IN MY OPINION

Interconnect Advances Fuel Technology Growth
By Orwill Hawkins, Vice President of Marketing, LadyBug Technologies

With increased frequencies, higher data rates, and lower noise levels, the microwave industry serves as a leader in technological capability. Demand for quality interconnects has increased right along with other higher-performance areas in the industry.
Read More...

FROM WHERE WE SIT

Uncertain Times for DefenseIn Defense of DARPA; Lamenting Bell Labs
By Barry Manz

A federal agency like DARPA is a sitting duck for politicians and assorted other critics. It has come up with some truly bizarre programs over years that ultimately either delivered no tangible results, were canceled before they could cause any damage, or attempted to answer questions that nobody was asking or needed answers to. Read More...


CURRENT ISSUE PRODUCTS


E-Band Active X5 Multiplier
Model SFA-743843516-12SF-N1 is an E-band X5 active multiplier with center frequency at 79 GHz with minimum +/-5 GHz operational bandwidth. It converts 14.8 to 16.8 GHz/+5 dBm input signal to deliver 74 to 84 GHz frequency band with more than +16 dBm power.
Sage Millimeter

Hand-Flex™ Coaxial Cable
Covering DC to 12.5 GHz, this 8” coaxial cable, 141-8SMNB+, has a bulkhead Female Type-N connector at one end and SMA-Male at the other. Features include low loss, excellent return loss, hand formable, and an 8mm bend radius for tight installations.
Mini-Circuits

Phase Trimmer Series
This new phase trimmer series is designed for RF applications where phase match between two cables is needed for proper system performance. Phase trimmers, offered from DC to 50 GHz, will give an accurate phase adjustment over a specified frequency range.
RLC Electronics

Planar Monolithics Industries
Model PTRAN-100M18G-SFB-3UVPX-MAH is a transceiver covering the frequency range of 100 MHz to 18 GHz. The transceiver fits into a 3U Open VPX form factor utilizing the high speed VITA 67 RF connector.
Planar Monolithics Industries

SMT High-Power Attenuators
Now available with full design support capabilities are three new SMT high-power attenuators from Anaren. These 30 to 50W devices are high-performance, high-power chip attenuators covering DC to 3.0 GHz and feature high return loss and small footprints.
Richardson RFPD

See all products in this issue


June 2008

Why Directional Couplers Are Better for High Power
Measurements vs. Attenuators
By MECA Electronics

Day-to-day field measurements of base station power has frustrated engineers and technicians alike because of the instability and uncertainty of measurement caused by using high power fixed attenuators to reduce the signal level into sensitive power Meters. Why? Attenuators de-rate as input power increases and their case temperature rises, so full-power measurements are far different from the initial calibration point. Directional couplers have very low insertion loss and high directivity, so the sampled power (at the coupled port) is extremely stable and isolated from changes in temperature or reflections as power levels increase. The unused power (and subsequent heat) is passed to the termination which is attached to the output of the coupler and away from your measurement path.

Directional Coupler Theory
When power is introduced at the input port of a directional coupler, all of the power appears at the output port except for the portion intended to be sampled. If power is reflected back from the output port, the ideal directional coupler does not allow any of the reflected power to appear on the secondary line. Regrettably, the ideal directional coupler does not exist in our world. Consequently, a small amount of backward power will be coupled to the secondary line 180° out of phase from the incident wave, canceling power on the secondary line and adding uncertainty to the measurement. The term directivity (Figure 1) denotes the ratio of forward to backward coupling and is defined as 10 times the common log of the ratio of forward and backward power D = 10 log10(Pf/Pb). The higher the value of directivity, the less backward power is sampled and measurement uncertainty is significantly improved. Directivity is the qualitative benchmark by which couplers are compared.

