An analytical approach to location and shape reconstruction of dielectric scatterers, that was recently proposed, is tested against experimental data. Since the cross-sections of the scatterers do not depend on the <i>z</i> coordinate, a 2D problem can be formulated. A closed-form singular value decomposition of the scattering integral operator is derived and is used to determine the radiating components of the equivalent source density. This is a preliminary step toward a more complete solution, which will take into account the incident field inside the investigation domain in order to provide the dielectric features of the scatterer and also the nonradiating sources. Reconstructions of the equivalent sources, performed on some scattering data belonging to the Fresnel database, show the capabilities of the method and, thanks to the closed-form solution, results are obtained in a very short computation time.

Gian Luigi Gragnani

Maurizio Diaz Mendez

Location and Shape Reconstruction of 2D Dielectric Objects by Means of  a Closed-Form Method:  Preliminary Experimental Results

This paper presents an ultra-wideband (UWB) rectangular ring antenna excited by a circular disc monopole (CDM) with a conducting rod and two double ridges to radiate bidirectional pattern with constant beam direction along the entire UWB frequency range of 3.1&#x2013;10.6&#x2009;GHz. The conducting rod and double ridges at the upper wall of the ring are added to solve the tilted beam problem at the higher edge frequency whereas the double ridges at the lower wall are used to enhance the impedance bandwidth. The dimensions of the rectangular ring and the CDM are initially considered to achieve the bidirectional pattern with the suitable resonant frequencies and bandwidth. Then, the parameters of copper rod and two double ridges are determined by parametric study using CST Microwave Studio simulation software. The prototype antenna was fabricated, and the measured results show good agreement with the simulated ones. The obtained bandwidth of <svg style="vertical-align:-3.13504pt;width:72.349998px;" id="M1" height="14.6" version="1.1" viewBox="0 0 72.349998 14.6" width="72.349998"  xmlns="http://www.w3.org/2000/svg">
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</svg> dB can cover the UWB frequency range as well as the bidirectional beam radiation with constant beam direction (<svg style="vertical-align:-1.76814pt;width:74.375px;" id="M2" height="13.025" version="1.1" viewBox="0 0 74.375 13.025" width="74.375"  xmlns="http://www.w3.org/2000/svg">
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			</text>

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	</g>
</svg> and <svg style="vertical-align:-2.29482pt;width:49.674999px;" id="M3" height="13.675" version="1.1" viewBox="0 0 49.674999 13.675" width="49.674999"  xmlns="http://www.w3.org/2000/svg">
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				<tspan style="font-size: 12.50px; " x="23.568155" y="0">9</tspan>
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</svg>). The minimum and maximum measured gains are 3.1&#x2009;dBi to 5.3&#x2009;dBi, respectively. The proposed antenna possesses compact size with good radiation performance that can be a promising candidate for UWB applications.

S. Vongsack

S. Lamultree

P. Osklang

C. Phongcharoenpanich

S. Kosulvit

K. Hamamoto

T. Wakabayashi

A UWB Bidirectional Rectangular Ring Antenna Fed by CDM with a Rod and Ridges for Constant Beam Direction

An ultra-wideband (UWB) modified 3-way Bagley polygon power divider (BPD) that operates over a frequency range of 2–16 GHz is presented. To achieve the UWB operation, the conventional quarter-wave transformers in the BPD are substituted by two tapered line transformers. For verification purposes, the proposed divider is simulated, fabricated, and measured. The agreement between the full-wave simulation results and the measurement ones validates the design procedure.

Khair Al Shamaileh

Abdullah Qaroot

Nihad Dib

Abdelfattah Sheta

Majeed A. Alkanhal

Analysis and Design of Ultra-Wideband 3-Way Bagley Power Divider Using Tapered Lines Transformers

Stability of electrical amplifiers is of crucial importance. Among the popular stability tests is the <i  >&#x3bc;</i>-test which has many advantages over other tests like the <i  >K</i>-&#x394; test. However, the value of <i  >&#x3bc;</i> parameter is dependent on the input/output terminal characteristic impedance <svg style="vertical-align:-3.2316pt;width:17.825001px;" id="M2" height="14.3625" version="1.1" viewBox="0 0 17.825001 14.3625" width="17.825001"  xmlns="http://www.w3.org/2000/svg">
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</svg> used and this raises the concern that the predictions of the test are dependent on the choice of <svg style="vertical-align:-3.2316pt;width:17.825001px;" id="M3" height="14.3625" version="1.1" viewBox="0 0 17.825001 14.3625" width="17.825001"  xmlns="http://www.w3.org/2000/svg">
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				<tspan style="font-size: 8.75px; " x="0" y="0">𝑜</tspan>
			</text>

