There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

https://dr.ntu.edu.sg/bitstream/10220/7680/2/Electrically%20tunable%20dielectric%20materials%20and%20strategies%20to%20improve%20their%20performances.pdf

Electrically tunable dielectric materials and strategies to improve their performances

Preface. 1: ELECTRICALLY SMALL ANTENNAS. 1.1 Introduction. 1.2 Fundamental Limitations. 1.3 Electrically Small Antennas: Canonical Types. 1.4 Clever Physics, but Bad Numbers. 1.5 Pathological Antennas. 1.6 ESA Summary. References. Index. 2: SUPERDIRECTIVE ANTENNAS. 2.1 History and Motivation. 2.2 Maximum Directivity. 2.3 Constrained Superdirectivity. 2.4 Bandwidth, Efficiency, and Tolerances. 2.5 Miscellaneous Superdirectivity. 2.6 Matching Circuit Loss Magnification. 2.7 Non-Foster Matching Circuits. 2.8 SD Antenna Summary. References. Index. 3: SUPERCONDUCTING ANTENNAS. 3.1 Introduction. 3.2 Superconductivity Concepts for Antenna Engineers. 3.3 Dipole, Loop, and Patch Antennas. 3.4 Phasers and Delay Lines. 3.5 SC Antenna Summary. References. Subject Index.

Electrically small, superdirective, and superconducting antennas

By using different preparation and processing methods, poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF−HFP)] films with different crystal orientations were fabricated. Anisotropic dielectric properties and different electric energy storages were observed in these films. When the PVDF crystals in a film oriented with their c-axes perpendicular to the applied electric field, they exhibited large polarizability because the CF2 dipole moments were randomly distributed in a plane parallel to the electric field. As a result, high dielectric constant and high electric energy density were achieved. On the contrary, when the crystal c-axes in a film oriented parallel to the electric field (or the CF2 dipole moments perpendicular to the electric field), polarization became difficult. Consequently, low dielectric constant and low electric energy density resulted. The anisotropic polarizability was also displayed at high electric fields as evidenced by the difference in the remnant/maximum polarization and th...

Crystal Orientation Effect on Electric Energy Storage in Poly(vinylidene fluoride-co-hexafluoropropylene) Copolymers

This review of array antennas highlights those elements of theory and hardware that are a part of the present rapid technological growth. The growth and change in array antennas include increased emphasis on "special-purpose" array techniques such as conformal and printed circuit arrays, wide angle scanning arrays, techniques for limited sector coverage, and antennas with dramatically increased pattern control features such as low sidelobe, adaptively controlled patterns. These new topics have substantially replaced large radar arrays in the literature and constitute a major change in the technology. The paper presents a tutorial review of theoretical developments emphasizing techniques appropriate to finite arrays, but indicating parallel developments in infinite array theory, which has become the useful tool for analysis of large arrays. A brief review of the theory of ideal arrays is followed by a generalized formulation of array theory including mutual coupling effects, and is appropriate to finite or infinite arrays of arbitrary wire elements or apertures in the presence of a conducting ground screen. Some results of array tolerance theory are summarized from the literature and retained as reference throughout discussions of array component requirements and device tolerance for low sidelobe arrays. Examples from present technology include conformal and hemispherical coverage arrays, lightweight printed circuit arrays, systems for use with reflectors and lenses in limited sector coverage applications, and wide-band array techniques.

Phased array theory and technology

The effects of anisotropic dielectric properties of ferroelectric Ba1−xSrxTiO3 (BST) films on the characteristics of the interdigital (IDT) capacitors have been studied in microwave regions at room temperature. Ferroelectric BST films with (001), (011), and (111) orientation were epitaxially grown on (001), (011), and (111) MgO substrates, respectively, by the pulsed laser deposition method. The microwave properties of orientation engineered BST films were investigated using interdigital capacitors. The calculated dielectric constant tunability with 40 V dc bias variation and the calculated dielectric quality factor values for IDT capacitors based on (001), (011), and (111) oriented BST films at 9 GHz with no dc bias were about 47%, 55%, 43%, and 12, 14, 21, respectively.

