Receiving Horn Antennas Research Articles

Full-Wave Modeling and Inversion of UWB Radar Data for Wave Propagation in Cylindrical Objects

The nondestructive characterization of cylindrical objects is needed in many fields, such as medical diagnostics, tree trunk inspection, or concrete column testing. In this study, the radar equation of Lambot et al. is combined with cylindrical Green’s functions to fully model and invert ultra-wideband (UWB) ground-penetrating radar (GPR) data and retrieve the properties of cylindrical objects. Inversion is carried out using a lookup table (LUT) approach followed by local optimization to ensure retrieval of the global minimum of the objective function. Numerical experiments were conducted to analyze the capabilities of the developed inversion procedure to estimate the radius, permittivity, and conductivity of the cylinders. The full-wave model was validated in laboratory conditions on metallic and plastic pipes of different sizes. The adopted radar system consists of a lightweight vector network analyzer (VNA) connected to a single transmitting and receiving horn antenna. The numerical experiments highlighted the complexity of the inverse problem, mainly originating from the multiple propagation modes within cylindrical objects. The laboratory measurements demonstrated the accuracy of the forward modeling and reconstructions in far-field conditions.

Determination of relative position of antenna system and RGB-D sensor in combined microwave imaging system

Microwave imaging technique allows obtaining images of hidden objects in structures and media using microwaves. This technique has various applications such as: nondestructive testing, medical imaging, concealed weapon detection, through-the-wall imaging, etc. Obtaining radar images in these applications is based on processing phase and amplitude of the reflected signal recorded over an aperture (a microwave hologram). Recently, systems began to appear in which the radar part is supplemented by an RGB-D sensor, which allows to obtain new capabilities. For example, there is the a microwave screening system architecture in which inverse synthetic aperture is formed by the natural motion of the subject in the vicinity of a stationary linear antenna array. The microwave system is complemented with an synchronous RGB-D video sensor which captures the trajectory of the moving subject in 3D and allows coherent processing of the radar signal. Another system detects objects buried under irregular surface and uses RGB-D sensor for capturing the surface relief for suppressing reflection of the sounding signal from the surface. Calibration between a radar and an RGB-D sensor is an essential process for microwave and optical data fusion. This article presents a novel approach for calibration, using a planar calibration target which is made of radiotransparent material (such a foam plastic sheet) with square marker and six small metal balls embedded in target surface and representing point objects. The proposed method exploits 3D-3D correspondences between coordinates of point objects in two coordinate systems associated to the sensor and to the radar. One points set is extracted from optical data, using marked corners of the target as a base points. Second points set is obtained from microwave data as local maxima of 3D volume of data reconstructed from one-frequency microwave hologram. Computer modeling were performed using Autodesk 3ds Max software by which models of all components of the system were built and the optical image from the sensor was modeled. Test experiments were carried out using a measurement system composed of the following components: a compact vector network analyzer (VNA), two mechanical scanners with stepper motors, one transmitting and one receiving horn antennas, mounted on the VNA, an RGB-D sensor, a microcontroller board, and a computer. The high accuracy of the method is confirmed both by computer modeling and physical experiment. The accuracy of determination of relative position between the radar and the sensor is about one fifth of the signal wavelength used.

Free space traveling–standing wave attenuation method for microwave sensing of grain moisture content

Moisture content is an important index to assess the grain quality and food processing conditions. A measurement system based on the traveling–standing microwave attenuation method is designed for a fast and nondestructive grain moisture content determination. The proposed system consists of a microwave cavity oscillator, microwave transmitting and receiving horn antennas, microwave detector, slide rail, sample container, weight sensor, temperature sensor, and controller. The traveling–standing wave caused by free space microwave multiple reflection is discussed. The moisture content calibration functions eliminated the interference of bulk density and temperature are proposed based on the attenuation of the maximum field strength of the transmission traveling–standing wave. The moisture content of rice, which ranges from 10.75% to 27.62%, is obtained with a standard error of prediction (SEP) of 0.586% and a coefficient of determination ( R2) of 0.988, whereas the moisture content of corn, which ranges from 7.72% to 24.46%, is obtained with a SEP of 0.340% and R2 of 0.991. The main results might provide technical support for the development of accurate and intelligent grain quality detection equipment.

