Selecting Antenna/Power Amplifier Combinations

TESTING PRODUCTS FOR SUSCEPTIBILITY to radiated fields above 1 GHz is on the horizon. The new medical standard now stipulates testing to 2.5 GHz, and this upper frequency may be adopted in the coming standard for fire detection products. Though far from certain, it looks as if 6 GHz is a strong candidate for the upper frequency for consumer products. When test facilities test products for compliance to these new RF immunity standards, which antenna/amplifier combination will prove the most effective at producing the necessary volts per meter over the new band? What is the cost-benefit trade-off? This article presents practical combinations using existing technology and highlights the inevitable trade-offs faced during the selection process.

Antennas and power amplifiers of various frequency bands and power capabilities are readily available within the EMC marketplace. Ideally, you would simply select an antenna covering 1 GHz to 6 GHz, combine it with a power amplifier covering 1 GHz to 6 GHz, and ‘hey presto’, you have the solution. Life, as we all know, is never that simple. Antennas covering this frequency band (and wider) that can handle the necessary input power are indeed available from many excellent manufacturers. In fact, antennas covering 25 MHz to 7 GHz exist, possibly allowing coverage of the old and new frequency in an uninterrupted sweep. Unfortunately, a power amplifier covering 1 GHz to 6 GHz and capable of delivering the necessary power level does not exist. The band will need to be covered by at least two amplifiers so that a switch is required to connect the antenna to the appropriate amplifier during the immunity test. Or, if preferable, two amplifiers and two antennas could be used. Clearly, the scene is set for the evaluation of a selection of mix-and-match permutations.