Antenna Area Research Articles

Novel closed-loop deployable mechanisms and integrated support trusses for planar antennas of synthetic aperture radar

Synthetic aperture radar (SAR) is indispensable electronic equipment in modern life, which has been widely used in the field of geological exploration, disaster monitoring, and environmental observation. With the increasing complexity of earth observation tasks, a higher receiving resolution of SAR is required, which needs the area of the radar antenna to be increased. However, there is a contradiction between the small launch space and the large working area. The deployable antenna mechanism is expected to meet the challenge. In this paper, a graphical type synthesis method is proposed to carry out the mechanism design of deployable mechanisms. According to the structural analysis and design requirements, the articulated form is adopted to carry sub-planes of planar antennas and provide one kinematic chain of the deployable mechanism. Then, different designed kinematic chains are synthesized to construct novel closed-loop deployable mechanisms. Mobility verification of a selected closed-loop deployable mechanism is carried out by screw theory to demonstrate the validity of type synthesis results. By sharing the provided kinematic chain and symmetrical design of two deployable mechanisms, deployable units with the driving unit are proposed as basic modules of support trusses for planar antennas. As a result, three novel deployable support trusses integrated by a series of deployable units and assembly mechanisms are proposed as the platforms for planar antennas. The deployable mechanisms and integrated support trusses proposed in this paper provide candidates for planar antennas of SAR.

Smart Antenna Systems

Abstract: Smart antennas have received increasing interest for improving the performance of wireless radio systems. These systems of antennas include a large number of techniques that attempt to enhance the received signal, suppress all interfering signals, and increase capacity, in general. The main purpose of this article is to provide an overview of the current state of research in the area of smart antennas, and to describe how they can be used in wireless systems. A smart antenna takes advantage of diversity effect at the source (transmitter), the destination (receiver), or both. Diversity effect involves the transmission and/or reception of multiple radio frequency (RF) waves to increase data speed and reduce the error rate. Thus, this article provides a basic model for determining the angle of arrival for incoming signals, the appropriate antenna beamforming, and the adaptive algorithms that are currently used for array processing. Moreover, it is shown how smart antennas, with spatial processing, can provide substantial additional improvement when used with TDMA and CDMA digitalcommunication systems.

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%.

SEBAT-Based Readout for FET THz Detectors With Intrinsic Power-to-Frequency Conversion

TeraHertz (THz) detection with Field-Effect Transistor-based (FET-based) detectors requires low-noise amplification, which typically involves trade-offs in terms of complexity, power, and area, resulting in severe scalability constraints for pixel integration into imaging arrays. The purpose of this paper is to describe a novel approach, from design to experimental validation, that enables active device-level amplification of the signal generated by a FET detector and converts it to a frequency suitable for digital processing. This has been done by exploiting a Single-Electron Bipolar Avalanche Transistor (SEBAT) to build a low-noise compact front-end circuit. The FET output is connected to the SEBAT forming a circuit element that here is defined as a TeraHertz Single-Electron Transistor (THzSET). The FET generates a detection current when it senses the THz signal; this current is then injected into the SEBAT, which generates an avalanche current pulse for each single electron, achieving a device-level amplification. The avalanche pulse rate is then evaluated from the signal measured at the SEBAT collector, and performing an FFT of the counts-per-second curve over time it is possible to measure the modulated THz signal applied to the device. The obtained Responsivity <inline-formula> <tex-math notation="LaTeX">$\text {R}_{\text {F}}$ </tex-math></inline-formula> and the Noise Equivalent Power NEP are respectively <inline-formula> <tex-math notation="LaTeX">$\frac {\text {4.61Gcps}}{\text {W}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\frac {\text {88nW}}{\sqrt {\text {Hz}}} $ </tex-math></inline-formula> at 330GHz illumination frequency. This is achieved with sub-<inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power consumption and minimal area overhead: indeed, the pixel and the interface have a total area of 0.146mm², where the antenna area is <inline-formula> <tex-math notation="LaTeX">${455} \times {320}\mu \text{m}^{{2}}$ </tex-math></inline-formula> and the SEBAT area is <inline-formula> <tex-math notation="LaTeX">${27} \times {22}\mu \text{m}^{{2}}$ </tex-math></inline-formula>.

