Metal Stub Research Articles

CPW fed optically transparent ultrawideband fractal MIMO terahertz antenna with meshed ground plane

Abstract An optically transparent UWB antenna element and its two-element pattern diversity MIMO configurations are presented in this paper. Three iterations of the quarter elliptical coplanar waveguide ground plane, rectangular microstrip feedline, and octagonal annular rings make up the antenna element. By metal meshing the ground planes and loading the radiator with several octagonal slots, the optical transparency is improved. It has a maximal achieved gain of 6.78 dBi and operates with steady radiation characteristics over the frequency spectrum of 4.52–28.64 THz (145.48%). The dimensions of the antenna element are 18 × 20.5 μm2. A metallic stub is positioned between two identical antenna components that are positioned orthogonally to one another to create a two-element pattern diversity MIMO antenna arrangement. The MIMO antenna is 20.5 × 42.5 μm2 in total. Its impedance bandwidth is 23.72 THz for port 2 and 22.68 THz for port 1. Using a rectangular stub results in an intraport isolation of >19 dB. Between the two ports, the planes in the radiation patterns have switched places. The diversity performance characteristics, which are considerably below the permissible limitations, are as follows: ECC > 0.01, CCL < 0.3 b/s/Hz, DG ∼ 10, TARC < 0 dB, MEG ∼ −3 dB, and 1≤VSWR_MIMO≤2. Compared to previously published structures, the suggested antenna structures have the advantages of smaller dimensions, a larger bandwidth, and improved optical transparency.

A 4-port flexible MIMO antenna with isolation enhancement for wireless IoT applications

This paper presents a conformal, miniaturized, and geometrically simple monopole antenna designed for Vehicle–to–Everything (V2X) communications. The antenna consists of a flexible substrate, radiating patch, ground, and metallic stubs. Meandered lines are added to the U-shaped radiator to achieve the required bandwidth of the antenna. The antenna has |S11|< −10 dB magnitude from 5.06 to 7.24 GHz, attaining a peak low magnitude of–68 dB. The antenna is configured into a 4-port Multiple–Input–Multiple–Output (MIMO) setup to minimize the mutual coupling between its elements. The proposed flexible MIMO antenna offers bandwidth from 5.37 to 7.34 GHz and a peak moderate gain of 4.63 dBi with omnidirectional stable radiation patterns. To improve the mutual coupling, two hollow concentric circular structures, in combination with a pair of stub networks are integrated between the elements of the MIMO system. The transmission coefficient and surface current analysis confirm the effectiveness of the decoupling structure. The presented MIMO antenna is characterized by high isolation, a low envelope correlation coefficient (ECC), and high diversity gain, suitable for V2X MIMO communication scenarios.

A Compact Circular Waveguide Directional Coupler for High-Order Mode Vacuum Electronic Devices

In this paper, a compact circular waveguide directional coupler for high-order mode vacuum electronic devices is presented and investigated. To reduce the size, the primary and secondary waveguides of this coupler are connected in an orthogonal way by two coupling holes. Moreover, to improve the directivity and operating bandwidth, a method of loading adjustable metal stubs on the isolating port is proposed and introduced in design. A Ka-band TE01-mode circular waveguide directional coupler was designed, and the structure parameters were optimized by electromagnetic simulation. To verify the design, a prototype sample was fabricated, assembled, and tested. The experimental results show good agreement with the simulations, and the directivity are improved by adjusting the metal stubs on the isolating port. In the experiment, a 26.7 dB directivity at 35 GHz was obtained, and the bandwidth of directivity above 20 dB was higher than 7 GHz, corresponding to a relative bandwidth higher than 20%. Meanwhile, the TE01° mode maintained good transmission efficiency in this compact high-order mode directional coupler.

