서강대학교

초록 (요약문)

Various applications utilized in millimeter wave such as the Ka-band (26.5–40.0 GHz) require high output power. As the frequency increases, the output power of a single power amplifier decreases, which does not satisfy the required performance of the application. In order to alleviate this problem, a power combining technique that combines multiple power amplifiers is becoming important. Planar power combining technique rapidly increases circuit size and loss as the number of devices combined increases. On the contrary, spatial power combining technique can solve the above problems and can be divided into tile type and tray type according to the power amplifier arrangement. In particular, a tray-type spatial power combiner is a method of power combining by inserting several dielectric substrates including active elements into a rectangular waveguide. However, as the frequency increases, the size of the standard rectangular waveguide and the number of dielectric substrates that can be accommodated decrease. This cannot efficiently obtain high output power. In addition, the non-uniform electric field distribution formed in standard rectangular waveguides leads to non-uniform power distribution to each active element, which leads to a degradation in overall system performance. In this work, we propose a spatial power combiner using H-plane oversized rectangular waveguide and dipole antenna array to address these problems. The proposed spatial power combiner consists of H-plane oversized rectangular waveguide and the dipole antenna array. The H-plane oversized rectangular waveguide is a structure that expands the width(a) of the standard rectangular waveguide three times and consists of a circular post, metal plates, and convex plates. The dipole antenna array is a simple structure without balun and consists of six dipole antennas. Higher-order modes excited by expanding rectangular waveguide increase losses and limit bandwidth performance. In this study, the waveguide was gradually expanded and the circular post was designed to sufficiently suppress the higher-order mode effect. In addition, metal plates and convex plates can solve not only uniform electric field and power distribution but also magnitude and phase imbalance. Theoretical analysis, simulation, fabrication, and measurement were conducted to verify. The proposed spatial power combiner was fabricated in a back-to-back structure, and VNA (Vector Network Analyzer) was used for measurement. The input return loss of the back-to-back module, including the dipole antenna array, is greater than 10 dB from 32.0 to 36.0 GHz and has an average insertion loss of 1.2 dB in the frequency range above. The input return loss of the back-to-back module excluding the dipole antenna array is better than 10 dB from 31.2 to 35.0 GHz in which insertion loss is 0.4 dB on average. The fabricated module can accommodate three times more trays than the previous studies in the same frequency band, so it is advantageous to obtain high output power. In addition, the proposed structure can be manufactured in high frequency such as millimeter wave by forming a uniform electric field without adding a dielectric.