Directional Antenna

In multipath environments, the transmitted signal polarization is affected by channel fading which results in a multipath polarized signal component on the receiver side. These receivers usually employ single polarized uniform linear antenna array (ULA) which measure one component of the received electromagnetic (EM) signal. In rich scattering environments, however, it may be possible to improve the performance by using "vector antennas", as they can detect up to six independent components of the EM field. In this paper, we consider the advantage of vector antenna (VA) over uniform linear array (ULA) receiver for code-division multiple-access (CDMA) signals in a multiuser environment. We consider a closed loop power control (CLPC) for a beamformer-RAKE receiver for wireless CDMA multiuser system. The performance enhancement in Bit Error Rate (BER) is investigated for matched-filter receivers using various VA's and ULA for a fading multipath channel. Analysis, theoretical curves, and simulations of VA and ULA receivers suggest that VA can better exploit multipath and therefore significantly improve the diversity gain and bit-error-rate performance of CDMA signals in the presence of a frequency selective rich multipath channel.

This paper presents the design, simulation, and fabrication of a new microstrip antenna of Ultra-Wide Band (UWB) technology operating within the frequency range of 3.4237 GHz to 10.824 GHz. The feeding technique used for the antenna is the Coplanar Waveguide (CPW) in conjunction with a slotted quasi-fractal patch on an FR4 substrate. The physical responses of this study show that the considered antenna covers the entire range of the UWB frequency spectrum providing the operational bandwidth of 7.4 GHz and obtaining input reflection of less than-10 dB. This type of design is different from planar antennas or microstrip patch antennas and has bidirectional radiation patterns. Its low mass, beneficial emission properties, and versatile frequency range make this small antenna suitable for many wireless communications uses, such as wireless body area networks (WBANs), microwave imaging and advanced radar systems.

In wormhole attack, an attacker node keeps data packets at one location in the network and forward to another attacker node far away by tunneling, which again broadcast them into the network locally. The proposed technique is an efficient detection and prevention method called Wormhole Attack Prevention and Detection Using Authentication Based Delay per Hop Technique for Wireless Network. Detection of wormhole attack is done using number of hops and delay of each node in different paths available in network. The sender node is capable to identify both types of wormhole attacks. Proposed technique detects the legitimate path and path under the wormhole attack. From quantitative viewpoint, relevant network simulations were conducted to validate the proposed scheme using a NS2 network simulator. General Terms Security, Wormhole attack, Authentication, Caeser Cipher, Inband Channel, Out of Band Channel.

The tapered aperture distribution of the substrate integrated horn antenna always limits its aperture efficiency and widens the antenna beam width. Therefore, the integrated H-plane horn has rarely been considered for the applications where fan-beam types of radiation pattern are required. Here, the amplitude distribution of the integrated horn aperture has been improved to be almost uniform by the three methods of applying hard boundary conditions to the lateral walls of the horn. Among these three methods, air-filled integrated horn in which the internal substrate is removed by keeping a thickness of the dielectric on the walls shows wider improvement over the bandwidth.

A new substrate integrated horn antenna with hard side walls combined with a couple of soft surfaces is introduced. The horn takes advantage of the air medium for propagation inside while having a thickness of dielectric on the walls to realize hard conditions. The covering layers of the air-filled horn are equipped with strip-via arrays, which act as soft surfaces around the horn aperture to reduce the back radiations. The uniform amplitude distribution of the aperture resulting from the hard conditions and the phase correction combined with the profiled horn walls provided a narrow beam width and -13 dB side lobe levels in the frequency of the hard condition, which is validated by the simulated and measured results. Keywords-Substrate integrated waveguide (SIW); horn antenna; hard horn; soft surface.

A new approach based on the superposition of sub-antennas radiating characteristics is used to get accurate models of real base station antennas. The sub-antennas are modelled by solving an over determined matrix equation using a least squares procedure. This process allows determining the gain of the sub-antennas while their fields are calculated analytically. The superposition of the fields of the sub-antennas gives the field of the studied base station antenna, which can then be used to assess the human exposure to the electromagnetic fields emitted by the base station antennas of mobile networks.

