EMC within electronic components has become an increasingly important issue for embedded designers to contend with. As system frequencies and the need for lower supply voltages increase, the end application becomes more and more vulnerable to the negative affects of EMI. These electrical influences can be generated by either radiated or conductive EMI sources. Radiated sources include anything electrical or electromechanical, including motors, power lines, antennas, traces on a PCB (Printed Circuit Board), and even the silicon components on the PCB. Conductive EMI primarily shows itself as electrical “noise” on the power supply lines of an application and can be caused by induced voltage spikes from other devices within a system.
Electromagnetic Interference (EMI): Electromagnetic emissions from a device or system that interfere with the normal operation of another device or system. EMI is also referred to as Radio Frequency Interference (RFI)
Electromagnetic Compatibility (EMC): The ability of equipment or system to function satisfactorily in its Electromagnetic Environment (EME) without introducing intolerable electromagnetic disturbance to anything in that environment
For an EMIC problem to exist:
System/Device that generates interference
System/Device that is susceptible to the interference
Coupling path: The coupling path may involve one or more of the following coupling mechanisms:
Conduction – electric current, power line
Radiation – electromagnetic field
Capacitive Coupling – electric field
Inductive Coupling – magnetic field
Mitigation of EMIC Issues:
Reduce interference levels generated by culprit
Increase the susceptibility threshold of the victim-Reduce the effectiveness of the coupling path
A Rotary Joint (RJ) is a wide spread microwave device that is used to change the direction of microwave propagation between two waveguides by rotating one with respect to another. Rotary joints find many applications in radar and satellite earth stations for functions such as polarization rotation; antenna feed systems and azimuth and elevation motions. Many styles of rotary joints are available for a variety of environmental conditions. Multichannel rotary joints must be carefully designed to achieve low channel loss and small rotational variations of this loss.
An investigation was first carried out to review the state of the art in the field of multiple-channel rotary joints and to select the types of propagation modes that best satisfied the special system needs. A review of possible design approaches led to the selection of a concentric coaxial line configuration for the main body of the rotary joint, with integral transitions to waveguide at both ends for minimum overall system losses. A sketch of the basic design layout is given in Figure.
Both coaxial line and circular waveguide (CWG) versions are used. To avoid amplitude / phase modulation of the signal transferred through the joint; the axial symmetry of the electromagnetic field is required. To achieve proper field symmetry, the design of the joint is based on using a coaxial microwave line where the TEM mode of the electromagnetic field is propagated. In case a long diameter of axis hole is required, the dimensions of the coaxial line can prove large enough to cause excitement of unwanted waveguide modes. A simple coaxial rotary section operating in the TEM mode is chosen as the basis for the design of this type of joint. Multi number of rotary channels has been increased by the concentric stacking simple coaxial forms. The joint to be described operates in the TEM mode and has low SWR and insertion loss over a wide band of frequencies. It also has no dead spots, showing only negligible variations transmission characteristics with rotation.
The choice of low impedance for this section permitted using a large center conductor, and so made possible the large hole required through the center. When the center conductor becomes this large, however, the increased dimensions introduce the possibility of higher-order circumferential modes existing in the coaxial section. Such a condition would be manifest by phase or amplitude variations of the output signal as the joint is rotated.
The tendency to excite these undesired modes is minimized by careful selection of designing dimensions of coaxial waveguides.A 4-channel C/Ku-band coaxial rotary joint has been designed axially to achieve the desired four-channel operation. To achieve proper field symmetry, the design is based on a coaxial microwave line where the TEM mode of the electromagnetic field is propagated. Multiple rotary channels have been incorporated the concentric stacking of simple coaxial forms. The joint to be described operates in the TEM mode and has low SWR and insertion loss over a wide band of frequencies. It also has no dead spots, showing only negligible variations in impedance and transmission characteristics with rotation. Multisection doorknob type transition is used to obtain broadband performance.
Slotted antenna arrays used with waveguides are a popular antenna in navigation, radar, and other high-frequency systems. A waveguide is a very low loss transmission line. It allows propagating signals to a number of smaller antennas (slots). Each of these slots allows a little of the energy to radiate. Slot impedance and resonant behavior for a single slot are dependent on slot placement and size. Its exceptional directivity in the elevation plane gives it quite high power gain. The slotted waveguide has achieved most of its success when used in an omnidirectional role To make the unidirectional antenna radiate over the entire 360 degrees of azimuth, the second set of slots are cut on the back face of the waveguide.
An 8×8 planar four pole X-band Tchebyshev dual inductive post substrate integrated waveguide filter from 10.15 GHz to 10.7 GHz is designed for terrestrial broadcasting. The filter is designed on the 5870 with a relative dielectric constant of 2.33, loss tangent of 0.0012 and thickness of 0.7874 mm. The diameter of all holes was chosen 1 mm and the distance between side wall holes is 1.5 mm. The width of the SIW is 13.27 mm and the total length of the designed filter is 77.7 mm. This structure is analyzed with FEM solver and Momentum in ADS. Good agreement between results was observed.