Nghia Nguyen-Trong

A Frequency- and Polarization-Reconfigurable Stub-Loaded Microstrip Patch Antenna

A stub-loaded microstrip patch antenna with reconfigurability in both frequency and polarization is presented. Using 12 varactors with two independent voltages, reconfigurability is achieved in a fractional bandwidth of around 40% while allowing selection between circular polarization (CP) with both rotating senses and linear polarization (LP). The design is optimized based on an analytical model, which significantly speeds up the process while yielding reasonably accurate predictions. For illustration of the concept, an antenna is designed, optimized, and manufactured for reconfigurable operation in the 2.4-3.6 GHz frequency range. A good agreement between simulations and measurements is obtained which validates the proposed method. A full reconfigurability is demonstrated in the operation band with the ability to both tune the antenna to a given frequency and select a polarization state among left-hand or right-hand CP or various states of LP.

A Wideband Omnidirectional Horizontally Polarized Traveling-Wave Antenna Based on Half-Mode Substrate Integrated Waveguide

A traveling-wave antenna based on a tapered half-mode substrate integrated waveguide is introduced in this letter. It uses a direct transition from a coaxial connector and radiates from the open side of the waveguide. The antenna exhibits a wide bandwidth, an omnidirectional radiation pattern, and horizontal polarization and can be integrated into metallic structures. The physical principle and design guidelines are summarized. A prototype of the proposed antenna has been realized and demonstrated a wide measured bandwidth extending from 6.7 to 16 GHz, with radiation characteristics corresponding very well with simulations.

Analysis and Design of a Reconfigurable Antenna Based on Half-Mode Substrate-Integrated Cavity

The detailed analysis, design, and optimization of a reconfigurable antenna based on a periodically stub-loaded half-mode substrate-integrated waveguide (HMSIW) cavity is presented in this paper. The analysis demonstrates an excellent prediction of the resonance frequency for the cavity with an error of less than 2% compared to numerical simulations performed over a wide range of parameters. The fast computation of the resonance frequency based on the analytical model gives deep insight into the antenna operation and allows an efficient optimization process. The reconfigurable antenna has been designed and optimized to cover the whole S-band (WR-284 waveguide band), i.e., 2.60-3.95 GHz, using three varactors with measured capacitance varying from 0.149 to 1.304 pF. Experimental results validate the concept across the whole tuning range, with a return loss and antenna gain greater than 15 and 2.1 dB, respectively at resonance.

A Frequency- and Pattern-Reconfigurable Center-Shorted Microstrip Antenna

A frequency- and pattern-reconfigurable antenna based on a center-shorted microstrip patch is presented. The novel design utilizes two resonance modes of a microstrip antenna with shorting vias at the patch center. To set up the antenna tuning mechanism, two groups of varactors with a measured tuning range of [0.149, 1.304] pF are placed at two opposite sides of the antenna, followed by open-circuited loading stubs. For a particular bias voltage configuration, the structure operates as a dual-band antenna with broadside radiation at the upper resonance frequency and monopole-like radiation at the lower band. By varying the dc bias voltage, both resonance frequencies can be changed simultaneously. Based on the proposed concept, a demonstration antenna has been designed so that the two types of aforementioned patterns can be reconfigured across a continuous fractional frequency range of more than 20%. Experimental results are provided, which validate the proposed concept and design procedure.

A Semi-Analytical Solution of a Tapered Half-Mode Substrate-Integrated Waveguide With Application to Rapid Antenna Optimization

A semi-analytical solution for the input reflections, inner field distribution and radiated fields for a wideband traveling-wave antenna based on a tapered half-mode substrate-integrated waveguide (HMSIW) is proposed in this paper. The analysis validates the operation mechanism for this type of traveling-wave antenna which exhibits omni-directional radiation properties with horizontal polarization (“magnetic dipole”). The derived expressions allows the design and efficient optimization of different antennas towards fulfilling various predefined specifications of reflection coefficient and operating bandwidth. The antenna utilizes a wideband transition from coaxial cable to a HMSIW, which is also considered in the model to provide highly accurate semi-analytical results. Utilizing the proposed method, three antennas of different specifications have been optimized, manufactured and tested. The analysis, simulation and measurement results show good correspondences, which verifies the design process and demonstrates the versatility of the concept.

Variational Analysis of Folded Substrate-Integrated Waveguides

An accurate numerical solution describing the propagation behavior of two types of folded substrate-integrated waveguide (FSIW) is demonstrated in this letter. The computation is based on a variational method which can be carried out efficiently by solving the stationary equation corresponding to each type of FSIW. The approach can be extended to solve various folded structures, i.e., with different gap positions, where the layers are made of substrates with different thicknesses and material properties.

A Frequency- and Polarization-Reconfigurable Circular Cavity Antenna

The principle and experimental validation of a frequency- and polarization-reconfigurable antenna using switching PIN diodes is presented in this letter. The antenna is based on a center-fed circular cavity with switchable shorting vias along its outer edge. Turning a set of shorting vias on on one side and off on the other side creates a radiating slot with controllable length and location along the side wall of the cavity that results in different antenna resonance frequencies and polarizations. As a proof of concept, a particular realization of the antenna is designed that can change the linear polarization in six different angles and at five discrete frequencies (spanning more than one octave). Based on the proposed concept, quasi-continuous frequency- and polarization-reconfiguration is feasible using individual control of a large number of switching devices.

Transmission-Line Model of Nonuniform Leaky-Wave Antennas

Nonuniform leaky-wave antennas (LWAs) are analyzed and synthesized using a lossy transmission line model. The analysis is based on a general waveguide circuit theory. Compared to the classical approach, the model yields a higher accuracy in the computation of both aperture field distribution and radiation patterns. The proposed analysis is also able to provide scattering parameters of the whole structure in a fraction of a second, which is valuable for antenna optimization. Based on the analysis, a general method for far-field pattern synthesis utilizing global optimization is presented. As an application demonstration, the half-mode substrate-integrated waveguide (HMSIW), or half-width microstrip line, has been selected as basis structure for the LWA designs. Two antennas have been optimized targeting different specifications, i.e., a low-sidelobe level and a wide null in the radiation pattern. Experimental results are provided for these selected examples of nonuniform LWAs, which ultimately validate the proposed technique as an improvement over the classical approach.

Wideband transition from coaxial line to half-mode substrate integrated waveguide

In this paper, a perpendicular transition from coaxial cable to Half-Mode Substrate Integrated Waveguide (HM-SIW) is proposed for wideband operation. The design places emphasis on the robustness and manufacturability of the transition, in particular with a reproducible realization of a matching capacitive gap. A prototype of back-to-back transitions with 64 mm length of HMSIW in-between is realized for operation in the frequency range of 10 GHz to 16 GHz. The return loss of the back-to-back transitions is measured to be close to 20 dB. A reasonable agreement between experimental and simulation results is achieved, validating the proposed transition geometry.

Optimization of leaky-wave antennas based on non-uniform HMSIW

In this paper, the optimization of leaky-wave antennas (LWAs) based on non-uniform half-mode substrate-integrated waveguides (HMSIWs) is presented. The optimization is based on a semi-analytical solution of a tapered HMSIW, which has been recently proposed by the authors in a previously published paper. This analysis is based on a transmission line model of the HMSIW, where the reflections along the LWA are considered. Compared to the traditional approach, the analysis demonstrates a higher accuracy on the pattern calculation. Two different optimizations with different objectives are demonstrated: a wideband omni-directional LWA and a LWA with minimized sidelobe level. The optimized results obtained with particle swarm optimization and genetic algorithm exemplify the versatility of the method for different target specifications.