Development of omnidirectional collinear arrays with beam stability for base station and mobile applications.

Since the 1800’s, inventors have considered electromagnetic radiation as a medium for communications between ship and shore and base to mobile. Generally, these were narrow band services, supported by simple series fed arrays. These arrays are limited in bandwidth by an inherent tapered phase profile which exhibits an undesirable vertical beam angle shift with excessive change in frequency. With a symmetrical tapered or linear phase profile, the radiation pattern remains on the horizon over at least 10% bandwidth. This thesis aims to presents the development of an antenna which has a unique compact planar architecture, and has achieved the performance required for broad band communications channels in the 900 MHz band. With low cost; volume manufacture, PIM and PIP considered. A major achievement in this work has been the development of a planar passive coupled dipole array with coplanar feed network presented on a single sided low cost flexible PCB. In this format, the array can be re produced accurately at a fraction of the cost of the conventional sleeve dipole arrays. Due to PCB processing limits for track spacing, the array has been designed with a main transmission line track spacing of 0.65mm resulting in a higher impedance of 86 Ohms. At this track spacing, the main transmission line can withstand a 2.1 kV ionisation test allowing for a PIP value of 1 Kw. To compliment this planar array, a specially designed planar dipole; matched to the new feed network scheme. With slots to augment the radiation pattern for improved directivity and reduced azimuth ripple, and notches to stagger tune the dipole to cover a broader than otherwise band and compensate for the reactance associated with close proximity to the slotline tracks. This dipole meets broad bandwidth and omnidirectional pattern specifications similar to cylindrical sleeve dipoles, while still maintaining inter-stage isolation. To further compliment the array attributes, a robust coaxial cable connection to the thin and flexible substrate employs a novel passive coupler transition circuit. The proposed transition is electromagnetically coupled to source and ground terminals of the array, eliminating the need for soldering, resulting in low loss, low PIM “Passive intermodulation” typically <-148 dBc, This coupler also provides the impedance transformation from 70 Ohms to 50 Ohms. An omnidirectional six element “coplanar waveguide(CPW)” fed collinear array was assembled from the planar feed network, dipole elements and passive coupler components, having a total length approximately 1.8 meters. This large array has the unique attributes of wide band, less than 1 degree beam tilt over a frequency range of 850 to 960 MHz (for a measured reflection coefficient magnitude greater than 14 dB), with low measured passive intermodulation below -140dBc “Decibel power ratio relative to transmit carrier”. The prototype collinear array can also withstand a wind loading of 240 km/h. The resulting antenna array meets the desired frequency band and has extremely stable radiation pattern, with a gain of 10 dBi

Compact and broadband antenna system at UHF

The aim of this research was to study a novel, broadband, low cost, low profile and a high-medium gain antenna in the UHF band. This has been achieved through numerical modelling, theoretical investigation and physical measurements. In this study two commercially available antenna systems are investigated in order to compare and establish potential deficiencies in the UHF antenna systems. A number of disadvantages are resolved within a novel antenna system design. The parametric study is performed for each element of the novel antenna system in order to optimise its overall performance. The indoor and outdoor measurements have been carried out in house, in order to validate the predicted results. The novel antenna system is compared to the most popular and commercially available UHF antenna systems. The study demonstrates that the novel antenna system has clear advantages such as broadband, balanced, compact and low cost when compared to the commercial antenna designs studied here. The comparison of the manufacturers’ data to the measured results shows a good match, validating the outdoor measurements technique used in this research

Refraction interference elimination employing smart arrays at VHF

Radio interference from the Middle East is one of the most significant problems plaguing the local radio services in Cyprus today. The issue is particularly noticeable on the highway, where it affects in-car tuners in all coastal areas of the island when the weather is hot and humid. In this work, the problem of interference from the Middle East was explored in the context of field strength variations versus the type of propagation mechanism favouring the radio waves in Band II, allowing them to travel from the Middle East to beyond the horizon in Cyprus. This problem was significant, since no line of sight exists between the two regions. After in-depth analysis adhering to the ITU (International Telecommunications Union) Recommendations, it was demonstrated that interference is caused by “Tropospheric Ducting”, i.e., trapping of the overseas transmitted signals between two layers of the troposphere at different heights. The upper air data were obtained using the Weather Research Forecasting (WRF-ARW version 3.4) model. The results yielded by the present study confirm that this model provides accurate prediction of interference for up to five days in advance. The interference problem is widely recognized, and therefore many attempts have been made to explicate its causes and provide solutions. The aim of the present study was to present a robust solution based on an innovative receiving antenna design. The antenna is a receiver’s component that collects electromagnetic waves from various directions. The rationale behind focusing on a circular array topology is that its tuning ensures that the receiver processes the desired signal only, while rejecting the unwanted interference. This can presently only be achieved by a large directional external antenna that must be steered mechanically in the desired direction. As this arrangement is not practical, an innovative smart antenna was proposed as an alternative. A circular phased array is a very compact antenna that produces a predicted radiation pattern, whereby it receives maximum energy from the desired direction without the need for mechanical control. Circular arrays exhibit high gain as well as immunity to interference, making them ideal for use in high interference environments. This combination allows the antenna to be incorporated into a commercial deck receiver or installed on vehicles

Impedance Transformers

Non

NASA Compendium of Satellite Communications Programs

A comprehensive review is presented of worldwide communication programs that range in time from the inception of satellite communications to August 1971. The programs included are: Echo, Courier, West Ford, Telstar, Relay, Syncom, Lincoln experimental satellites, Intelsat, Tacsat, Skynet, Nato system, and Telesat

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

NASA compendium of satellite communications programs

A comprehensive review of worldwide satellite communication programs is reported that ranges in time from the inception of satellite communications to mid-1971. Particular emphasis is placed on program results, including experiments conducted, communications system operational performance, and technology employed