The gap waveguide technology was recently introduced as an alternative to hollow waveguides and substrate integrated waveguides for millimeter-wave applications. This paper presents the design of a 4 ×4 planar dual-mode horn array with low loss corporate feed network realized by using an inverted microstrip gap waveguide. The dual-mode horns are compact and designed to reduce the power losses in grating lobes. It is because the diameters of the horn apertures are larger than two wavelengths to allow more space for the feed network and thereby lower conductive losses. The measurements show very good agreement with simulations, with 10% bandwidth of the return loss, 25 dBi realized gain and about 60% aperture efficiency.

Periodic surfaces made of patches with metallized via holes or grounding pins (ldquomushroomsrdquo) have been shown to have bandgaps in their dispersion diagrams, inside which surface waves cannot propagate. These bandgaps are defined in all directions in the surface structure. The purpose of this work is to show how by changing the position of the metallic via of the mushroom from its center to its edge, the bandgap moves towards lower frequencies. This allows an easy structure size reduction which is critical in many applications. Results prove a size reduction of the unit cell size by approximately 20% by only moving the via position. The conclusions have been validated with measurements.

This paper presents a study of the short circuited ring patch antenna based on the cavity model. Special attention has been paid to the fundamental mode in this geometry: the TM/sub 01/ mode. Analytical expressions for resonant frequency, fields, radiation pattern and input impedance based on this model have been developed. Simulations based on this theoretical model and experimental results show good agreement. The interesting radiation characteristics and resonant frequency of this mode are presented.

The results of a parametric study and design of an ultrawideband dual-polarized array of differentially-fed tapered slot antenna elements are presented. We examine arrays of bunny-ear antennas and discuss the capabilities and limitations of differential antenna technology. As we focus on radio astronomical applications, the absence of a balancing-feed circuit not only reduces the first-stage noise contribution associated to losses in the feed, but also leads to a cost reduction. Common-modes are supported by the antenna structure when a third conductor is present, such as a ground plane. We demonstrate that anomalies may occur in the differential-mode scan impedance. Knowledge of both types of scan impedances, differential and common mode, is required to properly design differential LNAs and to achieve optimal receiver sensitivity. A compromise solution is proposed based on the partial suppression of the undesired common-mode currents through a (low loss) balancing-dissipation technique. A fully steerable design up to 45° in both principal planes is achieved.

The purpose of this work is to propose a new method to suppress the harmonic radiation from a microstrip patch antenna with proximity coupled feeding line implemented in a multilayer substrate. The goal of the design is the suppression of the resonances at the 2nd and 3rd harmonic frequencies to reduce spurious radiation due to the corresponding patch modes to avoid the radiation of harmonic signals generated by non-linear devices at the amplifying stage. The study shows the possibility of controlling the second harmonic resonance matching by varying the length of the feeding line. On the other hand, the suppression of the third harmonic is achieved by using a compact resonator. This resonator consists of a printed metallization with a via connected to the ground plane (mushroom type) in a multilayer configuration. Comparing with conventional electromagnetically coupled patch antenna, the radiated power of the proposed antenna at the 2nd and 3rd harmonic frequencies is reduced by 14 dB and 8 dB, respectively.

Due to their impulsive nature, partial discharges in insulation systems emit in a broad band of frequencies ranging from tens of megahertz to gigahertz. Antennas can be placed at secure distances from the high-voltage source and measure partial discharges pulses on-line. The energy of partial discharges coexists with strong electromagnetic emissions such as frequency modulated radio, television broadcasting and mobile telephones. Then, the antennas should be tuned to detect the emission from partial discharges in bands where the electromagnetic noise is not so important. They should also be capable of receiving in a broad range of frequencies so resonant antennas should be avoided. Vivaldi antennas can be designed to detect emissions from a desired tuned frequency and extended to a band as wide as necessary. This makes them a valuable tool to detect partial discharges avoiding electromagnetic noise present at lower frequencies.