Kien Trung Pham

Dimensions, volume, and mass of agricultural goods are essential physical features to build sizing, grading, and packaging systems. Manual property measurements are time-consuming, costly, and labor-intensive due to traditional technologies while various devices need to be installed to adapt process requirements. Furthermore, it is very challenging to accurately measure product with irregular or specific shapes, such as starfruit (Averrhoa carambola). Recently, there have been several research results on estimating features of the irregularly shaped object, they are either get inaccurate results or need repeated captures, computational resources, and time to rebuild the three-dimensional representation of the goods. The starfruit has not been studied completely in this size and weight measurements. This paper focuses on new techniques which exhibit simple installation to generate multiple functions for estimating the dimensions, volume, and mass with high accuracy. In this proposed method, we separated the process into two main phases. In the first phase, a camera is used to capture a top-view image of a starfruit, then image processing and machine vision techniques are applied to process the acquisition image before the process slices numerically the starfruit into several pieces along the longitudinal axis and estimates the physical attributes of each pieces using disc method and conical frustum method. Its volume is the summation of the volume of each partial slice. In the next phase, the density is used to estimate the mass of starfruit since the correlation coefficient (R-squared) between the volume and mass of starfruit is nearly linear with 0.9205. The validated results are highly competitive with accuracy of about 99% for the volume and mass in 300 testing samples.

This paper presents the experimental validation of independent and wide beam scanning with a dual-band transmitarray antenna (TA) in Satcom up- and down-links at Ka-band. The TA consists of two sub-arrays, one operates in the down-link with central frequency at 19.5 GHz, while the other one operates in the up-link centered at 29 GHz. Both sub-arrays share a common radiating aperture to obtain compact configuration. The TA layout is made of 1-bit unit-cells and its design relies on the bifocal technique to extend the beam scanning capability. The proposed bifocal prototype includes 1500 up-link unit-cells in 30×50 matrix and 1581 down-link unit-cells arranged in 31×51 rectangular lattice. The 1D scanning is validated by displacing the feed horn along one direction. We show that the TA beam can be scanned in a ±40° and ±30° independently in each band while keeping a very low scan loss (< 2 dB).

This paper describes the performance of dual circularly-polarized transmitarray antennas at Ka-band with independent radiation characteristics. The proposed antenna architecture consists of a dual linearly polarized (dual LP) TA panel based on the interleaving technique combined to an add-on broadband polarizer, in order to generate independent RHCP and LHCP beams. This offers both dual-LP and dual-CP operation depending on the topology of the polarizer. The LP unit-cell are designed to achieve a 3-bit phase resolution, and the dual-LP TA panel is made of two interleaved single LP sub-arrays with 52-by-52 and 53-by-53 elements operating in 45° and 135° single linear polarization, respectively. The polarizer transforms the dual-LP into dual-CP while keeping radiation independence of each polarization across Ka-band. The experimental results obtained with three different prototypes pointing up to 50° validate the proposed concepts.

This paper presents the design, optimization, fabrication, and characterization of an electronically steerable transmitarray with 2 bits of phase quantization per unit cell. The proposed transmitarray operates in linear polarization at Ka-band and is composed of 14W14 reconfigurable unit-cells. Four p-i-n diodes are integrated on each unit-cell to control the radiated field phase distribution across the transmitarray aperture. The prototype demonstrates experimentally pencil beam scanning over a 120W120-degree window, a maximum gain at broadside of 19.8 dBi, and a 3-dB fractional bandwidth of 16.2%.

We present here a design of metal-only unit-cell for transmitarray antenna (TA) applications at Ka-band, and we introduce a solution to reduce the total number of layers by polarization manipulation. The corresponding unit-cell is based on a C-shaped slot radiating element, fabricated by laser ablation on a thin metal sheet and operating in linear polarization. Thanks to the rotation of the slot, polarization of radiated wave can be manipulated to any arbitrary direction, particularly in the orthogonal direction of the incident wave. By combining two unit-cells with opposite rotation directions, we show that metal-only unit-cells made of three layers can be obtained, with a 360° phase shift and insertion loss lower than 1 dB. This unit-cell with reduced profile is used to design several TA prototypes with a main beam direction pointing up to 50°. The experimental results demonstrate an 11% 3-dB fractional gain bandwidth with an aperture efficiency around 50% for a beam at boresight.

Dual-band transmitarray antennas are demonstrated at Ka-band with the capability of forming independent linearly polarized beams with a given polarization in each frequency band, while sharing the same radiating aperture. The proposed three-layer unit-cell is based on identical narrow microstrip patches printed on both receiving and transmitting layers and connected by a metallized via hole. The metal layers are printed on two identical substrates bonded with a thin film, and the designed unit-cell exhibits a 180° phase resolution (i.e., 1-b phase quantization). The dual-band dual-polarized property of the transmitarray is achieved by interleaving unit-cells operating in the down-link and up-link frequency bands. Four different prototypes are characterized to demonstrate the relevance of the proposed concepts. A good agreement is obtained between the radiation patterns, gain curves, and cross-polarization levels measured and computed in both frequency bands and polarizations.

Dual linearly polarized transmitarray antennas with wideband performance are investigated in X-band. Their designs are based on unit-cells with bandpass response. Their structures consist of three conducting layers printed on two identical dielectric substrates glued with a bonding film. Detailed experimental results demonstrate excellent polarization independence, with expected performance and properly preserved radiation characteristics for each polarization. The measured data are in excellent agreement with full-wave simulation results.