Operating Frequency Band Research Articles

Conformal Array Antenna for Applications in Wide-Scanning Phased Array Antenna Systems

A dipole with four branches, fed by Marchand balun, is designed to be conformal with wing of an unmanned aerial vehicle. With the help of branches, the proposed dipole element achieves a better impedance matching performance. Meanwhile, the metallic coupled strip is added to move the scanning blindness out of the operating frequency band, without deterioration at broadside radiation. Besides, the beamwidth in the vertical plane, i.e., the H-plane of the dipole, can be effectively compressed by loading three metallic strip directors, and the element gain increases as well. Based on the dipole element, a 12-element linear phased array is designed and simulated. The simulated results show that the array achieves ±60° scanning range in the horizontal plane, with the voltage standing wave ratio lower than 2.5 in the operating band of 2.4∼3 GHz. Moreover, the 3 dB beamwidth in the H-plane is 81° at the center frequency of 2.7 GHz. The measured results of the fabricated antenna prototype agree reasonably well with the simulated ones, which verify the feasibility of the wing-conformal linear phased array design.

Isolation Enhancement of UWB MIMO rDRA for 5G Outdoor Applications

In this paper, a two-port Ultra-Wideband Multiple Inputs Multiple Outputs (UWB MIMO) rectangular Dielectric Resonator Antenna (rDRA) is proposed for 5G sub-6 GHz outdoor applications. An edged hole is inserted at the rDRA edge for isolation enhancement purposes. The effect of edged hole radius on isolation is investigated. Both UWB MIMO rDRA with and without edged holes are investigated for both parallel and orthogonal feed schemes (four scenarios). Isolation better than -22 dB is obtained for orthogonal orientation and edged hole rDRA. Surface current density distribution is used to explain that isolation enhancement. UWB bandwidth and high efficiency are obtained on the operating bands due to the usage of an aperture-coupled feed system and edged hole rDRA. The proposed antenna has two -6 dB operating frequency bands, the lower band (2.25 GHz – 2.52 GHz) and the higher band (3.6 GHz – 5.7 GHz). The Envelope Correlation Coefficient (ECC) and diversity gain DG are used to justify the MIMO antenna performance. Good agreement is obtained between measured and simulated results.

Dual band‐notched ultra‐wideband antenna with T‐shape stub

An ultra-wideband (UWB) antenna with dual band-notched characteristics is proposed in this letter. The fabricated prototype of the proposed antenna has a compact size of 30 × 24 mm which operates at 3 to 14 GHz and attained dual notch-bands at 3.3 to 3.7 GHz and 5.15 to 5.825 GHz. The result shows that the proposed antenna is compact, easy to fabricate and provides good characteristics in radiation patterns and time-domain behaviours. The simulated and measured results displayed good agreement over the entire operating frequency band. The proposed antenna can be used for wideband frequency requirement systems like indoor positioning.

Design of a Frequency Selectable Rectifier Using Tuned Matching Circuit for RFEH Applications

RF energy harvesting (RFEH) is an emerging technique in the field of wireless technology. The key components of this system are receiving antenna, matching network, and rectifier circuit. A rectifier circuit based on a tuned matching circuit is demonstrated in this paper for RFEH applications. The topology of this rectifier circuit is suitable for selecting a wide range of operating frequency bands, realized by changing the value of the inductor in the matching network. For validation purpose, a rectifier has been designed, developed, and tested at 2.45 GHz. The rectifier achieved peak power conversion efficiency (PCE) of 64.5% at 0 dBm. The PCE is higher than 50% for input power in the range of −8.5–2 dBm. The proposed rectifier has a compact size of 20 × 15 × 1.524 mm3. By changing the value of the inductor in the matching network this rectifier can be redesigned for any other operating frequency in the range of 0.6–2.6 GHz.

Performance Evaluation of Triple band Microstrip Antenna using Hybrid SRRs on Fractal Ground Plane

A single-band monopole antenna, transformed into a triple-band antenna for S-band and C-band applications is reported in this paper. This transformation is done with the help of two different hybrid SRR unit cells, which are embedded on the truncated ground plane of the antenna. These hybrid SRR unit cells are created by combining square split ring and circular split ring into two different configurations. Simulated results are in coherence with the measured results and analysis is provided to evaluate the efficacy of the design. This analysis can be used to estimate the usefulness of metamaterial unit cells in generating multiple frequency bands. The operating frequency bands measured are 2.72-2.83GHz, 3.54-4.35 GHz, and 4.72-5 GHz respectively. These bands are being used in the mid-band frequency range of 5G communication in many countries. The developed antenna is miniaturized to the size of 0.19λ0 ×0.25λ0 (λ0 is the free space wavelength at 2.72 GHz). Two objectives i.e., miniaturization and multi-banding are fulfilled in a single design. The introduction of different hybrid SRR unit cells at defective ground plane causes multi-banding and resonance of a unit cell at a lower frequency leads to an increase in the effective electrical length of the antenna without increasing its physical size. The metamaterial characteristic of the unit cells is also verified in the article.

