Antenna Height Research Articles

Conformal platform‐embedded horn antenna with ultra‐wide bandwidth and low profile

This article presents an H -plane horn antenna exhibiting very wide bandwidth, low profile, and nearly end-fire radiation. A wideband coaxial-to-waveguide transition is proposed by employing ridged waveguide and metallic posts in order to enhance the bandwidth and to suppress the higher mode, respectively. An ellipse-shaped copper taper is extended along the horn aperture in order to obtain smooth transition from the aperture to free space. The proposed antenna can be fully embedded in a conducting platform. Simulated results show that the proposed conformal antenna achieves a very wide bandwidth from 3.4 to 18 GHz for VSWR ≤ 2.5 while retaining the antenna height of only 5.508 mm (0.062 λ 0 at the lowest operating frequency). Nearly end-fire radiation is obtained over the whole frequency band. The prototype of the conformal configuration with six antenna elements embedded into a large cylindrical platform is fabricated and tested, measured results are in good agreement with simulated ones.

Bistatic antenna configurations for air-launched ground penetrating radar

Ground penetrating radar (GPR) is valuable for the detection of subsurface objects with little or no metal content, such as plastics, ceramics, and concrete piping. However, the effects of antenna configuration parameters, such as height and angle, are not well studied for all sensing applications. GPR simulations and laboratory GPR experiments are performed to evaluate the effects of antenna angle and height on the sensitivity of bistatic air-launched GPR, to search for buried nonmetallic objects. The results presented provide guidance for the development of air-launched GPR systems installed on unmanned aerial vehicles for in-flight subsurface scanning of buried targets.

Measurement and Analysis of Near-Ground Propagation Models under Different Terrains for Wireless Sensor Networks.

The propagation model is an essential component in the design and deployment of a wireless sensor network (WSN). Although much attention has been given to near-ground propagation models, few studies place the transceiver directly on the ground with the height of antennas at the level of a few centimeters, which is a more realistic deployment scenario for WSNs. We measured the Received Signal Strength Indication (RSSI) of these truly near-ground WSNs at 470 MHz under four different terrains, namely flat concrete road, flat grass and two derived scenarios, and obtained the corresponding path loss models. By comprehensive analysis of the influence of different antenna heights and terrain factors, we showed the limit of existing theoretical models and proposed a propagation model selection strategy to more accurately reflect the true characteristics of the near-ground wireless channels for WSNs. In addition, we implemented these models on Cooja simulator and showed that simplistic theoretical models would induce great inaccuracy of network connectivity estimation.

Specific Direction-Based Outlier Detection Approach for GNSS Vector Networks.

In this paper we propose an outlier detection approach for GNSS vector networks based on the specific direction (i.e., SD approach), along which the test statistic constructed reaches the maximum. We derive the unit vector of this specific direction in detail, and prove that the unit vector is the same as that determined by the outlier estimates in three-dimensional (3D) approach, while the distribution of the maximum test statistic in this direction is the square root of Chi-squared distribution. Therefore, eliminating an outlier along this specific direction can get the same result as that of eliminating all three components of outlier vector in 3D approach. The mathematical equivalence of SD approach and 3D approach is further demonstrated by a real GNSS network. Moreover, preliminary application of the SD approach to detect the abnormal antenna height measurement is carried out in terms of numerical simulations of multiple baseline solutions, and it shows that the SD approach can effectively detect baselines that are directly infected by corresponding receiver antenna height errors.

Impact of Soil Texture on Path Loss Modelling of an FM Signal Using Diffraction Technique

A novel solution to predict path loss of an FM signal using diffraction technique is proposed. Diffraction technique and soil texture impact are used to improve the Friis free-space model to predict the received signal strength and propagation path loss of an FM signal between a transmitter site and receiver site, while studying the impact of soil texture to the FM signal in the case of surface wave propagation. Measurement of signal strengths with an interval of 5KM along two different routes (1 and 2) were taken with a Digital Field Strength Meter (DW-400), in some selected open/rural environments of Kogi State. A solid-state transmitter (BE 20S), with broadcast frequency of 101.5MHz at antenna height of 120m was considered as the transmitting point source. Bluetooth signal strength meter software was used to visualize this impact of soil texture, where different types of soil were considered within the coverage area of the FM radio station, with the application of a Wireless Personal Area Network (WPAN) technology. Measurements taken along the two different routes were compared against predictions made by the modified model of Friis Free Space. The model showed quite large mean path loss prediction errors, and places with poor signal strength for Prime FM Radio Nigeria were revealed. The result shows that an FM signal induces current in the ground over which it passes and it is attenuated as a result of absorption of energy by the soil, depending on the soil type.

