UWB radar is the most promising radar system for the future. In addition, by combining the UWB and array signal processing, one can obtain 3-D images of the objects for classification and identification, which is very useful in many applications. To achieve high-resolution real-time 3-D imaging radar, two essential items are missing in the current technology: dedicated antenna systems for sparse C-scan acquisition and fast high-quality imaging algorithms. In this thesis we have focused on the development of dedicated sparse antenna systems, including the sparse array topology development and antenna element development, while imaging algorithm is out of scope of this research. The main conclusions and their novelties are presented as follows: 1. Novel microwave ASP antenna: In this thesis a novel ASP antenna working from 10 GHz to 18 GHz has been developed. This antenna is aimed to be used for the time-domain UWB imaging array. The analysis demonstrated that the antenna not only has sufficient -10 dB impedance bandwidth from 9.95 GHz to 20 GHz, but also has good radiation characteristic within the impedance bandwidth. The antenna has gain of 5 to 10 dBi. The FBR is larger than 10 dB, and the -3 dB beamwidth is about ±30° is both E- and H-plane. The antenna has about 100 ps group delay and the impulse response has 1/e pulse width of about 200 ps. The analysis of radiated pulse distortion with respect to angle demonstrated that the pulse is very similar within the -3 dB beamwidth. This demonstrated that the antenna has small distortion and short after-time ringing, which makes the antenna suitable for time-domain application. The antenna coupling behavior analysis showed that the coupling between elements is small. Therefore, no severe performance degradation was expected when this antenna operates in the sparse MIMO array environment. 2. Investigation of LTCC technology: LTCC technology has been selected to manufacture mm-wave antennas to be integrated with MMICs. The multilayer nature of the LTCC technology makes it suitable for system-in-package. However, LTCC technology is a relatively new and not-yet standardized technology and LTCC material normally possesses high dielectric constant, which makes the design of UWB antenna difficult. As a result, we have investigated the properties of LTCC material and its impact on UWB antenna design. We have also explored the manufacturing limitations of the LTCC technology, and proposed solutions to overcome these limitations. The LTCC processing variations have also been studied. It reveals that the variation of substrate height has significant influence to the antenna resonance frequency, while the variation of relative permittivity has very small impact on the antenna reflection coefficient. 3. K-band LTCC antenna: A novel K-band antenna using the LTCC technology has been developed. This antenna is a differentially-fed, multi-staircase shielded elliptical dipole UWB antenna. The antenna has a novel differential feeding which enables it to be directly integrated with differential MMICs. The multi-staircase shield reduces the antenna back radiation and improves the antenna forward radiation, while keeping the antenna impedance bandwidth large. The antenna has a -7.5 dB impedance bandwidth from 24 GHz to 30 GHz, with a gain of approximately 5 dBi to 7 dBi. Thanks to the presence of the shield, the antenna radiation patterns are stable within the operating bandwidth, and the 3 dB beamwidth at the E-plane is of about 60° and 30° at the H-plane. 4. M-band LTCC antenna: A novel differentially-fed UWB antenna working at M-band using LTCC technology has been developed. The antenna is based on ASP type of antenna with novel differential feeding structure. With this feeding structure the antenna can achieve a -10 dB impedance bandwidth from 50 GHz to 78 GHz. The high dielectric constant of LTCC material induces severe surface wave which substantially degrade the antenna radiation characteristics. Although the multi-staircase shield proposed for the K-band antenna can solve this problem, it is far too complex to realize in the M-band. A novel simplified rectangular shield has been proposed to solve this. This shield does not have complex structure but can successfully confine the surface wave, thus improving the antenna radiation characteristics. The gain of the M-band antenna is from 3.5 dBi to 8 dBi from 50 GHz to 62 GHz, and the -10 dB beamwidth is at least from -45° to 45° for both E- and H-planes. 5. Element coupling investigation for imaging array: The influence of element coupling to the quality of image has been investigated. The antenna cross-talk does not pose severe threat to the image quality, because it can be eliminated by time-gating technique. The most influential coupling is the scattering coupling, which acquires fewer attentions in the antenna community. This type of coupling will alter the antenna receive sensitivity function. If at certain frequency the coupling is stronger than others, then the sensitivity function will have a spike at that frequency. This spike will cause long after-time ringing, masking small objects behind a large object. Another profound influence of scattering coupling to the image is that the scattering coupling will cause increase of sidelobe level, which increases the clutters. 6. 2-D sparse MIMO antenna array topology: Investigation demonstrated that MIMO array concept can achieve 2-D sparse real-aperture array for fine cross-range resolution and low sidelobe imaging system. The design of the 2-D MIMO array has been break down to two steps. The first step is to design a 1-D MIMO array with desired PSF properties. The next step is expand this 1-D MIMO array into 2-D array by firstly lay the designed 1-D array on two orthogonal axes, and then use the rotational 1-D array analysis to obtain the 2-D array. Two 2-D arrays based on the same 1-D array have been developed using this approach and manufactured. The measured results of small objects demonstrated that both arrays were capable to image small objects. It was also found that the sidelobe level is one of crucial specifications of the array, which should be specified by system designers in order to achieve proper performance of the whole imaging system. The 3-D imaging results proved high potential of using microwave 2-D UWB sparse MIMO array in real-time short-range high-resolution imaging applications.