IN MY OPINION
In Memoriam: Jerry A. Bleich
By Karen Hoppe

What can you say about a friend and colleague like Jerry Bleich, who left this world far too soon,
with more life to be lived, more love to share, adventures to plan, and future family joy to experience?
Read More...
MILITARY MICROWAVE DIGEST


MMD March 2014
New Military Microwave Digest

ON THE MARKET


Band Reject Filter Series
Higher frequency band reject (notch) filters are designed to operate over the frequency range of .01 to 28 GHz. These filters are characterized by having the reverse properties of band pass filters and are offered in multiple topologies. Available in compact sizes.
RLC Electronics


SP6T RF Switch
JSW6-33DR+ is a medium power reflective SP6T RF switch, with reflective short on output ports in the off condition. Made using Silicon-on-Insulator process, it has very high IP3, a built-in CMOS driver and negative voltage generator.
Mini-Circuits


Group Delay Equalized Bandpass Filter
Part number 2903 is a group delayed equalized elliptic type bandpass filter that has a typical 1 dB bandwidth of 94 MHz and a typical 60 dB bandwidth of 171 MHz. Insertion loss is <2 dB and group delay variation from 110 to 170 MHz is <3nsec.
KR Electronics


Absorptive Low Pass Filter
Model AF9350 is a UHF, low pass filter that covers the 10 to 500 MHz band and has an average power rating of 400W CW. It incurs a rejection of 45 dB minimum at the 750 to 3000 MHz band, and power rating of 25W CW from 501 to 5000 MHz.
Werlatone


LTE Band 14 Ceramic Duplexer
This high performance LTE ceramic duplexer was designed and built for use in public safety communication and commercial cellular applications. It operates in Band 14 and offers low insertion loss and high isolation to enable clear communications in the LTE network.
Networks International

See all products in this issue


August 2007

The Doherty Amplifier: New After 70 Years
By Freescale Semiconductor, RF Division

The Doherty amplifier architecture has in less than 5 years become the “amplifier of choice” for new wireless transmitters after essentially laying dormant since W.H. Doherty first described it in 1936. The Doherty’s obscurity is directly attributable to the predominant modulation schemes (AM and FM) employed in communication systems over the years, which do not possess high peak-to-average ratios (PARs). The resurgence of interest in the concept is based on its very high power-added efficiency when amplifying input signals with high PARs – precisely the type exhibited by WCDMA, CDMA2000, and systems employing Orthogonal Frequency Division Multiplexing (OFDM), such as WiMAX and the upcoming Long-Term Evolution (LTE) enhancement to the UMTS wireless standard.

In fact, when properly designed, a Doherty amplifier can produce increases in efficiency of 11% to 14% when compared to standard parallel Class AB amplifiers that have traditionally been employed in wireless base station transmitters. Since the transmitter accounts for a high percentage of overall system power consumption, the cost savings delivered by the Doherty amplifier’s efficiency can reduce base station annual electricity costs. Thus its appeal for wireless base station manufacturers and wireless service providers.

While the intrinsic high efficiency of the Doherty architecture makes it desirable for current and next-generation wireless systems, it presents unique challenges from a design perspective. The linearity and output power of the Doherty architecture are slightly less than exhibited by a dual Class AB amplifier, and it can produce higher distortion as well. Fortunately, the advancements in analog and digital predistortion and feed-forward linearization techniques can dramatically reduce the Doherty’s distortion. In addition, careful amplifier design can mitigate its inherently lower linearity. The remaining challenge is to create RF power transistors that can accommodate the requirements of the two types of amplifiers employed by the Doherty architecture and produce optimum RF output power over a wide array of signal conditions.

A Doherty overview
A “classic” Doherty amplifier (Figure 1) employs two amplifiers. The carrier amplifier is biased to operate in Class AB mode and the peaking amplifier is biased to operate in Class C mode. The input signal is split by a power divider equally to each amplifier with a 90-deg. difference in phase. After the signals are amplified, the signals are recombined with a power combiner. Both amplifiers operate when the input signal peaks, and are each presented with the load impedance that enables maximum power output. However, as the input signal decreases in power, the Class C peaking amplifier turns off and only the Class AB carrier operates. At these lower power levels, the Class AB carrier amplifier is presented with a modulated load impedance that enables higher efficiency and gain. The result is an extremely efficient solution for amplifying the complex modulation schemes employed in current and emerging wireless systems.

FREESCALE SEMICONDUCTOR
www.freescale.com
TXTLINX.COM105
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FROM WHERE WE SIT

Uncertain Times for DefenseWill OpenRFM Shake Up the Microwave Industry?
By Barry Manz

Throughout the history of the RF and microwave industry there has never been a form factor standardizing the electromechanical, software, control plane, and thermal interfaces used by integrated microwave assemblies (IMAs) employed in defense systems. Rather, every system has been built to meet the requirements of a specific system, which may be but probably isn’t compatible with any other system. It’s simply the way the industry has always responded to requests from subcontractors that in turn must meet the physical, electrical, and RF requirements of prime contractors. Read More...


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