Slotted Antenna Array with Enhanced Radiation Characteristics for 5G 28 GHz Communications

This paper presents a 1 × 4 linear antenna array working at 28 GHz for 5G communication systems. The proposed array employs four rectangular slotted antenna elements fed by a 1 × 4 T-power divider. An artificial magnetic conductor (AMC) layer is placed below the array for increasing the radiation intensity and improving overall array gain. The measured impedance bandwidth of the proposed array with (|S11| < −10 dB) is extended from 25.36 to 26.03 GHz (with a bandwidth of 0.67 GHz) and from 26.75 to 28.81 GHz (with a bandwidth of 2.06 GHz). The proposed array design exhibits a measured gain value that varies between 11.8 dBi and 13.1 dBi within the operating bands and reaches 13.1 dBi at 28 GHz. The proposed array achieves a radiation efficiency of 83.05%, and a front-to-back ratio ranging between 15 and 20 dB across the operating frequency band. The array is fabricated and tested with good matching between the simulated and tested outcomes. The improved performance of the array makes it a suitable candidate for 5G new radio (NR) communications.

A Wideband Single-fed circularly polarized dielectric resonator antenna with bandpass filtering response

ABSTRACT For integrated design of a filter and an antenna, a wideband circularly polarized (CP) dielectric resonator antenna (DRA) with filtering characteristics is proposed. A rectangular slot structure is etched on the ground to optimize the axial ratio (AR) bandwidth of the antenna singly fed by one port. Capacitive filtering branches are combined into the microstrip feeding line to effectively generate two radiation nulls outside the passband. To further enhance the suppression level in the high-frequency stopband, the stair-shaped DR is chamfered into a fish-shaped structure. A suppression level larger than 15 dB is found within the stopband. A prototype of the antenna is fabricated, and both of the simulated and measured results show a wide bandpass filtering performance over the operating frequency band. The antenna has an impedance bandwidth of 37.8%, an AR bandwidth of 25.1%, and a low profile of 0.078λ 0 (λ 0 is the free-space wavelength at 5.47 GHz), which can be a good candidate for 5 G and WLAN communication systems.

Frequency reconfigurable circular microstrip patch antenna with slots for cognitive radio

In this paper, a novel multi-frequency microstrip antenna with complementary ring slot resonator (CRSR) structure that satisfies Bluetooth, worldwide interoperability for microwave access (WiMAX), and wireless local area network (WLAN) applications is proposed. The conventional antenna consists of a circular microstrip patch at a resonance frequency band of 2.5 GHz. By loading two CRSR at the radiating element, three operating frequency bands 2.5 GHz, 3.6 GHz, and 5.2 GHz are achieved. The operational bands covered by the antenna are Bluetooth 2.5 GHz, WiMAX 3.6 GHz, and WLAN 5.2 GHz. The insertion of CRSR to patch antenna has made it possible to compact and simple design, and miniaturized antenna for cognitive radio. Moreover, the directivity of the proposed antenna is adequate with acceptable radiation properties and perfectly matches with the simulated and measured results.

Design of an omnidirectional transmit/receive antenna pair using mushroom‐like electromagnetic band‐gap structure

This paper presents a transmit-receive (T/R) antenna pair with omnidirectional and broadband radiation performance. The proposed antenna combines a patch with mushroom-like electromagnetic band-gap (EBG) structures. The mushroom structures are utilized to enhance the radiation characteristics such as impedance bandwidth, directivity, and gain. Two T/R antennas with 3 × 3 and 5 × 5 arrays working in K-band are designed and fabricated, the transmit (TX) and receive (RX) antennas are printed on a single-layer grounded dielectric substrate. Both the TX and RX antennas consist of an array of mushroom-like EBG structures around the monopole microstrip antenna, which is loaded with four stubs and fed by a 50 Ω coaxial probe. The dimensions of the fabricated prototype 3 × 3 array antenna are 3.58 λ 0 × 1.61 λ 0 ( λ 0 -the wavelength in free space at 24 GHz). The TX/RX measured impedance bandwidth ( ∣ S 11 ∣ < −10 dB) are 9.58% (23.6 ~ 25.9 GHz), 12.08% (22.8 ~ 25.7 GHz), respectively. The measured peak gain is 3.45 dBi at 24.8 GHz. For the 5 × 5 array antenna, the aperture size is 5.58 λ 0 × 2.61 λ 0 . The measured impedance bandwidth ( ∣ S 11 ∣ < −10 dB) is 9.17% (23.65 ~ 25.85 GHz) and 12.71% (22.65 ~ 25.7 GHz) for the TX and RX, respectively. The measured peak gain increases by nearly 2 dB. Measurement results show that both antennas have a TX/RX isolation level better than 20 dB and achieve monopole-like omnidirectional patterns over its operating frequency band.