Suburban Fixed Wireless Access Channel Measurements and Models at 28 GHz for 90% Outdoor Coverage

Achieving adequate coverage with high gain antennas is key to realizing the full promise of the wide bandwidth available at cm/mm bands. We report extensive outdoor measurements at 28 GHz in suburban residential areas in New Jersey and Chile, with over 2000 links measured for same-street link types (vegetation blocked LOS) from 13 streets and other-street link types (true NLOS) from 7 streets, using a specialized narrowband channel sounder at ranges reaching 200 m. The measurements, applicable to fixed wireless access, involved a 55$^\circ$ transmit antenna placed on the exterior of a street-facing window and a 10$^\circ$ receive horn antenna spinning on top of a van mast at 3 m height, emulating a lamppost-mounted base station. Measured path gain-distance dependence is well represented by power-law models, and azimuth gains at the base are degraded through scattering by more than 4.3 dB for 10% of links. It was found that, with 51 dBm EIRP at the base station and 11 dBi antenna at an outdoor mounted terminal, 1 Gbps downlink rate can be delivered up to 100 m from a base station deployed in the same street with 90% coverage guarantee.

Measurement of ICRF wave propagation using a microwave reflectometer with fast antenna switching on GAMMA 10

Slow Alfvén wave in ion cyclotron range of frequency (ICRF) is a powerful tool to heat ions confined in a mirror field. In spite of its efficient heating effect that has been attained in the central cell of GAMMA 10, there are still unknown characteristics concerning boundary condition, transient variation of heating effect, exact picture of cyclotron damping, and so on. To study these characteristics in detail, a multi-point measurement of the waves inside the hot plasma has been recently developed by using a microwave reflectometer. In addition to a radial profile measurement that is available by a usual reflectometer, an axial measurement has been achieved by arraying transmitting and receiving horn antennas in the axial direction, which are repeatedly switched in time during a discharge with PIN diode switches. Another transmitting and receiving horn antenna pair was newly added to the system and probing at five cross sections was achieved in a single discharge with time resolution of about 1 ms at each antenna pair position. With the upgraded reflectometer system, axial and radial distributions of wave-induced fluctuations and those temporal behavior were clearly observed, offering valuable data on wave physics in a hot mirror plasma.

A terahertz spatial power combiner based on 2D periodic hole-shaped grating using nongradient optimization method

ABSTRACTThis paper describes a terahertz spatial power combiner based on a periodic hole-shaped hologram for a two-dimensional (2D) horn antenna array. The combiner consists of a 2D array of rectangular horns, a dielectric hole-shaped hologram, a focusing reflector, and a receiving horn antenna. The hologram is realized as 2D periodic holes, which transforms the beams of the antenna array into a pseudoplane wave. The transformed wave is coupled into a rectangular output horn antenna by a parabolic reflector with a shaped surface relief. The field distribution on the receiving plane can be obtained by using a nongradient optimization method to optimize the reflector surface. An example operating at 300 GHz is described. The theoretical power combining efficiency is about 63.1%. The computed field distribution agrees well with the result obtained using the commercial software FEKO Suite.

Bendable Hexagonal Resonator Designs for Chipless Tag

This paper presented a new design of bendable hexagonal resonator for chipless RFID tag. A linearly polarized plane wave and Radar Cross Section (RCS) probes were used in simulation set-up. The optimized resonator was fabricated on a thin fast-film substrate with dielectric constant, εr=2.7 and substrate thickness, t = 0.13 mm. The fabricated resonator consisted of 3 hexagonal slots which represented three bit 1s. The measurement was performed to validate the designed resonator. It was measured using two transmitting and receiving horn antennas along with the network analyzer. The measured magnitudes were-24.292 dB, -28.854 dB and-32.234 dB.

