The insertion loss of different materials is measured at 2.4, 3.3 and 5.5 GHz bands. Directive antennas with a nominal gain of 19 dB are used in the measurement campaign. The height of the antennas has been selected to have the minimum possible reflection from around surfaces. Thick concrete wall, thick concrete column and tree's insertion loss are measured. It is noticed that the insertion loss increases with the increment of the operating frequency. For tress, the insertion loss for the leafless tress is 6 to 10 dB lower than the deciduous trees.
This paper presents two novel designs of truncated rhombus-like slotted antenna (TRLSA) based on aperture-coupled feeding technique. In conventional antennas, different patch dimensions are required to accommodate different frequencies which normally result in bigger antenna structures. Therefore, this paper proposes a unique structure of `zig-zag' slot embedded on two different antennas to achieve two different resonant frequencies but of the same patch dimensions. An analysis on design transformation which includes comparative simulation results of two reference antennas and TRLSAs has also been presented to provide better understanding on the design concept. CST Microwave Studio software has been used for design simulations and optimizations. The simulation and measurement results of TRLSAs are also presented. The results confirm that the antennas can operate at two different frequencies, 5.3 GHz and 5.8 GHz with the same patch dimensions by integrating the "zig-zag" slot at two different orientations in x- and y-axis respectively. Hence, size reduction is achieved for lower frequency patch which gives a great advantage for future development of a frequency reconfigurable antenna in an array configuration.
Passive millimeter (MMW) imaging can penetrate clothing to create interpretable imagery of concealed objects. However, the image quality is often restricted by low signal to noise ratio and temperature contrast as well as low spatial resolution. In this paper, we explore a four-channel passive MMW imaging system operating in the 8 and 3 mm wavelength regimes with linear vertical and horizontal polarization directions. Both registration between different channel images and segmentation of concealed objects are addressed. Multi-channel image registration is performed by geometric feature matching and affine transform, and then multi-level segmentation separates the human body region from the background, and concealed objects from the body region, sequentially. In the experiments, several metallic and non-metallic objects concealed under clothing are captured in indoors. It will be shown that our method can separate objects with higher accuracy than the conventional method.
A novel design of decoupling network for a compact three-element array is presented. The proposed decoupling network has simple and compact structure that can be implemented easily with microstrip lines. The conventional microstrip open stubs can be used to match the decoupled ports of the array. The proposed decoupling and matching network is applied to a compact three-monopole array operating at 2.4 GHz. Both the simulated and the measured results show that the ports of the array are well matched and decoupled at the operating frequency.
This paper presents a novel quasi-elliptic function lowpass filter (LPF) by using quasi-lumped elements. The proposed LPF is firstly based on a seven-order Chebyshev response lowpass prototype. Then, a series branches of shunt resonant LC circuit is introduced in the filter design to provide a transmission zero close to the transition band, which can improve the roll-off rate of proposed LPF significantly. To implement the lumped elements of lowpass prototype, the high-impedance meander lines are employed to realized the inductors while inter-digital microstrip lines and the microstrip parallel-plate structures are used to realize the capacitors. To validate the proposed method, a LPF with 3 dB cutoff frequency fc at 1.9 GHz is designed and fabricated. The measured results show that the fabricated LPF has a sharp roll-off rate up to -142 dB/octave and -15 dB harmonic suppression from 1.1fc to 9.7fc. Moreover, the fabricated LPF also has a compact size of 0.1λgc × 0.11λgc. Good agreement can observed between the simulation and measurement.
This paper presents a comparative study on practical evaluation of measurement uncertainty for complex-valued RF and microwave quantities in polar coordinate. The measurement uncertainty is first evaluated in rectangular coordinate to avoid the biased effect, and then transformed into the desired polar coordinate. In this work, uncertainty coordinate transformation from rectangular coordinate to polar coordinate is focused and performed in two ways; the law of propagation of uncertainty and the coordinate rotation. Their performances are compared through practical evaluations and simulations, and found to be highly consistent when the uncertainty region is distant from the origin of a complex plane.
