Friday, December 23, 2016

EMI & EMC Compliance of Smartphone

EMI & EMC Compliance of Smartphone

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:
emc5
  1. Conduction – electric current, power line
  2. Radiation – electromagnetic field
  3. Capacitive Coupling – electric field
  4. 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

Sunday, December 11, 2016

Dual Channel Rotary Joint


Dual Channel Rotary Joint

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.
4 CHANNEL ROTARY JOINTS
rj4

Monday, December 5, 2016

Slotted Waveguide Array Antenna


Slotted Waveguide Array Antenna
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.

Sunday, November 27, 2016

Array Antenna Feed Networks


There is various kind of feeding network of an array antenna. Feed network depend on antenna type and geometry. Feed network for microwave applications is a major design concern in terms of complexity and size.

Passive Antenna Array

(a) Corporate Feed Network : For a passive antenna, most popular feeding networks type is corporate feed network as shown below in fig. This technique integrates the RF feed network with the radiating elements on the same substrate. Due to a large number of the microstrip line in corporate feed, it’s lossy especially at high frequencies. Minimization of losses in the microstrip feed network may result in microstrip antenna arrays with high efficiency. The efficiency of microstrip antenna arrays may be improved by using a waveguide feed network. However, this results in a significantly increase in the antenna weight and dimensions. In this case, a transition from microstrip to the waveguide is required.
Corporate Feed Network

Another technique to minimize feed network loss is multi-layer configuration. Conductor loss may be minimized by designing the feed network length per wavelength as short as possible. By using a multi-layer feed network design, the feed network length per wavelength is minimized considerably. Corporate feed is also called parallel feed network, in this equal excitation can be achieved at the expense of compactness.
( b) Inline Series Feed Network : In a series-fed array the input signal, fed from one end of the feed network, is coupled serially to the antenna elements. The compact feed network of series-fed antenna arrays is one of the main advantages that make them more attractive than their parallel-fed counterparts. Beside compactness, the small size of series-fed arrays results in less insertion and radiation losses by the feed network Usually series fed arrays are more efficient than corporate fed arrays. However, corporate fed arrays have a well controlled aperture distribution. Series feed configurations suffer from narrow bandwidth and inherent phase difference caused by the differences in lengths of feed lines. Below is example of end-fed series feed network
End Series Fed Network
This is example of center fed series array
Middle Series Fed Network

Active Antenna Array

Active Phased arrays are usually composed of a feed network and a number of phase shifters. In Active phased-array antennae are antennae transmit power is produced by many TX/RX modules. In these antennas, each element is connected with separate transceiver module, so every radiating element got a small power amplifier in the antenna directly. Active antennae are usually phased array antennae. These antennas are primarily used in remote sensing satellite, adaptive antenna, 5G Beam forming antennas and Radars
Feed networks are used to distribute the output signal of the transmitter to the radiation elements and phase shifters control the phase of the signals at each radiating element to form a beam at the desired direction.

Feed Network for Shaped Beam pattern Arrays

Sometime special feed networks is design to obtained shaped antennas radiation pattern. Below is example of Cosec square shape beam pattern antenna feed network
                      Active Phased Array
More details


Saturday, November 26, 2016


DESIGN OF PLANAR ANTENNAS FOR WIRELESS APPLICATIONS

DESIGN OF PLANAR ANTENNAS FOR WIRELESS APPLICATIONS

Planar antennas, including microstrip and printed antennas, metal-plate antennas, ceramic chip and dielectric resonator antennas have a low profile hence, these antennas have extensive applications in mobile systems (such as 900/1800 MHz bands), wireless local area networks (WLANs, such as 2.4/5.2/5.8 GHz bands), ultra-wideband (UWB, such as 3.1 ~ 10.6 GHz band) communications.
Wireless antennas are used in GSM, WLAN, MAN, CDMA, Wireless Routers, Mobile Handsets, PDA. We can divide these into 3 main categories.
  1. Internal dual-/multi-band mobile phone antennas including PIFAs, very-low-profile monopoles, printed loop antennas, printed slot antennas for mobile phones, PDA or smart phones
  2. WLAN mobile-unit antennas, including dual-band and/or diversity operations and the antenna mountable above the system, ground plane of the mobile unit
  3. UWB antennas for mobile units and access points, including the design techniques for UWB impedance matching, improved Omni-directionality in the azimuthal radiation, pattern stability, polarization purity and band-notching.
Necessary Steps to Design Wireless Antenna
  1. First of all figure out wireless domain like GPS, DCS-1800, IMT-2000, WLAN Applications, Bluetooth…..
  2. Next steps are finding out major specification of antenna
    1. Resonating Frequency of antenna
    2. Antenna Gain requirement
    3. Bandwidth
    4. Antenna type
  3. Choose a suitable substrate , it may depend upon various factor like availability of material, integration of antenna with other circuit components on board. Dielectric constant and height of substrate are important for microstrip antenna parameter calculation
  4. Calculate Microstrip antenna dimension. Most of the time antenna used in wireless communication are not a simple antenna, these are customized structure.
  5. Draw substrate and antenna geometry, define materials
  6. Define feed-point and radiation boundary
  7. Run simulation and check data
  8. If need does interactions to get optimized result

