In this study, a novel Dual-band multiple-feed microstrip antenna is introduced for GNSS applications. The proposed antenna has a compact size of 1548 and counts as a low-cost, low-profile antenna. The mathematical equations of multiple-feed configuration are driven to analyze circular polarization ( ) generation and find the effective parameters on value. It is shown that for an n-feed symmetric antenna, the phase shift of between ports leads to pure , regardless of the electrical field pattern. However, if the first feed electric field has equal value in the x and y direction and also 90 phase shift, the value is increased. A symmetric four-feed configuration is employed on the antenna to generate . Also, fractal circular rings and perturbing sectors are applied to miniaturize the antenna and improve the value. Numerical simulation shows that all feeding network requirements are met and the phase shift is satisfied at both frequencies by using the coupler technique. Furthermore, results show desirable band width of 48 and 60 and high front to back ratio of 16.1 and 14 at =1.227 and =1.575 , respectively. The axial ratio ( ) beam-width at both frequencies is more than 66 .

In this paper, a new X band Metamaterial (MTM) based ferrite phase shifter is presented. The phase shifter is excited by circular polarized wave base on combination of TE10 and TE01 modes in a square waveguide. In order to synthesize negative index material (NIM), negative permeability of ferrite slabs in extraordinary mode is mixed with the negative permitivity of printed periodic metallic wires on substrate, in the same frequency band. By using the introduced new circular polarized MTM based layout, the proposed phase shifter loss is less than 3 dB, while the loss of MTM waveguide phase shifters is about 10 dB. Also, the proposed phase shifter profits the miniaturization property of MTM design usage. The total length of the phase shifter is 2 cm with 360° differential phase shift, compared to common Dual mode phase shifter with 6 cm length in X band.

Metasurfaces are two-dimensional artificial structures which have extraordinary electromagnetic properties. They have been used in myriad of devices such as nano-antennas, cloaking coatings, imaging devices, flat lenses, and polarization converters over a wide range of frequency. Due to high dependency of many devices on incident wave polarization, manipulating the polarization of electromagnetic waves would be useful, especially in the THz regime. In this study, we propose a linear to circular polarization converter (LTC-PC) based on a THz reflective metasurface. For a TE linear polarization incident wave, this structure has two distinct bands; the first one lays in a wideband frequency range of 0.5-1.41 THz, in which the reflected wave would be a left-handed circular polarization (LHCP) with minimum efficiency of 89% and maximum efficiency of more than 95% in 80% of the bandwidth. The second band lays in the narrowband frequency range of 1.45-1.55 THz, resulting a right-handed circular polarization (RHCP) wave with a minimum efficiency of 82%. The proposed polarization converter can be used in optical communication and electronic devices.

circular polarization is one of the most popular polarization approaches used in different communication systems such as radar, satellite, GPS and WiMAX systems. In this article, we want to design a wideband cylindrical antenna with circular polarization and maximum frequency coverage from 1. 7 to 2. 7 GHZ. If the optimum load impedance of the amplifier at different frequencies are close, the antenna can be used as an optimal load for the amplifier. In this paper the output of the antenna after application of signals in the S band is also investigated and the effects of the antenna radiation on the amplifier circuits have been considered to some extent.

Because of special structure, a Dual reflector antenna has beam rotation capability in azimuth and elevation directions. In this structure, the antenna beam can be placed in any point in the space by mechanical movement of twist reflector which it is the most important ability of the antenna. Due to the antenna structure, if the polarization of incident wave is linear, it is expected that the polarization of propagated wave is linear and in the direction of desired design. In this paper, for the first time, a nonlinear relation is extracted that it shows the propagated beam polarization has a polarization rotation. This formula is a mathematic closed form relation. These structures are very useful in airborne radar systems.

The demand for mobile communication systems with high data rate has drawn attention to the millimeter-wave frequencies to increases the channel capacity compared to current 4G cellular networks. So, the fifth generation (5G) mobile communications is presented which is to work in mm-wave frequency band to improve data rate, capacity and latency. One of the challenges of 5G application is the base station and mobile antennas which should be robust against fading. Therefore, in this paper, a two port substrate integrated waveguide (SIW) slot base station antenna for 5G application at 28 GHz is presented. The realized gain of the two-port antenna with a high isolation (20 dB) and circular polarization is 6. 35 dBi. The 5-element array of the two-port antenna with the same excitation can increase the gain 8 dB, but it has some nulls. With phase shift for excitation ports, the nulls are cancelled.