Open-ended Waveguide Antenna Research Articles

Dual Polarized Open-Ended Waveguide Antenna With Periodic Structure Loading for Gain Enhancement

Dual Polarized Open-Ended Waveguide Antenna With Periodic Structure Loading for Gain Enhancement

3-D Printed Circularly Polarized Open-Ended Waveguide Antenna Array Based on an In-Built Antipodal Exponential Groove Polarizer

This paper presents a novel 3-D-printed circularly polarized (CP) open-ended waveguide (OEW) antenna array. It aims to provide a lightweight scheme for OEW array design and concurrently address the high fabrication complexity problem of conventional OEW arrays. To realize these, the proposed design adopts dielectric 3-D printing technology to build the main body of the array and employs electroplating to form the waveguide walls. To attain CP radiation, an in-built antipodal exponential groove polarizer is proposed and applied to a square waveguide. With the perturbation of the grooves, degenerate modes T E 10 and T E 01 can be excited simultaneously, and their differential phase can be 90 degrees, resulting in CP radiation. Moreover, a novel matching cube based on effective medium theory (EMT) is proposed for the antenna to mitigate the reflections at the waveguide aperture and therefore realize good impedance matching. To validate the design idea, prototypes for a single element and a 2 × 2 array were fabricated and measured. Experimental results show that their weights are 15 and 76 grams, and their axial ratio bandwidths (ARBWs) are 16% (5.45-6.4 GHz) and 11.1% (5.52-6.17 GHz), respectively.

Broadband Millimeter-Wave Circularly Polarized Open-Ended Waveguide Antenna Using Stubs and Its Application in Forming an Array

A new broadband circularly polarized (CP) antenna using an open-ended waveguide is proposed in this article. By using two stubs at different positions of the open-ended waveguide, the amplitude and phase of the orthogonal fields are effectively adjusted. The method is applied to the millimeter-wave bands, and a single element as well as a four-element array are presented. Reasonable agreement between the measured and simulated results has been observed. The antenna element has a wide overlapping impedance bandwidth of 50% and a 3 dB axial ratio (AR) bandwidth of 50% covering 24–40 GHz, making it a promising candidate for wideband applications. The measured realized gains at 28 and 38 GHz are 6.7 and 6.9 dBic for an element and 12.3 and 13.9 dBic for an array, respectively.

A Dual-Wideband Cavity-Backed Antenna by Using Waveguide Transition and Short-Ended Groove Loading

A novel scheme is presented to control the frequency response on an open-ended waveguide antenna. A groove is loaded in the waveguide that is used to independently control the frequency response of the antenna without affecting the radiation pattern, and a transition is used to provide additional control. A dual-wideband antenna is taken as an example to verify the effectiveness of the scheme. To demonstrate the idea, an antenna element and its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times2$ </tex-math></inline-formula> array were designed, fabricated, and measured. Reasonable agreement between the measured and simulated results has been observed. The measured 10 dB impedance bandwidths of the lower and upper bands of the proposed element are achieved to be more than 22.2% and 14.2%, respectively, fully covering the 26/28 GHz band (24.25–29.5 GHz) and 39 GHz (37–40 GHz) band.

A Direction-Finding Antenna Inserted into the Surface of Cylindrical Conductor Body

In this letter, a direction-finding (DF) antenna inserted into the surface of a cylindrical conductor body, with the conductor material in front of the antenna, is presented. To minimize a gain reduction in the axis direction of the cylindrical conductor, an aperture of an openended waveguide antenna is modified, and the conductor body is deformed. The antenna is operated at the X-band, and its direction finding performance using an amplitude comparison method is analyzed. To verify the validation of the performance of the antenna, the analyzed results are compared to the measurement results.

