Abstract-In this paper, a wideband microstrip antenna for Xband (8.2 GHz-12.4 GHz) applications is introduced. First, simple patch antennas are studied, and a narrowband reflectarray antenna is designed. The resultant design demonstrates better performance than the previously published narrowband microstrip reflectarray antennas. The important features of the employed elements are simple structure, linear operation, and use of Radio Frequency Micro Electro Mechanical Systems (RF MEMS) switches for programmable pattern control. Next, employing our novel method, the designed narrowband structure is converted to broadband reflectarray antenna that can cover the whole X band. This novel idea is based on introducing several ground plane slots and controlling their electrical lengths by RF MEMS switches. By means of this method, 952 and 587 degree phase swing are achieved for continuous and discrete slot length variations, respectively. Application of this method along with smaller switches results in phase swing improvement of up to 1616 degree. In all structures a RT duroid (5880) substrate is selected to lower the back radiation. The achieved return loss in all cases is less than 0.32 dB. In comparison with the previous publications, our novel bandwidth enhancement technique has more generalization capability and results in single layered broadband reconfigurable microstrip reflectarray antennas with linear phase swing, lower cost, and ease of RF MEMS implementation.
Abstract-Modeling of a ferroelectric interdigital capacitor (IDC) and its incorporating in composite right/left-handed (CRLH) unit cells is represented. To evaluate the capacitance of a multi-layered IDC structures, conformal mapping and partial capacitance methods are utilized. Furthermore, the partial displacement method is utilized to calculate the electric field distribution and the its relation in the ferroelectric layer to applied voltage is obtained. Using this relation in a phenomenological model, dependency of the relative permittivity of ferroelectric on the applied voltage is obtained. The designed unit cell is comprised of IDCs and spiral inductors. To alter the propagation constant of the unit cell by varying the applied voltage, a thin layer of Ba 0.5 Sr 0.5 T iO 3 (BST-0.5) ferroelectric is incorporated underneath an IDC, called BST-0.5 varactor. The periodic structure based on the designed unit cell leads to a CRLH LWA. The Tunability of the periodic structure with three unit cell is demonstrated by varying the relative permittivity of the ferroelectric layer.
Abstract-Design procedure for a modified Composite Right/Left Handed (CRLH) unit cell is represented. The ferroelectric interdigital capacitor (IDC) is used as a tuned capacitor, and spiral inductor is utilized to implement inductors. A modified CRLH unit cell is attained by moving the shunt inductor of conventional unit cell to both ends with doubled values. In this manner, only one bias network would be required for each unit cell. The parameters of the designed unit cell are obtained so that the Bloch impedance to be equal to 50 Ω and the Bloch propagation constant to have one zero at the operational frequency. The operational frequency is chosen equal to 11.45 GHz, which is in the Ku-band and in middle of the up-link satellite communications. To design the modified unit cell, initially, the unit cell without a shunt capacitor is constructed. This would result in Π-model structure for which the element dimensions are varied to reach the desired values. Next, the shunt capacitor is added to the model and its length is varied until the balanced condition is achieved.
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