A dual-port, single-fed, integrated microwave and mm-wave MIMO antenna system with parasitic decoupling mechanism for 5G-enabled IoT applications

The integration of microwave and mm-wave antenna is recognized as a promising solution to ensure backward compatibility while effectively utilizing available space for 5G-enabled modern IoT devices. This paper proposed a very compact size multi-band dual-port MIMO antenna module, aiming to provide complete coverage in microwave frequency bands, including 2.4 GHz, 3.5 GHz, 5.3 GHz, and 7.5 GHz, along with 5G mm-wave bands such as 28 GHz. This is achieved through a common feedline by incorporating a semi-circular slotted monopole with strategically positioned quarter-wavelength metallic stubs on a partial ground plane. The proposed antenna exhibited -10 dB impedance bandwidths of 22.6% (2.16–2.71 GHz), 17.9% (3.36–4.02 GHz), 9.4% (5.18–5.69 GHz), 15.9% (7.29–8.55 GHz), and 15.5% (26.02–30.39 GHz) across diverse frequency bands. To attain compactness and high isolation capabilities, a composite three-dimensional parasitic element is employed as a decoupling structure to alleviate significant interference among closely positioned radiating elements. The proposed antenna provides radiation efficiency of > 85%, achieving necessary peak gains of 2.32 dBi, 3.46 dBi, 4.15 dBi, and 5.32 dBi at respective microwave frequencies. While in mm-wave frequency bands, radiation efficiency exceeds 95% having a measured realized gain of 6.2 dBi at 28 GHz. The proposed design successfully maintains an average isolation of > 28 dB in all frequency bands. The suggested MIMO configuration demonstrates outstanding diversity performance, which is evidenced by ECC, DG, MEG, CCL, and TARC.

A Compact Circularly Polarized Planar Spiral Antenna With Ultrawide Bandwidth and Directional Radiation Pattern

A compact circularly polarized (CP) planar spiral antenna with ultrawide bandwidth and directional radiation pattern is proposed for ultra‐wideband (UWB) positioning applications. The proposed antenna consists of a dual‐arm planar spiral with a tapered microstrip line, two L‐shaped metallic shorting stubs, and a square ground plane with four stepped slots. By connecting two L‐shaped metallic stubs to both the ends of the dual‐arm spiral through metal posts, the traveling wave current path is effectively extended, resulting in a significant improvement of the CP bandwidth. Additionally, both impedance bandwidth and circular polarization performance of the proposed antenna can be enhanced by adopting four stepped slots on the square ground plane. Measured results show that the planar spiral antenna features an impedance bandwidth from 3.23 GHz to 7.0 GHz (more than 73.7%), a 3‐dB axial ratio (AR) bandwidth of 62.1% (3.05 GHz–5.8 GHz), and finally achieves an overlapping bandwidth of 56.9% (3.23 GHz–5.8 GHz). On the overlapping bandwidth, this antenna maintains a gain consistently above 6 dBic while the peak gain reaches about 7.4 dBic. The overall size of the antenna is 0.59λg × 0.59λg × 0.17λg (λg is the free‐space wavelength at the lowest frequency, 3.23 GHz). Thanks to the ultrawide CP bandwidth and compact size, the proposed antenna can be a promising candidate for UWB positioning applications.

Triple band frequency tunable polarization insensitive metamaterial absorber for WLAN and 5G applications

A triple band metamaterial absorber (MMA) has been demonstrated in this paper that is developed on an FR4 substrate targeting WLAN and 5G frequencies. The resonating patch contains three modified concentric copper rings having overall unit cell dimensions of 0.16λ0 × 0.16λ0 × 0.0128λ0, where the wavelength, λ0 is for 2.4 GHz. The MMA exhibits 99.3%, 95.68%, and 99.5% peak absorption at 2.4, 3.5, and 5.85 GHz, respectively. Length variation of inwardly extended metallic stubs attached to the innermost ring provides frequency tuning flexibility for peak absorption within 5.67 GHz–5.98 GHz. The absorption process of the MMA is analyzed through the distribution of surface current. The MMA exhibits incident and polarization angle insensitive behaviour up to 60° for both TE and TM modes with near zero polarization conversion ratio. The resonance characteristics are justified through equivalent circuit modelling with validation by Advanced Design software (ADS). The measured absorption indicates a close resemblance with the simulation. Moreover, a good effective medium ratio of 6.25 shows the compactness of MMA. Due to its compact structure, incident, and polarization angle insensitivity, and near unity absorption at application-specific frequencies, this perfect MMA can be suitable for WLAN and 5G applications, especially for microwave shielding and sensing.

