Ali Kara

• Professor
• Professor at Gazi University

This paper introduces a high-resolution 77–81 GHz mmWave Synthetic Aperture Radar (SAR) imaging methodology integrating low-cost hardware with modified radar signal characteristics specifically for NDT applications. The system is optimized to detect minimal defects in materials, including low-reflectivity ones. In contrast to the existing studies,...

The increasing adoption of unmanned aerial systems (UAS) in diverse urban applications necessitates reliable and precise altimetry solutions for situational awareness and landing safety. Despite significant advancements in the realm of waveform design and signal processing, empirical validation of millimeter wave (mmWave) Frequency Modulated Contin...

Missiles posing a threat to naval platforms have become a significant danger today, especially considering advancements in IR or RF-guided missile seeker technologies. These threats render platforms open targets for hostile forces. Chaffs and flares can be launched from naval platforms as softkill countermeasures against such threats within Electro...

This paper presents a comprehensive evaluation of real-time radar classification using software-defined radio (SDR) platforms. The transition from analog to digital technologies, facilitated by SDR, has revolutionized radio systems, offering unprecedented flexibility and reconfigurability through software-based operations. This advancement compleme...

Introductory courses regarding radar technologies are very popular in the undergraduate curriculum of many electrical and electronics engineering departments. Hands-on experience is an essential part for understanding the theoretical concepts given in lectures. In most cases, it is not affordable for universities to acquire experimental radar syste...

In today's technology, the use of drones has become very popular for they can be easily purchased over the Internet and can be easily developed. With drones that have wide usage areas, swarm structures have become popular. However, this has brought about some problems. The issue of drone detection has emerged in order to prevent the uncontrolled us...

Unmanned aerial vehicles (UAVs) are increasingly significant in modern warfare due to their versatility and capacity to perform high-risk missions without risking human lives. Beyond surveillance and reconnaissance, UAVs with jet propulsion and engagement capabilities are set to play roles similar to conventional jets. In various scenarios, militar...

In aerospace engineering, radomes play an important role in protecting antenna systems from external interference and minimizing air resistance during flight. However, traditional radomes often fall short of providing the electromagnetic filtering and stealth capabilities important for modern aircraft applications. Conformal Frequency Selective Sur...

In recent years, technological developments with user demands, reduced production, and launch costs have rapidly increased the number of Low Earth Orbit (LEO) satellites in space. Since LEO satellites use the same frequency band as existing Geostationary Earth Orbit (GEO) satellites, the interference coordination between the two satellite networks...

Introductory courses regarding radar technologies are very popular in undergraduate curriculum of many electrical and electronics engineering departments. Hands-on experience is an essential part for understanding the theoretical concepts given in lectures. In most cases, it is not affordable for universities to acquire experimental radar systems,...

This research advances millimeter-wave (mmWave) altimetry for unmanned aerial systems (UASs) by optimizing performance metrics within the constraints of inexpensive automotive radars. Leveraging the software-defined architecture, this study encompasses the intricacies of frequency modulated continuous waveform (FMCW) design for three distinct stage...

Frequency hopping (FH) is a well-known technique that is commonly used in communication systems owing to its many advantages, including its strong anti-jamming capability. In this technique, basically, radio signals are transmitted by switching the carrier between different frequency channels. As a result, the FH signal is not stationary; hence, it...

Automatic modulation classification (AMC) algorithms are crucial for various military and commercial applications. There have been numerous AMC algorithms reported in the literature, most of which focus on synthetic signals with a limited number of modulation types having distinctive constellations. The efficient classification of high-order modula...

The radar cross-section (RCS) is a critical factor in the design and performance of modern airborne weapon systems. These systems utilize phased array antennas due to their low profile, advanced beamforming, and angle measurement capabilities. The effect of phased array antennas on platform RCS can be crucial. Addressing the RCS of phased array ant...

In recent years, millimeter wave (mmWave) frequency modulated continuous wave (FMCW) radars have gained popularity in radar imaging applications, coinciding with the advancement of mmWave technology. However, high cost and integration complexity still remain as issues in cases where the target aperture is large. This work introduces a low-cost, low...

A novel microwave sensor based on a branch line coupler (BLC) embedded with split ring resonators (SRRs) is proposed here for thickness and displacement measurement of thin dielectric layers. The SRRs introduce a transmission zero (TZ) in the BLC’s transmission coefficient, which serves as the sensing parameter. The sensor exhibits a compact design...

