Slot Array Antenna Research Articles

A Uniform Heating Technique for Cavity in Volatile Organic Compound (VOC) Removal System Using Slotted Waveguide Array

In this study, two types of slotted waveguide are designed in the frequency of 2.45 GHz to improve the microwave heating uniformity of a quadrangular prism-shaped cavity in a volatile organic compound (VOC) removal system. Both types adopt the equivalent circuit approach used for a waveguide slot array antenna. The difference between the two types is the slot impedance extraction method of the waveguide slot array: one calculates the impedance taking the cavity structure into account and the other finds it in free space. Both methods show that the heating uniformity is improved by 52% compared with that of the conventional horn-type feeding structure system according to the simulation results. Even though there is no difference in the heating uniformity between the two models, it is confirmed that the slotted waveguide array feeding model designed by using the impedance data of the slot incorporating the cavity (SAWFM<sub>cavity</sub>) has about 6.35 dB better impedance matching characteristics than the other model designed by extracting the impedance data of the slot in free space (SAWFM<sub>free</sub>). Also, it is found that the SAWFM<sub>cavity</sub> shows more stable impedance characteristics with respect to the loading condition than the SAWFM<sub>free</sub>. Therefore, it is concluded that the impedance of the slot should be extracted taking the cavity into account for the design of the slotted waveguide feeding structure since it improves the reflection characteristic as well as the heating uniformity compared with the horn-type feeding structure.

Frequency-Diverse Metamaterial Cavity Antenna for Microwave Coincidence Imaging

A frequency-diverse metamaterial cavity antenna (FDMCA) that can be used for the microwave coincidence imaging is proposed in this letter. The proposed FDMCA is a slot antenna array excited by a metamaterial-based cavity, which can generate diverse radiation patterns at different frequencies. The average electric-field variation (AEV) is introduced to forecast the correlation coefficients of radiation patterns generated by the antenna. The lower the correlation coefficients are, the better the quality of the reconstructed image is. To verify the validity of the AEV and the superiority of the FDMCA, a disordered-structure-based cavity antenna (DSCA) and a lumpy-floor-based cavity antenna (LFCA) are also presented for comparison. Performances of the FDMCA, including the reflection coefficient, the radiation efficiency, and the correlation coefficients, are evaluated too. Microwave coincidence imaging experiments using the DSCA, LFCA, and FDMCA are carried out under the same condition and the target image can be reconstructed with high quality. The comparison of different imaging results illustrates the feasibility and superiority of the FDMCA. All results are validated through the simulations and measurements.

Millimeter-Wave Switchable Quadri-Polarization Array Antenna Based on Folded C-Type SIW

Array antennas with multipolarization function have important research value to improve the stable transmission of communication systems by supporting antenna diversity technology. In this letter, a millimeter-wave (mm-wave) quadri-polarization array antenna based on folded C-type substrate integrated waveguide is proposed. The operating principle is that the proposed differential feeding network can flexibly provide the required amplitude and phase difference, so that four mutually perpendicular single-branch slot array antennas can achieve multiple polarization characteristics. In addition, by removing the metal floor around the array antenna, the distortion of the antenna's main beam is suppressed. Simulation and experimental results show that the proposed quadri-polarization array antenna can provide orthogonal dual-linear polarization and dual-circular polarization radiation patterns. At the same time, it has the advantages of low profile and easy integration.

Planar Dual-Polarization Bidirectional Multibeam Array Antenna for Millimeter-Wave Applications

A millimeter-wave (mm-wave) dual-polarization bidirectional multibeam array antenna based on substrate integrated waveguide (SIW) technology is presented in this article, which can generate 16 bidirectional radiation beams with two orthogonal linear polarizations. The proposed dual-polarization bidirectional multibeam array antenna, based on a new configuration, consists of two transverse slot array antennas (TSAAs), two longitudinal slot array antennas (LSAAs), and two dual-layer <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> Butler matrices (BMs). To realize dual polarizations, a new type of TSAA is designed and combined with a conventional LSAA. For the purpose of bidirectional radiation, two types of dual-polarization array antenna (DPAA), which are realized by combining different arrangements of the TSAA and the LSAA, is composited. In addition, a dual-layer <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> BM is developed, which can excite both the TSAA and the LSAA and generate dual-polarization bidirectional multibeam. Finally, the prototype of the planar dual-polarization bidirectional multibeam array antenna is fabricated, measured, and discussed. The measured results satisfactorily validate the simulated results.

