Research And Applications Of Loading Technology For Antennas

With the rapid development of the wireless communication technology and the high speed integrated circuit technology, the requirements for the antenna performance become more and more higher, as the antenna is an important element of the wireless communication systems. But in practical engineering projects, a single simple antenna often cannot satisfy the specific requirements of an application, thus loading some components or some structures on or near the antenna to improve the antenna radiation performance is in need. Loading technology is widely used in antenna design, and using the loading technology to achieve miniaturized antenna, multifunctional antenna and broadband antenna are the main research points with the development of modern wireless communication systems.Corresponding to the three research directions, this paper focuses on the design of miniaturized microstrip antenna, the multifunctional planar antenna, and on how to broaden the frequency band and suppress the tailing effect for pulse antennas by using loading technologies. Based on the design and the research of several kinds of the loaded antennas, the improvements on the antenna performance by using loading technology in various applications are studied. The work and the research achievements of this paper include:(1) This paper designs several miniaturized microstrip antennas by using distributed reactance loading technology, gives a detailed analysis of the operating mechanisum based on equivalent circuit models, and verifies the loading methods by full-wave simulation and measurement. This paper designs a suspended microstrip antenna loaded with a grounding strip to achieve the size reduction of the antenna. Results show that the loading structures introduce equivalent capacitance and inductance by the coupling between the grounded strip and the microstrip antenna, which decrease the working frequency of the antenna by 73.5%. This paper designs a suspended microstrip antenna loaded with Mushroom-like structure, and the equivalent capacitance and inductance introduced by the Mushroom-like structure decrease the antenna’s operating frequency by about 74.5%. And the coupling between the unit cells of the Mushroom-like structure introduces several resonant frequencies, which was used to realize a dual-band microstrip antenna with a frequency ratio of about 1.4. A suspended microstrip antenna loaded with Mushroom-like structure and capacitors was also designed, and it achieves similar radiation performance to the antenna with Mushroom-like structure in a low process precision. Considering that the aperture-coupled microstrip antenna is a three-layer structure and the fabrication of the loading structure is much difficult, this paper has also designed microstrip antennas loaded with embedded grounded strips and with embedded Mushroom-like structure. The two embedded loaded antennas are two-layer structures and show good characteristics of miniaturization and symmetrical radiation when compared to a miniaturized microstrip antenna loaded with shorting pins.(2) This paper proposes a method of design multifunctional band-notched antenna by loading band-notched reflector. The loading structure not only realizes band-notched characteristic for the loaded antenna in the notched frequency band which locates below the working frequency band, but also enhances the antenna gain in the working frequency band. It makes an integration of the functions of an image-rejected filter, an antenna and a reflector. Taking a plananr dipole antenna as example, this paper gives an equivalent circuit model of the antenna loaded with a band-notched reflector and analyzes the band-notched characteristic in detail based on the model, and discusses the reflector performance of the loading structure by full-wave simulation. Based on the mechanism analysis of this loading method, this paper designs a planar bow-tie antenna loaded with the band-notched reflector. Measured results show that the band-notched reflector suppresses the antenna radiation by about 44 dB at the image frequency which locates below the working frequency band, while enhances the antenna gain in the working frequency band by about 3 dB. This paper also designs a planar zigzag dipole antenna loaded with a band-notched reflector and a director. The simulated and measured results both show that the band-notched reflector suppresses the radiation in the image frequency band, and the band-notched reflector and the director corporately enhance the antenna gain in the working frequency band.(3) For the extending of the impedance bandwidth and the improvement of the radiation waveform in a pulse antenna, this paper designs several kinds of pulse antennas with terminated resistive loading, proposes and verifies the method of making resistive loading between the element of a antenna array. This paper designs a tapered slot antenna loaded with terminal extended resistive strips. By comparing the simulated results of the reflected signal, the radiation efficiency, the S-parameters, and the radiation waveforms for the loaded tapered slot antenna and an unloaded one, it is verified that this loading method can effectively reduce the internal reflection and the reflection at the radiation terminal, thereby can reduce the trailing pulse in radiation waveform and broaden the bandwidth at the lower frequency band of the antenna with little effect on the antenna radiation efficiency. This paper proposes a Gaussian tapered rhombic antenna with a smooth tapered edge, and the corresponding simulated and measured results show that this antenna presents a wider operating frequency band and smaller internal and terminal reflection than an ordinary rhombic antenna. This paper presents a method of loading resistance between the antenna array units. The research about loading resistors between elements of a planar bow-tie antenna array shows that this method can effectively reduce the reflected pulse at the element terminal, thus it is helpful to broaden the working frequency band.The above work focuses on the microstrip antenna with distributed reactive loading, the planar antenna with loading structure, and the pulse antenna with terminal resistive loading, and has studied the application and the effect of the loading technology in the realization of miniaturized antennas, multifunctional antennas, and in extending impedance bandwidth of pulse antennas. These loading methods are not confined to the related specific antennas, but also can be generalized to other antenna structures.