Design of compact planar rat-race and branch-line hybrid couplers using polar curves

An approach where polar curves are used to miniaturize hybrid couplers is presented. The design of such couplers can be done with the optimization of a few parameters using full-wave analysis software. The results show similar or better electrical performance for a rat-race and branch-line coupler with respectively a 75% and 50% size reduction.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1098-27602016-11-30hb201

High-gain dual-polarised planar slot array for WLAN applications

A high-gain dual-polarised planar etched slot array for use in wireless local area networks (WLAN) is presented. Two sets of four collinear slots are used as radiators for each polarisation. Each set of four collinear slots is constructed as a centre-fed long slotline, with etched crossovers to split the slotline into four resonant and in-phase halfwavelength slots. A reflector etched on a separate substrate spaced a quarter-wavelength away from the slot array ensures unidirectional radiation. The final antenna achieved a gain of 14.5 dBi, a return loss better than 10 dB, and port isolation in excess of 30 dB over the 2.4–2.484 GHz WLAN frequency band.http://www.ietdl.org/E

Design of center-fed printed planar slot arrays

Adesign approach for printed planar slot array antennas is presented. The antenna array consists of half-wavelength slot radiators positioned on a rectangular grid, and a slotline feed network. Three planar slot array antennas for use in IEEE 802.11a applications are designed, a 2 × 2, a 2 × 4, and a 4 × 2 array, all radiating above an electric conductor ground plane placed a quarter-wavelength below the printed slots. These slot arrays have higher aperture efficiencies and occupy less space than typical microstrip patch arrays. The measured impedance bandwidths of the designed unidirectional slot arrays were 19.8, 15.3, and 16.7%, respectively, with peak gains of 11.7, 13.9, and 14.4 dBi. Measured results show very good agreement with the simulated results, which serves as validation of the array design procedure and the accuracy of the simulated results.http://journals.cambridge.org/action/displayJournal?jid=MRFhb201

Anomalous reflection from a phase gradient metasurface with arbitrary incident angle

A planar phase gradient metasurface (PGM) with phase gradients in two in-plane directions will introduce two additional wave vectors to the reflected wave vector. For small incident angles, close to the normal vector, the magnitude of the reflected wave vector is smaller than that of the incident wave vector and the direction of the anomalous reflected wave can be determined from the incident wave vector components and additional phase gradient components. The expanded generalized Snell’s law, which includes diffraction order modes, is combined with array theory to accurately predict the directions of the reflected waves from a planar PGM for incident angles where the magnitude of the reflected wave vector is larger than that of the incident wave vector. The predicted directions of the reflected waves from a planar PGM are compared with simulated RCS results obtained with CST Studio Suite and measured results obtained in a compact range.https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639Electrical, Electronic and Computer Engineerin

Antenna with a reactive impedance substrate for mine rescue applications

Two electrically small, reactive impedance surface (RIS) backed, antennas are presented that can be used by rescue workers to locate miners in emergency situations in underground mines. One antenna was designed for optimum impedance bandwidth and the other for compact size, with at least 5% impedance bandwidth. At 433 MHz both antennas have maximum gain values above 5 dBi, and both antennas radiate on average at least 10 dB more power in the front hemisphere than in the rear hemisphere, to reduce interaction with the wearer and aid in locating the missing miners. The first antenna, a planar monopole antenna with RIS backplane had a −10 dB reflection coefficient bandwidth of 25.1%, and a form factor of 0.4 λ0 by 0.4 λ0 by 0.069 λ0. The second antenna, a loaded planar monopole antenna with RIS backplane had a −10 dB reflection coefficient bandwidth of 5.3%, and a form factor of 0.346 λ0 by 0. 346 λ0 by 0.107 λ0. Measured and simulated results for the two antennas are presented.National Research Foundation (NRF) of South Africa, Grant/Award Number: 114941.http://wileyonlinelibrary.com/journal/mop2020-01-01hj2018Electrical, Electronic and Computer Engineerin

The measurement of complex antenna transfer functions for ultra-wideband antennas in a compact range

