Plamen Dankov

• PhD
• Professor (Associate) at Sofia University "St. Kliment Ohridski"

In this paper, a flexible silicon-based elastomer Polydimethylsiloxane (PDMS) is characterized experimentally. For the characterization of the dielectric properties of PDMS, two experimental methods are applied. The first method is based on resonance measurements by the two-resonator method. This method allows the determination of the dielectric co...

In this paper, a wideband transmission-line method has been proposed for the characterization of the dielectric properties of a silicon-based elastomer Polydimethylsiloxane (PDMS), which can be used as a potential substrate for wearable antenna applications. For the measurements, three types of transmission line structures-coplanar waveguide (CPW),...

This paper could be considered as a part of the invited talk “Metamaterials and Their Characterization in the Microwave Range” presented on the 8th International Workshop and Summer School on Plasma Physics (IWSSPP’2018, Kiten, Bulgaria), which has been dedicated to the classification, development, characterization and main applications of the meta...

Full characterization of thin nano-carbon and nano-ferrite absorbers was performed in the frequency range 5-40 GHz by a combination of two microwave methods – a resonance one using a pair of cylindrical resonators with different excited modes, and a broadband one, where the samples cover a 50-ohm microstrip line. The results show a reliable extract...

In this paper, we investigate the changes of the dielectric properties of 0.7-1.2-mm thick-layer from Z-type hexaferite Sr3Co2Fe24O41 in the frequency range 5-40 GHz for the first time by a combination of two methods – a resonance method, which can give the dielectric and magnetic anisotropy of the samples and a broadband transmission-line method –...

In this paper, we consider the simultaneous influence of dielectric anisotropy of textile fabrics used for wearable antennas and their bending. Measurements of flat/bent microstrip patch radiators on selected isotropic/anisotropic textile substrates have been performed, and results have been compared with simulations. They show that both parameters...

In this paper, a complete characterization of the dielectric parameters of thin anodic Al2O3 membranes with formed nano-scale air-filled pores was performed in the frequency range 0-40 GHz by a combination of two microwave methods – a resonance method applying pair of cylindrical resonators that support excited modes with mutually perpendicular ele...

A coplanar waveguide (CPW) method has been developed for characterization of conductive materials like carbon-content samples (graphite, pressed graphene, N-doped graphene) and anisotropic metasurfaces with planar metal inclusions. The samples have been placed as covers on the CPW conductor layout and additional losses and phase delay/advance have...

The paper presents the past, present and possible future of the microwave research activities and applications in Bulgaria in the last 65 years. Bulgaria is an example for a not so big country in the European Union, with quite limited microwave engineering potential and more or less restricted research funding. Nevertheless, Bulgaria succeeded to d...

In this paper, the dielectric parameters (permittivity and dielectric loss tangent) of different single and poly-crystalline or crystalline-like samples have been characterized in the microwave range (especially in the C and X bands; 4-12 GHz). A proven specific property of many crystalline materials is their dielectric anisotropy – different diele...

The development of variety of new materials is a key issue in the modern world moving toward the 5G standards and Industry 4.0. Our laboratory in Faculty of Physics, Sofia University, Bulgaria, has been orientated to characterization of the dielectric properties of modern artificial materials: 3-D printed dielectrics, new generation of substrates,...

The equivalent conductivity has been measured in this paper for characterization of silver-coated plastic antenna components in Ku-Ka bands by especially developed resonance method. The aim is to replace the bulk conductivity of a given metal layers with the actual value of this parameter in the 3-D simulators for implementation of more reliable nu...

Characterization of 3-D printed materials for microwave/antenna applications; Effective medium models and material homogenization: they give the limits; How to evaluate the artificial anisotropy of the dielectric parameters of mixed dielectrics (incl. 3-D printed)?: an efficient numerical resonance method; The origin of the anisotropy in the 3...

The models, limitations and realization of homogenized foam-like 3-D printed dielectrics have been presented applying different fully symmetrical unit cells. The strategy for control of the absolute values of the resultant isotropic equivalent dielectric constant of these artificial dielectrics has been presented and verified and a possible anisotr...