Reconfigurable Compact Quad-port MIMO Antennas for sub-6 GHz Applications

This paper presents compact quad-port frequency reconfigurable multi-input multi-output (MIMO) antennas for 5 G applications that operate at sub-6 GHz. The proposed design provides more isolation (&gt;13 dB) and pattern diversity using four orthogonal radiating elements. C-shaped metal is used to extend the antenna's radiating elements by inserting one positive intrinsic negative diode (PIN) in the metal. The C-shaped metal and matching stub achieve frequency reconfigurability with a consistent radiation pattern. The PIN diode's switching characteristics allow the frequency to be shifted between two communication bands. One mode (diode ON) covers 2.5 and 5 GHz, while the second mode (diode OFF) covers another dual band of 3.5 and 5.7 GHz. Substrate dimensions are only 50 x 50 x1.6 mm3, making the proposed design compact. Antenna peaks at a gain of 4.18 dB and radiation efficiencies of 80 and 94% in the four frequency bands. The antenna design is appropriate for multi-functional wireless systems and cognitive radio applications since it spans frequency bands below 6 GHz and can be reconfigurable between wide and narrow bands.

A Bandpass Filter Realized by Using Pixel Structure and Genetic Algorithm Optimization.

This paper presents a flexible method for designing a bandpass filter (BPF) using pixel structure and genetic algorithm (GA) optimization. The pixel structure is made up of a grid of metallic microstrip stubs, and the GA is utilized to determine the connections between these stubs. The pixel structure enables the construction of step impedance and shunt branches, which are used to design a traditional BPF. To enhance the design freedom, one side of the discrete grids is connected to the ground via metallic holes. For verification, a BPF was designed, simulated, and measured. The experimental results showed that the 10 dB return loss bandwidth ranges from 1.1 to 1.9 GHz and the insertion loss is approximately 2.5 dB. There is good agreement between the calculation, EM simulation, and measurement results. The proposed GA-based design method offers significant advantages in terms of one-time EM simulation, feasibility, and labor time savings, making it more convenient than the traditional design method.

1-Bit Wide-Angle Folded Reflectarray Antenna at Ka-Band

This letter presents a folded reflectarray (FRA) capable of electrical beam steering in the Ka-band. The FRA consists of a low-profile feeding source, a dual-layer wire grid, and 36×36 polarization twisting reflective elements. An element of center shorted patch with two plated through holes is proposed where only two switches are required for polarization twisting and 1-bit encoding. A cavity is then introduced surrounding the element to improve the beam-steering performance. To verify the proposed element, two prototypes with 0° and 60° beam directions are designed and experimented where the metal stub and open circuit are used to model “ <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on/off</small> ” states of PIN diodes for simplification. The measured peak gain of 0°FRA is 27.5 dBi with 2 dB gain bandwidth of 28–32 GHz (13.3%). A measured gain drop of 3.25 dB is achieved by the 60°FRA, which verifies the wide-angle beam-steering ability. The measured reflection coefficient of the feeding source is less than −15 dB over the operating band. The proposed FRA has a good potential to realize beam-steering with real PIN diodes for the satellite communications.

Human choroid plexus in a patient with intracranial hypertension and hydrocephalus: scanning electron microscopy

