S. K. A. Rahim

Measurement of Wet Antenna Losses on 26 GHz Terrestrial Microwave Link in Malaysia

This letter discusses the effect of antenna losses due to rain on a 26xa0GHz microwave link and the technique of extracting the losses from the measured rain attenuation. A 2-feet parabolic dish antenna with horizontal polarization has been used in the study. The measurement results have been compared with those obtained from other locations in Malaysia and some other Published Research works. The study will provide useful information in the microwave link planning and design in tropical regions; and it can also be adapted to satellite communication operating at ka-band.

2.45 GHz and 5.8 GHz Compact Dual-Band Circularly Polarized Patch Antenna

A dual-band circularly polarized stacked microstrip antenna for ISM Bands (2.45 GHz & 5.8 GHz) applications is designed and implemented. By stacking two different corner-truncated square patches in a dielectric substrate layer, the microstrip antenna for dual-frequency circular polarization (CP) can be achieved with –11.5 dB and –12.8 dB measured return loss for 2.45 GHz and 5.8 GHz. Semicircular grooves are cut at the four sides of the low frequency patch to achieve compact design by ∼ 12% size reduction. Details of the obtained dual-band CP performances are presented and discussed. This antenna is a promising candidate to be installed for a smart antenna system, cognitive radio, radar application in the future.

Empirically Derived Path Reduction Factor for Terrestrial Microwave Links Operating at 15 Ghz in Peninsula Malaysia

This paper describes the technique of deriving path reduction factor from experimental rain rate and rain attenuation data over seven DIGI MINI-LINKs operating at 15 GHz in Malaysia (Lat.: 1.45°N and Long.: 103.75°E). The relationship between experimental path reduction factors with different link lengths has been studied, using multiple non-linear curve-fitting techniques. Based on these studies, an empirical path reduction factor model has been proposed and compared with the ITU-R model. The test results have shown that the ITU-R prediction model may not be appropriate for predicting rain-induced attenuation for the tropical Malaysian climate.

Comparative studies of the rain attenuation predictions for tropical regions

The radio waves propagating through the earth atmo- sphere will be attenuated due to the presence of atmosphere particles, such as water vapor, water drops and the ice particles. Meanwhile, the atmospheric gases and rain will both absorb and scatter the radio waves, and consequently degrade the performance of the link. The results of various studies conducted in temperate and tropical regions have been published in research papers. This paper presents the sum- mary of comparative studies on difierent rain attenuation prediction methods for terrestrial microwave links tropical regions. Basically the models described in this paper include those of the ITU-R, revised Moupfouma, revised Silva Mello and Lin model. The objective of this study is to reveal the most suitable rain attenuation prediction model for the Malaysian tropical region. This paper will provide useful in- formation for microwave engineers and researchers in making decision over the choice of most suitable rain attenuation prediction for ter- restrial links operating in a tropical region. Even though the ITU-R model underestimates the rain attenuation at higher frequencies, the test results have clearly indicated that it is most suitable for predicting terrestrial rain attenuation in tropical Malaysia, compared to others.

A single band dual-fed circular polarization microstrip antenna for RFID application

This paper presents new design for single band circular polarization (CP) antenna with dual feedings. This antenna is designed for RFID application at 2.45 GHz. In this antenna design, the left corner side of the square patch is truncated. Then, two perpendicular feeding is connected to the patch to achieve Circular Polarization antenna. By combining the two perpendicular feedings with the truncated square patch in a dielectric substrate layer, the microstrip antenna for single band frequency circular polarization (CP) can be achieved with - 12.1dB return loss for 2.45 GHz. The simulated and measured results show that the proposed antenna has good circularly polarized radiations and the 3 dB axial-ratio bandwidth is more than 7.2%. Details of the obtained dual-band CP performances are presented and discussed in this report.

Bandwidth enhancement and miniaturization of dielectric resonator antenna for 5.8 GHz WLAN

This paper presents the design of Dielectric Resonator Antenna (DRA) operating at 5.8 GHz, using the techniques of Two Segments DRA (TSDRA) and High-Aspect Ratio Structure. The aim of the paper is to reduce the size of the DRA while still maintaining its large impedance bandwidth. The requirements for WLAN applications are carefully taken into considerations in the design of the proposed structure. Comparison has been made between the proposed design and single layer DRA (SLDRA); and it has been found that the former has better performances than the latter.

