Multiband antennas have been rapidly developed since they can simplify the complex antenna systems for multi-frequency applications. Radiation properties those are often required for multiband antennas are stable frequency dependence of radiation pattern and gain over the operating frequencies. To deal with these requirements, a modification of a fractal Sierpinski gasket microstrip antenna (SG-MSA) was proposed with satisfactory performances of three operating frequencies [1]. The antenna was fed by the L-probe, which is already known as a wideband impedance matching feeder for an MSA. However, the need for antenna systems to cover more than three operating frequencies could not be satisfied by the SG-MSA due to the structural complexity. As alternative designs to overcome such problem, the rhombic MSA with slots [2] and the equilateral triangular MSA (ET-MSA) with folded slots [3], which are completely a non-fractal structure, were proposed. However, a double-layer dielectric substrate was used because these antennas were also fed by the L-probe. The use of a single-layer substrate is a promising design to be easily integrated with MMICs. In most of publications, the utilization of a single-layer substrate for dual frequency applications was reported. A circular microstrip antenna fed by a coaxial probe with one or two open-ring slots [4], a slot-loaded rectangular patch [5], a slot-loaded bow-tie MSA [6], and a rectangular MSA with a pair of bent slots [7] were proposed as a dual or broadband frequency antenna, while Suzuki et al. reported the utilization of coplanar waveguide (CPW) for multiband operation [8]. The rectangular MSA with two folded slots was confirmed to have three operating frequencies.
The microstrip ring antenna (R-MSA) system has been studied by many researchers, because it is possible to reduce the antenna size. However, since the R-MSA has high impedance characteristics at the feeding point, impedance matching is difficult. We investigate the R-MSA element fed by a symmetrical crossed slot (SCS-R-MSA) which easily permits impedance matching. We describe a new type of dual polarized planar antenna with two-port lines coupled to the R-MSA through a symmetrical crossed slot. A circularly polarized planar antenna using this R-MSA as a radiating element and its array are described. In order to evaluate the performance, some planar antennas were tested at C-band. In this experiment, the basic design of both the dual and circularly polarized planar antenna systems were investigated.
In this paper, the alternating-phase fed array with chokes is applied to the 76 GHz band. Two types of contact, just screwed at the periphery and tightly contacted by thermo compression bonding, are tested and compared.
In the fabrication of a large-scale multi-element planar array, reduction of the feeding loss is important for realization of high-efficiency performance. An array antenna fed by a radial line has been investigated by many researchers, because it has high-efficiency performance. This paper presents a basic design technique of the shaped beam antenna fed by a low-loss radial waveguide. In order to check the performance of this antenna, some planar arrays were constructed and tested at the SHF-band. As a result of experiments, satisfactory performance was achieved in both radiation pattern and directivity gain.
This paper presents circularly polarized microstrip antennas (CP MSA) for frequency control with a variable reactance. Operating frequency of circular polarization of the proposed antennas can be controlled by the variable reactance. 8% bandwidth with axial ratio less than 3 dB and over 3 dBi gain is obtained by the proposed CP MSA. In order to enhance the CP bandwidth, a stacked CP MSA for frequency control with the variable reactance is also designed. 23% bandwidth with axial ratio less than 3 dB and over 7 dBi gain is achieved by the stacked CP MSA. Stable LHCP radiation patterns with low cross polarization are observed in the CP bandwidth for the both CP MSAs. The variable reactance is realized by one varactor diode, therefore, it is demonstrated that frequency control of the proposed CP MSAs is accomplished by one varactor diode.
SUMMARY This paper presents design of an alternating-phase fed single-layer slotted waveguide array for a sector shaped beam in the Eplane radiation pattern. A sector beam pattern is very effective for radar applications for detecting obstacles in a certain angular range without mechanical or electronic scanning. The sector shaped beam with 13 degree beam width is synthesized by a cascade of T-junctions in the feed waveguide which excite the radiating waveguides with a longitudinal shunt slot array. In order to realize the required excitation distribution of the radiating waveguides for the sector shaped beam, 30 T-junctions with symmetrical arrangement are designed by tuning a width of the coupling window, an offset of the window, and a width of the feed waveguide cascaded to the subsequent T-junction, respectively. Design and measurement are performed in 60 GHz band. The prototype antenna assembles easily; the slotted plate is just tacked on the groove feed structure and is fixed by screws at the periphery, which is the key advantage of the alternating-phase fed arrays. The measured sector pattern with low sidelobe level agrees well with the predicted one. Validity of the sector beam design as well as the performance
This paper presents novel multi-band equilateral triangular microstrip antennas (ET-MSAs) fed by an L-shaped feeding probe. Two types of the ET-MSA are proposed in this paper; they are ET-MSA with closed folded slots and open folded slots with an embedded bridge. The antenna prototypes presented in this paper assume four folded slots in which a metal strip is inserted to realize a good multi-band performance. In addition, the open folded slots, in which the metal strip inside the folded slot is connected to the ET-MSA by the embedded metal bridge, leads to miniaturize the antenna. The proposed antennas are printed on the top layer of a PTFE substrate while the L-probe is printed on the bottom one. The L-shaped probe is utilized due to its tremendous performance in providing a wideband impedance matching. Five resonant frequencies of the ET-MSAs with closed folded slots and with open folded slots are predicted by the electromagnetic simulator (IE3D) based on the method of moment, respectively. Some parametric studies have been also investigated to meet an appropriate multi-band performance. A broadside radiation pattern and gain of 3.0-7.0dBi have been confirmed by the measurement for the entire observed frequencies. Measured results agree well with the prediction. Thus, these antenna systems are demonstrated to be useful models for a multi-band planar antenna.
