VCDRO by coupled microstriplines with a varactor diode has been demonstrated. Compared with a conventional VCDRO, the proposed VCDRO exhibits phase-noise reduction of more than 8 dBc/Hz. The proposed VC-DRO design and fabrication techniques seem to be applicable in many space and commercial products, such as the Ka-band satellite receiver, wireless LAN, and mobile-communication systems. Applying this idea to MESFET or HBT oscillators will also obtain better phase-noise-performance enhancement because these devices have an extremely low flicker noise.
INTRODUCTIONDespite of the great improvements of integrated circuits, waveguides are still essential parts of millimeter-wave technology. Due to their low-loss characteristic, they are often used for antenna or filter design, as well as for connecting the different parts of circuits. Nevertheless, monolithic integrated circuits and photonics devices are increasingly being developed in the mm-wave area. Therefore microstrip-to-waveguide transitions are critical for an efficient integration of waveguides with planar circuit. Many types of transitions are known, such as the probe type transition [1], the transition via antipodal finline [2], or via a ridged waveguide [3], and they provide reasonably good results; but these transitions are designed to work at the Ka-band or lower frequencies, or they might be too large for integrated circuits. One solution in the mm-wave band has been proposed and tested [4]. It is based on slot-coupled antennas radiating into a waveguide. The difficulty of fixing the small substrate in the waveguide has been overcome by making a step in it. Instead of modifying the waveguide, we propose a E-mode coupling-based transition that consists of inserting a small microstrip antenna inside a standard W-band waveguide, as shown in Figure 1. It is similar to the probe-type transition, but the orientation of the probe (antenna) is parallel to the electric field of the propagating TE 10 mode in the waveguide. The purpose of this change is to improve the performance of the transmission at the working frequency.In this paper, we present the design and measurements of the back-to-back transition based on the principle described above within the W-band. Transmission losses due to the relatively long microstrip line used for the back-to-back transitions have been measured on wafer.
DESIGN OF TRANSITIONThe aim of the design is to build a transition requiring a minimum modification of the waveguide as shown in Figure 1. The microstrip line shown in Figure 2 consists of two parts: the microstrip line outside the waveguide that is 50⍀ and the one inside the WR-10 waveguide that is enlarged (patch antenna) like a disk sector. The transition, based on the electromagnetic coupling of the TE 10 propagating mode in the standard WR10 waveguide, is performed via a patch antenna. It is printed on an alumina substrate with the ground plane removed on the other side. Furthermore, it has to be thin enough to avoid surface-wave propagation modes. Its shape is crucial ...