and Ku-bands. It consists of an inductive stub loaded circular ring resonator and a flower-shaped resonating patch on top of 0.8 mm thin FR-4 grounded dielectric substrate. A transmission line equivalent is proposed, and circuit simulation response is in good agreement with the full-wave analysis. The unit-cell architect's 4fold symmetry makes it polarisation-insensitive for different polarisation angles in the azimuthal plane (𝜃 = 0°) under normal incidence. Its good shows angular stability up to 45° under TE (75° under TM) incidences for all three frequencies. Surface current patterns are analysed at resonant frequencies to illustrate the mechanism behind the electromagnetic absorption. This design's novelty lies in the centre patch's dual-resonating behaviour, making this design compacted one. The absorber has low-profile nature with cell periodicity of 0.163λL and thickness 0.013λL, where λL is the lowest resonating peak wavelength. An X-band conventional MSA is fabricated on a thin FR-4 substrate. In-band RCS reduction (nearly 18 dBsm) of the antenna is verified after loading with the proposed absorber. The absorptivity peaks are optimised such that the same structure would be used in different applications like RF energy harvesting, RCS reduction and sensor applications.

Slim RFID Tag Antenna for Metallic Tools With Narrow Footprint

A slim and semi-flexible UHF RFID tag antenna, which has a compact dimension of 40 mm × 5 mm × 3.2 mm ( 0.1221λ×0.0153λ×0.0098λ), is proposed for tagging on metallic industrial tools with a narrow footprint. For a metal-mountable tag antenna, the unwanted electromagnetic antenna-metal interaction can deteriorate the tag read performances and it is particularly pronounced when the tag is attached to a narrow industrial tool. To achieve a size-reduction, the proposed tag is made of an inlay comprising a very compact 3-layer structure with two radiating patches. The currents on the top and middle patches can be made in phase for enhancing the radiated fields. Digital serrations, inductive stubs, and open slots loading have been studied for optimizing the antenna resonant frequency efficiently. With the use of the tuning mechanisms, when being tested on a narrow-body metal tool, the antenna impedance can be fully matched with the RFID microchip impedance, resulting in a good power transmission coefficient of ~ 1. Despite its compactness, the proposed tag antenna is readable from 11.0 m with an EIRP of 4W. To the best of our knowledge, the proposed tag antenna has a much better aspect ratio between its read distance and tag volume than most of the commercially available on-metal tags and it can be used for tagging on narrow metallic surfaces.

Miniature Folded Patch With Differential Coplanar Feedline for Metal Mountable UHF RFID Tag

In this paper, a pair of differentially fed coplanar waveguides is employed for exciting a folded patch antenna for designing a metal-mountable UHF RFID tag. The proposed tag has a compact size of 30 mm $\times \,\,25$ mm $\times \,\,3.0$ mm. Multiple slots are incorporated into the patch for tuning the resonant frequency and optimizing the impedance matching between the chip and the antenna. Two inductive stubs are introduced at two corners of the radiating patch to enable further frequency tuning. An equivalent circuit has been given for characterizing the tag’s impedance characteristics. When tested on a 20 cm $\times\,\,20$ cm metal plate, the read range of the proposed tag can achieve 8.9 m (4 W EIRP) using the Monza R6 microchip (with chip sensitivity of −20 dBm). Also, it has been found that the resonant frequency of the proposed tag antenna is stable and it does not shift much when the size of the backing metal is varied. The read distance is also more than 4 m when the proposed tag is attached to various dielectric materials with permittivity $\varepsilon _{r}$ in the range of 1–12.4.

Suppression of mutual coupling in rectangular dielectric resonator antenna arrays using Epsilon-Negative metamaterials (ENG)

ABSTRACTA double slotted symmetrical split ring resonator with an inductive stub in its inner ring is presented as a Single Negative Electric (SNG) metamaterial to suppress mutual coupling between two E-plane coupled microstrip line fed rectangular dielectric resonator antenna (RDRA) array. The proposed SRR exhibits two resonant frequencies and wide stop-bands. The -10 dB bandwidth of S21 from 2022MHz to 2720 MHz and from 2187 MHz to 3839 MHz are obtained for the first structure, #1, and the second structure, #2, respectively. By introducing an ENG layer between the two RDRAs, the experimental reduction in mutual coupling is more than 23 dB with a small frequency shift (∼ 20 MHz), while the impedance matching is improved. The radiation efficiency and total efficiency are increased while the far-field pattern in the E-plane is not disturbed.

