Hoang V. Nguyen

Substrate Integrated Artificial Dielectric (SIAD) Structure for Miniaturized Microstrip Circuits

A substrate integrated artificial dielectric (SIAD) structure for planar microstrip circuits miniaturization is presented. This structure is paraelectric and paramagnetic, i.e., provides enhancement of both the permittivity and the permeability from a given host substrate, and therefore achieves guided wavelength compression, leading to circuit size miniaturization. The SIAD is fully integrated and may be engineered by repeatable laser drilling and metal plating processes. By proper design of the SIAD, the effective parameters of a given host substrate are estimated to be increasable by up to 100% for the permittivity and up to 40% for the permeability, corresponding to a guided wavelength compression factor of up to 67%. Two practical applications are demonstrated for the proof-of-concept, a stepped-impedance low-pass filter and a branch-line coupler. For the proof-of-concept design used (nonoptimal in terms of size reduction), the former exhibits a length reduction of 16% and the latter exhibits an area reduction of 33%. The proposed SIAD structure may find many variations for manipulating the size, flexibility, and dispersion properties of microwave circuits, and may also be used for quasi-optical planar lenses.

Power-Recycling Feedback System for Maximization of Leaky-Wave Antennas' Radiation Efficiency

A novel power-recycling feedback scheme is proposed for systematic maximization of the generally poor radiation efficiency of leaky-wave antennas (LWAs). In this scheme, the nonradiated power at the end of the LWA structure, instead of being lost in the terminating load, is fed back to the input of the LWA through a power-combining system, which constructively adds the input and feedback powers while ensuring perfect matching and isolation of the two signals. As a result, the radiation efficiency of the isolated (or open-loop) LWA η0 is enhanced by the systems gain factor Gs (Gs > 1) to the overall radiation efficiency of ηs = Gsη0, which may reach 100% for any value of η0 in a lossless system. The design of the power-recycling system depends on η0 , which typically results from a tradeoff between required directivity and restricted size. The paper derives, for a rat-race-based implementation, the exact design equations, which determine both the rat-race impedance ratios and the feedback phase conditions of the system. The build-up of the steady-state regime from the transient regime at the onset of the system is explicated by transient circuit and electromagnetic simulations. Finally, an experimental power-recycling LWA system, including naturally ohmic and dielectric losses in addition to other imperfections, is demonstrated, where the isolated antenna efficiency η0 is enhanced from 38% to 68%, corresponding to a system efficiency enhancement of Gs = 1.8 . The proposed power-recycling feedback system applies to all LWAs and solves their fundamental efficiency problem in practical applications involving a tradeoff between relatively high directivity (higher than half-wavelength resonant antennas) and small size (smaller than open-loop LWAs or complex phased arrays).

CRLH Delay Line Pulse Position Modulation Transmitter

A composite right/left-handed delay line pulse position modulation (PPM) transmitter is proposed. This system, compared with conventional transmitters, exhibits the advantages of simple design, continuously tunable time delay and multiple order PPM capability. It is demonstrated by circuit and experimental results for both binary and quaternary PPM.

Pencil-Beam Full-Space Scanning 2D CRLH Leaky-Wave Antenna Array

A novel pencil-beam, full-space scanning 2D composite right/left-handed (CRLH) transmission line (TL) leaky-wave antenna (LWA) array is proposed. The proposed array achieves the same performance of conventional phase array antennas in a simpler manner. Moreover, array elements are fed by a CRLH infinite-wavelength series power divider and therefore the separation between array elements and the number of array element can be extended arbitrary. The CRLH series power divider eliminates the requirement of complex and high loss feeding networks commonly found in conventional arrays. Experimental results of each system components are presented along with analytical and simulation results of the complete array system.

Highly Efficient Leaky-Wave Antenna Array Using a Power-Recycling Series Feeding Network

A highly efficient leaky-wave antenna (LWA) array using a power-recycling series feeding network is proposed. The input power to the antenna array is efficiently recycled within the array elements and completely leaked out before reaching the terminations. Consequently, the array achieves high radiation efficiency and gain while maintaining a reasonable length in the direction of wave propagation. Simulated and measured results validate the proposed concept.

CRLH zeroth order resonator (ZOR): Experimental demonstration of insensitivity to losses and to size

The experimental demonstration of the insensitivity to losses and size of the composite right/left- handed (CRLH) zeroth order resonator (ZOR) is reported for the first time. The prototypes used for this demonstration are implemented in metal-insulator-metal (MIM) technology, which exhibits simplicity of design, high compactness and immunity to spurious resonances.

Performance-Enhanced and Symmetric Full-Space Scanning End-Switched CRLH LWA

An end-switched composite right/left-handed (CRLH) electronically scanned leaky-wave antenna (eLWA) is presented. The input signal is routed to either end of the CRLH eLWA via a switch, with each end providing half-space scanning (-90° ≤ θ ≤ 0°) . The end-switching scheme, which is applicable to any two-port LWA, enables full-space coverage using any half-space scanning only LWA. Compared to a conventional single-ended CRLH eLWA, which scans the full-space requiring a complex design, large capacitance values, and tuning range, the end-switched scheme simplifies the design and relaxes the constraints on the varactors, which lowers their cost. The conventional CRLH eLWA also suffers from a large scanning loss due to its large scanning range and from low efficiency due to its requirement for large capacitance values, which exhibit high loss. The end-switched CRLH eLWA reduces the scanning loss due to its smaller scanning range, while improving the efficiency due to its low capacitance values.

Metamaterial-based dual-band six-port front-end for direct digital QPSK transceiver

A composite right/left-handed (CRLH) transmission line (TL) dual-band (DB) six-port front-end is presented. The two key components in the six-port front-end, i.e. a 90deg hybrid coupler and a power splitter, are designed using CRLH TL sections and therefore are capable of operating at two arbitrary frequencies. The novel DB six-port front-end is well suited to a direct digital transceiver

First- and Second-Order Differentiators Based on Coupled-Line Directional Couplers

First- and second-order differentiators based on coupled-line directional couplers are presented. The time-derivative effect of coupled-line directional couplers is shown theoretically by applying Kirchhoffs laws to infinitesimal electromagnetically coupled transmission line sections. The time-derivation is accurate under the condition DeltaTf 0 Gt 1/4, where DeltaT is the pulse width and f 0 is the coupler center frequency; the required coupler operation frequency is thus inversely proportional to the pulse duration. The first-order differentiator, which is a simple coupled-line coupler, and the second-order differentiator, which requires in addition an interconnecting delay line, are demonstrated experimentally, and compared to ideal (mathematical) derivators.

Novel power recycling schemes for enhanced radiation efficiency in leaky-wave antennas

Two novel power recycling schemes for enhancing the radiation efficiency of leaky-wave antennas are proposed and demonstrated both theoretically and experimentally. The first scheme enhances the radiation efficiency of a single leaky-wave antenna by feeding the energy remaining at the output of the antenna back into its input terminal via a rat-race hybrid coupler. In this manner, the power associated with each information symbol loops several times along the structure until all its energy has been fully radiated, leading ideally to a 100% radiation efficiency. This is the self-recycling scheme. The second scheme enhances the radiation efficiency of a leaky-wave antenna array by re-injecting the energy remaining at the output of the excited element into the adjacent elements of the array via a series feeding network, and possibly including phase-shifters for full-space pencil-beam scanning. This is the cross-recycling scheme.