Microwave signals are sensitive to the changes of water content in tissues. Microwave imaging has been earning more attention in diverse biomedical applications, from breast imaging and radiation treatment monitoring to hydration monitoring. For all applications, antennas are one of the most important parts of the microwave imaging system, directly affecting the quality of measured signals. With more operational microwave imaging systems introduced and feasibility studies performed, there is a clear demand for more data to be measured during patient studies and trials, leading to higher resolution images. In addition to challenges in signal processing, this also presents requirements for hardware, namely implementing low-profile, miniaturized antenna elements into a dense array. This thesis investigates specific low-profile, miniaturized antenna solutions for a next-generation transmission system, which requires antennas to have direct contact with the skin. The wide-slot antenna is first investigated, which generates several different fork-shape monopole designs. The designs are optimized and modified through several techniques, including adopting high-permittivity substrates, folding the radiator and introducing an intermediate layer for improving both impedance matching with the skin and radiation pattern within the tissue. The final antenna element has a maximum aperture size of 16.8 mm by 18.6 mm and a height of 15mm. Stable radiation within the tissues is retained from 3 GHz to 6 GHz. The antenna element shows great potential to be implemented in an array for the next-generation transmission system.