Over the last years, a great number of substrate integrated circuits has been developed. These new circuits are a compromise between the advantages of classical waveguide technologies, such as high quality factor and low losses, and the advantages of planar circuits, such as low cost and easy compact integration. Although their quality factor and losses are better than for planar circuits, these characteristics are worse than in the case of waveguides, mainly due to the presence of the dielectric substrate. In order to improve the performance of the integrated circuits, a new methodology for manufacturing empty waveguides, without a dielectric substrate, but at the same time completely integrated in a planar substrate, is proposed in this work. A wideband transition with return losses greater than 20 dB in the whole bandwith of the waveguide allows the integration of the empty waveguide into the planar substrate so that the waveguide can be directly accessed with a microstrip line. Therefore, a microwave circuit integrated in a planar substrate, but at the same time with a very high quality factor (measured quality factor is 4.5 times higher than for the same filter in the substrate integrated waveguide), and very low losses is successfully achieved.

Recently, a new empty coaxial structure, entirely built with printed circuit boards, has been proposed. The resulting coaxial line has low radiation, low losses, high-quality factor, and is nondispersive. Up to now, this coaxial line has not been completely integrated in a planar substrate, since a working transition to a traditional planar line has not been defined yet. Therefore, in this paper, a high-quality transition from coplanar waveguide to this new empty coaxial line is proposed. With this transition, the coaxial line is completely integrated in a planar circuit board, so that it truly becomes an empty substrate-integrated coaxial line. The proposed transition has been fabricated. Both full-wave simulated and measured results show an excellent agreement. Therefore, the proposed transition is suitable to develop completely substrate-integrated components for applications in wideband communication systems that require very high quality responses and protection from external interferences. To show this fact, this new transition has been applied to integrate a high-performance empty coaxial filter in a planar substrate. The measured response of this filter is excellent, and proves the goodness of the proposed transition that has enabled, for the first time, the complete integration of an empty coaxial line in a planar substrate.

Multiple-input multiple-output (MIMO) radars have been shown to improve target detection for surveillance applications thanks to their proven high-performance properties. In this paper, the design, implementation, and results of a complete 3-D imaging frequency-modulated continuous-wave MIMO radar demonstrator are presented. The radar sensor working frequency range spans between 16 and 17 GHz, and the proposed solution is based on a 24-transmitter and 24-receiver MIMO radar architecture, implemented by time-division multiplexing of the transmit signals. A modular approach based on conventional low-cost printed circuit boards is used for the transmit and receive systems. Using digital beamforming algorithms and radar processing techniques on the received signals, a high-resolution 3-D sensing of the range, azimuth, and elevation can be calculated. With the current antenna configuration, an angular resolution of 2.9° can be reached. Furthermore, by taking advantage of the 1-GHz bandwidth of the system, a range resolution of 0.5 m is achieved. The radio-frequency front-end, digital system and radar signal processing units are here presented. The medium-range surveillance potential and the high-resolution capabilities of the MIMO radar are proved with results in the form of radar images captured from the field measurements.

The empty substrate integrated waveguide (ESIW) technology is recently receiving special attention, since it preserves the many advantages of SIW circuits but provides an enhanced behavior due to avoidance of dielectric filling. Many circuits have been designed in the ESIW technology, including several filters with different performances. The next challenge is to achieve the maximum possible compactness degree for these circuits. In this paper, we present the design of a multilayer empty substrate integrated filter with the same performance as if it were manufactured in a single layer but significantly increasing its compactness and mechanical resistance.

This letter presents a passive UHF printed loop antenna with left-handed loading. The RFID reader antenna can work at near- and far-field operation within the European UHF (865-868 MHz) band. The operation frequency and radiation properties can be modified by employing varactor diodes. Also, the antenna can work in the near-field region having a flat magnetic distribution in the interrogation zone. A comparative study with other passive RFID reader conventional antennas shows that the left-handed loop achieves stronger near H-field with good impedance matching. Design details, simulated results, and a fabricated prototype are presented. The concept significantly extends the design degrees of freedom for RFID antennas.

In this paper, a new method to efficiently analyze substrate integrated waveguide (SIW) based devices with multiple accessing ports is presented. The problem is considered as a 2-D electromagnetic problem assuming no field variation normal to the dielectric substrate. The incident and scattered fields from each circular cylinder are expanded with cylindrical modes, and the fields in the waveguide ports are expanded using progressive and regressive modal summations. The addition theorems of Bessel and Hankel functions are used to analyze the full-wave behavior of the SIW device. In order to extract the circuital parameters, the hybrid mode-matching between guided and cylindrical modes is done by projecting continuity equations in a circular boundary containing the whole SIW structure over the inner modes of each region. Applying this new technique, it is possible to analyze multiple port devices by solving a set of integrals that can be easily approached analytically or by using the inverse fast Fourier transform, avoiding the use of non efficient numerical methods. It is shown that the new method runs faster than commercial software packages and other techniques recently published.