Millimeter-Wave 45° Linearly Polarized Corporate-Fed Slot Array Antenna With Low Profile and Reduced Complexity

A millimeter-wave 45° linearly polarized corporate-fed slot array antenna is presented in this communication. A key feature is the much reduced number of metallic layers and, therefore, the complexity of the array, as compared with other competitive designs. With the reduced antenna profile, high cross-polarization discrimination (XPD) and low sidelobe level (SLL) are still achieved by a combination of techniques. The back cavity of the 2 ×2 slot subarray is optimized to confine the H-field along the direction of the radiation slots, enhancing its XPD. Stubs are loaded in the same cavity to compensate for the phase imbalance, suppressing both cross-polarization and grating lobes without introducing additional metallic layers. Combining these features, the proposed array antenna demonstrates high performance with only three essential metallic layers. A prototype with 8 ×8 radiation slots at the Ka-band is implemented for demonstration. Experimental results show that the grating lobes are suppressed to below -30.5 dB, and the first SLL (FSLL) of less than -26.2 dB. XPD of more than 31.3 dB is achieved over the frequency range of 26.5-32 GHz. The peak gain of better than 25 dBi and antenna efficiency of over 71.7% are also obtained over the same frequency range.

Low-cost high-order-mode cavity backed slot array antenna using empty substrate integrated waveguide for the 5G n260 band

Low-cost high-order-mode cavity backed slot array antenna using empty substrate integrated waveguide for the 5G n260 band

Low-Sidelobe Cavity-Backed Slot Antenna Array With Simplified Feeding Structure for Vehicular Communications

In this article, low-sidelobe cavity-backed slot antenna array with simplified feeding structure for vehicular communication is proposed. Conventional low-sidelobe antennas were realized using power dividing network to obtain the in-phase and nonuniform-amplitude excitation, which causes complicated antenna's structure and design. To tackle these challenges, a simplified feeding method without using power dividing network is introduced to design the low-sidelobe slot antenna array. The slots at the top walls serve as the radiation elements, and the slots are directly fed by the electric field of the cavity mode. Nonuniform amplitude is obtained by simply modifying the slots' sizes and positions, while the in-phase excitation of the elements is remained. The nonuse of power dividers brings out a simpler antenna structure than conventional full-metal waveguide-based antennas. Besides, the full-metal structure introduces a high power-handling capacity. Then, two linear arrays with 1 × 4, 1 × 7 elements and a planar array with 5×4 elements are presented to show the design feasibility. Finally, the 5 × 4 antenna array is fabricated and measured, which can achieve 18.2 dBi gain, -20 dB sidelobe level, 94% radiation efficiency, and -42 dB cross-polarization. Good agreement between measurement and simulation verifies the feasibility of the proposed design concept.

A compact 4 × 4 SIW beamforming network for 5G applications

This paper presents a compact SIW beamforming network (BFN) for feeding a four-beam slot array antenna, which can be used in 5G mobile applications. The proposed BFN is realized with a new 4 × 4 multi-aperture coupler (MAC) and a 4 × 4 “equal length unequal width” phase shifter. The antenna operates in the range of 28–32 GHz, and generates four beams with the maximum gain of 11.2 dBi in the directions of ±15° and ±49°. To validate the design procedure and the simulation results, the proposed antenna is fabricated and tested. The measured results show that the return loss for the input ports is more than 10 dB, and the isolations between them are more than 13 dB, across the operating frequency band. The overall occupied area of the antenna structure, including the proposed BFN, is 56.5 mm × 21 mm, which shows 33% size reduction compared to similar designs.

