Estimation of Detection Performance for Vehicle FMCW Radars Using EM Simulations

This paper proposes a systematic method for estimating detection performances of a frequency-modulated continuous wave radar using electromagnetic simulations. The proposed systematic method includes a radar system simulator that can obtain range-Doppler images using the electromagnetic (EM) simulations in conjunction with a test setup employed for performance evaluation of multiple targets at different velocities in a traffic environment. This method is then applied for optimizing the half-power beamwidths of the antenna array using an evaluation metric defined to improve the detection strengths for the multiple targets. The optimized antenna has vertical and horizontal half-power beam widths of 10??? and 60???, respectively. The results confirm that that the proposed systematic method is suitable to improve the radar detection performance with the enhanced radar-Doppler images

Millimeter-Wave Metal Reflectarray Antennas with Sub-Wavelength Holes

Reflectarray antennas composed of rectangular grooves with sub-wavelength holes on a metal plate are designed for millimeter-wave regions. All depths of multiple grooves in the metal reflectarray are elaborately manipulated for a high-gain reflector. A sub-wavelength hole in each groove reduces the mass of the reflectarray antenna, which rarely affects the re-radiated millimeter-wave filed from the groove. In this paper, we have demonstrated light high-gain reflectarray antennas and achieved a 25%-light reflectarray antenna compared with a metal reflectarray without sub-wavelength holes. The designed reflectarray antenna operates within the 15% wide-band bandwidth at 3 dB for millimeter-wave band

Design of microstrip patch antennas with parasitic elements for minimized polarization mismatch

This paper proposes the design of microstrip patch antennas to minimize the polarization mismatch. The proposed antenna consists of a circular radiating patch and multiple parasitic elements. The number, length, and angular positions of the parasitic elements are adjusted to vary the antenna polarization as well as the orientation of the main axis. To demonstrate the feasibility, we design two sample antennas with different axial ratios and the orientation angles. The first sample antenna has linear polarization with a orientation angle of 0??, and the second sample antenna is elliptically polarized with a orientation angle of 5??. The results prove that the proposed antenna can adjust the polarization in the entire range of the axial ratio with the capability of rotating the orientation angle

Design of a broad-band microstrip loop antennas with less-dispersive group velocity for accurate direction finding

This study proposes the design of broad-band microstrip loop antennas with less-dispersive group velocity of radiation patterns for accurate direction of arrival (DoA) estimation. The proposed structure consists of radiating and feeding microstrip loops, and the radiating loop is electromagnetically coupled to the feeding loop. This feeding mechanism helps to suppress phase variations of radiating patterns by avoiding dual resonances within a wide frequency band over 60 MHz, which allows to obtain the less-dispersive group velocity for accurate DoA estimation. The effectiveness of the less-dispersive behaviour is validated by implementing the proposed structure into a four-element array to estimate vertical and horizontal placements using dual-axis phase interferometry. The results confirm that the proposed antenna has less-dispersive group velocity compared to a conventional microstrip patch antenna and is more suitable for accurate DoA estimation

Design of mechanically rotatable microstrip patch antennas using an asymmetric polariser for adaptive polarisation adjustment

This paper proposes the design of a microstrip patch antenna with an asymmetric polariser for adaptive polarisation adjustment. The asymmetric polariser is placed in the outer perimeter of a circular radiating patch and is mechanically rotated from 0?? to 360?? to adjust the axial ratio (AR) and the tilt angle (TA). To verify the operating principle of the proposed antenna, its radiating properties are theoretically formulated based on the cavity model, and three sample antennas with different shapes of the polariser are fabricated to measure their antenna characteristics. Then, a field test is conducted to observe variations of the received signal strength for incoming signals with time-varying polarisation properties. The results demonstrate that the mechanical rotation of the polariser is suitable to minimise the polarisation mismatch with improvement of the received signal strength from ???44.0 to ???30.3 dBm in a harsh multipath environment

Design of microstrip patch antennas with improved low-elevation gain for CRPA applications

This article proposes the design of microstrip patch antennas to improve low-elevation gain for controlled reception pattern antenna (CRPA) applications. The proposed antenna consists of a main resonant patch and a subpatch that are electromagnetically coupled with each other to operate as a two-element array whose bore-sight direction points toward low-elevation angles. The array factor is then enhanced by inserting a ceramic substrate with a high dielectric constant to maximize the electrical distance between the patches. As a result, the average gain at =75 degrees is enhanced by 1.2 dB, which demonstrates that the proposed antenna is suitable to be used for the individual elements of CRPA arrays with the improved radiation gain at low-elevation angles

Design of spiral antenna using a Vivaldi-shaped balun

This paper proposes a design of a spiral antenna using a Vivaldi-shaped balun for broadband matching characteristic with high tolerance to fabrication error and low geometrical complexity. The proposed antenna consists of spiral arms, a Vivaldi-shaped balun, and a ground with a cavity-backed structure. The Vivaldi-shaped balun is connected to the spiral two arms to obtain broad matching characteristics, and the cavity-backed structure is employed to achieve a high directivity. To verify proposed antenna performance, such as reflection coefficients, bore-sight gains, and radiation patterns, the antenna is measured in a full anechoic chamber. The results confirm that the proposed antenna is suitable for broadband spiral antennas with high tolerance to fabrication error and low design complexity

Adaptive Adjustment of Radiation Properties for Entire Range of Axial Ratio using a Parasitic Microstrip Polarizer

This paper proposes the design of microstrip patch antennas for dual-band polarization adjustment. The antenna has a multi-layer structure for dual-band operation, and each layer contains a resonating patch with surrounding strips separated into two parts. The antenna polarization is adjusted by varying the separated positions of the strips, while fixing other design parameters. To demonstrate the feasibility, an antenna sample with right-hand circular polarization is fabricated, and its antenna characteristics are measured in a full anechoic chamber. The operating principle of polarization adjustment in the dual frequency bands is also verified by observing near electromagnetic fields and the magnetic surface current density around the antenna