Orientation dependent microwave dielectric properties of ferroelectric Ba1−xSrxTiO3 thin films

Compositionally graded (Bax, Sr1−x)TiO3 (BST) thin films were deposited on MgO substrates by pulsed laser ablation. The microwave properties of the graded BST thin films were investigated at microwave frequencies with coplanar waveguide (CPW) meander-line phase shifters as a function of the direction of the composition gradient with respect to the substrate at room temperature. CPW phase shifters using graded BaTiO3(BT)→SrTiO3(ST) and ST→BT thin films exhibited a differential phase shift of 73° and 22° at 10 GHz with a dc bias voltage of 150 V, respectively. The figure of merit of the phase shifters at 10 GHz was 14.6 deg/dB for the graded BT→ST film, and 10 deg/dB for the graded ST→BT film. The graded BT→ST thin films showed a larger phase tuning than the ST→BT thin films. The microwave properties of the graded BST films depended strongly on the crystalline structure and the direction of the composition gradient with respect to the substrate.

Microwave properties of compositionally graded (Ba, Sr)TiO3 thin films according to the direction of the composition gradient for tunable microwave applications

In the present work, we report the epitaxial growth and dielectric properties of barium strontium titanate (BST) thin film which can be used to make frequency and phase agile tunable microwave (MW) components with a high performance, such as tunable filters, tunable oscillators, and phase shifters for application in phased array antennas. Epitaxial BST thin films were deposited on a MgO substrate by the insertion of a thin BaTiO3 (BT) seed layer between the BST films and the MgO substrate using pulsed laser ablation. The crystalline structure, dielectric tunability and microwave properties of the epitaxial BST thin films depended strongly on the thickness of the BT seed layer. The dielectric tunability and microwave phase tuning increased with increasing thickness of the BT seed layer. An interdigitated (IDT) capacitor based on the epitaxial BST/BT(12 nm) film on the MgO substrate exhibited a large capacitance tunability of 78% at a frequency of 100 kHz and an applied electric field of 133 kV/cm. Also, a coplanar waveguide (CPW)-type phase shifter fabricated on the BST/BT(12 nm) film showed a phase shift of 153° at 10 GHz and 40 V. These results indicate that the thin BT layer with an intermediate lattice constant between those of the BST film and MgO substrate can be used as an excellent seed layer for improving the crystallization and dielectric properties of BST films, and the high microwave performance of ferroelectric MW devices.

High Dielectric Tunability of (Ba, Sr)TiO3 Thin Films and Their Coplanar Waveguide Phase Shifter Applications

Provided are a phase shifter with a photonic band gap (PBG) structure using a ferroelectric thin film. The phase shifter includes a microstrip transmission line acting as a microwave input/output line and a plurality of tunable capacitors arranged in the microstrip transmission line at regular intervals. Electrodes disposed on a substrate apply DC voltages to the plurality of tunable capacitors. Radio frequency (RF) chokes and quarter wavelength radial-stubs are connected between the electrodes and the microstrip transmission line in order to prevent high frequency signals from flowing into a DC bias terminal. A plurality of PBGS are periodically arrayed on a ground plane of the substrate.

Phase shifter with photonic band gap structure using ferroelectric thin film

It is very important to increase the input impedance of a antenna for continuous-wave terahertz photomixers because the output impedance of terahertz photomixers is extremely high compared to the antenna impedance. Folded dipole antennas are analyzed to increase the input impedance by varying geometrical dimensions. The input impedance of the optimized folded dipole antenna is about 40 times as high as that of a self-complementary antenna at the resonant frequency.

Min-Hwan Kwak

Papers

Orientation dependent microwave dielectric properties of ferroelectric Ba1−xSrxTiO3 thin films

Microwave properties of compositionally graded (Ba, Sr)TiO3 thin films according to the direction of the composition gradient for tunable microwave applications

High Dielectric Tunability of (Ba, Sr)TiO3 Thin Films and Their Coplanar Waveguide Phase Shifter Applications

Phase shifter with photonic band gap structure using ferroelectric thin film

A folded dipole antenna having extremely high input impedance for continuous-wave terahertz power enhancement