In this paper optimal design of time modulated linear antenna arrays (TMLAA) with optimal placement of nulls in the desired direction of elevation plane has been dealt with the approach based on evolutionary algorithm like collective animal behaviour (CAB). Analysis has been done in theoretical and practical environment. Firstly the current excitation weights of the linear array of isotropic elements have been optimized by CAB is applied to improve null performance of TMLAA by Radio Frequency (RF) switch in MATLAB environment. The nulls positions of a TMLAA can be reduced significantly by optimizing the static excitation amplitudes and proper design of switch-on time intervals of each element. The CAB adjusts the current excitation amplitude of each element to place deeper nulls in the desired directions. Secondly the obtained optimal current excitation weight of the array factor is practically implemented in computer simulation technology- microwave studio (CST- MWS) environment. The array of microstrip patch antenna has been designed to operate at 5.85 GHz.
TopIntroduction
Microstrip patch antennas have very attractive features and advantages due to their robustness, easy to fabricate and their small size and low cost, ease of installation and integration with feed networks (Ballanis, 2005). One of the downbeat limitations of this type of antenna is that it has limited bandwidth of operation at which the antenna can perform comfortably. These characteristics become an important factor while designing the antenna. This is mainly used in wireless and mobile communication. Patch antenna consists of a substrate followed by a ground plane at the bottom of the substrate. A patch antenna is placed at the top of the substrate which is made up of a perfect electrical conductor. This is connected to the feed line from where the patch is being excited. Substrate is made up of a perfectly dielectric material and the most commonly used material is FR-4 (Stutzman & Thiele, 2012). There are many ways to operate one antenna in the multiple bands. One way may be the perturbation slots in the patch and the other way may is the fractal approach. Due to the recent improved technologies coming day by day in the real world the enabled communication devices have to have smaller size. The size of the antenna is a key factor for the design of any communication devices or any antenna enabled devices. Due to this the small size antenna has a very high demand for WLAN and Wi-MAX. This technology gives great freedom and flexibility to move around the wide coverage area with all-time connection with network. Different applications of communication require various different types of antenna to improve the transmission and the reception of the desired signal.
During the last couple of decade time modulated antenna arrays have turned into an emergent research domain for the antenna designers due to their benefits in excess of conventional array antennas. Shanks and Bickmore first time introduced the exploitation of the time modulation technique as an additional degree of freedom for the synthesis of antenna arrays (Schrank, 1983). Time-modulated antenna arrays can be used to achieve the desired radiation patterns by utilizing on-off switching of the array elements (Hardel, Yalapragada, Mandal, & Bhattacharjee, 2011; Yang, Gan, & Tan, 2005; Yang, Gan, & Qing, 2002; Yang, Gan, & Tan, 2003; Fondevila, Brégains, Ares, & Moreno, 2004; Yang, Gan, Quing, & Tan, 2005; Yang, Gan, & Tan, 2004; Yang, Gan, & Quing, 2003). This feature can aid to accomplish a better radiation pattern than those of the traditional antenna array synthesis methods (Haupt, 1997; Steyskal, Shore, & Haupt, 1986; Haupt 1988; Chung & Haupt, 1999; Mandal, Ghoshal & Bhattacharjee, 2009a; Mandal, Ghoshal & Bhattacharjee, 2009b; Chen, Jan, Lee, & Chen, 2011; Ram, Mandal, Kar, & Ghoshal, 2013). For the implementation of any practical antenna, the consideration of parameter is very important. The simulation software used here is computer simulation technology Microwave Studio (CST-MW), which is a computing package established on Finite Integration Technique (FIT). CST-MW is the widely and simple to use electromagnetic field simulation software (Onol & Ergul, 2014; Jayasinghe, Anguera, & Uduwawala, 2013; Sorokosz, Zieniutycz, Pergol, & Mazur, 2011). It overtures discriminative, effectual simulation explication for the electromagnetic design and analysis. CST-MS is a powerful technique used in the range of low frequency to a very high frequency. After structure designing automatic meshing procedure is applied before a simulation is started. CST-MS works on Method on Demand which gives the choice of simulate or mesh type which suits for the particular problem. Patch antennas are low cost, have a low profile and are easily fabricated antenna. Due to simple structure it is widely used in telecommunication. It is widely used in cellular mobile communication. Also it is useful in designing of different types of antenna array like linear array, circular array and planar array. These days it is widely used in conformal array designing. An approach based on CAB (Ram, Mandal, Kar, & Ghoshal, 2013) algorithm is applied to introduce deeper nulls in the radiation pattern. Further, results obtained from CAB are implemented by the CST-MWS simulation software (CST, 2013) for the validation purpose. There are other research works carried out to improve the particular antenna elements (Onol & Ergul, 2014; Jayasinghe, Anguera, & Uduwawala, 2013; Pergol, Mazur, Zieniutycz, & Sorokosz, 2011). Evolutionary algorithms applied in the different field of engineering are also shown in (Kułakowski, Alonso, López, Ludwin, Haro, 2016).