Compact tunable cavity filter with high selectivity using double‐layer suspended stripline resonator

AbstractA compact tunable cavity filter based on double‐layer suspended stripline resonator (DSSLR) is proposed. The DSSLR consists of a thin substrate suspended in an air‐filled cavity, a stepped impedance resonator loaded with interdigital capacitor on the top layer of the substrate, and a parallel‐plate capacitor series with a varactor at the bottom layer. The multiple capacitors not only achieve compact size by large capacitive loading, but also broaden the tuning range with a small capacitance variation of varactor. The internal coupling of two DSLLRs increases with the height of the inductive stub while decreases with the distance between two resonators. A fifth‐order wideband tunable cavity filter using a common bias voltage is designed, fabricated, and measured, which has a tunable frequency range of 67 MHz, constant bandwidth of 64 ± 7 MHz, low return loss of 15 dB, and high suppression of more than 40 dB.

Interaction Between Closely Packed Array Antenna Elements Using Meta‐Surface for Applications Such as MIMO Systems and Synthetic Aperture Radars

AbstractThe paper presents a technique to enhance the isolation between adjacent radiating elements that is common in densely packed antenna arrays. Such antennas provide frequency beam‐scanning capability needed in multiple‐input multiple‐output (MIMO) systems and synthetic aperture radars. The method proposed here uses a metamaterial decoupling slab (MTM‐DS), which is located between radiating elements, to suppress mutual coupling between the elements that would otherwise degrade the antenna efficiency and performance in both the transmit and receive mode. The proposed MTM‐DS consists of mirror imaged E‐shaped slits engraved on a microstrip patch with inductive stub. Measured results confirm over 9–11 GHz with no MTM‐DS the average isolation (S12) is −27 dB; however, with MTM‐DS the average isolation improves to −38 dB. With this technique the separation between the radiating element can be reduced to 0.66λ0, where λ0 is free space wavelength at 10 GHz. In addition, with this technique there is 15% improvement in operating bandwidth. At frequencies of high impedance match of 9.95 and 10.63 GHz the gain is 4.52 and 5.40 dBi, respectively. Furthermore, the technique eliminates poor front‐to‐back ratio encountered in other decoupling methods. MTM‐DS is also relatively simple to implement. Assuming adequate space is available between adjacent radiators the MTM‐DS can be fixed retrospectively on existing antenna arrays, which makes the proposed method versatile.

Folded Patch Antenna With Tunable Inductive Slots and Stubs for UHF Tag Design

A miniature folded patch with a dimension of $40\,\,\text {mm} \times 40\,\,\text {mm} \times 1.6\,\,\text {mm}\,\,(0.1156\lambda \times 0.1156\lambda \times 0.0046\lambda $ at 867 MHz) is proposed for designing a passive metal-mountable tag. It consists of a square patch which is equally separated into two rectangular patches. Since the patch resonator usually has high resonant frequency, multiple tuning mechanisms are always needed to bring down the frequency so that it can be used for designing a tag antenna in the UHF band. In the proposed design, each patch is incorporated with a C-shaped slot and three thin inductive stubs for performing different levels of frequency tunings. An equivalent circuit has been built for estimating the input impedance of the antenna. Reasonable agreement is found between the measured, modeled, and simulation results. The proposed tag antenna is readable from 5 m with an EIRP of 3.28 W when placed on a 20 cm $\times20$ cm metal plate.

Miniaturization of multiband annular slot ring antenna using reactive loading

A multiband annular slot ring (ASR) antenna for mobile communications is designed and analysed in this paper. Then, the miniaturized multiband ASR antenna loaded with distributed inductive stub is proposed, which is miniaturized by 20.28%. Another multiband ASR antenna loaded with meta-material (ASR-SRR) inspired Electromagnetically Coupled Split Ring Resonator (EC-SRR) is proposed, it is miniaturized by 30.55%. The surface wave of the proposed miniaturized ASR-SRR in higher mode has reduced due to increase in reactive impedance of the antenna surface, thus aperture efficiency is increased. The radiation characteristics of miniaturized antennas are approximately similar to the ASR antennas. Behaviour of antenna characteristics such as gain (G), impedance bandwidth (BW), aperture efficiency (ηA), Chu condition (ka ≤ 1) of proposed antenna is also studied, observed and analysed in this paper.