Моделирование резонансной спиральной электрически малой антенны

Currently, the development of methods and means of data transmission through absorbing media and shielding obstacles for organizing wireless communication and remote control of technological equipment and industrial robots, including those in the mining industry, is an urgent area of research. As experimental studies in mine workings have shown, radio systems with high-quality tuned resonant antennas from hundreds of kHz to several of MHz with a narrow operating frequency band suitable for transmitting low-speed signals turned out to be promising. In this article, a model of a resonant helical electrically small antenna (ESA) with an electrical size of 0.025 is considered. An equivalent circuit of this antenna is presented using an analytical description of its components. The results of a full-wave finite element analysis of a helical ESA using finite conductivity boundary are presented. Graphs are constructed that explain the resonant increase in the efficiency of the antenna. The obtained values of the efficiency of the spiral ESA are sufficient to create means of data transmission through absorbing media and imperfectly shielding obstacles.

Compact Dual-Polarized Filtenna With Steep Roll-Off Rate for Base Stations

This letter presents a dual-polarized, band-pass filtering antenna, or “filtenna” with a steep roll-off rate and a compact size. To simultaneously support multiple communication standards in a shared aperture, base station antenna arrays need to operate in multiple closely-spaced frequency bands. However, each filtenna has a limited space in the aperture-shared array; therefore, it is challenging to achieve a high roll-off rate. To resolve this problem, we proposed a filtenna that consists of four stacked X-shaped patches, of which the second from the bottom is the driven patch and the rest are parasitic ones. These closely coupled parasitic patches switch rapidly from resonance to antiresonance; however, their radiations change because they together cancel one another and create a very steep roll-off rate. The aperture dimension of the proposed antenna is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.2 \, \lambda _{0} \times 0.2 \, \lambda _{0} \times 0.14 \, \lambda _{0}$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> is the wavelength in free space at the center frequency. The measurement results demonstrate a very steep roll-off rate up to 1795 dBi/GHz at the lower cutoff frequency of 1.8 GHz. The measured average gain was 8 dBi over the operating frequency band of 1.805–1.88 GHz, which makes the proposed filtenna a good candidate for multiband and multistandard base stations.

Operating Band Shifting of Resistor-Loaded Antenna-Based Absorber by Using Parasitic Element Concept

The size of an electromagnetic (EM) absorber is a critical design parameter since it determines the operating frequency band. The realization of lower starting frequency requires enlargement of the absorber which often is not desired. In this communication, a technique for overcoming this problem in the case of an absorber, constructed of a resistor-loaded wideband bowtie antenna, is studied. The method is about placing parasitic elements around the antenna in order to change its input impedance and thus to realize large shifting of the operating band of both single- and dual-polarized absorbers. Without using parasitic elements large move of the operating band can only be achieved by a considerable increase in the absorber’s size. However, the used method for absorption band shifting leads to shrinking of the bandwidth which means a compromise is to be made between these two parameters. For validation purposes, prototypes are fabricated and tested, and a good agreement between the simulation and measurement results is obtained.

A Compact Triple-Band UWB Inverted Triangular Antenna with Dual-Notch Band Characteristics Using SSRR Metamaterial Structure for Use in Next-Generation Wireless Systems

