In this communication, we present a new circularly-polarized array antenna using 2×2 linearly-polarized sub grid arrays in a low temperature co-fired ceramic technology for highly-integrated 60-GHz radio. The sub grid arrays are sequentially rotated and excited with a 90°-phase increment to radiate circularly-polarized waves. The feeding network of the array antenna is based on stripline quarter-wave matched T-junctions. The array antenna has a size of 15×15×0.9 mm3. Simulated and measured results confirm wide impedance, axial ratio, pattern, and gain bandwidths.

A Circularly-Polarized Array Antenna Using Linearly-Polarized Sub Grid Arrays for Highly-Integrated 60-GHz Radio

The design of a high-gain microstrip grid array antenna (MGAA) for 24-GHz automotive radar sensor applications is first presented. An amplitude tapering technique utilizing variable line width on the individual radiating element is then applied to lower sidelobe level. Next, the MGAA is simplified to a microstrip comb array antenna (MCAA). The MCAA shows broader impedance bandwidth and lower cross-polarization radiation as compared with those of the MGAA. The MCAA is designed not as a travelling-wave but a standing-wave antenna. As a result, the match load and the reflection-cancelling structure can be avoided, which is important, especially in the millimeter-wave frequencies. Finally, an emphasis is given to 45° linearly-polarized MCAA because the radiation with the orthogonal polarization from cars coming from the opposite direction does not affect the radar operation.

Microstrip Grid and Comb Array Antennas

We examine the current development of highly integrated 60-GHz radios with an interest in antenna-circuit interfaces. We design and analyze grid array antennas with special attention to the differential feeding and the patterned ground plane. More importantly, we integrate two grid array antennas in a package; propose the way of assembling it to the system printed circuit board; and demonstrate a total solution of low cost and thin profile to highly integrated 60-GHz radios. We show that the package in low temperature cofired ceramic (LTCC) technology measures only 13×13×0.575 mm3 ; can carry a 60-GHz radio die of current and future sizes with flip-chip bonding; and achieves good antenna performance in the 60-GHz band with maximum gain of 13.5 and 14.5 dBi for the single-ended and differential antennas, respectively.

Dual Grid Array Antennas in a Thin-Profile Package for Flip-Chip Interconnection to Highly Integrated 60-GHz Radios

The input impedance matrix element of the method of moments (MoM) for an arbitrarily shaped wire antenna printed on a dielectric material Z/sub m,n/ is formulated to be composed of three terms Z/sup /spl psi/s//sub m,n/, Z/sup /spl psi///sub m,n/, and /spl Delta/Z/sub m,n/ involving single-, double-, and triple-integral calculations, respectively. The MoM based on the Z/sub m,n/ formulated in this paper (new MoM) is applied to two antennas-a meander loop antenna and a grid array antenna-as well as a simple loop used as a reference antenna. The computation time to obtain the current distribution of each antenna by the new MoM technique is compared with the time required for the conventional MoM, which has an impedance matrix element composed of four terms, all involving triple-integral calculations. It is revealed that the new MoM drastically reduces the computation time: for example, by a factor of 937 for the grid array antenna. In addition, the radiation characteristics of these two antennas are discussed. It is found that a reduced-size meander loop (62% smaller than the simple loop reference) has a radiation pattern similar to the simple loop reference. It is also found that the grid array has an axial beam radiation pattern without side lobes in the principal planes.

A fast MoM calculation technique using sinusoidal basis and testing functions for a wire on a dielectric substrate and its application to meander loop and grid array antennas

The radiation characteristics of a wideband conformal end-fire antenna array mounted on a large conducting cylinder are investigated in this communication. By employing balanced Vivaldi antenna element, the antenna array has ultra-wide bandwidth, low cross-polarization levels, and wide 3 dB beam-width. It is shown that using a larger antenna height, shorter distance away from the edge of a hollow conducting cylinder, and bigger slant angle of antenna element leads to better end-fire radiation performances. Measured radiation patterns are compared with simulated values and a good agreement is observed. A radome-antenna system is also studied and it is found that the antenna has a larger beam-pointing angle in the H-plane owing to the electromagnetic waves reflected from a dielectric radome surface, while retaining its symmetric pattern in the E-plane. These findings may provide useful insights and guidelines for the design of large radome-antenna systems mounted a cylindrical platform.

A Wideband Conformal End-Fire Antenna Array Mounted on a Large Conducting Cylinder

A grid array antenna, which is backed by a conducting plane, is a low-profile flat antenna consisting of numerous radiation and transmission line elements. This paper presents a cross-mesh (CM) array antenna, which is regarded as an extension of the grid array antenna. The CM array antenna is decomposed into two grid arrays (x- and y-directed grid arrays). It is emphasized that the CM array antenna has four feed points, unlike the grid antenna: a, b, c, and d, where a and c belong to the x-directed grid array and b and d belong to the y-directed grid array. The purpose of this paper is to reveal the radiation characteristics of the CM array antenna.

A cross-mesh array antenna

A grid array antenna acts as a radiation element of linear polarization. This paper presents the radiation characteristics of two cross-mesh array antennas each composed of two grid array antennas. It is found that the cross-mesh can radiate a dual linearly polarized (LP) wave and a dual circularly polarized (CP) wave. The frequency responses of the gain and axial ratio are calculated.

Cross-mesh array antennas for dual LP and CP waves

A grid array antenna is a radiation element of linear polarization. The feed point is located at the left or right edge of the antenna structure. As the frequency changes, the beam direction varies due to the phase change in the current along the grid cells. This paper presents the radiation characteristics when the grid array antenna is excited from its center point. For this excitation a coaxial line is used. The frequency response of the gain in the broadside direction is evaluated. Special attention is paid to antenna dimension reduction. The antenna dimensions can be reduced by shortening the side length of each grid cell. A comparison between the gains of the grid array antennas with and without dimension reduction is made and discussed.

Grid array antennas

A conformal spiral antenna above a finite-length conducting cylinder has been numerically analyzed using the method of moments (MoM). In this paper, spiral elements are arrayed above a conducting cylinder. The radiation characteristics of the array are evaluated with emphasis on the radiation patterns. The formation of an omnidirectional radiation pattern is discussed. The mutual coupling among spiral elements is investigated. The radiation patterns calculated by the MoM are compared with those calculated by the pattern multiplication method (PMM). The limitations of the PMM calculation are revealed.

A conformal spiral array antenna radiating an omnidirectional circularly-polarized wave

It is known that a grid array antenna radiates a linearly polarized wave. This paper presents the radiation characteristics of the grid array antenna with c-figured elements. Calculations show that the radiation field is circularly polarized. The frequency responses of the gain and axial ratio in the broadside direction are evaluated. A comparison between the radiation characteristics of the grid array antennas with and without c-figured elements is made and discussed.

T. Kawano

Papers

A cross-mesh array antenna

Cross-mesh array antennas for dual LP and CP waves

Grid array antennas

A conformal spiral array antenna radiating an omnidirectional circularly-polarized wave

Grid array antenna with c-figured elements