In this article, a unique metamaterial (MTM) structure is presented that exhibits four resonances of transmission coefficient (S 21 ) that fall into S, X, and Ku bands. The MTM design is initiated on a Rogers (RT5880) substrate with an electrical dimension of 0.088 λ × 0.088 λ (λ is calculated at 3.424 GHz). The resonating patch contains four quartiles connected by a central metallic strip. The placement of each quartile is such that the whole resonator is mirror symmetric about the vertical axis. Two H-shaped modifiers connect two quartiles of each vertical half of the resonator. These H-shaped modifiers form the resonance cavity in its vicinity, and thus help significantly to orient the overall resonances of the proposed MTM at 3.424 GHz, 10 GHz, 14.816 GHz, and 16.848 GHz. The resonance phenomena are examined through equivalent circuit modeling and verified in Advanced Design Software (ADS). Metamaterial properties of the proposed MTM are extracted and it exhibits negative permittivity, permeability, and refractive index. The prototype of the MTM is fabricated and measurement is taken. The measured S 21 shows a close similarity with the simulated result. Moreover, effective medium ratio (EMR) is calculated for the proposed MTM and a high EMR of 10.95 is obtained that expresses its compactness. This compact MTM with negative permittivity, permittivity, and refractive index can be important component for improving the performance of the miniaturized devices for multi-band wireless communication systems.

A multiband printed dipole antenna is presented for use in wireless communication applications. The proposed fractal antenna design is based on fractal geometry of the second level tent function transformation. Due to the resulting geometrical structures of a fractal tent function curve depend on the starting angles of the initial tent function, many dipole antennas have been modeled and the corresponding radiation characteristics have been evaluated. Theoretical performance of these antennas has been calculated using the method of moments (MoM) electromagnetic simulator, IE3D. Simulation results of many tent fractal dipole antennas which have been modeled show that all of these antennas have multiband resonate behavior, but this resonate behavior is different according to the starting angle for each antenna. The results have shown that these antennas have acceptable performance for VSWR ≤ 2 (return loss ≤ -10 dB), using a 50Ω feed line, at most of the resonating frequencies. This feature provides antenna designer with more degree of freedom, and makes the proposed antenna (or its monopole counterpart) suitable for use in the modern multi-functions communication systems.

Multibeam antenna arrays are currently recognized as one of the enabling technologies for the next-generation communication standards. One of the key components of these systems is the beamforming network (BFN) that implements the array element excitations. This article addresses this issue by presenting a novel strategy to realize an analog feeding network, which allows an arbitrary linear array (LA) to radiate Manuscript

This master's thesis is intended for the solution of Microwave (MW) link alignment which has several applications in modern communication systems. MW communication is used for point to point links with small wavelength and simultaneously compact antenna dimensions. Assuring the automated alignment of antennas provides a better communication between switching stations and allow its subscribers to communicate ceaselessly. In the first part of the work; effects of downtime on a network are discussed and at later stage a mechanism is investigated which will reduce the downtime. MW antenna used in communication systems is regularly affected by environmental factor and generally by wear and tear of mounts. These factors cause the precisely directed antennas to be perturbed from respective main lobes. Larger antennas with narrow main lobes require more sophisticated designing while smaller antennas have a broader main lobe. An automated antenna alignment that works without human intervention can decrease the down time and ensure a reliable communication between the near end and far end terminals of the Base Transceiver Station (BTS). The focus has been laid on a system that works autonomously and for that LabVIEW design and RCX Robonics Kit is used. Results are presented to indicate antenna alignment in automatically synchronized manner. vi vii ACKNOWLEDGEMENTS First and foremost it has been a blessing of Almighty Allah that we have came this far. The project has been a team work and there are many individuals who have participated in its completion. Our supervisor Dr. Arild Moldsvor has helped us in formulation of the blue print at the impetus phase and at later stage gave recommendations to improve our report and overall presentation to adequate level. Magnus Mossberg and Jorge Sollis are our honorable examiners and they have helped us in academic co-operation and supported us in administrative issues. We would like thank Mr. Lars-Ove Larsson for his dedication and help during the implementation phase of model. Our classmates have encouraged and helped us with their inputs. Finally we thank our parents and family members whose inspiration was most important for us to achieve this goal. viii ix