Additively manufactured circularly polarized open‐ended waveguide antenna array based on a linearly tapered double‐ridge polarizer

This article presents a novel circularly polarized (CP) open-ended waveguide antenna array based on additive manufacturing technology. It is a one-dimensional four-element linear array and has a single piece configuration. Its main body is made of dielectric material and partial surfaces are coated by copper films through electroplating to form necessary metal components. Regarding to each element, it is based on a circular waveguide and employs an inbuilt linearly tapered double-ridge structure to act as a polarizer. To design such a polarizer, different shaped ridges are analyzed and a design evolution is presented and discussed. Compared to the conventional designs, the proposed element and array can avoid structure partitioning during the processing, and effectively reduce the fabrication difficulty and complexity, meanwhile, attain light weights. To validate the design idea, two prototypes corresponding to the element and the array are fabricated and tested. Experimental results indicate that their axial ratio bandwidth (ARBW) are 22% (8.9–11.1 GHz) and 11.8% (9.6–10.8 GHz), and the gain are 6.6 ± 1.1 and 10.6 ± 0.6 dBic, respectively. The proposed element and array could be potentially applied for satellite and other CP communication systems.

Microwave defectoscopy – detection of composite delamination

This paper is a short description of microwave non-destructive testing methods for composite material and presentation of a simple broadband microwave test method with an open-ended waveguide antenna for the purpose of non-destructive testing and quality evaluation of layered composite materials. Low-complexity experimental setup is shown. Research is aimed to determine the physical state of layered composite material especially in industrial pipelines. The overall applicability of the proposed system for detection purpose is demonstrated with use of experimental results. Suggestions for future researches is the need to develop more sophisticated waveguides systems to increase the scan resolution.

15–40 GHz and 40–110 GHz Double-Ridge Open-Ended Waveguide Antennas for Ultra-Wideband Medical Imaging Applications

This paper presents the design, fabrication, and measurement of two ultra-wideband doubleridge open-ended waveguide antennas (OEWAs) for emerging high-resolution millimeter-wave (mm-wave) medical imaging applications. The proposed antennas can collectively provide a 95-GHz synthetic imaging bandwidth in the mm-wave regime. The antennas feature the smallest aperture sizes while providing the widest bandwidths amongst all OEWAs reported in the literature. The proposed antennas consist of coaxial to double-ridge waveguide (DRW) transitions and free-space matching sections. Two DRWs with 8:1 single-mode bandwidth in the mm-wave regime are designed. In the transition structures, coaxial flange launchers are connected to the DRWs through customized $50-\Omega$ coaxial lines. To improve the impedance matching while meeting the fabrication requirements, an effective tuning technique is applied to adjust the input impedance of the transitions. Finally, to achieve a smooth transition and a well-matched impedance to the free space while maintaining small aperture sizes, piecewise tapered-ridge matching sections with the same aperture size as that of the designed DRWs are employed. The antennas are fabricated using the computer numerical control (CNC) milling process. Each antenna demonstrates $\left|\mathrm{S}_{11}\right|\lt -10 \mathrm{~dB}$ and stable and symmetric radiation patterns across $15-40 \mathrm{GHz}$ and $40-110 \mathrm{GHz}$ with aperture sizes of $9.47 \times 5.79 \mathrm{~mm}^{2}$ and $3.78 \times 2.27 \mathrm{~mm}^{2}$ , respectively, reporting state-of-the-art results.

Heatsink Antenna Array for Millimeter-Wave Applications

In this communication, a novel fin-shaped heatsink antenna array is designed and fabricated by 3-D printing and low-temperature cofired ceramic (LTCC) technologies. Its structure consists of 16 rectangular air cavities in the bottom base, which are used to form the open-ended rectangular waveguide antennas. Combined with the waveguide and metallic fins, a step-profiled horn is formed as the antenna element, which further enhances the radiation performance. This heatsink antenna array is soldered on an LTCC substrate and the feeding network is realized by the substrate integrated waveguides (SIWs) with numerous metallic vias. These metallic vias inherently provide an effective path for transferring the heat from chips to the heatsink. The simulated performance of this heatsink antenna array is in good agreement with the measured one. The measured broadside gain is 18.1 dBi at 60 GHz, and the 10 dB relative impedance bandwidth is 11.7%.

