Optimization Procedure for Wideband Matched Feed Design

The inherently high cross polarization of prime focus offset reflector antennas can be compensated by launching higher order modes in the feed horn. Traditionally, the bandwidth of such systems is in the order of a few percent. We present a novel design procedure where the entire matched feed and reflector system can be efficiently optimized. This allows the design parameters of the matched feed to be directly related to the desired design goals in the secondary pattern over a specified band. Using this procedure, we present a design of a die-castable axially corrugated matched feed horn that provides an XPD improvement better than 7 dB over a 12% bandwidth for a reflector with an f/D of 0.5. An investigation of the mode requirement for an arbitrary circular aperture feed is also presented

Development of a X-Band, Crosspolarization Compensating Feed Antenna for the Compact Test Range

In antenna measurements it is well known that single reflector and dual cylindrical reflector Compact Antenna Test Ranges (CATRs) suffer from a high cross-polarization level in the Quiet Zone (QZ). This limits their performance of measuring an Antenna under Test (AUT) with high cross-polar suppression. This issue is avoided by the development of a new three element feed array. The central horn antenna ensures the co-polar field, while the outer horns generate the so called conjugate matched field and hence reduce the cross-polarization. A nonlinear, numerical optimization is used to calculate the weighting factors of each element. It must consider also the limitations of the prototype-based feeding network. The feed array is capable of generating horizontally and vertically polarized waves and it operates in the X-band. The performance of the feed array is validated in High-Frequency Structure Simulator (HFSS) simulations, where an improvement of 8 dB in the cross-polar level is found in the QZ. A proof of concept demonstrator is measured in the Compact Test Range (CTR) of the Microwaves and Radar Institute of the German Aeorspace Center (DLR). A field probe scan shows a mean cross-polar level of −41.6 dB, over 9 dB better than the currently used reference. The cross-polarization is effectively reduced over a bandwidth of 900 MHz

Phased array-fed antenna configuration study: Technology assessment

Spacecraft array fed reflector antenna systems were assessed for particular application to a multiple fixed spot beam/multiple scanning spot beam system. Reflector optics systems are reviewed in addition to an investigation of the feasibility of the use of monolithic microwave integrated circuit power amplifiers and phase shifters in each element of the array feed

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

Advanced Design Methodologies and Novel Applications of Reflectarray Antennas

Reflectarray antennas combine the numerous advantages of printed antenna arrays and reflector antennas and create a hybrid high-gain antenna with a low-profile, low-mass, and diversified radiation performance. Reflectarrays are now emerging as the new generation of high-gain antennas for long-distance communications. In this dissertation, some advanced concepts demonstrating novel features of reflectarray antennas are presented. • First, various approaches for radiation analysis of reflectarray antennas are described and implemented. Numerical results are then presented for a variety of systems and the advantages, limitations, and accuracy of these approaches are discussed and compared with each other. • A broadband technique by using sub-wavelength elements is proposed and prototypes are fabricated and tested. This technique enables the reflectarray to achieve a significant bandwidth improvement with no additional cost. • Infrared reflectarrays antennas are studied for possible applications in concentrating solar power systems. Material losses, an important design issue at infrared frequencies, are investigated and reflectarrays consisted of dielectric resonant elements are proposed with low-loss features at infrared. • Multi-beam reflectarray antennas are studied and it is demonstrated that by optimizing the phase of the elements, a desirable multi-beam performance can be achieved using a single-feed. Local and global phase-only optimization techniques have been implemented. Two Ka-band quad-beam prototypes with symmetric and asymmetric beams have been fabricated and tested. • Different approaches for beam-scanning with reflectarray antennas are also revieand it is shown that for moderately wide angle beam-scanning, utilizing a feed displacement technique is more suitable than an aperture phase tuning approach. A feed displacement beam-scanning design with novel aperture phase distribution is proposed for the reflectarray antenna, and is further optimized to improve the performance. A high-gain Ka-band prototype achieving 60 degrees scan range with side-lobe levels below 15 dB is demonstrated. • The feasibility of designing reflectarray antennas on conformal surfaces is also studied numerically. A generalized analysis approach is presented and the radiation performance of reflectarray antennas on singly-curved conformal cylindrical platforms are studied and compared with their planar counterpart. It is revealed that conformal reflectarray antennas are a suitable choice for a high-gain antenna where curved platforms are required. In summary, different challenges in reflectarray analysis and design are addressed in this dissertation. On the element design challenges, bandwidth improvement and infrared operation of reflectarray antennas have been studied. On the system level challenges, multi-beam designs, beam-scanning performance, and conformal platforms have been investigated. Several prototypes have been fabricated and tested, demonstrating the novel features and potential applications of reflectarray antennas