A Compact Wideband Planar Magic Tee for Monopulse Antenna Array Applications

This letter presents a compact, wideband, planar, E-arm folded magic tee at $Ku$ -band for monopulse slotted waveguide antenna array applications. A novel impedance matching structure, an L-shaped septum, is implemented at the magic tee junction, which results in wide impedance bandwidth at all ports. The height of this septum is the same as that of the waveguide height, which allows the design to be very compact. An impedance bandwidth of 22% is achieved for a return loss of 20 dB. The magic tee is manufactured using a high-precision electric discharge machining (EDM) process and followed by the integration of subparts using silver epoxy bonding. Simulation and measured results are compared. Measured amplitude balance of < 0.1 dB, phase balance of <2°, and isolation of better than −35 dB have been achieved. The proposed design is a good technique for the design of broadband, miniaturized monopulse comparators for monopulse antenna array applications.

In‐band radar cross‐section reduction of the slot array antennas by RAM‐based frequency selective surfaces

A method for reducing radar cross-section (RCS) of the slot array antenna by utilising the radar absorbing material, while preserving the radiation performance simultaneously, is proposed and discussed. The scheme is based on the implementation of the multilayer frequency selective surface-radar-absorbing material (RAM) capable of operation over a wide frequency band. The use of radar absorbing material on an antenna’s radiation screen causes a change in surface current, resulting in the radiation pattern of the antenna. Therefore, by designing the coating pattern of the radar absorbent material as a substrate and a capacitive patch as a unit cell on the antenna board, the reduction of 19 dB RCS at X-band and minimum antenna gain loss (3dB) is achieved. To demonstrate the proposed solution, a 30-cm diameter slot array antenna, which is considered as a test case, is coated by RAM and radar cross section reduction (RCSR) is dramatically accomplished over a frequency band ranging from 8 to 12 GHz. It is worth mentioning that the obtained RCSR at 9.4 GHz is as much as 19 dB. Subsequently, the proposed method can be a candidate for reduction of RCS in slot array antennas, considering the remarkable RCSR and acceptable effect on radiation characteristics.

Compact Relativistic Magnetron With Omnidirectional Radiation Through a Slotted Waveguide Array Antenna

A compact relativistic magnetron (RM) system with diffraction output is proposed, whose novelty lies in the omnidirectional radiation through the slotted waveguide array antenna. In the array antenna, a periodically slotted ridged circular waveguide is employed to obtain omnidirectional radiation and decrease its radius. Meanwhile, the RF field is directly coupling and radiating without complex mode conversion. Moreover, the interaction resonant system applies a ten-cavity rising-sun slow-wave structure to optimize the dispersion characteristics of the operating mode. The particle-in-cell simulations demonstrate that the RM could achieve 70% device efficiency and gigawatt radiation with an operating voltage of 400 kV. Besides, the output RF field is omnidirectional radiating with a gain up to 12.77 dBi at the operating frequency of 1.32 GHz, which is likely to be used in the high-power microwave area defense.

Cutting Technique for Constructing Small Radial Line Slot Array Antennas

The design of small radial line slot array (RLSA) antennas requires more than simply decreasing the antenna radius, which leads to the problem of high reflection. To overcome this inconvenience, we introduce a technique for constructing small RLSA antennas with low reflection by cutting full-sized ones. We designed 42 ordinary full-size RLSA models with a radius of 75 mm and then cut them into 42 half RLSAs and 42 quarter RLSAs. The areas of the half RLSAs and the quarter RLSAs are equal to those of full-sized RLSAs with radii of 53 mm and 37 mm, respectively. Our results show that the gain of the quarter RLSA is less than that of the full RLSA by only 1 dB, whereas theoretically, the gain should decrease by 6 dB due to the size reduction. Interestingly, the gain of the half RLSAs is greater that of the full RLSA by 1 dB, whereas theoretically, a decrease of 3 dB was expected due to the size reduction. The half RLSA and the quarter RLSA also perform well in terms of reflection coefficient and bandwidth, thus demonstrating the efficacy of the cutting technique in constructing small low reflection RLSAs.

