In this paper, a CPW feed ultrawideband (UWB) slot antenna with a single reconfigurable notched band is proposed for overlay cognitive radio (CR) systems. The proposed antenna utilizes two symmetrical short circuited quarter wavelength resonators at the top layer and close to the ground to create a single notch. The switching reconfiguration is achieved by changing the length of resonators to prevent the interference to the primary users that are operating in the wireless local area network (WLAN) band at 5.725-5.825 GHz and the international telecommunication union (ITU) band at 8.05-8.4 GHz. The center frequency of the notched band can be tuned by selecting the length of the resonators, which is achieved by employing two ideal switches. Moreover, the proposed antenna has been fabricated and tested. The experimental data confirmed that the proposed design can selectively have a band notch over the two existent desired bands.

This article presents a method to characterize stochastic observables defined by induced surface currents and fields in electromagnetic interactions with uncertain configurations. As the covariance operators of the stochastic distributions and fields are not compact, a strict Karhunen-Loeve (KL) approach is not possible. Instead, we apply a point-spectrum regularization by expanding the stochastic quantities on a finite-element-like basis. The coefficients of the KL expansion are approximated analytically in a polynomial-chaos (PC) expansion. The novelty of our approach resides in its ability to handle multiple PC expansions simultaneously and determine the orders of the KL and PC expansions adaptively. Thismethod is illustrated through the example of the voltage induced at the port of a random thin-wire frame illuminated by random plane waves. The results show the accuracy and computational efficiency of the proposed method, which provides a complete characterization of the randomness of the observable.

A ground-based radio occultation (RO) technique is proposed to retrieve the atmospheric refractivity profile around a specific region at a higher sampling rate than conventional space-based RO techniques, making it more suitable for regional weather studies. A harmony search (HS) algorithm with ensemble consideration (HS-EC) based on atmospheric physics is proposed to retrieve the refractivity profile more efficiently without being trapped in suboptimal solutions. The highest altitude of profile is extended to 95 km from 40 km adopted in conventional ground-based RO techniques, leading to more accurate results.

Using the program of numerical simulation of ultrawideband pulse reflection from dielectric medium with random rough surface, a possibility to detect ideally conducting objects placed near the surface was investigated. Medium parameters corresponded to the cases of the dry and wet sandy ground. Based on the correlation analysis of the reflected objects with orthogonal polarizations, a decision about the presence or absence of an object was made. An ideally conducting rectangular object was buried into the ground with a random rough surface to different depth. A cross-shaped metal object was disposed above the surface.

A novel high-gain directional lens antenna is numerically designed and experimentally tested in terahertz atmospheric transmission I window. The lens antenna consists of two components: a diagonal horn is adopted as the primary feed antenna, and a multilayer stacked lens consisting of the concentric hatch-crosses is used to focus the electromagnetic waves. The far-field characteristics of the horn antenna and the lens antenna are both studied. Furthermore, the effects of the number of periods of the lens and the focus diameter ratio on radiation characteristics are studied by using variable-controlling approach. The experimental results show that both the diagonal horn antenna and the lens antenna have axisymmetric radiation patterns. The gain of the horn antenna ranges from 23.8 dB to 24.9 dB, and the 3 dB main lobe beamwidth varies from 10.8° to 12.4°. The gain of the lens antenna is higher than 26.4 dB, and the 3 dB main lobe beamwidth is lower than 4.8° across the operation bandwidth. The good focusing characteristics and great directionality indicate that the designed lens antenna is qualified for applications in THz wireless communication systems.

There are applications of the finite difference time domain (FDTD) method, which need to model thin wires in dispersive media. However, existing thin wire techniques in the FDTD method are developed only for the conductive and dielectric media. The article presents a modification of oblique thin wire formalism proposed by Guiffaut et al. and a minor modification for the technique proposed by Railton et al. for applications with Debye media. The modifications are based on auxiliary differential equation (ADE) method. The modifications are validated by calculations of grounding potential rise (GPR) of a horizontal electrode buried in soil with dispersive properties.

In this paper we demonstrate how so-called polynomial chaos expansions can be used to create efficient algorithms for uncertainty quantification in some classes of problems related to wave propagation in stochastic environment. We provide an example from telecommunication.

This paper presents the design of a compact printed multi-band antenna for satellite communications within vehicular applications. The designed antenna is characterized by its compact size of 24mm18mm and multiple resonances over WiMAX, WLAN, 5 GHz U-NII, C-band, X-band, Ku-band, Kband and Ka-band. The performance of the multi-band antenna is investigated, and its equivalent circuit model is presented. Good performance is achieved over all the operating bands, with a relatively high gain and efficiency. Furthermore, as the interference with coexisting wireless systems can have a severe impact on the performance of the antenna, four variants of the antenna are proposed incorporating band rejection features within the antenna design. Embedded quarter-wavelength spur-lines, slots, and parasitic elements were used.