The Impact of Soil Texture on Path Loss Modelling of an FM Signal Using Diffraction Technique

A novel solution to predict path loss of an FM signal using diffraction technique is proposed. Diffraction technique and soil texture impact are used to improve the Friis free-space model to predict the received signal strength and propagation path loss of an FM signal between a transmitter site and receiver site, while studying the impact of soil texture to the FM signal in the case of surface wave propagation. Measurement of signal strengths with an interval of 5KM along two different routes (1 and 2) were taken with a Digital Field Strength Meter (DW-400), in some selected open/rural environments of Kogi State. A solid-state transmitter (BE 20S), with broadcast frequency of 101.5MHz at antenna height of 120m was considered as the transmitting point source. Bluetooth signal strength meter software was used to visualize this impact of soil texture, where different types of soil were considered within the coverage area of the FM radio station, with the application of a Wireless Personal Area Network (WPAN) technology. Measurements taken along the two different routes were compared against predictions made by the modified model of Friis Free Space. The model showed quite large mean path loss prediction errors, and places with poor signal strength for Prime FM Radio Nigeria were revealed. The result shows that an FM signal induces current in the ground over which it passes and it is attenuated as a result of absorption of energy by the soil, depending on the soil type.

A New GPS SNR-based Combination Approach for Land Surface Snow Depth Monitoring

Snow is not only a critical storage component in the hydrologic cycle but also an important data for climate research; however, snowfall observations are only sparsely available. Signal-to-noise ratio (SNR) has recently been applied for sensing snow depths. Most studies only consider either global positioning system (GPS) L1 or L2 SNR data. In the current study, a new snow depth estimation approach is proposed using multipath reflectometry and SNR combination of GPS triple frequency (i.e. L1, L2 and L5) signals. The SNR combination method describes the relationship between antenna height variation and spectral peak frequency. Snow depths are retrieved from the SNR combination data at YEL2 and KIRU sites and validated by comparing it with in situ observations. The elevation angle ranges from 5° to 25°. The correlations for the two sites are 0.99 and 0.97. The performance of the new approach is assessed by comparing it with existing models. The proposed approach presents a high correlation of 0.95 and an accuracy (in terms of Root Mean Square Error) improvement of over 30%. Findings indicate that the new approach could potentially be applied to monitor snow depths and may serve as a reference for building multi-system and multi-frequency global navigation satellite system reflectometry models.

Pattern Reconfigurable, Vertically Polarized, Low-Profile, Compact, Near-Field Resonant Parasitic Antenna

A vertically polarized, low-profile, compact, near-field resonant parasitic antenna with pattern reconfigurability is demonstrated. The antenna has three dynamic end-fire states facilitated with only three p-i-n diodes. The radiation pattern in each state covers more than 120° in its azimuth plane and, hence, it achieves beam scanning that covers the entire azimuth plane. The antenna height and transverse size are, respectively, only $0.048\lambda _{0}$ and $0.1\lambda _{0}^{2}$ . Measured results, in good agreement with their simulated values, demonstrate that the antenna exhibits a ~11% fractional impedance bandwidth, and a ~6.6 dBi peak realized gain in all three of its pattern-reconfigurable states. Stable and high peak realized gain values are realized over its entire operational band surrounding 2.22 GHz.

