Antenna Design for Microwave and Millimeter Wave Applications III: Latest Advances and Prospects

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Electrical, Electronics and Communications Engineering".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 24997

Special Issue Editor

School of Electronic and Electrical Engineering, Hongik University, Seoul 04066, Republic of Korea
Interests: electrically small antennas for wireless communications; reader and tag antennas for RFID; on-glass and conformal antennas for vehicles and aircraft; array antennas for GPS applications
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Special Issue Information

Dear Colleagues,

Until recently, substantial efforts have been devoted to new approaches and attempts in the design of antennas for microwave and millimeter-wave applications. For example, advanced technologies such as antenna miniaturization, array optimization, and bandwidth enhancement have been extensively studied for over a decade, and are being applied to commercial applications such as 4G/5G mobile communications, autonomous driving, or military applications including radar, direction finding, and anti-jamming.

However, as these technologies have recently been employed in small mobile devices, the size and geometry of the antennas are more limited so that they can be mounted in a more compact space with better radiation performance. Accordingly, advanced antenna designs using novel approaches to this issue are required.

This Special Issue aims to collect relevant papers describing the latest advances and prospects in antenna design for microwave and millimeter-wave applications.

The fields of interest for this Special Issue include, but are not limited to, design methods of antennas such as miniaturization, optimization, and array. You are invited to submit a contribution of either an original research article or a review article to this Special Issue.

Prof. Dr. Hosung Choo
Guest Editor

Manuscript Submission Information

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Keywords

  • antenna design and optimization
  • antenna arrays
  • 5G communications
  • antenna measurement
  • manufacturing methods
  • miniaturized microwave and millimeter-wave antennas
  • radio propagation
  • automotive antennas
  • radar antennas

Published Papers (15 papers)

