Dielectric Resonator Oscillators (DRO)

Dielectric Resonator Oscillators (DRO) are used widely in today's electronic warfare, missile, radar and communication systems. They find use both in military and commercial applications. The DROs are characterized by low phase noise, compact size, frequency stability with temperature, ease of integration with other hybrid MIC circuitries, simple construction and the ability to withstand harsh environments.

These characteristics make DROs a natural choice both for fundamental oscillators and as the sources for oscillators that are phase-locked to reference frequencies, such as crystal oscillators.

This paper summarizes design techniques for DROs and the voltage- tuning DRO (VT-DRO), and presents measured data for them including phase noise, frequency stability and pulsing characteristics.

Design Techniques

The design technique we will discuss is for a dielectric resonator (DR) to be used as a series feedback element. Practically, a GaAs FET or a Si-bipolar transistor is chosen as the active device for the oscillator portion of the DRO circuit. The Si-bipolar transistor is generally selected for lower phase noise characteristics, while the GaAs FET is required for higher frequencies.

For example, a DRO with a DR as a series feedback element can be designed using following design procedure:

1. Select an active device that is capable of oscillation at the design frequency, and use the small signal S-parameter of the device for the design.
2. Add a feedback circuit to ensure that the stability factor of the active device with the feedback circuit is less than unity with enough margin.
3. Create an active one-port analysis that consists of the active device, the feedback circuit, the matching network and the load as shown as figure1. Optimize Za (?) with the parameters in the feedback circuit and in the matching network to ensure that Ra (?0) is less than or equal to -25 ohms and Xa (?) has the possible maximum variation near resonance in order to insure high circuit Q.

Wireless Optical Mesh Solution Networks

ClearMesh Networks Wednesday launched a wireless optical mesh solution designed to fill the gap between copper, RF and fiber in delivering 5mbps to 100mbps services to small and midsized businesses.

“There isn’t a cost-effective way for carriers today to extend fiber to SMBs,” said Fima Vaisman, ClearMesh’s senior vice president of marketing, explaining their monthly spend of $500 to $1,000 does not support a fiber trench where it is not already available. “What we provide is a solution that extends the fiber core without having to trench fiber.”

It also provides higher bandwidth than do copper and RF solutions, such as Wi-Fi and WiMAX, he said. “If a customer needs more bandwidth and they are looking for an SLA, we think there is a gap between those solutions provided at the entry level by WiMAX and Wi-Fi, and the high-end level by fiber. There is a gap in the middle. That is the gap we are trying to serve.”

Available immediately, the ClearMesh Metro Grid solution includes the ClearMesh 300 node, which can be mounted on a pole or rooftop, and the ClearMesh Management System, which provides tools for installation, diagnostics, service analysis and provisioning. The ClearMesh 300 node combines wireless and optical technologies with a Layer 2 mesh architecture to deliver business-grade Ethernet.

“The ClearMesh 300 Node is a switching platform,” explained Vaisman. “It has an Ethernet switch with 2-gigabit Ethernet capacity. Four of the Ethernet ports are copper and they are connected to optical transceivers.”

The optical transceivers, he said, are LED-based, which gives them a wider beam than systems using lasers, like free-space optics. “What that allows the product to do is be installed on a light pole as well as on top of a building,” said Vaisman. “A laser product cannot be installed on a light pole because the light pole has too much vibration, too much movement. The product wouldn’t stay locked on. With the product we have the light beams are locked on and stay locked on using automatic tracking whether on a light pole or building. With that you have a much broader ability to deploy a mesh in a metro area. If the device moves, the light cone still hits the other node.”

Each node has three optical transceivers, which operate on the license-free 850nm light band and reach 250 meters. Each transceiver is motorized, so it can move independently up and down, and 360 degrees around. “This allows each node to see three other nodes. Using that, we create a mesh,” said Vaisman, explaining the mesh requires one node to be fiber-feed, and several nodes can be fed from the same fiber to increase the capacity delivered into the mesh.

The ClearMesh node lists for $6,000, and less in volume. Considering installation costs, the company uses $5,000 per node in its ROI calculations. In contrast to trenching fiber, ClearMesh can cover seven buldings in a MetroGrid network for $35,000 in a matter of days while the fiber deployment over the same area will cost $180,000 and take months to install, he said. With a single customer per building and a single T1 replacement at $500 per month, the payback is 10 months, Vaisman said, adding a more realistic scenario is three customers per building paying $750 per month for a 10mbps service for an ROI of two months.

Yankee Group Analyst Tara Howard agrees that the ClearMesh solution serves “as a logical extension of a fiber network,” but she questions the market potential, discounting its appeal to Tier 1 companies that are laying fiber. “The opportunity is going to be with local LECs and municipalities,” she said, adding the fact that it does not compete with Wi-Fi or WiMAX is a plus.

“We don’t do what Wi-Fi does; we don’t offer mobility,” said Vaisman. “We don’t do what WiMAX does; we don’t offer five-mile reach. In a dense metro area, we offer high bandwidth and the ability to sign SLAs without any interference,” he said. The systems offers latency at one-tenth of 1ms, so 10 nodes equals 1ms of delay.

Wirelss Wide Area Network

Wirelss Wide Area Network A WWAN differs from a WLAN (wireless LAN) in that it uses Mobile telecommunication cellular network technologies such as WIMAX (though it's better applicated into WMAN Networks), UMTS, GPRS, CDMA2000, GSM, CDPD, Mobitex, HSDPA or 3G to transfer data. It can use also LMDS and Wi-Fi to connect to the Internet. These cellular technologies are offered regionally, nationwide, or even globally and are provided by a wireless service provider for a monthly usage fee.[1] WWAN connectivity allows a user with a laptop and a WWAN card to surf the web, check email, or connect to a Virtual Private Network (VPN) from anywhere within the regional boundaries of cellular service. Various computers now have integrated WWAN capabilities (Such as HSDPA in Centrino). This means that the system has a cellular radio (GSM/CDMA) built in, which allows the user to send and receive data. There are two basic means that a mobile network may use to transfer data:
Packet-switched Data Networks (GPRS/CDPD)
Circuit-switched dial-up connections
Since radio communications systems do not provide a physically secure connection path, WWANs typically incorporate encryption and authentication methods to make them more secure. Unfortunately some of the early GSM encryption techniques were flawed, and security experts have issued warnings that cellular communication, including WWANs, is no longer secure.[2] UMTS(3G) encryption was developed later and has yet to be broken.
Examples of providers for WWAN include Sprint Nextel, Verizon, and AT&T.

Oxygen Sensor Analyzer

An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O₂) in the gas or liquid being analyzed. It was developed by Robert Bosch GmbH during the late 1960s under supervision by Dr. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.

Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.

There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.