A Simultaneous Dual Channel Communication Concept over 4D Arrays in Satellite Networks Yasin YAVUZ, Ertugrul AKSOY, Mert KARAHAN Department of Electrical and Electronics Engineering Engineering Faculty, Gazi University Maltepe, Ankara, Turkiye Abstract— In this study, a dual channel transmission concept over a single array with different frequencies and angle of arrivals without time division is presented. A time modulation scheme is applied to an ordinary linear array and the difference between main and fundamental radiation which can be steered indepen- dently with different frequencies is exploited in order to achieve a dual channel. By this way, both the so-called wasted power may be used in communication, and an independently steerable dual beam array may be constructed which may be utilized especially in multi-terminal communication infrastructures such as satellite networks. Since it is one of the fundamental communication techniques that the advanced ones are constructed on, a dual channel FM receiver structure is presented as an illustrative example to show the proposed concept is utilizable. Keywords—time-modulated linear arrays, dual channel re- ceiver, satellite networks, frequency modulation. I. I NTRODUCTION At the late 1950’s, time is introduced as a new antenna array parameter by Shank and Bickmore in addition to excitation amplitude, excitation phase and Euclidean distance to the system origin and the concept so called time-modulation is approved by Kummer et al. [1], [2]. Since time-modulation requires periodic switching of antenna array elements, time variable becomes a multiplier in array factor. Additionally, as a natural result of periodic switching, infinite number of harmonic (i.e. sideband) radiations occur and some of the power inevitably is transferred to the sidebands [3]. In literature, there are many studies which focus on suppressing the sidebands to prevent power loss and shift the sideband power to the main radiation [4]–[14]. However, Tenant and Chambers proposed at 2007 that instead of suppressing the sidebands, they may be useful in some applications such as direction finding and Tenant experimentally proved the idea at 2010 [15], [16]. Further- more, studies showing that AM and FM reception with time modulated linear antennas (i.e. TMLA) and proposing secure communication using sideband radiations have been done by Yang et al. [17], [18]. In order to use harmonic radiation in different applications, it may be steerable irrelevant from the main radiation and its sidelobe levels should be controllable, so Aksoy proposed a new excitation strategy and a new approach to the harmonic beam steering technique at 2014 [19], [20]. Also a study about dual channel AM receiver using a sideband of the TMLA has been done by Aksoy et al. at 2015 [21]. Antenna arrays are being used in radars and satellite systems but using time-modulation is fairly a new idea. A study using time-modulation to have an isoflux radiation from a satellite system has been done at 2016 by Balderas et al. and it permits the antenna hardware reduction according to equivalent systems [22]. A novel approach may be suggested to use time-modulated arrays as a dual channel receiver to steer the fundamental harmonic radiation to communicate from satellite to satellite and assign main radiation to communicate from satellite to ground communication, or vice versa. In addition a scanning function may also be available without interrupting the main communication using sideband as a receiver. Since this study is aimed to be proof of concept that sidebands may be used as a second –or even third if there is enough power– receiver working on different frequencies without tuning the antenna and also without disturbing the main radiation, frequency modulation (i.e. FM) which is one of the most basic modulation method is selected. This study may easily be expanded to include any digital modulation technique and current demodulation methods but for this paper they stayed out of focus. The rest of the paper is organized as follows: a brief theory about TMLA is given in the next section. Then antenna array design method, calculated parameters and radiation patterns of main and first harmonic radiations are given in third section. In the following section, dual channel receiver and demodulator structure has been examined and the study is concluded in the last section. II. BACKGROUND The array factor of a time modulated linear antenna array which consists of N equally spaced identical elements located along z-axis can be written under far field approximation as F (θ)= N  n=1 I n e jβn e jkd(n−1)cosθ (1) where I n and β n represent the excitation amplitude and excitation phase of n th element, respectively. In addition d is the equal distance between the elements, k =2π/λ stands for wave number and θ is the elevation angle with respect to z-axis.