Introduction The daily production of 500 ml of cerebral spinal fluid (CSF) is largely carried out by the choroid plexus (CP), which is located in the cerebral ventricles. In recent years, much importance has been given to studies of the choroid plexus for a better understanding of the mechanism of headache associated with idiopathic intracranial hypertension or other etiologies. A few drugs acting on the CP to reduce CSF secretion are used to treat headache in patients with benign intracranial hypertension. Objectives To show scanning electron microscopy images of CP obtained from a pediatric patient with hydrocephalus. Method The CP sample was collected during a surgical procedure of a third ventriculostomy and CP coagulation as a treatment for hydrocephalus in a 2-year-old boy. A sample of uncoagulated CP (5 mm) was removed and immediately immersed in glutaraldehyde solution and refrigerated at 4°C. In the electron microscopy laboratory of UFPE, the sample. The sample was fixed with Karnovsky solution (2.5% glutaraldehyde, 4.0% formaldehyde and 0.1M sodium cacodylate buffer), later postfixed with 1% osmium tetroxide, dehydrated in an increasing series of alcohol (30%, 50%, 70%, 90% and 100%) and carried out the critical point for total drying. The samples were placed in metallic stubs containing a double-sided carbon tape and then metalized with gold-palladium in the Ion Sputter JFC-1100 (JEOL) equipment. Images were performed using the EVO LS-15 scanning microscopy (ZEISS). Results We present images of CP segments at 20,000 to 40,000x magnification, showing surface projections suggesting microvilli. Due to ethical issues, we do not have a control sample of healthy individuals for comparative purposes. Conclusion To the best of our knowledge, this is the first time human CP images of a patient with hydrocephalus are presented using scanning electron microscopy. Keywords: Choroid plexus, Headache, Intracranial hypertension, Hydrocephalus, Microscopy.

Tuning metallic stub loaded symmetrical resonator based dual band metamaterial absorber for wave shielding from Wi-Fi frequencies

In this article, a simple metamaterial absorber (MMA) is presented aiming absorption of microwave signals from Wi-Fi frequencies of 2.4 GHz, and 5 GHz. The MMA unit cell constructed on 20 × 20 mm2 FR4 substrate provides maximum absorption of 99.2% and 99.9% at 2.4 GHz and 5 GHz with the flexibility of on-design tuning of maximum absorption frequencies. The tuning metallic stubs connected with the outer ring provide the provision of frequency adjustment from 2.34 GHz to 2.45 GHz, whereas middle ring stubs along with the innermost ring assists for frequency tuning from 4.68 GHz to 5.1 GHz. Due to symmetrical structure, excellent angular stability up to 60° is achieved with near zero cross-polarization effect for both transverse electric (TE) and transverse magnetic (TM) modes of excitation. The measured result of the proposed MMA is analyzed that shows good similarity with the simulated one. Due to its simplistic design within nominal dimension, high absorption, flexibility to frequency tuning, wide angular stability, and no cross-polarization effect, this MMA can be a good candidate for absorber applications in wireless communication systems, especially for wave shielding from Wi-Fi frequencies.

Design of a dual-polarized aperture array for 6–18 GHz applications

A dual-polarized aperture array for 6–18 GHz applications is presented in this paper. Wide aperture is used as the array element owing to its simple structure, low-profile and broadband operation. The array elements are combined in a 2 × 2 arrangement to improve the pattern consistency in both polarizations. A metallic stub is placed at 45° between the orthogonal feeding structures to improve the port-to-port isolation, which improves the radiation efficiency in the low frequency band significantly. A corrugated reflector is proposed to replace traditional plane reflector for suppressing the parallel-plate mode, which improve the radiation patterns in the high frequency range. A prototype array with a compact size of 120 mm × 120 mm × 8.25 mm is fabricated. Simulated and measured reflection coefficients are mostly below −10 dB in the frequency range of 6–18 GHz. The radiation patterns are also well behaved with a realized gain ranging from 6.5 dBi to 15.4 dBi. This array is potentially useful for spectrum monitor, data transmission, and electronic warfare on compact airborne platforms.

A novel and efficient impedance matching technique based on fragment discrete structure and genetic algorithm

This paper proposes a novel and efficient design technique to achieve multi-frequency impedance matching. The matching network is mainly constructed based on fragment discrete structure, which consists of regularly distributed metallic microstrip stubs, where some of them are connected whereas others are not. Different designs are generated by determining the interconnections between each two stubs. To facilitate the design procedure, a theory based on port impedance substitution is rigorously developed to calculate the resulted performance (reflection coefficient) of each design. Finally, the optimal design is obtained by using the derived formulas and genetic algorithm. The full optimization procedure is totally free of electromagnetic (EM) simulation and is quite timesaving. Three different examples of mismatched frequency-varying complex load are adopted to illustrate the steps and functionality of the proposed method. The accuracy of the proposed fast-calculation method is also verified by EM simulation and experimental results.

