A new type of dual-band microstrip antenna was presented and tested. The experimental results had high performance in both the radiation pattern and gain within the desired frequency range. The antenna presented here is, therefore, considered to be effectively applicable as a new type of dual-band antennas.

This paper presents designs and performances of 76 GHz band alternating-phase fed single-layer slotted waveguide arrays. Two kinds of design, that is, uniform aperture illumination for maximum gain and Taylor distribution for sidelobe suppression of -25 dB, are conducted. High gain and high efficiency performance of 34.8 dBi with 57% is achieved for the former, while satisfactory sidelobe suppression of -20 dB in the H-plane and -23 dB in the E-plane with high efficiency is confirmed for the latter. The simple structure dispensing with electrical contact between the slotted plate and the groove feed structure is the key advantage of alternating-phase fed arrays and the slotted plate is just tacked on the feed structure with screws at the periphery. High gain and high efficiency performances predicted theoretically as well as design flexibility of the alternating-phase fed array are demonstrated in the millimeter wave frequency.

In this paper, mutual coupling S21 between RMSA (ring-shaped microstrip antenna) elements was estimated by the EMF method based on the cavity model. Then, the validity of the proposed method was tested by experiments. The experiments confirmed satisfactory agreement between the computed and experimental data for S21 in both E- and H-plane arrangements. In addition, a circularly polarized planar array composed of R-MSA elements was designed on the basis of the data of S21. The experimental results of such a planar array demonstrated high performance in radiation pattern as well as axial ratio property. Furthermore, the active reflection coefficient Γ in the R-MSA array was also investigated in both equilateral and square arrangements. The computed results of active reflection coefficient in the array demonstrated high performance in both arrangements.

In this paper we consider multiuser detection using a neural network in a synchronous code-division multiple-access channel. In a code-division multiple-access channel, a matched filter is widely used as a receiver. However, when the relative powers of the interfering signals are large, i.e. the near-far problem, the performances of the matched filter receiver degrade. Although the optimum receiver for multiuser detection is superior to the matched filter receiver in such situations, the optimum receiver is too complex to be implemented. A simple technique to implement the optimum multiuser detection is required. Recurrent neural networks which consist of a number of simple processing units can rapidly provide a collectively-computed solution. Moreover, the network can seek out a minimum in the energy function. On the other hand, the optimum multiuser detection in a synchronous channel is carried out by the maximization of a likelihood function. In this paper, it is shown that the energy function of the neural network is identical to the likelihood function of the optimum multiuser detection and the neural network can be used to implement the optimum multiuser detection. Performance comparisons among the optimum receiver, the matched filter one and the neural network one are carried out by computer simulations. It is shown that the neural network receiver has a capability to achieve near-optimum performance in several situations and local minimum problems are few serious.

This letter presents mutual coupling reduction in an E-plane arranged microstrip patch array fed by a triplate waveguide. Five mushroom-like electromagnetic band-gap (EBG) elements arranged in one column are embedded both between two radiating patches and between the feeding lines for suppression of the surface wave and the parallel plate mode, respectively. Validity of the proposed EBG elements is confirmed by the measurement.

Novel multiband circular microstrip antennas (C-MSAs) with multiple half-ring slots are presented in this paper. Two antenna-feeding systems, i.e. an embedded L-probe beneath the patch and a coplanar circular arc- shaped probe (T-probe), are used to feed the C-MSA with multiple half-ring slots. The embedded L-probe is used to excite the C-MSA with a double-layer dielectric substrate due to its tremendous performance to provide a wideband impedance matching. The coplanar T-probe is proposed to realize an excellent multiband C-MSA in a single-layer structure. The C-MSA with four half-ring slots fed by the embedded L-probe exhibits satisfactory radiation characteristics. Five frequencies with broadside radiation patterns and gains of at least 5.0 dBi are obtained. It is also confirmed by simulation that resonant frequency and gain can be easily controlled to meet the desired frequency requirements. Moreover, the C-MSA with three half-ring slots fed by the coplanar T-probe presents satisfactory performance over the four observed frequencies with good return losses (-10 dB reference). Broadside radiation patterns with acceptable cross-polarization level and gains in the range of 3.0-7.0 dBi are obtained. Couplings between the C-MSA and the coplanar T-probe have an important contribution to obtain good return losses. It can be controlled by adjusting the distance between them and the arc angle of the coplanar T-probe appropriately. Experiments of both types of antenna were conducted to verify the simulation results and good agreements are confirmed. Due to the performances, these two C-MSAs are considered to be an effective model as a multiband planar antenna.

This paper presents design of an alternating-phase fed single-layer slotted waveguide array for a sector shaped beam in the E-plane 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 of the alternating-phase fed array is confirmed by the measurement.

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 3.0-7.0 dBi 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.