Due to the features of circular polarization, circular polarized (CP) antennas are very useful for various wireless systems such as satellite communications, global navigation satellite systems, mobile communications, wireless sensors, and direct broadcasting service television reception systems. The CP antenna is very effective in combating multi-path interferences or fading. The reflected radio signal from the ground or other objects will result in a reversal of polarization, that is, right-hand circular polarization (RHCP) reflections show left-hand circular polarization (LHCP). An RHCP antenna will have a rejection of a reflected signal which is LHCP, thus reducing the multi-path interferences from the reflected signals. The second advantage is that CP antenna can reduce the ‘Faraday rotation’ effect due to the ionosphere. The Faraday rotation effect causes a significant signal loss (about 3 dB or more) if linearly polarized signals are employed. Another advantage of using CP antennas is that no strict orientation between transmitting and receiving antennas is required. This is different from linearly polarized antennas which are subject to polarization mismatch losses if arbitrary polarization misalignment occurs between transmitting and receiving antennas. This is useful for mobile satellite communications where it is difficult to maintain constant antenna orientation. With CP, the strength of the received signals is fairly constant regardless of the antenna orientation. These advantages make CP antennas very attractive for many wireless systems.

The letter [1] deals with innovative design for a circularly polarized circular patch antenna featuring coplanar parasitic components. The design consists of a circular patch at the top surrounded by two annular rings and a ground plane with a lateral cross-slot at the bottom. A novel technique is introduced in [2] to reduce the size of circularly polarized (CP) patch antennas by utilizing parasitic shorting strips, which can be adjusted to control the frequency. The research examined different types of shorting strips, including rectangular, U-shaped, and meandering, and demonstrated the possibility of reducing the dimensions and back radiation of a patch antenna without sacrificing favorable CP and load matching properties. In [3] , the proposed antenna is designed to be compact and suitable for Geo-positioning applications. It consists of a meandered ring patch that includes ground in a slotted manner and four parasitic patches. The patch is fed by two orthogonal T-shaped lines to achieve circular polarization. However, these techniques do not make it possible to increase the gain, which is very important for satellite communications.

High directional gain antennas offer a high degree of functionality and security in comparison to other signal transmission systems. These antennas feature a narrow radio beam, and this results in an improvement in the signal’s strength [4] [5] . The letters [6] - [10] detail study and demonstration of a rigorous method which synthesizes the feeds weights by considering the strong cumulative coupling between antennas. These papers consist in considering the couplings to obtain the objective pattern. The work in [11] presents a compact 4-element GNSS antenna array design that achieves a mutual coupling level less than −20 dB. They have used a high isolation method to reduce the mutual coupling between the elements. In [12] , a compact four element high isolation antenna array is presented for GNSS upper L-band application by using a defected ground structure (DGS) and a microwave absorber. These works have the capacity to amplify existing satellite signals. However, they are very complex and have high manufacturing costs.

So, our goal is to design a high gain circularly polarized antenna. Following this introduction, the rest of the paper is organized as follows: the next section explains the design process and the simulated results of the proposed antenna. In section 3, we show the measured results. Finally, a conclusion is presented in the last section.

In this paper, the truncated corner technique is used to produce circular polarization with an axial ratio <3 dB. To increase gain and bandwidth of the proposed antenna, an array method with 2 × 2 elements is applied by arranging the antenna in parallel which relates to the microstrip line. The focus of this study is to produce microstrip antenna with circular polarization with axial ratio <3 dB, return loss <−10 dB and gain ≤10 dB which works at L₁ [1.563 - 1.587] GHz GPS band. The antenna is simulated on a Rogers RO4350B substrate with a permittivity value of 3.66 and a depth of 1.524 mm. PEC is used as a conducting material with a depth of 0.035 mm. The antenna is modelled, simulated and optimized numerically using CST MWS software. The performances are analyzed in terms of reflection coefficient, axial ratio and radiation patterns at the operating frequency 1.575 GHz.

The antenna was manufactured as can be seen in Figure 11 . The measurement of S₁₁ was achieved by using a portable VNA. Figure 12 shows the comparison between simulated (blue curve) and measured (red curve) return loss. A slight discrepancy of 17 MHz can be observed compared to the simulation, but it represents only 1% of the frequency shift that can be due to manufacture and permittivity tolerance.

Several retro-simulations are made to know the difference between measurement and simulation results (S₁₁). After these retro-simulations (variation of permittivity, patch sizes), we found that the difference between the simulation and measurement results comes from the tolerance of permittivity as shown in Figure 12 . We note that the green curve in Figure 12 is closest to the measurement (red curve). This curve shows the S₁₁ when the permittivity of the antenna is equal to 3.59 (−1.9%).

The manufactured prototype is then used in the GNSS receiver system ( Figure 13 ) to capture satellite signals with high sensitivity. The signals received are first amplified by a Low Noise Amplifier LNA (powered via a Bias Tee), which is directly connected to the antenna to improve signal quality and reduce noise. The amplified signals are then fed into a USRP (Universal Software Radio Peripheral) card, which serves as the RF front-end for digitizing and processing the signals. The USRP is connected to a PC where a configuration file is used to control the signal acquisition and perform positioning calculations, enabling flexible and software-defined GNSS reception.

In this paper, microstrip antenna with Right-Hand Circular Polarization (RHCP) optimized with array techniques has been presented. For the patch array, the feed network has been designed and optimized to work at 1.575 GHz. In terms of performances, very good results were obtained (S₁₁, axial ratio, gain). Based on the results obtained from the simulation process, the proposed antenna has a return loss of −17 dB, an axial ratio of 0.4 dB and gain of 9.4 dB at the working frequency of 1.575 GHz. The achieved prototype presents performances like those obtained in simulation. The differences observed in terms of S₁₁ can be explained by the fact that it is impossible to accurately determine the characteristics of the used substrates especially in terms of relative permittivity. Several retro-simulations are made to know the difference between the results of measurement and simulation. We note that the antenna substrate has a permittivity value close to 3.59. This antenna can be used to receive GPS signals in GNSS receiver.