A stereo-synthetic aperture radar (stereo-SAR) technique is proposed to estimate the terrain height of a target area. A reference point with known altitude is located within the target area to calibrate the height estimation. The estimated height error can be reduced to one meter. This method requires the processing techniques of conventional SAR, while achieving a fairly fine resolution in height estimation for practical applications.

This paper presents a tri-band bandpass filter (BPF) using a novel stub-loaded resonator. Different from other stub-loaded resonator, this resonator utilized a short-ended main transmission line and a centerly-loaded open stub. The resonator is theoretically analyzed. The first three resonant frequencies can be individually adjusted and this enables the convenient designs of tri-band BPFs. For demonstration, a tri-band BPF is implemented. Transmission zeros are created close to each passband edge, resulting in high skirt selectivity. Comparisons of the measured and simulated results are presented to verify the theoretical predications.

This paper deals with a novel miniaturized FSS with wide stop band characteristics for UWB applications. The proposed FSS consists of garland like design printed on either side of the dielectric substrate. The design provides a bandwidth equal to 3.5 GHz at -20 dB reference level of insertion loss which lies within the UWB range. The design delivers stable response for various angular incidences. In addition to this, the symmetrical nature of the FSS holds identical response for both TE and TM Mode of polarization. The proposed geometry is fabricated and its simulated results are validated with measurements. A comprehensive analysis is made by adjusting various parameters associated with the proposed design.

The paper deals with the propagation of electromagnetic waves through twisted clad dielectric optical fibers. The structure of these fibers is analogous to travelling wave tubes used in microwave devices, and the usefulness would be in the areas of optical sensing. This is because the twists in fiber would be affected due to the imposed stress and/or strain, leaving thereby the possibility to alter the propagation characteristics. A rigorous analytical investigation has been carried out with the emphasis on the energy flux density patterns due to the different propagating modes in the fiber. The dispersion relations of the system are deduced and the energy flux densities are evaluated under different pitch angles of twist. The effect due to conducting helix pitch on the electromagnetic wave propagation is emphasized.

A compact multilayer substrate integrated waveguide (SIW) dual-mode filter with multiple transmission zeros for high-selectivity application is presented. By introducing mixed coupling between source and load, the proposed filter could have four transmission zeros which can be controlled flexibly. Owing to the multilayer structure, the proposed filter occupies similar area in comparison with conventional dual-cavity dual mode SIW filters, but exhibits better frequency selectivity. An experimental filter with a center frequency of 10 GHz is designed using low temperature co-fired ceramic (LTCC) technology to validate the proposed structure, and measured results agree well with simulated ones.

The Polar Format Algorithm (PFA) is suitable for spotlight synthetic aperture radar (SAR) image focusing either in monostatic or bistatic cases. The classic linear-trajectory PFA complete data correction in wavenumber domain, converting data from the polar format to the rectangular format. However, the two-dimension processing (either using interpolation or chirp-z transform) introduces heavy computational load, which limits its real-time applications. This study presents a conical-trajectory PFA for bistatic SAR, in which the transmitter and receiver are designed to fly on conical surfaces, to simplify image formation procedures via eliminating the necessity of range processing. Moreover, the conical-trajectory PFA provides a space-invariant range resolution to simplify the SAR image comprehension. A spotlight forward-looking bistatic missile guidance application was simulated for the algorithm validation and performance analysis.

A satellite-borne frequency selective surface (FSS) for atmospheric sensing application is presented. This brand new type of band-pass filter has an operating frequency at 183 GHz, which is a typical frequency on H₂O absorption line. Comprising an ultra-thin gilding layer and a SiO₂ substrate layer, this complex periodic component exhibits an extremely low insertion loss (< 0.22 dB) and high isolation (> 20 dB) between closely spaced frequency channels of 45° incident wave. Periodic Method of Moment (PMM) approach is applied to determine the initial geo-metrical parameters of FSS unit cell, and the optimization approach based on the Genetic Algorithm (GA) enables us to obtain the requisite spectral response and transmission characteristics for both TE and TM polarization. The experimental results show that the proposed PMM-GA technique is effective for analyzing space-borne FSS at millimeter wave range.

A novel triple-frequency fork-shaped antenna for WLAN/WiMAX applications is proposed and investigated in this paper. The presented antenna is simply composed of three radiating elements viz. Stub1, Stub2, Stub3. By adjusting the lengths of the three stubs, three desired resonant frequencies can be achieved and adjusted independently. Experimental results show that the antenna impedance bandwidths for S₁₁ ≤ -10 dB are 2.4-2.65 GHz, 3. 3.3-4.05 GHz, and 5-5.98 GHz, covering the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. Furthermore, nearly omni-directional radiation patterns over the operating bands have been obtained.

A one-step leapfrog alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method for lossy media is presented. Different from the method provided by others, the proposed method is originated from the conventional ADI-FDTD method instead of considering the leapfrog ADI-FDTD method as a perturbation of the conventional explicit FDTD method. Its unconditional stability is analytically proven through a method that combines the von Neumann method with the Jury criterion. In addition, its unconditional stability and computational efficiency are verified through numerical experiments.

