Analysis and Improvement of Bandwidth and Gain of Millimeter-Wave Microstrip Franklin Antenna With Proximity-Coupled Feed

In this paper, analytical equations drawn from previous literature on Franklin antenna designs are combined to provide a single solution with an objective of increasing the bandwidth and impedance gain. We adopt the method of a collinear planar antenna as realized in the Franklin antenna, which can reduce the dimensions of the antenna. The main advantage of using the Franklin antenna is that it has a high gain due to the structural characteristics of an array, but it results in a narrow bandwidth. Therefore we combine the Franklin array technique with the proximity couple feeding that can eliminate radiation scattering and can provide large bandwidth. The combined application of the two techniques aims to increase the impedance bandwidth and gain, jointly verified through simulation and measurement with similar results. A stringent full-wave solution is used to evaluate the suggested model, and an experimental antenna prototype is developed. The results for bandwidth and gain from the equations are found to be very similar to those from the simulation and measurement results. Specifically, from the simulation the largest bandwidth is 8.39 GHz with a frequency range of 26.96 - 35.35 GHz and a gain of 11.55 dBi at the frequency of 28 GHz, while the largest measured bandwidth is 9.34 GHz spanning a frequency range of 21.96 - 31.06 GHz. The difference between the analytical model proposed by simulation and measurement is less than 5%. This also shows that the microstrip Franklin antenna with proximity coupled feed (MF-PCF) is a strong candidate for 5G applications.