This paper proposes a novel planar direction-of-arrival (DOA) estimation antenna. The estimation capability of phase monopulse DOA estimation antennas is enhanced by integrating an RF multiplier that detects the phase relation between the sum and difference of the two received signals. So the proposed antenna provides a wide range of estimation whereas the conventional monopulse DOA estimation antennas determine the angles of half space. A prototype antenna has been fabricated, and the proposed concept was successfully confirmed.

Resonance frequency of a Circular Microstrip Antenna (CMSA) depends on its diameter. Hence when CMSA is truncated or sectored into smaller elements, keeping the diameter same, it resonates at almost the same frequency. An analysis of the new antenna arrays designed using these truncated non-identical CMSA elements, to realize an amplitude distribution over pedestals leading to a desired first side lobe level (FSLL) has been presented. Truncated elements are designed as non-identical elements based on their gain variation with respect to the standard normalized aperture distribution coefficients. Experimental verification to validate the proposed concept and simulated results has been carried out using an antenna array with eight non-identical elements. There is good agreement between simulated and measured results at 1.76 GHz.

Antenna miniaturization, which is a requirement of modern wireless communication systems, is usually concomitant with the reduction of impedance bandwidth. On the other hand, small antennas should also possess stable radiation patterns across a broad frequency band, such as in UWB systems. In this paper, we propose a UWB antenna structure with a novel feeding system composed of an open cavity resonator. It has a wide relative bandwidth (of about 120%) particularly at the lower frequency limits. The variation of radiation pattern across its operating bandwidth is also negligible. The proposed antenna with the novel feed system is smaller and has a wider frequency bandwidth than other available UWB antennas in the literature. Furthermore, another antenna is proposed, which has a feeding system composed of a surface integrated resonator cavity, fabricated on a two-layer microstrip structure. It has achieved better miniaturization and bandwidth, albeit somewhat lower gain. Three prototype models of the proposed antennas are fabricated and measured, of which the frequency response is in excellent agreement with computer simulation results.

In this paper, the analysis and design of a compact Multiple Split Ring Resonator (MSRR) inspired microstrip rectangular patch antenna is presented. The MSRR is used with four rings. The size of the antenna is 25 × 31 × 1.6 mm³ realized on a low cost FR4 substrate. The proposed rectangular microstrip patch antenna operates at the resonant frequency of 5.88 GHz prior to MSRR inclusion. The antenna characteristics are studied before and after inclusion of metamaterial. After including MSRRs at appropriate places, the proposed MSRR antenna induces a new resonant frequency of 2.78 GHz. In addition to rectangular patch's fundamental resonance, the additional resonance is obtained at 2.78 GHz, thus, exhibits dual bands. Hence, MSRR loading antenna attains a bandwidth of 197 MHz at 2.78 GHz and 703 MHz at 5.88 GHz. The prototype of the proposed antenna is fabricated and measured. Simulated results are verified with the measured ones. This proposed antenna can be effectively utilized for WLAN and RF-ID applications. Parametric studies are illustrated to yield the desired frequency bands. Equivalent circuit model analysis of the MSRR loading is determined. Band characteristics of split ring structure are used to determine the negative permeability characteristics.

The frequency response characteristics of a basic microstrip lowpass filter improved using H-shaped defected ground structures are presented. The proposed defected ground structures behave as a resonant element at high frequency and thus eliminate the stopband frequencies to achieve wide stopband rejection. The 3 dB cutoff frequency of the filter is 1.935 GHz. Due to the defects etched in the ground plane of the basic structure, the harmonic rejection is improved from 5th to 10th order along with low insertion loss and voltage standing wave ratio together with good selectivity. The compact filter has a size of 0.0338λ_g², with λ_g = 85.18 mm being the guided wavelength at cutoff frequency. The characteristics of the lowpass filter are verified through simulation and measurement. Consistent and stable results are obtained.

