Published May 8, 2006

In an effort to better combine the editorial content of our magazine with our newly developed and retooled on-line presence, we have decided to expand Harlan's RF and microwave engineering advice into a monthly feature that appears in Microwave Journal.

Harlan has selected one question from his "Ask Harlan" column to be featured in the March issue. Harlan will be monitoring the responses and will ultimately choose the best answer to the question. Although all of the responses to the featured question will be posted on our web site, we plan to publish the winning answer in the May issue.

You be the expert: The answers to the April Question of the Month are below

Renuka Wekhande from RF Arrays Systems India Pvt. Ltd. has submitted this month's question:

Dear Harlan,
1. What are the various parasitics that should be considered when designing a monolithic microwave integrated circuit (MMIC) for standard quad flat no-lead (QFN) packages?

2. What are the advantages of using a gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) over a pseudomorphic high electron mobility transistor (PHEMT)?

From: Clive McDonnell, Serco Defence Support Ltd.

1. Glass substrate and epitaxial wafer.

2. A single power source, horizontal operation and an all optical process.

From: Bhavin Shah, Hittite Microwave Corp.

1. The major parasitic component for a MMIC housed in a QFN package is the bondwire inductance.

2. GaAs HBT can be run at higher current densities thereby increasing their output power over the PHEMT. HBTs are inherently more linear compared to the PHEMT.

From: Elochukwu John Adisionu, Jonel Engineering Co.

1. MMIC is very useful in the exploration of heterostructures such as InAIAs/InGaAs. Modeling/designing of MMIC is done such as to take care of the following problems (parasites): problems associated with power handling; amplification problems; problems associated with pad compatibility; problems associated with signal tracking; chip response and stability; noise filteration problems; and electrical conductivity.

2. With GaAs, engineers/technologists can model MMIC of frequencies beyond 100 GHz. During the manufacturing of MMIC it is always observed that GaAs has the following advantages over PHEMT: good electron transport characteristics; small DC power dissipation; good high frequencies properties and high switching speed.

The winning response will win a free book from Artech House, along with an "I Asked Harlan!" t-shirt. In addition, everyone who submits a legitimate response will be sent an "I Asked Harlan!" t-shirt.

If your response is selected as the winner, you'll receive a free book of your choice from Artech House. Visit the Artech House on-line bookstore at www.artechhouse.com for details on hundreds of professional-level books in microwave engineering and related areas (maximum prize retail value $150).

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