Opening‐Angle Control of Quasi‐Thermal‐Noise Response in V‐Shaped Dipole Antennas

Abstract

Quasi‐thermal noise (QTN) spectroscopy is an important tool for plasma diagnostics in space missions, where the antenna geometry affects the measured voltage spectrum. Existing antenna response models mainly focus on linear dipole antennas, whereas the influence of finite opening angles in V‐shaped antennas has not been fully characterized. In this work, we develop a generalized response‐function model for symmetric V‐shaped dipole antennas with arbitrary opening angles. The formulation incorporates the wave‐vector projections along the two antenna arms and naturally recovers the classical linear‐dipole limit and short‐antenna asymptotic behavior. Comparisons with the projected‐equivalent linear‐dipole approximation demonstrate that the effective‐length description is valid only in the low‐wavenumber regime, whereas finite‐wavenumber deviations arise from the full two‐arm geometry. The dependence of the response function on the opening angle is investigated, showing systematic variations in the peak amplitude and characteristic wavenumber. The effects of finite center gaps and realistic current redistribution are further incorporated using an AWAS‐type current model. Solar Orbiter (SolO)‐like parameters are adopted to demonstrate the impact of antenna geometry on the impedance and absolute QTN spectrum. These results provide a generalized framework for interpreting QTN measurements with V‐shaped spacecraft antennas and highlight the importance of retaining the full antenna geometry beyond simple projected‐length approximations.