Pavel Pechac

This paper investigates the development of a clutter loss model specifically for slant paths involving directive antennas . Conventionally, clutter loss is characterized by using isotropic antennas to facilitate standard link budget calculations via single antenna gain values. Clutter loss may represent a significant excess loss relative to free‐space propagation . In scenarios such as coexistence interference between cellular and satellite systems, the former can employ highly directive, beam‐steering architectures . Since the transmitter–receiver (Tx‐Rx) link comprises multiple discrete propagation paths , each is subject to different antenna gains. This study proposes an extension to the five‐ray model (5RM) for clutter loss to account for these differential gains. The methodology effectively characterizes paths from terrestrial transmitters to elevated platforms , including satellites, airborne systems, and Unmanned Aerial Vehicles (UAVs).

In this paper, we present our work toward the development of a clutter loss model for slant paths. This loss must be added to that due to free space to work out the overall signal decay between a transmitter on the ground and an elevated receiver: satellite, airborne platform, UAV, etc. and vice versa. The calculation of this parameter is relevant in interference studies, especially at this point where there is a significant demand for spectrum and there is the need to share bands between different applications and services. We propose here a physical-statistical approach which is elevation-dependent while it encompasses all possible azimuths. It smoothly covers a wide range of frequencies from the low UHF to millimeter waves. The modeling is mainly oriented toward interference calculations. This paper presents material we have contributed to ITU-R efforts for developing an improved recommendation (ITU-R Rec. P.2108) on clutter loss modeling.

This paper presents a detailed design, simulation, measurement, and validation of an Inductive Intertwined Frequency Selective Surface (IIFSS) employing a 2.5D configuration (2.5DIIFSS). The proposed unit cell achieves high miniaturization, with dimensions as small as 0.0096λ₀ × 0.0096λ₀ at 0.268 GHz, using 4 vias per unit cell. The compact design delivers a fractional bandwidth of 87% for the passband associated with the fundamental harmonic. Additionally, the unique 2.5D configuration introduces extra inductance and capacitance, effectively shifting higher harmonics to higher frequencies, thus maintaining a stable stop band beyond the fundamental harmonic. The angular stability analysis reveals minimal variation up to an incidence angle of 60° for both TE and TM modes across the fundamental harmonic. To elucidate the underlying physics, an equivalent circuit model was developed, accurately capturing the fundamental harmonic behavior of the structure. To further validate the design and demonstrate its scalability, a prototype was designed and fabricated for operation at 2.4 GHz, addressing the measurement challenges associated with the original 0.268 GHz design. This prototype was rigorously tested in a transmission regime, with measurement results showing good agreement with simulation data, thereby confirming the efficacy and practicality of the proposed design.

The horizontal distribution of the vertical gradient of atmospheric refractivity is important for the assessment of the propagation of electromagnetic waves on nearly horizontal paths. A 5‐year set of meteorological data, obtained from the ERA‐Interim numerical weather product, has been used to analyze this distribution statistically. Vertical gradient maps of the Central European region have been processed to derive empirical probability distributions of the difference between local point gradient values at two locations. The difference of the effective (path‐averaged) gradient along the path and the local gradient is shown to be statistically distributed so that the quantiles increase linearly with distance in the interval from 100 to 1000 km. Finally, a spatial correlation function is obtained and described by an exponential model with correlation distances determined in the range of 400–700 km.

Following the increasing popularity of unmanned aerial vehicles (UAVs) for remote sensing applications, the reliable operation under a number of various radio wave propagation conditions is required. Assuming common outdoor scenarios, the presence of trees in the vicinity of a UAV or its ground terminal is highly probable. However, such a scenario is very difficult to address from a radio wave propagation point of view. Recently, an approach based on physical optics (PO) and the multiple scattering theory (MST) has been proposed by the authors, which enables fast and straightforward predictions of tree-scattered fields at microwave frequencies. In this paper, this approach is developed further into a generative model capable of providing both the narrowband and wideband synthetic time series of received/transmitted signals which are needed for both UAV communications and remote sensing applications in the presence of scattering from tree canopies. The proposed channel synthesizer is validated using both an artificially-generated scenario and actual experimental dataset.

An analysis of the accuracy of several deterministic and semideterministic propagation models related to calculating clutter loss for low elevation links is presented. Predictions are compared with measurements carried out at 2 GHz over three locations. By comparing prediction and measurement techniques, improved predictive capabilities of deterministic models are demonstrated and quantified in cases where a description of the propagation environment exists and an air-to-ground scenario is considered.

A detailed analysis of 1-year, long-term experimental measurements of signal enhancement at a terrestrial link between two cities in the Czech Republic is presented with respect to an interference and frequency coordination analysis based on recommendation ITU-R P.452-14. Three different models for terrain diffraction are considered to demonstrate a significant influence on signal enhancement predictions. The impact of radiometeorological parameters, serving as inputs for recommendation ITU-R P.452-14, was addressed by utilizing available ITU-R and ERA-Interim maps, or, their locally obtained values. Monthly and seasonal variations are discussed in addition to the 1-year signal enhancement statistics.

Tests using three selected terrain diffraction models, three available experimental datasets and three digital elevation products with different horizontal and vertical resolutions were carried out to assess the role of input terrain profile in diffraction modeling. It is demonstrated that low-resolution terrain maps are not, generally speaking, suitable for terrain diffraction modeling. Further, it is also shown that utilizing digital elevation products with medium spatial resolution results in predictions close to the case when high-resolution terrain maps are considered.