Marcos V. T. Heckler

CYLINDRICAL: an effective CAD package for designing probe-fed rectangular microstrip antennas conformed onto cylindrical structures

This paper presents a computer-aided design tool named CYLINDRICAL. The algorithm utilizes the cavity model to design and analyze linearly and circularly polarized probe-fed rectangular microstrip antennas conformed onto cylindrical structures. A brief description of the program is given. CYLINDRICAL was used to design a circularly polarized antenna to operate in the L1 band of GPS. Validation was further done with the Ansoft HFSS package. It was shown that the antenna dimensions given by the design algorithm of CYLINDRICAL needed to be only slightly changed in order to obtain an optimized circularly polarized radiator according to the HFSS software. The tool is also very suitable for teaching graduate courses on microstrip antennas.

Design of a circularly polarized microstrip array mounted on a cylindrical surface

Microstrip antennas are very well suited to conformal array applications. Mounted on cylindrical surfaces, most of the developments emphasize the design of N-element wraparound arrays for omnidirectional radiation in the cylindrical roll planes. This paper reports the design of a circularly polarized (CP) circumferential array for the SONDA IV, a Brazilian sounding rocket. Using an effective home made CAD tool (Cylindrical), the minimum number of radiating elements needed to obtain a radiation characteristic as close as possible to an isotropic pattern was determined. Then, constructive details were taken into account in order to finally define the total number of antennas. To validate our assumptions and the design procedure, a prototype of a sub-array of four CP microstrip patches was manufactured, and the tests results show very good agreement with the simulations.

Design and analysis of microstrip antenna arrays for meteorological nano-satellites for UHF uplink

This paper presents the study of microstrip antenna arrays for meteorological nano-satellites that are under development in the frame of UNIESPAÇO programme, which is supported by the Brazilian Space Agency (AEB). The main goal of such satellites is to serve as data relay for transmission of meteorological data collected by stations deployed in remote areas, such as in the rain forest, whereby no wired communication is possible. Arrays composed of linearly and circularly polarized microstrip antennas are investigated. The performance of such arrays is assessed including parameter variations, especially for the case of dielectric constant of the antenna substrate and misalignment in the orientation of the array elements. Such imperfections can occur due to mechanical stress and large temperature variations that are typical to the space environment. The antennas were modeled with the electromagnetic simulator Ansys HFSS. Good results have been observed in terms of the axial ratio, impedance bandwidth and gain for both of the proposed models.

Optimization of switched-beam arrays for communication systems

This paper presents the application of optimization methods for the synthesis of a linear array for communication systems. By means of suitably beam switching, the array should provide coverage of a given angular area in azimuth and should allow controlling the sidelobe level simultaneously. For this purpose, two optimization methods have been used to calculate the excitation coefficient for each desired beam. The synthesis technique is demonstrated for arrays composed of isotropic and microstrip elements. By comparing the results obtained for both arrays, the need of consideration of the array element pattern during the synthesis process is demonstrated.

A low-cost modular transmit front-end with analog beamforming capability

In this paper, we present a radio frequency (RF) transmitter front-end that can be used in analog beamforming applications. The proposed system is modular and can be employed at different frequencies whereby C-band operation is shown. Using low-cost components and substrates, this design makes analog beamforming affordable also for commercial applications with unit costs below 130 € and expected overall gain of 11.1 dB. We demonstrate the system performance in terms of S-parameter measurements with frequency translation to 7.0 GHz. Reproducibility of the achieved results is shown by analyzing multiple front-end prototypes. The beamforming capability is verified by antenna pattern measurements with an eight-element array.

A simulation technique for RF amplifier circuits using ANSYS electronics desktop

This paper describes a simulation technique for RF amplifier circuits using an electromagnetic simulator. To validate the proposed approach two RF circuits were designed, manufactured and measured. Simulated and measured results were compared and good agreement was observed.

Beam-shaped radiation pattern for uniform radiated power distribution

This paper presents the application of optimization methods for the synthesis of antenna arrays. The desired pattern shall exhibit a shape that allows uniform distribution of the radiated power on the Earth. Besides beamshaping, the optimization methods allow controlling the level of the sidelobes. The synthesis technique is used to calculate the excitation coefficients for arrays composed of cavity-backed circularly polarized annular slot antennas.

Annular slot antenna for high-precision GPS applications

This paper presents the design of a printed antenna with annular slot geometry for GNSS applications. Two prototypes were built in order to meet the requirements of these systems. Different feeding techniques have been proposed in order to obtain the right-hand circular polarization. Electrical walls were added in the prototypes to avoid losses by parallel plate modes, to improve the radiation efficiency, gain and axial ratio. The proposed geometries were designed and built with two different feeding schemes: the first one is based on a series feed, whereas the other is based on the integration of a 90°-hybrid. The results showed that the synthesized antenna has all features required to operate in the Global Navigation Satellite Systems (GNSS).

Discrete mode matching analysis of cylindrical microstrip structures

This paper presents the formulation to apply the discrete mode matching (DMM) method to analyze microstrip multilayer structures, such as transmission lines and antennas conformed to cylinders. The main advantage of the method is the need of discretization only along the azimuthal and the axial directions by sampling the fields and current densities in the interfaces between dielectric layers. The solution in the radial direction is obtained analytically with the dyadic Greens function, which is calculated using the full-wave equivalent circuit (FWEC) in the spectral domain. The method is used to analyze two structures: a multilayer conformal transmission line and a conformal antenna. Validation with the commercial software HFSS has been done and good agreement between the results has been observed.