Microwave Horn Antenna Research Articles

Microwave Metamaterial Absorber with Radio Frequency/Direct Current Converter for Electromagnetic Harvesting System

This article presents the analysis of the electromagnetic (EM) properties of a novel metamaterial (MM) array in the microwave frequency range. The background for this work is the rapid development of portable devices with low individual energy consumption for the so-called “Internet of Things” (IoT) and the demand for energy harvesting from the environment on a micro scale through harvesters capable of powering billions of small receivers globally. The main goal of this work was to check the potential of the novel MM array structure for EM energy harvesting. The proposed MM array was analyzed in the CST Studio simulation environment. This resulted in the determination of the substitute average EM parameters (absorption, reflection, and transmission) of the MM array. Then, the MM array was manufactured, and the simulation results of the MM array parameters were experimentally validated in a microwave waveguide test system. Based on this conclusion, a prototype of the microwave MM absorber, together with an RF/DC converter, was designed and manufactured for harvesting EM energy from the environment. The system’s energy efficiency was evaluated, and its potential application in energy harvesting technology was appraised. Using a microwave horn antenna, the EM energy harvesting efficiency of the prototype was evaluated. It was about 50% at a microwave frequency of about 2.6 GHz. This may make the prototype attractive as an EM energy harvester or bolometric sensor.

Graphene‐based low side‐lobe microwave horn antenna

In this study, a novel method is proposed to control and reduce the side-lobe level (SLL) of the pyramidal horn antennas. In this method, graphene sheets are deposited on the antenna walls to taper the aperture field leading to pattern engineering with the goal of the SLL reduction. In essence, graphene sheet acts as a high-impedance surface and hinders electromagnetic power from reaching to the horn antenna aperture edges, in such a way that the diffraction phenomenon could be drastically diminished. The proposed design is numerically analysed and optimised using full-wave three-dimensional simulation methods. Numerical full-wave results illustrate more than 17.6 dB reduction in the SLL of the proposed antenna.

An amplitude modulated radio frequency plasma generator

A glow discharge plasma generator and diagnostic system has been developed to study the effects of rapidly variable plasmas on electromagnetic wave propagation, mimicking the plasma sheath conditions encountered in space vehicle reentry. The plasma chamber is 400 mm in diameter and 240 mm in length, with a 300-mm-diameter unobstructed clear aperture. Electron densities produced are in the mid 1010 electrons/cm3. An 800 W radio frequency (RF) generator is capacitively coupled through an RF matcher to an internally cooled stainless steel electrode to form the plasma. The RF power is amplitude modulated by a waveform generator that operates at different frequencies. The resulting plasma contains electron density modulations caused by the varying power levels. A 10 GHz microwave horn antenna pair situated on opposite sides of the chamber serves as the source and detector of probe radiation. The microwave power feed to the source horn is split and one portion is sent directly to a high-speed recording oscilloscope. On mixing this with the signal from the pickup horn antenna, the plasma-induced phase shift between the two signals gives the path-integrated electron density with its complete time dependent variation. Care is taken to avoid microwave reflections and extensive shielding is in place to minimize electronic pickup. Data clearly show the low frequency modulation of the electron density as well as higher harmonics and plasma fluctuations.

Molecular Structure and Chirality Detection by Fourier Transform Microwave Spectroscopy.

We describe a three-wave mixing experiment using time-separated microwave pulses to detect the enantiomer-specific emission signal of the chiral molecule using Fourier transform microwave (FTMW) spectroscopy. A chirped-pulse FTMW spectrometer operating in the 2-8 GHz frequency range is used to determine the heavy-atom substitution structure of solketal (2,2-dimethyl-1,3-dioxolan-4-yl-methanol) through analysis of the singly substituted (13)C and (18)O isotopologue rotational spectra in natural abundance. A second set of microwave horn antennas is added to the instrument design to permit three-wave mixing experiments where an enantiomer-specific phase of the signal is observed. Using samples of R-, S-, and racemic solketal, the properties of the three-wave mixing experiment are presented, including the measurement of the corresponding nutation curves to demonstrate the optimal pulse sequence.

