Ali Mirkamali

A novel quadrifilar helix antenna for use in LEO satellite communications

A spherical quadrifilar helix antenna (SQHA) is introduced for producing a saddle point shaped radiation pattern. Radiation characteristics of the antenna have been simulated and the results have been compared with the characteristics of the cylindrical quadrifilar helix antenna (CQHA) which was previously used for this purpose. The results show an improvement in radiation pattern of the proposed antenna in comparison with the previous antenna.

Wideband Reconfigurable Printed Dipole Antenna with Harmonic Trap

Reconfigurable antennas have received a great deal of attention for their applications in wireless communications in recent years. They can be used for changing the operation frequency [1]-[6] or changing the radiation pattern [7]-[9]. In [1] a reconfigurable microstrip antenna was designed by placing MEMS series switches at the radiating edge. The series switches connect extra sections of transmission line to the microstrip antenna, thereby lowering its resonant frequency. In [2] a micromachined membrane was used as the ground plane below the microstrip patch antenna to design a frequency-agile patch antenna. In [3] a square patch antenna with switchable slots was proposed for dual band circular polarization operation. A dual band dipole using series MEMS switches was presented in [4] and a dual band reconfigurable Yagi antenna in [5]. A single-fed resonant slot, loaded with a series of PIN diodes switches, was designed in [6]. In [7] it was shown that by using RF switches the radiation pattern of the Hilbert curve fractal antenna could be made adaptively reconfigurable and also resonance frequency of the antenna was tunable by using the switches. In [8] a beam-switched Rhombic antenna was proposed. In [9] a reconfigurable single turn square microstrip spiral antenna was presented which can be reconfigurable in radiation pattern and frequency.

A modified broadband transmission line model for rectangular patch antennas

The purpose of this paper is to present a broadband circuit model for rectangular patch antennas. It has been shown that how the transmission line model can still be used to determine the input characteristic over a large band of frequencies with minor adjustments. The models developed by Deanley and Pues have been chosen as the basis for this work as they fairly complete and give good results. Pues model has been applied with adjustment for fundamental mode, whereas for obtaining accurate model for higher modes, Wilkinson power divider is used to combine them and filters and matching networks are added to obtain broadband circuit model, the effect of higher order modes excited in the patch, can easily be incorporated in CAD software, with little computational effort. Eventually, we have introduced a broadband circuit model for rectangular microstrip antennas. Finally our results are compared with the results obtained form Method of Moment for same antennas.

Ground Plane Effect on the Multi-band Multiple Ring Monopole Antenna

Multi-band and wideband monopole antennas due to their merits such as near omni-directional radiation patterns, simple structure and low cost have attracted a great deal of attention for modern wireless communication systems. Among these are circular disk and multiple ring monopole antennas. The circular disk monopole antenna with a very large impedance bandwidth was introduced in [1] and [2]. In [3] the effect of changing the circular to an elliptical disk was investigated. The microstrip fed monopole disk antenna, which is suitable to connect to printed circuit boards, was presented in [4]. The multi-band multiple ring monopole antenna was introduced in [5] and [6]. This antenna consists of a set of self-similar circular rings that are superimposed to form the antenna. Comparison between the multiple ring monopole antenna characteristics and disk monopole antenna shows that radiation pattern of the multiple ring monopole antenna at higher frequencies is better than the disk monopole antenna. In [7] this antenna was investigated more and the effect of the ellipticity ratio on elliptical multiple ring antenna was proposed. It has been shown that the wider bandwidths can be obtained by decreasing the ellipticity ratio. In this paper the effect of the changing the height from the ground plane perpendicular to the antenna plane and changing the position of the ground plane from perpendicular to parallel to the antenna plane, which leads to the microstrip fed multiple ring monopole antenna, on the multi-band multiple ring monopole antenna are presented. The results show that at higher frequency bands better matching can be obtained for smaller height from the perpendicular ground plane and it does not affect on the lower frequency bands. It is also shown that changing the position of the ground plane from perpendicular to parallel to the antenna plane improves the matching at the first band significantly. The microstrip fed multiple ring antenna can be integrated with printed circuit boards and used in low-profile applications.

A compact broadband slot-loaded Bowtie patch antenna

A compact broadband microstrip bowtie antenna is proposed. By loading properly arranged slots in a bowtie patch antenna, broadband operation of a bowtie patch antenna are presented. The maximum impedance bandwidth achieved is 27% centered around 1.8 GHz, with good pattern characteristics.

Influence of thickness of the rings and height from the ground plane on the input characteristics of the multiple ring monopole antennas

In this paper the effects of changing the thickness of the rings and height from the ground on the return loss of the multiple ring monopole antenna are presented. It is experimentally shown that the changing of the thickness of the rings causes a frequency shift at the fourth and the fifth bands but it does not have a significant effect on the lower bands. In addition, better matching at higher frequency bands can be obtained for smaller height from the ground plane but it does not affect on the lower frequency bands