Radial Line Slot Array Research Articles

A compact linearly polarized RLSA antenna integrated with circular ring resonator (CRR) for 5G mm-wave applications

This article introduces a compact linearly polarized (LP) radial line slot array antenna (RSLA) that incorporates a metamaterial of circular ring resonator (CRR) reflector for improving the bandwidth. Hence, this enables the antenna to operate at n257 (26.5–29.5), n258(24.25–27.5), and n261(27.5–28.35) frequency bands which are standardized by Federal Communications Commission (FCC) with a minor reduction of the directivity. Due to the short wavelength of the millimeter wave bands, the technique of the RLSA design has been advantageous for achieving high gain. The prototype of the RLSA antenna and the metamaterial CRR reflector are designed and fabricated at 28 GHz resonance frequency utilizing Rogers 5880 substrate and fed using an SSMA coaxial connector with an air gap cavity equivalent to half guide wavelength (λg/2) between substrate and ground plane. The method of integrating the CRR reflector with the LP-RLSA antenna delivered a passband transmission operating at (22–29.5) GHz. The proposed antenna has a similar agreement between simulated and measured for directivity and bandwidth. it achieved a peak directivity of 20 dB with a squinted main lobe at 12° and a fractional bandwidth of 29.13%. The fabricated RLSA antenna dimensions are 130 mm × 130 mm × 10.65 mm which is compact compared to conventional RLSA antennas.

Radial Line Slot Array of Low Radar Cross Section for Target Detection and Radar Stealth in Missile-Borne Sensing Systems

Radial Line Slot Array of Low Radar Cross Section for Target Detection and Radar Stealth in Missile-Borne Sensing Systems

Multibeam half radial line slot array (RLSA) antennas

ABSTRACT An original design of a multibeam Radial Line Slot Array (RLSA) antenna having two beams directed to the broadside and two beams directed to the backside is discussed in this research. The uniqueness of this design is the implementation of multibeam as a half-cut RLSA instead of a full-circle RLSA, which aims to make them more suitable for smaller devices. In order to produce a beam to the backside, the slots were placed on the backside ground plane. Furthermore, the use of the half-circle RLSA and the backside ground plane to generate the beam disrupted the power flow within the antenna’s cavity, which caused a problem of center frequency shift. A frequency design shift technique is then proposed to overcome this problem in this research with the modeling and simulation of 120 four-beams half RLSA in order to determine the most efficient model to be fabricated. The measurements carried out to verify the accuracy of the fabricated model were in good agreement with the simulation results and proved the validity of the antenna design. The result shows the possibility and effectiveness of designing four symmetrical beam antennas with gain of 8.1 dBi, directions of 60°, 150°, 210°, and 330°, and beamwidth of 22°. The gain of 8.1 dBi is 9 dB less than the gain of a single beam antenna, which is consistent with the theory of beam splitting. Moreover, the antenna offers low reflection and broad bandwidth for Wi-Fi needs.

Highly Efficient Circularly Polarized Radial Line Slot Array Antenna Using Non-Uniform Slot Density for 5G Communication System

Highly Efficient Circularly Polarized Radial Line Slot Array Antenna Using Non-Uniform Slot Density for 5G Communication System

A hemispherical near‐field focusing antenna for non‐metallic delamination detection

This paper proposes a novel hemispherical near-field focusing radial line slot array (RLSA) antenna to detect delamination within non-metallic composites. By adjusting the positions and dimensions of the antenna slots, the near-field focusing antenna produced a radiation pattern with a narrow beamwidth and a low side lobe level of the normal component of the electric field. Since the electromagnetic (EM) field of the near-field focusing antenna can be focused on the material under test (MUT), delamination within it will significantly affect the reflected information of the antenna. Simulation and measurement have shown the good focusing characteristics of the novel RLSA antenna, a low side lobe level (−19 dB) and a narrow beamwidth (6 mm) were attained. Taking glass fiber reinforced polymer (GFRP) sheets as MUTs, delamination with different thicknesses are detected using a set of mechanical scanning experimental devices. The results show that delamination as thin as 30 μm can be detected. The proposed near-field focusing antenna can detect thinner delamination inside non-metallic composites at a lower cost and in a simpler way than other microwave non-destructive testing (NDT) methods.