This paper proposes a novel corner-fed Circular Polarization (CP) reader antenna for handheld Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) application. The CP mechanism is accomplished by a multi-bending feeding strip located at corner of a high dielectric constant (K = 60) ceramic substrate. By using the high dielectric substrate, the dimension of the proposed antenna can be effectively reduced to 27 × 27 × 4 mm³, which consists of a top radiating patch, an antenna ground plane, a coupling multi-bending feeding strip, and a SMA connector for RF input. The top radiating patch is printed on the top surface of the ceramic substrate and the antenna ground plane is formed on the opposite side. The central frequency of resonant band can be easily controlled by adjusting the size of the top radiating patch. By optimizing the coupling feeding mechanism, not only impedance matching can be achieved for bandwidth operation in Taiwan's UHF RFID band, but also two orthogonal field components with 90° phase difference for circular polarization are obtained. In addition, the proposed antenna is placed on an 80 × 80 × 0.8 mm³ FR4 system ground plane for reducing hand holding effect.

This paper illustrates an explicit multiresolution time-domain (MRTD) scheme based on Daubechies' scaling functions with a spherical grid for time-domain Maxwell's equations. The stability and dispersion property of the scheme are investigated and it is shown that larger cells decrease the numerical phase error, which makes it significantly lower than FDTD for low and medium discretizations. Moreover, this technique is applied to the modeling of an air-filled spherical resonator, and numerical results demonstrate the effectiveness of the proposed algorithm.

In this paper, a new Frequency-Reconfigurable Stacked Patch Microstrip Antenna (FRSPMA) with a new coupling method applied in an aperture-coupled technique controlled by the switching circuit is presented. This antenna uses a combination of aperture-coupled technique and stacked patch in order for the radiating elements to increase the bandwidth. Two shapes (Ishape and H-shape) and sizes of aperture slots are etched onto the ground with a purpose to couple the energy between feedline and stacked patch. One PIN diode switch is integrated in the feed network to control the length of the feedline. A variation of the feedline length controls the selected aperture slots to be active. The waves from the selected activated aperture slots will radiate to particular radiating patch (top or bottom patch) and achieve the frequency reconfigurability. When the switch is in ON mode, the antenna has a capability to configure its operating frequency at 2.6 GHz and at 3.5 GHz during the OFF mode. Besides that, the air gap is used to improve and avoid any coupling problem between the aperture slots and both of the two patches. Improper alignment between the aperture slots and patches will interfere waves radiating from aperture slots to the particular patch. In addition, the proposed antenna produces a high gain of more than 5 dB during ON or OFF modes respectively. The simulated results are compared with measured results.

A hybrid tuning method for microwave filters is presented in this paper. This novel tuning technique is based on the combination of the Cauchy method and aggressive space mapping (ASM) technique. Cauchy method is applied to determine the characteristic polynomials of the filter's response, then the parameters (coupling matrix) of the low-pass prototype is extracted from the characteristic polynomials. The aggressive space mapping is used to optimized the fine model to guarantee that each step of a tuning is always in the right direction. The validity is verified by two examples. One deals with the four-resonator cross-coupled filter and the other one is an direct coupled six-resonator filter.

A cylindrical microstrip array antenna with 5 pairs of coupled slotted strip framed patches is analyzed. The patches are proximity-fed by a cylindrical microstrip line. In order to extract the reflection coefficient from the standing wave pattern on the microstrip line, its length is about 5 wavelengths. To the best of the authors' knowledge proximity-fed cylindrical arrays have not been analyzed before using a rigorous MOM model that takes into account all electromagnetic couplings between patches and feeding line. The paper consists of three parts. The first part describes a plane wave excitation of the cylindrical microstrip structure. It introduces some innovating theoretical developments, like the improvement of the asymptote for the spectral Green's function and the explicit surface wave contribution. The second part calculates the radar cross section of the cylindrical microstrip structure with single and coupled slotted strip framed patches. The resonant frequencies, and the amplitude and phase of the current distribution are analysed. The third part describes a design for a proximity-fed array of 5 coupled slotted strip framed patches. It gives the reflection coefficient, current distribution on the patches, and radiation pattern. A very low level of cross polarization (< -40 dB) is achieved. It is shown that the resonant frequencies of the cylindrical array and its planar analogue lie very close to each other. This is due to the common nature of the low frequency slot resonance for the slotted strip framed patch.

Focusing of electromagnetic plane wave from a large paraboloidal reflector, composed of layers of chiral and/or chiral nihility metamaterials, has been studied using Maslov's method. As a first step, the transmission and reflection of electromagnetic plane wave from two parallel layers of chiral and/or chiral nihility metamaterials are investigated using transfer matrix method. The effects of change of angle of incidence, chirality parameters and impedances of layers are noted and discussed. Special cases by taking extreme values of permittivity of second layer, while assuming value of corresponding chirality equal to zero, are also obtained for validating the methodology. These special cases are equivalent to reflection from a perfect electric conductor backed chiral layer and nihility backed chiral layer, respectively. Results of reflection from parallel layers have been utilized to study focusing from a large paraboloidal reflector. The present study, on focusing from a paraboloidal reflector, not only unifies already published work by various researchers but also provides better understanding of the problem.

