Millimeter wave beam shaping phased antenna array proposed for imaging reflectometry

A new microwave imaging reflectometry (MIR) system for KSTAR is being developed based on the experience gained via the TEXTOR proof-of-principle system [H. Park et al., Rev. Sci. Instrum. 74, 4239 (2003)] which aimed to measure the poloidal image of the electron density fluctuations essential for transport studies. The KSTAR system will adopt a multi-frequency probe beam source in the range of 90 ∼ 100 GHz (X-mode case), which will enable the measurement of 2-D (radial and poloidal) fluctuations of the multiple cut-off layers, simultaneously. The optical system of the MIR system will be combined with the 2nd ECEI system (identical to the first ECEI system [G.S. Yun et al., Rev. Sci. Instrum. 81, 10D930 (2010)]) on KSTAR. The design of the launching and receiving optics of the MIR system will be constrained in order to maintain the performance of the ECEI system and thus it is necessary to consider sharing the zoom lens of the ECEI system. This stringent constraint is a challenge considering the tight wavefront matching requirement to obtain proper images for a wide range of cut-off layers within the focal depth. This paper discusses the details of the MIR system design that is compatible with the 2nd ECEI system on KSTAR.

Electronically controlled phased-array antennas can adaptively scan radiated beams in three-dimensional space without mechanically moving parts. While most of the research on phased-array antennas has been focusing on broadband beam steering less attention has been devoted to null steering. Broadband null steering requires a beamformer that can generate variable and frequency independent true time-delays (TTD). In this paper we propose and demonstrate the concept of an Opto-VLSI-based tunable true-time delay generation unit for adaptive null steering in phased array antennas, where arbitrary single or multiple true-time delays can simultaneously be synthesized. Simulated azimuth gain patterns for a 4- element antenna arrays is presented, and experimental results are shown, which demonstrate the principle of the proposed true-time delay unit.

Beam-steering antennas are the ideal solution for a variety of system applications, it is most commonly achieved through using phased arrays, where phase shifters are used to control the relative of the main-beam. In this paper, a low-cost directive beam-steering phased array (DBS-PA) antenna using switched line phase shifters is demonstrated. The proposed DBS-PA antenna has four micro-strip patch antennas, three power dividers and four phase shifters printed on the same Rogers RT-Durroid substrate with a dielectric constant of 2.2 with dimensions of 8 × 3.5 cm. The phased array antenna has a directivity of 15 dBi and the main beam direction can be switched between the angles of ±30 degrees with a 3dB beam-width of 25 degrees. All design and simulations have been carried out using Agilent AdS and Ansoft HFSS software tools. The frequency considered for the operation is 10 GHz.

In this paper, we propose integrated one-dimensional (1D) grating waveguide-based true-time delay (TTD) lines on a silicon-on-insulator (SOI) platform. Through optimizing the structure of the proposed waveguide, a time delay of 77.23ps/mm can be readily achieved in a wavelength tuning range from 1540.20nm to 1558.97nm. Compared to conventional photonic crystal waveguide-based TTDs, the proposed waveguide occupies 70% less chip surface and has much lower propagation loss when compared with 2D photonic crystal devices. Therefore, a larger time delay can be achieved on-chip. To facilitate low loss coupling from strip waveguides to 1D grating waveguides and vice versa, a novel step taper is designed and shows a coupling efficiency of over 78%. Based on the 1D grating waveguide, a 1×4 beam steering module is designed and simulated. A wide beam steering angle from -67.84° to 67.84° for the X-band four-element phased array antenna with an array pitch size of 1.25cm is obtained.

This paper proposes a novel Opto-VLSI-based tunable true-time delay generation unit for adaptively steering the nulls of microwave phased array antennas. Arbitrary single or multiple true-time delays can simultaneously be synthesized for each antenna element by slicing an RF-modulated broadband optical source and routing specific sliced wavebands through an Opto-VLSI processor to a high-dispersion fiber. Experimental results are presented, which demonstrate the principle of the true-time delay unit through the generation of 5 arbitrary true-time delays of up to 2.5 ns each.

