Planar microwave devices for wideband microwave medical diagnostic and therapeutic systems

Abstract

Microwave systems for medical diagnosis and treatment have been of increasing interest in both academia and industry over the past few years. Among numerous biomedical applications, breast cancer, brain stroke and heart failure detection have been attracting significant interests. Microwave detection and treatment systems, which are compact, low-cost, and efficient, have great potential to become a complementary detection and diagnosis modality for biomedical applications. Moreover, microstrip antenna arrays are often used in modern telecommunication and radar systems which require a complicated feeding network consisting of several microwave devices such as power divider, phase shifter, etc. These outstanding merits ignite increasing investment and research into the design and building efficient microwave systems, which are composed of several main parts, namely the antenna array, microwave transceiver, and signal processing algorithms. This thesis investigates the key passive microwave devices, such as in-phase and out-of-phase power dividers, multiport feeding network, and leakage cancellation circuit, needed to build microwave systems. According to the particularity of the circumstances and the complexity of the system, many challenges in designing the devices as well as a sub-system are analyzed. For an efficient and reliable microwave based system, these devices have been designed to provide the required performance concerning the bandwidth, return loss, insertion loss, isolation etc. using compact and low-cost planar structures. This thesis develops five series of methodologies to tackle these challenges; several sub-systems based on these methodologies are successfully implemented in the laboratory environment. The contribution in the first series is designing a variety of power dividers that operate as the feeding network of the microwave system. To obtain a wideband operation, two approaches are investigated. For the first one, the single layer microstrip-slot technology is employed to obtain the successful development of the components. This technique is applied to the in-phase and out of phase power divider. The simulated and measured results of the microstrip-slot components show the wideband performances across 1-8 GHz. The contribution in the second series is to design power dividers with high power handling capability. Both in-phase and out phase power dividers is designed using parallel coupled microstrip lines in order to obtain wideband performance. In this case, several power dividers from medium to high power handling capability are designed from 1-3 GHz. Detailed design procedures and experimental verifications are introduced. The proposed devices are initially calculated using a proper theory, then simulated using full-wave EM simulators, and finally fabricated and tested. The contribution in the third series is to integrate a leakage cancellation circuit for monostatic radar applications, which is built using a combination of in-phase and out-of-phase power dividers, into a transceiver based microwave detection system, wideband performance is realized with the help of microstrip-to-slotline transition structures and thus the transmitting and receiving signals with different reflecting coefficients is easily collected with high isolation for further signal processing procedure. The main objective is to effectively cancel the leakage signal and to increase the transmitter-to-receiver isolation in the conventional monostatic radar-based head imaging system for which is susceptible to transmitter signal leakage to a receiving path through a circulator. The contribution in the fourth series is to design a multiway feeding network for antenna array in microwave brain hyperthermia applications. In this case, coupled line power divider is used to develop multiport feeding network with high power handling capability. The feeding network consists of four outputs with equal magnitude and phase operating from 1-2.5GHz. The contribution in the fifth and final series is to design a microwave induced brain hyperthermia system which consists of a tapered slot antenna, multiway power divider, transmission lines as phase shifters and head phantom. At first, the simulation environment is built consisting of antenna array of four elements along with head phantom. The simulation is done by changing the amplitude and phase at the target location and the results show the possibility of focusing hyperthermia treatment at the tumour location. At last, the simulated results observed at different heating times confirm that the effectiveness of the proposed microwave focusing technique is successful. e