Using microwave and macroscopic samples of dielectric solids to study the photonic properties of disordered photonic bandgap materials.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction. Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction. Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Passive polarization agile antenna based on the electromagnetically induced transparency-like effect

We propose a design method for a passive polarization agile antenna based on the electromagnetically induced transparency-like (EIT-like) effect. Benefiting from strong dispersion properties governed by EIT-like effects, the proposed structure can endow electromagnetic waves transmitted through it with quite different polarization states at very close frequencies. The experimental measurement was conducted to demonstrate agile polarization controls by placing a designed EIT-like waveplate in front of a standard microwave horn antenna. Results show that the polarization state of radiated waves by the horn antenna with a waveplate can be easily transformed among linear, circular and elliptical polarizations through fine-tuning the operating frequency, which is extremely important for certain special applications, e.g. electronic countermeasures. Our scheme could also be utilized at higher operating frequencies by the simply scaling principle.

Refractive properties of wire-grid metamaterials

This paper reports on a quantitative analysis of the electromagnetic properties of an arrangement of periodic metallic grids devised to provide in the 12.5–20.0 GHz frequency range a refractive index less than unity with view to enhance the functionalities of microwave horn antennas. Based on an analytical model, the ultra-refractive behavior of the metamaterial structure is demonstrated by the impedance and refractive index values retrieved from simulated scattering parameters.

Experimental study of broadband unidirectional splitting in photonic crystal gratings with broken structural symmetry

It is experimentally demonstrated that the combination of diode and splitter functions can be realized in one broadband reciprocal device. The suggested performance is based on the dielectric photonic crystal grating whose structural symmetry is broken owing to non-deep corrugations placed at one of the two interfaces. The study has been performed at a normally incident beam-type illumination obtained from a microwave horn antenna. The two unidirectionally transmitted, deflected beams can show large magnitude and high contrast, while the angular distance between their maxima is 90° and larger. The dual-band unidirectional splitting is possible when using TM and TE polarizations.

Experimental verification of the bending of electromagnetic waves using metamaterials

In this study, the bending of electromagnetic waves using metamaterials in free space was demonstrated. The optical transformation approach was utilized to design the bend, and the required metamaterials are inhomogeneous and anisotropic. The corresponding parameter-reduced metamaterials were realized using nonresonant cut-wire structures, which worked over an ultrabroad bandwidth with uniform permittivities and permeabilities. A microwave horn antenna focused the electromagnetic wave into the bend. The radiation patterns of the horn with and without bend were compared. The experimental and full-wave simulation results showed that the electromagnetic waves were bent in the desired direction.

An axial molecular-beam diode laser spectrometer

A mid-infrared tunable diode laser molecular-beam spectrometer for the purpose of trace gas sensing and the study of van der Waals complexes is described. The spectrometer employs a Herriott multipass cell with up to 72 passes. The sample gas is injected parallel to the optical axis through a hole at the center of the far mirror. The molecular absorption is Doppler split, resulting from the laser beam propagating parallel and antiparallel to the molecular-beam expansion. The axial expansion leads to narrower line widths and increased sensitivity, compared to the traditional vertical injection method, as a result of selective sampling of the central part of the molecular expansion with reduced Doppler broadening and longer residence time of the molecular sample in the laser beam. The molecular expansion leads also to selective signal enhancement of low-J transitions, as demonstrated for the ν3 antisymmetric stretch vibration of CO2. A microwave horn antenna was implemented into the spectrometer to enable microwave–infrared double-resonance experiments. The spectrometer performance was evaluated by recording spectra of the CO2–Ar, (CO2)2, CO2–He, and CO2–SO2 van der Waals complexes near the R(0) transition of the ν3 band of CO2 around 2349 cm−1. The feasibility of using a pulsed molecular expansion for trace gas sensing is explored.