Metamaterials: classifications, parameters and main properties; Selected applications of the metamaterials in the antennas, antenna arrays and antenna beamforming; Artificial anisotropy of the dielectric parameters of metamaterials: origin of the uni- and bi-axial anisotropy and how to characterize?; Modeling of the artificial dielectrics and m...

SAR, правила за използване на мобилните устройства; какво ново в 4G и 5G поколенията?) ЛЕКТОРИЯ "Светът на физиката на живо"

The paper presents a new concept for application of low-profile antenna arrays as two-way terminals for mobile ground stations for high-throughput satellite communications with small satellites. Three types of tracking antenna systems have been described and compared: with pure electronic or mixed (electronic-mechanical) beam steering with flat ant...

Two variants of resonance measurement methods have been described in the paper for characterization of uni-and bi-axial dielectric anisotropy of crystalline samples in the microwave range using cylindrical resonators. The dielectric parameters of several known and some new, unknown crystalline samples have been determined by a pair of cylindrical r...

Климентова лекция

The uniaxial anisotropy of natural and synthetic textile fabrics has been measured by two-resonator method. The reasons and ways for appearing of this type of artificial anisotropy have been numerically and experimentally investigated. Finally, the influence of the textile substrates' dielectric anisotropy on the main wearable antennas' parameters...

The measurements of the dielectric characteristics and the creation of a multi-layer model of gradient-carbon foamed absorbers have been considered in this paper. This model allows to construct effective analytical procedure for calculation of the reflectivity from these specific artificial structures and to compare the reflectivity of different ab...

The uniaxial anisotropy of small samples from plant fresh biomass has been investigated in this paper by micro-wave resonance method. The anisotropy means that the plant tissues have different dielectric constants in different directions according to the sample surface. The concrete investigations have been performed by determination of the relativ...

In this paper we perform a set of numerical and experimental investigations of the resulting uniaxial anisotropy of the modern artificial dielectrics with antenna applications – rein-forced substrates, 3-D printed and multilayer structures, textile fabrics, some metamaterials, etc. They all usually are mixtures between two or more dielectrics or me...

In this paper we compare the results from 3-D simulations of simple planar lines on anisotropic substrates in anisotropic and equivalent isotropic material option. We found out that there exist up to 3-4 % differences between the measured and calculated through the phase delay effective dielectric constants for the main types of planar transmission...

A two-stage small-spacecraft mission is described in this paper, which deals with the space debris identification, classification and aggregation. The first long-term submission is responsible for in-situ debris observation close to the most populated orbits ~800 and ~1400 km by an optimized combination of on-board laser illuminator (lidar) and las...

The paper considers the problems of the dielectric anisotropy and determination of so-called equivalent dielectric constant of different planar transmission lines on anisotropic substrates, when they have been covered with dielectric overlays with open or shielded top surfaces. The idea is to investigate the possibilities for direct measurements of...

Четирите уравнения на Максуел: 155 години в основата на електро-динамиката. Съвременните електромагнитни 3D симулатори (FDTD) са директно построени на основата на уравненията на Максуел; примери. Идеята за радиовълните и възникване на безжичните комуникации. Електромагнитният спектър – огромно световно богатство; как се използва? Кодиране, модулаци...

The paper presents a new concept for application of low-profile antenna arrays as two-way terminals for mobile ground stations for high-throughput satellite communications with small satellites. Three types of tracking antenna systems have been described and compared: with pure electronic or mixed (electronic-mechanical) beam steering with flat ant...

Dielectric anisotropy of the modern reinforced substrates for RF and MW electronics and how the main substrates’ producers consider this issue; Methods for characterization of substrate anisotropy; “two-resonator method” and data for same typical RF and MW substrates; Concept for equivalent dielectric parameters of the anisotropic microwave substr...

We can see a serious decrease of the microwave activities in all the countries in Group 8 in different degree (only Czech Republic keeps a relatively high level of visible “microwave activity”). •Is that really true? •Therefore, I decided not to consider the activities of the microwave communities in Group 8 countries in the past, even at near past...

As the most powerful CW sources of coherent radiation in the sub-terahertz to terahertz frequency range the gyrotrons have demonstrated a remarkable potential for numerous novel and prospective applications in the fundamental physical research and the technologies. Among them are powerful gyrotrons for electron cyclotron resonance heating (ECRH) an...

