In this study, the structure of a circular four-array antenna was designed for a monopulse radar attached to a conical small missile warhead with a diameter of 29 mm and a lateral length of 63 mm. A printed monopole Yagi-Uda antenna was adopted as the basic model for the antenna to decrease production cost and reduce weight. The director structure of the printed monopole Yagi-Uda antenna that we proposed was modified to λ/2 to improve the beam direction. Unlike the existing structure, the proposed director was made to be separated from the ground, so that it could act as a director. The antenna was expanded to a four-array structure for the detection of vertical and horizontal planes. As a result of the design, the S<sub>11</sub> had excellent matching characteristics at the center frequency of 9.375 GHz, and the beam pattern also had directivity in the same direction as the missile travel direction. In the case of gain, it showed more than 6 dBi performance. Finally, the proposed four-array structure antenna was fabricated to verify that the S<sub>11</sub> and radiation patterns were maintained.
In this study, we suggested a waveguide antenna for low-orbit satellite TC&R with hemispherical coverage in the X-band of 7.0~8.5 GHz required for the telemetry command system (Telemetry, Command, Ranging, hereinafter TC&R) for communication between the satellite and the ground station. The proposed antenna is designed using a septum structure inside the waveguide to generate a circularly polarized wave and expand the axial bandwidth. In addition, to extend the beam width of the radiation pattern within the range of maintaining the circularly polarized wave, an outer wall of a corrugated structure was added and offset at the end of the opening of the spherical waveguide. Consequently, the hemispherical coverage characteristics were satisfied, and an axial ratio of around 10 dB was obtained at ±90°. In addition, the average gain of all angles within the beam width at the resonant frequency was −2.9 dBi. Accordingly, sufficient beam width, axial ratio, and gain were secured as antennas for low-orbit satellite TC&R.
In contrast to existing antennas with polarization and directional characteristics, we propose a novel isotropic antenna that provides equivalent vertical and horizontal polarization in all directions. The final design was guided by simulations, with the performance characteristics of the fabricated antenna verified experimentally. In the proposed antenna, two λ/4 folded microstrip antennas were integrated into one antenna in a “+” shape to generate the isotropic radiation pattern, with the input impedance matched to the feeding position. The resonant frequency, horizontal width, radiation pattern, and axis ratio were adjusted by changing the length of the microstrip line. Both simulations and experiments confirmed that the radiation patterns of vertical and horizontal polarization on each plane show the characteristics of an isotropic antenna with nondirectional radiation pattern.
Subminiature GPS L1 band (center frequency: 1575 MHz, wavelength [ normalλ ${\rm{\lambda }}$]: 190 mm) microstrip antenna suitable for mounting in small electronic devices is proposed in this paper. The newly proposed antenna was transformed from the basic λ/2 microstrip patch antenna to a λ/4 microstrip antenna. To apply the perturbation theory, the width of the radiating element on the feeding point with strong magnetic field energy was narrowed. In addition, the open end of the radiating element with strong electric field energy was folded down in a “王” shape to reduce the antenna size. The size of the designed subminiature microstrip antenna is 10 mm (0.05 normalλ ${\rm{\lambda }}$) × 9.5 mm (0.05 normalλ ${\rm{\lambda }}$) × 8.5 mm (0.04 normalλ ${\rm{\lambda }}$). For impedance matching, the position of the feeding point and the gap between the feeding line and the short stub were adjusted. The fabricated antenna obtained S 11 ${S}_{11}$ of −17 dB at the center frequency of 1575 MHz. While the size of the ground plane was 48 mm (0.25λ) × 50 mm (0.26λ), the omnidirectional radiation characteristics for both E θ ${E}_{{\rm{\theta }}}$ in the xz‐plane and xy‐plane with average gain of −0.3 and −1.7 dBi, respectively. A size reduction ratio of 98.9% was secured from the results compared to the basic λ/2 microstrip patch antenna.
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