Increasing the Gain of Beam-Tilted Circularly Polarized Radial Line Slot Array Antennas

This article presents a new type of beam-tilted circularly polarized (CP) radial line slot array (RLSA) antennas. When the conventional beam tilting method is applied to CP-RLSA antennas, the aperture efficiency of the antenna degrades significantly due to very sparse slots in some parts of the antenna. A new method is presented to prevent this, and hence a much higher gain and aperture efficiency are achieved from the same antenna area. The key to the new method is an aggressively biased truncation of the slot layout that leaves out sparse slots. Consequently, the feed point moves closer to an edge of the TEM waveguide. A reflecting wall is introduced to prevent leakage from this edge. It is shown that the gain of RLSAs with beams tilted to 25° and 45° (measured from normal direction) can be increased by 5.5 dB (from 20.5 to 26 dBic) using the new method as opposed to the conventional method. The new concept and predicted results are validated using a prototype antenna with the beam-tilted to an angle of 25°. The aperture diameter and overall thickness of the prototype are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12\lambda _{0}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4\lambda _{0}$ </tex-math></inline-formula> , respectively, 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 operating frequency of 18 GHz. The measured results confirmed a higher gain of 26.2 dBic, an aperture efficiency of 30%, the overall efficiency of 93.2%, and sidelobe levels (SLLs) less than −25 dB at 18 GHz. The measured 10 dB return loss bandwidth of the antenna is greater than 63.7%, 3 dB axial-ratio bandwidth is 13.3%, and 3 dB gain bandwidth is 6.7%.

High-Efficiency Ka-Band Circularly Polarized Radial-Line Slot Array Antenna on a Bed of Nails

High-Efficiency Ka-Band Circularly Polarized Radial-Line Slot Array Antenna on a Bed of Nails

Dual beam half Radial Line Slot Array (RLSA) antennas

ABSTRACT Dual-beam half Radial Line Slot Array (RLSA) antennas were introduced for the first time in this article. Their uniqueness lies in the fact that only half model of RLSA antennas was used instead of full circle models to ensure they are applicable in small devices. Moreover, the slots were placed on the antenna’s background, which is unusual, to produce a beam on the backside. It is important to note that the half RLSA and the antenna background used to produce the beam affected the power flow orientation within the antennas’ cavity, thereby, causing a center frequency shift problem. This led to the proposal of a technique of frequency design shift to overcome this problem by designing and simulating 120 dual-beam half RLSA models after which the best model was fabricated and measured to verify the simulation. The results showed the possibility of designing dual-beam antennas with symmetrical beams having 10.1 dB gain, 30° and 150° directions, and 37° beamwidths. It was discovered that this gain is 3 dB lesser than the value for a single beam antenna and this is suitable based on the theory of beam splitting. Moreover, the antenna was also able to perform low reflection and quite broad bandwidth for Wi-Fi needs. The design of the antenna was further verified based on the similarity between the results of the measurement and simulation.

A Beam-Steering Solution With Highly Transmitting Hybrid Metasurfaces and Circularly Polarized High-Gain Radial-Line Slot Array Antennas

A continuous beam-steering solution for circularly polarized (CP) radial-line slot array (RLSA) antennas is presented and demonstrated with a fabricated prototype. The solution is based on the near-field meta-steering (NFMS) method, which is implemented through a pair of highly transmitting hybrid metasurfaces (HMs) that are placed above a high-gain CP RLSA antenna in the near-field region. Cells in HMs, unlike conventional metasurfaces (CMs), can provide exact or close to exact phase shift with transmission magnitude larger than −1 dB. This is achieved by combining the nonoverlapping phase ranges of two dramatically different phase-shifting cells. The RLSA is stationary, while the two HMs are rotated to steer the beam in a 2-D (azimuth and elevation) space. The measured results of the prototype demonstrate that the system can steer its beam to a maximum elevation angle of 40.6° with a maximum gain of 30.9 dBic. The axial ratio remained less than 3 dB in the 3 dB beamwidth even when the beam is steered. The height of the system is only 4.5 cm, which is much less than mechanically steered reflector antennas. Unlike electronically steered high-gain antenna arrays, this system requires only few watts of power only when rotating HMs and has zero power consumption when the beam is stationary.

Near-Field Bessel-Gauss Antenna for Nonmetal Internal Defects Detection

A radial line slot array (RLSA) is proposed for Bessel-Gauss beam generation with a narrow main beamwidth and low sidelobe characteristics for nonmetallic internal defects detection. Owing to the radial attenuation factor of Gaussian function, the sidelobe level of Bessel-Gauss beam can be suppressed. By accurately adjusting the slot position and size of the RLSA, the optimum aperture field distribution can be synthesized to generate the near-field Bessel-Gauss beam based on the projection method. The simulated/measured results have shown that the maximum nondiffraction distance of 70 mm/70 mm and the null-null beam width of the Bessel-Gauss main beam of 30 mm/30 mm are achieved at the operating frequency of 12.5 GHz/12.5 GHz, while low sidelobe levels (<−18.14 dB/−18.07 dB) are generated. Compared to other antennas for microwave nondestructive testing, the proposed RLSA has merits of low sidelobes, large E-field depth and narrow main beam; therefore, it can improve the detection performance in terms of sensitivity and depth, which can be widely, used for nonmetal internal defects detection applications.