Малкият спътник: наблюдателно, научно и технологично, комуникационно и учебно средство. Статистически данни за изстреляните досега малки спътници, вкл. университетските. Обучението по аерокосмическо инженерство във Физически факултет на СУ. Нашите проекти и дейности в областта на малките аерокосмически обекти. UNISEC Global

Антената – устройство, което превръща всяко друго устройство в безжично! Основни параметри на антените – диаграма на излъчване, ширина на лъча, усилване, насоченост, поляризация и др. Видове антени. Антенни решетки. Теми в лекцията Технология за подобряване на характерис-тиките на антените – по-широколентови, по-миниатюрни, реконфигурируеми, активн...

Как се подреждат устройствата в безжичните комуникации по степен на риск от облъчване за хората според последните изследвания? Какви са типичните нива на излъчените сигнали? Все пак влиянието на базовите станции се фаворизира от хората като степен на риск. Какви са фактите при последните изследвания? Резултати от наши измервания в Студентски град и...

2G GSM мрежата – най-успешната мрежа досега в целия свят? Какво постигна 2G GSM мрежата; какво се случи с поколенията след това: 3G GSM и новият 4G LTE? Каква е разликата? Какво определя скоростта при безжичните комуникации? Мобилен Интернет. Защо GSM и GSM+ мрежите са толкова успешни – физично обяснение за този успех. Клетъчни комуникации, архитек...

Outline: Small satellites as innovative investigation tools from the near Space and as educational instruments (university CubeSat’s; weight <1 kg; 10x10x10 cm). Statistical data for CubeSat’s on orbit; conclusions. Aerospace engineering education in Sofia university Our educational project in the area of small aerospace vehicles. How to be member...

The term “equivalent conductivity” has been used in this paper for characterization of metallized plastic antenna components in Ka band. The measured values of this parameter can be used to replace the bulk conductivity of metal bodies in the 3-D simulators for implementation of better simulations of the metallized plastic antenna structures. A res...

Powerful gyrotrons are necessary as sources of strong microwaves for electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) of magnetically confined plasmas in various reactors (most notably ITER) for controlled thermonuclear fusion. Adequate physical models and efficient problem-oriented software packages are essen...

Gyrotrons are the most powerful sources of coherent CW (continuous wave) radiation in the frequency range situated between the long-wavelength edge of the infrared light (far-infrared region) and the microwaves, i.e., in the region of the electromagnetic spectrum which is usually called the THz-gap (or T-gap), since the output power of other device...

The Management Committee Meeting took place at AULA MAGNA of Sofia University “St. Kliment Ohridski” on May 18th 2015 (Monday) between 16:15 and 18:00. The meeting chair was Dr. Marta Martínez-Vázquez. Short reports from the leaders of the different working groups and focusing areas were presented. Totally 25 abstracts have been received. After the...

Outline Dielectric anisotropy of the modern materials for electronics  Standard method for characterization (IPC TM-650 2.5.5.5) “Two-resonator method“ – an authorship method Examples for isotropic and anisotropic materials Concept for the equivalent dielectric constant of the microwave substrates Applicability to different planar transmissio...

Outline ●RaySat Phased Array System – Technology Development ●Mixed beam steering antenna - “Full size” antenna challenges - T2 mixed steering antenna prototype - Dedicated service solutions - Commercial applications – T7 CruiseCast project ●Conclusions ●References

Комуникационна функция на малкия спътник. Комуникационни функции на предния и задния панел – разлики и приложения Статистически данни за университетските малки спътници и мястото на комуникационните задачи в мисиите досега Нови честотни обхвати, достъпни за малките спътници Енергетичен баланс; ще има ли достатъчно мощност? Възможно ли е предава...

This paper, presented in the frame of 4th International Workshop and Summer School on Plasma Physics (IWSSPP'2010, Kiten, Bulgaria), is a brief review of the principles, methods and instrumentation of the microwave measurements of electrical fields in different media. The main part of the paper is connected with the description of the basic feature...

