Volume 70, Issue 5-6 -

In this paper, a numerical analysis of shielding properties of a protective metal enclosure has been performed by simulating a receiving antenna placed inside. Here, the main focus is put on the monopole antenna type. This antenna type is used in an experimental set-up to measure the shielding effectiveness (SE) of the enclosure as often as some other antennas such as dipole. Numerical model, based on the Transmission-Line Matrix (TLM) method, is applied to numerically investigate an impact this antenna might have on a detected level of electromagnetic (EM) field when it is used in the SE measurements. As in experiments, the estimation of SE of an enclosure in the numerical model is performed based on the current induced on the antenna, directly provided by a compact TLM wire model. The model accuracy is verified through a comparison with the experimental results from the literature. The analysis includes the monopole antenna with different radii and lengths, in order to consider changes in the resonant frequencies and the SE level of enclosure. Finally, the enclosure with either the monopole or the dipole is simulated in order to compare their influence on EM field distribution inside the enclosure.

In the present work two element magneto-dielectric resonator antenna configuration, designed using two different magneto-dielectric (MD) materials, separated by a distance of quarter wavelength (λ/4) and half wavelength (λ/2) has proposed. These materials have been designed such that their temperature coefficient value approaches to zero. The microwave dielectric constant (ε r ) and permeability (μ r ) of both materials are calculated by Nicholson-Ross-Weir conversion technique and found to be 8.02, 1.64 and 10.47, 1.52, respectively. For the inter element separation of λ/4 and λ/2, the first resonant frequencies of proposed antenna are 5.75 GHz and 5.78 GHz and showing penta-directional and tri-directional radiation patterns characteristics respectively. This property can be utilized for the diversity scheme to mitigate the problem of fading.

A compact dual-band asymmetric coplanar strip (ACS) fed printed monopole omnidirectional antenna with three radiating structures for 2.4/5 GHz WLAN/Bluetooth applications is presented. The designed antenna comprises of a simple ACS-fed (Asymmetric Coplanar Strip) monopole and three different strip radiating elements. It occupies a very compact overall size of 15×24 mm 2 including the ground plane, which is only about 0.12 λ×0.20 λ (λ is the wavelength at the frequency of 2.45 GHz in free space). So, it has the characteristics of miniaturization. A resonant mode at 2.45 GHz is created by adding a inverted-L branch, and the resonant mode at 5.62 GHz is co-produced by the horizontal strip and vertical strip including an element which is like a Chinese Tai Chi fish. Dual desired resonant frequencies achieved, and each of them can be tuned independently. Both the simulated and measured results show reasonable agreement, and the measured dates show that the antenna has an impedance bandwidth of 90 MHz (2.4–2.49 GHz) and 810 MHz (5.07–5.88 GHz), and a reflection coefficient of less than –10 dB, it is suitable for WLAN 2.4/5.2/5.8 GHz applications and 2.4 GHz Bluetooth bands.

This paper presents a small printed tri-band antenna with a reduced ground-plane effect for WLAN/M-WIMAX applications. The radiator and ground plane of the antenna are etched on a printed circuit board with an overall size of 25×24.5×0.762 mm 3 . A rectangular notch and a circular slot are cut from the radiator while an asymmetrical strip is attached to the radiator. The simulation and measurement suggest that the printed antenna achieves three operating bandwidths of 2.4–2.484 GHz and 5.15–5.35 GHz for WLAN, 3.3–3.69 GHz for M-WIMAX for a 10-dB return loss, and high gains on Y-Z plane of 2.1, 3.3 and 4.8 dB at 2.4, 3.5 and 5.2 GHz, respectively. In particular, the ground-plane effect on impedance performance is significantly reduced by minimising the size of the ground plane and then by cutting a notch and a circular slot from the radiator because the electric currents on the ground plane are significantly suppressed at all the operating bandwidths. In addition, a study on the geometrical and electrical parameters of the proposed antenna may be a useful reference for antenna engineers.

