Symon K. Podilchak

Compact Disc Monopole Antennas for Current and Future Ultrawideband (UWB) Applications

Circular disc monopole antennas are investigated for current and future ultrawideband (UWB) applications. The studied antennas are compact and of small size (25 mm × 35 mm × 0.83 mm) with a 50-Ω feed line and offer a very simple geometry suitable for low cost fabrication and straightforward printed circuit board integration. More specifically, the impedance matching of the classic printed circular disc UWB monopole is improved by introducing transitions between the microstrip feed line and the printed disc. Two particular designs are examined using a dual and single microstrip transition. By using this simple antenna matching technique, respective impedance bandwidths (|Sn | <; -10 dB) from 2.5 to 11.7 GHz and 3.5 to 31.9 GHz are obtained. Results are also compared to a classic UWB monopole with no such matching network transitions. Measured and simulated reflection coefficient curves are provided along with beam patterns, gain and group delay values as a function of frequency. The transient behavior of the studied antennas is also examined in the time domain.

Surface-Wave Launchers for Beam Steering and Application to Planar Leaky-Wave Antennas

A linear array of surface-wave launchers (SWLs) is presented for surface-wave (SW) beam steering on a grounded dielectric slab (GDS). Specifically, a two-element array of directive Yagi-Uda like SWL antennas (operating between 21-24 GHz) is investigated. By varying the relative phase difference between SWL elements, the excited SW field distribution can be steered. In addition, a six-element linear array of SWLs with nonuniform weighting is also presented. If metallic gratings are placed on top of the GDS, the bound SW mode can be transformed into a radiated leaky-wave (LW) mode and directive beam patterns can be generated in the far field. A specific elliptical grating configuration is also investigated demonstrating single frequency cylindrical-sector LW beam steering. These slotted SWL arrays can be useful for novel SW beam scanning designs, millimeter wave power distribution systems and new LW antennas.

Controlled Leaky-Wave Radiation From a Planar Configuration of Width-Modulated Microstrip Lines

Planar leaky-wave antenna (LWA) designs that utilize a printed surface wave (SW) source are presented. Specifically, by the addition of a periodic arrangement of width-modulated microstrip lines on top of a grounded dielectric slab (GDS), a sinusoidally modulated reactance surface (SMRS) can be realized, providing appropriate conditions for leaky wave (LW) radiation. In addition, a transition section near the SW source improves antenna matching, while also, controlling the leakage rate and aperture distribution. A numerically computed dispersion diagram (DD) for the periodic structure is also calculated in terms of Mathieu functions. Full-wave simulations and measurements are in agreement with the developed numerical model and results suggest that these LWAs can offer broadside radiation as well as continuous beam scanning with radiation efficiencies of more than 85%. In addition, the investigated width-modulated microstrip lines offer ease of fabrication and may also be useful in the design of new periodic structures for wave guidance and other low-cost printed circuits and antennas.

Planar Leaky-Wave Antenna Designs Offering Conical-Sector Beam Scanning and Broadside Radiation Using Surface-Wave Launchers

Two planar antenna designs that utilize surface-waves for leaky-wave excitation are investigated. Specifically, a surface-wave launcher is implemented to excite cylindrical surface-waves, which are bound to a grounded dielectric slab. By the addition of circular metallic strip gratings, a partially reflecting surface is realized, providing appropriate conditions for 2-D leaky-wave radiation. In particular, two designs are investigated: a continuous circular strip and a segmented circular strip grating. Results illustrate conical-sector beam scanning for the continuous circular strip grating between 2022 GHz, while broadside radiation is observed at 21.2 GHz by the segmented circular strip design.

A Methodology for Mutual Coupling Estimation and Compensation in Antennas

A simple methodology is presented for the estimation and compensation of mutual coupling in antenna systems of arbitrary geometries, including antenna arrays in the vicinity of scatterers. The methodology includes both theoretical and experimental schemes, while also, does not resort to assumptions often encountered in previous mutual coupling estimation approaches. In particular, our methodology uses a matrix representation for the antenna system and is based on a new concept, the antenna current Greens function which uses the recently proven inverse reciprocity theorem, or more intuitively, a relation of the transfer function for the transmitting mode of the antenna system to the corresponding transfer function for the receiving mode. Validation is performed by comparing calculated predictions to measurements and simulations of a practical antenna system as well as a two- and four-element array. An algorithm using matrix interpolation, that aims at exploiting the antenna transfer function, is also developed and experimentally demonstrated for practical array calibrations and coupling compensation techniques in array signal processing. The developed procedures are non-specific and can also be applied to a diversity of antenna systems and other complex scattering problems.