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Research

12 pages, 4795 KiB  
Article
Ferrite-Loaded Inverted Microstrip Line-Based Artificial Magnetic Conductor for the Magnetic Shielding Applications of a Wireless Power Transfer System
Appl. Sci. 2023, 13(18), 10523; https://doi.org/10.3390/app131810523 - 21 Sep 2023
Viewed by 552
Abstract
In this paper, we propose a ferrite-loaded inverted microstrip line (IML)-based artificial magnetic conductor (AMC) with a novel design that can provide complete magnetic shielding at the backside of the transmitting (Tx) coil while slightly improving the power transfer efficiency (PTE) of a [...] Read more.
In this paper, we propose a ferrite-loaded inverted microstrip line (IML)-based artificial magnetic conductor (AMC) with a novel design that can provide complete magnetic shielding at the backside of the transmitting (Tx) coil while slightly improving the power transfer efficiency (PTE) of a wireless power transfer system (WPTS). The target frequency of the WPTS application is approximately 6.78 MHz. In the proposed design, the AMC is placed behind the Tx coil, and its magnetic shielding capability and PTE performance were verified through simulations and measurements. The size of the proposed AMC is 528 × 528 × 6.6 mm3. The measurement results verified that, compared with the Tx coil without an AMC surface, the proposed ferrite-loaded IML-based AMC can provide complete magnetic shielding while improving the PTE of the WPTS by approximately 8.05%. Full article
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10 pages, 3956 KiB  
Communication
Compact Dual-Circularly Polarized Traveling-Wave Series-Fed Patch Array for Use as a Non-Linear Tag Antenna for Bio-Sensing Applications
Appl. Sci. 2023, 13(13), 7729; https://doi.org/10.3390/app13137729 - 29 Jun 2023
Viewed by 808
Abstract
This paper proposes a compact K-band dual-circularly polarized antenna that can be implemented on a non-linear tag based on third-order intermodulation (IM3) for bio-sensing applications. The proposed antenna has the characteristics of being low-profile and lightweight, with opposite circular polarizations (CP) between ports. [...] Read more.
This paper proposes a compact K-band dual-circularly polarized antenna that can be implemented on a non-linear tag based on third-order intermodulation (IM3) for bio-sensing applications. The proposed antenna has the characteristics of being low-profile and lightweight, with opposite circular polarizations (CP) between ports. The non-linear tag-based bio-sensing scenario utilizes K-band millimeter wave frequencies, which allows for compact non-linear tags for attachment to the body. Also, the proposed antenna features dual-CP, which are for the reception and re-radiation of incident transmit signals and the IM3 responses, respectively. To this end, a two-port traveling-wave series-fed patch array with coplanar proximity coupling is designed. Here, to minimize the size of the antenna, we use only four circular patch elements with a modified diamond-shaped microstrip feedline. Through simulation and measurement, we demonstrate that the proposed antenna has an axial ratio of less than 3 dB from 23.25 GHz to 24.1 GHz, with the reflection coefficients below −10 dB and port-to-port coupling below −15 dB. These results indicate the potential utility of the proposed antenna as a tag antenna for non-linear detection-based bio-sensing applications. Full article
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14 pages, 10034 KiB  
Article
Compact Amplitude-Only Direction Finding Based on a Deep Neural Network with a Single-Patch Multi-Beam Antenna
Appl. Sci. 2023, 13(12), 7229; https://doi.org/10.3390/app13127229 - 16 Jun 2023
Viewed by 906
Abstract
In this paper, a compact direction-finding system based on a deep neural network (DNN) with a single-patch multi-beam antenna is proposed. To achieve multiple beams, the patch is divided into four sectors by metal vias, and the pattern is tilted in the theta [...] Read more.
In this paper, a compact direction-finding system based on a deep neural network (DNN) with a single-patch multi-beam antenna is proposed. To achieve multiple beams, the patch is divided into four sectors by metal vias, and the pattern is tilted in the theta direction due to the coupled mode of the divided patch structure. This design allows a single-patch multi-beam antenna to generate eight beams using a combination of four excitation ports assigned to the four-divided sectors. This approach increases the amount of training data required for DNN-based direction finding without requiring multiple antennas, thus improving the accuracy of estimation probability. Furthermore, compared to our previous work, the parasitic elements are applied to improve the estimation probability by reducing the beamwidth of the antenna. The size of the antenna for the proposed direction-finding system is 0.44λ × 0.44λ × 0.008λ with a 97.7% estimation probability. The direction-finding performance has been validated and compared through the experiment to show higher accuracy with compactness than previously studied works. Full article
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13 pages, 3768 KiB  
