7) Effect of metal on gain

This shows how antenna performance is degradaded by metal nearby. We used our standard antenna evaluation board and it was affixed to the center of a 500 x 300mm copper plate (Fig.7-1) set on a turntable in our anechoic chamber. We varied the distance between the copper plate and the evaluation board (10, 20, 30, 50, and 100mm).

・ Fig. 7-2 shows how VSWR changes when the distance between the copper plate and the antenna is changed. Fig. 7-3 shows the max gain for VSWR at 430MHz for different gap distances. When the antenna evaluation board is 10mm from the copper plate the maximum gain of V polarization in YZ plane is –30.07dBd which is 18dB worse than the original gain.
Resonance frequency shifts about 13MHz down. Lengthening the distance between the evaluation board and the copper plate dramatically improves gain.
・ We retuned with inductors for 10mm board gap and Fig. 7-4 shows the retuned VSWR. Average gain only improved 1.3dB (red in Fig. 7-3).





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