This paper verifies the accuracy of PO as applied to the scattering of dipole waves by a finite size reflector which is composed of strips on a grounded dielectric slab. By using the closed form expressions of reflected waves from the surface, PO calculation can be conducted straightforwardly. The calculated results are compared with the experimental ones for vertical and horizontal dipoles over a circular reflector.

Digitization of analog terrestrial TV broadcasting has recently been accelerated in many countries, and the effective utilization of vacant frequencies has also been investigated for new systems in each country. In Japan, a portion of vacant frequencies in the VHF-high band was allocated to the public broadband mobile communication (PBB) system. To evaluate the current PBB system and develop future broadband communication systems in this band, it is important to analyze the propagation channel more accurately. In this study, we characterize the propagation channel for 200MHz band broadband mobile communication systems, using measured channel impulse responses (CIRs). In the characterization process, the Saleh-Valenzuela (S-V) model is utilized to extract channel model parameters statistically. When evaluating the fluctuation of path power gain, we also propose to model the fluctuation of path power gain using the generalized extreme value distribution instead of the conventional log-normal distribution. The extracted CIR model parameters are validated by cumulative distribution function of root-means-square delay spread and maximum excess delay, comparing simulation result to measurement result. From the extracted CIR model parameters, we clarified the characteristics of 200MHz band broadband mobile communication systems in non-line-of-sight environments based on S-V model with the proposed channel model.

Equivalence of physical optics (PO) and aperture field integration method (AFIM) in the full 360 observation angle is discussed for polyhedron approximate reflectors; the necessary conditions of integration surface in AFIM for the equivalence to PO are presented. In addition to the condition that complete equivalent currents consisting of both geometrical optics (GO) reflected fields from the reflector and direct incident fields from the feed source are used, the integration surface should cap the reflector perfectly and should be in the illuminated region of the GO reflected field. Validity of the conditions is numerically confirmed for a two-dimensional (2-D) strip reflector, 3-D corner reflectors and a 2-D polyhedron approximate reflector.

The number of Internet-of-Things (IoT) devices will increase rapidly. In next-generation mobile communication systems, a base station (BS) must effectively accommodate massive numbers of IoT devices. To address this problem, we have proposed a novel up-link non-orthogonal multiple access (NOMA) system that can also be utilized for low latency communication. We have developed and evaluated the system through computer simulation. This paper describes experiments conducted on a prototype system in actual environments. The paper shows results of the experiments when 3 fixed user equipments (UEs) and 2 mobile UEs transmitted signals simultaneously to a BS and then the BS separated superimposed signals using successive interference cancellation (SIC). We also evaluated repetition transmission (RT) and space receive diversity (SD) techniques employed to enhance the signal separation performance for NOMA systems. The results of the experiments confirm that the system using neither SD nor RT could separate 3.5 UEs' signals on average while employing either SD or RT could make the number increase to 4.1 and 4.0, respectively. When both SD and RT were employed, the number rose to 4.4.

Physical optics (PO) is an approximation method for high-frequency scattering and diffraction problems. But PO fields are inaccurate in the shadow region where the source is screened by the scatterer. It has been difficult to extract the mechanism of this error because PO includes numerical integration. In 2-D problems, PO fields are analytically and accurately expressed in terms of PO equivalent edge currents (PO-EECs) which represent the leading contributions of PO original integration. Comparison of PO in this form and geometrical theory of diffraction (GTD) which gives accurate fields in the shadow region, clarifies the cause of PO errors. For a scatterer with a corner, PO errors are mainly due to the rays emanating from the invisible edges. For a curved surface scatterer, the contributions penetrating the scatterer are small and main PO errors generally consist in PO-EECs itself.

In practical applications of the artificial boundary surfaces, such as corrugation and strips on a grounded dielectric slab, the surfaces have finite sizes. The diffraction fields from anisotropic surface of this kind can not be calculated using conventional diffraction coefficients. In this paper, uniform diffraction coefficients for the strips on a grounded dielectric slab are given in the sense of physical optics, as functions of incident angle, polarization and structural parameters of the surface. Firstly, the incident plane wave is decomposed into the two special polarization directions. Then uniform diffraction coefficients originally derived for isotropic surfaces with arbitrary impedance can be applied for each polarization component. Finally, expressions for the diffraction coefficients from the anisotropic surface are given as the sum of those for two polarization components. The validity of the diffraction coefficients is verified theoretically and experimentally.

