A new sub-structure characteristic mode concept for electromagnetic systems is defined and used to extend the applicability of an existing antenna shape-synthesis technique that does not require the feedpoint location to be specified prior to shaping. Application of the procedure is successfully illustrated by a realistic example, with experimental results.Introduction: The theory of characteristic modes (CMs) for conducting objects was given in [1]. A moment method formulation [2], which uses RWG expansions functions [3] to model a conducting structure, converts the electric field integral equation into a matrix equation [Z][J ] = [V ]. Column vector [J ] contains the coefficients of the expansion functions for the unknown electric current density on the structure and [Z] is the operator matrix. Excitation vector [V ] accounts for one or more antenna feedpoints on the structure, modelled as gap-sources [3] at appropriate 'edges' with respect to which RWG functions are defined. Reference [1] gives the associated matrix eigenvalue equation [Z][J n ] = (1 + jl n )[R][J n ] for the current density [J n ] of the nth CM and its eigenvalue l n , with [Z] = [R] + j[X ]. We showed [4,5] that when an antenna only has a single CM that is of any significance (low magnitude eigenvalue) at its operating frequencies, the resonance frequency and smallest possible Q (at this resonance frequency) of such a singlemode antenna can be predicted without specifying the location of the feedpoint(s) beforehand. This leads to a novel approach for the shape synthesis of a wide class of antennas that are sufficiently small in terms of wavelength that they are singlemode, and that does not require the feed location to be specified a priori.
An antenna shape synthesis method is proposed that allows shaping of the antenna geometry prior to specification of the feed location and type. This reduces the constraints placed on the optimization process and can lead to potentially new designs due to the increased degree of freedom afforded. An appropriate feedpoint is easily chosen after shape optimization by selecting a location on the resulting structure for best impedance matching. The procedure is made possible through the use of characteristic mode concepts. Examples show that the antenna-Q values of the resulting shaped radiators closely approach the fundamental bounds.
In summary, we proposed and demonstrated a C band TEDFL which employs a BFM and a TFBG to form the laser cavity. The BFM acts as a broadband reflector both for the lasing signal and pump source. At pumping power of 100 mW, stable laser output power of 21.35 dBm is obtained with the threshold pumping power as small as 4.7 mW. A SMSR of 57.9 dB and 16 nm tuning range are demonstrated. This BFM-based TEDFL with graceful features as mentioned may find vast applications in fiber optics communications and fiber sensor technology. , Temperature-tuned erbium-doped fiber ring laser with polymer-coated fiber grating, Opt Commun 202 (2002), 331-334. ABSTRACT: In handheld communications devices there is not much room for the placement of antennas. This problem is exacerbated when more than one antenna is needed for use in a MIMO communications system. It is then useful to be able to utilize some of the existing device structure to form the required antennas. In this article, we show how the characteristic mode theory can be used to achieve this in a way that results in antennas with the low envelope correlation preferred for MIMO antennas. ABSTRACT: A broadband, circular switched parasitic array with two active elements, suitable for DVB-T applications at the V-UHF band is designed with the aid of a genetic algorithm. Numerical as well as measurements results are presented for a single switch position. Simulation results are also presented for switched-beam array operation, using the measured antenna radiation patterns.
A novel design approach is proposed for designing high performance reflectarrays using low-cost, lossy substrates. Using sub-wavelength coupled-resonant elements, in particular sub-wavelength loops, one can dramatically reduce losses in reflectarrays and not incur significant gain drop due to the use of the lossy, low-cost substrate. It is further shown that the subwavelength loop achieves sufficient phase variation in a single layer design with a modest requirement in etching tolerance, making the loop superior to both the single and double-layer subwavelength patch elements.
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