Reduction of Mutual Coupling and Return Loss in Microstrip Array Antennas Using Concave Rectangular Patches

An effective solution to reduce both the mutual coupling and return loss of a microstrip array antenna consisting of rectangular patches is proposed. The patch is made concave in both horizontal and vertical sides. Applying the proposed structure to a microstrip array antenna having two elements, the effects of patch concavity on the mutual coupling and return loss are simulated and studied. To obtain a concave rectangular patch array antenna having low amounts of mutual coupling and return loss, the patch length and width as well as the amounts of concavities are optimized using an enhanced genetic algorithm. To verify the simulation results, then, the optimal array antenna is fabricated. The simulation and experimental results confirm that the optimal concave rectangular array antenna has low amounts of mutual coupling and return loss. 1. Introduction Because of its benefits, such as small size, simple manufacturing, flexibility, light weight, and low cost, the usage of microstrip array antennas is quickly increasing [1–4]. They are widely used in applications such as pattern beam forming, smart antennas, and electronic scanning radars [5, 6]. Mutual coupling and return loss are important factors which must be considered in the design of array antennas. When one array element radiates, a portion of its radiated power is absorbed by other elements and induces current on them. The mutual coupling effect leads to problems such as beam forming error, scanning error, and input power wastage [7–9]. Therefore, the effect of mutual coupling must be reduced in array antenna design. To do this, several methods such as changing feed position, feed structure, or patch shape have been reported [10–14]. Employing concave rectangular patches [15] instead of ordinary ones, an efficient solution to reduce mutual coupling in a linear array of microstrip antennas was proposed in [10]. The effectiveness of the proposed method was approved by the simulation results. In this paper, the microstrip array antennas with both ordinary and concave rectangular patches are fabricated and tested to verify the simulation results given in [10]. 2. Structure of Array Antenna The antenna structure includes two dielectric layers. The patches are placed on the upper conductive layer. The middle conductive layer is a feed layer, and the lower one is assumed to be an infinite ground plane. Using commercial microstrip boards data sheets, the relative permittivity, , of the substrate and its dissipation factor, , are equal to 2.2 and 0.0009, respectively. Also, the thickness of dielectric