In this communication, a compact log-periodic dipole array (LPDA) antenna is developed at 0.5 – 10 GHz. This LPDA structure constitutes fewer dipole elements than a conventional LPDA antenna that exhibits similar resonant frequencies. In the design of a miniaturized LPDA antenna, various size-reduction techniques have been proposed in the open literature to decrease the lateral size of a conventional LPDA. However, little or no attention has been focused on reducing the size of the LPDA antenna by shortening the boom or axial length. In pursuit of reducing the total length of a conventional LPDA, a dual-band dipole antenna is proposed as the radiating elements for the LPDA antenna in this communication. The proposed dipole structure is a printed half-wave principal dipole loaded with a pair of resistive structures via sub feeding-lines. The pair of resistive loads forms the auxiliary (secondary) dipole of the proposed dipole antenna. The structure of the proposed dual-band dipole is achieved without a ground plane as opposed to many existing dual-band antenna types. As a result, the dipole antenna has a simple geometry with omnidirectional characteristics. Also, the feeding structure of this dipole can provide extra degree of freedom to tune the antenna for matching purposes. A 25-element LPDA antenna is designed with a much reduced boom length as compared with existing LPDA structures. To confirm the feasibility of the technique, the experimental results of the proposed LPDA prototype were analyzed and juxtaposed with a benchmark LPDA.

A compact planar log‐periodic dipole array (LPDA) antenna operating from 0.55 to 9GHz with high measured gain is proposed to be implemented in a reverberation chamber as a source antenna. To minimise the total size of the LPDA antenna, variants of top‐loading techniques are utilised, and a much smaller spacing factor is opted to specify the spacing between the elements. However, miniaturisation of the LPDA antenna limits the antenna's wideband characteristics over the desired range of frequencies. Hence, a feedline meander and a trapezoidal stub are incorporated into the design as impedance matching techniques to effectively enhance the bandwidth performance especially for the lower band of the antenna's operating frequency range. The LPDA antenna exhibits radiation patterns with and without a radome having the measured gain ranging from 2.48 to 7.89 dBi and from −1.20 to 7.94 dBi, respectively.

In this paper, a high efficiency broadband planar array antenna is developed at X-band for synthetic aperture radar (SAR) on small satellites. The antenna is based on a multi-layer element structure consisting of two dielectric substrates made of Taconic TLY-5 and three copper layers (i.e., the parasitic patch (top layer), the active patch (middle layer), and the ground plane (bottom layer)). The parasitic patch resides on the bottom surface of the upper TLY-5 substrate while the active patch is printed on the top surface of the lower substrate. A Rohacell foam material is sandwiched between the top layer and the middle layer to separate the two dielectric substrates in order to achieve high directivity, wideband, and to keep the antenna weight to a minimum as required by the SAR satellite application. To satisfy the required size of the antenna panel for the small SAR satellite, an asymmetric corporate feeding network (CFN) is designed to feed a 12 × 16 planar array antenna. However, it was determined that the first corporate feed junction at the center of the CFN, where higher amplitudes of the input signal are located, contributes significantly to the leaky wave emission, which degrades the radiation efficiency and increases the sidelobe level. Thus, a suspended microstrip slab, which is simply a wide and long microstrip line, is designed and positioned on the top layer directly above that feed junction to prevent the leaky waves from radiating. The experimental results of the antenna show good agreement with the simulated ones, achieving an impedance bandwidth of 12.4% from 9.01 to 10.20 GHz and a high gain above 28 dBi. The antenna efficiency estimated from the gain and directivity eclipses 51.34%.

A high-gain millimeter-wave patch array antenna is presented for unmanned aerial vehicles (UAVs). For the large-scale patch array antenna, microstrip lines and higher-mode surface wave radiations contribute enormously to the antenna loss, especially at the millimeter-wave band. Here, the element of a large patch array antenna is implemented with a substrate integrated waveguide (SIW) cavity-backed patch fed by the aperture-coupled feeding (ACF) structure. However, in this case, a large coupling aperture is used to create strongly bound waves, which maximizes the coupling level between the patch and the feedline. This approach helps to improve antenna gain, but at the same time leads to a significant level of back radiation due to the microstrip feedline and unwanted surface-wave radiation, especially for the large patch arrays. Using the SIW cavity-backed patch and stripline feedline of the ACF in the element design, therefore, provides a solution to this problem. Thus, a full-corporate feed 32 × 32 array antenna achieves realized gain of 30.71–32.8 dBi with radiation efficiency above 52% within the operational band of 25.43–26.91 GHz. The fabricated antenna also retains being lightweight, which is desirable for UAVs, because it has no metal plate at the backside to support the antenna.

This paper presents a new configuration of a slotted waveguide antenna (SWA) array aimed at the X-band within the desired band of 9.38~9.44 GHz for shipboard marine radars. The SWA array, which typically consists of a slotted waveguide, a polarizing filter, and a metal reflector, is widely employed in marine radar applications. Nonetheless, conventional slot array designs are weighty, mechanically complex, and geometrically large to obtain high performances, such as gain. These features of the conventional SWA are undesirable for the shipboard marine radar, where the antenna rotates at high angular speed for the beam scanning mechanism. The proposed SWA array herein reduces the conventional design’s size by 62% using a tapered dielectric-inset guide structure. It shows high gain performance (up to 30 dB) and obtains improvements in radiation efficiency (up to 80% in the numerical simulations) and weight due to the use of loss and low-density dielectric material.

In this paper, a printed monopole antenna with stable omnidirectional radiation patterns is presented for applications in ocean buoy and the marine Internet of Things (IoT). The antenna is composed of a rectangular patch, a cross-ground structure, and two frequency-selective surface (FSS) unit cells. The cross-ground structure is incorporated into the antenna design to maintain consistent monopole-like radiation patterns over the antenna’s operating band, and the FSS unit cells are placed at the backside of the antenna to improve the antenna gain aiming at the L-band. In addition, the FSS unit cells exhibit resonance characteristics that, when incorporated with the cross-ground structure, result in a broader impedance bandwidth compared to the conventional monopole antenna. To validate the structure, a prototype is fabricated and measured. Good agreement between the simulated and measured results show that the proposed antenna exhibits an impedance bandwidth of 83.2% from 1.65 to 4 GHz, compared to the conventional printed monopole antenna. The proposed antenna realizes a peak gain of 4.57 dBi and a total efficiency of 97% at 1.8 GHz.