J. Miyake

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 from antenna systems with homogeneous and inhomogeneous loops

Two antenna systems, each composed of a single fed antenna and a plane with periodically arrayed elements (PE plane), are investigated. The PE plane of square strip loops, all having the same outer side length and the same strip width (homogeneous PE plane), forms a narrow beam in the direction normal to the PE plane, leading to a high gain. Subsequently, this normal beam is tilted by gradating the strip width of the loops (inhomogeneous PE plane), holding the outer side length at a constant value. As an example, a narrow beam with a tilt angle of 35 degrees and a gain of 17 dBi is demonstrated. It is also found that a modified inhomogeneous PE plane forms a high-gain tilted beam, where the outer side length of the loops is gradated, while keeping the strip width at a constant value.

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.

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.

Recent progress in antennas with an EBG reflector and antennas with periodically arrayed loops

A low-profile curl antenna with an EBG reflector has a relatively wide input impedance bandwidth. Low-profile equiangular- and Archimedean-spiral antennas, each backed by an EBG reflector, have a wider input impedance bandwidth than the curl. A low-profile inverted F antenna above an EBG reflector radiates a tilted beam. An array composed of inverted F antennas combined with switching circuits has a beam that can be scanned. A layer of periodically arrayed loops transforms the axial beam of an antenna into a tilted beam with high directivity.

Effects of an inhomogeneous loop plate on tilted beam formation for a patch antenna

An inhomogeneous loop plate (iHomLP) is composed of M loops in the x-direction and (2N+1) loops in the y-direction. All the loops have the same peripheral length, and have different strip widths in the x-direction. It is found that, as the number of loops (2N+1) is increased, the gain increases gradually and reaches a maximum value. The frequency band of the VSWR is approximately 5.7% for M = 2N + 1 = 9.

Counter circularly-polarized curl antenna with a lossy structure

A curl antenna with a lossy structure is investigated. After presenting the lossless case (Case 0) as the reference for the investigation, the case where lossy capacitors are inserted into the curl arm (Case RCL) is analyzed. Subsequently, the case where lossy inductors are inserted into the curl arm (Case RLL) is investigated. It is found that the radiation pattern for each lossy case is similar to that for Case 0. The amount of reduction in the gain and radiation efficiency due to the losses is revealed.

Circularly polarized spiral antenna using a double negative property

A design process to realize a low-profile spiral antenna with an antenna height of approximately 1/100 wavelength is presented, where a negative phase constant for the current on the spiral arms is used. For circularly polarized radiation, frequency fN, called the N frequency, is located between the lower bound frequency fL for a fast wave and a transition frequency fTR. The antenna characteristics, including the radiation pattern, gain, and input performance (VSWR) are presented and discussed.