A uniplanar leaky-wave antenna (LWA) suitable for operation at millimeter-wave frequencies is introduced. Both unidirectional and bidirectional versions of the antenna are presented. The proposed structure consists of a coplanar waveguide fed linear array of closely spaced capacitive transverse slots. This configuration results in a fast-wave structure in which the n=0 spatial harmonic radiates in the forward direction. Since the distance, d, between adjacent elements of the array is small d/spl Lt//spl lambda//sub o/, the slot array essentially becomes a uniform LWA. A comprehensive transmission line model is developed based upon the theory of truncated periodic transmission lines to explain the operation of the antenna and provide a tool for its design. Measured and simulated radiation patterns, directivity, gain, and an associated loss budget are presented for a 32-element antenna operating at 30 GHz. The uniplanar nature of the structure makes the antenna appropriate for integration of shunt variable capacitors such as diode or micro-electromechanical system varactors for fixed frequency beam steering at low-bias voltages.

/pdf/leaky-cpw-based-slot-antenna-arrays-for-millimeter-wave-5aeciiaytj.pdf

Leaky CPW-based slot antenna arrays for millimeter-wave applications

A low profile coplanar waveguide (CPW) fed printed slot antenna is presented with uni-directional radiation properties. The slot antenna radiates above a closely spaced artificial magnetic conducting (AMC) reflector consisting of an array of rectangular patches, a substrate and an electric ground plane. The electromagnetic bandgap (EBG) performance of the cavity structure between the upper conducting surface in which the slot is etched, and the ground plane at the bottom of the reflector, is investigated using an equivalent waveguide feed in the place of a half-wavelength section of the slot antenna. From the reflection coefficient of the equivalent waveguide feed one can determine the frequency band where minimum energy will be lost due to unwanted radiation from the cavity sides. The dimensions of the cavity were found to be very important for minimum energy loss. Experimental results for the final antenna design (with a size of 1.02λ0×0.82λ0×0.063λ0), mounted on a 1.5λ0×1.5λ0 back plate, exhibit a 5% impedance bandwidth, maximum gain in excess of 10 dBi, low cross-polarization, and a front-to-back ratio of approximately 25 dB. This low-profile antenna with relatively high gain could be a good candidate for a 2.4 GHz WLAN application.

/pdf/cpw-fed-cavity-backed-slot-radiator-loaded-with-an-amc-24dfo68mp5.pdf

CPW-Fed Cavity-Backed Slot Radiator Loaded With an AMC Reflector

Gain enhancement of a V-band planar antenna in the form of a low-profile Fabry-Perot cavity (FPC) is proposed. This simple design is based on placing a perforated metallic cap, forming a frequency-selective-surface (FSS), over a printed-circuit-board (PCB). An integrated slot-dipole antenna is etched in a thin layer of copper (the ground plane) printed on the other side of the PCB. The metallic cap is self-sustained with surrounded metallic sidewalls. Besides showing the simplicity of such design, we also provide a novel comprehensive analysis using a transmission-line model of a FPC along with the two-port circuit model of the thick FSS. The leaky-wave interpretation for the cavity radiation is also addressed to estimate the effective radiation area and therefore the size of the cap. It will be shown that placing the cap on top of the PCB, besides enhancing the directivity of the feeding-slot reduces its backward radiation. A FPC prototype operating in the 60 GHz wireless band, is fabricated and measured showing good agreement between the simulated and measured results.

Gain Enhancement of a V-Band Antenna Using a Fabry-Pérot Cavity With a Self-Sustained All-Metal Cap With FSS

A number of new antenna-related applications that have recently been developed at the University of Toronto based on the concept of negative-refractive-index transmission-line metamaterials are reviewed. These include non-radiating phase-shifting lines that can produce either a positive or a negative phase-shift while exhibiting a broadband linear phase response, as well as compact and broadband series power dividers and associated planar series-fed printed dipole arrays with reduced beam-squinting. Moreover, a fully printed electrically small ring antenna featuring vertical polarisation and good radiation efficiency is also described.

Antenna applications of negative-refractive-index transmission-line structures

A packaging solution for the integration of an MMIC and a thin film antenna into a single surface-mountable package is presented. It is based on an air cavity in the package base into which the MMIC is placed. All package-to-MMIC interconnects are routed through the antenna substrate and all connections are realized using flip chip technology. Thus wire bonds are eliminated within the whole package. A broadband flip chip interconnect is used to connect MMIC and antenna. As the antenna is situated above an air cavity, a large bandwidth is also achieved for the antenna. An antenna-in-package prototype is presented to demonstrate the feasibility of the assembly process and to test the antenna performance including the flip chip interconnect. The influence of an additional package cover is analyzed by measuring the antenna covered with two different lids.

Integrated 122-GHz Antenna on a Flexible Polyimide Substrate With Flip Chip Interconnect

Introduces new techniques and architectures for the implementation of linear slot arrays on electrically thick dielectric substrates at millimeter-wave frequencies. The slot arrays are fed by a coplanar waveguide series line and lead to high gain by utilizing the phase cancellation technique to reduce coupling to the dominant surface-wave mode. Unlike traditional designs, no meander lines are used in the proposed structures, easing their fabrication by eliminating the need for air bridges and leading to patterns with low cross-polarization and high gain. In addition, the option of including a backing ground reflector to render the patterns unidirectional is explored and implemented. In this latter case, it is shown that simultaneous reduction of the dominant surface-wave and TEM modes through phase cancellation can be achieved. The design of the proposed arrays is based on an intuitive transmission-line model, which enables the implementation of arrays with a gradual current taper and, thus, maximum gain. This study is verified experimentally around a nominal frequency of 27.8 GHz.

High-gain meanderless slot arrays on electrically thick substrates at millimeter-wave frequencies

Although in the literature the back-reflector technique has been extensively used as a means of rendering the slot patterns unidirectional, there is no quantitative information on the effectiveness of this approach. In this work, the use of a back reflector as a means of increasing the efficiency and antenna gain of printed slot antennas is evaluated. For this purpose, the radiation efficiency of reflector-backed printed slot antennas on either electrically thin or thick substrates is thoroughly characterized; both single and twin slot elements are considered. Twin slot elements have been previously proposed for the reduction of the coupling to the dominant surface-wave mode in the case of electrically thick substrates. In this article, twin slot elements are explored as a means of enhancing the radiation efficiency of printed slots backed by a ground reflector. It is shown that in the case of thick substrates, simultaneous partial cancellation of the surface-wave and the parallel-plate TEM modes can be achieved. On the other hand, in the case of thin substrates where the back radiation is severe, the twin slot element can be utilized for the drastic reduction of the parallel-plate TEM mode.

Radiation efficiency of printed slot antennas backed by a ground reflector

This work concerns the performance of uniform broadside linear slot arrays on thick substrates and has a two-fold purpose. The first goal is to systematically examine the surface-wave efficiency with the number of slots and their inter-element spacing. The second goal concerns the optimization of the inter-element spacing for maximizing the overall gain for a given number of antenna elements.

Gain and efficiency of linear slot arrays on thick substrates for millimeter-wave wireless applications

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High-gain meanderless slot arrays on electrically thick substrates at millimeter-wave frequencies

Radiation efficiency of printed slot antennas backed by a ground reflector

Gain and efficiency of linear slot arrays on thick substrates for millimeter-wave wireless applications