A N. Alkhafaji’s research while affiliated with University of Baghdad and other places

In this article, a measurement technique based on the Nicholson–Ross–Weir formulation to retrieve the complex permittivity, "r = "0 r+i"r, of materials from the measured S-parameters, S11 and S12, at the X-band, 8 GHz up to 12 GHz, is discussed. Finite element method simulation based on Comsol software package formulations is invoked to evaluate the S-parameters based on the retrieved complex permittivity and to compare them to their measurements. Then, a parametric study is conducted for the simulation to match the numerical results to their identical measurements by considering the retrieved permittivity as an initial guess. Nevertheless, the complex permittivity is measured using network/impedance material analyzer in the frequency range from 1 MHz to 1.2 GHz to be compared against the evaluated values at the X-band. A PTFE sample is considered as an example to validate the precision of the proposed method. The obtained "r is found to be about 2.04􀀀i0.0001, which is very close to the manufacturer range. Finally, excellent agreement between the measured and simulated S-parameters is observed

In this paper, a new bandpass filter is designed using two open-loop resonators with polygonal forms. The use of polygonal forms leads to compact size and broad bandwidth behavior. The overall filter dimensions are 8×16 mm2, which correspond to 0.4λg × 0.2λg using a substrate with Rogers Ro 3010 with a relative permittivity of 10.2 and a thickness of 1.5 mm. The resulting filter exhibits enhanced passband behavior with two transmission zeros. The resulting passband has a centre frequency of 2.40 GHz, and a bandwidth of 230 MHz and fractional bandwidth (FBW) of 10%, with return loss of about −26 dB and insertion loss equal to −0.8 dB. The locations of the two transmission zeros are at 2.176 GHz and 2.638 GHz, which means that there is a sharp cut before and beyond the passband. The simulation and performance evaluation of the proposed filter were carried out using Microwave Studio Suite (MWS) Computer Simulation Technology (CST). The resulting performance of the proposed filter makes it very desirable for Bluetooth and WLAN applications (IEEE 802.11n).