A Proposal for Optical Antenna in VLC Communication Receiver System

Visible Light Communication (VLC) is an important emerging choice for high-speed wireless communication. In this perspective, light-emitting diodes as illuminators will be modulated to transmit data simultaneously. However, the receivers bring severe difficulties due to cost, response time, and sensitivity with a wide Field Of View (FOV). To avoid these problems, one approach is to apply a large area photodetector; however, this solution is slow and costly. Another method is to focus light on a fast photodetector by optical components, but the photodetector’s FOV decreases, resulting from the conservation of etendue. Another option is Luminescent Solar Concentrators (LSCs). This paper demonstrates a novel shape of LSC with advantages such as inexpensive, fast response time, small antenna area for VLC purposes with significant geometrical gain, FOV, and ultra-broad bandwidth. It does not require any complex tracking system and active pointing but, due to its tiny size, it can also be adapted in integrating and mobile devices. Numerical simulation is done using Monte-Carlo raytracing, and the results are demonstrated in the spectral domain. The optical efficiency of the proposed antenna is obtained at 1.058%, which is about 0.4% better than the efficiency levels reported in other works, and the geometric gain of the antenna is reported to be 44, which is significant.

Joint application of radar visibility reduction and anti-radar masking technologies to protect aircraft from remote monitoring systems

Using spectral energy equations of transmission-reception of wave processes in radio channel with scattering on object and direct radio channel, analysis of energy ratios of information signals and active masking interference at inputs of receivers of remote monitoring systems is carried out. Measures to reduce visibility are aimed at changing the reflective signatures of objects in the interests of reducing the de-masking features contained in secondary electromagnetic radiation to limits that exclude the performance of radar monitoring tasks at established distances and time intervals. Active interference is designed to mask information signals in receiving channels of radar at power that does not allow detecting their designers by passive radar. In case of joint application of not iceability reducing devices and active jammers, radar range reducing coefficient is determined by product of coefficient characterizing possibility of autonomous masking of information signals and coefficient achievable due to reduction of secondary electromagnetic radiation power in the second degree. The laws of increase of aircraft stealth from radar observation with joint application of technologies of reduction of radar visibility and masking by intentional interference created from sides of protected objects and from assigned points have been investigated. In order to maintain the desired signal-to-noise ratio at the output of the receiver with a decrease in the duration of the probing signal, it is necessary to proportionally increase the density of the emitted energy. With given antenna sizes, the maximum signal transmission range is proportional to the root square of their cyclic carrier frequency; increase of this parameter leads to increase of partial coefficient of directional action and effective area of antenna. With a decrease in the cyclic frequency of the carrier of the probing signal, inorder to maintain the required directional properties of the antennas, it is necessary to increase their dimensions.

Compact CPW‐fed ultra‐wideband ‐MIMO antenna with quad‐band notched characteristics

A compact CPW-fed ultra-wideband (UWB) multiple-input–multiple-output (MIMO) antenna with quad-band-notched characteristic is proposed in this work. The antenna elements are placed orthogonally, the introduction of defected ground structure (DGS) and double Y-shaped stub makes the isolation between different antenna ports better than 20 dB, and the cutting of the excess dielectric substrate part reduces the antenna area by about 30.75%. Complementary split-ring resonators and slots on the ground and the radiation patch have been introduced to achieve the four-notch characteristics at 7 GHz lower digital microwave relay communicator band, 5.8 GHz upper WLAN, 5.25 GHz lower WLAN, and 3.5 GHz WiMAX. The wide bandwidth of the antenna is obtained by applying tapered feed line and CPW feed, which covers 2.88–12 GHz with the four-notched bands of 3.34–3.93 GHz, 5.15–5.61 GHz, 5.72–6.0 GHz, and 6.75–7.6 GHz. Moreover, ECC (<0.02), DG (>9.99), the peak gain of 4.01 dB, good radiation pattern and TARC prove the presented antenna is suitable for UWB-MIMO systems.

Challenges and Opportunities in Smart Antenna

The ever-increasing demand for larger bandwidth with seamless and fast data access for commuters resulted in developing new challenges for wireless service providers. With the increasing network mobility, the communication channel based characteristics between base stations and mobile users are changing rapidly. To meet these challenges, smart antennas have become an essential component in the emerging wireless systems. The increasing requirement for increasing stable network performance and reducing electromagnetic pollution has strengthened smart antenna adoption. The primary objective of this research study is to highlight current research works in the area of smart antennas by evaluating the key technologies, service strategies, solutions and its importance in terms of 5G including network coverage enhancement, data speed, and Quality of Service (QoS).

