A. V. Alejos

Signaling Through Scattered Vegetation: Empirical Loss Modeling for Low Elevation Angle Satellite Paths Obstructed by Isolated Thin Trees

We propose a simple model to characterize the attenuation due to the isolated density of thin trees in an air-to-ground (satellite-to-mobile or helicopter-to-mobile) communication channel. We analyzed the effect of the mobile receiver displacement, moving from far to near the tree along the direct ray path direction for different species of trees at X band (8-12 GHz) and Ku band (12-18 GHz) frequencies. Apart from a free-space region, we have identified two different scattering zones: a diffuse scattering-dominant region around the tree trunk, within which the signal level is modeled according to a statistical distribution function; and a zone where the diffraction on the tree crown prevails, modeled considering knife-edge diffraction loss with a correction of the tree height.

Single notched-band UWB antenna for WLAN environment using complementary split ring resonators CSRR and spiral resonator CSR

Ultra-wide band (UWB) technology has become more popular due to various applications such as ground penetrating radar, medical imaging and sensor networks. The antenna is one of the key components of UWB systems and has drawn much attention in recent years. In this paper we propose the design of UWB monopole antenna, providing single notched-band for WLAN (5–6) GHz to avoid interference signals, using complementary split ring resonators CSRR and spiral resonator CSR. It consists of a microstrip patch with modified radiating element and ground plane, while the desired notch-band characteristic is achieved by etching separately CSRR and SCR in the radiating patch, in Fig.1. Investigations on the parameters of the CSRR were performed to obtain the same performance of CSR in high frequency keeping away it second resonance. Fig.2 shows simulated and measured return loss of proposed single notched-band UWB monopole antennas, compared to the antenna without filtering property. It can be seen that the monopole antenna covers the whole UWB band (3–11 GHz) with a good rejection of WLAN band for notched-band antennas. Also a good response is observed in high frequency of UWB band. for the antennas gain, it varies between 3dBi and 5 dBi. From it performances, The proposed antennas are a good candidate for UWB applications where notch-band for WLAN is required. All results indicate that the investigated CSSR works effectively to introduce a single notch-band characteristic for the UWB antenna, like CSR performances.

Detection of malicious base station attacks through the carrier analysis

In 2G and 3G mobile standards there are vulnerabilities caused by the use of false Base Station (BS). In 3G security architecture offers protection against BS attacks, however when the User Equipment (UE) is configured in automatic GSM/3G mode this UE can accept connections coming from GSM/GPRS BSs that are configured as an attacker finally establishing a connection with such malicious BTS located within the UEs coverage area. Even without the use of a frequency jammer, potential attack danger exists because the connection between an UE and the fake BTS can be achieved if the BS is transmitting with more power than the real base station, and the UE enters in the handover process imposed by the 2G standard.

UWB tapered microstrip antenna with wideband notch using single split ring resonators shaped parasitic conductor

This contribution presents the design of a wideband-notched UWB tapered antenna using a single split ring resonator (SRR). The SRR is etched as parasitic loaded on the back side of the radiator element of the monopole antenna to achieve a frequency notch at 5.05-5.95 GHz. The dynamic resonance of the SRR element drives the notched center frequency and the coupling gap between the antenna ground plane and the SRR-shaped parasitic determines both the impedance bandwidth and the rejection level. The measurement results demonstrated that the proposed antenna can guarantee a wide bandwidth of about 1GHz with an unwanted wideband notch avoiding interferences caused by coexisting WLAN systems. As part of the optimization design, we analyzed the effect of the coupling gap between the SSR parasitic and the antenna ground plane.

Low pass filter design with wide rejection based on array of modified CSRRs configuration

This contribution presents the design of a low pass filter LPF with wide rejection based on modified complementary single split ring resonator (CSRR). The CSRRs are etched on the back side of the transmission and connected by slot line to achieve the desired resonance frequency. The quasi-static resonance of the CSRRs elements drives the cut-off frequency of the LPF and closed fundamental resonances achieve the wide rejection. Two Array configuration are proposed and demonstrate a good improvement in term impedance bandwidth of LPF rejected band. A good agreement match is shown between presented measured and simulated results. As part of the optimization design, we analyzed the behaviors of the initial filtering structure with two different CSRR radius.

Experimental assessment of propagation models over sea for UHF and X bands

In this contribution we discuss the performance of two propagation models to characterize the propagation over sea at UHF and X frequency bands: two-ray model and log-distance. Experimental data were obtained for a calm sea scenario with two receiver antenna heights.

Selectivity improvement in dual-band band pass filter by coupled complementary split ring resonators

With the advent of modern wireless communication technologies, single transceivers operating at multiple frequency bands have become popular. However, there are challenges in the design of dual-band filter supporting high performances and compact size. In this paper we propose the design of dual-band bandpass filter for Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN) applications, providing selectivity enhancement using complementary split ring resonators CSRRs. It consists of two-pole parallel coupled bandpass filter with null coupling gap for middle section, as shown in Fig.1. From Fig.2, it can be observed that the filter exhibits good performance in term of return loss with low insertion loss in the desired frequency bands of 3.4 GHz and 5.5 GHz. However the rejection between bands is poor. This limitation can be overcomed by etching two CSRRs in the ground plane, exactly below the 50 Ω transmission line to improve the filter response. Fig.2 shows the cases implementing the CSRRs compared to the initial design. It can be seen that by using the same CSRR radius (2.2 mm) we achieve good rejection values at 4.2 GHz, whilst introducing slight band shifting and degradation in the WLAN band. However by applying two different radius (1.5 mm and 2.2 mm), a good response is obtained with insertion loss lower than the first case for the WiMAX band and sharp rejection at 6.7 GHz. The proposed design allows the potential implementation of simple and low cost dual band filters, scalable to different systems.

Metamaterial lenses for Electron Cyclotron Resonance Heating in nuclear fusion devices

Electron Cyclotron Resonance Heating (ECRH) is a technique for plasma breakdown and heating in nuclear fusion experiments. Hundreds of KW of microwave power are generated by gyrotron oscillators that operate with a strong magnetic field inside. Power is then transferred by using two different approaches: overmoded waveguides, used when the available space is limited or electromagnetic compatibility (EMC) and interferences are relevant factors. Otherwise, quasioptical (QO) waveguides where power is guided using metallic mirrors are preferred, since power coupling is much simpler and they are less sensitive to arcing. On the other hand, QO solutions need extra room to accommodate big metallic mirrors to avoid spillover effects, and are susceptible to the excitation of higher order modes and aberrations in the beam due to focusing with off-axis metallic mirrors. Lenses are interesting candidates to overcome all these problems. However, conventional lenses are made of dielectric materials which are easily degraded under high power exposition.

Stacked CPW-fed antenna for satellite applications with gain enhancement

This paper presents the design and implementation of a stacked CPW-fed antenna for satellite applications at Ku-, K-and Ka-bands for user terminals. The stacked structure combines two antennas. The base element consists of a CPW-fed patch antenna with modified CPW elements printed on Rogers TMM4 substrate. Above this base, a rectangular parasite patch was placed as a second layer using Arlon substrate with a high dielectric constant of 10.2. The two layers, base and parasitic patch, were separated by an air gap. This configuration reduces the antenna beam width and allows two-folding the antenna gain enhancement. The numerical simulations have been validated with experimental results.