This article basically deals with the implementation of a negligible resistance varactor with a wide capacitance value into a modified version of a cedar shape antenna [1]. The electromagnetic characteristics of the antenna are manipulated both at the level of fractal geometry and electrical length using diodes. The antenna achieves tunability in a wide frequency range as a quad band antenna operating between 1.45 GHz and 4.6 GHz when 3 pairs of varactors are connected across slots. Pin diodes are also implemented leading to tunability in triple frequency bands between 3.7 GHz and 5.8 GHz. Moreover, implementing pin diodes as switches allows frequency reconfigurability of a dual band between 2.5 and 4 GHz and a single band of 6.6 GHz. The antenna RF frequencies have many applications in wireless communication that cover GPS, Bluetooth, WIFI, WIMAX and WLAN.

Dielectric or magnetic materials introduced in a wireless power transfer (WPT) system affect the properties of WPT. This paper quantitatively studies the coupling between the transmitting and receiving elements for a WPT system including either dielectric or magnetic materials. The transmitting and receiving elements are open spirals and solenoid coils which are usually used in WPT systems. The analysis method is the perturbation method which can calculate the total coupling coefficient k, the electric coupling component k_e and the magnetic coupling component k_m simultaneously. This paper gives quantitatively analyzed data on k_m and k_e to indicate how much k_m and k_e are affected by a dielectric or magnetic material introduced in a WPT system.

The well-known ``Sommerfeld radiation problem" of a small -Hertzian- vertical dipole above flat lossy ground is reconsidered. The problem is examined in the spectral domain, through which it is proved to yield relatively simple integral expressions for the received Electromagnetic (EM) field. Then, using the Saddle Point method, novel analytical expressions for the scattered EM field are obtained, including sliding observation angles. As a result, a closed form solution for the subject matter is provided. Also, the necessary conditions for the emergence of the so-called Surface Wave are discussed as well. A complete mathematical formulation is presented, with detailed derivations where necessary.

The Meissner effect is explored based on the acceleration-dependent component of the Weber force. According to the Maxwell theory, a steady circulating current does not produce any dynamics on external resting charges; however, according to the Weber theory, the charges of the circulating current exhibit a centripetal acceleration, which affects the external charges at rest. It is demonstrated that the current generated in this manner can explain the Meissner effect in classical physics.

This paper considers an ideal planar transformer wherein only the electromagnetic parasitics (stray capacitive and leakage inductance) arising out of the transformer geometry are taken into account, assuming lossless conditions. A suitable electrically equivalent circuit model for the planar transformer is used to analyze its frequency and power transfer characteristics; this model was validated by a three dimensional electromagnetic simulation of the planar transformer structure in FEKO electromagnetic simulation software. The effect of dielectric thickness on the bandwidth of the transformer has been analyzed based on the premise that the inherent stray capacitance and leakage inductance elements would affect the power transfer characteristics of the transformer. It has been found that the dielectric thickness of a planar transformer can be optimized so as to maximize the frequency bandwidth. It is also shown that the bandwidth is found to be sensitive to the thickness of the dielectric beyond the optimum thickness threshold topt. Convenient closed form analytic expressions for the optimum dielectric thickness and the resultant maximum bandwidth are derived and presented. It is argued that these results can be readily used to benefit the design of air-core PCB/Planar transformers.

A compact ultra-wideband (UWB) antenna with simple structure is presented. To achieve UWB performance with a compact size, two open ended rounded inverted L-shaped slots are etched on the square ground plane. Moreover, further bandwidth enhancement is obtained by cutting a bevel on the asymmetrical radiating patch. The antenna is fed by a 50 Ω microstrip line and has a small size of 28 × 28 × 1.6 mm³. The simulation time- and frequency-domain results obtained from HFSS simulator package are verified by experimental measurements. Both simulated and measured results show that the antenna can provide a wide impedance bandwidth of more than 129% from 2.7 to 12.55 GHz with -10-dB reflection coefficient. Besides, it is shown that by introducing several antenna designs, the impedance bandwidth can be enhanced from 58% to 129%. The effects of the key design parameters on the antenna impedance bandwidth are also investigated and discussed. Measured results for the reflection coefficient, far-field radiation patterns, radiation efficiency, gain, and group delay of the designed antenna over the UWB spectrum are presented and discussed. Measured data show good concordance with the numerical results. Also, the fidelity factor is calculated in both E- and H-plane by using CST Microwave Studio. The obtained results in both time- and frequency-domain indicate that the antenna is a good option for UWB applications.

А rigorous approach to study the fast H-waves which propagate across an infinite double comb array (IDCA) is proposed. It is based on the Floquet theorem combined with the advanced moment method (Galerkin) scheme in which the basis explicitly satisfies the edge conditions at the rectangular wedge. An exhaustive analysis of the regular and singular modes of the IDCA is made. Normalized critical wave numbers and modal fields are investigated in terms of geometrical parameters. Coupling effects between different IDCA modes are found. For the singular modes a new analytical formula for the critical normalized wave numbers is obtained.