Recent Advancement of Wearable Reconfigurable Antenna Technologies: A Review

Wireless Body Area Network (WBAN) technology is gaining popularity in personal communication due to the expanding improvement in wireless technology. Wearable antennas are utilized in various WBAN applications including personal healthcare, entertainment, military, and many more due to their attractive characteristics and the potential for integrating lightweight, compact, low-cost, and adaptable wireless communications. A wearable reconfigurable antenna will allow a single antenna to operate at multiple resonant frequencies, radiation, polarization or hybrid between them, by using single or multiple active switching devices for signal transmission and reception in different parts of human body, rather than using multiple antennas. Over the years, several review papers were reported on wearable antennas which discussed the requirements and issues of wearable antennas in terms of their design, fabrication, and measurement. Nowadays, WBAN technology employs a single wearable reconfigurable antenna to perform multiple functions in different parts of human body. Recently, a significant amount of work has been carried out in the area of wearable reconfigurable antennas for WBAN applications. This paper presents a comprehensive review of the requirements and analysis needed for wearable reconfigurable antennas such as Specific Absorption Rate (SAR) for on-body analysis, investigation of the antennas in bending conditions, reconfigurable techniques and reconfigurable performance metrics.

An Advanced Scheme for Range Ambiguity Suppression of Spaceborne SAR Based on Blind Source Separation

Due to the minimum antenna area constrain of synthetic aperture radar (SAR), high-resolution and wide-swath (HRWS) imaging is difficult to be achieved using classical modes, such as scan, spotlight, and so on. Range ambiguity is one of the main technical challenges limiting HRWS imaging in spaceborne SAR. Insipred by the cocktail party effect, an advanced scheme based on blind source separation is put forward to suppress the range ambiguity of spaceborne SAR in this paper. In the scheme, multiple subantennas are used to collect multiple echo data sets, which are given different patterns. In this way, the echo signal of the desired region and that of the ambiguous region are weighted using different coefficients. During postprocessing, a detailed flow with the blind source separation algorithm is proposed to separate the desired echoes from those data sets. To verify the scheme, point target and scene simulations based on GF3 are carried out. The results indicate that the range ambiguity can be reduced by more than 15 dB using the proposed scheme, the processing flow is effective, and the scheme has a good performance without increasing the complexity of the system design under the current SAR system conditions. The scheme has the potential to be adopted in future spaceborne SAR missions.

Low-Profile Wideband Solar-Cell-Integrated Circularly Polarized CubeSat Antenna for the Internet of Space Things

This paper proposes a low-profile wideband circularly polarized (CP) antenna using solar cell patches as radiation elements and a sequentially rotated feeding network for CubeSat applications. To realize a wide axial ratio (AR) bandwidth with a compact size, a sequentially rotated feeding network was designed by modifying a quadrature hybrid coupler and a rat-race coupler that has a small change in phase difference even when the frequency changes. A wideband CP patch array antenna was designed by combining a C-shaped slot-coupled solar cell patch in conjunction with a novel feeding network. The overall size of the proposed CP CubeSat antenna is 100 &#x00D7; 100 &#x00D7; 7.2 mm³ (0.83 &#x03BB;_o &#x00D7; 0.83 &#x03BB;_o &#x00D7; 0.06 &#x03BB;_o at 2.5 GHz). Solar cells occupy 79% of the antenna area, enabling efficient energy harvesting. The &#x2013;10 dB impedance bandwidth is 1.98&#x2013;3.0 GHz, which is a fractional bandwidth of approximately 41.0%. The 3-dB AR and 3-dB gain bandwidths are 1.98&#x2013;3.0 GHz (41.0%) and 1.82&#x2013;2.98 GHz (46.6%), respectively. The proposed CP solar patch array antenna demonstrates a constant radiation pattern within the &#x2013;10 dB impedance bandwidth. The proposed CubeSat antenna is suitable for use in an Internet of Space Things (IoST) autonomous communication system.

An Efficient Multichannel SAR Channel Phase Error Calibration Method Based on Fine-Focused HRWS SAR Image Entropy

Azimuth multichannel synthetic aperture radar (SAR) is a useful approach to solving minimum antenna area constraint and realizing high resolution and wide swath (HRWS) imaging by multichannel signal reconstruction. However, channel phase error will significantly degrade the reconstruction performance and leads to azimuth ghost. This article presents an efficient minimum entropy channel error estimation method based on fine-focused SAR image. The multichannel SAR images are obtained by using Range-Doppler imaging algorithm applied for preprocessed data of each channel. Then, the reconstruction and the residual range cell migration and residual second range compression compensation are performed to achieve multichannel fine-focused SAR images. After overlapping these multichannel fine-focused SAR images and iteratively calibrating the channel phase error, fine-focused HRWS SAR image can be achieved. Therefore, the SAR image used in the channel error estimation process can directly obtain the fine focused HRWS SAR image after minimum entropy iteration without additional imaging operations. Compared with the minimum entropy method by using the coarse-focused SAR image based on azimuth deramp, redundant reconstruction, and imaging operations are avoided. Thus, error estimation and imaging processing procedures are optimized. Processing efficiency improvement are analyzed, and simulation and acquired data processing verify the effectiveness of the proposed method.