Article
Rapid Prototyping of Reduced-Height Dielectric Lens with One-Take 3D Printing for Antenna Directivity Enhancement
Appl. Sci. 2022, 12(22), 11811; https://doi.org/10.3390/app122211811 - 20 Nov 2022
Cited by 3 | Viewed by 1782
Abstract
In this work, we present a method for designing a dielectric lens with a reduced height that is easily printed with one-take 3D printing. For the first time, we prove that the configuration of a printout made of resin material can be modified [...] Read more.
In this work, we present a method for designing a dielectric lens with a reduced height that is easily printed with one-take 3D printing. For the first time, we prove that the configuration of a printout made of resin material can be modified for effective permittivity variation and apply the technique to a lens antenna design. The lens is printed with SLA printing and mounted on top of a conventional patch antenna, resulting in a 6.87 dB directivity improvement. The height of the proposed lens is reduced by about 15% compared to the reference lens design. The final proposed lens antenna operates at 5.8 GHz, with a height and diameter of 1.35 λ and 1.35 λ, respectively. A prototype was built, and all of the computed expectations from the full-wave electromagnetic simulations in this work were verified experimentally. Full article
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17 pages, 103440 KiB  
Article
Integrated Module Antenna for Automotive UWB Application
Appl. Sci. 2022, 12(22), 11423; https://doi.org/10.3390/app122211423 - 10 Nov 2022
Cited by 1 | Viewed by 1572
Abstract
In this paper, an integrated module antenna for automotive UWB application is proposed. The target applications of the proposed antenna are for UWB localization and rear passenger detection. The purpose of this work is to design an antenna with a wide and narrow [...] Read more.
In this paper, an integrated module antenna for automotive UWB application is proposed. The target applications of the proposed antenna are for UWB localization and rear passenger detection. The purpose of this work is to design an antenna with a wide and narrow beamwidth that can be attached to the exterior/interior of a vehicle for simultaneous UWB localization and a rear passenger detection sensor with a single-module substrate in a limited space. For UWB localization, the wide beam coverage is required so the antenna receives the signal from any incident angle in horizontal plane. Meanwhile, the rear passenger detection sensor requires a relatively narrower beamwidth than the localization antenna for accurate detection within the vehicle. To integrate two different antennas into a single compact module substrate, modified ground stubs and parasitic radiators are applied. The size of the entire antenna structure is 35 mm × 65 mm × 1.156 mm. The proposed antenna designed on the multi-layered FR-4 substrate with a dielectric constant of 4.3. The bandwidth of the monopole is 6.14~8.24 GHz, and the patch array is 6.95~8.47 GHz. The isolation between the monopole and the patch array is less than −23 dBi in the target band. The performance of the proposed antenna is verified with simulation and measurement. In addition, a simulation of the proposed antenna with the real vehicle model is also conducted to verify the feasibility on actual vehicle. Based on this work, the proposed antenna can be applied to multi-function antenna for automotive application with low cost. Full article
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15 pages, 7002 KiB  
Article
Wideband Ring-Monopole Flexible Antenna with Stub for WLAN/C-Band/X-Band Applications
Appl. Sci. 2022, 12(21), 10717; https://doi.org/10.3390/app122110717 - 22 Oct 2022
Cited by 4 | Viewed by 1493
Abstract
In this paper, we designed a flexible antenna operating in the WLAN/C-band/X-band and analyzed the antenna bending characteristics. It is advantageous to have a wide bandwidth because the resonant frequency of the flexible antenna can be changed when it is bent. The proposed [...] Read more.
In this paper, we designed a flexible antenna operating in the WLAN/C-band/X-band and analyzed the antenna bending characteristics. It is advantageous to have a wide bandwidth because the resonant frequency of the flexible antenna can be changed when it is bent. The proposed antenna was designed based on a ring monopole antenna with broadband characteristics. Slots and t-strip lines to the ring, stubs to the feed, and stepped structures to the ground plane were added to increase bandwidth. As a result of analyzing the characteristics of the proposed antenna when bent through the S-parameter, it was confirmed that the proposed antenna is suitable at the target frequency, even if it is bent. The size of the antenna is 0.256 λ × 0.32 λ × 0.0016 λ (32×40×0.2 mm3) at 2.4 GHz, and the antenna bandwidth is 15.68% (2.36 GHz~2.87 GHz) at 2.615 GHz and 111.69% (3.4 GHz~12 GHz) at 7.7 GHz. Full article
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18 pages, 5868 KiB  
Article
Dual Band Antenna Design and Prediction of Resonance Frequency Using Machine Learning Approaches
Appl. Sci. 2022, 12(20), 10505; https://doi.org/10.3390/app122010505 - 18 Oct 2022