Àííîòàöèÿ.  ñòàòüå ïðåäñòàâëåíà øèðîêîïîëîñíàÿ ïðÿìîóãîëüíàÿ äèýëåêòðè÷åñêàÿ ðåçîíàíñíàÿ àíòåííà DRA (dielectric resonator antenna) â ôîðìå êîâðà Ñåðïèíñêîãî, ðàáîòàþùàÿ â X-äèàïàçîíå, êîòîðàÿ õàðàêòåðèçóåòñÿ ìîäåëüþ äèýëåêòðè÷åñêîãî âîëíîâîäà DWM (dielectric waveguide model). Äëÿ ñíèaeåíèÿ ñòîèìîñòè DRA â êà÷åñòâå ìàòåðèàëà èñïîëüçîâàí äåøåâûé òåôëîí. Ðåçóëüòàòû ìîäåëèðîâàíèÿ ïðîâåðåíû ñ ïîìîùüþ ðåàëèçîâàííîãî ïðîòîòèïà.  ñòàòüå îáû÷íàÿ ïðÿìîóãîëüíàÿ DRA ñðàâíèâàåòñÿ ñ ïðÿìîóãîëüíûìè DRA â ôîðìå ôðàêòàëà ïåðâîé è âòîðîé èòåðàöèé. Îáñóaeäàåòñÿ ìåòîäîëîãèÿ ïðîåêòèðîâàíèÿ àíòåííû è åå ðåçîíàíñíûå è ðàäèàöèîííûå õàðàêòåðèñòèêè. Îáîñíîâàííîñòü ïîëó÷åííûõ ðåçóëüòàòîâ ïîäòâåðaeäàåòñÿ áëèçêèì ñîâïàäåíèåì ýêñïåðèìåíòàëüíûõ è ìîäåëèðîâàííûõ ðåçóëüòàòîâ. Èçìåðåíèÿ íà ïðîòîòèïå ïîêàçàëè øèðèíó ïîëîñû ïðîïóñêàíèÿ 48%, îïðåäåëÿåìóþ ïî ïîëíîìó âõîäíîìó ñîïðîòèâëåíèþ. Ïðè ýòîì îíà îõâàòûâàåò âñþ ïîëîñó ÷àñòîò Õ-ñ ïîäîáíîé äèàãðàììîé íàïðàâëåííîñòè âî âñåé ïîëîñå è óñèëåíèåì 7,5 äÁè â äèàïàçîíå 9,0-11,5 ÃÃö.

Stealthiness can be described as a disposition to be sly and to do things surreptitiously. This paper presents a new architecture for flexible and secure networking in battlefields that enables stealthy and covert communication in the presence of node mobility. Our architecture is based on the combination of optical (fiber) and wireless links. Our objective is to be able to carry on undeterred communication without the attack/eavesdropping nodes being able to detect the presence of any communication. This objective is not only crucial for successful completion of the operation, but also for the safety of our mobile nodes, by not giving out their locations. We combine the advantages of optical links, such as high bandwidth, low delays, low error rates, good security, with the advantages of wireless links, such as mobility and flexibility, along with directional antennas for communication. From security point of view, we also assume presence of red zones, which are the ones controlled by the adversary or where the adversary can trace wireless activities.

We present two on-demand MAC protocols to provide differentiated service classes over multiple beam antennas. We use embedded feedback from neighboring nodes to synchronize data communication at multiple beams. The protocols use multilevel queues to organize data, and employ a quality of service (QoS) aware packet scheduler to facilitate disparate traffic flows. We further present a novel paradigm in wireless channel access -receiver initiated choice of sender (RICS). RICS organizes the senders into multilevel queues providing an elegant method to bias the probability of channel award to these nodes. Simulation results demonstrate successful provision for multiple service classes.

Broadband antennas are very useful in many applications because they operate over a wide range of frequencies. The objective of this paper is to study the transient responses of various well-known antennas over broad frequency ranges. As such, the phase responses of these antennas as a function of frequency are of great interest. In the ensuing analysis, each antenna is excited by a monocycle pulse. Many antennas show resonant properties, and numerous reflections exist in the antennas' outputs. The first part of this paper deals with ways of converting various resonating antennas to traveling-wave antennas by using resistive loading. Appropriate loading increases the bandwidth of operation of the antennas. However, the drawback is the additional loss in the load applied to the antenna structure, leading to a loss of efficiency to around fifty percent. However, some of the antennas are inherently broadband, up to a 100:1 bandwidth. Hence, the transient responses of these antennas can be used to determine their suitability for wideband applications with a low cutoff frequency. The second part of the paper illustrates the radiation and reception properties of various conventional ultra-wideband (UWB) antennas in the time domain. An antenna's transient response can be used to determine the suitability of the antenna in wideband applications. Keywords: Traveling-wave antennas; time domain analysis; dynamic response; antenna transient analysis; transient response; resistance; loaded antennas; pulse excited antennas; electromagnetic transient analysis; reciprocity; wideband antennas; ultrawideband antennas; log periodic antennas; spiral antennas; Vivaldi antennas; dipole antennas; horn antennas; biconical antennas; volcano smoke antennas; diamond dipole antennas; helical antennas; ridged horn antennas; bowtie antennas