A great number of problem-oriented software packages (e.g., DAPHNE, ESRAY, GYROSIM, just to name a few) are used for computer-aided design (CAD) and optimization of high-power gyrotrons for fusion research (most notably for ECRH and ECCD). In them, adequate self-consistent physical models formulated in a two-dimensional space (2D) are implemented....

he paper presents the concept, architecture, solutions, performances, advantages and some applications of antenna systems for modern satellite communications based on low-profile movable antenna platforms –“Satcom-On-The-Move” (SOTM).The concept is proven in several one-and two-way antenna systems in different frequency ranges.

Powerful gyrotrons with megawatt output power and frequencies ranging from 77 to 170 GHz are necessary for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD) and ECH-assisted start-up of magnetically confined plasmas in various reactors for controlled thermonuclear fusion (tokamaks and stellarators) as well as for...

Near-field electromagnetic scanners are widely used for microwave, antenna and electromagnetic compatibility measurements. The scanner determines the spatial distribution of an electrical quantity provided by a single or multiple field probes in the near-field region of a device under test (DUT). Depending on a signal receiver detecting the probe s...

An integrated long-term interactive approach is proposed for combining academic science education with additional methodology for enhancement of personal skills. It aims at making students more efficient both in their studies and further career development. The scope of communication skills includes both teamwork interaction and effective presentat...

The necessity for development of the so-called communication function of university small satellites is considered in this paper. This function can be successfully applied to serve the increasing needs of backhaul and off-line operational communications in the both polar regions. Suitable frequency bands, on-board and ground-station antennas and ac...

The hairpin probe is considered in this paper as an effective tool for determination of the plasma density by accurate resonance method. Multi-mode operation is considered and the unloaded Q factor of the modes is associated with the collisions in the plasma discharge. The sensitivity of the hairpin probe is investigated in details by numerical sim...

The paper considers several spread internal EMC problems, which take place in some microwave passive non-antenna devices – parasitic radiation, "high-altitude" fields, crosstalk, grounding inefficiency, etc. Near-field scanning combined with electromagnetic simulations have been used for their prediction and detection. Several design rules have bee...

The paper considers several spread problems, which take place in many microwave non-antenna devices (antenna feed lines, hybrids, filters, diplexers, LNAs, etc.) - parasitic radiation, “high-altitude” fields, crosstalk, grounding inefficiency. Near-field scanning has been used for their detection and then, for verification of their minimization. So...

An interdisciplinary format of a masters program in microwave communication has been designed and applied as a combination of engineering physics and innovation management training, taking into account latest research on worldwide requirements of business leaders. In addition, students are guided into strategic mentoring relations with academic sta...

In this paper the split-post dielectric resonator is investigated as a measurement tool for dielectric substrate parameters characterization by using a suitable 3D model, assisted by modern 3D electro-magnetic simulators. The dielectric parameters of a known substrate are measured by a set of different dielectric resonators in order to find the mos...

In this paper the split-post dielectric resonator is investigated as a measurement tool for dielectric substrate parameters characterization by using a suitable 3D model, assisted by modern 3D electro-magnetic simulators. The dielectric parameters of a known substrate are measured by a set of different dielectric resonators in order to find the mos...

The importance of the dielectric anisotropy of the modern RF substrates is the main focus of the investigations in this chapter. There are two main reasons to want to have information for the actual anisotropy of a given substrate ­ to control the technology (necessary for the manufacturers) and to conduct more realistic simulations of the structur...

The influence of the material dielectric anisotropy in the planar antenna design is considered in this paper. The principles of measurements of the parallel and normal dielectric parameters of the samples are described and data for some substrates are presented. The possibility to take into account of the material anisotropy into the modern simulat...

A hairpin-resonator probe is designed to measure the spatial distribution of the electron density in RF plasmas. An effective simulation procedure with the commercial software simulator Ansoft(®) High Frequency Structure Simulator 8 in eigen-mode option was applied to evaluate the influence of the resonator structures on the resonance frequency (fv...

Hairpin quarter-wavelength resonator is a very effective resonance tool for measurement of the local distribution of the electron density and the electron temperature in RF plasmas. An effective design procedure is described based on electromagnetic simulations of realistic resonance structures. The sensitivity of the hairpin probe is considered an...

