Center Operating Frequency Research Articles

A Dual-Layer Full-Phase Frequency-Selective Surface for Continuous 2-D Beam Scanning

Based on the generalized frequency selective surface (FSS) theory, we prove that the dual-layer dual-polarization transmission FSS can achieve 360° phase coverage at a limited loss. As a verification, a dual-layer dual-polarization full-phase unit cell with vias is proposed, which can achieve a phase range of more than 360° under 2 dB transmission loss. In addition, we innovatively apply the proposed dual-layer full-phase FSS to the design of a continuous 2-D beam scanning antenna based on the Risley prism (RP). This scheme effectively reduces the number of dielectric substrate layers required by the phase shifting surface (PSS), reduces the rotating scanning inertia, and effectively improves the aperture efficiency. The measured results show that the maximum scanning range of the 2-D beam scanning antenna can reach ±46° in the elevation plane and 360° in the azimuth plane. When operating at the center operating frequency of 21 GHz, the maximum gain of the antenna is 35.75 dBi with an aperture efficiency of 44.1%.

Optimization of a Cusp Gun With a Grid for a Terahertz Gyrotron Traveling-Wave Amplifier

A magnetic cusp gun with a control grid was optimized through parametric simulations for a gyrotron traveling-wave amplifier with an output power of 10 kW and a central operating frequency of 220 GHz. The ON and OFF of the electron beam are controlled by applying appropriate biases to the grid. An axis-encircling electron beam of current 1.5 A, a pitch factor of 1.23, and a relative pitch-factor spread of ~3.5% were predicted when the gun was operated at 70 kV.

An Omni-Directional Wideband Patch Antenna with Parasitic Elements for Sub-6 GHz Band Applications

An omni-directional inset fed wideband microstrip patch antenna (MPA) for Sub-6 GHz applications has been presented. Initially, a slotted small patch antenna with a full ground plane is designed and then partial ground plane and electromagnetically coupled parasitic elements have been incorporated and optimized to get desired performance. The volume of the studied antenna is 40 × 40 × 1.575 mm3 having a partial ground plane. Rogers RT 5880 is used as the dielectric substrate tier. The simulated operating band of the MPA ranges from 2.67 GHz to 4.20 GHz, covering the N77 and N78 bands with a centre operating frequency of 3.29 GHz. The antenna can also be used for WiMAX rel 2 (3.4–3.6 GHz) applications. After fabrication and testing, the antenna also shows almost the same working band extending from 2.67 GHz to 4.15 GHz. The use of a partial ground plane plays a vital role in making it an omni-directional antenna, and the existence of a rectangular parasitic element in the ground plane influences the improvement of gain and directivity of the antenna. The designed MPA allows it to run as a wide band antenna with a good reflection coefficient profile, high average efficiency, and 1 < VSWR < 2. At a resonant tip of 3.29 GHz, the simulated gain and directivity are 3.16 dB and 3.38 dBi, respectively. The measured gain is slightly higher than the simulated gain. The computer simulation technology (CST) is used for modelling and exploring all the performance matrices of the antenna. The results of the fabricated prototype present very good similarity with the simulated results and both simulated and measured results also support the Sub-6 GHz band. The antenna prototype shows a very well balanced set of radiation characteristics with a miniaturized volume and high efficiency. Therefore, the inset fed MPA can be contemplated as a candid model for Sub-6 GHz band applications.

Wideband directional coupler based on zigzag coupling and wedge structure for isolation enhancement

This paper presents the design of wideband directional coupler with enhanced isolation performance. Studies show that introducing the zigzag coupling releases the phase-velocity difference between the even- and odd-mode in the coupling region, thus improving the directivity. To further improve the performance, wedge structure is proposed, and therefore, a wideband coupled-line directional coupler is developed with enhanced isolation responses. The presented coupler characterizes simple architecture, planar layout, symmetric topology, symmetric coupling and isolation responses that are the basic difference among many reported works, wide operation bandwidth and more importantly, the wedge structure can be independently loaded and designed, and features a great advantage in this contribution. To validate this study, a prototype coupler that works from less than 7 GHz to over 13 GHz is optimally designed, fabricated and examined experimentally. The developed prototype has a size of 11.1 × 5.4 mm2 (corresponding to 0.69 × 0.34λg2 at the center operation frequency of 10 GHz) on a microwave substrate with a relative permittivity of εr = 3.5 and a thickness of h = 0.508 mm. The measurement and simulation results are in good agreement, thus confirming the design methodology.

