The performance characteristics of Fresnel zone plates are described with emphasis on applications at millimeter wavelengths. Recent results are included along with a summary from numerous earlier investigations. Parameters described include design information, efficiency, bandwidth, focal characteristics, off-axis performance, axial intensity dependence, aberrations, and far-field pattern. Both transmission and reflection configurations are discussed, mostly for cases where the focal length and diameter are comparable. This type of zone plate has advantages (compared to a lens or paraboloid) of reduced loss, weight, volume, and cost, as well as simple planar construction, with similar diffraction-limited beamwidth and major sidelobe performance, but lower efficiency.

Fresnel zone plate antennas at millimeter wavelengths

Grooved-dielectric, phase-correcting, Fresnel zone plate antennas are analyzed using the body-of-revolution finite-difference time-domain (BOR-FDTD) method. Parametric studies of the focusing ability of these antennas are performed to examine the effects of the focal length, diameter, number of zones, and the thickness of the lens, as well as the number of phase corrections per zone. The results of these studies are presented as design graphs and are used to lend insight into the focusing mechanism of phase-correcting zone plates. The BOR-FDTD analysis is validated by comparison with previous measurements.

A Full Electromagnetic Analysis of Grooved-Dielectric Fresnel Zone Plate Antennas for Microwave and Millimeter-Wave Applications

This paper summarizes some of the growth in technology for Fresnel zone plate antennas in the microwave and millimeter-wave regions. A description is given of the earliest developments of Fresnel zone plates at optical frequencies. Most of the material concerns previous results obtained for microwaves and millimeter-waves.

History and evolution of Fresnel zone plate antennas for microwaves and millimeter waves

Having the device simplicity and high output-power capacity, the capability of the virtual cathode oscillator (vircator) for emitting high power microwaves is demonstrated. We have investigated the axial-typed vircator in our pulsed power generator, “Chundoong” (Max 600 kV, 88 kA, and 60 ns), and simulated the vircator using the 3-D particle-in-cell simulation code called “MAGIC.” We try to find out the position of the virtual cathode inside the drift tube and enhance the power of microwaves by focusing them at the focus point using the ring-typed zone plate with a focal length of 18.8 cm. The dominant frequency is obtained as 3.5 GHz measured by fast Fourier transform, which is in good agreement with simulation frequency. It is found that the mean position of the virtual cathode is almost the same as the A-K gap distance of 10 mm, in which the virtual cathode oscillates from 7.9 mm to 12.1 mm behind the meshed anode, as verified by the simulation results. The maximum output power without the zone plate is obtained as 0.66 GW with the efficiency of 27%, which is maximized up to 1.22 GW with the efficiency of 51% at the focus point by using the zone plate. The microwave emission mode from the vircator is the TM01 mode based on the simulation results. The zone plate contributes significantly in enhancing the power efficiency and determination of the position of the virtual cathode. These observations might be used in developing a high efficient microwave source by using a zone plate under the decision of the position of the virtual cathode.

Enhancing the power of high power microwaves by using zone plate and investigations for the position of virtual cathode inside the drift tube

Based on the Kirchhoff-Huygens diffraction theory, a simple analytical method of a planar folded Fresnel zone-plate (FZP), that is the case when a planar reflector is placed behind the zone plates, has been developed. According to the numerical calculation results, the design procedure of the FZP antenna has been presented, and its focusing characteristics and gain-optimized conditions have been discussed. The variations of the focal field distribution with the antenna parameters such as zone numbers, focal length and antenna diameter and the radiation power patterns of the FZP have been simulated numerically. To take a good balance of both receiving and transmitting antennas, at 60GHz operating frequency, the focal length should be designed as a half of the antenna diameter and the zone number should be from 10 to 15. The results in this work show that the folded FZP has good focal characteristics and off-axis performance, and its antenna gain can be optimized by the suitable antenna parameter design. The possibility of applying the folded FZP as a low cost and high gain antenna without strict manufacturing requirement for millimeter-wave communications has been shown.

Design and analysis of a folded Fresnel Zone Plate antenna

The paper describes the design of a Fresnel zone plate suitable for use as an antenna in the centimetric or lower wavelength range. It has been shown that such antennas can be fabricated by using either metal or dielectric rings. Its properties have been analysed by employing the simple methods of electromagnetic diffraction. Experimental results are reported showing close agreement with the theory. A theory has been presented explaining the working of the dielectric ring zone plate. The investigation leads to the conclusion that both the metal and dielectric zone plates are useful as low gain antennas.

G. S. Sanyal

Papers

Fresnel Zone Plate Antenna