C band transhorizon signal characterisations in evaporation duct propagation environment over Bohai Sea of China

Evaporation duct is an anomalous mechanism of transhorizon propagation in marine and coastal regions. In order to better understand the characteristics of signal fading, a C band signal transhorizon propagation experiment was carried out with a 107km path length over the Bohai Sea of China. Using an iron tower with meteorological and oceanographic (METOC) sensors at multiple altitudes, a direct diagnostic method of evaporation duct is presented. The dependence of signal strength on evaporation duct height, antenna height, and METOC parameters is analysed. The experimental results indicate that the signal strength tends to be linearly dependent on the evaporation duct height when the transmitter and receiver antennas are submerged within the duct layer. Normally, the signal strength is stronger when the relative humidity is lower. Stronger signal strength tends to occur under near-neutral or stable atmospheric conditions or when the air-sea temperature difference is higher. The results indicate that the signal strength distribution of fast fading is close to Rayleigh distribution, and the probability density of fade slope is symmetric at 0dB/s. These results have important implications for the design of ducting communications system.

Low-profile Equiangular Spiral Antenna Based on an Artificial Magnetic Conductor Reflector

In this paper, a low-profile equiangular spiral antenna is designed. The bi-directional beam from an equiangular spiral antenna (EAS) is changed to a unidirectional beam using an artificial magnetic conductor (AMC) reflector. The antenna height, measured from the upper surface of the AMC reflector to the spiral arms, is chosen to be extremely small to realize a low-profile antenna: 0.07 wavelength at the lowest analysis frequency of 3 GHz. The analysis shows that the EAS backed by the AMC reflector does not reproduce the inherent wideband axial ratio characteristic observed when the EAS is isolated in free space. To solve this problem the AMC reflector is modified by gradually removing the patch elements from the center region of the reflector. The results show that the spiral antenna with a modified artificial magnetic conductor reflector reduces the axial ratio in the working frequency band from 3 to 10 GHz, and greatly broadens the working bandwidth of the spiral antenna. A viable way is proposed to optimize the performance of the low-profile equiangular spiral antenna without change the dimensions.

Wireless Channel Models for Over-the-Sea Communication: A Comparative Study

Over the past few years, the modeling of wireless channels for radio wave propagation over the sea surface has drawn the attention of many researchers. Channel models are designed and implemented for different frequencies and communication scenarios. There are models that emphasize the influence of the height of the evaporation duct in the marine environment, as well as models that deal with different frequencies (2.5, 5, and 10 GHz, etc.) or the impact of various parameters, such as antenna height. Despite the increasing literature on channel modeling for the over-the-sea marine environment, there is no comprehensive study that focuses on key concepts that need to be considered when developing a new channel model, characteristics of channel models, and comparative analysis of existing works along with their possible improvements and future applications. In this paper, channel models are discussed in relation to their operational principles and key features, and they are compared with each other in terms of major characteristics and pros and cons. Some important insights on the design and implementation of a channel model, possible applications and improvements, and challenging issues and research directions are also discussed. The main goal of this paper is to present a comparative study of over-the-sea channel models for radio wave propagation, so that it can help engineers and researchers in this field to choose or design the appropriate channel models based on their applications, classification, features, advantages, and limitations.

AMC surface based on spiral strips and its applications for low‐profile broadband planar antennas

A novel artificial magnetic conductor (AMC) surface based on spiral strips is proposed, which consists of 9 × 9 AMC cells. Each AMC cell includes a spiral strip to increase its inductance, thus featuring a wide bandwidth of 42% for ±90° reflection phase. The AMC surface is applied to three planar dipole antennas for lowering the antenna heights, including a linearly polarised (LP) antenna, a dual-polarised (DP) antenna, and a circularly polarised (CP) antenna. It is shown by simulation and experiment that the LP antenna achieves an impedance bandwidth of 40% (0.68-1.02 GHz) for | S 11 | <; -15 dB and a gain of 8 dBi, the DP antenna realises an impedance bandwidth of 33% (0.69-0.96 GHz) for | S 11 | <; -15 dB, an isolation of 30 dB, and a gain of 8 dBi, and the CP antenna has an overlapped bandwidth of 33% (0.75-1.05 GHz) for | S 11 | <; -15 dB and axial ratio <;3 dB. The heights of all the three planar antennas are lowered from 0.265-0.3 λ 0 to 0.083 λ 0 .

Investigating the Performance of Bi-Static GPR Antennas for Near-Surface Object Detection.