Miniature Coplanar-Fed Folded Patch for Metal Mountable UHF RFID Tag

A folded patch, which is centrally fed by a coplanar feedline, is proposed for designing a miniature UHF tag antenna for mounting on metal surfaces. The tag is designed using a flexible polyethylene terephthalate substrate with a very compact size of 25 mm × 40 mm × 3 mm (0.0767λ × 0.123λ × 0.0092λ). Conjugate match is attainable between the antenna and the microchip and it is able to achieve a maximum read distance of 10.7 m at the effective isotropic radiated power of 4 W. In the design, two notches have been incorporated with an inductive stub for tuning of the tag's resonance over a larger frequency range. Also, a simple equivalent circuit has been derived to characterize the impedance of the tag antenna. The resonant frequency of the proposed tag antenna is found to be insensitive to various sizes of the backing metal object, which is a very desirable feature for tag design. The proposed tag can achieve a read distance of greater than 10 m when placed on metal. It is able to be read beyond 5 m when it is placed on dielectrics with permittivity in the range of 1-5.8.

Reduced size dual band pass filters for RFID applications with excellent bandpass/bandstop characteristics

This paper presents the design of two reduced size dual-band metamaterial bandpass filters and its simulation followed by measurements of proposed filters. These filters are supporting different frequency bands and primarily could be utilize in radio frequency identification (RFID) application. The filter includes three cells in which two are symmetrical and both inductively coupled with the third cell which is present in between them. In the proposed designs, three different metamaterial composite right/left handed (CRLH) cell resonators have been analysed for compactness. The CRLH cell consists of an interdigital capacitor, a stub/meander line/spiral inductor and a via to connect the top of the structure and ground plane. Finally, the proposed dual band bandpass filters (using meander line and spiral inductor) are showing size reduction by 65% and 50% (with 25% operating frequency reduction), respectively, in comparison with reference filter using stub inductor. More than 30 dB attenuation has been achieved between the two passbands.

Design of a Compact UWB Bandpass Filter using Via-Less CRLH TL

A novel compact ultra wideband (UWB) bandpass filter (BPF) based on composite right/left handed transmission line (CRLH TL) is reported in this paper. The proposed UWB BPF is designed and developed by coupling of two unit-cells of via-less CRLH TL, excited by asymmetrical coplanar waveguide (CPW) feed-line. The unit cell of CRLH TL is designed using series interdigital capacitor (IDC) in shunt with the shorted inductive stub. Because of the CPW-fed, no via is required to get the shunt inductance for the realization of CRLH TL, which minimizes the fabrication steps. The filter is compact in size 11.9 x 6 mm 2 . The proposed filter exhibits the return-loss (|S 11 |) more than 11.2 dB and insertion-loss (|S 21 |) less than 0.5 dB and low and flat group delay response throughout the passband, 3.3 GHz to 13.0 GHz. The proposed UWB BPF also shows the good stopband rejection (|S 21 | > 20 dB and |S 11 | < 0.8 dB) from 13.6 GHz to 15 GHz and steep roll-off from passband to stopband. The fractional bandwidth (FBW) of the filter is found to be 119 %. The equivalent lumped circuit model of the filter is obtained through Ansoft Designer. All simulated results are extracted through method of moment based simulator, IE3D. Agilent vector network analyzer (VNA) is used to get the measured results. All measured results are found in close similarity with the simulated results.