A wideband differential bandpass filter (BPF) with differential mode passband and common mode suppression is proposed and implemented on microstrip lines for wideband application in this letter. The initial BPF is similar to a single ring resonator with two unequal feed lines which have 180^o separation and T-shaped stubs are loaded on the ring resonator to form an improved one for better performances. The lengths and widths of these stubs can be adjusted to produce a highly selectivity under the differential mode and improved attenuation under the common mode. This simple, compact structure is easy for construct without any coupling structure. Finally, a microstrip differential wideband BPF is designed, simulated, fabricated, and measured. The presented differential BPF has a 3-dB fractional bandwidth (FBW) of 38% for the differential mode and insertion loss greater than 17 dB for common mode. Good agreement between simulated and measured results is obtained.

An improved double ridged horn antenna (DRHA) is proposed in this paper. By adding the dielectric lens at the aperture of the horn, radiation pattern distortion arising in the high frequency band of conventional DRHA is improved, which leads to higher radiation gain. Meanwhile, ridge slot loading contributes to better impedance matching characteristic, broadening the impedance bandwidth efficiently. The improved antenna is fabricated and measured, with the measured results consist with the simulation perfectly, which proved the viability of the improvement.

In this paper, a direct time domain approach based on the corresponding transmission lines equations and Finite Difference Time Domain (FDTD) method is proposed to analyze a direct lightning strike to a cascade of transmission line towers. The proposed model deals with a real case of towers being connected by ground wires and equipped with grounding systems with different topologies, as well(vertical or horizontal conductor buried in the ground, crow's feet in the ground...). In particular, this work realistically represents the tower geometry and accounts for the propagation phenomena along the tower and between the towers. The proposed direct time domain approach deals with rather complex electrical devices (towers, ground wires and grounding systems), but at the same time requires very low computational cost and also provides relatively simple implementation. Some illustrative computational examples related to some engineering applications are given in the paper.

A collocated surface impedance boundary condition (SIBC)-finite difference time domain (FDTD) method is developed for conductors coated with lossy dielectric coatings at oblique incidence. The method is based on the collocated electric and magnetic field components on the planar interface between two media, and rational approximation for tangent function of surface impedance formulation is adopted. In contrast to the traditional SIBC-FDTD implementation which is approximated with the magnetic field component on the boundary located at half-cell distance from the interface and half time step earlier in time, the collocation approach is more accurate for both magnitude and phase of reflection coefficient. By the comparison with exact results, the proposed model is numerically verified in the frequency domain for both parallel polarization plane wave and vertical polarization plane wave at varying oblique angles of incidence.

Radio frequency (RF) dielectric heating was tested to control Cryptolestes ferrungineus S. in the bulk wheat samples (ca.152 g, dia. = 50 mm, ht.= 100 mm) at the MCs (%, w. b.) of 12, 15, and 18 using a pilotscale RF heater (1.5 kW, 27.12MHz) in the batch mode. When the temperature of the hottest spot (geometric center) of the sample, TH was at 80°C, all the adult insects were found dead at the cold spots, near bottom-wall, at 50.7°C to 56.0°C depending up on the wheat MCs. The temperatures of the insect-slurries higher than that of the bulk wheat by 0.8°C to 15.1°C indicated the selective heating of the insects. The mortalities of adult insects were almost constant within the quarantine period, QP1 (5 wk). The elapsed time during QP1 had a significant effect only on the insects' mortalities with the wheat at 12% MC. The wheat MC had only marginal significance on the absolute mortalities of insects. The larvae were completely destroyed at temperatures between 55°C and 60°C. The complete mortality of all life stages (eggs, larvae, pupae, and adults) of the insect was achieved at T_H = 80°C without any emergence of the insects during QP2 (8 wk). The RF treatment enhanced the germination of the wheat kernels at 12% MC while it was decreased by 2% to 33% depending up on the wheat MC, and the treatment temperature. Temperature had no significant effect on the falling numbers, and the yields of flour, bran, and shorts, and the peak-bandwidth and the MC of the wheat, and the flour protein values. The means of the mixing-development-time deferred from the controls mostly for the wheat at 15% MC and T_H = 70°C, and 18% MC and T_H = 70°C and 80°C. The mean-peak-height and the color values varied between 4% and 16%, and 3% and 6% off the controls depending up on the temperatures. The uniform temperature of 60°C should be enough to control all life stages of the insect completely with a little or no changes in the important product quaities and germination of the wheat at MCs safe for the storage. Future research mainly focused on better estimation of the insect-to-grain electric field intensities is essential.