Studies have been reported in the literature on High Frequency (HF) radio channels in mid-latitude areas more frequently than in low-latitude areas. Ionosphere as a reflector of HF radio waves in low-latitude areas might behave differently from that in mid-latitude. This paper reports a statistical model of sky wave HF channel complex impulse response and its parameters, such as channel gain, path gain, phase shift, and delay spread statistics, derived from both simulation and measurement of a 3044 km link in Indonesia. From the evaluations it can be concluded that the multipaths observed with respect to their propagation delays form multiple clusters corresponding to their propagation modes. The channel gain is found to follow Rayleigh distribution, whereas the rms and maximum delay spread exhibit Rayleigh and Gaussian distributions, respectively. This model can be used in performance evaluation of digital communication schemes in low-latitude HF channels.

In this paper a miniaturized dual wideband bandpass filter is designed by the modified extended composite right/left-handed transmission line (ECRLH-TL) under balanced conditions in each right/left-hand passbands. A novel equivalent circuit is proposed to provide the design and an implementation of ECRLH unit-cell by means of the complementary, split ring resonator (CSRR) on the ground plane. Since CSRR is utilized as an alternative to implementing one of the resonators of ECRLH unit-cell, the size and complexity of the structure can be consequently reduced. An example of a dual band pass filter with 3 dB frequency bands from 3.2 to 4.8 GHz and from 6 to 7 GHz is investigated. There is a good agreement among circuit, electromagnetic simulations and measured results in both passbands. The measured insertion loss is better than 0.5 and 1 dB in first and second bands central frequency, respectively. The group delay which is an important factor in wideband communications is about 0.62 ns and 0.71 ns, respectively, in the first and second band central frequencies. The final dimensions of the miniaturized filter are reduced to 8.88 mm X 8.18 mm.

A broadband end-fire antenna loaded with magneto-electro-dielectric metamaterial (MED-MTM) is presented in this paper. Based on a planar printed structure, many periodic structures are investigated in antenna design. The metal patch is embedded with a C-shaped complementary split-ring resonator (CSRR) array, and many cross slots are etched on the ground plane. The zeroth-order resonance (ZOR) and first-order resonance (FOR) can be excited. As a result of electromagnetic coupling effect, the C-shaped patch and ground plane compose metamaterial transmission line (MTL). For potential applications, the broadband and end-fire antenna can work with a 53.5% (3.81-6.59 GHz) impedance bandwidth. The proposed antenna achieves size reduction, gain improvement and bandwidth enhancement.

In this study, the scattering map of the breast is reconstructed by applying the matching-pursuit algorithm (MPA) to the simulation data obtained by the monostatic inverse synthetic aperture radar (ISAR) principle, and the locations of the tumors are determined by considering the peaks on the scattering map. The MPA iteratively searches the true solution by assuming every discrete point in the solution space to be a scattering center by dividing the imaging region onto a discrete grid. In order to obtain images with better resolution, the fine granularity of the grid for accurate solutions is provided at the expense of increased processing times. First, our approach based on MPA is tested on simulated data generated by MATLAB for breast tumor detection and imaging. Perfect reconstruction for the locations of the hypothetical breast tumor points is attained. Then, a full-wave electromagnetic simulation software named CST Microwave Studio (CST MWS) is used to generate backscattered electric field data from a constructed scenario in which a tumor is located in a breast model. Next, we use the collected data from the defined scenarios as an input to our algorithm. Resultant images provide successful detection and imaging of the tumor region within the breast model. The accuracy of the MATLAB and the CST MWS simulation results demonstrate the availability of our MPA-based focusing algorithm to be used effectively in medical imaging.

A passband filter where the central frequency can be one of seven selectable frequencies is presented. Its operation region ranges from 325 to 455 MHz, and each bandwidth is about 20 MHz. The filter is based on a highly miniaturized ring resonator with a size reduction from about 77% to 83% compared to a conventional closed ring. The reconfiguration of its resonant frequency is implemented by shifting a short location, thus changing its effective inductance. This is opposed to the conventional capacitance change of other reconfigurable filters. Simulated and experimental results are in good agreement. Reflections are below -10 dB at central bandpass frequencies for all selectable bands.

