Journal of Electromagnetic Analysis and Applications, 2013, 5, 79-84 http://dx.doi.org/10.4236/jemaa.2013.52013 Published Online February 2013 (http://www.scirp.org/journal/jemaa) 79 Wideband Demodulator Based on Five-Port Correlator for Channel Sounding Applications Imen Sfar, Lotfi Osman, Ali Gharsallah “CSEHF” Research Unit, Department of Physics, Faculty of Sciences of Tunis, Tunis El Manar University, Tunis, Tunisia. Email: imen.sfar@voila.fr, lotfi.osman@supcom.rnu.tn, ali.gharsallah@gmail.com Received November 14 th , 2012; revised December 16 th , 2012; accepted December 29 th , 2012 ABSTRACT We present in this paper a wideband RF demodulator using a five-port correlator and a power detector for channel sounding applications. The demodulator has been fabricated using microstrip components. The correlator receives from the five-port qualities that allow it to be low-cost and less sensitive to the phase and amplitude imbalances. A calibra- tion procedure is proposed to find the complex envelope of the RF signal applied at the input of the five-port correlator. Simulation with Advanced Design System software and measurement results have been conducted to demonstrate its capabilities as a RF signal demodulator operating in a wideband around 2.4 GHz frequency. Keywords: Calibration Procedure; Channel Sounder; Diode Power Detector; Five-Port Correlator 1. Introduction Wireless communication systems development and opti- mization require a good knowledge of the radio propaga- tion channel. The wideband channel sounder has been al- ready discussed by several studies in the time-Frequency domain [1-3], but a few are carried out in the spatial do- main [4,5]. An experimental characterization of the com- plex wideband propagation channel is necessary in order to propose models for the development of such systems. Single Input Multiple Output (SIMO) or Multiple Input Multiple Output (MIMO) wideband systems use this complexity to increase the channel capacity [6,7]. To op- timize the performance of these techniques, it is impor- tant to quantify the propagation channel parameters in time and space domain [8,9]. Sounders are the tools used to characterize a radio channel. Several wideband sound- ers are based on Single Input Single Output (SISO) sys- tem using a Vector Network Analyzer (VNA) for fre- quency domain characterization, and digital oscilloscope for time domain characterization [10]. But these systems are very constraining in terms of measure duration and equipment size, and do not provide the spatial charac- terization by measurement. MIMO system is more rec- ommended to characterize the space domain [11]. It used a discriminator circuit to obtain the channel response. Five-port correlator is the phase/amplitude discriminator chosen to perform the sounding of the MIMO propaga- tion channel operating in ISM frequency band. Five-port wave correlator carries out a direct conversion of RF sig- nal like an I-Q system, but it has a redundant access, which makes the correlator more robust against the phase and amplitude unbalance of the local oscillator (LO) [12]. In addition, the five-port has the ability to be easily inte- grated thanks to its small size and low-cost production [13]. The object of this paper is to present a new homodyne demodulator based on a five-port correlator and power detectors in order to design a low-cost/high performance circuit. Simulation study was validated by measurement performed on the fabricate five-port. The paper is organ- ized into six sections. The operating principle of the five- port correlator and its architecture will be presented in Sections 2 and 3, respectively. The calibration method will be detailed in Section 4; and in Section 5, measure- ment results of the prototype will be exposed. Section 6 will conclude this study. 2. Description of the Five-Port Correlator The five-port correlator is described in Figure 1. It con- sists of an RF interferometer circuit with two inputs, three outputs, and three RF power detectors instead of conventional mixers. The RF five-port can be designed with a five-port ring [12]. This linear circuit performs three vectorial additions of the two input signals a 1 (RF signal) and a 2 (LO signal), the power detectors measure the power of these three interferometric mixtures. The five-port correlator is modeled by the following equations: 3, 4, 5 , k LO k RF k Aa Ba    (1) Copyright © 2013 SciRes. JEMAA