Mutual Coupling Reduction Techniques for Multi-band Base Station Antennas

This dissertation proposes antenna design techniques which suppress mutual coupling in densely populated dual-polarized broadband multi-band base station antenna (BSA) arrays for improved radiation characteristics. Array face densification without the proposed techniques leads to undesirable interactions between arrays and radome cover. This research is supported by extensive full-wave electromagnetic simulations, characteristic mode analysis, equivalent circuit models, and array theory. The results are validated through measurements of the radiation patterns and scattering parameters of fabricated prototypes.Upon excitation of a mid-band (MB) array, an electrically long low-band (LB) parasitic, necessary for broadband matching of the baseline LB dipole, exhibits dipole-like induced currents which degrade the MB radiation patterns. The currents are suppressed through parallel plate series capacitance integrated along the length of the LB dipole arms to lower the dipole self-impedance, enabling broadband matching using an electrically short LB parasitic. The proposed technique improves MB radiation pattern symmetry, cross-polar radiation (CPR), sidelobe level, and gain. Upon excitation of the proposed LB dipole, the baseline MB dipole balun feed stems exhibit induced common mode currents, which radiate as electrically short monopoles over a conducting ground plane, that degrade the LB radiation characteristics. These currents are suppressed by integrating parallel plate series capacitance along the length of the balanced ports of the MB balun. The proposed balun improves the LB beamwidth stability, CPR, and gain stability. The proposed serially loaded LB dipole and MB dipole balun feed stem are implemented simultaneously in a six-foot BSA in which the system performance improvements are verified. Upon excitation of a high-band (HB) array in a tri-band array environment, the dielectric radome behaves as a partially reflecting surface. The reflected waves interfere with the HB excitation, resulting in significant boresight radiation attenuation in the upper part of the HB operating band. A Fabry-Perot cavity antenna (FPCA) operating in the second resonance mode (N=1) is proposed to improve this attenuation through increasing the boresight directivity. Upon HB excitation of the proposed FPCA, circular-disk MB parasitics, necessary for broadband matching of the neighboring MB array, exhibit dipole-like induced currents. The induced currents radiate as dipoles which reduce the HB half power beamwidth (HPBW) in the lower and middle part of the HB operating band. These currents are suppressed by introducing electrically thin radial slots in the baseline MB parasitic. The radial slots change the characteristic modes and lower their modal significance, which eliminates the secondary radiation sources. The proposed technique increases the HPBW in the lower and middle part of the HB operating band. These proposed design techniques provide new tools to antenna designers which allow for the densification of BSA arrays for use in next generation cellular networks, while minimizing radiation pattern degradation otherwise present in baseline BSA designs using existing techniques

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Single-band and Dual-band Beam Switching Systems and Offset-fed Beam Scanning Reflectarray

The reflectarray has been considered as a suitable candidate to replace the conventional parabolic reflectors because of its high-gain, low profile, and beam reconfiguration capability. Beam scanning capability and multi-band operation of the microstrip reflectarray have been main research topics in the reflectarray design. Narrow bandwidth of the reflectarray is the main obstacle for the various uses of the reflectarray. The wideband antenna element with a large phase variation range and a linear phase response is one of the solutions to increase the narrow bandwidth of the reflectarray. A four beam scanning reflectarray has been developed. It is the offset-fed microstrip reflectarray that has been developed to emulate a cylindrical reflector. Unlike other microstrip reflectarrays which integrates phase tuning devices such as RF MEMS switches and another phase shifters to the reflectarray elements and control the reflected phase, the beam scanning capability of the reflectarray is implemented by a phased array feed antenna. This method can reduce the complexity of the design of the beam switching reflectarray. A simple method has been investigated to develop multi-band elements in this dissertation. In approach to increase the coverage of the operation bands, a six-band reflectarray has been developed with two layers. Each layer covers three frequency bands. A Butler matrix is one of the useful beamforming networks for a phased array antenna. A Double-Sided Parallel-Strip Line (DSPSL) is adapted for the feeding network of eight array elements. The DSPSL operate very well to feed the microstrip antenna array over the bandwidth to reduce the sidelobe level and a high gain. In another topic of a Butler matrix, a dual-band Butler matrix has been proposed for multi-band applications. A modified Butler matrix is used to reduce a size and a sidelobe level. The bandwidth of the microstrip antenna is inherently small. A broadband circularly polarized microstrip antenna with dual-offset feedlines is introduced in this dissertation. Aperture-coupled feed method is used to feed the stacked patch antennas and a slotcoupled directional coupler is used for the circularly polarized operation. The research presented in this dissertation suggests useful techniques for a beam scanning microstrip reflectarray, phased array antenna, and wideband antenna designs in the modern wireless communication systems

Personal Access Satellite System (PASS) study. Fiscal year 1989 results

The Jet Propulsion Laboratory is exploring the potential and feasibility of a personal access satellite system (PASS) that will offer the user greater freedom and mobility than existing or currently planned communications systems. Studies performed in prior years resulted in a strawman design and the identification of technologies that are critical to the successful implementation of PASS. The study efforts in FY-89 were directed towards alternative design options with the objective of either improving the system performance or alleviating the constraints on the user terminal. The various design options and system issues studied this year and the results of the study are presented