Accuracy of corrections for the measured short-range gain of microwave horn antennas

Two methods of calculating correction factors for the measured short-range gain of tapered horns, a method of transmitting power from one aperture to the other and a method based on the geometric diffraction theory, are compared. The accuracy of correction factors is estimated from experimental data as a function of the parameter n=Rλ/D2.

Application of optical ray technique to the design of short microwave horn antennas with low side lobe levels

Optical ray theory is used to design a phase-corrected microwave horn antenna of shortlength which produces a tapered aperture amplitude distribution in the E-plane. The basis of the design is the creation of a region where the effective refractive index varies with hyperbolic secant (HYSEC) form in a direction normal to the horn axis. In a practical realisation this effective refractive index distribution is achieved in both smooth and stepped form by varying the plate separation of the planar waveguide supporting a TE01 mode. Good agreement is found between predicted and experimentally determined aperture and far-field distributions. Finally, the study is extended to the design of a novel antenna incorporating dielectric loading which, in theory, allows for operation at even shorter horn lengths.

Surface electromagnetic wave coupling efficiencies for several excitation techniques

The excitation efficiencies for coupling surface electromagnetic waves onto aluminum at a microwave frequency (f = 8.445 GHz, lambda = 3.55 cm) were studied experimentally for several different standard microwave techniques as well as two optical techniques (prism and grating) applied to the microwave frequency region and two new techniques (hump and valley). The peak measured efficiencies found were: for the standard rectangular waveguide, 92%; for the horn antenna, 73%; for the right angle prism properly gapped above the metal, 60%; for the hump of 10-wavelength radius of curvature, 35%; for the thin grating strips on polystyrene coated metal, 30%; for the grating bars gapped (1/2) wavelength above the metal, 26%; and, for the valley of 10-wavelength radius, 12%. The measurement of the excitation efficiencies for prism and grating coupling techniques sometimes required that the prism or grating be in the near field of the antenna. In addition to measuring peak efficiencies, the efficiencies were measured as functions of the gap heights, the angular orientations, the different diffraction modes, the shapes, and the materials of the grating bars. The coupling efficiencies for both prism and grating couplers show a strong dependence on gap height above the metal. Dielectric grating bars were found to be inefficient compared to solid or hollow metallic bars, or thin metallic strips. The distance between the target point of the center line of the microwave horn antenna and the corner of the prism was found to be about 1 wavelength for maximum prism coupling efficiency.

Thermistor Probe Error in an X-Band Microwave Field*

ABSTRACTThe reasonable assumption is made that a stainless steel hypodermic needle containing a thermistor does not couple with the electric field from a microwave horn antenna emitting 9.31 GHz radiation when the probe is perpendicular to the electric field vector in air or in solutions having approximately the salinity of tissue or blood. The degree of error in the measurement of temperature by the same probe in air orientated parallel to the electric field is 0.6°C. However, when used to measure temperature in 0.9%NaCl solutions the parallel thermistor probe did not interact with the microwave field in such a way as to change the temperature or to render the temperature readings inaccurate. These results provide a basis for considering that the use of metallic thermistor probes for the measurement of temperature increases produced by microwave irradiation of living tissue does not result in inaccuracies produced by probe orientation, provided the probe is below the surface of the tissue.

Measurement of Electron Temperature of a Plasma by Microwave Method

Thermal radiation in 9000 Mc/sec region emitted from a steady plasma without external magnetic field is received by a microwave horn antenna and measured with an eletcric field meter. The electron temperature is obtained, taking by antenna factor and the absorptivity of the plasma into consideration. Langmuir probe measurements are also made. Both results show good agreement. A method for measuring the absorptivity of a plasma in the far field by the use of antenna is investigated both theoretically and experimentally.