18 Microwave Properties of Dielectric Materials
In recent years, the study of newer types of dielectric materials and compositions has been of great interest. The quest for new, innovative and easily obtainable dielectric materials that yield predictable and controllable permittivity and permeability values with very low dielectric loss has always been fruitful. New ideas and designs to implement these materials in microwave devices and structures with the most efficiency and performance are also of equal importance. The book chapter covers the synthesis and characterization of new dielectric material compositions and the design, implementation and testing of a prototype dielectric resonator antenna and filter utilizing the fabricated dielectric material. It also covers the use of different design and testing techniques in this research. By studying different methodologies and new material types that were previously published in cited technical journals such as Science Direct, different types of materials and synthesis methods were able to be identified. The appropriate materials and method of synthesis were then derived and utilized in the fabrication of the new type of dielectric ceramic substrate material. After extensive literature reviews, research and analysis, various methods used in dielectric resonator designs were studied and analyzed. An overview of the synthesis process associated with the fabrication of the new dielectric composition will be discussed. Next, with the primary objective of investigating the microwave properties of a new composition of high permittivity ceramic dielectric substrate at microwave frequencies, research is then carried out on designing an electrical model in order to utilize the newly fabricated dielectric material in a microwave environment. The electrical model that is proposed will be of dielectric resonator devices which will incorporate the new dielectric material type. Tests and measurements will also be carried out at various microwave frequencies in order
SIMULATION OF ULTRA WIDEBAND MICROSTRIP ANTENNA USING EPML-TLM
In this paper the simulation of ultra wideband microstrip antenna is considered.Because of the ultra wideband characteristics of this antenna, it is better to use time domain simulation methods. In this work we use three dimensional transmission line matrix method (3D-TLM) and EPML-TLM algorithm for modeling PML boundary condition directly applied to TLM algorithm.Finally simulation results of some kinds of this antenna (e.g., linear tapered slot antenna and modified planar inverted cone antenna) are presented and compared with measurements and some commercial software's output.
An adaptive feedforward power amplifier for UMTS transmitters
The new communication standards like UMTS increase the spectral efficiency but a high linearity is required. RF power amplifiers are basic components of all wireless transceivers used in the communication systems, and their efficiency directly influences on the complete communication system efficiency. It is proposed the implementation of a linearization technique like feedforward to achieve lower cost and higher efficiency amplifiers with the same linearity. First, it is shown an adjusting method for balancing the amplitude, phase and delay elements in both loops of the feedforward architecture during the prototyping. Secondly, a prototype for UMTS downlink has been developed. This implementation demonstrates that with dynamic adjustment architecture and the proposed method, the linearity level is increased outstandingly in the range of -20 to 70 /spl deg/C. For a two tone signal separated 5 MHz the IMD3 raise is 37.5 dB and for a UMTS signal (test 1-64 channels) the ACPR increase is 15 dB.