Cited by 17 | Viewed by 3824
Abstract
An inset fed-microstrip patch antenna (MPA) with a partial ground structure is constructed and evaluated in this paper. This article covers how to evaluate the performance of the designed antenna by using a combination of simulation, measurement, creation of the RLC equivalent circuit [...] Read more.
An inset fed-microstrip patch antenna (MPA) with a partial ground structure is constructed and evaluated in this paper. This article covers how to evaluate the performance of the designed antenna by using a combination of simulation, measurement, creation of the RLC equivalent circuit model, and the implementation of machine learning approaches. The MPA’s measured frequency range is 7.9–14.6 GHz, while its simulated frequency range is 8.35–14.25 GHz in CST microwave studio (CST MWS) 2018. The measured and simulated bandwidths are 6.7 GHz and 5.9 GHz, respectively. The antenna substrate is composed of FR-4 Epoxy, which has a dielectric constant of 4.4 and a loss tangent of 0.02. The equivalent model of the proposed MPA is developed by using an advanced design system (ADS) to compare the resonance frequencies obtained by using CST. In addition, the measured return loss of the prototype is compared with the simulated return loss observed by using CST and ADS. At the end, 86 data samples are gathered through the simulation by using CST MWS, and seven machine learning (ML) approaches, such as convolutional neural network (CNN), linear regression (LR), random forest regression (RFR), decision tree regression (DTR), lasso regression, ridge regression, and extreme gradient boosting (XGB) regression, are applied to estimate the resonant frequency of the patch antenna. The performance of the seven ML models is evaluated based on mean square error (MSE), mean absolute error (MAE), root mean square error (RMSE), and variance score. Among the seven ML models, the prediction result of DTR (MSE = 0.71%, MAE = 5.63%, RMSE = 8.42%, and var score = 99.68%) is superior to other ML models. In conclusion, the proposed antenna is a strong contender for operating at the entire X-band and lower portion of the Ku-band frequencies, as evidenced by the simulation results through CST and ADS, it measured and predicted results using machine learning approaches. Full article
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9 pages, 5085 KiB  
Communication
Target Classification Using Frontal Images Measured by 77 GHz FMCW Radar through DCNN
Appl. Sci. 2022, 12(20), 10264; https://doi.org/10.3390/app122010264 - 12 Oct 2022
Cited by 1 | Viewed by 1139
Abstract
This paper proposes a target classification method using radar frontal imaging measured by millimeter-wave multiple-input multiple-output (MW-MIMO) radar through deep convolutional neural networks. Autonomous vehicles must classify targets in front of the vehicle to attain better situational awareness. We use 2D sparse array [...] Read more.
This paper proposes a target classification method using radar frontal imaging measured by millimeter-wave multiple-input multiple-output (MW-MIMO) radar through deep convolutional neural networks. Autonomous vehicles must classify targets in front of the vehicle to attain better situational awareness. We use 2D sparse array radar to capture the frontal images of objects on the road, such as sedans, vans, trucks, humans, poles, and trees. The frontal image includes information regarding not only the shape of a target but also the reflection characteristics of each part of the target. The measured frontal images are classified by deep convolutional neural networks, and the classification rate yielded 87.1% for six classes and 92.6% for three classes. Full article
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9 pages, 2660 KiB  
Article
Investigation of the Feasibility of Extracting the Characteristics of Sealed Boxes Using an Automotive FMCW Radar
Appl. Sci. 2022, 12(20), 10243; https://doi.org/10.3390/app122010243 - 12 Oct 2022
Viewed by 1026
Abstract
This paper investigates the feasibility of extracting the characteristics of sealed paper boxes based on range profiles using a millimeter-wave automotive FMCW radar. Radar is one of the key basic sensors for driving assistance and collision avoidance. Target classification using radar has been [...] Read more.
This paper investigates the feasibility of extracting the characteristics of sealed paper boxes based on range profiles using a millimeter-wave automotive FMCW radar. Radar is one of the key basic sensors for driving assistance and collision avoidance. Target classification using radar has been studied extensively, yet the detection of sealed material requires further investigation to improve situational awareness for better judgment. We suggest the classification of sealed paper boxes with different materials based on range-profile plots, which capture wave reflection from the box and wave attenuation when traveling through a lossy material. We measure the range profiles of sealed boxes encompassing paper in five different quantities using a millimeter-wave FMCW radar. A theoretical approach is used as a proof of concept, which supports the results of the range-profile measurements. The range profiles of the box with several other materials are also obtained and their characteristics are compared. Full article