Compact SIW 2-D Butler Matrix and Its Multibeam Application

This letter presents a compact 2-D Butler matrix (BM) realized by multilayer substrate integrated waveguide (SIW) technology. The 2-D BMs in the open literature suffer from either bulky size or poor integration with the radiation portion. Facing this issue, a new SIW 2-D BM is developed and realized in planar configuration easily integrated with the slot antenna array. The key point of this letter is to design planar 2-D components, including 2-D couplers, 2-D crossovers, and 2-D phase shifters, of the proposed SIW 2-D BM, which can perform coupling, intersection, or phase shifting in both E- and H-planes. The proposed SIW 2-D BM also has the merit of ease integration with radiation portion and it is used to build a compact 2-D multibeam antenna in this letter. Simulation, fabrication, and experiments are conducted to verify the performance of the realized 2-D multibeam antenna.

Conversion Donut-Shaped Pattern to Directive Without Using Any Mode Converter

In this paper, an electromagnetic diode with TEM mode, such as MILO, is connected directly to a Dual Mirrored Slotted Array Antenna (DMSAA). To convert a donut-shaped pattern of the electromagnetic source into a directive pattern, mode converters have been used in the past. But their losses, weight, size, and cost additions impact negatively on total system performance. Due to not using any mode converters, this is useful. Given the input is an electromagnetic diode with a TEM output mode, a large bandwidth is unnecessary. Therefore, slot antennas are used. Usually, array antennas were commonly used to increase the directivity and beamforming at the output of mode converters. To convert a donate-shaped pattern into a directive, half of the aperture fields must be rotated 180°. Here, the diode outlet is connected to the DMSAA with an inherent phase difference of 180° of the electric fields. For this purpose, a power divider and a pair of narrow wall slotted array antennas (NWSAA) have been used. The antenna is simulated at 10GHz frequency. The results show a fully directive beam with a side lobe level (SLL) below -10dB. Also, S11 is -16.5dB, at 10GHz frequency. Because the mode converter is completely removed, this structure is very suitable for compact applications.

5G dual-band slotted SIW array antenna

A dual-band slotted substrate-integrated waveguide four-element array antenna for the 5G communication system is presented in this manuscript. Two longitudinal slots are responsible for generating frequency bands of 28 and 38 GHz. The proposed antenna is designed on the substrate duroid 5880/Rogers having a loss tangent and dielectric constant of 0.003 and 2.2, respectively. The developed single-element design at 28 GHz provides 6.35 dBi gain, while at 38 GHz it provides 7.3 dBi gain and the simulation is carried out with CST Microwave Studio, 2018. To accomplish high gain, an optimized four-element array antenna is designed with a parallel feeding network on the same substrate that covers 28 GHz (27.6–28.1 GHz) and 38 GHz band (37.9–38.69 GHz). The designed antenna array attains the radiation efficiency of 88.08% with 12.7 dBi gain at 28 GHz and the efficiency of 84.44% with 15.5 dBi gain at 38 GHz band.

Analysis of Transmission Loss and Boresight Error of a Curved FSS Radome-Enclosed Antenna

In this paper, we numerically study a curved frequency selective surface (FSS) radome, which encloses a waveguide slot array antenna operating at 10GHz, using the ray tracing technique and flat model. The transmission loss (TL) and boresight error (BSE) are calculated for various degrees of freedom, such as elevation and azimuth angular scanning or gimbal systems of array antennas to examine the electromagnetic properties of the curved FSS radome. Our calculations of radiation patterns, TL, and BSE for a multi-layered dielectric radome are compared with those of a commercial EM solver for validation. Importantly, we quantify phase distortions, incurred by the curved FSS radome, using the insertion phase delay (IPD) of transmitted fields on the radome surface. Thereby, we demonstrate that the BSEs strongly depend on (1) the spatial distribution of phase distortions on the radome surface and (2) their average level. The present method is highly suited for analyzing radomes with arbitrary surface patterns inserted.

