Payam Nayeri

3D Printed Dielectric Reflectarrays: Low-Cost High-Gain Antennas at Sub-Millimeter Waves

Dielectric reflectarray antennas are proposed as a promising low-loss and low-cost solution for high gain terahertz (THz) antennas. Variable height dielectric elements are used in the reflectarray designs, which allow for the use of low dielectric-constant materials. Polymer-jetting 3-D printing technology is utilized to fabricate the antenna, which makes it possible to achieve rapid prototyping at a low-cost. Numerical and experimental results are presented for 3 different prototypes operating at 100 GHz, which show a good performance. Moreover the methodology proposed here is readily scalable, and with the current material and fabrication technology, designs up to 1.0 THz can be realized. This study reveals that the proposed design approach is well suited for low-cost high-gain THz antennas.

Dual-Band Circularly Polarized Antennas Using Stacked Patches With Asymmetric U-Slots

In this letter, a new design for single-feed dual-band circularly polarized microstrip antennas is presented. A stacked- patch configuration is used for the antenna, and circular polarization is achieved by designing asymmetrical U-slots on the patches. The dimensions of the U-slots are optimized to achieve circular polarization in both bands. A prototype has been designed to operate at two frequencies with a ratio of 1.66. Both experimental and theoretical results are presented and discussed. The circularly polarized bandwidth of the antenna is 1.0% at 3.5 GHz (WiMax) and 3.1% at 5.8 GHz (HiperLAN).

Broadband Reflectarray Antennas Using Double-Layer Subwavelength Patch Elements

This letter investigates a novel bandwidth improvement method, which combines the multilayer approach with the subwavelength element technique. A new definition of phase error has been introduced to quantitatively analyze the performance of the reflectarray elements. It is shown that double-layer subwavelength elements exhibit a superior phase performance across the band, namely an increased phase range and a reduced phase error over frequency. Numerical analysis is then performed to calculate the bandwidth of reflectarray antennas using these elements, where the practical fabrication tolerances at high frequencies are considered. Finally, a 1-dB gain bandwidth of 19.1% has been demonstrated for a double-layer -band reflectarray using elements with a periodicity of λ/4.

Radiation Analysis Approaches for Reflectarray Antennas [Antenna Designer's Notebook]

This paper compares two basic methods for analysis of the radiation performance of reflectarray antennas. Two different approaches - array theory and aperture field - are first described, and numerical results are then presented for various reflectarray configurations. The advantages and limitations for each method are discussed, and the numerical results are compared with each other, showing very good agreement. Comparison with full-wave simulations showed that these approaches are time-efficient methods that can accurately calculate the reflectarray antennas pattern shape, main-beam direction, beamwidth, and sidelobe and cross-polarization levels. As such, these methods can be efficient tools for antenna engineers for designing and analyzing reflectarray antennas.

A broadband microstrip reflectarray using sub-wavelength patch elements

The concept of using sub-wavelength elements in reflectarray antenna designs has been investigated both numerically and experimentally. Two Ka-band reflectarrays have been designed, fabricated and tested for the operational frequency of 32 GHz. One array uses the conventional λ/2 element spacing and the other one is designed with λ/3 element spacing. It is shown that the reflectarray antenna with λ/3 element spacing achieves a larger gain bandwidth and a better overall antenna performance.

BANDWIDTH IMPROVEMENT OF REFLECTARRAY ANTENNAS USING CLOSELY SPACED ELEMENTS

A bandwidth improvement method in re∞ectarray anten- nas by using closely space elements, i.e., unit-cell sizes smaller than ‚/2, has been investigated both numerically and experimentally in this paper. A new deflnition of phase error has been introduced to analyze the broadband mechanism of closely spaced phasing elements. Through full wave EM simulations, it is revealed that closely spaced elements achieve a smaller phase error over the band. Based on these theoretical studies two Ka-band re∞ectarrays were fabricated and their performance was measured across the frequency range of 30 to 34GHz. It is demonstrated that the re∞ectarray designed with closely spaced elements achieves a notable improvement in gain bandwidth perfor- mance.

Design and Experiment of a Single-Feed Quad-Beam Reflectarray Antenna

Reflectarray antennas show momentous promise as a cost-effective high-gain antenna, capable of generating multiple simultaneous beams. A systematic study on various design methods of single-feed multi-beam reflectarray antennas is presented in this communication. Two direct design methods for multi-beam reflectarrays, geometrical method and superposition method, are investigated first. It is demonstrated that although both methods could generate a multi-beam radiation pattern, neither approach provides satisfactory performance, mainly due to high side-lobe levels and gain loss in these designs. The alternating projection method is then implemented to optimize the phase distribution on the reflectarray surface for multi-beam performance. Mask definition and convergence condition of the optimization are studied for multi-beam reflectarray designs. Finally a Ka-band reflectarray prototype is fabricated and tested which shows a good quad-beam performance.

Beam-Scanning Reflectarray Antennas: A technical overview and state of the art.

A detailed overview of various design methodologies and enabling technologies for beam-scanning reflectarray antennas is presented in this article. Numerous advantages of reflectarrays over reflectors and phased arrays are delineated, and representative beam-scanning reflectarray antenna designs are reviewed. For limited field-of-view beam-scanning systems, utilizing the reflector nature of the reflectarray antenna and the feed-tuning technique can provide a simple solution with good performance. On the other hand, for applications where wideangle scan coverage is required, utilizing the array nature of the reflectarray and the aperture phase-tuning approach are the more suitable choices. There are various enabling technologies available for both design methodologies, making them a suitable choice for the new generation of high-speed, high-gain beam-scanning antennas.

Design of Single-Feed Reflectarray Antennas With Asymmetric Multiple Beams Using the Particle Swarm Optimization Method

Single-feed reflectarrays with asymmetric multiple beams are studied in this paper. The conventional methods for designing multibeam reflectarrays are first reviewed and the limitations of these approaches are delineated for asymmetric designs. A generalized design approach based on a global search optimization technique, namely the particle swarm optimization, is proposed for single-feed asymmetric multibeam reflectarray designs. Practical considerations in implementing a global search for phase optimization of reflectarrays with several hundreds of elements are addressed, and several designs of multiple beam reflectarrays with asymmetric beam directions and gain levels are presented. Furthermore, a single-feed asymmetric quad-beam Ka-band reflectarray prototype is fabricated and tested, which shows a good multibeam performance. This study demonstrates the effectiveness and robustness of the particle swarm optimization approach for designing complicated multibeam reflectarray antennas where conventional design approaches fail.

Bifocal Design and Aperture Phase Optimizations of Reflectarray Antennas for Wide-Angle Beam Scanning Performance

A new design methodology is proposed for high-gain beam-scanning reflectarray antennas. Various approaches for designing beam-scanning reflectarray antennas are first reviewed and it is shown that for limited scan coverage, utilizing the feed displacement technique is a convenient design approach. To improve the scan coverage, a single-reflector bifocal aperture phase distribution is proposed for the reflectarray antenna, and is further optimized to improve the beam-scanning performance. Four reflectarray prototypes, each corresponding to a specific aperture phase distribution, have been fabricated and tested. A Ka-band reflectarray antenna with 60 degrees scan coverage achieving 30-dB gain and side-lobe level below 15 dB is demonstrated.