The knowledge of the dynamics of soil water is essential in agricultural, hydrological and environmental engineering as it controls plant growth, key hydrological processes, and the contamination of surface and subsurface water. Nearby remote sensing can be used for characterizing non-destructively the hydrogeophysical properties of the subsurface. In that respect, ground penetrating radar (GPR) constitutes a promising high resolution characterization tool. However, notwithstanding considerable research has been devoted to GPR, its use for assessing quantitatively the subsurface properties is constrained by the lack of appropriate GPR systems and signal analysis methods. In this study, a new integrated approach is developed to identify from GPR measurements the soil water content and hydraulic properties governing water transfer in the subsurface. It is based on hydrodynamic and electromagnetic inverse modeling. Research on GPR has focused on GPR design, forward modeling of GPR signal, and electromagnetic inversion to estimate simultaneously the depth dependent dielectric constant and electric conductivity of the shallow subsurface, which are correlated to water content and water quality. The method relies on an ultrawide band stepped frequency continuous wave radar combined with an off-ground monostatic TEM horn antenna. This radar configuration offers possibilities for real time mapping and allows for a more realistic forward modeling of the radar-antenna-subsurface system. Forward modeling is based on the exact solution of Maxwell's equations for a stratified medium. The forward model consists in elementary linear components which are linked in series and parallel. The GPR approach is validated for simple laboratory and outdoor conditions. GPR signal inversion enables the monitoring of the soil water dynamics, which can be subsequently inverted for estimating the soil hydraulic properties. A specifically designed hydrodynamic inverse modeling procedure which requires only water content data as input is further developed and validated to obtain the soil hydraulic properties under laboratory conditions.

The thesis is focused on the research of THz antenna arrays to be used for communications. Attention is turned to modeling metallic surfaces at THz frequencies, a proper characterization of gold conductivity, its relation to Drude model and corresponding measurements. Moreover, the best methods for modeling thin metallic layers (depending on the skin depth related to the metal thickness) are presented. An optimized element of a THz 2×2 antenna array designed for the application of communications is developed in a way that enables an expansion to a larger array. The expansion ability is demonstrated on a 4×4 antenna array which is presented in the thesis too. The designed antennas achieve parameters better than the state-of-art antennas. The presented antennas radiate circularly polarized wave at THz frequencies, operate in a wide bandwidth, have a high gain and are of a compact size. In the thesis, an 8×8 antenna array with a beam steering capability is presented. The main beam of the antenna array can be controlled in two dimensions. A high gain of the radiated circularly-polarized wave can be achieved that way. Different approaches to modeling antennas with thin metallic layers are compared and the best methods are recommended from the viewpoint of different requirements. The designed 2×2 and 4×4 antenna arrays are manufactured using a microfabrication technology. Each step of the fabrication is described in detail and discussed. The reflection coefficient at the input of antennas is measured and compared with simulations. Discrepancies in results are associated with surface roughness which is analyzed by a scanning probe microscope and a scanning electron microscope. By down-scaling the developed THz antenna, a low-profile high-gain antenna for Ka-band space applications is designed. The presented antenna achieves better results than state-of-art CubeSat antennas. The antenna performance is verified by a prototype to be operated at 9 GHz, and the radiation characteristics are experimentally confirmed.

To investigate near-eld contributions for installed antennas, an in-house code iswritten to incorporate near-eld terms in Shooting and Bouncing Rays (SBR). SBRis a method where rays are launched toward an object and scatter using GeometricalOptics (GO). These rays induce currents on the object, from which the totalscattered eld can be found.To gauge the eect of near-eld terms, the in-house code can be set to excludenear-eld terms. Due to this characteristic, the method is named SBR Includingor Excluding Near-eld Terms (SIENT). The SIENT implementation is thoroughlydescribed. To make SIENT more exible, the code works with triangulated meshesof objects. Antennas are represented as near-eld sources, allowing complex antennasto be represented by simple surface currents. Further, some implementedoptimizations of SIENT are shown.To test the implemented method, SIENT is compared to a reference solution andcomparable commercial SBR solvers. It is shown that SIENT compares well to thecommercial options. Further, it is shown that the inclusion of near-eld terms actsas a small correction to the far-eld of the installed antenna. / För att undersöka närfältsbidrag för installerade antenner, har en kod skrivits för‌att ta med närfältstermer i Shooting Bouncing Rays (SBR). SBR är en metod där strålar (”rays”) skjuts mot ett object och sprids via Geometrisk Optik (GO). Dessa strålar inducerar strömmar på objectet, från vilka det totala sprida fältet kan hittas. För att undersöka bidraget från närfältstermer, så kan koden exkludera dessa. På grund av denna karaktär, kallas koden SBR Including or Excluding Near-field Terms (SIENT). Implementationen av SIENT beskrivs utförligt. För att göra SIENT mer flexibel, arbetar SIENT med triangulerade nät av objekt. Antenner representeras av närfältskällor, vilket låter komplexa antenner representeras med enkla yt-strömmar.Implementerade optimeringar av SIENT visas också.För att testa den implementerade metoden, jämförs SIENT med en referenslösning och jämförbara kommerciella SBR-lösare. Det visas att SIENT överensstämmer bra med kommerciella alternativ. Det visas också att närfältstermer agerar som enmindre korrektion till fjärrfältet av den installerade antennen.

The thesis is aimed to analyze parameters of antennas, and work out the computer, which can be used to the modeling of the radiation of antennas of the VUT 100 aircraft. First, used antennas are divided according to the operation frequencies, and the polarization. Second, a MATLAB program is developed and described. The program computes radiation patterns at different frequencies for the different location of antennas on the VUT aircraft. Finally, the MATLAB optimization program is develop and described. The program changes the position of antennas so that the requirements of aircraft producer can be met.