The automatic dependent surveillance broadcast (ADS-B) system is one of the key components of the next generation air transportation system (NextGen). ADS-B messages are transmitted in unencrypted plain text. This, however, causes significant security vulnerabilities, leaving the system open to various types of wireless attacks. In particular, the...

Precise altitude data are indispensable for flight navigation, particularly during the autonomous landing of unmanned aerial systems (UASs). Conventional light and barometric sensors employed for altitude estimation are limited by poor visibility and temperature conditions, respectively, whilst global positioning system (GPS) receivers provide the...

A highly sensitive microwave sensor for solid material characterization is proposed. A novel design consisting of split ring resonators (SRRs) within a three‐port power divider is developed. The three‐port junction is employed as the host to provide two output channels, and SRRs are loaded through electric coupling to the power divider as the sensi...

As the millimeter‐wave (mm‐Wave) spectrum is considered to be an essential enabler to the fifth generation (5G) wireless communication systems. Human movements are one of the most significant factors that cause transient blockage in indoor mm‐wave channels. In this letter, human blockage measurements and shadow fading statistics due to human body m...

In this study, a Machine Learning (ML)-based approach is proposed to enhance the computational efficiency of a particular method that was previously proposed by the authors for passive localization of radar emitters based on multipath exploitation with a single receiver in Electronic Support Measures (ESM) systems. The idea is to utilize a ML model...

The Internet of Things (IoT) has significantly improved location-based services in smart cities, such as automated public transportation and traffic management. Estimating the location of connected devices is a critical problem. Low Power Wide Area Network (LPWAN) technologies are used for localization due to their low power consumption and long co...

Smart grids incorporate diverse power equipment used for energy optimization in intelligent cities. This equipment may use Internet of Things (IoT) devices and services in the future. To ensure stable operation of smart grids, cybersecurity of IoT is paramount. To this end, use of cryptographic security methods is prevalent in existing IoT. Non-cry...

The shift from analog to digital technologies has transformed radio systems, and Software Defined Radio (SDR) has introduced unparalleled flexibility and adaptability by executing operations through software-based approaches. In recent times, the burgeoning popularity of SDR has augmented their applicability within the realm of Electronic Support M...

This study presents an improved hybrid-flipped classroom (hybrid-FC) education method based on technology-enhanced learning (TEL) along with diluted classes for a course on probability and random processes in engineering. The proposed system was implemented with the participation of two student groups who alternated weekly between attending face-to...

Vehicle classification has an important role in the efficient implementation of Internet of Things (IoT)-based intelligent transportation system (ITS) applications. Nowadays, because of their higher performance, convolutional neural networks (CNNs) are mostly used for vehicle classification. However, the computational complexity of CNNs and high-re...

A novel dual band microwave sensor for non-invasive detection of glucose concentration is presented. The proposed sensor consists of an open loop resonator coupled to the input and the output of the structure. The resonator is loaded with a modified split ring resonators for dual band operation as sensing area. The open loop resonator with electric...

Nowadays, Visible Light Communication (VLC) has gained much attention due to the significant advancements in Light Emitting Diode (LED) technology. However, the bandwidth of LEDs is one of the important concerns that limits the transmission rates in a VLC system. In order to eliminate this limitation, various types of equalization methods are emplo...

Brain tumors have been the subject of research for many years. Brain tumors are typically classified into two main groups: benign and malignant tumors. The most common tumor type among malignant brain tumors is known as glioma. In the diagnosis of glioma, different imaging technologies could be used. Among these techniques, MRI is the most preferre...

This paper presents a novel sensor topology employing an Interdigital Capacitor (IDC) integrated in Half Mode Substrate Integrated Waveguide (HMSIW) for permittivity measurement of solid materials. HMSIW with around 50% smaller size compared with SIW offers a compact solution for hosting the sensing section. Capacitive-like characteristic of IDC fu...

Millimeter-wave (mm-Wave) spectrum is an essential enabler to the fifth generation (5G) wireless technology. Humans are one of the most noticeable blockers that cause temporal variation in indoor radio channels. This paper presents human blockage measurements at 28 GHz, with several humans of different sizes. The effect of the crossing orientations...