Proposal and Synthesis of Wideband Multilayer Planar Magic-T With Independent In-Phase and Out-of-Phase Chebyshev Filtering Responses

A wideband planar multilayer filtering magic-T is proposed and developed. The proposed magic-T uses coupled microstrip slotlines (CMSs) and microstrip-slot transitions. With the orthogonality of even and odd modes of the CMS, the Chebyshev filtering responses of both the in-phase divider part (H-T) and out-of-phase divider part (E-T) are independent of each other. The microstrip-slot transitions act as a part of filtering structures to realize vertical transmission of energy. With equivalent impedance transformer models, the synthesis processes of a four-pole Chebyshev filtering H-T and a three-pole Chebyshev filtering E-T are derived and analyzed. To verify the proposed concept, a prototype with an operating center frequency of 3 GHz, a 100% equal ripple fractional bandwidth, and a different H-T and E-T in-band ripple are synthesized and implemented on a three-layer printed circuit board. The synthesized, simulated, and measured results show good agreements among them, verifying the feasibility of the proposed planar magic-T.

Gradient Relative Permittivity Superstrate for Decoupling of Two Closely Located Dual-Polarized Slot Antennas

A simple decoupling method between two closely located dual-polarized slot antennas is proposed in this communication. Based on substrate integrated waveguide (SIW), the dual-polarized antenna is realized using cross-shaped slot and U-shaped feed line, and two identical elements are closely located in edge-to-edge space of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.031\lambda _{0}$ </tex-math></inline-formula> to form the multiple-input–multiple-output (MIMO) array, 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 free-space wavelength at the center operating frequency. Wideband characteristics, high dual-polarized isolation, and low envelope correlation coefficient (ECC) are realized by introducing a superstrate with gradient relative permittivity (GRP) above the array. The GRP is obtained using drilling hole arrays on low-cost FR-4 materials. To validate the proposed design, the antenna array is fabricated and measured. The measured result shows that 13 and 16 dB isolation enhancements are provided for two orthogonally polarized fields, simultaneously. Moreover, the measured operating bandwidth is from 8 to 10.35 GHz (about 25.6%, the isolation is more than 20 dB), and the ECC between two antennas is less than −52 dB for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{1}$ </tex-math></inline-formula> -pol and −62.4 dB for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{2}$ </tex-math></inline-formula> -pol over entire operating band. The proposed method has the potential to be used in MIMO wireless systems.

An Unequal Wilkinson Power Divider Based on Integrated Passive Device Technology and Parametric Model

A new on-chip unequal Wilkinson power divider (WPD), developed on a silicon-based integrated passive device (IPD) process and parametric model, is proposed. The central operating frequency is at 4.8 GHz for sub-6G applications. The design process achieves a balance between circuit simulation efficiency and full-wave simulation accuracy based on the parametric model. The size of a fabricated sample for the proposed unequal WPD is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6\times2.1$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A good agreement between the simulated and measured results is achieved.