This letter presents a dual-wideband bandpass filter (BPF) by using open and shorted stubs loaded ring resonator. The resonator can excite multiple resonant modes. The transmission zeros (TZs) analyzed by the transversal signal interference concepts can divide the resonant modes into two groups that form dual-wide passband. The even-mode resonant frequencies can be controlled by the stubs parameters, and the TZs can be tuned by the port angle independently. So the center frequency (CF) and the bandwidth of each passband can be flexibly controlled. An experimental dual-wideband BPF with CF of 1.48/5.7 GHz and 3 dB FBW of 137.8%/49.3% is implemented, and the experimental results are presented for validation.

A theoretical analysis of a printed dipole antenna on a gyrotropic-anisotropy chiral dielectric substrate is presented. The study is based on numerical techniques for the characterization of electromagnetic propagation in chiral media. The general complex wave equation and the dispersion relation for such a medium are derived in the spectral domain. The spectral Green's function of a grounded dielectric chiral slab is developed, and the spectral domain moment method impedance matrix elements are calculated. The effect of the chiral gyrotropy element on the input impedance of a dipole antenna printed on a grounded chiral substrate is analyzed using the Galerkin-based Method of Moments.

High-altitude electromagnetic pulse (HEMP) radiated from both primary and secondary currents, which are induced by a nuclear explosion, is computed by using the Jefimenko's equation. The effects of geomagnetic field is considered in computing the primary current, and the rough sea surface is considered in computing the reflected electric field in the frequency domain. The waveforms of HEMP near sea surface and a few km above it are simulated. The impulse and pulse characteristics are discussed, as well as the variation of peak field magnitude when the observation point is moved away from beneath the burst point.

A circularly polarized substrate integrated waveguide (SIW) cavity-backed antenna with the feasibility of obtaining a wide bandwidth is proposed and demonstrated. Fed by a modified inverted-T stripline, the proposed double-layered stacked antenna, consisting of an improved circular SIW cavity and a conventional perturbed circular patch radiator, is designed, analyzed and fabricated. Good agreement between simulated and measured results is observed. Simulation and measurement results reveal that the proposed antenna can provide an impedance bandwidth of 22.1% (4.94-6.17 GHz) and a 3-dB axial ratio (AR) bandwidth of 18.7% (5-6.03 GHz). Additionally, within the effective circular polarization (CP) bandwidth of 18.7% (5-6.03 GHz), the proposed antenna has gains from 4.3 dBic to 7.1 dBic with an average gain of 5.9 dBic. The measured CP bandwidth of 18.7% (5-6.03 GHz) not only meets the need for certain Wi-Fi (5.2/5.8 GHz) or WiMAX (5.5 GHz) band communication application, but also provides the potential to implement multiservice transmission.

A novel microstrip coupled-line directional coupler is proposed in this paper. It is based on the introduction of a complementary split ring resonator and dumbbell-like defected ground structure on the coupled lines to strongly enhance the designed backward coupling. The designed frequency band is from 1.2 to 1.5 GHz. The coupler is fabricated and tested. The insertion loss is less than 3.5 dB. The simulated and measured return losses are better than -13.5 dB, and the isolation is higher than 20 dB across the operating band. The overall size of the coupler is 80 mm×70 mm, which is about 0.36λ×0.32λ at the central frequency 1.35 GHz.

A method for predicting the behavior of the permittivity and permeability of an engineered material by examining the measured S-parameters of a material sample is devised, assuming that the sample is lossless and symmetric. The S-parameter conditions under which the material parameters extracted using the Nicolson-Ross-Weir method may be associated with a lossless homogeneous material are described. Also, the relationship between the signs of the real and imaginary parts of the permittivity and permeability are determined, both when the extracted material parameters are real and when they are complex. In particular, the conditions under which metamaterials exhibit double-negative properties may be predicted from the S-parameters of a metamaterial sample. The relationships between material characteristics and the S-parameters should prove useful when synthesizing materials to have certain desired properties. Examples, both from experiment and simulation, demonstrate that the relationships may be used to understand the behavior of several different categories of engineered materials, even when the materials have appreciable loss.