Ship Focusing and Positioning Based on 2-D Ambiguity Resolving for Single-Channel SAR Mounted on High-Speed Maneuvering Platforms With Small Aperture

Due to the constraint of minimum antenna area, 2-D ambiguity resolving is a challenging task in ship focusing of single-channel SAR mounted on high-speed maneuvering platforms. In order to accommodate the issues, a ship focusing and positioning algorithm based on 2-D ambiguity resolving is proposed. First, we analyze the constraint of minimum antenna area and the distribution of the 2-D ambiguity area. An optimal-PRF SAR concept is proposed, where the signal ambiguity is evenly distributed to the range and azimuth directions. In this concept, the timing sequence of the orthogonal phase-coded waveform is designed to make the target echoes in different regions orthogonal. Then, an orthogonal matching filter is used to suppress the signal energy in range ambiguity regions. Aiming at the target defocus and position shift caused by the Doppler ambiguity, we propose an azimuth ambiguity resolving method. The Doppler ambiguity number can be estimated by residual envelope inclination. Subsequently, the target can be relocated and accurately focused by the estimated Doppler parameters. After the operation of each target is completed, the focusing SAR image of the whole scene can be obtained. Finally, simulation results and real data processing are presented to validate the proposed algorithm.

Millimeter Wave and Terahertz Urban Microcell Propagation Measurements and Models

Comparisons of outdoor Urban Microcell (UMi) large-scale path loss models, root mean square (RMS) delay spreads (DS), angular spreads (AS), and the number of spatial beams for extensive measurements performed at 28, 38, 73, and 142 GHz are presented in this letter. Measurement campaigns were conducted from 2011–2020 in downtown Austin, Texas, Manhattan (New York City), and Brooklyn, New York with communication ranges up to 930 m. Key similarities and differences in outdoor wireless channels are observed when comparing the channel statistics across a wide range of frequencies from millimeter-wave to sub-THz bands. Path loss exponents (PLEs) are remarkably similar over all measured frequencies, when referenced to the first meter free space path loss, and the RMS DS and AS decrease as frequency increases. The similar PLEs from millimeter-wave to THz frequencies imply that spacing between cellular base stations will not have to change as carrier frequencies increase towards THz, since wider bandwidth channels at sub-THz or THz carrier frequencies will cover similar distances because antenna gains increase quadratically with increasing frequency when the physical antenna area remain constant.

A Miniaturized Planar Monopole Antenna Based on a Coupling Structure for Compact Mobile Internet of Things (IoT) and Electric Vehicles (EVs) Device Applications in 5G, LTE, WLAN, WiMAX, Sirius/XM Radio, V2X, and DSRC Wireless Systems

A miniaturized internal antenna with monopole structure is constituted, including three radiating strips of a compact prototype and a back-coupling pad to improve the impedance matching, which achieves a wide bandwidth of 2.972 GHz between the operating frequencies of 2315–5285 MHz, and is introduced and researched. There is an urgent need for a complete frequency-continuous and large bandwidth design in the current wireless communication design to achieve a multimode, multifrequency, physical phenomenon design with large bandwidth and continuous operating frequency. The recommended antenna provides a broadband operation in an electric vehicles (EVs) and Internet of Things (IoT) devices application embedded in the wireless communication standard for 5G, LTE, V2X, WLAN, WiMAX, Sirius/XM Radio, V2X, and DSRC to support the multiband application. This design is embedded side edge of overall placement in the device and is integrated applicable to the trend of heterogeneous wireless multiple access networks in electric vehicle and Internet of Things system devices, which covered the 5G with supporting the band of n7/n38/n40/n53/n77/n78/n79/n90, the 4G with supporting the band of 7/38/40/41/42/43/48/67, the V2X and DSRC for the operating frequencies between 2500 and 5000 MHz, the Sirius/XM Radio for the operating frequencies of 2320–2345 MHz, the ISM band of WiFi and BT covering the band of 2450–2483.5 and 5150–5350 MHz, and the WiMAX also supporting the band of 2300–2690 and 3400–3690 MHz. Moreover, the compact antenna manufactured an FR4 material with the antenna area of 5 × 10 × 0.8 mm3 and the ground area of 33.5 × 10 × 0.8 mm3. The proposed design better benefits a narrow space on the PCB with a low profile and is easy to make with a circuit board design.