Multiple band notch and Dual-Band filter using concentric and contiguous split ring resonators (CCSRR)

A novel, compact, multiple band notch filter and dual-band filters are presented. Contiguous and concentric split ring resonators (SRRs) and Ring resonator are used to achieve desired multiple narrow band notches. These band notches have been designed to avoid the undesired interference between co-existing wireless channels. The dual-band filter consists of a dual SRR having splits on the opposite sides with Inductive Short Stub Split Ring Resonator. Even- and odd-mode analyses have been performed to calculate the resonance frequencies. Three transmission zeros are achieved between the two passbands by both dominant electric or dominant magnetic coupling and also cancellation effect of electric and magnetic coupling. This results in high passband selectivity and improved band-to-band isolation. The proposed dual-band pass filter has the advantages of being compact with more degree of freedom to achieve desired passbands by controlling the electric and magnetic coupling independently. Proposed filter is implemented on RT/Duroid 5880 (εr = 2.2) substrate of thickness 0.785 mm and surface area of 0.27λg × 0.27λg. Insertion loss of the proposed filter at notch bands is high (>13 dB) and low (<0.8 dB) in pass band. Measured results correlate with the simulated results and thus ensure that the proposed filter is a suitable candidate to mitigate interference caused by the co-existing and emerging wireless technologies.

Design of Active Frequency Selective Surface with Curved Composite Structures and Tunable Frequency Response

We present an active frequency selective surface (AFSS) consisting of a curved composite structure that provides structural stability and robustness. The proposed structure can operate on either the C-band (OFF state) or X-band (ON state) by controlling the PIN diode located between the cross-shaped loop and the inductive stub on the surface. Moreover, it minimizes parasitic couplings through grid-type on/off bias circuits and via holes. Thus, the AFSS guarantees isolation from the unit cell, which is a downside of a previous control technique called reconfigurable frequency selective surface. We analyzed the impact of composite structures and the three-dimensional shape on the AFSS transmission with a foam-core sandwich structure, which is light and mechanically strong, by considering conditions of a real application environment.

Trap Design and Construction for High-Power Multinuclear Magnetic Resonance Experiments.

Performing multinuclear experiments requires one or more radiofrequency (RF) coils operating at both the proton and second-nucleus frequencies; however, inductive coupling between coils must be mitigated to retain proton sensitivity and coil tuning stability. The inclusion of trap circuits simplifies placement of multinuclear RF coils while maintaining inter-element isolation. Of the commonly investigated non-proton nuclei, perhaps the most technically demanding is carbon-13, particularly when applying a proton decoupling scheme to improve the resulting spectra. This work presents experimental data for trap circuits withstanding high-power broadband proton decoupling of carbon-13 at 7 T. The advantages and challenges of building trap circuits with various inductor and capacitor components are discussed. Multiple trap designs are evaluated on the bench and utilized on an RF coil at 7 T to detect broadband proton-decoupled carbon-13 spectra from a lipid phantom. A particular trap design, built from a coaxial stub inductor and high-voltage ceramic chip capacitors, is highlighted owing to both its performance and adaptability for planar array coil elements with diverse spatial orientations.

격리도가 향상된 X-Band 재구성 주파수 선택 표면구조 설계

본 논문에서는 X-대역 동작 주파수 재구성이 가능하며, 격리도가 향상된 대역 통과 재구성 주파수 선택 표면구조(frequency selective surface)를 설계하였다. 제안된 재구성 FSS의 단위구조는 Four-legged loaded 소자와 인덕턴스 성분의 스터브 그리고 전원 인가를 위한 바이어스 그리드로 구성되어 있으며, Four-legged loaded 소자와 스터브 사이에 위치한 핀 다이오드의 ON/OFF 상태를 통해 단위구조의 전기적인 길이를 조절함으로써 동작 주파수의 재구성 특성을 구현하고, 스터브의 길이 조절을 통해 원하는 동작 주파수의 조절이 가능하며, ON/OFF 상태의 투과 특성간 향상된 격리도 특성을 얻을 수 있다. 재구성 FSS를 제작하여 구형 도파관 WR-90을 이용한 투과 특성 측정을 통해 설계 결과와 비교적 잘 일치하는 것을 확인하였다. This paper presents the design of reconfigurable frequency selective surfaces for X-band bandpass operation with improved isolation. The proposed reconfigurable FSS is composed of a four-legged loaded element, a inductive stub and a bias grid. The PIN diode is located between the four-legged loaded element and the stub, which can control the frequency response of reconfigurable FSS by ON/OFF state. By adjusting the length of the stub, the desired bandpass frequency and the improved isolation between ON and OFF state can be obtained. For validation of simulated results, we have carried out transmission characteristic measurements using rectangular waveguide of WR-90. The measured results are in good agreements with the simulated results.