In this paper, a multi-carrier nonlinear frequency modulation system based on pseudo-random frequency offset is designed. The reduction of the main lobe 3\,dB width and the side-lobe peaks cannot be realized simultaneously in conventional beamforming schemes, especially when the number of array elements remains unchanged. The proposed system can reduce the main-lobe 3 dB width and suppressing the side-lobe peaks simultaneously. This is done by adjusting the number of sub-signals, frequency offset coefficient and the inter-element spacing. Then, through time slot processing, signal power is focused on different targets. Numerical simulation experiments are implemented to validate the theoretical analysis of the proposed methodology, and comparisons with other techniques are made.

In this paper, a CPW-fed compact metamaterial-inspired monopole antenna is proposed for Industrial, Scientific and Medical radio band (ISM, 2.4-2.483 GHz). The proposed antenna consists of a T-shaped patch and a set of split ring resonators (SRRs). The miniaturization is attained after loading SRRs in proximity to the T-shaped radiator, which makes the antenna structure electrically small. The measured fractional bandwidth of the antenna is 4% (2.42-2.52 GHz), and its size is 0.22λ_o× 0.098λ_o×0.013λ_o. In addition, the electrically equivalent circuit of the proposed antenna is modeled, and the resonant frequency is calculated by using an analytical approach. Also, the permeability plot of SRRs is extracted using Nicolson Ross weir method. The measured peak gain and radiation efficiency of the antenna are obtained as 1.76 dBi and 78.5%. The simulated results and measured results are found in a good agreement.

A simple broadband circularly polarized (CP) aperture antenna is proposed in this letter. The antenna is composed of an L-shaped feed line and a circular aperture. With the newly introduced perturbation slots, a new resonant mode TE₃₁ is generated, which can widen the CP bandwidth without increasing the antenna size. Measured results of the fabricated antenna shows 93.5% (2.9-8 GHz) impedance bandwidth (|S₁₁|<-10 dB) and 66.6% (3-6 GHz) 3 dB axial-ratio bandwidth. The overlapped CP working band covers the entire WiMAX, WLAN and lower frequency 5G bands. Its peak gain is 4.9 dBic at 3.5 GHz, and its gain variation is less than 1 dBic within 3-5.8 GHz band. Design considerations, empirical formulas and surface current analysis are also presented and discussed.

Structural buildings are vulnerable to many types of damages that can occur through their life period. These damages may cause structure failure or at least decrease its efficiency. Dangerous damages occurring in concrete structures are surface opening cracks or sub-surface cracks. So, the determination of location of these cracks is very important, because the crack location is one of the important factors that affect the degree of danger of the damage. The Rayleigh waves have many advantages, as they can be easily recognized due to the maximum energy of the wave components. So, it was used to determine the crack location in the previous works. In this paper, two different techniques are used to determine the crack location; one of them depends on the healthy case, and the other deals only with the cracked case. Common finite element software (Abaqus) is used to model the numerical simulation, and the experimental test is also performed to verify the obtained numerical results. Good agreement between the simulated and experimental results is obtained by employing both techniques to find the crack location.

In present scenario, this paper intends to demonstrate the practicality of a miniaturized coplanar waveguide fed metamaterial inspired antenna that can be effectively operated at dual bands. A broad-side coupled Split Ring Resonator is used to obtain dual bands with an impedance bandwidth (-10 dB) of 840 MHz (3.00-3.84 GHz) and 310 MHz (5.94-6.25 GHz), which resonates at dual bands, viz., 3.42 GHz and 6.07 GHz. The impedance bandwidth (S₁₁<-10 dB) is 25% for the first band and 5.1% for the second band. The size of the antenna is 31 × 25 × 1.6 mm³ realized on a low-cost FR-4 Epoxy substrate. This antenna can be effectively utilized in worldwide interoperability for microwave access (WiMAX) and wireless access in vehicular environments (WAVE) applications. The prototype of the proposed antenna is fabricated and measured. Simulated and measured results are in agreeing nature. Experimental and simulated analyses of the antenna including parametric and dispersion characteristics are dealt in this communication.