In this paper, a novel second-order tri-band bandpass filter (BPF) is presented by using the first three modes of stubs loaded stepped-impedance resonators (SIRs). The resonant behavior of proposed stubs loaded SIR is analyzed by even-/odd-mode method and parameters sweep, which shows its controllable first three resonant modes. As an example, a second-order tri-band BPF operating at 3.5/5.2/5.8 GHz for WiMax and WLAN applications is designed, fabricated and measured. The fabricated filter has a compact size of 0.21λ g × 0.28 λ g . Good agreement is shown between the simulated and measured results.

In this paper, two single- and dual-band equal power dividers (PDs) integrated filtering responses are proposed using quarter-wavelength stepped-impedance resonators (SIRs). By appropriately adjusting the impedances and electric length ratios of SIRs, the proposed structures can achieve compact sizes and wide stop-band performances. In addition, source-load coupling is applied to create a pair of transmission zeros at each side of the pass-bands, which can improve effectively the frequency selectivity and the out-of-band rejection. To validate the design theory, two single- and dual-band PDs with good filtering responses are designed, implemented and measured, respectively. The predicted results on S parameters are compared with the measured ones and good agreement is achieved.

In this letter, a microstrip lowpass filter (LPF) using bend configuration with several excellent features such as a compact size, great roll-off rate and high rejection in the stopband is presented. This structure is composed of a spiral transmission line loaded by several stepped impedance and T-shaped resonators. The cut-off frequency of the proposed filter is equal to 2.73 GHz and the transition band is from 2.73 up to 2.82 GHz with –3 and –20 dB attenuation point, respectively, which represents a very high sharpness in the transition band. To achieve a –40 dB rejection level in the stopband, multiple open stub and T-shaped patches are utilized. An acceptable agreement between EM-simulation and measurement results is observed.

This paper focuses on through wall stationary human target detection and localization using an OFDM based Ultra-Wide Band radar (OFDM-UWB). Our investigations relate to a monostatic UWB radar operating in the band [1.99–3] GHz at central frequency 2.5 GHz and emitting a power of –22 dBm, meeting FCC UWB spectrum density requirements. The detection of a human being is possible due to respiratory movements of the chest. Using the short-term Fourier transform, along with the optimal filtering and an averaging technique for background clutter suppression, interesting information could be extracted from the recorded waveforms about the presence and position of a human being behind a 20-cm-thick concrete wall. The results of the experimental simulations under Matlab/simulink are then presented. A maximum range of 4 m was found to be possible with a minimum system operating SNR of 5 dB.

In cognitive radio systems, the random nature of primary users’ activities heavily influences the performance of spectrum sensing techniques. Considering both of the primary user random arrival and departure in one model is essential for mitigating the performance degradation in spectrum sensing. In this paper, we apply the probability based weighting energy detector (ED) to overcome the effect of random arrival and departure of primary user (PU), on a single carrier-frequency division multiple access (SC-FDMA) signal used in LTE uplink physical channel. Then compare the performance of weighted ED to the second order Cyclostationarity detector with/without the random arrival and departure of primary user signal during the secondary user’s sensing period. The simulation shows that the weighting ED approaches the performance of Cyclostationarity detector in the normal case, where there are no random activities of primary user signals during the secondary user’s sensing period, with less computational complexity. Moreover, the weighted ED outperforms the Cyclostationarity detector in the case of random arrival and departure of PU.

Today, spectrum is scarce because of the growing number of wireless devices and the steadily increasing demand for high data rates. Streaming and online gaming are a new kind of challenge for wireless networks in terms of delay and throughput. Systems like LTE enable high data-rates (100 MBit/s and above) combined with a low latency. Despite of all these new transmission technologies a major bottleneck is caused by the available spectrum. Furthermore this problem gets exacerbated by a static frequency assignment. To overcome this bottleneck new concepts for adaptive spectrum assignment with respect to load situation need to be developed. In this article we describe and evaluate an architecture which is able to handle different kinds of spectrum sharing techniques. Furthermore, our approach is able to deal with short time sharing (up to one minute). Therefore, we developed a Spectrum Management System (SMS) which is based on a hierarchical organized distributed hash table (DHT) architecture. Additionally, our system deploys databases for additional information like spectrum usage rules, incumbents or network coverage information (described by polygons). To enable the handling of time-critical spectrum data, we introduce a time synchronisation protocol named Lightweight Time Synchronisation (LT-Sync) which considers the system architecture and estimates transmission delays.