Conformability helps microstrip antenna to mount on any geometry platform and can also be used for multiple frequency systems without any complexity. The designing of a frequency reconfigurable antenna conformal to cylindrical surface using the combination of metamaterial (MTM) and substrate integrated waveguide (SIW) is proposed. The single and dual antenna models resonate at various frequencies of C-band by means of changing the cylindrical curvature. The results also show a considerable improvement in bandwidth and gain for dual antennas as compared to the single antenna. The antenna parameters are simulated on HFSS tool, and validation process is done by experimental setup.

Thomson scattering of an electromagnetic wave in a plasma density irregularity is considered. A new effect is found that the scattered waves generation and superposition near the electron density extremum may result in a substantial modulation of the scattered signal frequency spectrum. Due to this effect, the observable spectrum shape will be substantially different from that for the electron density fluctuations. This fact should be taken into account when interpreting Thomson scattering experiments.

A broadband ultra-high frequency reader antenna based on magnetic coupling is proposed for radio frequency identification (RFID) near-field applications. The design utilizes four quarter-wave impedance transformer double-side parallel stripline (QDSPSL)-fed dipoles to form a square region to achieve broadband impedance matching and strong and uniform magnetic field distribution. The phases of currents on each dipole are kept same, thus, strong distribution of magnetic can be generated by the antenna. A 200 × 200 × 1.6 mm³ antenna has been fabricated on an FR-4 substrate to fit RFID near-field application. The measured 10-dB impedance bandwidth is 107 MHz (860-967 MHz), which covers the entire UHF RFID frequency band (860-960 MHz). Measured tests on the antenna read range are carried out by observing the feedback received signal strength indication (RSSI) values, exhibiting a large reading region of 140 × 140 mm² and 100% reading rate within 100 mm for near-field tags.

Two approximation methods are presented for fast calculations of the monostatic scattering from axially symmetric scatterers coated with electromagnetic absorbers. The methods are designed for plane wave illumination parallel to the axis of rotation of the scatterer. The first method is based on simulating the scattering of a perfect electric conductor (PEC) enclosing the absorber coated scatterer, and multiplying the result with the squared magnitude of the absorber reflection coecient in a planar scenario. The second method is based on simulating the scattering scenario in a physical optics (PO) solver, where the electromagnetic absorber is treated as reflection dyadic at the outer surface of the scatterer. Both methods result in a significant acceleration in computation speed in comparison to full wave methods, where the PO method carries out the computations in a number of seconds. The monostatic scattering from different geometries have been investigated, and parametric sweeps were carried out to test the limits where the methods yield accurate results. For specular reflections, the approximation methods yield very accurate results compared to full wave simulations when the radius of curvature is on the order of half a wavelength or larger of the incident signal. It is also concluded that the accuracy of the two methods varies depending on what type of absorber is applied to the scatterer, and that absorbers based on ``volume losses'' such as a carbon doped foam absorber and a thin magnetic absorber yield better results than absorbers based on resistive sheets, such as a Salisbury absorber.

A compact via-less metamaterial (MTM) wideband bandpass filter using split circular rings, meander-line and rectangular stub is reported in this letter. The split circular rings produce series capacitance and a meander line along with a rectangular stub gives shunt inductance and capacitance. The measured insertion loss has 0.60 dB and return loss above 15 dB with 3 dB fractional bandwidth 74.28% at centre frequency 3.5 GHz. The zeroth order resonance frequency of proposed filter is guarded by shunt parameters due to its open ended boundary condition. The electrical size of the suggested filter is 0.12λ_gx0.22λ_g at ZOR frequency of 2.3 GHz. The designed structure has been fabricated and experimentally validated. The designed filter offers group delay variation between 0.2 ns to 0.7 ns within the passband. It is suitable for WLAN, WiMAX, Bluetooth applications.

An antenna array system configured to offer directional dependent modulation has the capability to prevent eavesdroppers' attacks, thereby enhancing the security level of data transmission. In this paper, we propose artificial-noise-aided directional modulation transmitter utilizing a 4×4 Butler matrix with a four-element 2-D (i.e., range and angle) frequency diverse array (FDA) antenna to achieve secure transmissions, which outperforms the 1-D (i.e, angle) phased array scheme. The proposed scheme utilizes FDA Butler matrix excited by information data and injected artificial noise interference which radiates along all directions except the main information data direction. Thus, the radiation pattern during a particular transmission period will be range-angle dependent. The proposed scheme is evaluated by using constellation points in IQ space, bit error probability (BER), and secrecy capacity. Simulation results demonstrate that: 1) our scheme scrambles the constellation points along undesired direction(s) in both amplitude and phase, while preserving a clear constellation points along the pre-specified direction(s); 2) the scheme achieves better BER and secrecy capacity than that of the phased array based directional modulation scheme and other existing scheme; 3) the scheme significantly improve security performance especially in the range dimension.