Radio frequency fingerprinting (RFF) is based on identification of unique features of RF transient signals emitted by radio devices. RF transient signals of radio devices are short in duration, non-stationary and nonlinear time series. This paper evaluates the performance of RF fingerprinting method based on variational mode decomposition (VMD). Fo...

Recently, network security has become a major challenge in communication networks. Most wireless networks are exposed to some penetrative attacks such as signal interception, spoofing, and stray. Radio frequency (RF) fingerprinting is considered to be a promising solution for network security problems and has been applied with various improvements....

This study proposes a simple convolutional neural network (CNN)-based model for vehicle classification in low resolution surveillance images collected by a standard security camera installed distant from a traffic scene. In order to evaluate its effectiveness, the proposed model is tested on a new dataset containing tiny (100 × 100 pixels) and low...

Automatic Modulation Classification (AMC) algorithms play an important role in various military and civilian applications. There have been numerous AMC algorithms reported in the literature, most of which focus on synthetic signals with a limited number of modulation types having distinctive constellations. The efficient classification of high-orde...

The recognition of modulation schemes in military and civilian applications is a major task for intelligent receiving systems. Various Automatic Modulation Classification (AMC) algorithms have been developed for this purpose in the literature. However, classification with low computational complexity as well as reasonable processing time is still a...

This study aims to evaluate the accuracy of a method proposed for passive localization of radar emitters around irregular terrains with a single receiver in Electronic Support Measures systems. Previously, the authors targeted only the theoretical development of the localization method. In fact, this could be a serious concern in practice since the...

Linear Wireless Sensor Networks (LWSNs) are used in applications where deployment scenarios necessitate sensor nodes to be placed over a line topology. However, such a deployment raises reliability concerns because almost all the nodes in the network are critical with respect to the survivability of the LWSN. It is possible that an LWSN can stay co...

Radio frequency fingerprinting (RFF) is used as a physical‐layer security method to provide security in wireless networks. Basically, it exploits the distinctive features (fingerprints) extracted from the physical waveforms emitted from radio devices in the network. One of the major challenges in RFF is to create robust features forming the fingerp...

In the development of radiofrequency fingerprinting (RFF), one of the major challenges is to extract subtle and robust features from transmitted signals of wireless devices to be used in accurate identification of possible threats to the wireless network. To overcome this challenge, the use of the transient region of the transmitted signals could b...

The microwave sensors have been successfully used for permittivity measurement. These sensors suffer from limited sensitivity and environmental effects. This paper presents a novel T-junction highly sensitive microwave sensor for permittivity measurement of low loss solid materials. The proposed sensor operation principle is based on downshifting t...

This study aims to evaluate the accuracy of a method proposed for passive localization of radar emitters around irregular terrains with a single receiver in Electronic Support Measures (ESM) systems. Previously, only the theoretical development of the localization method was targeted by the authors. In fact, this could be a serious concern in pract...

This article presents a sub-GHz ISM band microstrip patch antenna based on the use of multi-layer compact structure, which overcomes the shortcomings of typical microstrip antennas such as low gain and high resonant frequency. The antenna was simulated using an electromagnetic simulator, ANSYS HFSS, and fabricated on two different substrates: RT Du...

The number of satellites has been increasing in both geostationary (GEO) and non‐geostationary (NGEO) earth orbits. Due to the limited availability of spectrum resources, the interference risk among these satellite networks has been increasing consequently. In such a scenario, the protection of existent GEO transmissions is crucial. In this paper,...

A novel dual band, highly sensitive Substrate Integrated Waveguide (SIW) sensor for permittivity measurements is presented. A pair of modified Complementary Split Ring Resonators (CSRRs) is etched on SIW surface. CSRRs are located in the center of SIW, where the electric field distribution is high so that the coupling be maximized. The coupling bet...

None-invasive blood glucose measurement enables effective diagnosis and treatment of diabetic patients. The existing microwave sensors suffer from low sensitivity and large size. This article presents a highly sensitive and compact size non-invasive microwave sensor for real-time blood glucose measurements. We have developed a new sensing technique...

The recognition of modulation schemes in military and civilian applications is a major task for intelligent receiving systems. Having no previous knowledge of the transmitted signal as well as uncertainties in the channel and the receiver makes the identification of the modulation scheme a difficult task. Various Automatic Modulation Classification...