Motivated by the widespread proliferation of wireless networks employing directional antennas, we study some capacitated covering problems arising in these networks. Geometrically, the area covered by a directional antenna with parameters α, ρ, r is a set of points with polar coordinates (r, θ) such that r ≤ r and α ≤ θ ≤ α + ρ. Given a set of customers, their positions on the plane and their bandwidth demands, the capacitated covering problem considered here is to cover all the customers with the minimum number of directional antennas such that the demands of customers assigned to an antenna stays within a bound. We consider two settings of this capacitated cover problem arising in wireless networks. In the first setting where the antennas have variable angular range, we present an approximation algorithm with ratio 3. In the setting where the angular range of antennas is fixed, we improve this approximation ratio to 1.5. These results also apply for a related problem of bin packing with deadlines. In this problem we are are given a set of items, each with a weight, arrival time and deadline, and we want to pack each item into a bin after it arrives but before its deadline. The objective is to minimize the number of bins used. We present a 3-approximation algorithm for this problem, and 1.5-approximation algorithm for the special case when each difference between a deadline and the corresponding arrival time is the same.

This article examines the issue of extending the inter‐element spacing between slots of equally‐spaced linear grounded frequency selective surface (FSS) arrays with spacing beyond half a wavelength in W‐band (75–110 GHz). We present the design, processing, and testing of W‐band grounded FSS arrays with different inter‐element spacings along transverse electric (TE) and transverse magnetic (TM) field directions separately. The comparison of periodicity changing effects along TE and TM field directions has been reported. The inter‐element spacing versus phase curves demonstrate that in some extent the inter‐element spacing can be a phase optimization parameter for complex array design. We fabricated the corresponding FSS arrays on quartz substrate with photolithographic etching technique, and characterized the vector S‐parameters with a free space MVNA. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 155–160, 2010; Published online in Wiley InterScience (www.interscience...

The Global Positioning System (GPS) has become a mature technology and is continually being applied in new and more demanding applications. A current effort in this area is the development of compact, durable but lightweight GPS antennas on conformal surfaces for handheld devices. Because modeling the electromagnetic performance of these antennas is often difficult, prototypes are typically built, measured and redesigned in an iterative process. We demonstrate the fabrication of a GPS conformal antenna under ambient-temperature conditions using a combination of laser micromachining and/or laser direct-write processes. The electromagnetic behavior of the antennas is then characterized and the design of the antenna structures is further optimized. Pattern simulations and input impedance measurements of the antenna are presented that demonstrate the usefulness and success of the iterative process made possible with this fabrication technique .

A new design approach for a microstrip patch antenna to achieve reconfigurable dual-band operation with tunable frequency ratio is introduced. The approach uses a lumped capacitor in the middle of a slotted patch antenna, which results in two resonant frequencies. The two resonant frequencies and their ratio are functions of the capacitance value. If a varactor with an appropriate biasing network is used, electronic tuning is realized by changing the applied DC voltage. To understand the dual-resonance behavior of the proposed antenna, an equivalent circuit model based on the transmission line theory of the antenna is established, considering the slot effect and the lumped capacitor. The results are verified with full wave simulation. Furthermore, measurements for fabricated antenna prototypes operating in 2-4.5 GHz are carried out for validation, and the performance shows a tunable frequency ratio from 1.45 to 1.93 with a capacitance range from 0.31 to 0.74 pF. It is worthwhile to point out that the radiation patterns are similar at both bands because both resonances are due to the fundamental TM01 mode.

In this letter, a new design for single-feed dual-band circularly polarized microstrip antennas is presented. A stackedpatch configuration is used for the antenna, and circular polarization is achieved by designing asymmetrical U-slots on the patches. The dimensions of the U-slots are optimized to achieve circular polarization in both bands. A prototype has been designed to operate at two frequencies with a ratio of 1.66. Both experimental and theoretical results are presented and discussed. The circularly polarized bandwidth of the antenna is 1.0% at 3.5 GHz (WiMax) and 3.1% at 5.8 GHz (HiperLAN).

