This paper presents the most valuable theoretical results that confirm the possibility of practical realization of a wideband volume horn array antenna with the switchable polarization capability. Among key features of the proposed antennas are their high stability of switchable linear polarization tilt angle of radiated electromagnetic wave, radiation pattern of sector type and wide operating frequency band. The paper focuses on characteristics of linear horn antenna subarrays as key components of the described volume array antenna. Subarrays fully comprise double-ridge waveguide sections. The cutoff wavenumbers calculation algorithm is developed for the symmetrical double-ridge waveguides to estimate frequency bandwidth of power dividers in their different cross sections. The problem is solved numerically by partial regions method taking into account field singularity on rectangular metal ridges.

An effective technique to the design of dual band coaxial waveguide feed horn for reflector antenna excitation has been developed and tested. Matching the feed horn with free space in upper frequency range is achieved by dielectric insert disposed inside the circular waveguide fabricated in interior conductor of open ended coaxial waveguide. The presence of dielectric insert causes the high level of reflection in lower frequency range from the boundary between the open end of coaxial waveguide and free space. A novel technical solution of highly complicated matching problem has been proposed. The matching design was performed as the series of finite thickness diaphragm arranged on outer surface of interior conductor of coaxial waveguide. To obtain the rigorous solution of given electromagnetic problem for the complicated structure consisting of a great number of connected coaxial waveguide sections and dielectric insert, a new effective approach has been proposed. The distinctive feature of this approach consists in combination of rigorous procedure based on computation of generalized scattering matrices and another rigorous procedure based on the finite difference time domain method. To combine these essentially different approaches, the metallic discontinuity equivalent to overall investigated structure was employed. An optimization of equivalent matching structure has been performed by the variant of the evolution strategy method. The obtained design with metallic discontinuities was converted into real structure comprising the dielectric insert. The final calculations of real structure were performed by the finite difference time domain methods. The effectiveness of proposed technique was confirmed by the results of testing the developed feed horn in reflector antenna system.

The class of resonators which allows building mechanically tunable waveguide bandpass filters with near constant bandwidth in overall a wide tuning frequency range has been investigated. The concept comprising in a successful combining inductive and capacitive discontinuities to obtain near constant quality factor of resonators in wide frequency variation range is implemented. It is proved that the most technologically advanced solution can be obtained by using the waveguide connections containing double ridged sections for compensation of phase shifts in resonators appearing because of frequency variation. Adequate mathematical models of the resonators based on generalized scattering matrix approach are obtained. The diffraction problems for doubled discontinuities, such as doubled ridged sections in rectangular waveguide, have been solved by the integral equation method. The calculation of resonance frequencies and quality factors of resonators are carried out in wide dimension range variations. Due to near constant quality factors over wide tuning frequency range, the developed waveguide resonators open new possibilities in realization of high efficient and cost effective frequency tunable filters of transmit tropospheric stations and various telecommunication systems for tropospheric communication.