The technique to design multibeam Radial Line Slot Array (RLSA) antennas

The Technique, to design multibeam Radial Line Slot Array (RLSA) antennas optimally, was proposed in this study, using high beam squint values to produce more slots. This is necessary to maintain gain, which dropped due to the beam splitting. A gap was also incorporated between the slots group to overcome a coupling between adjacent beams which can lessen gains. RLSA models for 42 dual and 42 triple-beams were simulated after which a prototype for each was measured to verify the simulation. The results showed the possibility of obtaining multibeam antennas with similar symmetrical beams in terms of beamwidth, gain, and direction. The gains obtained were 13.5 dBi for the dual-beam and 10.5 dBi for the triple-beam, indicating a difference of 3 and 4.77 dB, respectively, with the single-beam antennas, thereby, making them suitable for the theory of beam splitting. The antennas also have sufficient bandwidth and a good reflection coefficient.

Monopulse Radial Line Slot Array Antenna Fed by a 3-D-Printed Cavity-Ended Modified Butler Matrix Based on Gap Waveguide at 94 GHz

This article presents the design and fabrication of a monopulse radial line slot array (RLSA) antenna excited with a circular cavity connected to a modified Butler matrix at 94 GHz. The antenna consists of two pieces: the RLSA antenna implemented over a low loss dielectric substrate and a 3-D-printed Butler matrix based on gap waveguide. The interface between both parts is a circular cavity that couples two different modes into the RLSA through a coupling slot in the dielectric substrate. The coupled mode depends on the input excitation of the Butler matrix for the generation of simultaneous sum and difference radiation patterns. This interface is deeply detailed in this article, together with the design of the RLSA antenna and the integration of the full monopulse antenna. The measured S-parameters fit very well with simulations. The operation is inherently narrowband with a realized gain of 27.8 dBi at 94 GHz, a radiation efficiency of 70%, 0.3 dB axial ratio, and a maximum null relation between sum and difference patterns higher than 50 dB.

Return Loss Improvement of Radial Line Slot Array Antennas on Closed Ring Resonator Structure at 28 GHz

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The Utilization of Backgrounds as Radiating Elements to Construct Multibeam Radial Line Slot Array (RLSA) Antennas

RLSA antennas normally have a single beam produced by slots installed on their radiating element. A technique was, therefore, introduced in this study to optimally design multibeam RLSA antennas. This involved the utilization of the antennas’ background to radiate signals by installing slots on it just like the radiating element to ensure the creation of multibeam after which the effects of this method such as signal flow disturbances and gain reduction were discussed. Moreover, 105 multibeam RLSA models were designed and simulated to verify the technique developed after which a prototype of the best model was fabricated and measured to verify the simulation. The result showed it is possible to obtain multibeam antennas with similar symmetry in terms of beamwidth and directions. Furthermore, the gain recorded for beams 1, 2, 3, and 4 was 8.28 dBi, 6.28 dBi, 6.38 dBi, and 8.18 dBi respectively, and were averagely about 6 dB lower than the value for single beam RLSA antennas, therefore, they suit the theory of beam splitting. The antennas were also found to have more than enough bandwidth and good reflection coefficient and the technique’s validity was verified by a strong agreement between the simulation and measurement results.

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.

Significant Bandwidth Enhancement of Radial-Line Slot Array Antennas Using a Radially Nonuniform TEM Waveguide

Radial line slot array (RLSA) antennas have attractive features, such as high gain, high efficiency, and planar low profile, but their gain–bandwidths have been limited to less than 10%. This article presents a method to significantly increase the gain–bandwidth of RLSAs to over 30%. The key to the method is the application of a nonuniform radial TEM waveguide as opposed to the radially uniform TEM waveguide used in conventional RLSAs. Hence, the condition for maximum radiation is satisfied at a wide range of frequencies by different sections of the RLSA. To demonstrate the concept, several circularly polarized RLSA designs and one prototype are presented. The measured results of the prototype demonstrate an unprecedented 3 dB gain–bandwidth of 27.6%, a peak gain of 27.3 dBic, 3 dB axial ratio bandwidth greater than 31.1%, and a 10 dB return loss bandwidth greater than 34.8%. The overall measured bandwidth of the RLSA in which gain variation and axial ratio are within 3 dB and return loss is greater than 10 dB is from 9.7 to 12.8 GHz or 27.6%. Its extremely high measured gain–bandwidth product per unit area (GBP/A) of 88 indicates excellent overall performance in terms of bandwidth, gain, and area.