Recently, a concept of linear wireless sensor networks (LWSNs) has attracted much attention. For such networks, one of the key challenges in sensor node design is to couple transceiver modules with bidirectional antennas placed back‐to‐back for opposite radiation. As is known, simply, this can be achieved by using well‐known coupling options like r...

Human activities around the communication link in an indoor environment have a significant impact on millimeter-wave (mmWave) communication systems, which are used for the new generation of communication networks (5G). Therefore, it is essential to evaluate short range indoor links from the link blockage point of view. This paper presents the propa...

The fifth generation (5G) technology is expected to allow connectivity to billions of devices, known as Internet of Things (IoT). However, IoT devices will inevitably be the main target of various cyberattack types. The most common one is known as distributed denial‐of‐service (DDoS) attack. In order to mitigate such attacks, network functions virt...

Due to the environmental pollution threatening human life, clean water accessibility is one of the major global issues. In this context, in literature, there are many portable water disinfection systems utilizing ultraviolet (UV) radiation. UV water disinfection systems employ piezoelectric-based electric power along with UV light-emitting diode (L...

This study aims to provide a simple approach to characterize the effects of scattering by human bodies in the vicinity of a short-range indoor link at 28 GHz while the link is fully blocked by another body. In the study, a street canyon propagation characterized by a four-ray model is incorporated to consider the human bodies. For this model, the r...

This article presents a preliminary propagation study on the accuracy of empirical path loss models for efficient planning and deployment of a linear wireless sensor network (LWSN) based on long range (LoRa) enabled sensor nodes in suburban and rural environments. Real-world deployment of such network requires accurate path loss modelling to estima...

The methods used in engineering education have gained diversity in parallel with rapidly evolving technology. New technological methods along with the traditional methods have been adopted for undergraduate education. Today, Simulink‐based educational materials are used in many fields in engineering education. However, in the literature, the contri...

Time synchronization is fundamental in the distributed networked systems, especially in Wireless Sensor Networks where a global time is essential to make sense of the events like collection of data and scheduled sleep/wake-up of nodes. There exists numerous time synchronization algorithms and techniques in the literature. Nonetheless, these propose...

This article indicates a thus far unexplored area of applied research and development to the application and system engineers and researchers from broad engineering backgrounds. Results of a study are presented for measurement of calibrated Radar Cross Section (RCS) of a 9‐mm bullet (projectile) model by using a commercial‐of‐the‐shelf (COTS) milli...

Radio frequency fingerprinting (RFF) based on RF transients is one of the most effective techniques for improving wireless security. For an efficient RFF development, RF transients need to be accurately detected. However, the detection of the transient starting point remains a main challenge due to the channel noise. In the literature, several meth...

Radio frequency fingerprinting (RFF) is a promising physical layer protection technique which can be used to defend wireless networks from malicious attacks. It is based on the use of the distinctive features of the physical waveforms (signals) transmitted from wireless devices in order to classify authorized users. The most important requirement t...

Radio frequency fingerprinting (RFF) could provide an efficient solution to address the security issues in wireless networks. The data acquisition system constitutes an important part of RFF. In this context, this paper presents an implementation of a modular RF front end system to be used in data acquisition for RFF. Modularity of the system provi...

Abstract We explored the joint effect of synchronization window and offset/drift mode selection on the time synchronization of linear wireless sensor networks (LWSNs). Recent advances in the field along with the availability of capable hardware led to adoption of LWSNs in diverse areas like monitoring of roads, pipelines, and tunnels. The linear to...

In this study, a novel method is proposed to detect and classify the threats for fiber optic distributed acoustic sensing (DAS) systems. In the study, phase-sensitive optical time-domain reflectometry (phase-OTDR) is realized for the sensing system. The proposed method is consisted of three main stages. In the first stage, Wavelet denoising method...

Radio frequency fingerprinting (RFF) is one of the communication network’s security techniques based on the identification of the unique features of RF transient signals. However, extracting these features could be burdensome, due to the nonstationary nature of transient signals. This may then adversely affect the accuracy of the identification of...