Linear antenna array design is a multi-parameter, multi-objective, and nonlinear problem which requires optimal design parameters to get desired performance. To achieve desired performance through multi-objective optimization process, a compromise among desired objectives is essential. In such a situation to make a rational decision on global optimization to avoid arbitrary compromise to any objective, we introduced two fuzzy logic biased/fuzzy biased optimization techniques. We proposed fuzzy logic biased biogeography based optimization algorithm and fuzzy biased gravitational search optimization algorithm to solve M-element nonlinear linear antenna array design problem. In our design problem, we have considered a 16-element dipole-linear antenna array. The optimal design problem incudes thirty one design parameters (sixteen lengths, and fifteen spacings) and four performance parameters such as directivity, front to maximum side-lobe level, half power beamwidth, and front to back ratio. The result shows that applications of fuzzy biased optimizations are more efficient for solving multi objective problem. While analysing the linear antenna array, mutual coupling is taken into account for numerical analysis using method of moment.

In this paper, a broadband planar modified quasi-Yagi antenna using a two-element log-periodic dipole array as a driven element is proposed. To feed the two-element log-periodic dipole array, a simple microstrip to stripline transition as a balun is designed, which converts the unbalanced input to balanced output. The antenna is fabricated on a low cost glass epoxy FR4 substrate with dielectric constant = 4.4, substrate thickness = 1.6 mm, and loss tangent = 0.02. The overall size of the antenna is 84 mm×111 mm, which is 0.41λ_o×0.54λ_o at the center frequency of 1.45 GHz. Measured results show a bandwidth of 41.4% for VSWR≤2. A gain of 6.5 dBi±0.5 dB and front to back ratio (F/B) of better than 20 dB are achieved over the bandwidth. Measured results are in good agreement with the simulated ones. This antenna is useful for RFID, portable direction finding, spectrum monitoring systems, etc.

The bandwidth of OAM antennas, which have a great potential for multiple-input multiple-output (MIMO) communication, must be wide enough. Unfortunately, most of researchers only care about the generation and characteristics of vortex beams carrying orbital angular momentum (OAM) but ignore the bandwidth of OAM antennas. To develop OAM antenna suitable for MIMO communication, Vivaldi antenna is used as the element of circular array because of its wide bandwidth. Three compact wideband circular Vivaldi antenna arrays that can generate vortex beams carrying OAM with numbers of modes l=0, -2, +2 are proposed and experimentally validated in this paper. Measured results show that the proposed antennas can radiate vortex beams with different numbers of modes over a frequency range of 2.7-2.9 GHz.

A novel W-band WR 10 waveguide to microstrip line transition is designed, simulated in a 3D full-wave EM simulation software, fabricated, and evaluated by measurements. The main advantages of this transition are frequency-flat transmission, low reflection, and uncomplicated fabrication. Simulation shows a reflection coefficient of better than -23 dB from 75 to 90 GHz for one hollow waveguide to microstrip line transition. The port reflections increase for a fabricted prototype with two transitions and a connecting microstrip line to a level of about -14 dB. This is mainly caused by fabrication tolerances. The overall transmission of the dual transition prototype is found at a very satisfactory level of about -4.8 dB at 90 GHz for a connecting microstrip line with a length of 45 mm corresponding to an estimated loss of approximately 0.6 dB for a single transition.

In this paper, measurement, modeling and validation of existing models on the effect of nonhomogeneous vegetation on UHF radio-wave propagation through a long forested channel at frequency of 1835 MHz are reported. The paper focuses on vegetation attenuation measurement through a long forested channel of about 8 km long with mixed vegetation of different density. The measured data were fitted using exponential decay function, and a new model was proposed from the fitted curve. The new proposed model will take care of the limitation in vegetation depth posted by some existing models. Generic models, mainly modified exponential decay and analytical models were also fitted to the data and validated, while RMSE was used to determine the best model that describes the data. The evaluated data results show that all the models tested give significant errors which show that they are not suitable for long forested channel scenario. Though COST 235 has the least error (17.05 dB), the error is still significant because COST 235 could only account for vegetation attenuation of short distance scenario. Attenuation shows corresponding increase with increase in leaves thickness in the forested channel considered, which was due to complex permittivity of the leaves moisture content and the dielectric properties of the leaves saline water. The developed model and other results obtained in this study will help to improve prediction accuracy of the effects of vegetation attenuation in nonhomogeneous vegetation along forested channels and also help in establishing efficient UHF radio link budget for long forested channel scenario.