Design of a filter-antenna subsystem for UWB communications

In this paper, we discuss about the design of a filter-antenna subsystem for UWB communications, which can appears optimum physical and electrical characteristics. A UWB antenna can´t obtain a good performance in the passband and restrain the upper-passband (higher than 10.6 GHz) very well at the same time by itself. So we propose a filter-antenna subsystem. In this subsystem, we associate a UWB filter with a UWB antenna. The UWB filter is placed where the microstrip feed line was located. By this way, several subsystems´ advantages can be obtained. First of all, UWB filter can be used as a wideband match circuit to enhance the performance of antenna in the passband. Secondly, we can get an improved out-of-band performance. Thirdly, the subsystem has a small dimension, which is very essential to the modern radio communication system. In this subsystem, S₁₁ is smaller than -10 dB between 3.3-10.4 GHz and higher than -3 dB until nearly 18 GHz. A quasi-omnidirectional radiation pattern can also be remained. The measured results are well matched to the simulations.