Novel high‐efficiency and ultra‐compact low‐pass filter using double‐layered spoof surface plasmon polaritons

AbstractIn this letter, a novel ultra‐compact spoof surface plasmon polaritons (SSPPs) low‐pass filter which shows a high‐efficiency transmission and an excellent out‐of‐band suppression is investigated. It consists of a pair of double‐layer SSPPs, the top layer using interdigital strip and meander‐line, and the bottom layer is metal gratings of fish‐bone shape. The vast advantages of the proposed SSPPs structure in lower asymptotic frequency mode compared with traditional SSPPs structure with the same size enables the proposed low‐pass filter to be more miniaturized. The dimensions of the miniaturized structure are 0.75λ0 × 0.1λ0 (λ0 is the wavelength corresponding to the central operating frequency). The high‐efficient mode conversion is achieved by gradient meander‐line lengths. Moreover, we also investigate the transmission performance of the proposed structure when it is conformal. To validate the design concept, the prototype of a straight and bend low‐pass filter has been manufactured and measured. The experimental results of the fabricated sample agree with the simulation results well, in which the insertion loss is less than 0.5 dB, the reflection coefficient less than −15 dB, and excellent out‐of‐band rejection of the attenuation is greater than 30 ‐dB, which proves the design validity. The proposed ultra‐compact SSPPs structure may have great potential applications in miniaturized integrated circuits in the microwave and terahertz (THz) frequencies.

CPW-fed printed tapered slot antenna loaded by a wideband stacked artificial magnetic conductor with a progressed performance

AbstractA low profile printed slot antenna (PSA) backed by broadband stacked artificial magnetic conductor (AMC) is introduced in this study. First, a suggested PSA with the radiating tapered slots excited by coplanar-waveguide (CPW) is used to expand the bandwidth in the measured range of 9.05–10.95 GHz (S11 ≤ −10 dB). Then, the suggested stacked AMC surface as the ground plane of the antenna is inserted into the PSA to gain improved radiation efficiency. The realized result from the PSA with the 11 × 17 stacked AMC array exhibits −10 dB measured impedance bandwidth from 6.97 to 13.34 GHz (62.73%). The suggested PSA with AMC compared to the PSA without AMC exhibits a size reduction of 52%, enhanced bandwidth of almost 44%, and excellent impedance matching with uni-directional radiation patterns. The novel AMC unit cell is realized based on the recognized method of stacked elements. The stacked AMC design operates at 10.63 GHz with an AMC bandwidth of 8–12.84 GHz (45.8%) for X-band operation. Besides, by introducing a specific method based on the reflection results of the equivalent waveguide feed, the number of AMC unit cells is investigated to obtain an optimal AMC array. In this approach, an equivalent waveguide feed corresponding to the center operating frequency is considered to choose the number of AMC array reflector.

Quad-Furcated Profiled Horn: The Next Generation Highly Efficient GEO Antenna in Additive Manufacturing

A novel compact and highly efficient dual-polarized horn-like antenna is presented. It exploits a radiating aperture that is fed by four smaller waveguides via a quad-furcated junction. The antenna also comprises the full feed network for the feed waveguides including an integrated 4-way orthomode power divider. Design principles are described in detail and illustrated by means of an example involving an antenna with aperture size of 2.6λ0×2.6λ0 (λ0 the wavelength at the central frequency of operation) intended primarily for Geostationary Orbit (GEO) satellites. The antenna feed was designed to comply with the Additive Manufacturing rules and exhibits aperture efficiency levels close to the theoretical maximum ones over the entire transmit Ku band (10.7 -12.75 GHz), while at the same time its profile is highly compact (6.4λ0). The measured results of a prototype 3D-printed in Selective Laser Melting (SLM) verified experimentally the calculated high aperture efficiency (over 90%). The total antenna feed attains return loss > 19 dB and maximum cross-polarization isolation (XPI) > 24 dB over a bandwidth of 18%. In light of the favorable electrical performances and compact size, the proposed solution constitutes an appealing alternative to profiled (or spline) horns for satellite antenna systems used either as reflector feeds or direct radiating arrays.