The image guide (IG) has been traditionally considered as a perspective for millimeter wavelengths. The transition between the standard metal rectangular waveguide (SMRW) and the IG usually exists in every experimental set- up involving the IG. Here we have examined experimentally using electric probes the distribution of the electric field compone...

Some practical problems concerning the characterization and modeling of microwave absorbers are discussed in this paper. First, a number of measurement methods are considered for determination of the relative and absolute absorbing ability of the most popular absorbing materials – foams, rubber sheets, coatings and thin films. Next, several more co...

The measurement of the dielectric constant and loss tangent anisotropy of the planar RF substrates by the two-resonator method is considered in this paper. The principles of the separate determination of these parameters parallel and perpendicular to the substrate surface is discussed by three pairs of cavity measurement resonators, based on cylind...

This work includes both experimental and numerical analysis of coupled image guide structures (CIGSs) at millimeter wavelengths. The experimental measurement of the electric field components has been performed using electric probes. The experimental research has been complemented by a numerical simulation of the CIGSs using a finite element method...

Когато пишех първите две части на статията “Как работи GSM мрежата?”, поне 5-6 човека ми се обадиха и ме питаха за вредата от “джиесемите” и особено за вредата от базовите станции. Преди 3 седмици дойде един човек на средна възраст и ми каза, че на 25 метра от къщата му, върху покрива на съседен блок, има антени на GSM базови станции на два операто...

В първата част разгледах само клетъчната архитектура и комуникационния капацитет на GSM мрежата, без да става дума за това, какви са сигналите в мрежата, какви честотните канали се използват и как отделните потребители могат да “влязат” в мрежата. В този раздел ще се дискутират именно тези въпроси, но без много подробности, защото материята е огром...

GSM има вече над 2.1 млрд. абоната в целия свят. Това отскоро я направи най-голямата телефонна мрежа в света (по-голяма от доскорошния фаворит – фиксираната телефонна мрежа). Хората от всички възрасти свикнаха с GSM (няма как – съществува вече над 17 години). Малко хора, обаче, са наясно как точно функционира тази огромна комуникационна мрежа (всъщ...

The paper is dealing with the principles for modeling and simulating by 3D simulators of the well-known Lüneburg lenses used as communication antenna devices. The models of spherical, semi-spherical and cylindrical multi-layer dielectric lenses are discussed. The results show the effectiveness of the proposed simulation procedures for investigation...

The paper is dealing with the principles for modeling and simulating by 3D simulators of the well-known Lüneburg lenses used as communication antenna devices. The models of spherical, semi-spherical and cylindrical multi- layer dielectric lenses are discussed. The results show the effectiveness of the proposed simulation procedures for investigatio...

The paper discusses the problems of the antenna radomes fabricated by anisotropic materials: analytical CAD model, radome measurements, radome simulations and characterization of the multi-layer radome materials. A modified Paris’ model for CAD radome analysis is presented, which takes into account the dielectric material anisotropy of the layers....

A two-resonator method, based on TE011-mode and TM010-mode resonance cavities with a disk sample has been developed for measurement of the longitudinal and transversal dielectric constants and dielectric loss tangent of dielectric substrates (dielectric anisotropy), used in modern electronics. The the- oretical background of the method is presented...

Two types of split-cylinder resonators are used for characterization of the longitudinal dielectric parameters of reinforced RF substrates. The novelty of the method is the introduced theoretical 3D model of the measurement cavities, which allow determination of the parameters with the help of arbitrary 3D electromagnetic simulators. Two known isot...

The characterization of the dielectric anisotropy of the high-permittivity materials (ceramics, glasses, ferrites) is considered in this paper. The measurements are based on two-resonator method described elsewhere. The determination of the dielectric parameters could be simple assisted by electromagnetic simulators introducing 3D equivalent models...

Characterization of the dielectric parameters of substrates in relatively low frequency bands with re-entrant resonator is considered. The novelty is the proposed 3D model of the re-entrant cavity. Thus, the determination of the dielectric constant and dielectric loss tangent could be simple assisted by numerical simulations of a stylized 3D model...