DESIGN OF CONTINUOUS BEAM STEERABLE AND SCALABLE UNIT MODULE FOR WIRELESS POWER TRANSMISSION USING INJECTION-LOCKED OSCILLATOR ARRAY

Long-range wireless power transmission (WPT) is implemented with the beamforming using the phased array transmitter technology, which has been extensively applied in the radar systems. The cost of a conventional phased array transmitter module scales up in proportion to the number of antenna elements, as the massive number of transmit channels results in the increasing complexity of hardware and feeding antenna elements. Besides, the conventional phase-shifting transmitter architecture has lower DC to RF power conversion efficiency due to the insertion loss of power combining network at microwave frequency. In this paper, the concept of spatial power combining transmitter is utilized, and the upconversion circuit is greatly simplified to an injection locked oscillator. Our WPT system is implemented with the technology of oscillator array antenna at 2.4 GHz, which converts DC power to RF power and radiates into the air directly. The feedback voltage controlled oscillator (VCO) is implemented as the microwave source using a off-the-shelf bandpass filter, and the external signal is injected to the oscillator via a microstrip coupler. The oscillator core shows the DC-to-RF conversion efficiency of 45.87% with the injected power of 0 dBm at 2.4 GHz. Then the digital phase shifter is used to phase shifting the injected signal to extend the beam coverage. From the link budget analysis, the overall DC-to-DC efficiency of our highly-integrated system shows 1.5 times (0.22%) of the conventional phased array (0.15%) when the separation between the transmit array and the receive horn antenna is 1.2 meters. Therefore, as an modularized array, the proposed system demonstrates the promising capability of upscaling to an efficient massive array with greatly reduced bill-of-materials (BOM).

A broadband free-space dielectric properties measurement system at millimeter wavelengths

A free-space system operating in the 75 GHz to 95 GHz range for measurement of the complex permittivity of matter is presented. The complex transmission coefficient of a parallel polarized quasiplane wave through a planar sample is determined for different incidence angles. The quasiplane wave is realized by a collimated Gaussian beam. The complex permittivity is subsequently calculated from the measured data by applying a nonlinear least-squares method. Errors induced by multiple reflections between the transmitting and receiving horn antennas are removed by a time-domain gating technique. The design of the quasioptical measurement setup is based on Gaussian beam optics. A dielectric lens collimates the beam of the transmitting horn antenna for minimization of diffraction effects at the edges of the sample. In order to verify the Gaussian beam and thin lens approximations at millimeter wavelengths, the far-field pattern of the horn antenna and the dielectric lens system has been measured. The performance of the measurement setup has been tested using glass samples.

Experimental demonstration of the "apparent wavelength"

In this paper, an experimental demonstration of the apparent using microwaves incident on a plane conductive surface obliquely, with the electric field polarization parallel to a reflecting plane, is presented. Standing wave measurements were obtained by utilizing the interaction between the transmitting and the receiving rectangular horn antennas using the receiving horn antenna as a probe. This technique demonstrates to the students that the wavelength along the normal, the apparent is longer than the wavelength of the free-space incident or reflected waves and is in agreement with the theory. Finally, the proposed technique demonstrates high sensitivity and accuracy for tutorial demonstrations of standing wave pattern measurements despite the large cross-section of the receiving antenna. >

Influence of a cylindrical glass tube on the microwave field in the region occupied by the plasma column

The possibility of making full use of the focusing effect of a cylindrical glass tube in which the parameters of a plasma column are measured is investigated. A cylindrical glass tube was placed between the rectangular apertures of two horn antennas. The distribution of electromagnetic energy in the plane perpendicular to the optical axis of both horn antennas was investigated at different distances of sending and receiving horn antennas by means of a probe. (C.E.S.)