Design Of Leaky-wave Antenna Research Articles

New Approach of Radiation Pattern Control for Leaky-Wave Antennas Based on the Effective Radiation Sections

In this paper, a new radiation pattern-control approach for leaky-wave antenna designs is proposed based on the theory of effective radiation sections. This approach can be used to generate radiation null regions around desired direction or to reduce the side lobe levels of leaky-wave antennas in a simple and efficient way, i.e., by controlling the radiation from the effective radiation sections. The traveling-wave line-source model is employed for simplifying the analysis at first. Then, the approach is implemented in the sub strate integrated waveguide (SIW) long-straight slot Leaky-wave antennas (LWA) by changing the slot width at the locations corresponding to the effective radiation sections (ERSs). The simulation results show that the radiation null region can be introduced around the desired direction, and the side lobe level can be reduced. Furthermore, the cross-polar level can be controlled to a very low level. Experimental results are also given as verification. In addition, the proposed method still has some limitations, which are discussed in detail and will be improved in the future.

Analysis and Design of Leaky-Wave Antenna with Low SLL Based on Half-Mode SIW Structure

This paper presents a novel leaky-wave antenna based on the Half-Mode Substrate Integrated Waveguide (HMSIW) structure with low side lobe level. The effect of the structural parameters of the LWAs on the radiation performances is studied. Using beam-forming technique, the leakage loss factorαalong the radiation aperture is designed in a tapered way by controlling the aperture depth along the structure. This controls the radiated power along the antenna aperture and finally achieves the radiation pattern with low SLL. Furthermore, the antenna structure is optimized to get an even lower SLL.

Periodic Ridged Leaky-Wave Antenna Design Based on SIW Technology

A periodic long slot leaky-wave antenna (LWA) based on a ridged substrate integrated waveguide (RSIW) is proposed. To reduce the cross polarization, the long slot is placed on the SIW centerline, and a sinusoidal ridge is used to produce a controllable asymmetric electric field around the long slot. Also, only a small stopband occurs when the beam is scanned through the broadside. Varying the amplitude and width of the sinusoidal ridge provides a fixed phase constant and controllable leakage rate to achieve the desired sidelobe level of less than $-$ 30 dB. Measurement results are consistent with the simulation results.

Nonreciprocal and Magnetically Scanned Leaky-Wave Antenna Using Coupled CRLH Lines

A new class of miniaturized nonreciprocal leaky-wave antenna (LWA) is proposed for wide angle scanning via magnetic tuning. A design is proposed based on coupled composite right left handed (CRLH) transmission lines (TLs) on a ferrite substrate for miniaturization with an external magnetic field control. Coupled TLs were previously utilized in a nonreciprocal LWA design with separate transmitter (TX) and receiver (RX) ports. In this work, CRLH TLs are employed to realize miniaturization, nonreciprocal properties and wide-angle scanning at the same time. To design the LWA, a circuit model was developed with the nonreciprocal propagation properties analytically calculated. For experimental validation, a 15-unit-cell prototype with a unit-cell length of only λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /20 was manufactured and tested. The TX and RX beams were independently scanned in the E-plane up to 80° by changing the bias field ±50 Oe. The associated antenna gain varies between 3.5 and 5 dB at the operating frequency of 1.79 GHz as the beam is scanned. This is unlike traditional LWAs that achieve beamscanning via frequency control. Additionally, measured isolation between TX and RX ports was ~ 10 dB.

Controlled Leaky-Wave Radiation From a Planar Configuration of Width-Modulated Microstrip Lines

Planar leaky-wave antenna (LWA) designs that utilize a printed surface wave (SW) source are presented. Specifically, by the addition of a periodic arrangement of width-modulated microstrip lines on top of a grounded dielectric slab (GDS), a sinusoidally modulated reactance surface (SMRS) can be realized, providing appropriate conditions for leaky wave (LW) radiation. In addition, a transition section near the SW source improves antenna matching, while also, controlling the leakage rate and aperture distribution. A numerically computed dispersion diagram (DD) for the periodic structure is also calculated in terms of Mathieu functions. Full-wave simulations and measurements are in agreement with the developed numerical model and results suggest that these LWAs can offer broadside radiation as well as continuous beam scanning with radiation efficiencies of more than 85%. In addition, the investigated width-modulated microstrip lines offer ease of fabrication and may also be useful in the design of new periodic structures for wave guidance and other low-cost printed circuits and antennas.

New Design of Leaky Wave Antenna Based on SIW Technology for Beam Steering

New Design of Leaky Wave Antenna Based on SIW Technology for Beam Steering

Full-Wave Analysis and Design of Circular Half-Width Microstrip Leaky-Wave Antennas

A half-width microstrip leaky-wave antenna on a circular substrate is proposed and investigated. A microstrip on a circular substrate has a broader bandwidth for free-space leaky-wave radiation than a planar microstrip. A half-width microstrip has similar radiation characteristics to a full-width microstrip, but it does not require complex feeding structures. Full-wave analysis based on the extended spectral domain approach (ESDA) is applied to analyze the propagation characteristics of the circular half-width microstrip. The ESDA accounts for field singularities near a conductor edge of finite thickness and it does not require a virtual boundary to obtain the finite extent of the analytical space. Consequently, the ESDA is more suitable for analyzing leaky-wave structures than other conventional analysis methods. Numerical calculations are performed to determine the characteristics of the leaky-wave radiation from half-width microstrips on circular and semicircular substrates. The leaky radiation elements can be efficiently designed based on these numerical results. Two practical antennas with leaky radiation elements and feeders are designed and implemented. The measured bandwidths of the free-space leaky-wave radiation indicate that these cylindrical antennas have better performances than planar ones and they are in reasonable agreement with theoretical results. The measured radiation patterns with frequency-scanning characteristics also agree well with the simulation results.

