I Zivkovic

CHARACTERIZATION OF MAGNETICALLY LOADED MICROWAVE ABSORBERS

This work presents new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers. Permittivities and permeabilities are extracted from free space transmission measurements for frequencies from 22 up to 140GHz. For validation of the results re∞ection measurements (samples with and without metal backing) are performed and are compared with simulations that use extracted models. The proposed new method solves some shortcomings of the popular methods: extracts both permittivity and permeability only from transmission parameter measurements, gives good results even with noisy data, does not need initial guesses of unknown model parameters.

Free-space transmission method for the characterization of dielectric and magnetic materials at microwave frequencies

In this work we will present new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers (CR Eccosorb). Permittivity and permeability are extracted from free space transmission measurements for frequencies up to 140GHz. For the results validation, reflection measurements (samples with and without metal backing) are performed and are compared with simulations that use extracted models. The same method is applied in complex and frequency dependent permittivitymodel extractionof commercially available epoxies StycastW19andStycast 2850FT.

Development of microwave calibration targets for upcoming ESA missions

Microwave radiometers are widely used for remote sensing and radio astronomical observations. Their absolute accuracy depends on the performance of the blackbody targets which are used for the radiometric calibration. In this paper we summarize the performance aspects of such calibration targets and present different designs for upcoming ESA missions.

A new inovative antenna concept for both narrow band and UWB applications

In this paper, we propose a new antenna structure that can be adjusted for narrow band as well as UWB applications. The proposed antenna is of very simple geometry and easy to manufacture. It is monopole type antenna and made of copper. We present antennas with the same geometrical concept and difierent dimensions. Antenna designed for narrow band operation exhibits 3.7% bandwidth at 800MHz frequency (S11 < i10dB). Two UWB antenna designs exhibit 77% bandwidth (from 2 to 4.5GHz) and 54% bandwidth (from 2.6 to 4.5GHz) and are of smaller size compared to the dielectric resonator antennas (DRA). Furthermore, it can be easily shown that using the proposed geometry broad family of antennas (for operation in various frequency bands) can be designed.

Low Mass Calibration Target for MM-Wave Remote Sensing Instruments

The reliability of millimeter and sub-millimeter wave radiometer measurements is dependent on the accuracy of the loads they employ as calibration targets. In the recent past on-board calibration loads have been developed for a variety of satellite remote sensing instruments. Unfortunately some of these have suffered from calibration inaccuracies which had poor thermal performance of the calibration target as the root cause. Stringent performance parameters of the calibration target such as low reflectivity, high temperature uniformity, low mass and low power consumption combined with low volumetric requirements remain a challenge for the space instrument developer. In this paper we present a novel multi-layer absorber concept for a calibration load which offers an excellent compromise between very good radiometric performance and temperature uniformity and the mass and volumetric constraints required by space-borne calibration targets.

Dielectric loading for bandwidth enhancement of ultra-wide band wire monopole antenna

This work presents the results of numerical simulations and parametric studies of dielectric loaded wire monopole antenna, of which the main advantage is bandwidth enhancement. Introducing dielectric loading makes it possible to tune antenna to operate over a frequency range not covered with unloaded antenna, while maintaining an omnidirectional radiation pattern. The simulations are performed when loading is done with lossy as well as lossless dielectric and the results are compared. The observational frequency range is extended up to 40GHz. In addition, the simulated results are compared with the measured S11 of four fabricated antennas loaded with lossy dielectric and a good agreement is obtained.

Extraction of dielectric and magnetic properties of carbonyl iron powder composites at high frequencies

In this paper, we examine carbonyl iron composites in silicone rubber and epoxy matrices. Transmission measurements were performed at W (70 to 110 GHz) and Ka (26 to 40 GHz) bands and effective permittivity and permeability of composites with 10% volume fraction of carbonyl iron powder (CIP) were extracted at these frequencies. To extract permittivity and permeability of carbonyl iron powder in W and Ka bands, we use Looyenga formula. We extract permittivity and permeability of CIP from both silicone rubber and epoxy based composites and good agreement is achieved.

Characterization of open cell SiC foam material

This paper presents characterization and modeling of microwave characteristics of SiC foam material. Transmission and reflection measurements are performed in X, K and Ka band for the samples of two different pore sizes and three different thicknesses. Effective and frequency dependent dielectric permittivity is extracted for 50PPI 10mm sample, while for the other samples it was not possible because of density gradient in the samples. By calculation of Mie scattering efficiencies approximate magnitude of dominant loss mechanism (scattering or absorption) at certain frequencies is predicted.

Candidate for Tissue Mimicking Material Made of an Epoxy Matrix Loaded with Alginate Microspheres

We present a new composite material containing calcium alginate microspheres incorporated into an epoxy matrix. The new material is mechanically stable and does not degrade over time. Its dielectric properties are extracted by model calculations and compared to the properties of some selected human tissues. Good agreement is observed, which identifles the proposed composite material as a good candidate for the use as a phantom material. The presented material is a two component composite and it is shown how its efiective properties can be predicted by using appropriate mixing formulas.

Alginate beads and epoxy resin composites as candidates for microwave absorbers

This paper presents a new composite material, which is developed by mixing calcium alginate spheres with commercially available epoxies Stycas 2850 FT (s2850) and Stycast W19 (W19). The resulting composite material is examined in terms of transmission and re∞ection coe-cients in microwave frequencies (26 to 40GHz, 70 to 110GHz and 300 to 320GHz). The study reveals that the new material exhibits re∞ection coe-cients much lower than some commercial CR absorbers from the Eccosorb group. The experimental results justify the use of the new composite material as absorber at microwave frequencies.