Short Monopole Research Articles

Design and validation of impedance probe for platform-independent ionospheric plasma diagnostics

The design of an impedance probe (IP), which is one of the instruments in the package called IAMMAP for the CAS500-3 satellite, and related plasma chamber experiments are introduced. The characteristics of the IP were estimated based on plasma and antenna theory. Trade-off studies on the possible geometry and on the circuit configuration were carried out. It was shown that the combination of a short wave monopole antenna and a capacitor bridge with a heterodyne configuration is suitable for ionospheric plasma diagnostics. The plasma chamber experiments reveal that the upper hybrid resonance frequency measured by the IP is compatible with the plasma model and with the Ne values estimated by the Langmuir probe (LP). This suggests that the compactly-designed IP and LP can serve as a good combination for in-situ measurement of the ionospheric plasma providing self-calibrated plasma parameters.

Electrically Small Water-Based Hemispherical Dielectric Resonator Antenna

Recently, water has been proposed as an interesting candidate for use in applications such as tunable microwave metamaterials and dielectric resonator antennas due to its high and temperature-dependent permittivity. In the present work, we considered an electrically small water-based dielectric resonator antenna made of a short monopole encapsulated by a hemispherical water cavity. The fundamental dipole resonances supported by the water cavity were used to match the short monopole to its feed line as well as the surrounding free space. Specifically, a magnetic (electric) dipole resonance was exploited for antenna designs with a total efficiency of 29.5% (15.6%) and a reflection coefficient of −24.1 dB (−10.9 dB) at 300 MHz. The dipole resonances were effectively excited with different monopole lengths and positions as well as different cavity sizes or different frequencies in the same cavity. The overall size of the optimum design was 18 times smaller than the free-space wavelength, representing the smallest water-based antenna to date. A prototype antenna was characterized, with an excellent agreement achieved between the numerical and experimental results. The proposed water-based antennas may serve as cheap and easy-to-fabricate tunable alternatives for use in very high frequency (VHF) and the low end of ultrahigh frequency (UHF) bands for a great variety of applications.

Characterization and Performance of an Ultra-Wideband Wide-Coverage Multimode MIMO Antenna

A new ultra-wideband multimode (MM) antenna design that enables the detection/transmission of two orthogonal field components over a nearly hemispherical coverage area is presented in this paper. It integrates and colocates two perpendicularly oriented bow-tie dipole elements, a short convex monopole and four horizontally oriented tapered slot antenna (TSA) elements (formed by the dipoles) in order to produce four decoupled and complementary gain patterns. The antenna feeding structure includes four single-ended transmission lines supporting the desired set of individual excitation modes. Experimental verification confirms the predicted negligible coupling between the antenna operating modes and orthogonality of the corresponding radiated field patterns. These unique features can be exploited in applications where pattern and polarization diversity are of importance. In this study, we have evaluated the proposed antenna as a MIMO base station antenna and characterized it in two different propagation scenarios. For this example, it has been shown that the utilization of the additional monopole and TSA modes plays an important role in maximizing MIMO efficiency in line-of-sight (LOS) scenarios and at the same time provides additional independent data streams in rich scattering scenarios. In both considered scenarios, the antenna is shown to have a MIMO frequency bandwidth of 85%.

A Low Frequency Short Active Monopole Antenna Design and Sensitivity Analysis

A conventional passive matching method cannot be used for a low-frequency ultrawideband (UWB) antenna of high performance. In this paper, an amplifier module is combined with a short monopole antenna to design a high-performance active receiving antenna for 10 kHz–100 MHz UWB through model simulation. In addition, theoretical analysis of the antenna’s noise is made, and the theoretical basis for improving the sensitivity of the active antenna is obtained. Finally, the amplifier module is fabricated and the sensitivity of the antenna is tested using the equivalent capacitance substitution method. Tests show that the active antenna has very high sensitivity, bandwidth, and gain, and can be applied to cosmic radio signal detection.