A compact triple-band operation ultra-wideband (UWB) antenna with dual-notch band characteristics is presented in this paper. By inserting three metamaterial (MTM) square split-ring resonators (MTM-SSRRs) and a triangular slot on the radiating patch, the antenna develops measured dual-band rejection at 4.17–5.33 GHz and 6.5–8.9 GHz in the UWB frequency range (3–12 GHz). The proposed antenna offers three frequency bands of operation in the UWB range, which are between 3–4.17 GHz (~1.2 GHz bandwidth), 5.33–6.5 GHz (~1.17 GHz bandwidth), and 8.9–12 GHz (~3.1 GHz bandwidth), respectively. The higher resonating frequency band can be tuned/controlled by varying the width of the triangle slot, while the medium operational band can be controlled by adjusting the width of the SSRR slot. Initially, the simulated S-parameter response, 2D and 3D radiation patterns, gain, and surface current distribution of the proposed UWB inverted triangular antenna has been studied using epoxy glass FR4 substrate having parameters εr = 4.3, h = 1.6 mm, and tan δ = 0.025, respectively. In order to validate the simulation results, the proposed UWB antenna with dual-notch band characteristics is finally fabricated and measured. The fabricated antenna’s return-loss and far-field measurements show good agreement with the simulated results. The proposed antenna achieved the measured gain of 2.3 dBi, 4.9 dBi, and 5.2 dBi at 3.5 GHz, 6.1 GHz, and 9.25 GHz, respectively. Additionally, an in-depth comparative study is performed to analyze the performance of the proposed antenna with existing designs available in the literature. The results show that the proposed antenna is an excellent candidate for fifth-generation (5G) mobile base-stations, next-generation WiFi-6E indoor distributed antenna systems (IDAS), as well as C-band and X-band applications.

Ultrathin chiral metasurface with multiple functionalities

This paper presents an ultrathin multiband chiral metasurface having good angular stability. The metasurface consists of two patterned metallic sheets placed on opposite sides of a microwave substrate. It has twelve operational bands. It achieves asymmetric linear-to-circular polarization transmission within three frequency bands and asymmetric cross-polarized transmission of linearly polarized incident waves within seven frequency bands. It also exhibits two symmetric co-polarized transmission bands for both x- and y-directed incident E-field orientations. The structure gives favorable response for incident angles up to 60° till 11 GHz and up to 40° from 11 to 13 GHz for both transverse-electric and transverse-magnetic incidence. Its ultrathin nature makes it lightweight. The twelve operational frequency bands of the metasurface can be tuned and adjusted to meet user specifications.

A study on axial‐mode helical antennas with spiral strip arms

An axial-mode helical antenna with a spiral strip arm excites circularly polarized plane waves propagating along the axis of a drill string bore. This antenna extends the transmission distance of downhole signals in drill strings, thereby increasing the depth of possible measurements. The half-power lobe width and directivity of the axial-mode helical antenna matched the microwave channel of the drill string bore. The helical radiator in the antenna was optimized to ensure that center frequency was within the optimal operating frequency band of microwaves in the drill string bore. The reflector in the antenna was optimized through the creation of gas vents, which reduced its cross-sectional area. The axial-mode helical antenna reduced the effects of drill string twisting on the microwave channel, reduced reflection in the walls of the drill pipe, and reduced the loss of microwave signals. Compared to linear antennas, the axial-mode helical antenna had superior performance because S21 increased to about 45 dB in the 2.4 GHz frequency band. The use of axial-mode helical antennas in drill string bores during microwave measurement while drilling (MMWD) helped in monitoring downhole safety risks and expanding the scope of gas drilling. Therefore, axial-mode helical antennas have practical applications and require further research.

A new L-shaped rigid beam FBG acceleration sensor

Acceleration detection is an important technology in the fields of seismic monitoring, structural health monitoring and resource exploration. A FBG acceleration sensor with the combination of L-shaped rigid beam and spring structure based on bearings is proposed against the low sensitivity that predominates in the low-frequency vibration measurement by FBG acceleration sensors, where L-shaped rigid beam is utilized to amplify the vibration signal, and is fixed by the bearings at both ends to effectively suppress the transverse crosstalk. The effects of structural parameters on the sensitivity and natural frequency of the sensors were analyzed using Origin theory, and such parameters were optimized; next, static stress and modal simulation analysis was made using COMSOL; in the end, a test system was built to test the performance of the real sensors. According to the findings, the acceleration sensor, whose natural frequency is 57 Hz, is of a flat sensitivity response in the low frequency range of 1–35 Hz, with the dynamic range being 89.83 dB, the acceleration sensitivity being up to 1241.85 pm/g, the coefficient of determination R2 for the sensitivity fit is 0.9997, and the transverse crosstalk being -26.20 dB within the operating frequency band. The findings offer a reference for improving the low-frequency vibration measurement capability of FBG acceleration sensors.

