Problems connected with designing devices for measuring complex impedance of antenna and standing wave ratio in antenna feed line intended for usage in high frequency band antenna tuning units are discussed in this article. Structural schemes of devices implementing two different approaches to determination of the sign of the imaginary part of antenna impedance are proposed. Problems connected with practical realization of the proposed schemes of devices are investigated, in particular the task of designing a linear amplitude detector with the adjustable detection slope. Results of the computer modelling of the performance of detector channels and results of practical experiments carried out with the laboratory model of investigated device are proposed in this article.