Sinusoidally Modulated Graphene Leaky-Wave Antenna for Electronic Beamscanning at THz

This paper proposes the concept, analysis and design of a sinusoidally-modulated graphene leaky-wave antenna with beam scanning capabilities at a fixed frequency. The antenna operates at terahertz frequencies and is composed of a graphene sheet transferred onto a back-metallized substrate and a set of polysilicon DC gating pads located beneath it. In order to create a leaky-mode, the graphene surface reactance is sinusoidally-modulated via graphene's field effect by applying adequate DC bias voltages to the different gating pads. The pointing angle and leakage rate can be dynamically controlled by adjusting the applied voltages, providing versatile beamscanning capabilities. The proposed concept and achieved performance, computed using realistic material parameters, are extremely promising for beamscanning at THz frequencies, and could pave the way to graphene-based reconfigurable transceivers and sensors.

Efficient Analysis and Design of Novel SIW Leaky-Wave Antenna

A novel transverse equivalent network is developed in this letter to efficiently analyze a recently proposed leaky-wave antenna in substrate integrated waveguide (SIW) technology. For this purpose, precise modeling of the SIW posts for any distance between vias is essential to obtain accurate results. A detailed parametric study is performed resulting in leaky-mode dispersion curves as a function of the main geometrical dimensions of the antenna. Finally, design curves that directly provide the requested dimensions to synthesize the desired scanning response and leakage rate are reported and validated with experiments.

A simple and efficient finite difference frequency domain method for the analysis and design of leaky-wave antennas

The finite difference frequency domain method for the analysis of periodic structures will lead to a large-scale nonsymmetrical generalized eigenvalue problem, especially when the open periodic structures are analyzed.In this article, the method is greatly simplified, because the large-scale sparse matrix technique and the shift-and-invert Arnoldi technique, which must be applied to significantly reduce the memory need and increase simulation speed, are implemented by means of some existed codes, for example, matlab codes. Besides, the difference equations of this method are much simpler than those of the previous method, because the longitudinal field components do not have to be eliminated to approximately transform the generalized eigenvalue problem to a standard eigenvalue problem. As a result, the method proposed here is quite simple and efficient for the analysis of leaky-wave antenna, because a leaky-wave antenna can be regarded as direct geometrical evolution from a guided-wave structure that permits to leak energy along its longitudinal direction. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2814–2817, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27216

Periodic Leaky-Wave Antenna Array With Horizontally Polarized Omnidirectional Pattern

A novel periodic leaky-wave antenna for broadside radiation with horizontally polarized omnidirectional pattern is proposed, designed and demonstrated experimentally. The objective is to achieve a horizontally polarized omnidirectional antenna array with highly directive beam. The proposed structure is based on combining the rotating electric field method and a leaky-wave antenna design. By properly designing a unit cell with a pair of crossed dipoles spaced at a distance approximately equal to λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /4 at the center frequency, not only omnidirectional radiation pattern with horizontal polarization is obtained by crossed dipoles fed in phase quadrature, but also the open-stopband effect exhibited at broadside scan is significantly reduced. The analysis and design of this structure are performed on the basis of a simple equivalent network model. A finite structure formed by 16-unit cell (32-element) for broadside beam is developed at the 2.4 GHz band, which offers a horizontally polarized omnidirectional radiation pattern with enhanced gain of 9.9-10.6 dBi and measured radiation efficiency of 90% for the covering bands.

Rectilinear Leaky-Wave Antennas With Broad Beam Patterns Using Hybrid Printed-Circuit Waveguides

A theoretical study on the design of broadbeam leaky-wave antennas (LWAs) of uniform type and rectilinear geometry is presented. A new broadbeam LWA structure based on the hybrid printed-circuit waveguide is proposed, which allows for the necessary flexible and independent control of the leaky-wave phase and leakage constants. The study shows that both the real and virtual focus LWAs can be synthesized in a simple manner by tapering the printed-slot along the LWA properly, but the real focus LWA is preferred in practice. Practical issues concerning the tapering of these LWA are investigated, including the tuning of the radiation pattern asymmetry level and beamwidth, the control of the ripple level inside the broad radiated main beam, and the frequency response of the broadbeam LWA. The paper provides new insight and guidance for the design of this type of LWAs.