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	</g>
</svg>. This paper proves that the conclusions of the <i  >&#x3bc;</i>-test regarding stability/instability remain invariant with <svg style="vertical-align:-3.2316pt;width:17.825001px;" id="M4" height="14.3625" version="1.1" viewBox="0 0 17.825001 14.3625" width="17.825001"  xmlns="http://www.w3.org/2000/svg">
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	</g>
</svg>. This proof is necessary for gaining confidence in the results of the <i  >&#x3bc;</i>-test and should benefit circuit designers. Similar proofs should be extended to all other stability tests for additional insights into their validity under different circuit termination.

Amr A. Ibrahim

Ali M. Darwish

H. Alfred Hung

Invariance Property of the <svg style="vertical-align:-3.56265pt" height="12.175" version="1.1" viewBox="0 0 9.5625 12.175" width="9.5625" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,7.675)"><path id="x1D707" d="M538 96q-38 -45 -84 -76.5t-71 -31.5q-44 0 -15 117q12 49 18 89h-2q-99 -128 -163 -178q-36 -28 -70 -28q-26 0 -44 38h-2q-16 -69 -16 -129q0 -43 11 -75.5t24 -42.5l1 -6q-7 -12 -24.5 -23t-37.5 -11q-40 0 -40 76q0 52 35 202l94 407l78 24l5 -5q-32 -122 -72 -310&#xA;q-7 -33 0 -55t25 -22q36 0 105.5 75t107.5 145l32 146l75 26h10q-50 -197 -78 -347q-7 -38 6 -38q7 0 31 17t47 39z" /></g></svg> Stability Test with respect to the Characteristic Impedance

A nonuniformly spaced linear antenna array with broadside radiation characteristics is synthesized using firefly algorithm and particle swarm optimization. The objective of the work is to find the optimum spacing between the radiating antenna elements which will create a predefined arbitrary radiation pattern. The excitation amplitudes of all the antenna elements are assumed to be constant. The optimum spacing between the array elements are obtained using firefly algorithm. The minimum allowed distance between the antenna elements is defined in such a way that mutual coupling between the elements can be ignored. Numerical analysis is performed to calculate the far-field radiation characteristics of the array. Two numerical examples are shown to form two different desired predefined radiation patterns.  The performance of the firefly algorithm and particle swarm optimization is compared in terms of convergence rate and global best solution achieved. The performances of the optimized nonuniformly spaced arrays are analyzed. Finally, contour plots of the radiated power from the optimized array in the horizontal plane and vertical plane in the far-field region are provided.

Mohammad Asif Zaman

Md. Abdul Matin

Nonuniformly Spaced Linear Antenna Array Design Using Firefly Algorithm

We present the results of the measurement of complex dielectric permittivity, in the microwave frequency region, on glass reinforced polybutylene terephthalate (PBT) with blue inorganic pigments. The cavity resonant method had been used in order to measure the shift in the resonant frequency of the cavity, caused by the insertion of a sample, which can be related to the real part of the complex permittivity. Also, the quality factor of the cavity decreases with the insertion of a sample. The changes in the inverse of this quality factor give the imaginary part. In order to predict the dielectric behavior of this composite, we had developed a program of numerical simulation to calculate the complex permittivity of the inclusion. By using some of dielectric mixture laws (Maxwell-Wagner-Sillars, Hanai, Looyenga, inverse and direct Wiener, and Bruggemann), we can predict the dielectric behavior of the composite in a large range of volume fraction of inclusions.

L. C. Costa

F. Henry

The Impact of Blue Inorganic Pigments on the Microwave Electrical Properties of Polymer Composites

Physical principles for designing a multipurpose set of high <svg style="vertical-align:-1.90608pt;width:12.325px;" id="M2" height="12.925" version="1.1" viewBox="0 0 12.325 12.925" width="12.325"  xmlns="http://www.w3.org/2000/svg">
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</svg>-factor quasioptical and corrugated resonators with automatic frequency tuning (<svg style="vertical-align:-1.90608pt;width:78.199997px;" id="M3" height="16.362499" version="1.1" viewBox="0 0 78.199997 16.362499" width="78.199997"  xmlns="http://www.w3.org/2000/svg">
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</svg>) that can operate in the frequency band from 37.5 to 400&#x2009;GHz are presented. The electrodynamical calculation methods of resonators, the constructive particularities of resonators, the methods and results of the experimental researches are considered. This set of resonators can be used as a universal measuring resonator for measuring radio-signal fluctuations and parameters of different media, in particular, nanotube composites and high-temperature superconductors.