An integrated compact circular-polarized annular ring slot antenna is proposed in this paper. It consists of an annular ring slot radiator and a hybrid patch coupler. The hybrid patch coupler is integrated with the annular ring slot antenna to radiate the circular-polarized wave, while size of the antenna remains the same. Both the impedance bandwidth and axial ratio bandwidth of the proposed design almost cover the entire UHF band of RFID system and it has the features of easy fabrication and low cost. To verify the proposed design, a prototype is fabricated. Measured results agree well with the simulated results.
Spacial coaxial resonator plays an important role in spacial system. However, its multipactor effect has not been reported so far. This paper presents a novel type of coaxial resonator structure with low multipactor risk. Compared with conventional coaxial resonator structures, the proposed structure improves the multipactor threshold of filters nearly 3 dB. Experimental results and 3D full-wave analysis show good accordance with the predicted characteristics.
New multiband integrated slot antennas for mobile handsets are presented for GSM, DCS, PCS and WCDMA, GPS and WIFI 2.4 GHz. Prototypes, both simulated and measured, are realised in the metal back cover away from the hand. Perturbations due to tissue proximity are simulated using a CTIA compliant hand phantom.
A novel compact coplanar waveguide (CPW)-fed printed antenna with triple bands for WLAN and WiMAX applications is presented. By using a parasitic circular patch, a pair of symmetrical inverted-L strips and a 50-Ω transformer, the antenna can effectively provide a good input impedance matching. The tuning effects of the ground size, the parasitic circular patch and the symmetrical inverted-L strips to the resonance and matching condition are then examined, and the prototype of the proposed antenna is further fabricated and measured. The experimental and numerical results exhibit that the antenna has impedance bandwidth for S11≤-10 dB of 2.32-2.80 GHz, 3.06-4.13 GHz and 5.03-6.04 GHz, which can cover both the WLAN 2.4/5.2/5.8 GHz bands and the WiMAX 2.5/3.5/5.5 GHz bands. Also, a stable monopole-like radiation pattern and an average antenna gain of 3.06 dBi across the operating bands have been obtained.
This letter demonstrates a technique for a folded slot antenna fabricated on low resistive silicon wafer, using pre-etched cavity and Benzocyclobutene (BCB) support membrane. The most distinctive feature of this method is that a cavity is pre-etched before the antenna fabrication process using low-cost potassium hydroxide (KOH) wet etching. BCB membrane is employed to support the antenna above the cavity for its low permittivity as well as excellent thermal and mechanical stability. The fabrication process discussed in detail and the fabricated antenna was characterized. Experimental results show that the antenna resonates at 15.4 GHz with a very wide impedance bandwidth, up to 14.6%.
In this work a new quality indicator for two-tier calibration procedures that use only reflection standards is presented and applied to coaxial-to-waveguide transitions. The quality indicator is based on the algebraic conditioning of the system of equations solved for obtaining transition characteristics. The study has been carried out in a wide bandwidth as a difference with previous works. The obtained results indicate that a threshold value for this indicator around 10% can be established. For values below this limit the error grows to unacceptable values. Additionally, it has been shown that an exponential relationship between quality indicator and the error can be predicted.
In this article, an S-band two-way inverted asymmetrical Doherty power amplifier (IADPA) using LDMOS FET is proposed. Due to the compact inverted load network with low inserted loss and the asymmetrical structure, the amplifier exhibits a high efficiency when operating at an output power back-off beyond 6 dB. For experimental verification, an IADPA has been implemented and a modulated Long Term Evolution (LTE) signal with 20-MHz channel bandwidth is applied as excitation. According to the measured results, the proposed amplifier can achieve a drain efficiency of 47.6% at the output power back-off of 7.7 dB from saturated power point and an adjacent channel power ratio (ACPR) less than -53 dBc with digital pre-distortion (DPD) when operating at 2.65 GHz.