A Tunable, High-Gain, Very Low-Profile Composite Monopole Antenna for Low-Frequency Applications

This paper presents an extremely low-profile frequency-tunable composite antenna with enhanced gain and an omnidirectional radiation pattern. The antenna is based on a recently developed very short two-legged monopole antenna and consists of one driven element and eight identical parasitic coupled elements. By utilizing the mutual coupling between elements, the radiation resistance of the antenna is significantly increased, leading to considerable gain enhancement and better matching performance. The composite antenna has the same height as the single monopole ( $\lambda _{0}/150$ ) but a larger lateral dimension ( $\lambda _{0}/16$ ). The performance of the proposed antenna is compared with that of a single monopole antenna. It is shown that the peak gain of the composite antenna is about 10 dB higher than that of the monopole antenna. The design is then modified for frequency tunability to achieve frequency agility and higher bandwidth for certain modulations like frequency hopping spread spectrum. The fractional bandwidth of the tunable antenna is 3.32%, and the gain is further improved at higher frequencies. A new method of effectively measuring a monopole antenna with an electrically small ground plane using cascaded transformers is also presented and discussed.

Modelo de la tensión inducida por un rayo sobre líneas de distribución

En este trabajo se han modelado las emisiones electromagnéticas ocasionadas por la descarga de un rayo, considerando al rayo como una antena monopolo corto sobre un plano de tierra perfectamente conductor. Mediante esta analogía se calculan los campos eléctricos y magnéticos radiados, y luego se calcula la tensión inducida en una línea de distribución considerada como un lazo corto. La expresión matemática utilizada para el cálculo de la tensión inducida ya fue propuesta en un trabajo previo y en el presente trabajo es validada mediante su confrontación en un escenario simulado con dos expresiones conocidas para el cálculo de la tensión inducida, una recomendada por la IEEE y desarrollada por S. Rusck y otra desarrollada por Barbosa. Sobre la base de las consideraciones realizadas por Rusck para la obtención de su expresión para la tensión inducida, la geometría relacionada con la expresión propuesta es adaptada para hacerla comparable con el referente internacional de Rusck en la norma IEEE. Posteriormente se han analizado los comportamientos dV_ind/dy de las tres expresiones en la región de radiación de campo cercano del rayo, determinando que las tendencias (las cuales son de carácter hiperbólico) de la expresión propuesta y la desarrollada por Rusck (estandarizada a nivel internacional en la norma IEEE 1410) presentan una gran similitud cuando los campos radiados sobrepasan los 20 m, dando validez a la expresión propuesta.

Hornet biological radar for detection, tracking, direction finding, and long distance communication: Is this possible?

The late, great entomologist, Prof. Jacob S. Ishay, from the faculty of medicine in Tel-Aviv University, dedicated his life to hornet research. He found that the hornet's body produces a considerable amount of electrical energy by means of photovoltaic and piezoelectric effects. Using an electronic microscope, Prof. Ishay showed to the authors the existence of two-dimensional arrays of very short spikes on the body skin of hornets, not unlike antenna arrays for radar and wireless communication systems. Later, Prof. Ishay and his team also found that the hornet's two antennas produce electricity and include spikes. These three radiation sources enable direction finding - even at great distances - from cooperative targets by wireless communication, allowing a new hypothesis of triangulation and an inverse GPS property for hornets. In this paper, a hypothetical biological radar for hornets is presented. In particular, we present a hypothesis regarding short spikes that may act as three phased arrays with extremely short monopole antenna elements. Due to their tiny physical dimensions, the frequency range of the antennas was estimated to be beyond 250 GHz, in the THz band. A comparison with other biological radar and direction-finding wireless communication systems is also provided.

Numerical compliance testing of human exposure to electromagnetic radiation from smart-watches

In this study, we investigated the electromagnetic dosimetry for smart-watches. At present, the standard for compliance testing of body-mounted and handheld devices specifies the use of a flat phantom to provide conservative estimates of the peak spatial-averaged specific absorption rate (SAR). This means that the estimated SAR using a flat phantom should be higher than the SAR in the exposure part of an anatomical human-body model. To verify this, we numerically calculated the SAR for a flat phantom and compared it with the numerical calculation of the SAR for four anatomical human-body models of different ages. The numerical analysis was performed using the finite difference time domain method (FDTD). The smart-watch models were used in the three antennas: the shorted planar inverted-F antenna (PIFA), loop antenna, and monopole antenna. Numerical smart-watch models were implemented for cellular commutation and wireless local-area network operation at 835, 1850, and 2450 MHz. The peak spatial-averaged SARs of the smart-watch models are calculated for the flat phantom and anatomical human-body model for the wrist-worn and next to mouth positions. The results show that the flat phantom does not provide a consistent conservative SAR estimate. We concluded that the difference in the SAR results between an anatomical human-body model and a flat phantom can be attributed to the different phantom shapes and tissue structures.

