Leaky travelling wave antennas that use the first microstrip higher-order mode are analysed. The antennas investigated here are only half the width of previous leaky wave designs and utilise a structure that inherently suppresses the fundamental mode. Since mode purity is assured, the need for an elaborate feed structure is eliminated. A means for extracting the complex propagation constant of a leaky wave antenna is presented using the finite difference time domain (FDTD) method. Agreement is shown between the resulting propagation constant and another established theoretical method, the transverse resonance method. Representative measured far-field patterns are included, which are consistent with the computed propagation constants. The properties of curving the leaky wave structure are also studied.

Half width leaky wave antennas

A new method for designing the multilayered filter, diplexer, and triplexer is proposed in this paper. The main structure of the multilayered filter is a parallel-coupled line connected with a capacitor. By properly controlling the coupling coefficient between the parallel-coupled line and the capacitor, the transmission zero will appear at the lower or higher passband's skirt. Moreover, such characteristics can be employed to design the diplexer as well for dual- or quad-band portable telephones. In order to miniaturize the size of the circuit and to improve its performance, multilayered structure and the low-temperature co-fired ceramic technology are employed to design and fabricate the filter. Theoretical analysis and design procedures are also provided. Measurement results of fabricated examples are shown to match well with the electromagnetic simulation, which validate the proposed structure.

Design methodologies of LTCC bandpass filters, diplexer, and triplexer with transmission zeros

A new type of circularly polarized printed periodic leaky-wave antenna (LWA) structure with a wide scanning range and reduced sidelobe level (SLL) is presented Fifteen matched unit cells (UCs) are cascaded along the direction of propagation to provide seamless frequency scanning from 20 to 29 GHz with a scanning range of 95° from backward to forward quadrant The open-stopband has been suppressed around the broadside region by matching the input impedance of the UC to the characteristic impedance of the transmission line Two empirical transmission line models are presented to describe the behavior of the periodic LWA Parametric study using full-wave simulation is used to improve the SLL and minimize the axial ratio of the circular polarization leading to a fully optimized periodic leaky LWA

Backward to Forward Scanning Periodic Leaky-Wave Antenna With Wide Scanning Range

In this paper, the use of a dispersive prism with a triangular shape is proposed to reduce the dispersive radiation nature of a leaky-wave antenna (LWA) in groove-gap waveguide technology. The operation of gap waveguide technology is based on the use of metallic pins that act as an artificial magnetic conductor, so the electromagnetic fields are confined and guided in the desired directions. To control a leaky-wave radiation of these confined fields is possible by tailoring the height of the pins, its periodicity, and the waveguide width. This radiation, as in any conventional LWA, is dispersive, leading to beam squint as the frequency is varied. Here, we mitigate this beam squint by using a prism made of dispersive pins and choosing appropriately their periodicity and height. With this prism, the leaky-wave radiation is focused into one single direction in a wide frequency band. This concept is demonstrated with a prototype designed to radiate at $\varphi =41^\circ $ with a central frequency of 12 GHz and the high gain of 16.5 dBi. A 22% frequency bandwidth for the 3 dB realized gain at $\varphi =41^\circ $ is achieved, and the main radiating direction, with half-power beamwidth of 5°, steers only ±0.5° from 11.4 to 13.4 GHz.

/pdf/low-dispersive-leaky-wave-antenna-integrated-in-groove-gap-3c35lpqd6l.pdf

Low-Dispersive Leaky-Wave Antenna Integrated in Groove Gap Waveguide Technology

New communications systems require high-speed data transfer and need high frequency, wideband, and directive antennas. Leaky-wave antennas are a desirable type of antennas for millimeter and submillimeter waves, since they can produce a high directive radiation with a single feeding. The latter is an enormous advantage to reducing the cost and losses at high frequency. Despite these advantages, their dispersive nature inherently produces a beam squint effect in their radiation patterns. Here, we propose the use of a lens that compensates for the dispersion of the leaky wave, making the overall antenna broadband. This concept is demonstrated in substrate integrated waveguide technology at Ka-band, and the lens is integrated in the same technology. Full-wave simulations and experimental results are presented to demonstrate the potential of our proposal. Our manufactured prototype has more than 20% frequency bandwidth for the 3-dB pattern at $\varphi =31^\circ $ , and the main radiating direction steers only ±0.5° from 35 to 40 GHz with a half-power beamwidth of 8°.

Substrate Integrated Waveguide Leaky-Wave Antenna With Wide Bandwidth via Prism Coupling

This study proposes a novel scheme based on the characteristics of leaky-wave antennas for the empirical design of broadband tapered microstrip leaky-wave antennas. This scheme can explain and approximately model the radiation characteristics of a linearly tapered leaky-wave microstrip antenna. A broadband feeding structure that uses the balanced and the inverted balanced microstrip lines to form a pair of broadband baluns is also presented. The measured return loss of the inverted balanced microstrip lines has a VSWR/spl les/2 from dc to 18.6 GHz and that of the back-to-back feeding structures has a VSWR/spl les/2 from 2.2 to 18.6 GHz. This feeding structure can be used to feed a broadband planar leaky-wave antenna with a fixed mainbeam that uses the tapered microstrip structure. The measured bandwidth of the antenna for a VSWR/spl les/2 exceeds 2.3:1.

https://ir.nctu.edu.tw:443/bitstream/11536/27679/1/000184769400024.pdf

Broadband tapered microstrip leaky-wave antenna

A chip-type low-temperature co-fired ceramic (LTCC) multilayer ceramic (MLC) balun is presented in this paper. This balun is designed using the stepped impedance method. It uses a multilayer structure, meander lines, and multisection coupled lines. The use of multisection couple lines that have various characteristic impedance ratios can shrink the length of a quarter-wavelength coupled-transmission line and makes it very easy to match various impedances of balanced output. The proposed chip-type balun operates over a bandwidth of 2.25-2.65 GHz. The in-band phase and amplitude balances are excellent because of the symmetric structure and transmission-line trimming section. Measured results of the chip-type LTCC-MLC balun match well with the computer simulation. Index Terms—Balun, chip-type component, LTCC, MLC, mul- tisection coupled lines, stepped impedance method.

http://ieeexplore.ieee.org/iel5/22/20945/00971619.pdf

Chi-Yang Chang

Papers

Broadband tapered microstrip leaky-wave antenna

Chip-Type LTCC-MLC Baluns Using the Stepped