Selective Metallization on CFRP Composites by Laser Radiation and Electroless Plating

Selective metallization of carbon fiber-reinforced polymer composites (CFRP) was conducted by laser ablation with 1064 nm laser radiation and electroless plating in nickel solution. A rough caterpillar-like structure and polar surface with high property of absorption and anchoring for active seeds were produced by laser ablation. The laser treatment produce had a pronounced influence on nickel deposition. After immersed in nickel solution for 150s, a homogeneous and dense nickel film was selectively deposited on the laser treatment area of CFRP by electroless plating successfully. The Ni plating exhibited excellent adhesion on the CFRP. The technique in this study would widespread the application of CFRP in the area of spacecraft microwave components and waveguide antenna.

Optimum Separation for Performance Improvement of RFID Solenoid Coil Antenna in Metallic Environments

A metal pipe is a key factor affecting the performance of the oil well downhole radio frequency identification (RFID) system. This letter investigates the optimum separation for coping with the impact of metal pipe on the solenoid coil antenna so as to improve the performance of the downhole RFID system. Through the equivalent circuit model of RFID communication, a new objective of maximizing the reader antenna inductance is introduced from the perspective of demodulating the tag data easily. Then, a small optimum separation with a large antenna diameter is given out by the electromagnetic simulation of solenoid antenna in the metal pipe, which could not only ensure the trafficability of tag ball and decrease the tag speed in the antenna area but also reduce the minimum magnetic field required for the reader to read the tag. Finally, the calculation of optimum separation is compared with that of the experimental test and shows good agreement.

Design of a Dual-Purpose Patch Antenna for Magnetic Resonance Imaging and Induced RF Heating for Small Animal Hyperthermia

The popularity of patch antennas in magnetic resonance imaging (MRI) has reduced because of the large size required for patch antennae to resonate. Since the size of the patch antenna is associated with the wavelength and the wavelengths that are used in MRI are substantially large, large antennas are used. Methods of reducing patch antenna sizes have been proposed; however, these methods reduce the penetration depth and uniformity. In this study, we reduced the area of the patch antenna by 30% by folding the ground and patch planes in a zigzag pattern. The patch antenna produced two main resonant modes. The first mode produced a uniform magnetic field that was used for MRI. The second mode produced a strong and focused electric (|E|)-field, which was used for radiofrequency (RF) heating. Furthermore, we explored the use of a combination of two patch antennas aligned along the z-axis to provide a circular uniform magnetic flux density (|B1|) field at 300 MHz, which corresponds to the Larmor frequency in the 7T MRI system. In addition, the patch antenna configuration will be used for RF heating hyperthermia operating at 1.06 GHz. The target object was a small rat with insertion of colon cancer. Using the proposed configuration, we achieved |B1|-field uniformity with a standard deviation of 3% and a temperature increment of 1 °C in the mimic cancer tissue.

A High-Efficiency Zeroth-Order Resonant (ZOR) Antenna Fed by Printed Ridge-Gap Waveguide Technology

In this paper, a zeroth-order resonator (ZOR) antenna fed by a printed ridge gap waveguide (PRGW) is reported for 5G/6G applications in millimeter-wave bands. A zeroth-order resonance (ZOR) order technique with omnidirectional pattern feature is incorporated into a slot antenna to increase the coverage area of the slot antenna with high gain and directive pattern. The proposed antenna supports a high radiation efficiency and stable high coverage directional gain characteristic.

The effects of channel imbalances on the azimuth multi-channel SAR

Azimuth multi-channel (AMC) synthetic aperture radar (SAR) is an effective technology to conquer the minimum antenna area constraint and can provide high-resolution and wide-swath (HRWS) SAR images compared with the conventional strip-map SAR. In order to suppress azimuth ambiguity, AMC SAR will face an important problem: channel imbalances estimation and compensation. At first, this paper theoretically analysis the effects of channel imbalances including amplitude imbalance, phase imbalance and range sampling time imbalance (RSTI) on AMC SAR images, where all these channel imbalances will introduce false targets in azimuth, and RSTI will also make a significant influence on the range of SAR images. And then, in order to validate the above result, some simulations based on the parameters are carried out, and the real image acquired by GF-3 is also described. In addition, the intensity, number, and position of false targets are discussed. Finally, this paper makes some conclusions and points out the problems of these results.