Impedance Transformers

Non

Bending Loss Mitigation by Surface Plasmon Resonance

Surface plasmon resonance can be used to confine a wave within a thin metal film. The resultant wave is very well-confined by the extreme refractive index difference between the metal and the ambient medium. Such confinement can be used to guide waves under extreme conditions such as subwavelength channels or through extremely tight bends where radiation losses would normally dissipate the wave. A nichrome thin film was deposited and etched as a shadow alongside a series of multi-mode SU-8 slab waveguides with extremely sharp angled bends. Light from a Helium-Neon laser was coupled into these waveguides and the power transmitted was measured and compared to a sample without a nichrome thin film. A total attenuation of signal was found in the non-metallic sample, while a steady signal was successfully transmitted through the sample with the thin film

Temperature- and Time-Dependent Dielectric Measurements and Modelling on Curing of Polymer Composites

In this book a test set for dielectric measurements at 2.45 GHz during curing of polymer composites is developed. Fast reconstruction is solved using a neural network algorithm. Modeling of the curing process at 2.45 GHz using both dielectric constant and dielectric loss factor results in more accurate model compared to low frequency modelling that only uses the loss factor. Effect of various hardeners and different amount of filler is investigated

Temperature- and Time-Dependent Dielectric Measurements and Modelling on Curing of Polymer Composites

In this book a test set for dielectric measurements at 2.45 GHz during curing of polymer composites is developed. Fast reconstruction is solved using a neural network algorithm. Modeling of the curing process at 2.45 GHz using both dielectric constant and dielectric loss factor results in more accurate model compared to low frequency modelling that only uses the loss factor. Effect of various hardeners and different amount of filler is investigated

Inverse scattering applications for dielectric loaded metallic waveguides

Kısmen dielektrik yüklü dalga kılavuzları çok sayıda mikrodalga cihazında kullanılmaktadır. Kısmen dielektrik yüklü dikdörtgen dalga kılavuzları ile malzemelerin karmaşık dielektrik geçirgenliklerinin ve dielektrik yüklü metalik dalga kılavuzlarında propagasyon karakteristiklerinin belirlenmesi birçok mühendislik uygulamasında önemlidir. Bu çalışma bahsedilen her iki alandaki mevcut literatüre katkı yapılmasını amaçlamaktadır. Dielektrik yüklü metalik dalga kılavuzları için yansıma iletim ölçmeleri ile malzemelerin karmaşık dielektrik geçirgenliklerinin belirlenmesi amacıyla yapılmış olan çalışmalar nispeten basit durumları içermektedirler. Bu çalışmada, dikdörtgen dalga kılavuzu içerisine yerleştirilen sütun şeklindeki dielektriğin geçirgenliğinin belirlenmesi ters saçılma problemi olarak formüle edildi ve literatürdeki sınırlamalar ortadan kaldırıldı. Oldukça esnek ve genel tipteki problemleri içerecek şekilde, doğru ve sayısal olarak verimli bir algoritma verildi. Aynı zamanda bu çalışmada, kayıpsız periyodik yapılardaki birim hücrenin Genelleştirilmiş Saçılma Matrisi için bir sakınım ilişkisi ortaya konuldu. Bu sakınım ilişkisi, tek Floquet modlu bölge içerisinde yer alan iletim/durdurma band geçiş frekanslarını doğru olarak kestiren yeni bir yöntem sağlamaktadır. Bu yöntem iletim durdurma band bölgeleri verilen/ölçülen periyodik yapıyı kullanarak belirli topolojiler için birim hücre boyutlarının belirlenmesi ters problemine uygulanabilir niteliktedir.    Anahtar Kelimeler: Karmaşık dielektrik geçirgenlik, periyodik yüklü dalga kılavuzu.Partially dielectric loaded waveguides have been used in many microwave devices. Determination of complex permittivity of materials with partially dielectric loaded rectangular waveguides and propagation characteristics of periodically dielectric loaded metallic waveguides are important in many engineering applications. This study aims to extend the grounds thus far covered in both of the areas mentioned above. The methods reported in the literature on determination of complex permittivity of materials via transmission/reflection measurements for dielectric loaded metallic waveguides include relatively simple scenarios. These approaches either treat a simplified scenario wherein the sample fills the entire cross-section of the waveguide or in considering partial filling they do not accurately account for interactions between higher order modes. In this study the determination of the complex permittivity of dielectric posts in rectangular waveguides is formulated as an inverse scattering problem and these limitations are removed. An accurate and numerically efficient algorithm is given which is quite flexible and can easily be modified to address problems involving more general types of inhomogeneous dielectric loadings in waveguides. The predicted results are compared with measurements and good agreement is obtained. Propagation of waves in periodic struc-tures has long been an area of interest for physicists and engineers. Periodically loaded waveguides can be considered as one of the simplest subsets of periodic structures which exhibit 1-D discrete translational symmetry and which can be completely defined by specifiying the loading over an interval equal to the period p, or in other words by specifing the unit cell of the structure. Propagation characteristics of such waveguides play an important role in the design problems encountered in many engineering applications such as, slow-wave structures, filters, phase shifters, polarizers, impedance matching devices, antennas, antenna feeds, and pulse compressors. Periodicity encountered in such devices is comprised of a cascade of a limited number of unit cells connected to appropriate terminations. Unit cell approach of analysis then provides an approximate description of device propagation characteristics, the accuracy of which improves with the number of unit cells utilized in the design. More then of-ten the actual device design involves a fine-tuning of the parameters characterizing the unit cell and the terminations via a multiparameter optimization scheme. The generalized scattering matrix representation of unit cell in terms of the modes of the uniform waveguide provides a convenient and efficient approach which has been used by several researchers in addressing a fairly broad range of problems involving periodically loaded waveguides. The results reported in the literature on propagation in periodically loaded waveguides also include investigations of the features of the eigenvalue spectrum of Floquet modes supported by such structures, as well as derivations of certain conservation relations satisfied by the generalized scattering matrix in the absence of losses. Probably an interesting contribution of this paper, from an applicational point of view, is the formulation of an approximate relation between the elements of the generalized scattering matrix of a symmetric unit cell, which can be used to obtain rather accurate estimates for stop-band/pass-band transitions frequencies in single Floquet mode regions of symmetric structures. The proposed approach can be implemented in a very efficient manner, without having to impose Floquet condition and solve the resulting eigenvalue equation. The method can be used in addressing the inverse problem of determinating unit cell dimensions for a specified topology using measured/given values of pass-band/stopband regions. As a result, we believe that the proposed method may effectively be used in the design of microwave bandpass/stopband filter. In order to demonstrate the validity and applicability of the several points made in this paper we present some typical results. We also investigate dependence of estimated values of the band-edge frequencies obtained via the proposed approximation scheme on the parameters of the unit cell. For verification/validation purposes we have compared our mode matching generalized scattering matrix (MM-GSM) results with those calculated via an independent commercial software package (HFSS). Numerical results obtained for a typical periodically loaded waveguide are in perfect agreement with the theory and demonstrate the validity, applicability as well as the numerical efficiency of the proposed approach.  Keywords: Complex dielectric permittivity, periodically loaded waveguide

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance