Research On Wideband Wearable Antennas And The Control Of Antenna Radar Cross Section

As the modern communication technology develops quickly, communication electronic devices with compact size and broadband are becoming more and more attractive. The antenna is one of the most important parts of a communication device, and its miniaturization and broadband design have become an important aspect of the antenna design. Wideband wearable antennas and the method of reducing the RCS of UWB antenna have drawn great interest recently. Body-centric wireless communication is an important part of the fourth generation of mobile phone mobile communication. One of the important research topics for body-centric communications is wearable antenna. It could be integrated into cloths and carried easily. Stealth technique is playing an important role in the war. The scattering from an antenna becomes a key to restrict the stealth effect of the whole system. Development of the antennas with good scattering performances is very important. This dissertation mainly concerns with textile antenna, wearable UWB button antenna, wearable wideband PIFA antenna, and the method of reducing the RCS of UWB antenna. The main contributions are as follows:1. Several major design features of textile antennas in the wearable system are analyzed. Firstly, the textile material that could be used to produce textile antenna is studied. The permittivity of the substrate is measured. The permittivity of silk, cotton, fleece fabric and nylon are measured. A microstrip antenna with fleece fabric substrate is fabricated. The permittivity of fleece fabric is confirmed by compared the measured and simulated VSWR. As an example, a microstrip antenna with fleece fabric substrate is given to study the aspect of the change of the fabric. The effect of the wetness of the fabric on the performance of the textile antenna is studied. Since fabric antennas are used near the human body, the fabric may be wrinkle. The performance of the textile microstrip antenna is given when the fleece antenna changed its shape. A simple body phantom is built, the performance of the dipole antenna and microstrip antenna is analyzed in different frequency when the antennas are placed on the body phantom. The results show that the microstrip antenna is less affected by the body phantom. The ground plane serves as a shield against the effect by the body phantom. The ground plane is helpful to reduce the human body effect in the textile antenna design.2. A novel compact UWB textile button antenna is presented and studied. The fleece fabric substrate is used in the textile button antenna. The proposed antenna is fabricated and measured. The simulated and measured performance shows a good agreement. Simple brain and chest phantom are built. The performance of the proposed antenna is analyzed in different frequency when the antenna is placed on the phantom. SAR values are given to evaluate the effect of the antenna on the human body. The result shows the proposed antenna meet the required standards. The ground plane reduces the interplay between the human body and proposed antenna. The effect of the body on S21 between two identical button antennas is studied. The human body obstructs the transmission between two button antennas in the different plane. The performance of the proposed antenna is studied when the ground plane is bent. Finally, a modified antenna is given.3. A novel wideband wearable PIFA antenna used in smart watch is presented and studied. The radiation characteristics of the proposed antenna are analyzed by parameter analysis. Simple wrist phantom are built. The performance of the proposed antenna is studied when it is placed on the phantom. SAR values show the proposed antenna meet the required standards. As metal frame may be used in part of smart watch, the performance of the proposed antenna with metal frame is analyzed. The proposed antenna with metal frame works well in the designed frequency and the gain of the antenna increases. The metal frame is helpful to reduce the effect of the antenna on the human body.4. A novel stealth Vivaldi antenna with low radar cross section is presented and studied. The radiation performance of the proposed antenna is studied. The configuration of the metal patch is modified, based on the difference of the current distribution while the antenna radiates and scatters. To clarify the effect of the modified parts on reducing monostatic radar cross section, two antennas is defined to be compared with the proposed antenna. The proposed antenna is fabricated and measured. Results are provided to demonstrate that the excellent radiation and perfect stealth performance is achieved.