Low-Profile Broadband Dual-Polarization Double-Layer Metasurface Antenna for 2G/3G/LTE Cellular Base Stations

A double-layer metasurface is proposed to realize the low profile of a broadband dual-polarized antenna for cellular base-station applications. The proposed metasurface is formed by the two layers of printed metallic patch unit cells on either substrate surface to miniaturize the metasurface size and enhance design flexibility by regulating the extent of electromagnetic coupling between the two layers. Despite the low profile of the antenna, a wideband operation is accomplished by operating the metasurface in the nonresonant region that facilitates wideband phase compensation and its truncation to a finite dimension with an additional transverse electric (TE) surface wave resonance. The guidelines for the design of the surface is derived from a comparison of unit cell structures and an approach is introduced to correlate their potential with surface susceptibility parameters. A detailed parametric study addresses the critical concern on the overall dimensions of the finite metasurface. A ±45°-polarized dipole antenna with an overall thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15~\lambda _{0}$ </tex-math></inline-formula> ( <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 operating frequency) is designed as example. The measured results show a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert \le -10$ </tex-math></inline-formula> dB impedance bandwidth of 46.4% over the frequency range of 1.69–2.71 GHz with average boresight gain of 9 dBi with a ground plane of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1\lambda _{0} \times 1.1\lambda _{0}$ </tex-math></inline-formula> , well covering 2G (1.71–1.92 GHz), 3G (1.88–2.17 GHz), and LTE (2.3–2.4 GHz and 2.5–2.69 GHz) bands.

Self-Sustained Rigid Fully Metallic Metasurfaces to Enhance Gain of Shortened Horn Antennas

This paper presents mechanically robust, low-cost, lightweight, and polarization-independent metallic metasurfaces (MMs) to enhance the gain and directivity of shortened horn antennas. The MM was designed based on the strategy of correcting the actual phase errors probed on the aperture of the horn using the near-field phase-transformation principle. The fundamental unit cell of the MM is made of a pair of cross slots created in a monolithic thin conductive sheet and is entirely free from high-cost dielectrics. The lack of dielectrics makes MM lightweight, cost-efficient and easy to fabricate the prototype for mass production. The MM has a 2D array of unit cells arranged to increase the gain of the shortened horn by improving aperture efficiency through local phase transformation in a wide frequency band. The concept is demonstrated by designing MMs for shortened horns with different heights and the same physical aperture at the center operating frequency of 12.5 GHz. The maximum gain-bandwidth with MM is achieved for the shortest horn, which is validated by measuring the physical prototype. The results indicate that horn gain with MM increases by 9.2 dB (from 11.1 to 20.3 dBi) and has a 3-dB fractional gain-bandwidth of 10.4%. The weighted density of the fabricated MM is only 0.87 g/cm². Including MM, the total antenna height is around 61% shorter than a conventional air-filled horn having a similar peak gain.

First Observations of the New MEXART's Digital System

AbstractThe Mexican Array Radio Telescope (MEXART) is a transit instrument mainly dedicated to performing interplanetary scintillation (IPS) observations with a central operating frequency of 139.65 MHz. The main scientific objective is to perform studies of solar wind properties and space weather effects. MEXART initially operated with an analog beam former (16 × 16 Butler matrix), which produced 16 fixed latitudinal beams. MEXART began operations and reported the first measurements of IPS sources. MEXART's beam forming system had several problems, however. The North‐South beams had poor directivity, with large side lobes, and the instrument did not achieve the expected performance. Therefore, we commissioned the design and construction of a digital back‐end. The digital system solved the problems with the beam forming, increases the bandwidth, and significantly improves the instrument's sensitivity. In this paper, we present the first light of MEXART's digital system. We describe the new technical capabilities of the instrument, and we show some preliminary results: an estimation of the radio telescope's sensitivity (ΔSmin = 2.28 ± 0.23 Jy), the transit of the Galaxy at 140 MHz with the simultaneous tracking of 62 latitudinal beams, and an example of an IPS observation and the single‐station methodology for calculating the solar wind speed. The new technical capabilities of the radio telescope will provide the potential for participating in several scientific studies. These include solar wind properties, space weather forecasting, ionospheric perturbations, and astrophysical aims such as the monitoring of repeating fast radio bursts and pulsars' observations.