Beyond fifth-generation (5G) heterogeneous networks (HetNets) are facing the challenge of accommodating enormous mobile users and data traffic with scarce spectrum resources in the microWave (µWave) band. In this work, we consider both challenges in HetNets comprising large size, high power base station (LHB) and relay operating in µWave band and small size, low power base station (SLB) and device-to-device (D2D) operating in millimeter wave (mmWave) band. We formulate user association optimization problems to pitch user association schemes based on downlink uplink decoupled (DU-DPL) access against traditional downlink uplink coupled (DU-CPL) access in HetNets to gauge the performance of these access schemes in terms of accommodating users and spectrum efficiency in µWave and mmWave bands. Formulated problems are non-deterministic polynomial-time hard (NP-hard) and solved using -optimal algorithm. Simulation results show the edge of DU-DPL access over DU-CPL access in terms of users association and spectrum efficiency.

The problem of synthesizing "optimal" sum and difference patterns subject to arbitrary sidelobe bounds by means of a simple feeding network is dealt with. It is shown how a hybrid optimization procedure properly acting on both clustering into subarrays and excitations of these latter greatly improves performances of known feeding architectures with respect to existing procedures. Results of the proposed technique, which significantly outperform existing methods, renew the interest of these simple feeding architectures, and emphasize the effectiveness of this kind of hybrid procedures exploiting the convexity of the problem with respect to a part of the unknowns.

Adaptive array antennas use has been limited to non-commercial applications due to their high cost and hardware complexity. The implementation cost of adaptive array antennas can be kept to a minimum by using cost effective antennas, reducing the number of elements in the array and implementing efficient beamforming techniques. This thesis presents techniques for the design of adaptive array antennas which will enable their cost effective implementation in wireless communication systems. The techniques are investigated from three perspectives, namely, reconfigurable antenna design, wide scan array design and single-port beamforming technique. A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing the shape of the main radiating structure of the antenna. The...

A comparison analysis between two different types of antenna arrays in direction-of-arrival (DOA) estimation is presented. This study was undertaken to point out any difference in the process of DOA estimation between isotropic and directional antenna array. To the best of our knowledge, there is no previous work that analysed the DOA estimation between these two antenna arrays. The approach taken was to estimate all predetermined angle-of-arrival (AOA) correctly by using MUSIC, a spectral-based DOA algorithm. Results obtained show that, to perform the DOA estimation, isotropic antenna array depends entirely on DOA algorithm, whereas directional antenna array required both the DOA algorithm and the position of the main beam at any instant. This work concludes that, in practical application, it is essential to consider both the performance of DOA algorithm and the beam pattern to ensure the DOA estimation is carried out correctly.

This work proposes a new direction-of-arrival (DOA) estimation algorithm for directional antenna arrays. Most of the existing DOA algorithms are difficult to work with directional antenna arrays due to the characters of directional elements and thus proper modification is required. The proposed algorithm is based on Capon algorithm through the introduction of a new optimisation problem, which aims to maintain the array gain in the 'look direction', so that the DOA can be estimated correctly using a directional antenna array. To verify the performance of the proposed algorithm, computer simulations are performed and then the results obtained are compared with the Capon algorithm. The results show that the proposed algorithm outperforms the Capon algorithm.

The problem of direct excitation of the shear Alfvén wave by antennas in the boundary of a fusion plasma is considered. In the plasma scrape-off layer the physics of this wave is determined by finite electron inertia. Expressions for the wave electric and magnetic field are derived without any assumption on the smallness of the ratio of frequency to ion cyclotron frequency. It is shown that the shear Alfvén wave propagates as a guided beam along the steady magnetic field over a wide range of frequencies below the ion cyclotron frequency, and is predominantly excited by current elements parallel to the steady magnetic field. A simple transmission-line analogy suggests that guidance of the Alfvén wave is also expected in the presence of strong plasma inhomogeneity.

Within the Surveillance function in the A-SMGCS frame, Multilateration (MLAT) systems are being more and more used for location and identification of aircraft and of cooperating vehicles [1] on the airport surface. This situation, with increasing traffic in the downlink SSR channel, may lead to a too high number of superimposed, i.e. garbled, signals. The aim of this work is the need for reliable, simple effective algorithms to separate overlapped SSR signals. We proposed earlier some solutions [2,3], as well others can be found in the literature [5,6]. All of them require an array antenna at the receiver stations, while today's receiver stations are equipped with only one omni-directional antenna. In this paper, the sources separation algorithm based on array processing (PA: Projection Algorithm) is adapted to a single-antenna configuration, where the variation of carrier frequencies of different vehicular transponders [8] is exploited. Simulations with signals synthesized from real measurements give results that demonstrate the effectiveness of the algorithm in a frequency agility environment.

