Feature: RF design


Figure 1: Different matching component values in switched-circuit antenna


Figure 2: Switched-circuit antenna covering a broad frequency range


Figure 3: Placement of cellular and GNSS PIF antennas With suitable matching components, these antennas can be


designed to cover the full LTE band, from 700MHz to 2.7GHz, with high radiation efficiency. For loop antennas, the ideal placement is the middle of the board edge, rather than a corner.


GNSS antennas For GNSS service, ceramic patch and ceramic loop antennas are oſten used. Teir circular polarised response ensures good sensitivity to GNSS signals. Tis allows the use of small-size antennas where there are size constraints. However, if the antenna is excessively small, circular polarisation can be lost, impairing performance. Antennas as small as 9mm x 9mm are available, although 18mm x


28 November 2022 www.electronicsworld.co.uk


Figure 4: Using S2,1 parameters to assess antenna spatial separation


18mm and 25mm x 25mm are more commonly used. Te directionality of the patch-type antenna makes it a


good choice for fixed positions or where it can be controlled to continuously face the sky, which is not always possible, especially in wearable devices or asset trackers. Ceramic loop antennas offer a better alternative here, owing to their omnidirectional response. Also, they can be smaller than ceramic patch types. As with any loop, such an antenna should ideally be


positioned in the middle of a board edge. For multi-constellation applications, multi-band ceramic-loop antennas are available off the shelf from various manufacturers. An attractive new option in this category is the stamped metal


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