This paper presents the theory, design, and experimental investigation of an ultra thin (6% λ0) and triple band metamaterial radar absorber. The theoretical design of the reported absorber is investigated. The absorber performance was validated using the electromagnetic simulations and confirmed by experimental measurements for different incidence angles. The results confirm that the proposed metamaterial absorber can demonstrate triple bands with better than -15 dB reflection coefficient for all incident angles.
A miniaturized crossed-dipole fractal antenna with circular polarization is presented in this letter. The radiating elements of the antenna were built as the Koch curve, and the antenna was mounted on a specially designed ground plane. Furthermore, the influence of fractal dimension to bandwidth and axial ratio of fractal antenna is also experimentally studied. The bandwidth of the VSWR≤ 1.5:1 within 3dB axial ratio for the fractal antenna is about 5.98%. The measured results show that the proposed fractal antennas have good circular polarization property, efficiency and 23.4-33.5% size reduction comparing with the conventional crossed-dipole antenna. The tested results are in good agreement with that of the simulations.
This paper describes how information about the electromagnetic structure of targets can be obtained from direct detection radar techniques, where the relative phase of the transmitted and received signals is not measured. A comparison is made between the resolved structure of a simple test target from an ultra wide band, pulse synthesis direct detection radar system at 14-40 GHz and an equivalent heterodyne radar receiver where phase information is recorded. The test targets employed are wax sheet of thickness 20 mm and 80 mm which are illuminated alone and in contact with the human body. A vector network analyser is used as the radar system. The simplicity of constructing ultra wide band direct detection radar systems combined with their cost makes the use of such radar systems appealing for applications such as concealed threat detection and nondestructive testing, where absolute range to the target, if required, can be determined by other methods.
We develop a method for calculating transverse static polarizability (per unit length) of a bulk nanowire by taking in to account the temporal and spatial dispersion. To describe these phenomena, we developed analytical theory based on local random-phase approximation and plasmon pole approximation. Our theory is very general in the sense that it can be applied to any material which can be characterized by a bulk dielectric function of the form ε(w,k). The theory is applied to calculate the transverse static polarizability of dielectric nanowire.
This paper presents a simple microstrip filtering-antenna with compact size for WLAN application. The T-shape resonator through an inset coupling structure can be treated as the admittance inverter and the equivalent circuit of the filtering-antenna is exactly the same as the bandpass filter prototype. With a little extra circuit area, the proposed filtering-antenna has almost twice wider bandwidth, good skirt selectivity and high suppression in the stopband compared to the conventional microstrip antenna.
A new frequency reconfigurable unequal U-slot antenna is presented in this paper. The U-slot antenna loaded with two lumped variable varactors is capable of 6 different frequencies switching between 2.3 GHz and 3.6 GHz. The small slots in the ground plane are employed for the biasing circuit to minimize the parasitic effects towards the performance of the antenna. It is found that the unequal U-slot fed by an L-shaped feed line can reduce 30% of the size of the conventional U-slot antenna. Moreover, the proposed antenna offers stable radiation characteristics for each operating frequency in the tunable range. The antenna offers a gain of 4.5 dB in average. The designs are verified through both numerical simulations and measurements of an experimental prototype. Details of the antenna designs and measured results are presented and discussed.
This paper presents a compact conical beam antenna based on quarter-mode substrate integrated waveguide (QMSIW). The antenna array is consisted of six isosceles right-angled triangle metallic patch printed on the upper side of the substrate in a windmill-shape and diagonal periodic metallic via holes drilled along the hypotenuse of the triangle patch. The planer structure exhibits conical beam radiation. The typical radiation is obtained at 5.2 GHz with conical beam radiation pattern. The measured gain is about 5.36 dBi and the radiation efficiency is around 50%.
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