Friday, November 25, 2016

SIW (Substrate Integrated Waveguide) Patch Antena


SIW (Substrate Integrated Waveguide) Patch Antena

SIW technology is essentially a hybrid of microstrip and dielectric-filled waveguide (DFW) technologies. Starting with a PCB substrate, top and bottom metal layers provide two of the waveguide walls. Then, two parallel rows of vias are added, forming the side walls of the waveguide. Figure 1 shows a microwave filter constructed using SIW technology. The SIW technology for passive circuit design has been  implemented for its low cost, compact topology and high performance. There has been increasing interest in implementing SIW technology in active circuits and complete systems, including active integrated antennas.
Antennas designed with SIW technology have excellent performance because they suppress the propagation of surface waves, increase the bandwidth, and decrease both end-fire radiation and cross-polarization radiation. The cavity-backed antenna structure also overcomes potential problems such as heat dissipation and unwanted surface wave modes. These low cost implementations are useful in radar and communication applications. SIW technology can also be utilized for microwave cavity-backed antennas like the one shown in Figure 2. Circuits like these can be found in compact receiver front-end modules and self-oscillating mixer arrays.
In order to design these antennas, full-wave EM solvers can be used to analyze the performance of the antenna before fabrication, and try several “what-if” scenarios to optimize the antenna geometry. The most popular EM solver technologies for this type of analysis are Method of Moments (MoM), Finite Element Method (FEM) and Finite Difference Time Domain (FDTD).

Saturday, November 12, 2016

Higher ORDER MODE ANALYSIS USING FINITE DIFFERENCE

HIGHER ORDER MODE ANALYSIS USING FINITE DIFFERENCE

Coaxial waveguides and the determination of their cutoff frequencies have been discussed by Marcuvitz . This involves finding zeros of a function that involve products of Bessel functions of 1st kind and 2nd kind for TM modes and products of derivatives of Bessel functions of 1st kind and 2nd kind for TE modes. These zeros pertain to a certain order and need a number of iterations to be performed to obtain a set of cutoff wavenumbers. Finite difference methods in the conventional form have been applied t0 a variety of cross sections. However, the same technique involving the formation of rectangular meshes to a circular coaxial waveguide does not seem to be appealing in context with the selection of truncation boundaries and appropriate adjacent node points for the region between the inner and outer conductors. The increase in the number of spurious modes generated and the decrease in accuracy are also detrimental to this choice of meshing technique.
In my approach, the curvilinear rectangular grid formation  is used to mesh the region between the two conductors which enables us to encompass the cross-sectional region completely thus eliminating the necessity of truncation of the boundary. This also yields much accurate result than the conventional rectangular grid formation and is much simpler than the cumbersome method of finding roots from the closed form expressions. The Laplacian operator appearing in the Helmholtz equation in polar form is represented as a five-point difference operator along the radial and circumferential directions. The eigen values which give cutoff frequencies are evaluated from the characteristic equation expressed in terms of matrices obtained from a set of simultaneous equations satisfying the boundary conditions.
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Monday, November 7, 2016

MODELING AND SIMULATION OF CHAFF CLOUD

MODELING AND SIMULATION OF CHAFF CLOUD

Chaff finds are mainly used in electromagnetic countermeasures. A cloud of chaff is an artificial target made up of a bunch of small thin metallized glass fiber or wire. Chaff consists of thin dipole elements cut to resonate at radar frequencies. Chaff Clouds are dispensed in the air through the chaff cartridge on aircrafts. Chaff Cloud masks the real target return signal therefore, the detection of target become more complicated. The reflected signal from the chaff cloud disturbs the opponent’s radar system and creates a false signature in the enemy radar. Because of high RCS signature, after launching a chaff cloud, the incoming missile tends to track on the chaff. The aircraft can then perform a fast, sharp maneuver, deviating from the missile path.
Radar Cross Section (RCS) is defined as the area a target would have to occupy to produce the amount of reflected power that is detected back at the radar, and is classified according to the types of mono-static or bi-static radars. Most RCS measurements of interest are of monostatic case, for which the radar transmitter and receiver are sensibly at the same point in space. For the bistatic case, the transmitter and receiver are separated. In RCS calculation the radar target scattering data is collected.
The calculation of electromagnetic scattering by a chaff cloud is complex and no exact theory is currently available for calculation of all the phenomena observed. Several technique has been proposed for chaff cloud modeling [1, 2]. In conventional method, usually the RCS of a unitary strip is computed and later the statistics of a chaff cloud are taken into consideration, in order to evaluate its global electromagnetic characteristics. One disadvantage of this computation approach is, it does not consider the coupling among adjacent strips and does not include the target in the scenario.
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Monday, October 31, 2016

Signal Integrity Analysis of High-Speed Interconnects

Signal Integrity Analysis of High-Speed Interconnects

Signal integrity (SI) addresses two key aspects in high-speed digital designs: signal timing and quality. SI analysis aims to ensure signals reach their destination in good condition. In a system, signals travel through various kinds of interconnections (e.g., from chip to package, package to RF board trace and trace to high-speed connectors), with any electrical impact happening at the source end, along with the transmission path or at the receiving end, which affects both signal timing and quality. Connector performance directly affects system performance and reliability. As a result, designing and modeling connectors for multi-gigabit applications is one of the greatest challenges in high-speed digital applications.
When designing high-speed applications, the signal transmission quality is a critical factor. At gigabit speeds, high-speed interconnects must be characterized along with the RF board traces. The ever-increasing demand for cleaner signal transmission means that maintaining good signal quality throughout the high-speed interconnects is crucial. Modern high-speed, multi-pin connectors are required to enable data transmission in systems at a very high rate (~ 5 Gbps). Early design changes based on accurate simulations can be indispensable and worthy investments for interconnect realization. Likewise, use of an accurate electromagnetic (EM) model is highly desirable during the design and implementation stage of high-speed interconnects. To achieve good SI, the designer must not only understand the system in which the connectors will be deployed but also perform SI analysis of the RF board along with the connectors.

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