The choice of element for constructing a phased antenna array (PAA) providing a relative frequency bandwidth up to 9% for the transmission or reception of wireless communication system information was carried out. There are three methods to suppress of side lobes and diffraction of PAA in the radiation far field. Superposition of excitation signals of a flat PAA for simultaneous emission of several independent beams in a radiation far field was used. Сalculation and optimization of progressive distribution of phase shifts in the excitation signal group in the horizontal and vertical directions in the plane of PAA for radiation (reception) of independent beams in spherical coordinates (azimuth and elevation) in space was performed. An experimental sample of a phased antenna array was developed using microstrip technology, which forms several beams in a radiation far field. An experimental measurement of the voltage standing wave ratio and relative frequency bandwidth of the sample developed by phased array microstrip and printing technology was carried out.

A wideband phased array antenna (PAA) is designed and numerically demonstrated with ultrawide scanning angle up to 70 degree. A tapered slot antenna (TSA) is chosen as the PAA element which is optimized in a full wave solver. Results shows its capability to provide VSWR≤3 from normal to 70 degree from 2.17GHz to 6.71GHz. To study the broadband radiation patterns at the normal direction, a PAA composed of 9×9 TSA elements is built in the full wave solver. The scanning performances at 6GHz are also studied, with scanning angles from 0 to 70 degree by changing the feeding phases.

Simulation and experimental measurement of digital multi-beamforming phased antenna array in the frequency range C

We have designed, assembled and tested a phase-array antenna using fiber Bragg gratings in the highly dispersive transmission region as our tunable true-time delay (TTD) generators. The TTD generator is designed by cascading 29 identical fiber gratings and 1×2 fiber splitter pairs. Tapping from each fiber splitter allows us to steer our RF microwave beam from a 30×4-element antenna by tuning the wavelength of a laser. The 10Ghz RF signal is superimposed upon a laser beam by means of a LiNbO₃ modulator. However, with a conventional modulator, the optical frequency spectrum of the modulated beam consists of two sidebands on opposite sides of the optical carrier; all three of which may experience very different time delays due to dispersion. This may have detrimental effects on time-delay sensitive processes such as antenna beamforming. Therefore, we studied the use of single-sideband versus double-sideband modulators in the transmitters of photonic phased array antenna. We focus in particular on the effect of the different spectral profiles of single and double sideband modulators on beamforming when using the fiber Bragg gratings as TTD generators. With very high dispersion in our fiber Bragg gratings close to the band edge, the absolute propagation times are different for each sideband and the optical carrier. Therefore double sideband modulated signals will generate two sets of separate delays in the same microwave signal which causes beam deterioration and increased side-lobes. We demonstrated this theoretically and verified experimentally by comparing the antenna patterns generated by single-side-band and by double sideband modulators.

An optical true time delay (OTTD) unit based on uniform fiber Bragg gratings, photonic crystal fiber and wavelength converter array is proposed for the phased array antennas (PAAs) beamforming system. The PAAs system based on the proposed OTTD unit can provide the scanning range from − 69.7° to + 69.7° and resolution of 1° with greatly reduced number and length of the time delay lines. The PAAs beamforming system equipped with this OTTD unit is compact, and has low bandwidth requirement on the tunable laser source. Theoretical analysis and numerical simulations are presented to demonstrate the feasibility of the proposed system.

Formulation of the problem. Many electronic applications (for example, satellite communications) impose significant restrictions on the weight and dimensions of the antenna devices used. In addition, the antennas used should have the lowest possible cost and simplicity of design. To solve these problems, it is proposed to use a method for reducing the number of antenna elements in phased antenna arrays based on the method of point sources. Purpose. The purpose of this work is to develop a method for reducing the number of antenna elements in phased antenna arrays while maintaining the parameters of their radiation patterns. Results. As a solution, it is proposed to place the antenna elements above the metal sheet at a distance 1.5–2 times smaller than the size of the antenna array itself, which will significantly reduce the number of elements of the latter without deteriorating its radiation pattern during wide-angle two-coordinate scanning of space with the main lobe. Practical significance. Obtained results can be used to create phased antenna arrays with a reduced number of elements, which will reduce the size, weight and cost of the device.