This paper presents a simplified Multiple-Input Multiple-Output (MIMO) antenna tailored for dual-band applications, featuring a co-planar waveguide (CPW) fed configuration that integrates ultra-wideband (UWB) and narrowband capabilities. The single element design employs a circular patch with a central rectangular bar and circular slot, achieving impedance bandwidths from 3.96-9.89 GHz and 12.09-18.16 GHz, with a peak gain of 3.83 dBi. In MIMO configuration, a parasitic element effectively reduces mutual coupling, achieving mutual coupling less than-20 dB, while orthogonal element placement enhances the polarization diversity, crucial for the multipath environments. The antenna's compact size (18.5 mm × 46.8 mm) facilitates integration into various platforms, delivering a peak gain of 4.77 dBi at 7.65 GHz, low envelope correlation coefficients (ECC < 0.001), and high diversity gain (approximately 10 dB). Comparative analysis highlights the design's competitive advantages in bandwidth, isolation, gain, and efficiency, addressing miniaturization and coupling challenges, and making it a robust solution for next-generation wireless systems.

Hierarchical wireless networks have the potential to provide the needed capacity to a large number of mobile stations (MSs). According to this system architecture, the MSs are served by a dense network of fixed relay nodes (RNs) fed by a small number of large hub base stations (HBSs). In such deployment, high spectral efficiencies can be achieved if the RNs act as twoway relays; however this gives rise to co-channel interference (CCI) which needs to be mitigated. In order to gain insights on the impact of CCI to this scenario we consider an HBS with two highly directional antennas communicating with two MSs via two interfering two-way RNs. We investigate the average maximum sum-rate of two cooperative strategies. The first is based on Decode-and-Forward (DF) and network coding and acts as a baseline. The second strategy is based on Amplifyand-Forward (AF) and Network MIMO processing over both the backhaul and access channels. Furthermore we devise some cooperative protocols that utilize two, three or four time slots. It is shown that the 2-slot schemes perform generally better and that the DF strategy achieves superior performance when CCI is low while AF with Network MIMO is superior when CCI is high.

A high-gain low-profile Fabry-Pérot (FP) leaky-wave antenna (LWA) presenting one-dimensional high beam steering properties is proposed in this letter. The structure consists of a ground plane and a varying inductive partially reflective surface (PRS). A microstrip patch antenna is embedded into the cavity to act as the primary feed. As design examples, antennas are designed to operate at 9.5 GHz. Subwavelength FP cavities with fixed overall thickness of (where is the free-space operating wavelength) are fabricated and measured. The impact of varying the PRS inductance is analyzed. It is shown that a high beam steering angle from broadside toward endfire direction close to 60 can be obtained when judiciously designing the inductive grid of the PRS.

The design of a locally one-dimensional inductive-varying metamaterial operating near 10 GHz is reported. This is combined with a fixed capacitive grid to design a phase-varying metasurface. This composite metasurface is then used as a partially reflecting surface (PRS) together with a perfect electric conductor surface to form a resonant Fabry-Pérot type cavity. A patch antenna acting as a primary source is embedded in the cavity to constitute a highly beam-steerable directive antenna. A 56°deflection of the antenna beam is experimentally observed.

Dalam era modern ini, telekomunikasi  memainkan  peran vital dalam kehidupan manusia. Perkembangan  teknologi  yang  sangat  pesat  dan  terus  berinovasi  seiring  perkembangan zaman membuat kebutuhan masyarakat akan telekomunikasi  menjadi suatu hal yang harus terpenuhi  setiap  saat. Guna  memenuhi  kebutuhan masyarakat  akan  telekomunikasi  yang cepat,  akurat,  dan  praktis  yang  semakin  meningkat,  perusahaan  penyedia  jasa telekomunikasi  terus  meningkatkan  mutu  layanan  agar  hal  itu  dapat tercapai.  Untuk itu, diperlukan  suatu  sistem  yang  dapat  mengantisipasi  mobilitas  pengguna  serta  mampu melayani  lebih banyak pengguna yang jumlahnya  semakin hari semakin bertambah.