Fractal loaded six element multiple‐input‐multiple‐output antenna configuration for super wideband operation

In this article, a planar six port multiple-input-multiple-output (MIMO) antenna configuration, fabricated on 80 × 120 mm2 FR4 substrate has been presented for super wideband (SWB) operation. The different co-planar waveguide (CPW) fed antenna elements are placed in side by side, perpendicular and upside down arrangements among themselves. A combination of Minkowski and modified Hilbert fractal curve has been applied on half elliptical patch antenna elements. Two pairs of antenna elements operate from 1.2 to 20 GHz and the other pair of antenna elements covers a bandwidth ranging from 1.4 to 20 GHz. Due to the utilization of different metallic stubs, fractal curves and proper positioning of the antenna elements, inter-element isolation more than 20 dB is achieved over the whole frequency band. The proposed design also exhibits suitable radiation characteristics with enough gain and better diversity performance parameters. The time-domain analysis of the proposed design in terms of group delay also confirms its application as a good SWB MIMO antenna configuration.

Decoupling and Matching Network for Dual-Band MIMO Antennas

This article presents a novel method to design the decoupling and matching network (DMN) for dual-band multi-input–multioutput (MIMO) antennas. The DMN consists of a grid of metallic microstrip stubs, some of which are connected while others are not. The connecting condition in the DMN is the only unknown variable for realizing high antenna isolation. It is determined by rigorous design formulas upon scattering matrix and optimized by the binary optimization algorithm, e.g., genetic algorithm (GA). Thus, high isolation among antennas can be achieved without requiring the optimization process in the electromagnetic simulation tool. Three decoupling examples of two two-element symmetric and asymmetric arrays and a four-element array are presented to elaborate the design procedure and verify the advance of the proposed decoupling method. Results show that the adoption of DMN offers enhancement in impedance matching, isolation, and efficiency, as well as the reduction of envelop correlation coefficient within two desired frequency bands for all cases, validating the proposed decoupling method.

Isolation and Gain Improvement of a Rectangular Notch UWB-MIMO Antenna

This paper presents the performance improvement of a co-planar waveguide rectangularly notched UWB-MIMO antenna. The isolation and gain of the antenna are enhanced by using a parasitic isolator. The antenna consists of four microstrip patch antennas and an isolator. The UWB characteristic of the antenna is achieved by truncating the lower ends of the radiating patch by a semicircle. The rectangular notch characteristic is obtained by adding two electromagnetic bandgap structures on the backside of the antenna, which is attached to the radiator via shorting pin. The performance, especially the decoupling of the MIMO antenna is improved by using a novel parasitic decoupler, which is placed between the antennas to receive uncorrelated signals. The decoupling structure consists of a square shape metallic element with a circular slot inside and a half-semicircle slot edged at each corner. Four rectangular metallic stubs are extended from opposite parallel sides to improve further isolation. The simulated and measured results show that the antenna has a rectangular notch band (5.25–5.85 GHz) across the working band of 3–12.8 GHz. In addition, the antenna has a planar structure with an overall size of 60 × 60 × 1.52 mm3 and offers stable gain, reduced mutual coupling (<−21 dB), and lower envelop correlation (<0.001).

A goblet-shaped quad band-notched UWB antenna and its MIMO configurations

Abstract A goblet-shaped quad band-notched antenna is proposed as a prototype antenna. With three CSRR slots and two symmetrical C-like metal stubs, the antenna produced four notched bands to suppress 3.5 GHz WiMAX, 5.3 GHz lower band of WLAN, 5.8 GHz upper band of WLAN and 8.3 GHz X-band. To increase channel capacity and data rate, a two-port UWB-MIMO antenna-1 with quad notched-bands is introduced by placing two identical prototype antenna perpendicularly. The UWB-MIMO antenna-1 easily achieves high isolation of more than 25 dB, but it has big volume of 30 × 60 × 0.8 mm3. To keep miniaturization in size, a two-port UWB-MIMO antenna-2 is constructed by arranging two identical prototype antenna in parallel. With a slot in the common ground and an I-type metal parasitic stub, better than 15 dB port isolation is realized. The simulated and measured data indicate that the UWB-MIMO antenna-2 can reject the above four bands in working band of 3–11 GHz. Meanwhile, other characteristics of high port isolation, good radiation pattern and stable gain are observed. Having compact structure and favorable characteristics, the UWB-MIMO antenna-2 not only realized four notch bands, but also effectively improved the spectrum utilization, which is the highlight of the work.