A NOVEL ACTIVE ANTENNA BEAMFORMING NETWORKS USING BUTLER MATRICES

In this paper, a novel architecture of using cascaded Butler Matrices (BM) integrated with Low Noise Ampliflers (LNAs) is proposed. By using the narrow beams available from the Butler Matrix, it is possible for a receiver to increase the gain in the desired signal directions and reduce the gain in interference directions. Hence, high-gain narrowbeam signals for long-range application are produced. A novel technique is introduced which uses high linearity LNAs and a second Butler Matrix, acting as a mirror of the flrst Butler Matrix, reconstructing the antenna patterns of the individual radiating elements. The resulting outputs have high linearity and broad beam width that can be used for short-range communication. Design of the Butler Matrix, Low Noise Amplifler, Wilkinson Power Divider and High Linearity Low Noise Amplifler are presented in this paper. A flnal design of active antenna beamforming network using cascaded Butler Matrices integrated with LNAs is proposed. The beamforming network provides a method, which could be applicable in vehicle communication systems, where long-range communications with roadside beacons and short-range communications with the fast moving vehicle are both required.

Directional UWB antenna with a parabolic ground structure and split ring resonator for a 5.8 GHz band notch

A simple and compact circular planar monopole ultra-wide band antenna with a 5.8u2009GHz band rejection and directional radiation pattern is proposed in this paper. The split ring resonator (SRR) technique has been utilized to produce band rejection at 5.8u2009GHz. Some results and analysis on several SRR placements are highlighted in this paper. The parabolic ground structure is used to produce a directional radiation pattern together with bandwidth enhancement. The proposed prototype antenna has acceptable performances in terms of gain, efficiency, and directional radiation pattern. Simulated and experimental results are discussed.

Application of negative selection algorithm in smart antenna system for LTE communication

Interference and multipath is one of the current issues in a wireless communication system, with complicated scenarios of environment especially in urban areas with a high number of users. Introducing smart antenna systems at the base station can contribute to reducing interference and improve quality of service. This paper proposes and explores the application of artiflcial immune system and negative selection algorithm to the prototype of smart antenna, where the proposed smart antenna is a hexagonal structure with 6-elements of the antenna array and working in LTE band at 2.6GHz. Initial testing was done to deflne the RSSI value by calculating the average of the signal then comparing RSSI value deflned by implementing artiflcial immune algorithm. To proof and determine actual RSSI signal received, a test in an anechoic chamber is conducted as reference that assumes free interference and multipath then compared to both of results. X-Bee module was used for transmitter and receiver in system at 2.4GHz band, and the proposed system prototype with hexagonal structure also used dual ARM microprocessor. Negative selection algorithm is applied in smart antenna programming to deflne actual values of receiving signal and angle of arrival. Every beam of the antenna was installed with an X-Bee module then connected to microprocessors, with an LED installed at each of the antenna as an indicator of beam switching or angle of arrival signal.

Interference Coupling Loss Between Highaltitude Platform Gateway and Fixed Satellite Service Earth Station at 5850–7075 MHz

High Altitude Platform Station (HAPS) is a new type of communications station that is expected to operate in parallel with terrestrial and satellite systems. Under agenda item 1.20 of next World Radio Conference 2012 (WRC-12), a new spectrum allocation for HAPS gateway link is proposed in the frequency band 5850–7075 MHz. Although the proposed band will provide reliable communication, the band is already saturated by the allocations of Fixed Satellite Service (FSS) earth station transmissions that have signal levels much higher than those in HAPS systems. Besides, the current HAPS spectrum sharing regulation method has limitations, such as coordination using separation distance as a dominant factor, ignoring the frequency isolation effects, and implementing Free Space Loss (FSL) model as a default propagation mechanism; thus, pessimistic results lead to large separation distances. To illuminate HAPS chance for spectrum sharing with existing services, this paper proposes a new spectrum-sharing prediction method using the spectral technique of Net Filter Discrimination (NFD) along with the antenna height within a deployment area. Reduction in required physical isolation is achieved, and frequency isolation produces an Interference Coupling Loss (ICL) that can utilize the radio spectrum resource as efficiently as possible.