A simple dual-wideband magneto-electric (ME) dipole directional antenna is proposed in this letter. The antenna is composed of a ground plane, four Γ-shaped parasitic strips and an ME dipole fed by a Γ-shaped feed strip. Simulated results show that the ME dipole can only work in the higher frequency band from 1.7 to 2.7 GHz. By adding four Γ-shaped parasitic strips at each corner of the ground plane, the lower frequency band (0.788~1.17 GHz) impedance matching is improved. The antenna is prototyped and measured. Measured results show that the antenna obtains -10 dB impedance bandwidths of 39% (0.788~1.17 GHz) and 51.7% (1.62~2.75 GHz) for the lower and higher bands. The achieved gains are 5.5±0.5 dBi in the lower frequency band and 7±1 dBi in the higher frequency band. The proposed antenna has good impedance and directional radiation characteristics in the whole frequency band. It can be widely used for 2G, 3G, LTE, WLAN, etc. communication systems.

A planar power divider with unequal power division and out-of-phase feature is presented. Firstly, the principle of the proposed power divider containing transmission lines with the same characteristic impedance is analyzed. The power dividing ratio can be adjusted by only the elctrical lengths of the transmission lines. Design equations of the proposed circuit are derived. Secondly, the method to reduce the size of the power divider is discussed. For illustration, a 2:1 prototype operating at 1.5 GHz is designed, fabricated and measured. The measured results show that S₂₁, S₃₁, and S₁₁ are about -1.84, -4.96 and -28.4 dB at 1.5 GHz, respectively, that the isolation S₂₃ is better than -20 dB from 1.44 to 1.56 GHz and that the phase difference between two output ports is about 180.54˚ at the center frenquency.

This paper proposes an ultrawideband (UWB) Vivaldi antenna with switchable and tunable band-notch characteristics. One stepped-impedance resonator (SIR), which has high quality factor Q and small size, is introduced to create band-notched characteristic with narrow notch band and high notch band edge selectivity. By loading two varactor diodes, a wide tunable notched band is achieved. The center frequency of notch band can tune from 3.1 GHz-6.8 GHz. In order to make the full use of UWB spectrum when there is on coexisting narrow-band applications, switchable band-notch characteristic is desired. Through rational parameters design, the center frequency of notched band is out of UWB range when the DC bias voltage of the varactor diode is 0 V. In this way, switchable band-notch characteristic is achieved.

In this paper, we discuss the impedance and radiation properties of planar UWB (any ultra wide frequency band) dual-polarized antennas. While their performance is usually defined using the impedance bandwidth, some applications require pattern stability over broad frequency bands. An analysis of the behaviour of three UWB dual-polarized antennas (Bowtie Antenna, Toothed Log-Periodic Antenna and Sinuous Antenna) showed interesting conclusions in terms of impedance matching bandwidth and radiation pattern steadiness. Starting from there, we then developed a method that consists in meandering the original structure. This method allows for miniaturization as well as radiation bandwidth enhancement. As a final result, an electrically small antenna with an impedance bandwidth of more than a decade and a steady radiation pattern over it has been developed.

A frequency reconfigurable antenna suitable for handset is proposed in this research. The antenna structure includes an inverted-L shaped monopole and two meandered shorting strips. A wide high frequency band is excited from the inverted-L shaped strip monopole by direct feeding, and then the low and middle frequency bands are excited from two meandered shorting strips. Furthermore, a PIN switch diode is added at the end of shorting strip1 to implement the frequency reconfigurable property. The antenna was fabricated on an FR4 substrate and with a volume of only 9×50×5 mm³. It can cover the operation bands of LTE700/2300/2500, GSM850/900/1800/1900, UMTS2100, and WLAN2400. The detailed considerations and analyses of the design are studied in this paper.

Communication `blackout' is a big challenge for modern space engineering. In the recent decade, the terahertz (THz) technology is believed to be an effective solution for the `blackout' problem. Many research works about the transmission of THz waves in plasma slabs have been carried out. According to those works, the radio attenuation of THz waves in plasma slabs strongly depends on thickness of the slab, electron density, electron collision frequency and temperature. However, few previous works have paid attention to realistic reentry plasma sheath. In the present paper, a hypersonic fluid model is introduced in order to investigate the structure of the realistic plasma sheath which covers a blunt coned vehicle. The scattering matrix method is employed to study the transmission of THz waves in realistic plasma sheath. According to the present study, the wave frequency, electron density and collision frequency are the most significant factors which determine the attenuation of the THz waves in the plasma sheath. Since the whole plasma sheath is inhomogeneous, to install the antenna at an appropriate position helps mitigate the `blackout'. For the blunt coned reentry vehicle, installing the antenna on the wall close to the bottom is helpful for mitigating the `blackout' problem.