Electrically Small Folded Dipole Antenna for HF and Low-VHF Bands

A novel, highly miniaturized, lightweight antenna operating at the low-VHF band is presented. Earlier studies on an extremely short HF monopole antenna consisting of two in-phase vertical elements face an inevitable issue regarding an unbalanced coaxial cable feed due to the very small ground plane . To resolve this problem, as well as to achieve higher bandwidth, we introduce an electrically small folded dipole version of the same antenna having a fully balanced structure. The overall dimension and total mass of the proposed antenna are $10 \times 10 \times 15 ~\hbox{cm}^3$ . ( $0.013{\lambda _0} \times 0.013{\lambda _0} \times 0.02{\lambda _0}$ at 40 MHz) and 98 g, respectively. The gain and pattern of the fabricated antenna are measured in an elevated range that is in nearly free-space conditions. Measurements are shown to be in good agreement with the design predictions from simulation.

LOW-PROFILE AND SMALL CAPACITIVELY FED VHF ANTENNA

A low profile, compact antenna operating around 162MHz with omnidirectional vertically polarized radiation is proposed. The antenna is a short monopole capacitively coupled to shortend quarter-wavelength printed line optimized at 162MHz for Automatic Identification System (AIS) application. The antenna dimensions are less than λ/185 in height and λ/20 in lateral dimension, and the small size of antenna provides a narrow band of 0.34% and gain of −11.6 dBi. The simulated and measured results are in good agreement. © 2016 Electromagnetics Academy. All Rights Reserved.

Ionosphere plasma electron parameters from radio frequency sweeping impedance probe measurements

AbstractIn this work we will describe the technique of using an RF sweeping impedance probe (SIP) to measure the AC impedance of an electrically short monopole immersed in a plasma. We analyze the SIP measurements which are taken from the payload of the Storms sounding rocket, launched from Wallops Island, Virginia, in 2007. The scientific objective of the Storms mission was to concentrate on whether density irregularities observed in midlatitude spread F could arise from ionospheric coupling to terrestrial weather. As such, independent measurements of the electron density profile are crucial. Since the inherent nature of the SIP technique makes it relatively insensitive to errors introduced through spacecraft charging, probe contamination, and other DC effects, it is an ideal instrument to employ under disturbed plasma conditions. The instrument measures both the magnitude and phase of the AC impedance from 100 kHz to 20 MHz in 128 frequency steps, performing 45,776 sweeps over the entire flight. From these measurements we infer both the absolute electron density ne and the electron neutral collision frequencies νen throughout the flight trajectory. The SIP data can be approximately analyzed using a fluid formulation and thin sheath approximation particularly at altitudes below 200 km, which allows us to match the measurements to quasi‐static analytical formulas. At about 265 km on the upleg, the magnitude data transitioned to a highly damped response with increasing altitude. The phase data, on the other hand, continued to indicate increased plasma density and reduced collisionality as expected. For a large portion of the flight, the payload of the Storms mission exhibited an uncontrolled coning motion, making the local magnetic field orientation with respect to the dipole difficult to decipher. Despite these difficulties, we were able to obtain robust estimates of the electron density profile, using the phase information from each sweep. In addition, the electron neutral collision frequency obtained from matching to phase data alone was on the correct order of magnitude with respect to Naval Research Laboratory Mass Spectrometer Incoherent Scatter‐Extended model values in the ionosphere between 100 km and 150 km.