Electron Bernstein wave conversion of high-field side injected X-modes in QUEST

This paper presents a detailed design of the Q-shu University experimental steady state spherical tokamak’s (QUEST’s) high-field side (HFS) injection system for electron Bernstein wave (EBW) excitation and the results of an experimental comparison of the HFS eXtraordinary X-mode and low-field side (LFS) ordinary O-mode injection of 8.2 GHz radio frequency (RF) power. Waveguides, as an alternative to mirror polarizers for transmitting RF X-mode power from LFS to HFS for EBW conversion, were used instead of the installation of an RF mirror. Testing of LFS-to-HFS RF power transmission at 8.2 GHz, using an RG-50-type vacuum waveguide in a bench-scale device filled with SF6 gas at 0.03 Mpa, revealed that an RF power of 10.8 kW could traverse the fundamental electron cyclotron resonance layer for 60 s without breakdown. The short-length, open-ended waveguide antenna used in the HFS injection-induced wave diffraction reduced the efficiency of power delivery to the upper hybrid resonance (UHR) by approximately 7% at an electron temperature of 50 eV. The HFS injection was able to produce brighter camera images than the standard LFS injection. The location of the UHR, as estimated by measuring the density with an interferometer, agreed with its location as measured by plasma radiation low-field, side-edge positions shown by fast camera imaging. This indicates that the plasma was produced by mode-converted EBW. The HFS injection had an absorption efficiency of 96%, compared to 40% for LFS. A greater fluctuation of floating potential adjustable to the lower hybrid wave (LHW) was observed in the HFS case by installing a Langmuir probe, confirming that EBW conversion efficiency was higher in the HFS case. Moreover, after setting the poloidal field to BPF = 7.6 mT, plasma current (IP) in the HFS peaked at 1.3 kA, as opposed to 0.3 kA for LFS, despite LFS injection having a total power of 55 kW, compared to 40 kW for HFS. However, as the impurity level was comparatively high, it is believed that this IP is dominated by pressure-drive, which makes it difficult to analyze EBWCD. Finally, the line-integrated density in the HFS injection peaked at 1.6 × 1018 m−2, compared to 8 × 1017 m−2 in the LFS one.

Technical Note: Design of a handheld dipole antenna for a compact thermoacoustic imaging system.

Conventional antenna used in thermoacoustic imaging (TAI) is often bulky, making it difficult to translate TAI from the bench to the clinic. In this paper, we proposed a handheld dipole antenna which will be a good candidate for the construction of a compact TAI system. Here, we propose a TAI system based on a handheld dipole antenna with an aperture of 6cm and a weight of 230g. Compensation of the electric field attenuation for such a system was also investigated. Compared to the conventional open-ended waveguide and pyramidal horn antenna used in TAI, our results reveal that the electric field attenuation induced distortion is effectively reduced by using the attenuation factor 1/r2 for compensation and that the handheld dipole antenna provides the highest efficiency of microwave delivery. This study suggests that the handheld dipole antenna has the potential to be utilized for the construction of a compact TAI system, making TAI more suitable for preclinical and clinical applications.

Dual-Band Open-Ended Waveguide Feeder Antennas With Collinear Feed Design

This communication presents two classes of dual-band open-ended circular waveguide antennas with a compact collinear end-launcher-type feed design. The proposed antennas consist of an open-ended circular waveguide, radial cavities, and resonators. The collinear feed is connected to the body of the circular waveguide, providing a high power-handling capability. The proposed structures can generate a mixed mode close to TE11 on the aperture of the open-ended waveguide in both bands. As a result, stable broadside gains over each band of interest are achieved for both antennas. The proposed antennas are good candidates to be used as feeder elements in several high-gain antennas such as bull’s eye antennas, surface-wave antennas, and metasurface antennas.

