H. Nakano

Metamaterial Spiral Antenna

Conventional spiral antennas radiate either a left-handed circularly polarized (CP) wave or a right-handed CP wave in a specific direction (single CP radiation). This letter presents a novel spiral antenna, designated as the metamaterial spiral, which radiates a dual CP wave. First, the principle for left-handed CP radiation and right-handed CP radiation is explained using “current bands.” Second, based on this principle, a prediction for dual CP radiation is made for a spiral structure. Third, for confirming this prediction, spiral arms are constructed using numerous straight filaments, each having a left-handed property with an inherent right-handed property. Numerical simulation confirms the predicted dual CP radiation. The gain and radiation pattern are discussed.

Dual-Band Counter Circularly Polarized Radiation From a Single-Arm Metamaterial-Based Spiral Antenna

A single-arm spiral antenna whose arm is made of a metamaterial (MTM) transmission line having right- and left- handed properties is discussed. This antenna, abbreviated as the 1-MTM-SPA, has an extremely low-profile structure (0.016 wavelength at a balanced frequency of 3 GHz) and does not need a balun circuit. It is predicted that the 1-MTM-SPA will operate as a circularly polarized (CP) antenna, where right-handed CP radiation is obtained within a particular frequency band and left-handed CP radiation is obtained within a different frequency band. Numerical analysis results obtained using two different techniques confirm the prediction for this dual-band counter-CP radiation. The 1-MTM SPA used for the confirmation shows an overlapping gain and axial ratio bandwidth of approximately 7%. The VSWR relative to the Bloch impedance value is less than two within the overlapping bandwidth, as desired. Experimental data are also presented.

Radiation Characteristics of a Metaloop Antenna

A dual-band counter-circularly polarized (CP) square loop antenna is investigated. This loop antenna has a single feed point, and the loop arm is composed of numerous segments with capacitive and inductive elements that generate a negative phase constant. When the loop is wound in the counterclockwise direction from the feed point, a left-handed (LH) CP wave is obtained below the balanced frequency (3 GHz), and a right-handed (RH) CP wave is obtained above the balanced frequency. Such counter CP radiation cannot be obtained using a conventional single-feed loop antenna. The LHCP and RHCP radiation patterns are compared, and the frequency bandwidths for the axial ratio and gain are revealed. The VSWR within these CP radiation bands is small, as desired. The experimental results validate the theoretical results.

Metahelical antenna using a left-handed property

A dual-band metahelical antenna that has a negative phase constant for the current on the helical arm is realized. A left-handed circularly polarized (CP) wave is obtained within a specific frequency band and a right-handed CP wave is obtained within a different frequency band. The antenna characteristics, including the radiation pattern, gain, and input performance (VSWR) are presented and discussed.

Extremely low-profile metamaterial-based curl antenna

A curl antenna is designed using the metamaterial concept (left-handed property). The antenna radiates a circularly polarized (CP) wave, and has a small antenna height. When the antenna height is 1.6 mm= 0.016 wavelength at 3 GHz, the curl has an approximately 10% gain bandwidth. The rotational sense of the radiated CP wave below the balanced frequency is opposite to the arm winding direction.

Metaloop for linearly polarized radiation

A metaloop antenna that has a negative propagation phase constant for the current on its closed arm is proposed and investigated. A linearly polarized (LP) broadside radiation pattern is obtained at different frequencies below and above frequency fT, where the propagation phase constant is zero. In addition, it is revealed that the metaloop forms an LP dual-peak radiation pattern at different frequencies below and above fT. The gain and input performance (VSWR) are also presented.

Left-handed loop antenna

This paper presents the radiation characteristics of a low-profile circularly polarized loop antenna that has a left-handed property. The antenna height is set to be small (less than 0.03 wavelength). The gain, axial ratio, radiation efficiency, and VSWR are discussed.

Effects of pitch and ground plane size on monofilar metamaterial spiral antenna characteristics

A monofilar rectangular metamaterial spiral (MTM SPA) is composed of a ground plane, a dielectric substrate, a conducting spiral arm with capacitors and inductors. The height of the spiral arm above the ground plane is extremely small: approximately 0.01 wavelength. The MTM SPA acts as a counter circularly-polarized radiation element (anti-CP radiation element). This paper discusses the effects of the pitch and the ground plane size on the antenna characteristics. The squint of the radiation is also discussed.

Counter circularly-polarized loop antenna

A dual-band counter circularly-polarized (CP) loop antenna is proposed, where the antenna has a single feed point. Analysis is performed to reveal the effects of a lossy antenna structure on the radiation characteristics. The amount of reduction in the maximum gain and radiation efficiency due to the losses is revealed.

Metamaterial-based curl antenna

The MTM-based curl (having a height of approximately λ/100) radiates a dual-band anti-CP wave. It is found that the radiation pattern remains unchanged, as long as the substrate side length s_sub (= ground plane side length s_GP) is greater than 0.22λ_N. It is also found that the frequency response of the gain does not change when the ground plane side length s_GP is varied with a fixed s_sub = 0.22λ_N. The frequency band width is 9.6% for gain G_L and 9.7% for gain G_R.