Analysis and Design of Conformal Tapered Leaky-Wave Antennas

The theory to analyze and design tapered conformal line-source leaky-wave antennas is described in this letter. The deformation in the radiation pattern associated to the bending of the antenna is accurately predicted, and useful expressions are derived to taper the leaky-mode complex propagation constant in order to restore the high-directive radiated beam scanning at the desired angle. The analysis method and the design approach are validated with full-wave simulations of a curved tapered leaky-wave antenna in hybrid technology.

Superluminal Waveguides Based on Non-Foster Circuits for Broadband Leaky-Wave Antennas

Non-Foster circuits such as negative capacitors can be used to create superluminal waveguides for broadband leaky-wave antennas. The negative capacitors effectively cancel part of the dielectric constant within the waveguide to provide a broadband relative permittivity between 0 and 1. When used as a leaky-wave antenna, the beam angle is independent of frequency over a broad bandwidth because the waveguide provides a frequency-independent phase velocity greater than the vacuum speed of light. Thus, this approach eliminates beam squint, which is a primary drawback of passive leaky-wave antenna designs. Simulation results using ideal negative capacitors are presented, and the effects of causality are analyzed.

Leaky-wave antenna with arbitrary scan in the frequency band

A wide-angle frequency-scanned leaky-wave antenna design is presented. The proposed antenna operates in the nonfundamental mode and uses a meandered feed line to produce the exact phase-delay relationship necessary for achieving the desired scan in the specified frequency band. Experimental results obtained for a four-element antenna designed for the 6.05 – 6.75 GHz frequency band, show a low-loss scanned radiation pattern in the range of ± 45°. The measured gain is 5.75 ± 0.5 dBi. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2441–2444, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25496

Design of Short Microstrip Leaky-Wave Antenna With Suppressed Back Lobe and Increased Frequency Scanning Region

We demonstrate a short (1.08lambdao) microstrip leaky-wave antenna (MLWA) with suppressed back lobes and doubled frequency scanning region. The configuration of the proposed LWA contains three parts: the conventional open structure MLWA, the added monopole connected to the end of the MLWA on a defected ground plane, and the Yagi-Uda-like elements fabricated along the monopole. Because of the open structure of the MLWA, the reflected power produces a large back lobe radiated backwardly. By using the method of the added monopole connected to the end of the antenna, the remainder power could radiate through the added monopole without reflecting at the end. In addition, the Yagi-Uda-like elements fabricated along the added monopole enlarge the frequency scanning region due to the Yagi-Uda antenna characteristic. Compare to the conventional MLWA, the back lobe of the proposed LWA is suppressed about 8 dB at 5.0 GHz. The frequency scanning region of the H-plane (YZ-plane) of the proposed LWA can scan from 34deg to 57deg (total 23deg) while the frequency is operated from 4.6 GHz to 5.0 GHz; meanwhile the conventional MLWA scans from 30deg to 41deg (only 11deg) at the same frequency region.

LEAKY WAVE ANTENNA REALIZATION BY COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINE

This paper presents a realization of composite right/left handed transmission lines using coupled microstrip lines. This structure exploits the advantages of the microstrip lines, while increases the coupling by a ∞oating conductor at the ground plane. The performance of this composite right/left-handed line is demonstrated by both simulated and measured results, and they show good agreement. The designed line has broad bandwidth with low losses and small size. A novel dominant mode leaky wave antenna design, using the previous structure, is presented with backward to forward scanning capability.

Characterization and Design of Cylindrical Microstrip Leaky-Wave Antennas

The spectral-domain approach is applied for the analysis and the design of the cylindrical microstrip leaky-wave antenna. The first higher-order leaky-mode is thoroughly investigated. We perform the well-known spectral-domain approach and Galerkin's method to acquire the complex propagation constants of leaky modes, which are verified with results obtained by the scattering-parameter extraction technique. Two practical antennas are designed and implemented. Measured return loss and radiation patterns show a good performance of these cylindrical antennas, compared to that of the planar ones.

Application of FDTD Method to the Analysis and Design of Leaky-Wave Antennas at Microwaves and Millimeter Waves

The Finite-Difference Time-Domain (FDTD) method, though rather heavy from the computational point of view, allows a complete characterization of a radiating structure, permitting also the accuracy evaluation of the other available solutions. Numerical results have been derived for a broad class of leaky-wave antennas proposed in the literature, always revealing a very good agreement with the methods previously employed. By the FDTD technique it is possible to easily determine the propagation and radiation characteristics of such structures, to obtain the radiation pattern in the far field, and to simulate the longitudinal tapering, necessary to satisfy the design requirements usually imposed to reduce sidelobes in the radiation diagram.

Beam-Splitting Condition in a Broadside Symmetric Leaky-Wave Antenna of Finite Length

In this letter, the influence of the truncation effects on the beam-splitting property of a broadside symmetric leaky-wave antenna (LWA) is presented. It will be shown that for finite length LWAs, the maximum broadside beam exists at higher phase constant values than suggested by infinite LWA analysis. The accurate beam-splitting conditions are obtained using a computer search algorithm and are reported for a range of practical LWA lengths. The behavior of the aperture distributions at the split conditions is then discussed. To illustrate the application of the result, the theoretical beam-splitting condition plot is used to identify the beam-splitting point of a microstrip based LWA design. Finally, other design implications of the findings are discussed.