فهرست مطالب s. h. mohseni armaki

This study aims to present a new structure based on coaxial waveguide, which can change the bandwidth, return losses, and input impedance by changing the plasma parameters of the coaxial waveguide. This structure consists of a metal body and a gas tube inside it, which uses a high voltage alternating current converter, can change the plasma parameters and, consequently the waveguide parameters. The input and output of the waveguide are also designed using the indirect capacitive coupling method. In the Field of plasma research and related emerging technologies, recently, it has achieved a special place in various industries such as radar and Aerospace industries. The creation of telecommunication structures such as antennas and Waveguides with plasma, has given features such as adaptability, the ability to reconfigure the characteristics of the structure, and improve the sensitivity of this type of structure. By applying and changing the plasma excitation parameters, a change in the bandwidth was observed in the frequency band range of 0.5-4 GHz and a maximum of 1.38 GHz. Also, increasing the intensity of the excitation current improved the return losses in the resonance frequencies and, on the other hand, increased the band ripple. According to the results, the change of Plasma parameters depends on the change of plasma excitation frequency, and the value of Excitation current applied. As the Value of excitation current increases, the matching to the resonance frequencies improves, but on the other hand, the passband ripple of the plasma waveguide filter increases. As the plasma excitation pulse frequency increases, the bandwidth and resonance frequencies change to higher frequencies, and the matching to the resonance frequencies improves. But on the other hand, the passband ripple increases. This new waveguide filter can be used in cognitive/ adaptive telecommunication systems due to the constant change of frequency band.

Unlike conventional phased arrays that produce an angle-dependent radiation pattern, frequency diverse arrays (FDA) generate a radiation pattern dependent on the range, angle, and time, which results in the use of a frequency offset instead of the phase shift along the array. In recent years, a lot of research has been carried out on this topic, and various frequency arrangements, both linear and nonlinear, have been proposed which mainly use continuous waves to excite elements of array. In this paper, we use pulses instead of continuous waves, to stimulate the array elements, and we extend the array geometry to two dimensions, and we plot its radiation pattern for different times. The beam is formed and focused on a specific point by applying a coefficient weighting in the array.

In this paper, a Gaussian corrugated profile horn is designed, simulated and compared with a Gaussian profile horn with flat wall, at central frequency of 94 GHz. The proposed horn antenna consists of a corrugated section(mode converter and phase section) and a Gaussian profile section. The Gaussian profile Horn Antenna provides a smooth transition from waveguide to aperture, which improves matching between antenna and free space. This ensures better matching, better radiation pattern, more bandwidth and increases overall system efficiency. The corrugated horn also has low edge diffraction, improved pattern symmetry, and reduced transverse polarization, because these corrugations create same boundary conditions for electric and magnetic fields. The  symmetry pattern on the E and H orthogonal planes, the broad bandwidth as well as low sidelobes of this designed corrugated Gaussian profile horn, make it a good representative for use as a feed in millimeter wave imaging system in W band.