A Low-Cost High-Gain Filtering Patch Antenna Using SISL Technology for 5G Application

This letter presents a wide band high-gain filtering antenna for fifth-generation (5G) applications based on substrate integrated suspended line platform. The filtering antenna mainly consists of a driven patch, a stacked patch, and a rectangular loop. By adding a rectangular loop to the conventional patch antenna, an additional resonance can be excited. Meanwhile, the frequency selectivity of the lower band is obtained due to the formation of a radiation null. Then, a patch is stacked on the driven patch, which also generates an extra resonance mode and a radiation null at the upper band edge. Therefore, a bandpass filtering function is realized and the bandwidth is greatly improved with three resonance frequency points. The fractional bandwidth is from 4.28 to 5.34 GHz (22.04%), covering the specific 5G n79-band (4.4–5.0 GHz). Moreover, the height of the antenna is only 0.08 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength in free space of the central operating frequency), and the peak gain of the antenna is 10.4 dBi. It is worth mentioning that the whole design is low-cost since it is based on full FR4 substrates.

Compact wideband five‐port reflectometer based on symmetrical waveguide ring junction for synthetic microwave imaging applications

SummaryA compact and symmetrical five‐port reflectometer (FPR) for microwave imaging application is introduced in this paper. The proposed FPR shows a wide operational impedance matching bandwidth in the frequency span of 1.55–5.31 GHz (about 109.6%). It consists of three layers with a compact size of 42.4 × 42.4 × 3.2 mm3 and comprises five symmetric branch lines which were designed and optimized as a star junction topology and placed at the middle layer to realize an equivalent value of 70 dB for reflection coefficients at a center operating frequency of 2 GHz. Moreover, the measured results indicate that the FPR prototype has realized accuracies of approximately ± 120° in phase, 0.04 and 0.5 magnitudes of reflections and transmission coefficients, respectively, which are relative in parallel to the simulated and theoretical results. The proposed FPR proves higher efficacious capabilities to be used in microwave imaging for biomedical application systems.

Dual-Polarized Filtering Transmitarray Antennas With Low-Scattering Characteristic

A filtering transmitarray antenna (TAA) with high-gain in-band radiations at the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band and an out-of-band low-scattering characteristic is presented in this communication. The proposed composite TAA element consists of a dual-polarized resistive sheet, a fixed bandstop frequency-selective surface (FSS) element, and an adjustable bandpass FSS element also serving as a phase shifter. The resistive element is constructed by inserting a parallel inductor–capacitor (PLC) resonant structure into the center of a lumped-resistor-loaded metallic dipole. A transparent frequency-domain window at the center operating frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> ) is created by the PLC resonance and is further shared by both FSS elements, hence allowing for high in-band transmission herein. At frequencies below or above <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> , the whole composite TAA element acts as an absorber with the bandpass or bandstop FSS elements as the ground planes for the resistive sheet, respectively. The measured results show that the composite TAA can achieve gain-filtering responses with out-of-band suppression levels ≥25 dB, ~8 dB scattering cross section (SCS) reductions in 4–7 and 14–20 GHz, and the radiation gain of 25.3 dBi simultaneously. Because of these merits, the proposed design can relieve the stress on filtering circuit designs, also offering an attractive solution in stealth technology.

A Compact Active Ka-Band Filtenna for CubeSats

This letter describes the design of a right-hand circularly polarized planar filtenna (filter + antenna) that can reconfigure its operation between two center frequencies in the Ka-band. The filtenna structure is composed of a four-element array radiator and a reconfigurable bandpass filter, occupying an area of 31 × 14 mm. The circularly polarized array elements are fed by a sequential power divider for an enhanced polarization purity. The filter is based on a ring resonator loaded with a variable open stub. The length of the stub extends through a p-i-n diode switch, resulting in a change of the loaded reactance into the ring, and consequently tuning the filter's operating center frequency from 30.3 to 29 GHz. The proposed low-loss filtenna structure exhibits a reconfigurable fractional bandwidth up to 7.74%, a peak realized gain that can reach up to 11.5 dBic, an axial ratio of less than 1 dB, and a sidelobe level that can go as low as −12 dB. The prototype filtenna is fabricated and tested, where the measured results verify the simulated data. A figure of merit is proposed to highlight the superior performance of the presented Ka-band structure in terms of the polarization, size, reconfiguration ability, and radiation characteristics as proven by the comparison with other works in the literature.

