This work covers two aspects of microwave communication technology. The first is the analysis and design of new wideband high gain microstrip antennas and the second aspect is the design of compact high performance low-pass and band-pass filters. We have introduced the resonating coupling slot in the aperture coupled microstrip antenna to increase its bandwidth. A new method is reported for impedance matching of the antenna structure with 50-Ohm microstrip feed line. Also we have developed the concept of the short surface mounted horn to increase the gain without adversely affecting its bandwidth. By inserting the horn into the substrate, the gain of the patch antenna has been increased by more than 6 dB. The surface mounted horn has been applied around the four and eight element arrays. An increase of 3.5 dB in gain has been obtained with the horn frame around the array elements. For the compact microstrip based filter design we have adopted the defected ground structure (DGS). We have shown that proper selection of the shape and position of DGS slot is important for the improved performance of the low-pass filter in the stop and transition bands. We have also introduced the band-pass structure in the DGS configuration and used it to design a new compact band-pass filter.