This article proposes a novel design for a patch array antenna using a double indirect coupled feeding structure to achieve broad matching and gain bandwidths for automotive radar applications. The proposed radar antenna consists of a microstrip line, an elliptical radiator, and a waveguide feeding structure. The indirect coupled feeding mechanism is first applied to the elliptical radiator, which is placed at an adjacent distance from the microstrip line. To further improve the broad matching and gain characteristics, another indirect coupled feeding structure is applied to the transition between the microstrip line and the waveguide feeding network. To verify the proposed antenna performance, including impedance matching, bore-sight gain, and the radiation pattern, the proposed antenna is measured in a compact antenna test range chamber. The results confirm that the proposed patch array antenna using a double indirect coupled feeding structure is suitable for the individual element of the 79 GHz radar array.

The radio frequency (RF) signal generation method using an external modulator is widely used in microwave photonics applications because it has the advantage of being able to generate coherent and stable RF signals with a higher resolution performance compared to the conventional method. A Mach–Zehnder modulator is widely used as an external modulator due to its high electro-optic coefficients and low attenuation characteristics but has a critical problem in that its electrical characteristics are changed by external environments such as temperature. In this paper, we considered the stabilization configuration to overcome this problem and propose an automatic bias control technique based on the simulated annealing algorithm of a dual-parallel Mach–Zehnder modulator (DPMZM) for quadruple signal generation. The proposed technique searches for the bias voltages of the modulator in real-time through the temperature test. In addition, the output of the quadrupled signal of the DPMZM is constantly controlled throughout the temperature range. Finally, it is confirmed that signals of a 10 GHz and 22 GHz frequency are generated using the intermediate frequency signals of a 2.5 GHz and 5.5 GHz frequency with the proposed automatic bias control technique, respectively.

Digitized beam-forming metal reflectarray antennas are designed for the millimeter-wave region. The phase control of antennas has been implemented by the reconfiguration of rectangular grooves on a metal plate. The antenna has 1147 elements arranged in an aluminum metal plate. The depths of all metal grooves are manipulated for designed phase control of high-gain beam-aimed reflectors. We have demonstrated a digitized reconfigurable metal reflectarray to steer a re-radiated millimeter-wave field from the reflector in a two-dimensional scanning plane from −20${}^{\circ }$ to 20${}^{\circ }$. The far-field patterns show that the measured gain of the 2-bit reflectarray is only 1 dB lower than that of a non-digitized reflectarray antenna. The measured peak gain is higher than 31.7 dB, and the measurements show that the gain of the full 40${}^{\circ }$ scanned beam is 31.7 dB and well-defined scanned beams are obtained with a maximum scan gain loss of 0.2 dB. The proposed reconfigurable antennas can be a useful candidate for high-gain beam-aimed antennas for practical reflecting surfaces and a variety of wireless and satellite communication systems.

This paper proposes a FMCW radar transceiver with photonic elements. The proposed radar system is efficiently designed by budget analysis, and a wideband signal is generated using photonic elements. To verify the performance of the proposed radar system, field tests including changes in bandwidth are conducted. The results confirm that the resolution of ISAR images improves as the bandwidth increases as expected through the budget analysis.

This article proposes the design of a coupled-fed printed dipole antenna for direction finding (DF) systems. The antenna consists of a radiating 50 angled expanded-arm printed dipole as well as a fan-shaped feeder that is located on the opposite side of the radiating dipole. The 50 angled expanded-arm structure results in a wide beam-width and broadband-matching characteristics. The more the arm angle is bent, the wider the beam-width pattern. Note that the expanded structure to the side of the dipole arm allows the wide beam-width of the radiation pattern. The printed dipole is then electromagnetically coupled with the fan-shaped feeder to obtain broadband-matching characteristics. To obtain additional broadband-matching characteristics, the circular cavity and the four-step tapered structures of the radiating printed dipole are carefully tuned by considering the coupled fields induced by the indirect feeding structure. The reflection coefficients are-14.6 dB and-11.9 dB at 1.575 GHz and 2.4 GHz, and the boresight gains are 4.8 dBi and 1 dBi, respectively. To confirm the DF capability of the proposed antenna, the pattern of the 4×4 arrays is observed by varying the steering angle.

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.