A broadband high-efficiency rectifier with shunt-diode circuit topological structure is presented in this paper. By utilizing the two-level impedance match network, the rectifier can achieve a high microwave-direct current (mw-dc) conversion efficiency within a broad range of operation bandwidth. A stepped microstrip line and a cross-shaped microstrip stub as two-level match network is designed to extend the operation bandwidth. A cross-shaped stub connected to the capacitances act as a dc-pass filter to block the fundamental frequency wave and the high order harmonics and further improve mw-dc efficiency within a broad bandwidth. Experimental results show that the peak conversion efficiency is 80.3% at the frequency of 1.9 GHz when the input power is 22 dBm. When the input power is 19.5 dBm, the bandwidth of efficiency higher than 70% is 40% (1.80 GHz-2.72 GHz). This rectifier has the characteristics of low profile and easy integration, which is suitable for RFIDs, WSNs, and other applications.

Microwave Staring Correlated Imaging (MSCI) is a high-resolution radar imaging modality, whose resolution is mainly determined by the randomness of radiation source. To optimize the design of random radiation source, a novel concept of temporal-spatial relative distribution entropy (TSRDE) is proposed to describe the temporal-spatial stochastic characteristics of radiation source. The TSRDE can be utilized as the optimization criterion to design the array conguration and signal parameters by means of optimization algorithms. In this paper the genetic algorithm is applied to search for the best design. Numerical simulations are performed and the results show that the TSRDE is an effective method to characterize the randomness of radiation source, and the source parameters optimized by this method can dramatically improve the imaging resolution.

In this paper, a novel CPW-fed triple band metamaterial inspired antenna with modified ground plane is presented. The metamaterial inspired structures such as split ring resonator (SRR) and non bianisotropic complementary split ring resonator (NBCSRR) are embeded in this antenna for triple band operation. The proposed antenna with a compact size of 25 x 31.7 x 1.6 mm³ is fabricated and tested. The antenna with good radiation characteristics is suitable for WIMAX, C band and WLAN applications The simulated and measured results are discussed and are in good agreement with each other.

In this paper, we propose a novel architecture of full-duplex millimeter-wave radio-over-fiber (RoF) system based on polarization division multiplexing (PDM) and wavelength division multiplexing (WDM) technology. In our scheme, the light waves for downlink and uplink transmission are provided by the same laser, which realize the source-free base station (BS) and multi-services transfer for next generation wireless access network. Since the uplink optical carrier is Y-polarized light wave which does not bear the downlink signal, no cross-talk from the downlink contaminates the uplink signal. At the BS, it is detected by a high-speed photoelectric diode (PD) to generate a 15 GHz intermediate frequency (IF) and a 63 GHz radio frequency (RF) signal. This reduces the system complexity and cost. The simulation with 2.5 Gbps NRZ signal transmission exhibits good performance both at 15 GHz (Ku-band) and 63 GHz (V-band).

A Double-Octagon Fractal Microstrip Yagi Antenna (D-OFMYA) which is aimed to cover unlicensed frequency of 5.8 GH is presented in this paper. The primary purpose of this experiment is to enhance gain of conventional microstrip antenna. The proposed antenna built on Arlon CuClad 217 substrate with thickness of 0.787 mm and dielectric permittivity of 2.2. A 3D full-wave EM simulator was used to design and to simulate the antenna. A computerized simulation model of the proposed antenna showed that the antenna is able to generate a maximum gain of 14.49 dB with S₁₁ of -24.2 dB in a surface size of 80 mm x 120 mm. By contrast, results of an experiment indicated the fabricated D-OFMYA can reach a gain as high as 14 dB with the value of S₁₁ is -19.8 dB. It can be concluded that a nominal gain of the D-OFMYA comes in higher than other microstrip Yagi array antennas and size reduction can be achieved through this design.

A two-step method is proposed to estimate the direction-of-arrivals (DOAs) of quasi-stationary source signals, with a partlycalibrated uniform linear array (PC-ULA). The special structure of Toeplitz matrix is utilized to estimate the sensors' uncertainties. Then, a Khatri-Rao (KR) based multiple signal classification (MUSIC) algorithm is proposed to estimate the DOAs of source signals. Simulation results show that the proposed method renders lower root-mean-square-error (RMSE) than existing KR-based ESPRIT algorithms, especially under low signal-to-noise-ratio (SNR) and small angle separation between DOAs. It is also shown that the proposed method increases the degree-of-freedom (DOF) by one, as compared to the counterpart ESPRIT methods.

For energy harvesting applications a new design of a coplanar waveguide (CPW) fed monopole antenna is presented. It covers almost all useful band ranges from 900 MHz-9.9 GHz (Radio, GSM, ISM, UWB bands). It also provides band reject characteristics for the range 3.1 GHz-5.6 GHz (HIPERLAN, C-Band, and W-LAN) to avoid interference from this range. The new design is based on the modification of coplanar waveguide (CPW) structure and optimizing the gap between patch and CPW ground for covering the ultra wideband (UWB) range and other useful ranges (Radio, GSM and ISM). Bandwidth enhancement and impedance matching for UWB range have been obtained by chamfering the corners, cutting two slots in CPW ground and dual stubs. The new design incorporates a parasitic patch above the antenna patch for tunning the desired band rejection. The entire design has been optimized at various stages during its evolution. The structure is compact in size 50×40×1.6 mm³. It may also be used for mobile, military and satellite applications.