Tatiana Gaevskaya

Victor Karpovich

Valentina Rodionova

High <svg style="vertical-align:-2.2932pt" height="14.3125" version="1.1" viewBox="0 0 13.175 14.3125" width="13.175" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.4)"><path id="x1D444" d="M745 361q0 -134 -83.5 -233t-214.5 -130l16 -11q97 -67 250 -132l-8 -23q-76 3 -131 16q-81 19 -242 125l-20 13q-129 8 -209 91t-80 208q0 160 116 271t289 111q136 0 226.5 -83t90.5 -223zM645 356q0 127 -57.5 201.5t-169.5 74.5q-126 0 -210.5 -104.5t-84.5 -248.5&#xA;q0 -97 46 -166.5t129 -87.5l84 15l29 -19q104 21 169 121.5t65 213.5z" /></g></svg>-Factor Wideband Resonators for Millimeter and Submillimeter Applications

The fully Cu-metalized GaAs pHEMT using developed Cu/Ge-based ohmic contacts and T-gate Ti/Mo/Cu with  length of the 150&#x2009;nm has been successfully fabricated for the high-frequency applications. The fabricated Cu-metalized pHEMT has a maximum drain current of 360&#x2009;mA/mm, an off-state gate-drain breakdown of 7&#x2009;V, and a transconductance peak of 320&#x2009;mS/mm at <svg style="vertical-align:-3.22281pt;width:46.662498px;" id="M1" height="14.7125" version="1.1" viewBox="0 0 46.662498 14.7125" width="46.662498" xmlns="http://www.w3.org/2000/svg">
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					</g>
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			</svg>&#x2009;V. The maximum stable gain value was about 15&#x2009;dB at frequency 10&#x2009;GHz. The current gain cutoff frequency of the copper-metalized device is about 60&#x2009;GHz at <svg style="vertical-align:-3.22281pt;width:46.662498px;" id="M2" height="14.7125" version="1.1" viewBox="0 0 46.662498 14.7125" width="46.662498" xmlns="http://www.w3.org/2000/svg">
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			</svg>&#x2009;V, and maximum frequency of oscillations is beyond 100&#x2009;GHz. This work investigated in detail the formation of Cu/Ge ohmic contacts to <i>n</i>-GaAs with an atomic hydrogen preannealing step. It was shown that after the first preliminary annealing is carried out in a flow of atomic hydrogen with a flow density of atoms of <svg style="vertical-align:-0.17555pt;width:58.849998px;" id="M3" height="14.2875" version="1.1" viewBox="0 0 58.849998 14.2875" width="58.849998" xmlns="http://www.w3.org/2000/svg">
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			</svg> at. <svg style="vertical-align:-0.12538pt;width:25.3125px;" id="M4" height="13.925" version="1.1" viewBox="0 0 25.3125 13.925" width="25.3125" xmlns="http://www.w3.org/2000/svg">
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					</g>
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			</svg> a reduction in specific contact resistance by <svg style="vertical-align:-0.17555pt;width:31.825001px;" id="M6" height="11.1" version="1.1" viewBox="0 0 31.825001 11.1" width="31.825001" xmlns="http://www.w3.org/2000/svg">
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							<tspan style="font-size: 12.50px; " x="6.2515001" y="0">/</tspan>
							<tspan style="font-size: 12.50px; " x="9.727334" y="0">2</tspan>
							<tspan style="font-size: 12.50px; " x="15.978834" y="0">.</tspan>
							<tspan style="font-size: 12.50px; " x="19.104584" y="0">5</tspan>
						</text>
					</g>
				</g>
			</svg> times is observed. The reduction in specific contact resistance is apparently caused by the action of the hydrogen atoms which minimise the rate of the oxidizing reactions and activate solid phase reactions forming the ohmic contact during the thermal treatment process.

E. V. Anichenko

V. S. Arykov

E. V. Erofeev

V. A. Kagadei

Copper-Metalized GaAs pHEMT with Cu/Ge Ohmic Contacts

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International Journal of Microwave Science and Technology - Table of contents 2012

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International Journal of Microwave Science and Technology