C. I. Kolitsidas

Array Antenna Limitations

This letter defines a physical-bound-based array figure of merit for both single and multiband array antennas. It provides a measure to compare their performance with respect to return loss, bandwidth(s), thickness of the array over the ground plane, and scan range. The result is based on a sum-rule result of Rozanov-type for linear polarization. For single-band antennas, it extends an existing limit for a given fixed scan-angle to include the whole scan range of the array, as well as the unit-cell structure in the bound. The letter ends with an investigation of the array figure of merit for some wideband and/or wide-scan antennas with linear polarization. We find arrays with a figure of merit >0.6 that empirically defines high-performance antennas with respect to this measure.

Exploiting asymmetry in a capacitively loaded strongly coupled dipole array

The scope of this work is to investigate asymmetry in a strongly coupled dipole array and exploit its effect for bandwidth and scanning improvement. Typically, antenna array elements are symmetrical in E- and H-plane. Introducing non-symmetric elements offers additional freedom to improve the array characteristics. The effect of non-symmetric elements is studied and a reference case is created with a symmetric element in unit cell design. The obtained bandwidth for the reference case is a 6:1 at the broadside. Using this element as a base for this work, we pixelate parts of the element and optimize this parts with a genetic algorithm. Having an initial design (solution) reduces significant the number of iterations needed for the genetic algorithm to converge. The element was studied in a rectangular and in triangular lattice. The results indicate that in both cases the performance is improved. Finally, the performance of the developed array element was investigated in terms of the array figure of merit, a general measure of array element performance. This resulted in the best known array figure of merit; 0.84.

Rectangular vs. equilateral triangular lattice comparison in a T-slot loaded strongly coupled dipole array

This work is focused on the impact of the array lattice in a strongly coupled dipole array. In order to study this, a wideband (6.2:1 BW ratio) dipole based array element was designed and used to compare lattice impact in our analysis. The element was designed using the unit cell analysis. In order to improve the bandwidth at the lower end of the frequency band the dipole was loaded with a T-slot increasing the electrical length. Based on this design a comparative analysis was conducted between rectangular and isosceles triangular lattices with respect to return loss, embedded element pattern and inter-element coupling. Emphasis was given to the analysis of the lattice comparison in the E-plane of the array as it is the most prone to variations with the array scanning.

A wideband switched beam antenna system for 5G femtocell applications

This work introduces a wideband switched beam system for femtocell 5G base stations. The system consists of a 4 × 1 Vivaldi linear array and a 4 × 4 Butler matrix able to operate from 1.9–5.1 GHz. A soft surface is introduced along the outer edges of the vivaldi elements of the array for side lobes and back radiation suppression.

A novel efficient multiple input single output RF energy harvesting rectification scheme

In this work an implementation of an ambient radio frequency harvesting system utilizing multiple input single output approach is demonstrated. Measurements of typical ambient radiation have been conducted with respect to power levels and frequency to determine which communication signals are suitable for harvesting. The measurement campaign showed that the WiFi frequency band at 2.45 GHz is a good candidate for indoors applications. A Greinacher voltage doubler is used for the rectification. A multiple input single output — MISO scalable scheme approach is implemented that is able to provide a DC differential output voltage. Simulated and experimental results proved the MISO rectenna to be an efficient scheme for RF harvesting.

A novel 32 port cube MIMO combining broadside and endfire radiation patterns for full azimuthal coverage — A modular unit approach for a massive MIMO system

In this paper we propose a novel 32 antenna port multiple-input-multiple-output (MIMO)-cube. The total volume of the cube is 320 × 320 × 120mm3. On two faces, endfire radiating linear tapered slot antennas (LTSAs) are placed and on the remaining sides, a mix of both LTSAs and broadside patch antennas are placed. In total 16 LTSAs and 8 dual polarized patches are used. The LTSA is designed to operate at the GSM and 3G bands, from 1.7 to 2.3 GHz. A corrugation pattern is introduced along the edges of the LTSAs covering one face to increase directivity and decrease sidelobes. The LTSAs are placed in two different orientations in order to receive two polarisations. The patch antenna is dual band and dual polarized. It operates in the frequency bands 2.4–2.5 and 5.45–5.6 GHz where Wi-Fi communication is made. The spatial placement, with antennas on all sides of the cuboid, ensures full azimuthal coverage despite the high directivity of the antennas. Using different antennas on different faces of the cube further optimizes the volume efficiency of the cube for azimuthal coverage.

Exploiting antenna array configurations for efficient simultaneous wireless information and power transfer

Different patch antenna array configurations for Simultaneous Wireless Information and Wireless Power Transfer — SWIPT — were simulated and evaluated. The scope of the work is to provide configurations that can be used to minimise the interference between information and power transfer as well as provide some beamforming capabilities. Our assumption for all the evaluated structures are that two receive antennas are used for RF energy harvesting and one antenna is used for information exchange. The choice for two antennas for energy harvesting is based on that a differential DC output full-wave rectifier is used. Our analysis is based on patch antennas.

A high gain dual-polarised differential rectenna for RF energy harvesting

A rectenna for radio frequency (RF) energy harvesting is presented in this paper. We introduce a novel technique for RF rectification that is based on differential field sampling and a Greinacher voltage doubler rectifier. The proposed rectification antenna is a dual polarized patch with 4 ports that operates for the WiFi frequency band of 2.4–2.5 GHz and has a gain of 6.75 dB at each port. The proposed novel topology doubles the amount of input power accepted for each polarization and then quadruples the overall output power. In addition we have a differential output voltage source that is typically required for the electronics connected to the harvesting system.

On methods to estimate bandwidth performance for array antennas with ground plane

Array antenna impedance bandwidth performance is a critical factor for antenna design, in particular for arrays in radar application and more recently for array antennas in communication systems. A priori methods to quantify bandwidth include stored energy-based estimates through the quality factor antenna Q, and sum-rule based estimates based on the antenna as a scattering object. A recently introduced, array figure of merit, uses a square window or walltype estimate on the return-loss to obtain bounds in terms of return-loss level, bandwidth, scan-range and unit-cell specific geometrical and material information, it is based on a fundamental physics result, linking bandwidth to essentially the thickness of the array. An alternative approach is based on the Bode-Fano theory, resulting in bandwidth measures in terms of one or several quality factors. Both methods apply both to single and multi-band array antennas. Here we present these methods and make a comparison between the two approaches.