Analysis and Design of Annular Microstrip-Based Planar Periodic Leaky-Wave Antennas

A low-cost leaky-wave antenna using cylindrical surface waves propagating on a grounded dielectric slab is proposed. The excited surface waves are then perturbed into a leaky-wave regime, by the addition of annular microstrip-based (“bull-eye”) gratings. Various surface-wave modes may be considered, however, we desire to achieve radiation from the fundamental TM0 mode due to its zero cutoff frequency and possibility for efficient excitation. A comprehensive design strategy is detailed in the paper. It is based on both an accurate knowledge of the modal spectrum, obtained with the method of moments, and an analysis of the resonant modes supported by the constituent microstrip rings. To further support our methodology, numerical calculations, full-wave simulations, and antenna measurements are reported for the basic structure. Also, additional designs for enhanced gain at broadside, reduced cross-polarization levels, and improved wide-angle frequency beam scanning are presented.

Optimization of a Planar “Bull-Eye” Leaky-Wave Antenna Fed by a Printed Surface-Wave Source

A microstrip-based leaky-wave antenna for two-sided frequency beam scanning and broadside radiation is presented. In particular, the optimized “bull-eye” ring structure is designed to support leakage of the fundamental TM mode of the guiding structure in a regime without any other leaky- or surface-wave modes. Also by following suggested design rules, to achieve good isolation between the printed rings and the TM source, a beam scan angle range of 121° can be realized over an operating bandwidth of more than 40% with antenna mismatch losses of less than 0.14 dB. Supporting numerical calculations are also in agreement with the simulations and antenna measurements.

Broadside Radiation From a Planar 2-D Leaky-Wave Antenna by Practical Surface-Wave Launching

A planar 2-D leaky-wave (LW) antenna, capable of broadside radiation, is presented for millimeter wave applications. A directive surface-wave launcher (SWL) is utilized as the antenna feed exciting cylindrical surface-waves (SWs) on a grounded dielectric slab (GDS). With the addition of a segmented circular strip grating, cylindrical LWs can be excited on the antenna aperture. Measurements illustrate maximum gain at broadside at 19.48 GHz in both the E and H planes with a 10deg half power beamwidth. Specifically, a directive pencil beam is observed just at the edge of the TE1 SW mode cuttoff frequency of the slab (19.47 GHz), suggesting maximum radiation at the edge of a TE stopband.

Planar Surface-Wave Sources and Metallic Grating Lenses for Controlled Guided-Wave Propagation

Guided surface-waves (SWs) on planar substrates are generally an adverse effect that can degrade the performance of monolithic integrated circuits and antenna arrays. However, with appropriate boundary conditions, such SWs can be harnessed as an efficient means of power transport achieving bound propagation along a dielectric slab. Furthermore, by the addition of planar metallic grating configurations an effective dielectric constant can be achieved, refracting cylindrical SWs transmitted from a central surface-wave launcher (SWL) source. Specifically, two metallic grating lenses are investigated for millimeter-wave frequencies of operation, offering either the convergence or divergence of bound SWs. In addition, design concepts are extended to a novel planar coupler. These metallic grating lenses and directive SWL sources can be useful for new quasi-optical millimeter-wave circuits and planar leaky-wave antennas.

Planar circular disc monopole antennas using compact impedance matching networks for ultra-wideband (UWB) applications

Two planar circular disc antennas that utilize compact impedance matching networks for current and future ultra-wideband (UWB) applications are investigated. The proposed designs have a physically small size (30 mm × 35 mm) and simple geometry, and offer a relatively large bandwidth (BW). Input energy is launched through a 50-Ω feedline (attached to a K-Connector) and broadband antenna matching is improved by introducing transitions between the feedline and the printed circular discs. Specifically, two designs are investigated using single- and duel-microstrip line transitions. By using this antenna matching technique, respective BWs (|S11|≪−10 dB) of 3.18 to 11.74 GHz and 3.47 to 31.94 GHz are obtained. Results are compared to an analogous UWB monopole with no matching network transitions. Measured and simulated radiation patterns are presented along with reflection loss values up to 40 GHz.