Definisi  antena  adalah  piranti  (device)  logam,  digunakan  untuk  memancarkan  atau menerima gelombang radio seperti batang atau kawat, menurut IEEE (IEEE Std 145-1973) adalah  peranti  untuk  memancarkan  atau  menerima  gelombang  radio.  Dengan  kata  lain, antena adalah struktur peralihan antara ruang bebas dan piranti pemandu (guiding device), seperti yang ditunjukkan pada Gambar 1.1. Peranti pemandu atau kabel transmi-si dapat berbentuk  kabel  koaksial  atau  pemandu  gelombang  (wave  guide)  dan  alat  pemandu  ini digunakan untuk membawa energi elektromagnetik dari sumber ke antena atau dari antena ke  penerima,  dan  masing-masing  antena  disebut  sebagai  antena  pemancar  atau  antena penerima.  Saluran  transmisi  pada  Gambar  1.1  diekivalensikan  dengan  Thevenin  dalam mode transmisi yang ditunjukkan Gambar 1.2 dengan sumber sebagai pembangkit ideal, saluran transmisi sebagai saluran dengan impedansi karakteristik Zc, dan antena dinyatakan sebagai beban ZA [ZA = (RL + Rr) + jXA].

Near-field focusing characteristics of transmitarray antennas are investigated. The design procedure is summarized and a Ku-band focused transmitarray antenna is presented where the elements are aperture-coupled patches interconnected with stripline delays. The focusing performance of the transmitarray is compared with classic far-field designs. It is shown that a near-field focused reflectarray can be a good candidate for applications requiring high microwave power.

This paper derives a new expression of the correlation coefficient for two omni-directional antennas in terms of the easyto-measure S-parameters. The omni-directional antennas can be monopole or dipole antennas and they are aimed for use in MIMO communication systems whose capacity performance is significantly affected by signal correlation. With this new expression, it can greatly reduce the computational complexity of antenna correlation calculations since the embedded radiation patterns of the antennas are no longer necessary. Numerical calculations demonstrate the accuracy and efficiency of the new formula.

The objective of this paper is to summarize the work that has been developed by the authors for the last several years, in order to demonstrate that the Theory of Characteristic Modes can be used to perform a systematic design of different types of antennas. Characteristic modes are real current modes that can be computed numerically for conducting bodies of arbitrary shape. Since characteristic modes form a set of orthogonal functions, they can be used to expand the total current on the surface of the body. However, this paper shows that what makes characteristic modes really attractive for antenna design is the physical insight they bring into the radiating phenomena taking place in the antenna. The resonance frequency of modes, as well as their radiating behavior, can be determined from the information provided by the eigenvalues associated with the characteristic modes. Moreover, by studying the current distribution of modes, an optimum feeding arrangement can be found in order to obtain the desired radiating behavior.

A composite right/left-handed (CRLH) leaky-wave antenna (LWA) can effectively scan the radiation beam from backward to forward direction. However, in most cases a large range of frequency sweep is required to achieve a wide-angle beam scan, which could limit their applications. An in-depth study is conducted on an equivalent circuit model for a CRLH LWA unit cell to find the controlling parameters on the frequency sweeping range. A systematic design guideline is given for a CRLH LWA for a wide-angle beam scan in a flexibly chosen frequency range. It is shown that beam scanning by sweeping frequency in a target range can be achieved by systematically designing the unit cell parameters. To verify our approach a novel CRLH unit cell is developed and used to design an LWA for a wide-angle beam scan in a narrow frequency range. Finally, the concept is validated through realization of the antenna and its measurement. The measured results show that the antenna prototype can scan its beam from −56 • to +51 • when frequency sweeps from 5.1 to 6.11 GHz (i.e., 18.02% of fractional bandwidth).

This paper presents the design of two types of S-band antennas suitable for mobile satellite communication applications. One design is based on omnidirectional radiating elements and targets consumer systems installed on cars. The other uses an array of four elements with electronic switching, controlled by embedded sensors, to generate directive beams with gain higher than the one that could be provided by an omnidirectional antenna. This latter design targets primarily applications for professional vehicles requiring higher data rates, but it also enables the use of S-band in a wider satellite footprint. The main aspects of antenna design and of validation results are described.