A New Size Reduction Method for Radial Line Slot Array (RLSA) Antennas

A new size reduction method was introduced in this study for the radial line slot array (RLSA) antenna with the effects of the cutting used on antennas’ performance discussed to analyze the possibility of the method’s implementation. Moreover, the RLSA model and its cut version were designed, simulated, and fabricated to verify the method and its simulation, after which their performances were measured in terms of gain, S11, and bandwidth. The analysis of the simulation and results showed the method has the ability to minimize antenna size by up to four times while maintaining its gain which was observed to have decreased by only approximately 50%. The other good effect of the method is the wider bandwidth of the antenna which was estimated to be 0.2 GHz.

Simultaneous Generation of Three OAM Modes by Using a RLSA Fed by a Waveguide Circuit for 60 GHz-band Radiative Near-field Region OAM Multiplexing

This article reports for the first time the design of a 60 GHz planar antenna system for radiative near-field region line-of-sight (LOS) link based on an orbital angular momentum (OAM) multiplexing. The antenna system is composed of a radial line slot array (RLSA) fed by a Butler network, made in post-wall waveguide technology, and located underneath the array. The network can launch different progressive phase states in the RLSA parallel-plate waveguide (PPW) to radiate three different OAM beams. To focalize each beam in the radiative near region, the use of a modified Laguerre–Gaussian aperture distribution is proposed to extend the range where the link is guaranteed. The design concept has been verified by prototyping and testing a 20 free-space wavelengths’ radius antenna. The measurements show that the proposed antenna can generate simultaneously the three OAM-mode states $n =0$ , −1, and +1.

A Radial Line Slot-Array Antenna With Low Side Lobes and a Uniform-Phase, Tapered-Amplitude Aperture Field Distribution

The paper presents a circularly polarized radial line slot array (CP RLSA) antenna with a nearly optimal monotonic variation of slot length with radius, in order to simultaneously reduce antenna side-lobe levels and to make the aperture phase distribution nearly uniform. It has additional advantages of excellent radiation efficiency, high gain and good overall bandwidth. The antenna comprises a single-layer radial transverse electromagnetic quasi-TEM waveguide with radiating slots on the aperture. The amplitude tapering is implemented by gradually varying slot lengths on the antenna aperture as a function of radial distance, utilizing a slot coupling analysis. Several antenna designs were investigated, each having a physical diameter of 345 mm ( $23\lambda _{0}$ ) and a thickness of 4.6 mm ( $0.3\lambda _{0}$ ), where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 20 GHz. A prototype was fabricated and measured, showing a good agreement between the predicted and measured results. The sidelobe levels at the operating frequency are less than −20 dB due to tapering in the near-field amplitude distribution. The measured magnitude of the input reflection coefficient ( $S_{11}$ ) of the antenna is below −10 dB within the frequency range of 19 GHz to 21 GHz. The antenna has a measured peak directivity and a peak gain of 34.3 dBic and 33.8 dBic, respectively. Both the measured 3dB directivity bandwidth and 3dB gain bandwidth are 5.4%. Aperture efficiency is 48% and radiation efficiency is 94.2% at the operating frequency. The fabricated antenna also successfully fulfilled the condition of circular polarization with an axial ratio bandwidth exceeding 5%.

An All-Metal High-Gain Radial-Line Slot-Array Antenna for Low-Cost Satellite Communication Systems

This article presents a method to produce a highly directive circularly polarized radiation beam (gain>35 dBi) from an all-metal circularly polarized radial-line slot array (RLSA) antenna. The antenna comprises a single-layer radial TEM waveguide, fully filled with air, formed between a metal ground plate and a parallel metal slotted sheet, leading to simple, low-cost fabrication. A prototype of the new antenna having a diameter of 0.4 m or $27\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 20 GHz, was fabricated and tested. Its measured peak broadside directivity and measured peak realized gain are 36.3 dBic and 35.9 dBic, respectively. The total thickness of the antenna is only 6.5 mm or $0.43\lambda _{0}$ . The aperture efficiency of the prototype is 56%, total efficiency is 95.4%, and measured 3-dB axial ratio bandwidth is 4.9 GHz (22.9%). The antenna has excellent cross-polar rejection, with a measured cross-polar level of −24.4 dB in the broadside direction. This antenna has been targeted for low-cost SATCOM terminals and wireless backhauls but due to the lack of dielectrics, it may also be useful for space and high-power microwave applications.