An Efficient Analytical Method for Electromagnetic Field to Transmission Line Coupling Into a Rectangular Enclosure Excited by an Internal Source

A simple and efficient analytical method has been developed for predicting the electromagnetic field coupling with a lossless transmission line (TL) located in a rectangular enclosure. The metallic enclosure is excited by an internal electrical short dipole or monopole source. The electric fields generated inside the rectangular enclosure and excited by some simple sources are calculated by using the electric-type dyadic Green's function. Our approach combines, on one hand, a lumped-pi circuit model of TL and, on the other hand, the Agrawal coupling model. A simple equivalent circuit has been derived which can give prediction for the coupling between the cavity field and the TL. This method is computationally less intensive compared to other numerical methods to solve such a problem. The analytical results have been successfully compared over a wide frequency band with the finite-difference time domain and experimental results carried out in different combinations of source and line position.

Experimental investigation of microwave interaction with magnetoplasma in miniature multipolar configuration using impedance measurements

A miniature microwave plasma source employing both radial and axial magnetic fields for plasma confinement has been developed for micro-propulsion applications. Plasma is initiated by launching microwaves via a short monopole antenna to circumvent geometrical cutoff limitations. The amplitude and phase of the forward and reflected microwave power is measured to obtain the complex reflection coefficient from which the equivalent impedance of the plasma source is determined. Effect of critical plasma density condition is reflected in the measurements and provides insight into the working of the miniature plasma source. A basic impedance calculation model is developed to help in understanding the experimental observations. From experiment and theory, it is seen that the equivalent impedance magnitude is controlled by the coaxial discharge boundary conditions, and the phase is influenced primarily by the plasma immersed antenna impedance.

A 2-D Multibeam Half Maxwell Fish-Eye Lens Antenna Using High Impedance Surfaces

This letter describes the design and measurement of a planar multibeam half Maxwell fish-eye (HMFE) lens antenna with seven beams in azimuth based on variable high impedance surfaces (HISs). The desired refractive index profile is controlled by using slotted square mushroom metallic cells of different sizes on a grounded dielectric slab. The lens antenna, 6.2λ×3.1λ in lens plane and 0.65 λ total height, is fabricated and characterized in TM mode at 13 GHz for both single- and multiple-beam configurations. The optimized lens for single-beam operation achieves 14.1 dBi measured gain, 67 ° and 12 ° half-power beamwidth for E-plane and H-plane, respectively, and 55.3% impedance bandwidth for -10-dB return loss. This lens can be used to launch multiple beams by implementing an arc array of seven-element short monopoles at the periphery of the lens. The measured overall scan coverage is up to 45 ° with gain drop less than 2.4 dB. Its low profile, light weight (only 136 g), and ease of manufacturing makes it well suited for Local Multipoint Communication Systems (LMCS).

Development of a Low Power Multipole Confined Microwave Plasma Ion Thruster

A modified magnetic multipolar plasma source is developed and tested for application as an ion thruster for space propulsion. The configuration consists of eight samarium-cobalt bar-magnets, symmetrically surrounding a cylindrical discharge volume of 21 mm diameter, with their magnetization in the radial direction. A donut magnet is placed at one axial end of the discharge volume with its magnetization along the cylindrical axis. A short monopole antenna, coaxial with the donut magnet is used for launching microwaves in the discharge volume. The resulting magnetic configuration due to the radial and axial magnetic fields, help in generation and sustenance of microwave induced electron cyclotron resonance plasma. Ions are extracted from the plasma by high voltage grids, attached to the end, opposite to the donut magnet. Two different magnetic configurations obtained by reversing the magnetization direction of the donut magnet are compared. Three dimensional magnetic field simulations and ion saturation current measurements at various microwave frequencies are used to determine the optimum magnetic configuration. Ion beam current extraction measurements, using the grids is carried out. Typical ion beam current of 9.9 mA is obtained, with calculated thrust of 0.63 mN at 8 W for 1600 MHz, with a Xenon mass flow rate of 20 Pg/s.

