1 Radio Frequency Pulsar Signal Simulator Jo˜ ao Santos, Gonc ¸alo Tavares, Jorge Fernandes, Diogo Brito INESC-ID / Instituto Superior T´ ecnico - TU Lisbon, Portugal Email: joao.carlos.palma.santos@gmail.com, {goncalo.tavares,jorge.fernandes,diogo.brito}@inesd-id.pt Abstract—Pulsars are subject of research by agencies such as NASA, ESA, and others, to study gravitational waves, the cosmos itself, deep-space, plane localization methods and other topics. This paper approaches the characteristics of the signals emitted by these objects and implements a prototype that generates a signal resembling the signals emitted by pulsars, a pulsar simulator. This prototype can be used to test pulsar signal receivers in real time, since testing them with real signals is inconvenient given the interferences they are subject until reaching Earth. The design and implementation of the electronic system of the prototype, and its results are all reported in this thesis. The pulsar simulator is composed of several blocks, namely, a profile generator, noise generators, mixers and adders, all of which are essential to obtain the desired signal. The constructed prototype simulates three different pulsar signals, in real time, is portable, and is capable of adjusting the Signal to Noise Ratio (SNR) and bandwidth of the generated signals, as desired. I. I NTRODUCTION Pulsar are highly magnetized rotating neutron stars which emit a very wide electromagnetic radiation [1], that scatters throughout the universe, [2]. They have great rotational speed and a very strong magnetic field, thus emitting an electromag- netic beam, thus emitting light in short periods of time, similar to a lighthouse. Fig. 1, from [1], illustrates the basic structure of a pulsar. Fig. 1: Basic structure of a pulsar [1] Space agencies such as ESA, NASA and other institutions have investigated these objects, their characteristics, variety and how they may contribute to humanity. Today, more than a thousand pulsars are known and new ones are being discovered everyday. For instance, pulsars are commonly used to study gravitational waves. Also, the PulsarPlane project investigates the possibility of a navigation system inside the Earth’s atmosphere using signals from millisecond radio pulsars [3]. In the PulsarPlane project, the feasibility for a navigation method based in acquiring the signals emitted by a few pulsars, and thus identify a plane’s location was evaluated [4]. Even though these receivers are purposely designed to acquire these signals they can’t be properly tested with actual pulsar signals while on earth due to several factors, such as distance, Radio- frequency interferences, and the Earth’s atmosphere [3]. These receivers could be tested with a source capable of producing a signal with the same characteristics as pulsar signals, in other words, they could be tested by a pulsar simulator, which hasn’t been developed so far. This also brings the opportunity to study new tools of simulation based on signal processing, new and improved architectures of genera- tors, a way to test receivers anywhere, and in real time, and even to generate pulsar data without allocating slots in radio telescopes. The aim of this work is to successfully implement a pulsar simulator prototype that will serve to test pulsar receiver systems. The pulsar simulator must have several adjustable parameters, that will be discussed further. Furthermore, it must be a portable system and perform a real time simulation. The deployed system is an analogue system, mainly because of the fact that it can output signals with wider ranges of frequency than a digital system since the last one would be dependant of the bandwidth of a converting component, such as a Digital to Analogue Converter (DAC). This extended abstract is divided in six sections. The first section introduces the pulsar simulator, its background, motivation, objectives and the structure of this paper. Section II formulates the problem, specifying the characteristics of pulsar signals and establishes a bond between these characteristics and the design of the pulsar simulator. Section III approaches the employment of the pulsar simulator system. Section IV approaches the system’s results. Section V the conclusions of the work are summarized. And finally, in section VI the acknowledgements are given. II. PULSAR SIGNALS The signal emitted by pulsars has a broadband electromagnetic radiation from radio (that can range from a few kHz to a few hundred GHz) to X and γ -ray frequencies (that can range from dozens of PHz to dozens of EHz). Each pulsar has an individual signature, its pulse, which has a particular shape and period [1]. The pulsar signal s p (t) corresponds to a random signal with time-varying statistics, at the pulsar’s location, and can be expressed as Eq. 1. s p (t)= a(t) · p rot (t)= a(t) · ∞  n=-∞ p(t - nT p ) (1)