Compact Broadband Circularly Polarized CPW-Fed Antenna with Characteristic Mode Analysis

A compact circularly polarized (CP) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). A ring patch with a gap and two arc-shaped metallic stubs as the radiator is analyzed and optimized by CMA to figure out the orthogonal modes and operating frequency band for potential good axial ratio (AR) performance. The studies of these CP modes provide a physical insight into the property of broadband circular polarization. Such an in-depth understanding paves the way for the proposal of novel CP antenna with separation between the design of radiator and feeding network. A 50-Ω coplanar waveguide (CPW) is introduced and placed appropriately to excite the desired modes based on the information from CMA, which employs two asymmetric ground planes to improve the performance in terms of AR and impedance matching. The antenna with a compact size of 0.71λ0 × 0.76λ0 × 0.038λ0 (λ0 is the free-space wavelength at the center frequency of the 3-dB AR bandwidth) is fabricated and measured for validation. The realized gain varies from 1.6 to 3.1 dBic over the operating bandwidth characterized by the measured 10-dB impedance bandwidth of 83.8% (3.98–9.72 GHz) and 3-dB AR bandwidth of 70.3% (4.59–9.57 GHz), respectively.

Symmetric resonator based tunable epsilon negative near zero index metamaterial with high effective medium ratio for multiband wireless applications

In this paper, a tuned metamaterial (MTM) consisting of a symmetric split ring resonator is presented that exhibits epsilon negative (ENG), near zero permeability and refractive index properties for multiband microwave applications. The proposed metamaterial is constituted on a Rogers (RT-5880) substrate with 1.57 mm thickness and the electrical dimension of 0.14λ × 0.14λ, where wavelength, λ is calculated at 4.2 GHz. The symmetric resonating patch is subdivided into four equal and similar quartiles with two interconnecting split rings in each quartile. The quartiles are connected at the center of the substrate with a square metal strip with which four tuning metal strips are attached. These tuning metal strips are acted as spacers between four quartiles of the resonator patch. Numerical simulation of the proposed design is executed in CST microwave studio. The proposed MTM provides four resonances of transmission coefficient (S21) at 4.20 GHz, 10.14 GHz, 13.15 GHz, and 17.1 GHz covering C, X and Ku bands with negative permittivity, near zero permeability and refractive index. The calculated effective medium ratio (EMR) is 7.14 at 4.2 GHz indicates its compactness. The resonance frequencies are selective in nature which can be easily tuned by varying the length of the tuning metal stubs. The equivalent circuit of the proposed MTM is modelled in Advanced Design Software (ADS) that exhibits a similar S21 compared with CST simulation. Surface current, electric and magnetic fields are analyzed to explain the frequency tuning property and other performances of the MTM. Compact size, ENG with near zero permeability and refractive index along with frequency selectivity through tuning provides flexibility for frequency selective applications of this MTM in wireless communications.

Isolation improvement in dual‐band astroid shaped MIMO DRA for LTE and ISM applications

This article presents the design of a novel astroid shaped dielectric resonator antenna (DRA) constructed from PTFE Teflon material with a dielectric constant of εr = 2.1 and a loss tangent tan δ = 0.0002 on an FR4 grounded substrate for LTE and ISM band applications. Inverted Omega ℧-shaped feed along with asymmetric E-shaped dual metallic strips in the partial ground is used to obtain dual-band characteristics. A light weight, cost-effective plastic material is used to design the antenna. An isolation of 26.5 dB and 24.6 dB is achieved in the two frequency bands 1.8 GHz and 2.4 GHz respectively by modifying the ground plane. Metallic strips and stubs in the ground are used to enhance the isolation in the proposed MIMO system. The obtained impedance bandwidths in both the bands are 14.5% and 13%. The performance of the MIMO system is characterized by the envelope correlation coefficient and diversity gain. Good agreement is found between simulated and measured results.