Antennas are an important component in ground penetrating radar (GPR) systems. Although there has been much research reported on the design of individual antennas, there is less research reported on the design of the geometry of bi-static antennas. This paper considers the effects of key parameters in the setup of a GPR head consisting of a bi-static bow-tie pair to show the effect of these parameters on the GPR performance. The parameters investigated are the antenna separation, antenna height above the soil, and antenna input impedance. The investigation of the parameters was performed by simulation and measurements. It was found when the bi-static antennas were separated by 7 cm to 9 cm and were operated close to the soil (2 cm to 4 cm), the reflected signal from a near-surface object is relatively unaffected by height variation and object depth. An antenna input impedance of 250 Ω was chosen to feed the antennas to reduce the late-time ringing. Using these results, a new GPR system was designed and then evaluated at a test site near Benkovac, Croatia.

Low-Profile Low-Cost Ultra-Wideband Circularly Polarized Slot Antennas

Aiming for ultra-wideband (UWB) indoor wireless access, three low-profile UWB circularly polarized slot antennas are proposed in this paper, all of which are made by a pair of curved tapered slots. The slots are miniaturized to allow a short direct microstrip feeding. The first antenna is a bidirectional antenna with a measured -10 dB impedance bandwidth of 110% (2.94 - 10.06 GHz), and a 3 dB axial ratio (AR) bandwidth of 89% (3.19 - 8.26 GHz). Its measured peak gain is 7.5 dBic and its size is 0.80 λ max × 0.80 λ max × 0.5 mm (λ max is the free-space wavelength at the lowest frequency, 3.19 GHz). Its performance is similar to that of a traditional spiral antenna, but it has a much simpler structure with a more complete ground plane, making it possible to integrate with other components (e.g. filter and amplifier) on the antenna body to reduce the overall size of the system. The second antenna is a directional antenna with a simple solid metal reflector placed 21 mm away from the radiator. This configuration increases the peak gain to 8.6 dBic, but reduces the impedance bandwidth to 52% only. The third one is a directional antenna with a meshed reflector. It has a maximum gain of 9.6 dBic, which is higher than that of the second antenna, while its -10 dB impedance bandwidth is 99% (3.37 - 9.94 GHz) and its 3 dB AR bandwidth is 84% (3.70 - 9.07 GHz), which is similar to that of the first one. Also distance between the radiator and the reflector (antenna's height) is reduced to 9 mm only (0.111 λ max ). The proposed antennas demonstrate high efficiency, simple and low profile structures, wide impedance and AR bandwidth, making them excellent candidates for in-door base station and UWB positioning systems.

Considering the environment's characteristics in wireless networks simulations: case of the simulator NS2 and the WSN

Recently, the wireless networks, particularly the wireless sensor networks (WSN) occupy an important place in several application areas due to the progress in microelectronics and wireless communications domains. Thus, a set of researches had addressed this issue in order to broaden the possibilities offered by these networks and circumvent the encountered problems. The test of any new solution is an essential phase to validate its performances. This phase is done in network simulators; which NS is the most used. The impact of the physical layer and the radio signal propagation environment criteria on the simulations results is indisputable. In this context, and after presenting and classifying the radio propagation models, we study in detail the implemented models in NS-2. The focus is on the ability of these models to consider the characteristics of the wireless networks deployment environment (e.g., nature, position and mobility of the obstacles). And to consider the specificities of WSN, the effect of other parameters (e.g., antenna height) will be discussed.

Current Distribution and Input Impedance of a Horizontal Linear Antenna in the Presence of a Layered Region

In this paper, the current distribution and an input impedance of a horizontal linear antenna in the presence of a layered region are investigated both analytically and numerically. In particular, we demonstrate the case of a four-layered region. The wave-number and characteristic impedance of an eccentrically insulated antenna are obtained first. Subsequently, the analytical formula for the current distribution on the antenna in a four-layered region is derived by applying a limiting process. The computational results show that the upper and lower dielectric layers have different effects on the current distribution and input impedance of the antenna. It is also found that the imaginary part of the input impedance as a function of antenna length has two zero points, where the first and second zero points correspond to a half-wavelength antenna (series resonance) and a full-wavelength antenna (parallel resonance), respectively. It is indicated that when the thickness of the dielectric layers or the antenna height changes, variations on the resonance length of the antenna are observed by examining the imaginary part of the input impedance.

