Reseach And Design Of Filtering Patch Antenna

In RF front-end systems, filters and antennas are two important passive devices. Filter function is to allow a certain band signal passed and suppress the other signal bands. Usually, filter can be divided into three types: high-pass filter, low pass filter, band pass filter, such as a high-pass filter can only receive high-frequency signals, the low-frequency signals were filtered out. Since more and more available frequency bands are applied in the mobile communication, band-pass filter is most widely used. Antenna is as the forefront of RF systerm, its role is primarily to receive and transmit signals. Since the antenna itself has not the filtering response, it received and transmitted signals in unnecessary bands may also have some energy radiated, so the RF system typically requires a filter to realize frequency selection. Both devices are often simultaneously used in modern wireless communication systems, which will occupy a large area in the RF front-end system. In order to achieve the overall miniaturization, integrated filter and antenna can be megered. Thus, not only can system size and system cost be reduced, but also can the performance of the system be improved to a certain extent.This topic is in premise of in-depth study of filter and antenna theory premise, three new filtering antennas are designed. They can exhibit excellent radiation performance and filtering performance without additional filter circuit. The main work of this thesis is as follow:(1) Compact differential-fed filtering patch antenna; This chapter introduces the design of a differential-fed filtering patch antenna. The antenna gets a band-pass filtering response without extra filtering circuit. It is realized through generating two zeros in the gain curve by a parasitic patch and a u-slot on the driven patch. At the same time, this antenna is fed differentially, which solve the traditional issues that differential feed signals radiate difficultly. And obtain a high gain in the compact size.(2) High gain filtering patch antenna without extra circuit; this chapter is mainly based on the previous work, designing a single-fed filtering antenna for better out-of-band rejection(try to achieve suppression standard of filters). Based on the parasitic patches and U-slot, three shorting pins are inserted in the driven patch, so that the low-frequency electric field mode change on the driven patch, commen mode rejection is obtained. In this situation, low frequency currents around three shorting pins cancel each other. Then the far field radiation also cancels each other. So a radiation null at the frequency in the gain curve is obtained, which improves low-frequency filtering characteristics.(3) Dual-polaried filtering patch antenna with high selectivity and low cross-polarization. This chapter is to resolve the dual-polarization issues which can not be realized by previous two types of antennas. This antenna is fed by H-shape transmission line, resulting in a very good high-pass filtering performance. And parasitic patch generates a high frequency zero, two zeros can realize a good band-pass filtering characteristics. Since the height of the antenna is very low and the structure is symmetrical, the cross-polarization and the other radiation performance of the antenna are also very good.