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9 pages, 7790 KiB  
Communication
Design of a Compact Indirect Slot-Fed Wideband Patch Array with an Air SIW Cavity for a High Directivity in Missile Seeker Applications
Appl. Sci. 2022, 12(19), 9569; https://doi.org/10.3390/app12199569 - 23 Sep 2022
Viewed by 1409
Abstract
This research proposes a compact indirect slot-fed wideband patch array antenna for a missile seeker application. The proposed single antenna consists of three dielectric layers for a radiator, an air substrate-integrated waveguide (SIW) cavity, and an indirect feeding network. The rectangular patch is [...] Read more.
This research proposes a compact indirect slot-fed wideband patch array antenna for a missile seeker application. The proposed single antenna consists of three dielectric layers for a radiator, an air substrate-integrated waveguide (SIW) cavity, and an indirect feeding network. The rectangular patch is used as a radiator on the first substrate layer, and the air SIW cavity (ASIWC) is employed to obtain high directivity and low mutual coupling characteristics in the second substrate layer. In the third layer, an indirect feeding structure is used to achieve the wideband characteristics in the Ka-band. The single element is extended to a 4 × 1 linear array with fabrication, and the fabricated array characteristics are measured in a full anechoic chamber. The measured operating fractional frequency bandwidth is 9.2%, and the measured array gain is 11.7 dBi at the bore-sight direction (θ0 = 0). Full article
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10 pages, 3322 KiB  
Article
Multi-Band Array Antenna Sharing a Common Aperture with Heterogeneous Array Elements
Appl. Sci. 2022, 12(18), 9348; https://doi.org/10.3390/app12189348 - 18 Sep 2022
Cited by 1 | Viewed by 1603
Abstract
This paper proposes a multi-band array antenna that shares a common aperture with heterogenous array elements. The multi-band array antenna includes one printed dipole antenna for the S-band and 3 × 3 array E-shaped patch antennas for the X-band. The current directions of [...] Read more.
This paper proposes a multi-band array antenna that shares a common aperture with heterogenous array elements. The multi-band array antenna includes one printed dipole antenna for the S-band and 3 × 3 array E-shaped patch antennas for the X-band. The current directions of the printed dipole and E-shaped antenna are orthogonal to each other, which properly diminishes the mutual coupling interference. To decrease the mutual coupling interference among the X-band components, we placed cavities using multiple vias surrounding the X-band components. To check the validity of the proposed design, the unit-cell was expanded to a 12 × 12 X-band array configuration, and then the beam steering properties were examined. The proposed antenna’s average gains are 5.2 dBi in the S-band and 5.2 dBi in the X-band. The bore-sight gain of the extended array configuration on the ship mast is 35.6 dBi. The results confirm that the proposed design is suitable for MFR applications even in a shared aperture. Full article
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9 pages, 2723 KiB  
Article
Design of a Planar Antenna Array with Wide Bandwidth and Narrow Beamwidth for IR-UWB Radar Applications
Appl. Sci. 2022, 12(17), 8825; https://doi.org/10.3390/app12178825 - 02 Sep 2022
Cited by 2 | Viewed by 3515
Abstract
This paper presents the design of an H-band planar antenna array with broad bandwidth and narrow beam width for an IR-UWB radar application. The basic single wideband microstrip antenna is achieved by adding slots and the inset-fed technique. Then, we proposed a planar [...] Read more.
This paper presents the design of an H-band planar antenna array with broad bandwidth and narrow beam width for an IR-UWB radar application. The basic single wideband microstrip antenna is achieved by adding slots and the inset-fed technique. Then, we proposed a planar antenna array on a limited area that obtains an essential narrow beamwidth for the radar of a Non-Contact Human Vital Signs Detection application. The experimental and simulated results of the microstrip antenna array are in good agreement. The measured results show that the proposed antenna array exhibits a wide impedance bandwidth of 10.7% at around 7.5 GHz and a narrow beamwidth of 40 degrees vertically and 50 degrees horizontally, respectively. Full article
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9 pages, 3144 KiB  
Article
Study of an Atmospheric Refractivity Estimation from a Clutter Using Genetic Algorithm
Appl. Sci. 2022, 12(17), 8566; https://doi.org/10.3390/app12178566 - 26 Aug 2022
Cited by 1 | Viewed by 1058
Abstract
In this paper, a method for estimating atmospheric refractivity from sea and land clutters is proposed. To estimate the atmospheric refractivity, clutter power spectrums based on an artificial tri-linear model are calculated using an Advanced Refractive Prediction System (AREPS) simulator. Then, the clutter [...] Read more.
