A novel structure for a composite right/left-handed (CRLH) corrugated waveguide in the millimeter-wave band is proposed. The CRLH waveguide is composed of a rectangular waveguide with tilted corrugations on its bottom broad wall. By operating above and below the cutoff frequency of the dominant mode of the rectangular waveguide, the CRLH waveguide provides, respectively, an inherent series inductance and shunt capacitance, and an inherent shunt inductance. Moreover, the tilted corrugations provide a series inductance and a series capacitance, which can support CRLH propagation. A frequency-scanning antenna using this CRLH waveguide is also studied numerically and experimentally. The results demonstrate that the antenna can provide backward-to-forward beam scanning, including the broadside direction. A scanning angle from -9.9 to +2.2 is achieved within a 1.8-GHz frequency range in the 60-GHz band.

In order to improve the antenna gain, a composite right/left-handed (CRLH) leaky-wave (LW) antenna composed of symmetrical unit cells with short stubs terminated by vertical vias is designed. The use of symmetrical unit cells suppresses the cross-polarization of radiation to less than 23 dB. By comparing the measured radiation characteristics to that of a conventional CRLH LW antenna without short stub in the X-band, it is shown that the presented CRLH LW antenna with 51 unit cells offers a narrower beam and the antenna gain improves 4.1, 2.2 and 3.1 dB in the backward, broadside and forward directions of radiation, respectively.

A novel two-dimensional (2D) beam scanning antenna array using composite right/left-handed (CRLH) leaky-wave antennas (LWAs) is proposed. The antenna array consists of a set of CRLH LWAs and a Butler matrix (BM) feeding network. The direction of the beam can be scanned two-dimensionally in one plane by changing frequency and in the other plane by switching the input ports of the BM. A four-element antenna array in the microstrip line configuration operating at 10.5 GHz is designed with the assistance of full-wave simulations based on the method of moment (MoM) and the finite-element method (FEM). The antenna array is fabricated and radiation characteristics are measured. The wide range 2D beam scanning operation with the angle from -30 deg to +25 deg in one plane by sweeping frequency from 10.25 GHz to 10.7 GHz and with four discrete angles of -46 deg, -15 deg, +10 deg, and +35 deg in the other plane by switching the input port is achieved.

A novel planar composite right/left handed (CRLH) transmission line (TL) with double-sided metal patterns, which is advantageous in high scalability and low-cost fabrication, is proposed. Fundamental characteristics of the unbalanced and balanced CRLH TLs are confirmed numerically and theoretically both by full-wave finite-element method (FEM) simulations and the equivalent circuit analysis in terms of dispersion characteristics and characteristic impedances for the periodic structure. It is also shown that the relations between the left-handed circuit parameters and the geometrical parameters of the unit cell are simple and intuitive, which is useful for designing the CRLH TL. Experiments on 10-cell unbalanced and balanced CRLH TLs are carried out and the left-handed and right-handed wave propagations are confirmed by scattering parameter and near field measurements.

A novel structure for a frequency-independent steerable composite right/left-handed (CRLH) leaky wave (LW) antenna in the millimeter-wave band is proposed. This has the advantages of wide beam scanning and low profile, and is a suitable structure for mass-production. The proposed antenna has features wherein a movable dielectric slab is placed above the CRLH LW antenna, and the radiation angle can be steered by changing the distance between the slab and the antenna using compact actuators. Moreover, slots are added to the antenna to control the aperture amplitude distribution of the array antenna in order to enhance aperture efficiency. A prototype CRLH LW antenna has been fabricated with these slots, and backward-to-forward beam scanning characteristics at 76 GHz have been demonstrated successfully by measurement. A wide scanning angle from 73 to 114 deg. has been achieved experimentally. The aperture efficiency is 25.3%.

A planar composite right/left-handed leaky wave antenna which operates at W-band is fabricated and its backward to forward beam scanning operation including broadside direction is confirmed experimentally. The scanning angle from 61 to 114 degrees with a frequency scanning range of 76 to 79 GHz is achieved.