Research And Applications Of Planar Horn Antennas

Horn antenna is one of the most classic, most simple, and most widely used antennas in the family of microwave antennas. With the continuous development of modern microwave and millimeter wave circuits and systems, it requires the volume to be more compact, the weight to be lighter, the performance to be more reliable, and the cost to be lower, etc. However, due to the disadvantages of the bulky, heavy weight and difficulty for integration, the traditional metal-wall horn antennas are limited to the applications and developments in modern microwave and millimeter wave circuits and systems. With the introduction and development of substrate integrated waveguide (SIW) technology, horn antennas could be realized in planar forms in general printed circuit boards (PCB), that is substrate integrated horn antenna. The substrate integrated horn antenna features high gain, high power capacity, low loss, small size, light weight, simple fabrication, low cost and so on. Moreover, it could be integrated in one PCB board with the other active and passive components, which will make the whole microwave and millimeter wave systems very compact and united.However, there are still some problems of the SIW horn that need to be solved urgently till now, such as the nonuniform of the phase and amplitude distribution on the SIW horn aperture, which will lead to low aperture efficiency and low gain. In addition, the impedance matching and radiation characteristics of the thin SIW horn antenna is very poor. And the polarization of the present SIW horn antennas is only the vertical polarization. Moreover, in the present application of the SIW horn as a planar feeding structure, it need to add some additional structures in front of the horn aperture to keep the uniform phase. To solve the above problems, the main work of this paper is as follows:Firstly, this paper has proposed two structures, metal-via arrays and gap SIW, to correct the nonuniform of the phase distribution on the horn aperture, so as to increase the aperture efficiency and antenna gain. The phase correcting solution of metal-via arrays is to embed multiple metal-via array inside the SIW horn, to make sure that all the electromagnetic (EM) wave travels to the horn aperture with the same phase, with the theory that the phase velocity of the EM wave is related to the width of the SIW. So the transmitting velocity of the EM wave could be controlled by changing the positions and lengths of the metal-via arrays. As for the phase correcting solution of gap SIW, it applies the phase characteristics of the asymmetric gap SIW to tune the transmitting velocity of EM wave with multiple gaps, to ensure all the EM wave of equal phase on the horn aperture. These two phase correcting solutions not only can correct the phase distribution on the horn aperture, but also can control the amplitude distribution on the horn aperture, which will enhance the gain with 2 dB to 3 dB higher. Both of the two phase correcting structures are inside the SIW horn, which will not add any extra volume size of the SIW horn antenna, to keep its original compact size.Secondly, this paper has introduced a horizontally polarized SIW horn antenna with thin substrate. This antenna is loaded with a compact antipodal linearly tapered slots array (ALTSA), to change the polarization from vertical to horizontal, and to improve the antenna matching. To obtain a miniaturized ALTSA, some metal-via arrays are embedded inside the SIW horn to guiding the feeding currency, to miniaturize the longitudinal and transverse dimensions of the ALTSA to 0.19λ0 and 0.35λ0, to improve the uniform of the phase and amplitude distribution on the horn aperture, and to enhance the aperture efficiency of the SIW horn antenna. As a result, a compact 1×8 ALTSA loaded thin SIW horn antenna with horizontal polarization is designed and experimented. What’s more, based on the horizontally polarized thin SIW horn antenna, another compact 1×8 LTSA loaded thin SIW horn antenna with vertical polarization and compact 1×8 cross-LTSA loaded thin SIW horn antenna with circular polarization are also proposed and studied, to extend the applications of the SIW horn antenna to multi-polarized systems.Finally, some planar array antennas fed by the SIW horn antenna are presented. With the phase and amplitude correcting technologies of metal-via arrays inside the SIW horn, three types of SIW horn fed planar array antennas, such as 1×8 ALTSA antenna,1×8 log-periodic dipole array antenna, and 1×8 quasi-Yagi array antenna are designed and fabricated. Comparing with the classic planar feeding structure using SIW power divider, this planar feeding structure using phase-and-amplitude-corrected SIW horn is more compact, more flexible in the array number, and with higher aperture efficiency and higher aperture utilization rate.All the above work not only keeps the compact structure of the SIW horn antenna while improving and enhancing the performance of the antenna, but also extends the function of the SIW horn antenna to feature multi-polarization. Thus, all these efforts have enrich the applications of the SIW horn antenna. Nevertheless, the proposed phase correcting solutions can also be used for other applications.