Since we are on the subject of measurement errors, we should also deal with the importance of Voltage Standing Wave Ratio (VSWR) because reflections will add to and subtract from the incident signal, causing uncertainty in the coupling factor. VSWR is defined as the ratio of incident to reflected signals and is ideally 1.00:1, meaning these signals are in phase and will not cancel. The better the VSWR, the less return loss is encountered. Unsatisfactory coupler VSWR will degrade measurement accuracy and is usually attributable to lesser quality connectors or inadequate design techniques.

Attenuator De-Rating
As discussed in the introduction, attenuators will handle the specified power ratings at ambient temperatures. Most attenuators are convection cooled, meaning no forced air (fan) is required to cool the unit. As the ambient and case temperature of the unit rises due to increased input power, the attenuator de-rates linearly to zero at 150º C. For instance, a 50w attenuator is rated for full power at 25º C and 0 watts at 150º C. If plotted on graph paper, you will find that the attenuator will dissipate 25w at 88º C (midpoint), which is far different from the initial calibration point. (See Figure 2)

MECA Power Measurement Kit
MECA has designed the MFK-PMK-1 Power Measurement Kit to replace high power attenuators as a means of reducing signal levels into sensitive power meters. The kit features a 500w, 30 dB, 0.800 – 2.200 GHz, directional coupler (MECA 715-30-1.500V) furnished with albaloy plated connectors, gold plated contact pins, and a rugged aluminum housing for long lasting performance. Different directional couplers can also be specified for many frequency band specific measurements, such as TETRA/Public Safety (400 – 800 MHz) and WiMAX (2.000 – 4.000 GHz) applications.

For the output of the coupler, MECA has included a 100w, N-Male termination (MECA 490-1) which will provide a 2X safety margin for full power BTS measurements at 46 dBm. The termination has an albaloy plated N-Male connector, silver contact pins and a black anodized convection cooled heatsink. The kit also contains 1 each of a 2w, N-Type attenuators in 6, 10 and 20 dB (MECA 605-dB-1). The additional attenuators can be added to the coupled port to optimize the input signal level into the power meter.

All of the components are furnished in a hard-shell case with form-fitting foam inserts that eliminate concerns of damaging the RF components in transit. These sturdy cases can be stored in a technician’s vehicle or remote switch locations and are rugged enough to be stored among toolboxes and cable spools.

MECA Electronics, Inc.
Since 1961, MECA has designed and manufactured an extensive line of RF/Microwave components with industry leading performance, including fixed attenuators, directional and hybrid couplers, isolators/circulators, power divider/combiners, RF loads, DC blocks and bias tees. MECA serves all areas of the RF and Microwave industries, including world class network providers and supporting supply chain infrastructure, and has long been the “backbone” of high performance wired and air-interfaced networks such as in-building applications, satellite communications, radar, radio communications, telemetry applications, mobile radio, aviation and air traffic communications.

MECA Electronics, Inc.
www.e-meca.com
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WHITE PAPERS

The Design of Ultra Narrowband Amplifiers Using Small-Signal Varactor Upconverters
This paper presents a method of realizing tunable microwave amplifiers with ultra narrow bandwidths that can be less than 0.5% by the use of a varactor up-converter (UC).
Planar Monolithics

Directivity and VSWR Measurements
Return loss and VSWR measurements are complicated by the finite performance of the directional device used to measure the reflected power. The only accurate and convenient way to make return loss measurements is with a well matched high directivity directional coupler or bridge.
Marki Microwave

Switch Solutions for Systems with Low PIM Requirements
Dow-Key Microwave has invested in R&D for new RF switch products designed specifically to reduce intermodulation (IM) in coaxial switches.
Dow-Key Microwave

How to Specify RF and Microwave Filters
Covers cavity, ceramic, LC, crystal and helical filters.
Anatech Electronics

Mounting Considerations for Medium Power Surface-Mount RF Devices
Covers all factors that must be considered when mounting SMT devices.
TriQuint Semiconductor

Biasing MMIC Amplifiers
How to bias MMICs along with theory and techniques.
Mini-Circuits


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