Extremely Small Two-Element Monopole Antenna for HF Band Applications

This paper presents a novel antenna architecture to achieve an extremely small form factor for HF band applications. The approach is based on manipulating the topology of a short monopole antenna without utilizing a high index material. A new architecture incorporating two radiating elements is configured, which allows significant gain enhancement. It is shown that such architecture can render a miniaturized HF antenna on air substrate having lateral and height dimensions as small as 0.0115λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.0115λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.0038λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (150 mm× mm × 50 mm for operation at 22.9 MHz). It is found that the measured gain of such architecture can be as high as - 18.1 dBi, which is 16.7 dB higher than a reference inverted-F antenna realized on a high index material (ε <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> = 10.2) having exactly the same dimensions. The proposed antenna architecture is composed of two in-phase radiating vertical elements connected to two inductors between which a capacitive top load is connected to achieve the desired resonant condition. The two vertical elements act effectively as a monopole having increased height. It is also shown that the gain of the antenna can be increased monotonically by increasing the quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) of the phase shifter. High <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> air-core inductors that can be accommodated in electrically small monopole antenna are designed and incorporated in the phase shifter to achieve a gain value of - 17.9 dBi. Details about the proposed design approach, simulation, and measurement results are discussed.

Low‐cost intelligent antenna with low profile and broad bandwidth

In this paper, a low-cost intelligent antenna, which has a low profile, high gain and broad bandwidth, is presented. The proposed antenna is an extension of the conventional Electronically Steerable Parasitic Array Radiator (ESPAR) antenna. It consists of one short monopole and twelve folded monopoles. The short monopole is placed in the centre and serves as the driven element, and the twelve folded monopoles serve as parasitic elements. The coupling between the driven and parasitic elements provides capacitive loading to the driven element, leading to a low profile antenna. The use of twelve PIN diodes enables the beamforming being performed by using Transistor-transistor logic (TTL) supply. When interference signals exist, an adaptive beamforming algorithm is employed to choose a radiation pattern with the best signal-to-noise ratio (SNR). The front-to-back ratio (FBR) and SNR is improved by introducing a reconfigurable chock ring (RCR) surrounding the antenna. To validate the concept, a prototype at S band is developed. Both measured and simulated results are presented. The antenna has a height of 24 mm only (0.16 at 2.0 GHz). The measurement results confirm that the antenna is capable of beamforming and beam scanning over 360°range in horizontal plane. The antenna has a broadband bandwidth from 2.0 to 2.5 GHz. Finally, the antenna is employed in a wireless communication system in an office environment and the system link quality is tested. It is shown that the antenna can boost the throughput of wireless system significantly.

Planar Printed Shorted Monopole Antenna with Coupled Feed for LTE/WWAN Mobile Handset Applications

A shorted monopole antenna with coupled feed for LTE/WWAN mobile handset applications is described. The basic resonance of the shorted monopole combines with the resonance formed by the coupling between the coupling strip and the feeding pad to cover the LTE700, GSM850, and GSM900 bands. Both the feeding pad and the coupling strip operate with the shorting strip as a loop antenna. The resonance of the loop antenna and the harmonics of the shorted monopole combine to cover the GSM1800, GSM1900, UMTS, and LTE2300 bands. A stable and omnidirectional radiation pattern with reasonable gain has been observed over the operating bandwidth.

Matching the input impedance of a short monopole to the wave impedance of the feeder with the use of an L-network consisting of finite-Q inductances

Design relationships for the elements of an L-network consisting of finite-Q inductances and intended for matching the impedance of a shortened electric monopole to the wave impedance of the feeder have been obtained. Plots that make it possible to estimate the dependence of the bandwidth and dissipation loss of the matching network on the degree of the monopole shortening with respect to the nominal λ/4 length have been constructed. The obtained estimate makes it possible to take a trade-off decision between the desired degree of decrease in the overall dimensions of the m antenna and the acceptable degree of its performance degradation.

One-piece, flat-plate, coupled-fed shorted monopole for 2.4-GHz wireless local area network operation

A novel, one-piece, coupled-fed, short-circuited monopole antenna for wireless local area network applications in the 2.4-GHz (2400–2484 MHz) band is proposed. The monopole is in the shape of an inverted hook, short circuited to a small antenna ground of size 10 × 15 mm2 and capacitively excited by a driven coupling strip. The coupling strip is located in between the monopole and the ground by a tiny gap and grounded at one end. In this case, the antenna can be fabricated from a single metal plate at a low cost. The results showed that the antenna was very well matched with a return loss of 14 dB across the operating band and generated good dipole-like, omnidirectional radiation patterns. Details of the design are discussed in this article. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:936–940, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26681