Two types of CPW-fed active antenna for television receivers, printed on thin dielectric film, are analyzed numerically and experimentally and their broadband operations are reported. The actual gain of the receiving active antenna is expressed in terms of the transducer power gain of the amplifier circuit and the effective length of the passive antenna. Between the feed point of the passive antenna element and the CPW, the silicon transistor 2SC2585 or 2SC3604 is integrated with a dipole antenna or loop antenna. The actual gains of a dipole antenna with 24 cm length are more than 8 dBd (relative gain to the standard half-wave dipole) at frequencies from 470 to 770 MHz for television channels 13-62 in Japan. In the case of a loop antenna with a size of 25. 8 cm12 cm, actual gains of more than 3. 5 dBd are obtained for channels 1-12, from 90 to 222 MHz, and more than 6. 5 dBd for channels 13-62, from 470 to 770 MHz.

The electric currents on the upper, lower and side surfaces of the patch conductor in a circular microstrip antenna are calculated by using the integral equation method and the characteristic between the electric currents on the upper and lower surfaces is compared. The integral equation is derived from the boundary condition that the tangential component of the total electric field due to the electric currents on the upper, lower and side surfaces of the patch conductor vanishes on the upper, lower and side surfaces of the patch conductor. The electric fields are derived by using Green's functions in a layered medium due to a horizontal and a vertical electric dipole on those surfaces. The result of numerical calculation shows that the electric current on the lower surface is much bigger than that on the upper surface and the input impedance of microstrip antenna depends on the electric current on the lower surface.

The wall admittance of an arbitrarily shaped microstrip antenna is generally formulated. As examples, elliptical microstrip antennas with and without a circular slot are calculated. The wall admittance is determined by the spectral domain analysis in order to consider the effect of the dielectric substrate. The electromagnetic fields within the cavity are expanded in terms of the eigenfunctions in the cylindrical coordinate system and their expansion coefficients are determined by applying the impedance boundary condition at the aperture in the sense of the least squares. The calculated input impedance and axial ratio agree fairly well with the experimental data. The proposed method is valid for the microstrip antennas with a patch whose geometry deviates from the particular coordinate system, such as single-feed circularly polarized microstrip antennas.

The formulation of the wall admittance of a circular microstrip antenna by the spectral domain method is presented. The circular microstrip antenna is calculated using the cavity model. The electromagnetic fields within the antenna cavity are determined from the impedance boundary condition at the side aperture. The contribution from the region outside the antenna is taken into account by the wall admittance. The wall admittance is defined by the magnetic field produced by the equivalent magnetic current at the aperture. The magnetic field is calculated by the spectral domain method. The wall admittances obtained by this method are compared with the results calculated by Shen. The calculated input impedances of the microstrip antenna agree fairly well with the experimental data for the substrate thickness of up to 0.048λg. The formulation of wall admittance presented here is easily applicable to arbitrarily shaped microstrip antennas.