The key concept of Physical Optics (PO), originally developed for a perfectly electric conductor (PEC), consists in that the high frequency fields on the scatterer surface are approximated by those which would exist on the infinite flat surface tangent to the scatterer. The scattered fields at arbitrary observation points are then calculated by integrating these fields on the scatterer. This general concept can be extended to arbitrary impedance surfaces. The asymptotic evaluation of this surface integration in terms of diffraction coefficients gives us the fields in analytical forms. In this paper, uniform PO diffraction coefficients for the impedance surfaces are presented and their high accuracy is verified numerically. These coefficients are providing us with the tool for the mechanism extraction of various high frequency methods such as aperture field integration method and Kirchhoff's method.

This paper describes a nonblind digital beamformer for SDMA (space division multiple access) systems used when channels are power-limited. An array antenna with many elements is usually required to obtain high antenna gain for the reception of a low-level desired signal and the degree of freedom for the spatial discrimination of many users using the same frequency. The proposed beamformer is designed for such array antennas by employing the combination of a multibeam former and a maximal-ratio-combining (MRC) technique. The MRC technique is extended to a nonblind combiner that uses a training sequence contained in the desired signal. Basic analysis and numerical simulations of its performance, under the power-limited condition and with fixed user terminals, show that the speed and robustness of desired-signal acquisition and undesired-signal suppression may outperform recursive-least-squares (RLS) beamformer with less computation, when it is applied to an array antenna with many elements.

A method for fast calibration of digital-beam-forming (DBF) receiving array antennas by means of digital signal processing is described. It uses plane wave arriving from a known direction that contains a known reference sequence. Non-uniformities of the amplitude and phase in the branches are detected and calibrated in real time by the complex correlation of a replica of the known reference sequence with the received signal obtained from the output signals of each element. No special circuit for calibration is required, and the non-uniformities can quickly be compensated for by digital signal processing even for an array antenna with many antenna elements. This method enables highly accurate calibration of large-scale array antennas operating at a high frequency even under a low signal-to-noise power ratio (SNR).

The effects of finite ground plane upon the patterns of the GPS patch antennas are analyzed by EEC with modified edge representation (MER). The comparison with UTD and measurements shows that low elevation patterns including axial ratios are successfully predicted.

Physical optics(PO) and the aperture field integration method (AFIM) give accurate and similar field patterns near the first few sidelobes of reflector antennas. It is widely accepted that the use of AFIM is restricted to norrower angles than PO. In this paper, uniform equivalent edge currents of PO and AFIM are compared analytically and their equivalence in high frequency in discussed. It is asymptotically verified that the patterns by AFIM are almost identical to PO fields in the full 360angular region, provided that AFIM uses the equivalent surface currents consisting of two components, that is, the geometrical optics(GO) reflected fields from the reflector and the incident fields from the feed source, the latter of which are often neglected. Slightly weaker equivalence is predicted for cross polarization patterns. Numerical comparison of PO and AFIM confirms all these results, the equivalence holds not only for large but also for a very small refiector of the order of one wavelength diameter.

Precise and quick multi-beam forming including null control will be one of the key technologies for the future satellite communication systems utilizing SDMA (Space Division Multiple Access) and DOA (Direction of Arrival) estimation. In order to realize the precise multi-beam forming, calibration procedure is indispensable since there are several unavoidable factors that degrade the multi-beam patterns of the array. Particularly amplitude and phase imbalance between RF circuits needs to be calibrated frequently and quickly when the array system exists in changeable environment since the imbalance easily occurs due to thermal characteristics of each RF circuit. This paper proposes a simple and high-speed remote calibration scheme compensating for amplitude and phase imbalance among RF circuits of a transmitting adaptive array antenna onboard satellite. This calibration is conducted at a remote station such as a gateway station on the ground in the satellite communication system, by utilizing the received signal including the temporally multiplexed orthogonal codes transmitted from the array antenna onboard satellite. Since the calibration factors for all the antenna elements can be simultaneously obtained by the parallel digital signal processing, calibration time can be drastically reduced. The accuracy of this calibration is estimated by simulation. Simulation results show that the amplitude imbalance among RF circuits can be suppressed within the range from -0.5 dB to +0.25 dB for the initial imbalance ranging from -2 dB to +3.5 dB, phase imbalance can be suppressed within the range of -3 deg. to +3 deg. for the initial imbalance ranging from -120 or +180 deg. by this method. The amplitude and phase deviations among the elements can be suppressed within 0.36 dB and 2.5 degrees, respectively, in 80% of probability. Simulation results also show that this calibration method is valid under the relatively bad carrier-to-noise conditions such as -10 dB at the receiver. Good improvement of the multi-beam patterns by this calibration is shown under the low carrier-to-noise ratio condition.