УВОД Лекция 1: Общи въпроси на съвременните комуникационни системи Лекция 2 Комуникационни сигнали и канали за тяхното пренасяне Лекция 3 Технология на кодирането и достъпа до комуникационните сигнали Лекция 4 Разпространение на сигналите в комуникационните канали Лекция 5 Съвременни комуникационни системи Лекция 6 Електромагнитна съвместимост в с...

A modified Paris' model (Paris, 1970) for computed-aided radome analysis is presented, which takes into account the dielectric material anisotropy of the radome layers. The analytical model is combined with a practically realized two-resonator method for characterization of the normal and parallel to the surface dielectric parameters of the radome...

The principles for utilization of the modern 3D simulators are considered in the paper as assistant tools for determination of the dielectric material parameters by resonance measurements. 3D models of several types of measuring cavities are introduced: regular cylindrical TE011-mode and TM010-mode resonators, reentrant cavity, split-cylinder reson...

Quasi-optical (QO) mode converters are used to transform electromagnetic waves of complex structure and polarization generated in gyrotron cavities into a linearly polarized, Gaussian-like beam suitable for transmission. The efficiency of this conversion as well as the maintenance of low level of diffraction losses are crucial for the implementatio...

Computer aided design (CAD) based on numerical experiments performed by using adequate physical models and efficient simulation codes is an indispensable tool for development, investigation, and optimization of gyrotrons used as radiation sources for electron cyclotron resonance heating (ECRH) of fusion plasmas. In this paper, we review briefly the...

A two-resonator method, based on TE₀₁₁-mode and TM₀₁₀-mode resonance cavities with a multilayer disk sample, has been developed for measurements of the longitudinal and transversal dielectric constant and dielectric loss tangent of each layer (if the other ones have known parameters) or in the whole sample averaging over the l...

Предговор Микровълнова лаборатория (уводно упражнение 1) Технология на микровълнови хибридни интегрални схеми (уводно упражнение 2) I част: (Пасивни микровълнови устройства) 1.1 Микролентова линия и микролентови резонатори 1.2 Измерване на S-параметри на микровълнови устройства и интегрални схеми 1.3 Планарни микролентови хибридни мостове, делители...

The principles for utilization of the electromagnetic 3D simulators for determination of dielectric constant and loss tangent of anisotropic materials by microwave cavity resonators are described. Two-resonator method (described elsewhere) based on TE₀₁₁-mode and TM₀₁₀-mode resonators with disk-shape sample is applied for sepa...

Two-resonator method, based on TE011-mode and TM 010-mode resonance cavities with multi-layer disk sample is developed for measurement of longitudinal and transversal dielectric constant of each layer or in the whole sample averaging layer contribution. Dispersion equations for the considered modes in the both types of cavities with three, two or o...

Two problems concerning laminated RF plates are considered - the anisotropy and local inhomogeneity of their dielectric parameters. Three resonance methods are used for the measurement of the longitudinal, transverse and equivalent (in microstrip configuration) dielectric constant and loss tangent. A large number of samples has been extracted from...

Insertion loss and return loss expressions are derived for a plane multilayer radome consisting of anisotropic materials at normal, parallel and circular polarization of the incident electromagnetic wave. Numerical optimization of three layer radome based on thin honeycomb core is demonstrated for a wide range of elevation angle θ in the frequency...

The paper presents studies on the microwave properties of two types of polymer composites based on acrylic resin and polyurethane with nanosized magnetic (magnetite) and dielectric (carbon) fillers. The microwave (MW) absorption was measured at 9.4 GHz, while the dielectric and magnetic properties were investigated in the frequency range 1-18 GHz....

Investigations of dielectric and magnetic properties and absorbing abilities of thin polymer nano-composites of carbon (~ 5 nm) and ferroxide particles (800 nm) are described in this paper. Dielectric and magnetic parameters are estimated by two-cavity resonator method developed for two-layer sample – absorbing layer (~30-130 um) on supporting subs...

Brief review is presented of cavity-resonator methods for measurement of complex permittivity of dielectric materials in microwave frequency range. Utilization of 3D electromagnetic simulation of cylindrical resonator partially filled with measured dielectric disk sample is proposed. That allows improving possibility for complex permittivity estima...