Design of triangular shaped slotted patch antennas for both wideband and multiband applications

In this article two fractal geometry-based slotted patch antennas are designed to achieve wideband response with multiband characteristics and reduced cross polarized radiation in both E- and H-plane for all the resonating bands. The proposed antennas are fed with microstrip line feeding formed on a FR4 substrate of size 0.25𝜆0 × 0.25𝜆0 × 0.02𝜆0 mm3 and loaded with a partial ground plane at the bottom of the substrate. HFSS is used to design and simulate both the antennas. Wideband behavior and impedance matching of Antenna-1 are improved by optimizing the factor of iteration and length of the ground plane. Due to addition of 3 identical split ring resonators (SRR) with the antenna geometry leads to achieve multiband response in Antenna-2. The dimensions of the SRR connectors and feedline have been optimized through parametric analysis to match the impedance properly at all the three resonating bands. It has been found that simulated and measurement results of both the antennas are properly matched.

A Circularly Polarized, Flexible and Compact Quad-Band Wearable Antenna for Off-Body Communication Applications

A compact wearable textile antenna with multiband and circular polarization characteristics is proposed in this work for Wireless Body Area Networks (WBAN). An asymmetrically connected vertical stub as a radiator with the partial ground for quad-band (3.03–3.76[Formula: see text]GHz, 5.48–6.24[Formula: see text]GHz, 7.10–7.40[Formula: see text]GHz, 7.93–8.22[Formula: see text]GHz) operation and horizontal stubs on the radiator with L-slots in the ground is proposed for the triple band (3.16–3.22[Formula: see text]GHz, 7.25–7.36[Formula: see text]GHz and 7.93–8.08[Formula: see text]GHz) circularly polarized radiation. Jeans fabric is used as substrate with dielectric constant [Formula: see text] and loss tangent ([Formula: see text]). The dimensions of the proposed antenna are [Formula: see text][Formula: see text]mm3. Various conductive fabrics are investigated and analyzed as a radiating element. The proposed jeans antenna provides the gain ([Formula: see text] dB) and radiation efficiency ([Formula: see text]%) for all operating bands. The impact of the human body right arm loading on the antenna has been presented in terms of the reflection coefficient ([Formula: see text]) and gain using the CST Microwave studio simulation environment. The proposed antenna provides stable performance under bending conditions and the SAR values that are under acceptable limits ([Formula: see text][Formula: see text]W/kg for 10[Formula: see text]g of tissue). The flexibility, compactness and radiation properties make it suitable as a wearable textile antenna for off-body communication applications.

Generalized Optical Theorem and Point Sources

A simple derivation of the general form of the optical theorem (GOT) is given for the case of a conservative scatterer in a homogeneous lossless medium, suitable for describing point sources and an observation region close to the scatterer. The presentation is based on the use of the operator approach and scalar wave equation in the limit of vanishingly small absorption. This approach does not require asymptotic estimates of rapidly oscillating integrals, does not use the integration of fluxes, which leads to the loss of information about the energy conservation law, and allows a natural generalization to the case of polarized radiation, as well as more complex multi-part fields. Such GOT generalizes the results known in the mathematical literature for models to the case of any conservative (real) scattering potential and arbitrary sources.

An Unofficial Account of the Beginnings of VLBI Polarimetry: From Jodrell Bank to the Event Horizon Telescope

I offer a brief and personal history of the development of polarization sensitive observations with widely separated antennas. The story starts at Jodrell Bank in the late 1960s with a 24 km baseline radio linked (but not phase stable) interferometer and reaches to the present Event Horizon Telescope (with global span and independent atomic clocks) which has just published an image of the linearly polarized radiation surrounding the black hole shadow of M87*. I was privileged to be witness to many of the developments along the way, either as an instigator, a bystander, or an unindicted co-conspirator. I am most interested in the technical developments that enabled these increasingly sophisticated observations, and in the ideas that advanced the data analysis and imaging.

Formation of Inverse Energy Flux in the Case of Diffraction of Linearly Polarized Radiation by Conventional and Generalized Spiral Phase Plates

Recently, there has been increased interest in the shaping of light fields with an inverse energy flux to guide optically trapped nano- and microparticles towards a radiation source. To generate inverse energy flux, non-uniformly polarized laser beams, especially higher-order cylindrical vector beams, are widely used. Here, we demonstrate the use of conventional and so-called generalized spiral phase plates for the formation of light fields with an inverse energy flux when they are illuminated with linearly polarized radiation. We present an analytical and numerical study of the longitudinal and transverse components of the Poynting vector. The conditions for maximizing the negative value of the real part of the longitudinal component of the Poynting vector are obtained.