Low-Profile ESPAR Antenna for RSS-Based DoA Estimation in IoT Applications

In this paper, we have introduced a low-profile electronically steerable parasitic array radiator (ESPAR) antenna that can successfully be used to estimate the direction-of-arrival (DoA) of incoming signals in wireless sensor network (WSN) applications, in which the height of the complete antenna has to be low. The proposed antenna is over three times lower than high-profile ESPAR antenna designs currently available in the literature for the DoA estimation; it can provide eight unique main beam directions and relies on simplified beam steering, which makes it applicable to simple and inexpensive WSN nodes. Measurements using our fabricated ESPAR antenna prototype indicate that relying solely on the received signal strength values recorded at the antenna output port, it is possible to achieve accurate DoA estimation results with error levels similar to those available for high-profile ESPAR antennas relying on the similar energy-efficient simplified beam steering concept and having 12 unique main beam directions. As a consequence, the overall time required for the DoA estimation using the proposed antenna can be reduced by 33%.

A Comparative Study on Evolutionary Multi-objective Optimization Algorithms Estimating Surface Duct.

The problem of atmospheric duct inversion is usually solved as a single objective optimization problem. Based on ground-based Global Positioning System (GPS) phase delay and propagation loss, this paper develops a multi-objective method including the effect of source frequency and receiving antenna height. The diversity and convergence of solution sets are evaluated for seven multi-objective evolutionary algorithms with three performance metrics: Hypervolume (HV), Inverted Generational Distance (IGD), and the averaged Hausdorff distance (). The inversion results are compared with the simulation results, and the experimental comparison is conducted on three groups of test situations. The results demonstrate that the ranking of algorithm performance varies because of the different methods used to calculate performance metrics. Moreover, when the algorithms show overwhelming performance using performance metrics, the inversion result is not more close to the real value. In the comparison of computational experiments, it was found that, as the retrieved parameter dimension increases, the inversion result becomes more unstable. When the observed data are sufficient, the inversion result seems to be improved.

Analysis and Investigation on Lightning Electromagnetic Coupling Effects of a Dipole Antenna for a Wireless Base Station

To study the coupling effect of an antenna near the lightning channel when the wireless base station lightning rod is attacked by lightning, the simulation models of lightning channel–communication tower and dipole antenna working on the communication frequency of 900 MHz are constructed in this paper based on the CST Studio Suite and FEKO. The results of $S_{2,1}$ calculated by the two simulation software are compared to verify the reliability of the models, then the coupling characteristics of the 900 MHz dipole antenna is discussed in terms of the heights of tower, the heights of the antenna, the horizontal distances of the antenna from the tower, and the polarization directions of the antenna. We find that the induced voltage of the antenna in vertical polarization is much larger than that in horizontal polarization. The further the antenna from the base station tower top, the smaller the induced voltage. When the antenna is within the range of 5 m below the tower top with set heights of 30, 25, 20, and 15 m, the induced voltage of the antenna decreases greatly in response to the reduction of antenna's height, and the closer the antenna to the tower, the greater the change. While outside the range, the induced voltage decreases slowly as the antenna's height reduces, until it almost remains unchanged, and the effect of antenna's horizontal distance from the tower on the induced voltage is not obvious. The induced peak voltage of the antenna is almost linearly decreased with its polarization rotation from vertical to horizontal polarization.

Design and Analysis of Ultra Low-Profile ILA on a Rectangular Conducting Plane

The unbalanced fed ultra low profile inverted L antenna on a rectangular conducting plane is proposed and analyzed numerically and experimentally. By adjusting the length and height of inverted L antenna, the feed point position, and the size of conducting plane, the return loss bandwidth and the directivity can be controlled. The return loss bandwidth of 2.57 % and the directivity of 4.34 dBi are obtained, when the size of conducting plane is 0.245  (: wavelength) by 0.49 , and the antenna height is /30. The input impedance of the proposed antenna is compared with those of the conventional base-fed inverted L antenna and the base fed inverted F antenna. Although the directivity of base-fed inverted L antenna is almost same as that of proposed antenna, its input resistance becomes very low. In the base fed inverted F antenna, the return loss larger than 10 dB is not satisfied in the case of the antenna height less than 0.05 .