Advanced high-gain slot antenna arrays for 5G and radar applications

This paper presents an advanced design of high-gain slot antenna array at K-band using slots as radiating elements serially fed by coplanar waveguide (CPW). The arrays consist of identical slots of rectangular shape positioned symmetrically relative to the CPW feeding line. Firstly, the linear arrays of 14 slots are examined considering mainly their bandwidth and radiation characteristics. In addition, two identical linear sub - arrays of 14 slots are investigated when they have separate feeding in the form of two generators for each sub - array. Last, a CPW T-junction is employed to feed the antenna consisting of 2 x 14 slots which resulted in a wide operating bandwidth and maximum gain of 21.0 dBi which proved to be 2.25 dB less gain than with independent feeding. In order to enhance the antenna gain, both arrays are terminated with open-circuited stubs, so that the energy remaining after the last array element is reflected from the stub and re-radiated through the slot arrays. The length of the stubs is optimized to provide that the reflected wave is in phase with the forward-traveling waves at all the slot locations. In that way, very little energy is wasted and consequently the antenna gain is increased. The feed simplicity and uniplanar configuration of the slot arrays, designed for the frequency range 24.25-27.5 GHz, makes them attractive for radar sensors and high capacity 5G technology applications.

Technology Assessment of Aperture Coupled Slot Antenna Array in Groove Gapwaveguide for 5G Millimeter Wave Applications

A compact triple-layer series fed slot unit array using Groove Gap Waveguide (GGW) technology for 5G millimeter-wave applications is presented in this paper. The design employed a two-step coupling mechanism for the radiating slots. The aperture coupling design when combined with the groove gapWaveguide (GGW) technology allows achieving three different goals: First, a reduction of the array size in the transversal direction, so more unit arrays can be added without grating lobes. Secondly, low insertion losses with high radiation efficiency. And third, a reduction of the manufacturing complexity with good stability against fabrication tolerances of up to 0.1 mm, making the design feasible to be massively deployed. The antenna was fabricated and measured showing good agreement with the numerical simulation results, the antenna provides a peak realized gain of 12.15dB at the central frequency of operation and a fractional bandwidth (FBW) of 9%.

A new feeding topology with internal 180° phase reversal for wideband series‐fed slot array antennas

AbstractThis paper proposes a new feeding topology with internal 180° phase reversal for wideband series‐fed slot array antennas. As a demonstration, a serial fed, half‐wavelength separated, 7‐element array is designed at 5.8 GHz. Comparing with conventional series‐fed arrays, which require one‐wavelength separation, the phase difference between adjacent elements varies less with frequency. Thus, the proposed array has more stable beam pointing and wider 1 dB gain bandwidth. A prototype was fabricated and measured to validate the performance of the feeding topology. A wide operating bandwidth of 22.4% for S11 &lt; −10 dB, a 1 dB gain bandwidth of 14% and bi‐directional peak gain of 10.01 dBi are achieved with the array length of 2.7λ0. The proposed feeding topology shows its potentials in realizing signal coverage on some special occasions, such as coal mines and tunnels.

Millimeter-Wave Near-Field-Focused Full 2-D Frequency Scanning Antenna Array With Height-Modulated-Ridge Waveguide

A millimeter-wave near-field-focused (NFF) full 2-D frequency-scanning antenna array is presented in this article. The proposed antenna is achieved by combining an NFF ridged-waveguide slot array with a double-layer folded focused progressive feeding network. The linear ridged-waveguide slot array antenna is designed with a height-modulated ridge to focus on the power in one direction. The folded feeding line with different length is used to generate the desired focused phase and frequency-dependent progressive phase shift in the other direction. In this case, as the working frequency is swept in the considered range, the inherent frequency-dependent behavior of the linear NFF leaky-wave antenna (LWA) allows a single-scanning sweep in one direction, whereas the focused progressive feeding network ensures multiple-scanning sweeps in the other direction. A full 2-D electronic scanning with no coverage blindness in the scanning area is achieved. To the best of our knowledge, the proposed NFF antenna array is the first design to achieve the full 2-D scanning focus in the near-field (NF) region only by sweeping the frequency, which means that the testing information in the NF region can be directly obtained with a certain band of frequency. This type of antenna is a good candidate in NF fast-scanning applications, e.g., electromagnetic imaging/detecting systems.