This letter presents beam tilting characteristics of a slot antenna element with reactance loading. It is found that the beam tilt is obtained by controlling aperture electric field distributions with a loaded reactance on the slot. A large beam tilt angle is obtained when an inductive reactance element is loaded.

A rigorous and systematical analysis of the performance of the power inversion adaptive array is shown where the method of moments is applied to analyze the antenna system and the electric field intensity is used as the descriptive parameter of the incident signals. This method can be easily extended to analyze adaptive arrays with arbitrary array structure and with wire antenna elements other than monopoles and dipoles. To show the adavantages of the method, the performance of adaptive arrays with mutual coupling effect among the array elements is considered and the inverted-F antennas (IFA) are used as the elements. The steering vector in the presence of mutual coupling which differs from that in the absence of the mutual coupling is derived. The output signal-to-interference-plus-noise ratio (SINR) of two kinds of adaptive arrays composed of IFA elements is computed and the importance of properly selecting steering vector is demostrated by means of the quiescent array patterns and the output SINR performance.

Characteristics of a cavity-backed annular slot antenna with one point shorted are investigated. Resonance frequencies, bandwidths and radiation patterns with respect to a slot width and a slot shorting position are studied experimentally. By selecting a slot shorting position, the bandwidth of more than 10% for the input impedance and circular polarization of the bandwidth of about 3.2% for the axial ratio are obtained.

A broadband rhombic loop antenna is introduced to radiate a circularly polarized wave. This antenna has a single feed and is located above a ground plane. The perimeter of the loop is typically about 1.3 wavelength. One gap is made on the loop to produce a traveling wave distribution of current. Antenna characteristics are calculated by the method of moments and compared with the measured data. By adjusting a perimeter and a gap position of the loop, circular polarization is obtained. In addition, with the appropriate vertex angle of the rhombus, the bandwidth of about 20% for the axial ratio (2dB) is attained and the possibility of controlling the input impedance is found. Finally, it is observed that sense of circular polarization can be changed easily from left-hand to right-hand, and vice versa by switching one gap position to the other on the rhombic loop.

High power interference rejection characteristics of a sidelobe canceller which have not been well discussed yet are investigated through computer simulation and experiment in the real radio wave environment. To improve the high power interference rejection performance, a new method is considered. The performance of the method is also analyzed through computer simulation and experiment.

The reduction of coupling between two wire antennas operating at different frequencies on an infinite ground plane is considered. An impedance loaded slot is introduced between the two antennas. A coupling coefficient and a transmission coefficient are used to evaluate the coupling behavior. It is found that by an appropriate choice of the slot length, location and load impedance the coupling coefficient can be reduced significantly. The problem is analyzed by the method of moments. Port parameters are used to relate a feed port, load ports on the two wire antennas and a load port on the slot. In so doing, a large amount of computation time is saved in calculating the antenna characteristics for various loads on the slot.

Coupling between two slot antennas on an infinite ground plane and radiation patterns on a finite ground plane are calculated. We introduce a parasitic wire between slot antennas to reduce coupling. Two typical cases with a monopole or a half-loop are considered in this paper. Numerical results show that the reduction of 13.9 dB is obtained by adjusting a monopole height to about a quarter wavelength of the operating frequency. Also a properly adjusted parasitic half-loop reduces the coupling coefficient by 24 dB. Radiation patterns of the antennas on a 365 mm 465 mm ground plane at 1.5 GHz are calculated where the diffracted fields are taken into account. It is found that the parasitic elements little affect the antenna patterns around the +z-axis that is perpendicular to the ground plane although the reduction of coupling between slot antennas is obtained.

A cavity-backed two-element rectangular loop slot antenna for circular polarization is presented and investigated by using the generalized network formulation based on the equivalence principle. By applying the method of moments, the magnetic current including the effect of the cavity is obtained for a thin rectangular loop slot. Two short-circuiting points are introduced on the slots to get circular polarization and symmetrical radiation pattern. The axial ratio bandwidth (3 dB) with VSWR (2) reaches 7.6%. The measured and computed results are in good agreement.

This paper presents the basic characteristics of a beam tilting slot antenna element whose forced resonance is realized by reactance loading; its structure complements that of a dipole antenna element. The radiation pattern is tilted using a properly determined driving point position; a single loading reactance is used to obtain the forced resonance without great changes in the tilt angle. Numerical results show that the reactance element needs to be loaded near the driving point in order to obtain the forced resonance of the antenna and the minimum changes in the beam tilt angle at the same time. When the proposed forced resonant beam tilting slot antenna with a 0.8 λ length is driven at -0.2 λ from the center, the main beam tilt angle of 57.7 degrees and the highest power gain of 3.8 dB are obtained. This slot element has a broad bandwidth, unlike the complementary dipole element.

This paper presents the forcible resonant characteristics of a cutoff cavity-backed slot radiator. It has a feed post and a parasitic post inserted parallel to the slot width, done by adding a single external reactance to the top or the bottom side of the parasitic post. The basic radiator characteristics for a perfect matching to a 50-Ω coaxial line due to the connecting position of the external reactance are discussed. Comparisons show that the bandwidth of the top side loading is narrower than the bottom side loading case. The theoretical analysis is verified by the measured return loss.

In this paper a new method for the design and optimization of microstrip parallel coupled-line bandpass filters is presented which allows for the specification of frequency bandwidths and arbitrary source and load impedance transformation. The even- and odd-mode theory and the relationships between impedance, transmission and scattering matrices and their properties are used to construct a positive definite error function using the insertion losses at discrete frequencies in the pass, transition and stop bands. The dispersion relations for the coupled line are also taken into account. The minimization of the error function determines the widths, gap spacings and lengths of the coupled-line filter, for the optimum design and realization of filter specifications. The proposed filter design and optimization method is coded by computer programs and the results of simulation, fabrication and testing of sample filters together with comparisons with available full-wave analysis softwares, indicate the efficacy of the proposed method. Filter design with up to 50% bandwidth and the design of shorter lengths of coupled line sections are achievable by the proposed method in part due to the incorporation of impedance matching.