| In recent years, novel wireless communication technology is developed rapidly. Spectrum congestion will cause communication interference. Under this background, ultra-wideband(UWB) technology as an emerging communication technology is applied in the short-range communication system. The operating frequency band of the UWB communication system overlaps that of the multiple narrow-band communication systems existed. When multiple communication systems exist, signal interference occurs among them. To solve the signal interference, the UWB antenna with band-notched characteristics is needed. At present, the differential circuit is widely used in the RF circuits, but the traditional single-ended antenna cannot be directly connected to the differential circuit. So, a balun is needed to transform the differential signals into the single-ended signals. In this case, the differential antenna which can directly put the received differential signal into the differential circuit is particularly important. The main contribution can be listed as follows:1. A UWB square slot antenna with rectangular-ring differential feeding is presented. Rectangular rings are employed to differentially feed the square slot antenna. The influence of some parameters on the performance of the antenna is studied. Measured results show that the antenna has an impedance bandwidth from 2.83 to 10.79 GHz. By introducing a C-shaped stub and an inverted-? slot into the proposed antenna, a differential microstrip-fed UWB antenna with dual band-notched characteristics is proposed. The key parameters affecting the notched bands are studied, and the value of the antenna structure size optimized is given. Measured results show that the antenna has a wideband performance from 2.53 to 11 GHz covering the operating band of the UWB communication system, along with two notched bands of 3.27-4.13 GHz and 4.95-6.28 GHz covering the operating bands of the worldwide interoperability for microwave access(3.4-3.69 GHz) and the wireless local area network(5.15-5.825 GHz), respectively. In addition, the proposed antenna has good radiation characteristics.2. A UWB polygon slot antenna with stepped monopole differential feeding is proposed. Stepped monopoles are employed to differentially feed the polygon slot antenna. The key parameters affecting the performance of the proposed antenna are studied. Measured results show that the obtained impedance bandwidth of the antenna is from 2.82 to 10.71 GHz which can cover the operating band of the UWB communication system. Two split ring resonators and a complementary split ring resonator are introduced into the antenna, and a differential CPW-fed UWB antenna with triple band-notched characteristics is proposed. The structural parameters affecting the notched bands are studied, and the value of the antenna structure size optimized is given. Measured results show that the antenna has a wideband performance from 2.55 to 10.86 GHz covering the operating band of the UWB communication system, along with three notched bands of 3.21-3.86 GHz, 4.93-6.13 GHz and 7.87-8.89 GHz covering the operating bands of the worldwide interoperability for microwave access(3.4-3.69 GHz), the wireless local area network(5.15-5.825 GHz) and ITU-8GHz(8.025-8.4 GHz), respectively. Also, the proposed antenna has good radiation characteristics and low cross polarization level. |
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