Nelson Fonseca

Planar

In this paper, a 4 × 4 Nolen matrix beam-forming network for multibeam antenna applications is designed and demonstrated at 12.5-GHz center frequency. The structure is implemented using substrate integrated waveguide (SIW) technology for its attractive advantages including compact size, low loss, light weight, and planar form well suitable for high-density integration with other microwave and millimeter-wave planar integrated circuits. SIW cruciform couplers are used as fundamental building blocks for their wide range of coupling factors and their specific topology well adapted to the serial feeding topology of a Nolen matrix. The network performances are investigated over a 500-MHz frequency bandwidth ranging from 12.25 to 12.75 GHz. The matrix definition based on SIW cruciform couplers is similar to its microstrip counterpart in terms of coupling factors and phase delays. The whole network is fabricated. Measured results are in good agreement with the theoretical predictions, thus validating the proposed design concept. Using this matrix with a four radiating elements array antenna enables us to investigate the impact of the proposed matrix on the beam pointing angles versus frequency.

Ku

This letter addresses the miniaturization of the open-ended quadrifilar helical antenna for satellite VHF frequency band telemetry links systems. The miniaturization is achieved using combinations of sinusoidal profiles, and several designs are obtained using an optimization process based on intensive electromagnetic simulations. The design and experimental validation are reported in this letter, and a significant height reduction from 48% to 72% is obtained using various combinations of sinusoidal profiles (i.e., wires mathematically described by sinusoidal functions) without a significant degradation of the radiation pattern, directivity, and polarization purity. Moreover, the input matching is slightly improved for the compact antennas. It was observed that the efficiency and gain do not decrease linearly with the reduction of the antenna height.

-Band 4

In this letter, a technique for the miniaturization of conventional printed quadrifilar helical antennas using simple sinusoidal profiles is described and supported by experimental results. The challenge is to reduce the size of the antenna while maintaining iso-flux radiation patterns and high cross-polarization discrimination. The miniaturization design approach simulation and measurement results are given in the case of a specific design of L-band telemetry link antenna for meteorological stratospheric balloon payloads, but the achieved results can be extended to any quadrifilar helical antenna with shaped pattern. Size reduction close to 50% is reached while preserving major radiation pattern characteristics and good axial-ratio performance over a wide angular range.

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This paper describes a beamforming network well adapted to produce evenly distributed multiple-beam coverage over a full 360° angular range in azimuth. This structure is very simple, flexible, and compatible with low-cost manufacturing processes such as printed technology. The proposed design is based on balanced power dividers and combiners arranged in such a way to feed a sector of a circular array antenna with Gaussian amplitude distribution and in-phase signals. The first characteristic provides control on the radiation pattern shape, including main lobe shape and sidelobe level, while the second ensures stable beam pointing over a wide frequency range. The proposed azimuth beamforming network is described, and a specific design in microstrip technology is presented with a center frequency at 6 GHz. Simulation results are supported by the measurement of several prototypes. In particular, two designs including the circular array antenna are compared to investigate the impact of the circular array antenna radius on radiation patterns. Despite the assumptions, good correlation is found between simulation and measurement results, thus confirming the properties of the proposed beamforming network concept. Integration of phase controls in the feeding network and its impact on the overall antenna efficiency are also discussed.

4 Nolen Matrix in SIW Technology

This paper describes a concept combining beam hopping and size reduction of effectively used spots that can be implemented on multiple-beam antennas to improve their performance, namely the carrier-to-interference ratio, the minimum directivity, and the roll-off. The expected impact on antenna RF performance is demonstrated based on simplified models. A more-realistic focal-array-fed reflector antenna is also presented, based on a cell-reuse scheme of 12 reduced to four (one-third of the coverage receiving all the available bandwidth according to a cell-reuse scheme of four at a given instant), with performance in line with the simplified model. This specific design enabled improving the antennas performance without drastically increasing its complexity: the minimum directivity and C/I were respectively 1.67 dB and 3.65 dB higher when compared to a standard antenna implementation with a cell-reuse scheme of four.