Design, simulation, implementation and measurement results of multiline and multilayer microstrip directional couplers are given with closed form relations. Step-by-step design procedure reflecting the design practice of directional couplers, which requires only information on coupling level, port impedances and operational frequency, is presented. The method based on the synthesis technique applied in the design of conventional two-line microstrip symmetrical directional couplers is adapted to design multilayer directional couplers with the aid of electromagnetic simulators using parametric analysis with curve fitting method. The proposed design method is compared with the measurement results and accuracy is verified. It has been also shown that the directivity of the couplers designed using the multilayer structure is improved significantly. A method such as the one presented in this paper can be used to design multilayer two-line and three-line directional couplers which can be integrated to the front end of an RFID systems to provide the required isolation between transmitter and receiver and prevent signal leakage due to use of conventional circulators.

An X-band radiator as an open-ended waveguide with a hybrid dielectric insert is proposed. The insert is in the form of a parallelepiped, which fills the entire cross section of the waveguide and constitutes a Teflon matrix with local inhomogeneities in the form of dielectric cylinders with a different permittivity. The design allows for forming various near-field distributions and, hence, the radiator performance by means of definite combinations of the local inhomogeneities can be modified. A number of configurations in the location of air and quartz cylinders are investigated. The calculated and experimental results are in good agreement. The proposed approach to the near-field formation of the aperture antenna is promising, because the variety of possible configurations in the location of local inhomogeneities with different permittivity provides new opportunities in terms of designing both single radiators and antenna arrays.

A Frequency Selective Surface (FSS) reflector with wideband response for 4G/X-band/Ku-band is proposed. The wideband FSS reflector consists of cascaded dual-layer patch FSS which is etched on separate layers of FR4 substrate. The targeted frequency range is 5–16 GHz. A wide stopband of 10.4 GHz (100% percent bandwidth) is obtained with two layers in cascade. The Equivalent Circuit (EC) method is used to approximate the simulated results. An extensive parametric study is also carried out to understand the effect of various combinations of FSS layers and their disposition. A panel of final FSS is fabricated where measured and simulated results agree well.