Vol. 72

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.

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.

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.

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.

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.

In this letter, an electrically-small circularly polarized (CP) quasi-Yagi antenna is presented. It is composed of three elements; i.e., a compact single-feed crossed-dipole antenna acted as the driver and two parasitic elements acted as the reflector and director, respectively. Each arm of all elements contains a meander line with an arrowhead ending to realize compactness. The driver has double vacant-quarter printed rings incorporated into it to generate the CP radiation. The parasitic elements are incorporated with the crossed-dipole driver to not only produce a directive radiation, but also broaden the antenna bandwidth. The final design with overall size of 35 mm×35 mm×27 mm (0.184λ_o×0.184λ_o×0.142λ_o at 1.575 GHz, ka = 0.93) a measured 10-dB bandwidth of 19.23% (1.476-1.790 GHz), 3-dB axial ratio bandwidth of 7.67% (1.505-1.625 GHz), a broadside gain of 3.0 ± 0.2 dBic, and the maximum front-to-back ratio of 8.2 dB. The proposed antenna is applicable to a variety of wireless system operating near 1.575 GHz, such as Global Positioning Systems, Global Navigation Satellite Systems, as well as international maritime satellite organization (Inmarsat) networks.

This paper, published on Progress In Electromagnetics Research Letters, Vol.~72, 69--74, 2018, was withdrawn on March 20, 2018, due to academic plagiarism as per the authors' request.

A wide half-power beamwidth antenna based on magnetic coupling in near-field (NF) regions and circular polarization (CP) in far-field (FF) is proposed for RFID multiservice applications in UHF band. The prototype consists of a cross-strip and an L-shaped strip on the top layer, fed by an F-shaped network on the bottom layer. CP electromagnetic wave is radiated by the cross-strip, and the antenna also simultaneously brings opposite directed currents (ODC) to generate strong magnetic field in near-field region. Half-power beamwidth is 100˚ in xoz-plane and 102˚ in yoz-plane, which can be used to scan for large regions. An 88 × 88 × 1.6 mm³ antenna has been fabricated on an FR-4 substrate to fit RFID applications. Measured tests on read range by observing feedback received signal strength indication (RSSI) values are carried out, exhibiting 100% read rate for near-field tags within 25 mm and exciting read distance for far field tags up to 1 m for large reading region of 170 × 170 mm².

This paper presents a broadband switchable 3D structure, which can be used to protect the information equipment from high intensity microwave wave. Compared to other defending designs, the proposed structure in this paper has wider working band. When the amplitude of incident wave within working band is low, the structure would allow them to pass with little loss. As the amplitude of incident wave is high enough to activate diode, the wave would be reflected. The Full-wave simulations are performed in CST to analyze the transmission performance. The simulated results verify the transmission performance and defending function. Its working principle is explained through change of the effective material parameters at two states. A prototype is fabricated. The protection property of the structure as a function of intensity of incident wave is verified in waveguide simulator.

A research of millimeter wave high order frequency multiplier based on the fierce inductive nonlinearity of avalanche diode is presented. The operation of high order frequency multiplication is introduced, and the high order harmonics generation character under external RF field modulation is analyzed. The characteristc of multiplier circuit is also discussed. Maximum output power of 6 mW and minimum conversion loss of 17 dB are obtained at output frequencies of 94 GHz and 96 GHz with 15th multiplication order. The phase noise of output 94 GHz signal is about -90 dBc/Hz and -94.33 dBc/Hz at 10 kHz and 100 kHz offset.

This communication presents a novel compact and wideband circularly polarized (CP) slot antenna fed by microstrip feedline. The proposed antenna consists of a corner-truncated square-ring slot patch and a novel bent strip. The CP radiation is formed by using the bent strip to excite CP resonance modes. By intruding several open stubs to the corners of the square-ring slot patch, the impedance matching and axial ratio (AR) bandwidth are improved. The measured results show that the proposed antenna has the advantage of wideband characteristics in terms of an impedance bandwidth of 90.59% (3.2-8.5 GHz) and 3-dB axial ratio bandwidth of 84.2% (3.3-8.1 GHz). The principle as well as simulated and measured results of the proposed antenna is revealed.

A new compact ultra-wideband (UWB) bandpass filter (BPF) with triple sharply notched bands and good stopband performance has been studied and implemented using a triple-mode stepped impedance resonator (TMSIR). The proposed TMSIR is found to have the advantages of introducing triple-notched bands and providing a higher degree of freedom to adjust the resonant frequencies. To validate the design theory, a new microstrip UWB BPF with three notched bands respectively centered at 5.2 GHz, 6.8 GHz, and 9.2 GHz is designed and fabricated. The simulated and experimental results are provided with good agreement.

This paper proposes a 77GHz microstrip series-fed patch antenna arrays for automotive radar applications. Based on the Taylor Distribution Principle, we designed a six-units series-fed weighted antenna array. A Wilkinson 1∶8 un-equal divider is employed to connect eight antenna arrays to form a whole planar antenna. In antenna far-field patterns, the E-plane side-lobe level is approximately below -20.15 dB, and the H-plane side-lobe level is about -15 dB. Good accordance is obtained between simulated and measured results. The designed antenna has great value in the application fields of 77 GHz automotive radar antenna.

This paper presents a compact slotted MIMO cube antenna operating at 5.8 GHz, consisting of three orthogonal slots, each with a distinct main direction of radiation. Each slot produces linear polarization enabling the structure to radiate three orthogonal polarizations. This provides spatial diversity which helps mitigating the effects of multipath propagation and enhances the diversity gain. The cube is filled with a dielectric with a relative permittivity, ε_r thus reducing the minimum dimension of the cube by a factor of 1/√ε_r . The antenna has a return loss of 20 dB and a coupling of less than -26 dB between the ports. This paper describes the principle operation as well as the design and manufacturing process of the proposed antenna.

A method aiming to widen the upper stopband in a microwave bandpass filter based on two-conductor suspended-substrate stripline resonators is described in this letter. Applicability of the method is illustrated by simulating and fabricating fourth-order filter that has a very wide upper stopband: Δf_stop/f₀=7.92 measured at a level -50 dB, which is achieved because the widths of the inner resonators in the structure are 1.4 times greater than that of the outer ones.

The removal of ground surface influence from ground penetrating radar (GPR) signals in shallowly-buried objects is of great importance. The ultra-wideband (UWB) radar is a solution which uses short pulse to distinguish ground surface from shallowly-buried objects. In this paper, a novel method optimizes bandwidth based on designing a Gaussian signal. Experimental results confirm the proposed method efficiency.

A portable microscope has been created through our work, so that we can observe and collect images in future scientific research whenever and wherever possible. The portable microscope is made up of a small LED chip, compact lens modules, a commonly used SLR camera and a USB driven power. The microscopic morphological features can be observed through our system. We also demonstrate that this standalone system can work well in moving state. Therefore, the portable microscope that has the potential for becoming a point-of-care setup in terms of health monitoring is appropriate for on-site micro-imaging.