For a fair coexistence of multiple Radio Access Technologies (RATs) in unlicensed millimeter-wave (mmWave) bands, where directional transmissions/receptions are needed, two techniques are being considered for channel access: omnidirectional Listen-Before-Talk (omniLBT) and directional LBT (dirLBT). Under directional transmissions and receptions, om-niLBT is overprotective and depresses spatial reuse, while dirLBT enables spatial reuse but may create hidden node problems. In this regard, this paper proposes a paired LBT (pairLBT) solution, which aims at taking the best of omniLBT and dirLBT. The key idea is to perform directional LBT in paired-directions: the direction of the receiver and the opposite direction(s), so that spatial reuse is permitted while hidden nodes are avoided, hence stimulating a fair multi-RAT coexistence. We derive analytic expressions to properly configure the beamwidth and the energy detection threshold of LBT in the opposite direction(s) in a way such that the impact of hidden node problems is minimized.

The characterization of the UWB channel own behaviour 'without antennas' requires a huge measurement and processing work, which should be greatly and efficiently reduced with the help of low angular distortion antennas. Obviously, usual specifications for UWB channel measurements like particularly good matching, omni-directionality and a large frequency-independent horizontal main lobe have to be respected. Two UWB Bicone antennas designed with respect to these specifications and operating over two different bands have been designed and tested. Characterization tools in the Time Domain (TD) were used to analyze the distortion introduced by these antennas, and both antennas were found to be slightly distorting while comparing the radiated waveform to the excitation one, on one hand, and, more interestingly while comparing the radiated waveforms at different directions on the other hand.

This paper presents some of the work carried out within ULTRAWAVES in the area of antenna design and analysis. Several radiators have been designed, either without or with gain, and either to be used in channel measurements or for the system demonstration. In addition analysis of the antenna operation in pulsed mode is considered.

Intelligent antennas offer the possibility of greatly increasing the capacity of cellular mobile radio systems. We give a comprehensive overview of the literature concerning model scenarios for applications of direction-selective intelligent antennas. Measurement campaigns and simplified models are described that have been derived from these measurements or from physical considerations. Furthermore, directional fading simulators are reviewed which are essential for

 Microstrip patch antenna was designed and simulated using Duroid as a substrate with graphene as a conductive patch material. Four different models were designed and simulated with different slots which includes 1,2 3 and without slot of different dimensions. The single-slot based antenna showed better performance in terms of gain and bandwidth. The antenna can be used for X-band applications.

Thanks to the availability of large bandwidth and high-gain directional antennas at the millimeter-wave (mmWave) bands, mmWave communications have been considered as one of the primary solutions to meet the high data rates needs in vehicular networks. Unicast in mmWave vehicle-to-vehicle (V2V) communications has been well-studied, but much less attention has been paid to V2V broadcast which is required by many V2V applications such as active safety. To fill the gap, this paper systematically investigates mmWave V2V broadcast by considering the unique properties of mmWave signal propagation in V2V environments as well as the impacts of directional antennas and interference. Based on widely-accepted, high-fidelity system models, we mathematically analyze the receiver-side signal-tointerference-plus-noise-ratio (SINR) and broadcast coverage, and we study the impacts of blockage, inter-vehicle distance, vehicle density and beam pattern. Through comprehensive numerical analysis, we find out that, instead of a single unique optimal beamwidth, there exists an optimal range of beamwidth, in which the beamwidths have similar performance and can maximize the coverage. We also find out that the selection of carrier sensing range plays an important role as it highly influences the performance of the whole vehicular networks. Our analysis provides unique insight into mmWave V2V broadcast, and it sheds light on designing effective V2V broadcast protocols.

In this paper, a novel on-glass antenna which is transparent, miniaturized and multiband is presented. First of all, the antenna achieves more than 80% transparency. This is realized by removing as much as possible the metal pattern, without compromising the operational electric current flow. Second, the antenna is electrically small, at 0.95 GHz. This is realized by choosing a proper topology for the remaining metal pattern. Third, the antenna is triple band, covering the ranges 0.88-1.03 GHz, 1.47-2.74 GHz and 3.32-5.97 GHz, respectively. The radiation is omnidirectional in all bands, which is suitable for GSM900/1800, 3G, 4G, 5G (2.55-2.65 GHz), WLAN (2.4/5.2/5.8 GHz), and WiMAX (2.5/5.5 GHz). The maximum gain in the three bands is equal to-0.18 dBi, 3.66 dBi and 4.35 dBi with corresponding radiation efficiencies of 66%, 87% and 88%, respectively. A prototype is made by first printing a metallic circuit on a thin FR-4 substrate and then gluing it on a glass substrate. Measurement results are in good agreement with simulations.