Phased antenna arrays patterned on optical waveguides can strongly affect mode coupling and propagation in the waveguides. The unidirectional effective wavevector provided by the phased antenna array can facilitate phase matching between different waveguide modes; the effective wavevector can also breaks the symmetry of optical power flow in waveguides. These effects can be used to realize novel integrated photonic circuits. We used full-wave simulations to demonstrate broadband, small-footprint optical waveguide mode converters, polarization converters, and optical power diodes in the telecom and mid-infrared spectral ranges. The designed optical devices have small footprints (i.e., length of antenna arrays ranges from a few to ten times of the free-space wavelength). The efficiency of mode conversion (defined as the percentage of optical power coupled from one waveguide mode to the other) ranges from 10% to 60%, and the purity of converted modes approaches unity. The on-off ratio of optical power diodes (defined as the ratio between optical power transmission in two opposite directions) can be larger than 20dB over a broad wavelength range. We developed a coupled mode theory to model the asymmetric coupling between different waveguide modes and between waveguide modes and surface waves propagating along antenna arrays. The results calculated using the coupled mode theory can successfully explain mode evolution in our waveguide structures observed in simulations. We believe the platform of optical waveguides integrated with phased antenna arrays offers great opportunity to study novel physics originating from interaction between guided waves and designer structures. The platform also has great implication for integrated photonics device applications.

A space-fed X-band phased array antenna (PAA) is presented. The space-fed PAA uses physically autonomous individually addressable unit cells as the building blocks of an arbitrarily large array antenna. The X-band PAA unit cell consists of both a feed facing printed antenna element and a target facing printed antenna element. These elements are related by an RF phase shifter placed in the RF signal path between them which introduces relative phase delay and enables analog beam forming. Unit cell autonomy is realized by wirelessly transferring power and command signals required to operate a microcontroller (MCU) and the RF phase shifter at each unit cell. Each unit cell includes RF to DC conversion circuitry as well as an MCU designed to interpret a common control signal and command unit cell phase delay. The wireless phased array unit cell can be replicated in configurations of size and shape that are independent of RF, power, and array module control distribution networks. To demonstrate feasibility a four-element wireless PAA is constructed and antenna patterns for various control states are shown.

We present an application of fiber Bragg gratings as tunable optical delays in transmission for use as true-time-delay line in a RF-Photonic phased array antenna. Most delay line applications using fiber gratings require that they be used in reflection mode and they can provide only discrete variation of time delay. It also requires the use of bulky and expensive optical circulators. We have designed an optical true time delay array generator using fiber gratings in cascading transmission mode for such applications which significantly simplified the system and lowered the cost. A wavelength tunable laser is used as the light source. The laser light is modulated by an RF-microwave input signal, then enters into the optical true time delay array generator to provide a sequence of time delays Δt, 2Δt,...nΔt. The goal is to obtain large group delay Δt with low loss and with the capability of tuning Δt continuously by varying the wavelength of the laser. We combined an apodized grating profile, large index step and increased grating length to achieve our goal. We fabricated and tested the grating with about 100mm length which showed at least Δt=60 ps tunable time delay range. We have demonstrated the applicability of the transmission-mode fiber Bragg gratings in an optical true-time-delay type of phased array antenna.

In this article we perform a numerical study of microwave imaging reflectometry (MIR) and compare it with conventional reflectometry system. As an approximation to the reflections by real plasma fluctuations, a corrugated wheel is used. As far as general performance is concerned, our simulations confirm the results by Munsat et al. [Plasma Phys. Controlled Fusion 45, 469 (2003)] that the MIR system reproduces shape of corrugation far from the wheel while conventional systems fail to do so. We addressed the effects of asymmetry and defocusing of the wheel-reflectometer system as well as spectral sensitivity of the imaging reflectometer. For a particular geometry we estimated the deterioration of the MIR performance due to misalignments and existence of broadband fluctuations.