A Quantum-Based Microwave Magnetic Field Sensor.

In this paper, a quantum-based method for measuring the microwave magnetic field in free space is presented by exploring atomic Rabi resonance in the clock transition of 133Cs. A compact cesium glass cell serving as the microwave magnetic field sensing head was used to measure the spatial distribution of microwave radiation from an open-ended waveguide antenna. The measured microwave magnetic field was not restricted by other microwave devices. The longitudinal distribution of the magnetic field was measured. The experimental results measured by the sensor were in agreement with the simulation. In addition, a slightly electromagnetic perturbation caused by the glass cell was investigated through simulation calculations.

Source Current Polarization Impact on the Cross-Polarization Definition of Practical Antenna Elements: Theory and Applications

With the growing interest in polarization diversity in communications and radar systems, the use of Ludwig's second and third definitions has become controversial among scientists and antenna engineers. Therefore, this paper is an attempt to clarify some of the ambiguity and confusion caused by these definitions. A detailed comparison of Ludwig's second and thirrd definitions of cross polarization, as applied to linearly polarized antennas, was performed. The results show that, in the diagonal plane, Ludwig's second definition leads to a lower crosspolarization level than the third definition for x- or y-polarized current sources. For a Huygens source, by Ludwig's third definition, the radiation pattern has a lower cross-polarization level than that obtained by Ludwig's second definition. For some applications, the antenna is usually placed in the yz plane. Therefore, new polarization bases are proposed according to which the source is used as a reference, and also on how this source is oriented in the yz plane. To complement the theoretical framework demonstrated in this contribution and to provide readers with a better and simpler understanding of the crosspolarization definition, the analysis of several practical antennas for diverse applications was presented. Numerical and measured radiation patterns of wire and printed dipoles, rectangular patch, pyramidal horn, and open-ended rectangular waveguide (OEWG) antennas were investigated according to the polarization formulations presented in this paper. In addition, a dual-polarized element and a dual-polarized active phased array at broadside were utilized to generalize the application.

Polarization-dependent bi-functional metasurface for directive radiation and diffusion-like scattering

In this paper, we design a bi-functional metasurface with different spatial distribution of reflection phase responses depending on the incident polarization. The metasurface with a thickness of only 0.067 λ0 (λ0 is the working wavelength) is constructed by unit cells composing two orthogonal I-shaped metallic structures, and the reflection phase for x- and y-linearly polarized incidence can be independently controlled by the geometric parameters. The metasurface can work as a flat parabolic reflector antenna with a maximum gain reaching about 22 dBi around 9.5 GHz, when it is illuminated by the x-polarized feed source of an offset open-ended waveguide antenna. Meanwhile, designed with randomly distributed reflection phases, the proposed metasurface can behave as an electromagnetic (EM) diffusion-like surface, which is capable of suppressing the backward scattering in a broadband from 8.5 GHz to 14 GHz for y-polarized incidence. By this strategy of EM functionality integration, a metasurface reflector antenna equipped with stealth technique to achieve simultaneously high gain and low backward scattering is obtained. Finally, experiments have been carried out to demonstrate this design principle, which agree with the simulation results. The proposed metasurface could offer a promising route for designing EM devices with polarization-dependent multi-functionalities.

Superstrate and CSRR Loaded Circularly Polarized Dual-Band Open-Ended Waveguide Antenna With Improved Radiation Characteristics and Polarization Reconfiguration Property

A circularly polarized dual-band open-ended waveguide (OEW) antenna, loaded with double complementary split-ring resonator (DCSRR) and superstrate, has been presented in this communication. The DCSRR has been placed on the aperture of a standard WR-90 waveguide, whereas the superstrate has been placed at an optimized distance from the aperture. Analysis and optimization have been carried out using Ansys high frequency structural simulator (HFSS) 14.0. Measured result shows two 10-dB return loss bandwidth with left-hand circular polarization. It has been shown that the antenna can be reconfigured for right-hand circular polarization by rotating the superstrate by 90°. The gain and front-to-back radiation ratio of the proposed antenna is higher than that of a conventional OEW antenna. It also provides less mutual coupling when used as an array element.

