In this present paper, attention is focused on the rectangular block TM’101 moantennade with monopole excitation because it proved to be most appropriate for the handset installation. Three samples of hexagonal ferrite material were cut to size and drilled to accommodate the 0.5 mm radius monopole excitation probe that was back-fed on a 250 X 250 mm ground plane. The radiation efficiency η of the TM’101 mode was then measured using the Wheeler cap method. The cap diameter was 73 mm, which satisfied the radian sphere limitation. Sample 1 had dimensions 50 X 50 X 18 mm and a monopole of length 15 mm. The following properties were assessed from measurements: ε’~5.5, μ’~1.5, tanδε~0.03 and tanδμ~0.14 indicating a high magnetic loss, as confirmed by the measured and simulated data in Table I. For this sample was also checked using a transmission system test.
TABLE I
MEASURED AND SIMULATED RESONANT FREQUENCY foE’ , S11 AND
η OF FERRITE ANTENNA SAMPLES IN THE TM’101 MODE
Sample 2 had dimensions 25 X 2 X 27 mm cut from MF112 material manufactured by Emerson and Cuming with quoted properties: ε’~5.2, μ’~1.5, tanδε~0.05 and tanδμ~0.03. Although intended for screening purposes, this material was far less lossy than that in sample 1 and gave a reasonably high η as seen in Table I, using a 12 mm monopole; a--10 dB BW of 44% was measured at 2.45 GHz.
A 2-mm thick flexible sheet of material intended for use as a white-board marker, was found to possess magnetic properties at the lower microwave frequencies. The material was cut into square pieces and stacked to provide sample 3 with dimensions 20 X 20 X 30 mm. The antenna resonated at 2.43 GHz with a 12 mm monopole probe. The assessed material properties were: ε’~4.3, μ’~1.4, tanδε~0.03 and tanδμ~0.02 resulting in a less compact but higher efficiency antenna, as shown in Table I. It is concluded that the simulations and measurements are in good agreement considering that the latter have tolerances of the order 5%. |