Flexible ultra-wideband cartoon-shaped antenna based on a composite with customizable dielectric properties

This paper presents a flexible ultra-wideband (UWB) and deformation-insensitive antenna. The proposed antenna was based on a Mickey-shaped patch, a coplanar waveguide fed, and a flexible composite substrate, which was built by a polydimethylsiloxane (PDMS) matrix and short-diameter powders of polytetrafluoroethylene (PTFE), with customizable dielectric properties. Furthermore, PTFE, magnesium oxide, titanium oxide, and zirconia powders were used as four fillers with different weight ratios to modify and control the dielectric properties of the dielectric substrate (the relative permittivity: 2.75–3.07, the dielectric loss tangent: 0.02–0.05), and then we characterized PDMS-based composites through Young’s modulus, Raman spectra, and surface topography. Finally, we fabricated and measured the proposed antenna with the dimensions of 50 mm × 60 mm × 0.5 mm. The measured reflection coefficient curves showed an operating frequency band from 1.9 GHz to 43.5 GHz, and the measured fractional bandwidth reached 183.3%. It was proved that the antenna had stable performance when it was bent or stretched. Moreover, the antenna was simulated and measured in the proximity of the human body, which verified the antenna robustness and safety for use on a human. The proposed UWB and deformation-insensitive antenna is a promising candidate for wearable applications and wireless communication.

Portable Wideband Directional Antenna Scheme with Semicircular Corrugated Reflector for Digital Television Reception.

This research proposed a portable wideband horizontally-polarized directional antenna scheme with a radome for digital terrestrial television reception. The operating frequency band of the proposed antenna scheme is 470–890 MHz. The portable antenna scheme was an adaptation of the Yagi-Uda antenna, consisting of a folded bowtie radiator, a semicircular corrugated reflector, and a V-shaped director. Simulations were carried out, and an antenna prototype was fabricated. To validate, experiments were undertaken to assess the antenna performance, including the impedance bandwidth (|S11| ≤ −10 dB), gain, and unidirectionality. The measured impedance bandwidth was 75.93%, covering 424–943 MHz, with a measured antenna gain of 2.69–4.84 dBi. The radiation pattern was of unidirectionality for the entire operating frequency band. The measured xz- and yz-plane half-power beamwidths were 150°, 159°, 160° and 102°, 78°, 102° at 470, 680, and 890 MHz, with the corresponding cross-polarization below −20 dB and −40 dB. The radome had a negligible impact on the impedance bandwidth, gain, and radiation pattern. The power obtained for the outdoor test, at 514 MHz, was 38.4 dBµV (−70.4 dBm) with a carrier-to-noise ratio (C/N) of 11.6 dB. In addition, the power obtained for the indoor test was 26.6 dBµV (−82.2 dBm) with a C/N of 10.9 dB. The novelty of this research lies in the concurrent use of the Yagi-Uda and bowtie antenna technologies to improve the impedance bandwidth and directionality of the antenna for digital terrestrial television reception.

Microstrip-Fed 3D-Printed H-Sectorial Horn Phased Array.

A 3D-printed phased array consisting of four H-Sectorial horn antennas of 200 g weight with an ultra-wideband rectangular-waveguide-to-microstrip-line transition operating over the whole LMDS and K bands (24.25–29.5 GHz) is presented. The transition is based on exciting three overlapped transversal patches that radiate into the waveguide. The transition provides very low insertion losses, ranging from 0.30 dB to 0.67 dB over the whole band of operation (23.5–30.4 GHz). The measured fractional bandwidth of the phased array including the transition was 20.8% (24.75–30.3 GHz). The antenna was measured for six different scanning angles corresponding to six different progressive phases , ranging from 0° to 140° at the central frequency band of operation of 26.5 GHz. The maximum gain was found in the broadside direction = 0°, with 15.2 dB and efficiency = 78.5%, while the minimum was found for = 140°, with 13.7 dB and = 91.2%.

Design of ultra-thin underwater acoustic metasurface for broadband low-frequency diffuse reflection by deep neural networks

Underwater acoustic metasurfaces have broad application prospects for the stealth of underwater objects. However, problems such as a narrow operating frequency band, poor operating performance, and considerable thickness at low frequencies remain. In this study a reverse design method for ultra-thin underwater acoustic metasurfaces for low-frequency broadband is proposed using a tandem fully connected deep neural network. The tandem neural network consists of a pre-trained forward neural network and a reverse neural network, based on which a set of elements with flat phase variation and an almost equal phase shift interval in the range of 700–1150 Hz is designed. A diffuse underwater acoustic metasurface with 60 elements was designed, showing that the energy loss of the metasurface in the echo direction was greater than 10 dB. Our work opens a novel pathway for realising low-frequency wideband underwater acoustic devices, which will enable various applications in the future.