A Novel Compact Magneto-Electric Dipole Antenna for Millimeter-Wave Beam Steering Applications

A novel compact magneto-electric (ME) dipole antenna with size of 0.31λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.31λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.12λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at central frequency herein and after), gain of around 8 dBi, and bandwidth of 39.7% is presented for millimeter-wave beam steering applications with the combination of the fractal technique and reactive impedance surface (RIS) loading. In particular, a fractal ME dipole antenna with four modified second-order Minikowski structures is firstly designed, where an aperture size of 0.38λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.38λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is achieved. Herein, the antenna gain is dropped with the size reduction. Then a capacitive RIS structure is designed and loaded to improve the antenna gain and further lower down the antenna operating frequency range. With the RIS structure, the antenna gain is increased by around 4 dB, and the operating center frequency is shifted to left side by 9.0 GHz, thus achieving a further size reduction. Simulation and measurement results are provided to demonstrate the excellent properties of the proposed antenna. Subsequently, the antenna is arranged into a 5 mm-spaced (half wavelength at 30 GHz) 16-element uniform linear array. The beam steering characteristics of the array are investigated with the influence of phase quantization errors into consideration.

A simple and compact broadband circularly polarized circular slot antenna for WLAN/WiMAX/DBS applications

Abstract A simple and compact circularly polarized broadband circular slot antenna is proposed for WLAN/WiMAX/DBS applications. The main objective of this work is to design a microstrip line fed broadband circularly polarized antenna that is achieved by introducing an asymmetric perturbation over the circular slot onto the ground plane. A broad axial ratio bandwidth is achieved by using a small circular segment cut into the circular slotted ground and by adding a short stub on the feedline. To achieve a broad impedance bandwidth, a horizontal strip onto the slotted ground is placed just above the feed line on the opposite side. The proposed antenna is fabricated with an overall dimension of 20 × 20 × 1.6 mm3 (0.34λ o × 0.34λ o × 0.03λ o, where λ o represents the free-space wavelength at the center operating frequency). It is found that the impedance bandwidth of 75.82% ranges from 3.21 to 7.13 GHz and the 3 dB axial ratio (AR) bandwidth reaches 54.27% from 3.8 to 6.6 GHz. Throughout this paper, the improvement and validation process of the proposed antenna outcomes to accomplish desired characteristics are discussed.

Simultaneous Conversion of Polarization and Frequency via Time‐Division‐Multiplexing Metasurfaces

AbstractMetasurfaces are artificially engineered two‐dimensional materials composed of sub‐wavelength meta‐atoms, which have shown unprecedented capabilities in manipulating the amplitude, phase, frequency, and polarization states of electromagnetic waves. Specifically, polarization control can be attained via suitable anisotropic, linear, and time‐invariant designs, while frequency conversion is realized via nonlinear or time‐varying platforms. Simultaneous manipulations of polarization and frequency would be of considerable practical interest in many application scenarios, but remain unattainable with current approaches. Here, a time‐division‐multiplexing metasurface is proposed to realize the simultaneous conversion of polarization and frequency. The platform relies on time‐modulated polarization switches and, by varying the duty cycle and time delays of the polarization channels, can arbitrarily rotate the polarization at the central frequency of operation, and synthesize various polarization states at selected harmonic frequencies. Theoretical predictions are validated via measurements on a prototype operating at microwave frequencies, providing the first experimental evidence of simultaneous polarization and frequency conversions via time‐division‐multiplexing metasurfaces. The outcomes open a new pathway in manipulating the electromagnetic waves via time‐varying metasurfaces, and may be of interest for a broad variety of applications in scenarios ranging from polarization imaging to quantum optics.