The radiation characteristics of strip-loaded dielectric-coated conducting cylinder are investigated theoretically for the infinite and finite periodic structures. For the infinite case, the strip electric current expansion satisfying edge condition and the field expression with a summation of space harmonics are applied to solve a homogeneous matrix equation. The integral equation is derived for the finite structure by using the inverse Fourier transform and the strip current expansion. The influences of the strip width, cylinder radius, and finite strip number on the radiation characteristics (leakage constant, phase constant, radiation pattern, and beam scanning) are investigated. The results of the finite periodic strips are compared with those of the infinite extent structure and good agreement is found.

In this paper, a quadrafilar antenna is designed to have a lower profile as an essential part of the size reduction technique and lower back radiation(i.e. higher forward radiation) for the S-band telemetry/telecommand(TM/TC) function of a communication satellite. Particularly, to meet the challenging requirements on the higher isolation between the TM/TC antennas and simultaneously a smaller size, the lowest back radiation and lowest cross-polarization, the optimal physical dimensions of the quadrafilar antenna are found by using the Genetic Algorithm(GA). To prove the validity of the proposed antenna design, its 3D electromagnetic analysis and measured results are compared, showing good agreement.

Recently spaceborne SAR systems are increasing image resolution and frequency. As a high quality image resolution, the wider bandwidth is required and a wideband signal generator with RF component is very complicated and RF impairments of device is increased. Therefore, it is very important to improve performance by reducing these errors. In this study, the transmission signal of the wideband signal generator is applied to the phase noise, IQ imbalance, ripple gain, nonlinear model of high power amplifier. And we define possible structures of wideband signal generator and measure the PSLR and ISLR for the performance assesment. Also, we extract error of the amplitude and phase from the waveform and use a quadratic polynomial curve fitting and examine the performance change due to nonlinear device. Finally, we apply a high power amplifier predistortion method for non-linear error compensation. And we confirm that distortion in the output of the amplifier by intermodulation component is decreased by 15 dB.

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