Application of SRR to achieve performance improvement and multi‐band characteristics in aperture antennas

This study presents a split-ring resonator (SRR) loaded tri-band open-ended waveguide (OEW) antenna that has higher gain, higher front-to-back radiation ratio and lower mutual coupling characteristics compared to a simple OEW antenna.Tri-band response of the proposed OEW antenna has been achieved by placing three SRRs on the waveguide transverse plane with uniform spacing between them. The reduced mutual coupling makes the antenna suitable for array applications. Lumpled element equivalent circuit of the proposed antenna has also been presented.

Enhancing Exposure Efficiency and Uniformity Using a Choke Ring Antenna: Application to Bioelectromagnetic Studies at 60 GHz

An effective solution for increasing the exposure uniformity and efficiency of biological samples in in vitro bioelectromagnetic experiments at 60 GHz is proposed by introducing a novel choke ring antenna (CRA). The CRA is optimized to provide a uniform exposure of samples, whose dimensions are equivalent to those of a standard 35-mm Petri dish, positioned close to the antenna aperture, i.e., 10–20 wavelengths. The antenna prototype is fabricated in metallized foam. The realized exposure efficiency of the sample exceeds 55% (if estimated for an exposure uniformity better than ${-}$ 0.5 dB). To validate the numerical results, the field intensity profiles on the surface of a high-water-content phantom have been experimentally obtained using a high-resolution infrared camera. Compared to the standard open-ended waveguide and horn antennas, typically used for millimeter-wave dosimetry, a twofold advantage of the proposed CRA is demonstrated, namely, the improvement of the exposure efficiency by a factor of 1.5 to 2 with a simultaneous reduction of the exposure distance by a factor of 8–2, respectively, depending on the type of the reference antenna. These advantages make the proposed CRA an excellent candidate for 60-GHz short-range exposure systems for in vitro bioelectromagnetic studies.

Increased Bandwidth Evanescent Open-Ended Waveguide Antenna Design Using the Imaginary Smith Chart

We present a novel antenna matching technique that uses the Imaginary Smith Chart to permit wideband matching of an evanescent open-ended waveguide antenna using a dielectric sheet air-spaced from the aperture. The fabricated antenna design is demonstrated to have a measured bandwidth of 24%, from 2.13–2.7 GHz, for reflection coefficient <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\qquad{&lt;} -\!\!10~{\rm dB}$</tex></formula> , with 2.725 GHz waveguide cutoff. The antenna's maximum aperture dimension is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt; 0.5}\lambda_{0}$</tex></formula> at the upper frequency in the bandwidth and so it is suitable for use in a wide angle scanning phased array.

Distributed Amplifiers Based on Spindt-Type Field-Emission Nanotriodes

In this paper, we discuss and analyze the design of a high-frequency, broadband distributed amplifier (DA) based on a 2-D array of field-emission nanotriodes (FENT) consisting of self-aligned gate around a nanomaterial field emitter. We propose here a physics-based device model to characterize dc properties of individual FENTs and a transmission-line circuit for evaluating and optimizing relevant ac properties, including power gain and impedance matching. Our discussion starts from the FENT array's dc characteristics and covers its radio frequency and microwave properties, considering effects of array density, geometry, FENT dimensions, and nanoemitter work function, in order to maximize power gain and bandwidth for high-frequency applications (30-100 GHz). Finally, we consider the practical design of a transmitter front end for wireless systems, combining the FENT-array DA with a tapered open-ended waveguide antenna, significantly improving matching and power radiation efficiency. Our results are of interest for imaging, sensing, satellite communications, defense, and security at 94 GHz.