Literatürde, kısa mesafe iç mekân haberleşme linklerinde insan vücudu blokajının sebep olduğu kaybın tahmininde matematiksel olarak sade bir yapıya sahip olması sebebiyle Çift Bıçak Kenarlı Kırınım (ÇBKK) modeli sıklıkla kullanılmaktadır. Fakat modelde insan vücudu benzetimi için kullanılan dikdörtgensel ekran, insan vücudu fiziğini temsil etmek iç...

Radio frequency fingerprinting (RFF) is based on identification of unique features of RF transient signals emitted by radio devices. RF transient signals of radio devices are short in duration, non-stationary and nonlinear time series. This paper evaluates the performance of RF fingerprinting method based on variational mode decomposition (VMD). Fo...

Electronic Support Measures (ESM) systems have many operational challenges while locating radar emitter's position around irregular terrains such as islands due to multipath scattering. To overcome these challenges, this paper addresses exploiting multipath scattering in passive localization of radar emitters around irregular terrains. The idea is...

This study presents a simple approach to characterize the effects of scattering objects around indoor links at 28 GHz while the link is fully blocked by human body. The effects of scattering objects nearby the link were studied by conducting measurements with a metallic reflector and human body. Here, basic mechanisms of wave propagation such as re...

This study presents the design and the fabrication of a miniaturised sub‐GHz antenna for remote control applications. Miniaturisation techniques were examined to identify the most appropriate topology for sub‐GHz band requirements. First, the design parameters of the antenna were determined, and then, a commercial electromagnetic simulation tool wa...

Recently, network security has become a major challenge in communication networks. Most wireless networks are exposed to some penetrative attacks such as signal interception, spoofing, and stray. Radio frequency (RF) fingerprinting is considered to be a promising solution for network security problems and has been applied with various improvements....

This paper presents a better understanding of the use of finite integration techniques (FIT) and finite element method (FEM) in different types of microstrip antennas in order to determine which numerical method gives relatively more accurate results. Although the theoretical formulation based on Maxwell's equations of both FEM and FIT are approach...

This study presents experimental analysis of range error of modular FMCW (frequency modulated continuous wave) radar operating at C-band. As FMCW utilizes frequency modulation, it can measure both range and speed of targets. One of the problems arising in the design of modular FMCW radar is error due to time delays in components and/or modules (Mod...

Flipped classroom is an emerging course delivery method, where the traditional in-class and out-of-class activities flip places. The lectures are given out-of-class with electronic resources and in-class time is reserved for group activities and discussion with the instructor. In this study, we present our implementation of a flipped classroom in a...

This paper presents some preliminary results of design and development of sub-GHz multilayer microstip antenna for use in near ground communication applications. In design stage of the antenna, iterative approach was applied. Firstly, a two layer microstrip antenna design process is presented. Next, the corners of the patch were cut, and a vertical...

In a single-receiver source localization scenario, pulses radiated from an emitting source (emitter) are reradiated from distributed points over the irregular terrain due to the diffuse scattering. Obviously, diffuse scattering may be occurred at anywhere over irregular terrains in dense scattering environments. Hence, a particular region from whic...

An electronic support system receiver which is a passive receiver picks up an interleaved stream of pulses and extracts their pulse parameters. These parameters are sent to a deinterleaving subsystem which sorts them and forms pulse cells that each are assumed to belong to a specific emitter. In this paper, we develop a method for this task of dein...

In this study, line of sight and obstructed line of sight temporal fading measurements were carried out in factory environment. Measurements are done at 315 MHz, 870 MHz, 915 MHz and 2400 MHz operating frequencies. Temporal fluctuations which are obtained from measurements analysed according to Rayleigh and Rician distributions. It has been shown t...

Estimating in-factory radio signal propagation characteristics accurately provides robust communication link configuration in these areas. In line with this purpose, this work here provides propagation path loss measurement results carried out in three heavy industrial environments at 315, 434, 870 ve 915 MHz frequency bands.

This paper presents a new feature set for the problem of recognizing pulse repetition interval (PRI) modulation patterns. The recognition is based upon the features extracted from the multiresolution decomposition of different types of PRI modulated sequences. Special emphasis is placed on the recognition of jittered and stagger type PRI sequences...

Estimating in-factory radio signal propagation characteristics accurately provides robust communication link configuration in these areas. In line with this purpose, this work here provides preliminary propagation path loss measurements carried out in ten different factory environments at the sub-GHz frequency bands. Path loss measurement data at t...