In this paper, a method for estimating atmospheric refractivity from sea and land clutters is proposed. To estimate the atmospheric refractivity, clutter power spectrums based on an artificial tri-linear model are calculated using an Advanced Refractive Prediction System (AREPS) simulator. Then, the clutter power spectrums are again obtained based on the measured atmospheric refractivity data using the AREPS simulator. In actual operation, this spectrum from measured reflectivity can be replaced with real-time clutter spectrums collected from radars. A cost function for the genetic algorithm (GA) is then defined based on the difference between the two clutter power spectrums to predict the atmospheric refractivity using the artificial tri-linear model. The optimum variables of the tri-linear model are determined at a minimum cost in the GA process. The results demonstrate that atmospheric refractivity can be predicted using the proposed method from the clutter powers. Full article
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11 pages, 7531 KiB  
Article
Design of an Interface Layer Using CPW between an Array Antenna and TRM in X-Band Radar Systems to Minimize Leakage Fields and Improve Transmission Characteristics
Appl. Sci. 2022, 12(17), 8514; https://doi.org/10.3390/app12178514 - 25 Aug 2022
Cited by 2 | Viewed by 1527
Abstract
In this paper, we propose an interface layer using the coplanar waveguide (CPW) between an array antenna and transmitting receiver modules (TRMs) for X-band military ship radar systems. To improve transmission characteristics, the interface layer with the CPW has three transition parts: Transition [...] Read more.
In this paper, we propose an interface layer using the coplanar waveguide (CPW) between an array antenna and transmitting receiver modules (TRMs) for X-band military ship radar systems. To improve transmission characteristics, the interface layer with the CPW has three transition parts: Transition part A is between the sub miniature push-on (SMP) connector and the interface layer. Transition part B is the CPW in which the thickness gradually increases. Transition part C is for connecting the interface layer and the antenna. The measured reflection and transmission coefficients of the fabricated interface layer are −22.4 dB and −0.82 dB, respectively. To verify the proposed interface layer, we then apply the layer to a 2 × 2 X-band array antenna and measure the array antenna characteristics, such as reflection coefficients, array antenna gain, and half-power beam widths (HPBWs). The measured reflection coefficient is under −10 dB from 8.6 GHz to 10.2 GHz, and the bore-sight array gain of the 2 × 2 array antenna is 10.5 dBi at 9.5 GHz. In addition, the measured HPBWs under the same conditions are 47.8° and 39.1° in the zx- and zy-planes, respectively. The results demonstrate that the proposed interface layer using the CPW is suitable for X-band radar systems. Full article
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12 pages, 2535 KiB  
Article
Steering of Beam Using Cylindrical Arrangements in a Metallic Parallel Plates Structure Operating over Ku-Band
Appl. Sci. 2022, 12(12), 6074; https://doi.org/10.3390/app12126074 - 15 Jun 2022
Cited by 2 | Viewed by 1457
Abstract
A novel flat beam steering prototype based on the specific arrangement of a cylindrical unit cell is designed, manufactured and tested. The wideband and broad scanning capability is demonstrated at the Ku-band. We have considered two configurations, first with circular rings (CR) of [...] Read more.
A novel flat beam steering prototype based on the specific arrangement of a cylindrical unit cell is designed, manufactured and tested. The wideband and broad scanning capability is demonstrated at the Ku-band. We have considered two configurations, first with circular rings (CR) of the defined permittivity values for respective radial distance from the center of the aperture, second with cylindrical rods that shall be placed on a respective CR, which mimics the defined permittivity. The structure is generated from Vero CMYK full color wax, which utilizes the Multijet 3D printing method. The proposed prototype is designed in the operating frequency of 12 GHz (λ = 25 mm) and separation distance between the two parallel plates are maintained at 12.5 mm (0.5λ) for the TE10 mode of operation. The diameter of the two parallel plates and the proposed structure is of 100 mm (4λ) where the radius of cylinders varies from 0.5 to 3.5 mm and corresponding relative permittivity varies from 0.6687 to 2.4395. The overall height of the structure is 12.5 mm and is placed between two parallel plates. The minimum separation distance is maintained between the proposed structure and the feed WR-75 waveguide. Irises effect is performed to obtain impedance matching in the operating frequency bands. Beam steering of the radiated waves is observed for relative rotation angles of 0, 30, 45, 75 and 90 of the WR-75 waveguide along the edge of parallel plates. The overall proposed system weighs 179 g, which signifies the light weight characteristics. Moreover, the proposed structure shows low return loss over 10 GHz to 15 GHz operating frequency band. Full article
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