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For a microstrip antenna (MSA) with a ring-shaped slot on formed on the ground plane, downsizing the microstrip patch and expanding the circularly polarized bandwidth have been achieved successfully. The dimensions of the patch are 6.8 mm7.4 mm and the minimum axial ratio (AR) of 0.6 dB is obtained at 6.1 GHz. In addition, its AR is less than 3 dB at the relative bandwidth of 3.5%. The bandwidth of the proposed MSA is twice that of conventional single-feeding circularly polarized MSAs; however, its size is only half that of conventional MSAs.
Microstrip antennas on various Uniplane Compact Photonic BandGap (UC-PBG) substrates are investigated. Particularly, anisotropic characteristics of UC-PBG is studied and applied to the design of microstrip diplexer antennas. Moreover, an Embedded UC-PBG (EUC-PBG) scheme is presented to overcome the strong backward radiation caused by the conventional UC-PBG antennas. Such antennas demonstrate the improved radiation properties over the conventional UC-PBG antennas, and the evidence on surface wave suppression is also demonstrated. Experimental results show very good agreement with theoretical predictions.
The results of experiments on the effect of the height and diameter of the cup on cup microstrip antennas are presented. The results show that the optimum height of the cup for the narrowest beamwidth and the highest gain is about 1/3 λ, and that the beamwidth decreases and the gain increases as the diameter of the cup increases.
Daniel THOUROUDE Mohamed HIMDI Jean Pierre DANIEL
A cavity model well suited for computed-aided design is developed to synthesize the dimensions of patches for a given resonant frequency, an input resistance and a substrate. The antennas which have been investigated are rectangular patches fed with either a microstripline or a coaxial probe.
Mohamed HIMDI Jean Pierre DANIEL
Recent works have shown that the size reduction of printed dipole antennas was possible thanks to a proper shaping of the radiating element. Following the same idea (choice of suitable shape), a shortened slot fed patch antenna exhibiting two step discontinuities, is described, analysed and optimized with a simple transmission line model. The shortening ratio (ρ) can reach 80% for matched antenna, printed on a substrate with a low dielectric constant (εr=2.2). The calculated results of input impedance are validated by experiment.
A new approach using radiation mode expansions is presented for calculating radiated fields from arbitrary distribution of electromagnetic sources in the half space region partitioned by a dielectric layer with a ground conductor. This method is applied to the calculation of radiation from microstrip-type antennas with a dielectric substrate of theoretically infinite extent. To be able to use this method, it is necessary to obtain first the field distribution around antenna patches, which is accomplished rather easily by using the FD-TD method. Radiation pattern calculations are presented for a rectangular patch antenna to verify the feasibility of this approach.
Kazuhiro UEHARA Kenichi KAGOSHIMA
We analyze the mutual coupling between two microstrip antennas (MSAs) with the finite-difference time-domain (FDTD) method. It is suitable for substrates which have a complex configuration or include feed line structures. The mutual coupling between two MSAs on discontinuous orthogonal substrates is successfully calculated.