Integrated amplifier/antenna elements for gallium arsenide monolithic phased arrays

Future communications and radar systems operating at frequencies above 20 GHz are expected to make use of monolithic phased arrays based on GaAs Monolithic Microwave Integrated Circuit (MMIC) technology. This thesis investigates the integration of amplifiers and antennas on GaAs to form active amplifier/antenna elements suitable for use in such arrays.;The evolution of phased arrays is first considered, and it is seen that recent technological progress has led to the possibility of realizing phased arrays in monolithic form not only with microwave circuit techniques, but also with the use of emerging digital and optical technologies. Then, an overview of active antenna realizations is given, in which various transmitting, receiving and transmitting/receiving configurations are assessed in terms of the applicability to monolithic phased arrays. It is found that the desired active antenna element consists of an amplifier/antenna.;After studying the characteristics of resonant type antenna structures, the most efficient radiating element on GaAs MMIC substrates is determined to be the slot radiator. As a result, an analytical tool is developed to obtain the slot input impedance in terms of its geometry for subsequent integration with active devices. The analysis is based on an integral equation formulation for a magnetically coated dipole, this being the complementary/dual structure of the slot on a dielectric substrate, and a moment method solution is employed to obtain the input impedance numerically. Results of the computations compare favourably with experimental data. In addition, newly developed on-wafer techniques are described for the measurement of integrated-circuit slot antenna parameters such as input impedance and radiation patterns.;To demonstrate the feasibility of MMIC phased array realization, an optimum monolithic array configuration is proposed and the form of the constituent active amplifier/antenna elements is defined. The amplifier/antenna is a new MMIC structure, consisting of a P-HEMT device connected without matching circuitry to a slot radiator on the opposite side of the substrate by means of metallized via holes. A method is presented for the analysis of the amplifier/antenna using the slot input impedance calculation previously developed, and a commercial microwave circuit CAD package to represent the device and antenna feed characteristics.;The practical MMIC implementation of a novel transmitting amplifier/antenna is then described along with the results of its performance. At the 30 GHz design frequency, a gain of 7.4 dB is obtained from the amplifier portion of the active antenna, while the radiation pattern exhibits a symmetrical, single lobe characteristic, is predicted. This is the first demonstration of an MMIC which incorporates a P-HEMT and a slot radiator, and the first time via holes have been used to connect between circuit components on both sides of the wafer. It is concluded that the principle of the amplifier/antenna, as well as its analysis method, are validated. A more exhaustive study of slot antenna input impedances is recommended as future work to allow the realization of increasingly compact, enhanced performance transmit- and receive-mode amplifier/antennas.