Ultra-wideband (UWB) communications technology increasingly plays an important role in modern communications systems. The complex antenna transfer function (CATF) of an UWB antenna provides valuable information that can be used for better UWB channel and communication system designs. Currently only the two-antenna and three-antenna measurement techniques are used to measure the transfer function and impulse response of UWB antennas. In this paper a modified version of the gain-transfer method is presented to enable the characterization of UWB antennas using a compact antenna test range facility (CATR). A double-ridged guide horn (DRGH) antenna is used as UWB transfer-standard and the CATF of the transfer-standard is determined a priori using full-wave simulations. The gain-transfer method to measure the CATF of UWB antennas in a CATR is illustrated with two test cases. In the first test case the measured CATF of an ETS-LINDGREN DRGH antenna was verified with numerical data from a FEKO model of the antenna. The second case compares the CATF of an UWB circular disc monopole antenna measured in a CATR to measured data usingNational Research Foundation of South Africa.http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7011037hb201

Wideband antenna for 4G MIMO applications

A small, wideband, multiple-input-multiple-output antenna is presented for 4G long term evolution (LTE) applications. The proposed antenna consists of a vertically polarized wideband stepped slot, as well as a horizontally polarized narrowband, uniform slot, integrated on a single substrate and fed by two ports. A prototype of the proposed antenna was designed, fabricated, and measured. The stepped slot antenna achieves an enhanced bandwidth of 122% from 0.77 GHz to 3.12 GHz, covering the 2G, 3G, and 4G bands. The narrowband slot achieves a bandwidth of 35% from 2.11 GHz to 3.01 GHz, covering the 4G band frequencies only. The isolation between the two slots is greater than 21 dB over the entire band of interest. The radiation pattern of the wideband slot in the horizontal plane is omnidirectional in nature while the narrowband slot exhibits a bidirectional radiation pattern in the horizontal plane. The proposed antenna is suitable for indoor, ceilingmount, microcell 4G LTE applications.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1098-27602018-03-31hb2017Electrical, Electronic and Computer Engineerin

Elliptically shaped quad-ridge horn antennas as feed for a reflector

Quad-ridge horn antennas of various geometries are considered as possible candidates for a wideband reflector antenna feed. It is demonstrated that shaping the sidewalls of the ridge horns significantly improves the radiation characteristics of the horns. The conical quad-ridge horn with an elliptically shaped sidewall shows the most promise as a wideband reflector antenna feed. The radiation patterns are rotationally symmetric, and the 10-dB beamwidth is reasonably constant over a wide frequency range.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?reload=true&punumber=772

Quad-ridge horn antenna with elliptically shaped sidewalls

We present a quad-ridge horn antenna as a feed for a reflector antenna for use in radio astronomy applications. The antenna uses elliptically shaped sidewalls to limit the variation of beamwidth over a wide frequency range and to obtain greater radiation pattern rotational symmetry. The antenna is dual-polarized and matched over more than a 4:1 bandwidth. A design procedure is presented and a prototype designed according to this procedure is shown. Measured and simulated results of the prototype agree with each other well. The antenna is analyzed with a prime focus reflector to determine the range of efficiencies that can be expected.National Research Foundationhttp://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=8hb2014ai201

A dipole with reflector-backed active metasurface for linear-to-circular polarization reconfigurability

DATA AVAILABILITY STATEMENT : The data presented in this study are on request from the main author.In recent years, significant advances have been made in diversifying the capabilities of communication systems by using reconfigurable antennas. There are many types of reconfigurable antennas—to achieve pattern, frequency, or polarization reconfigurability. These antennas are reconfigured either by the mechanical rotation of surfaces or by enabling or disabling specific sections of the structure using electrical switches. This paper focuses on the concept of a polarization reconfigurable antenna based on an active reflector-backed metasurface. An antenna system based on an active reflector-backed metasurface combined with a planar dipole is designed to achieve reconfigurable polarization. The polarization of the designed antenna can be switched between linear and circular polarization states using positive-intrinsic-negative diodes located in the unit cell elements of the metasurface. The measured results correlate well with the simulated results. The antenna has a physical size of 308 × 162 × 35 mm3 with an impedance bandwidth of 4.5% in the linear state and 7% in the circular state, as well as an axial ratio bandwidth larger than 8.3%.http://www.mdpi.com/journal/materialshj2023Electrical, Electronic and Computer Engineerin