Abstract

A key feature required by next generation satellite platforms (commercial, military, and scientific ones) is the ability to exploit multiple radio bands and data formats to communicate with the highest number of ground stations. In this scenario, microwave photonics (MWP) techniques can be instrumental in implementation of software-defined radio (SDR) systems featuring high frequency flexibility and data transparency. Using the MWP, a single photonic SDR system covering transmissions from S band to Ka band (and above) can be demonstrated, surpassing the capabilities of commercial state-of-the-art electronic SDR systems that are limited to ~20GHz in the most up-to-date cases. We propose and demonstrate an innovative SDR Multiband Transponder to be used in Ground Stations (or in satellite platforms), capable of simultaneously managing bidirectional communications in X and Ka band, using a single reference photonic oscillator and easily available digital electronics. The general architecture of the photonics-based Multiband Transponder consisting of an SDR unit and RF/IF modules is shown in Fig. 1(a). The heart of the proposed transponder consists in a generic Photonic Mixer that replaces the frequency converters (one per operating sub-band) commonly used in traditional architectures. The Photonic Mixer is composed of a Mach Zehnder modulator (MZM) and a photodiode (PD) and is driven by a laser comb working as Photonic Local Oscillator (LO) with comb spacing f_LO. The f_LO and f_IF are chosen such that N·f_LO ± f_IF falls within the given frequency range, N is comb harmonic number. This solution performs a so-called "band-pass" sampling [1] and is capable of simultaneously realizing both up-conversion and down-conversion over a wide range of spectral bands, virtually from DC to above 40 GHz. Single Photonic LO is shared by multiple RF/IF modules and is composed of a laser followed by two cascaded MZMs, the second of which is driven by RF clock after a x3 frequency multiplication for better spectral flatness and RF/IF and IF/RF conversion efficiency [2]. A proof-of-concept implementation of proposed transponder architecture was realized, and its relevant performance in terms of conversion loss (CL), dynamic range, signal to noise ratio (SNR), noise figure (NF) and error vector magnitude (EVM) was also evaluated, results are reported in Fig. 1(b-e).

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