Adaptive Clutter Cancellation Techniques for Passive Radars

In radar systems, the ambiguity function of the applied illuminator signal essentially determines the detection capabilities. Zero Doppler interference (ZDI) or close targets returns can mask weak target reflections from higher distances. This is particularly the case for passive radars where the illuminator signal is not under the control of the radar designer. In recent times, great efforts have been carried out to research and develop efficiently working filter algorithms. These adaptive algorithms aim to cancel the undesired interference components in order to enhance the useful dynamic range. A number of different algorithms are operating in the space and also in the time domain. Spatial algorithms apply beamforming techniques, while temporal algorithms utilize the available reference signal to suppress the interferences. The main goal of this chapter is to present and compare the available spatial and temporal adaptive interference cancellation techniques in terms of filtering efficiency and computation cost on real-life data

PULSE COMPRESSION IN SEARCH RADAR

Pulse compression is a vvidely used method to maintain the range resolution ot radar while increasing the average power per pulse that can be placed on a target. Using all these methods a wideband modulation is added to the transmitted pulse and a filter matched to this modulation is used in the receiver. There are several kinds of these additional modulations, and each has different properties, therefore simulation of these methods is essential during design of modulation. In this article an overview of pulse compression techniques is given, the benefits and disadvantages of these methods are discussed. Biphase coded systems are detailed, because they are easy to implement with digital hardware. At the end, our simulation hardware and software tools are described, giving some illustrations from the results

ADAPTIVE ALGORITHMS IN RADIO DIRECTION FINDING

Conventional radio direction finding methods suffer a lack in performance under certain configurations of the radio frequency environment. A typical example is the case of two or more transmitters spaced closely in terms of azimuth angle. Several adaptive algorithms have been introduced to enhance the angular resolution and accuracy of radio measurement. Compared to the traditional methods these algorithms provide considerably higher accuracy in determining the direction of arrival and higher grade of radiating source separation can be achieved. In this paper a brief overview of conventional and two adaptive estimation methods is provided as a literature summary, which is followed by a qualitative analysis and comparison of these three methods in terms of dynamic range and resolution as new results. Finally software simulation results are presented to demonstrate the advantages of adaptive methods as well as their sensitivity to versatile performance degrading conditions

Digitalno oblikovanje dijagrama zračenja dvodimenzionalnog antenskog niza za pojas frekvencija X

Our aim is to develop a microwave antenna whose radiation pattern is electronically controlled. The radiation pattern of regular antennas is determined by the Fourier-transform of the complex illumination function on the antenna aperture. This radiation pattern is mechanically fixed so its alteration is impossible. Therefore we construct an antenna system of several antenna elements. All elements are actuated by separate transmitters; we control the amplitude and the phase of the supplying currents of the antenna elements. This way, we are able to control the radiation pattern of the antenna system. The control is computerized so that there is a possibility to change the radiation pattern quickly.Naša je namjera razviti mikrovalnu antenu čijim se dijagramom zračenja može upravljati elektronički. Dijagram zračenja običnih antena odreden je Fourierovom transformacijom kompleksne funkcije pobude aperture antene. Taj je dijagram zračenja odreden izvedbom antene i njegova izmjena nije moguća. Stoga se naš antenski sustav sastoji od više antenskih elemenata. Svi se antenski elementi pobuduju odvojenim odašiljačima pa je moguće ugadati amplitude i faze pobudnih struja antenskih elemenata. Na taj način možemo upravljati dijagramom zračenja antenskog sustava. Upravljanje je izvedeno pomoću računala tako da je moguće vrlo brzo mijenjati dijagram zračenja

Quad channel software defined receiver for passive radar application

In recent times the growing utilization of the electromagnetic environment brings the passive radar researches more and more to the fore. For the utilization of the wide range of illuminators of opportunity the application of wideband radio receivers is required. At the same time the multichannel receiver structure has also critical importance in target direction finding and interference suppression. This paper presents the development of a multichannel software defined receiver specifically for passive radar applications. One of the relevant feature of the developed receiver platform is its up-to-date SoC (System on hip) based structure, which greatly enhance the integration and signal processing capacity of the system, all while keeping the costs low. The software defined operation of the discussed receiver system is demonstrated with using DVB-T (Digital Video Broadcast – Terrestrial) signal as illuminator of opportunity. During this demonstration the multichannel capabilities of the realized system are also tested with real data using direction finding and beamforming algorithms

Space-Time Adaptive Cancellation in Passive Radar Systems

A critical issue in the realization of passive radar systems is the effective suppression of the zero Doppler interference (ZDI). The performance of the clutter cancellation relies much on the used algorithms. Several state-of-the-art approaches consist in the independent use of spatial and temporal algorithms for ZDI suppression. In this paper, a novel interference cancellation algorithm is proposed, which jointly exploits the available information from both space and time domains. We call this novel method Space-Time Adaptive Cancellation (STAC), and it differs from previous schemes included among the tools of Space-Time Adaptive Processing (STAP). The STAC algorithm is able to cancel out the high power direct and multipath signals on all the surveillance antenna channels prior to the beamforming and other space domain processing methods. The proposed preprocessing technique facilitates the detection of targets even in the direction of the illuminator or large static scatterers. Moreover, the interference rejection capability is also enhanced in the space domain. The performance of the presented algorithm is verified through simulations and field measurements. The experiments show improvement over the currently available filtering techniques

First operation of the KATRIN experiment with tritium

The determination of the neutrino mass is one of the major challenges in astroparticle physics today. Direct neutrino mass experiments, based solely on the kinematics of β β -decay, provide a largely model-independent probe to the neutrino mass scale. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly measure the effective electron antineutrino mass with a sensitivity of 0.2 eV 0.2 eV (90% 90% CL). In this work we report on the first operation of KATRIN with tritium which took place in 2018. During this commissioning phase of the tritium circulation system, excellent agreement of the theoretical prediction with the recorded spectra was found and stable conditions over a time period of 13 days could be established. These results are an essential prerequisite for the subsequent neutrino mass measurements with KATRIN in 2019