This thread was motivated by a discussion initiated within another thread. The question is whether using a heatshrink protective cover over a GPS patch antenna is detrimental to the antenna's, and subsequently, the GPS receiver's performance. I found a number of papers discussing the application of a dielectric layer over a patch antenna. The thickness of the dielectrics in these studies typically ranged from 0mm (no dielectric) to 6mm. Heatshrink might be of the order of 1mm, or less, when applied.
Plastic heatshrink is a dielectric material with a dielectric constant of perhaps 2-3, depending on its composition and the frequency. When it is employed to secure a GPS patch antenna, the heatshrink covering the patch becomes what is termed a superstrate layer. Dielectric superstrate layers are employed to modify the characteristics of some patch antennas including: the gain, bandwidth and beamwidth. These parameters are modified by increasing the thickness of the dielectric layer above the patch.
Some studies suggest that the impedance, gain and bandwidth display a periodic variation as the thickness increases. In some cases the gain and bandwidth can actually increase, before falling off with a periodic variation. It was also found that the antenna impedance varies periodically about its normal value, typically 50 Ohms (Real component). Interestingly, the resonant frequency does not change as rapidly as the other parameters, but tends to drop as the dielectric thickness increases. The on-axis beamwidth tends to narrow with the formation of sidelobes as the thickness increases.
Anyone with differing experiences and knowledge are invited to join the discussion, particularly if they can provide actual data. Which ever way this goes, we can only benefit from the outcome. I certainly hope to perform some measurements when I can.
Plastic heatshrink is a dielectric material with a dielectric constant of perhaps 2-3, depending on its composition and the frequency. When it is employed to secure a GPS patch antenna, the heatshrink covering the patch becomes what is termed a superstrate layer. Dielectric superstrate layers are employed to modify the characteristics of some patch antennas including: the gain, bandwidth and beamwidth. These parameters are modified by increasing the thickness of the dielectric layer above the patch.
Some studies suggest that the impedance, gain and bandwidth display a periodic variation as the thickness increases. In some cases the gain and bandwidth can actually increase, before falling off with a periodic variation. It was also found that the antenna impedance varies periodically about its normal value, typically 50 Ohms (Real component). Interestingly, the resonant frequency does not change as rapidly as the other parameters, but tends to drop as the dielectric thickness increases. The on-axis beamwidth tends to narrow with the formation of sidelobes as the thickness increases.
Anyone with differing experiences and knowledge are invited to join the discussion, particularly if they can provide actual data. Which ever way this goes, we can only benefit from the outcome. I certainly hope to perform some measurements when I can.
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