Miniaturizing Patch Antenna with Multi-layer Soft Ferrite and Dielectric Substrate Structure

Abstract

The patch antenna is advantageous in many applications because of its simple and inexpensive structure. However, one disadvantage is its large size. One of the methods to reduce the size of an antenna is to utilize ferrite material [1]. While this does effectively miniaturize the antenna, the peak realized gain (PRG) is decreased by 8.3 dBic due to the magnetic loss of the ferrite core.In this paper, we take the multi-layer ferrite and dielectric approach to reduce the patch antenna size. All antennas were simulated using ANSYS HFSS for their performance. Fig. 1 shows the specifications and designs of the patch antennas. The baseline patch antenna has the dimensions given in [2] and uses a 1.4 mm thick FR-4 substrate (permeability (μr) = 1, permittivity (εr) = 4.4). The dielectric and magnetic loss tangents (tanδe and tanδu) are 0.02 and 0.00, respectively, at UHF band frequency, and its volume (V) is 9800 mm3. To realize the multi-layer concept in the antenna size reduction, 0.8 mm thick layers of ferrite (μr = 6, εr =13, tanδu = 0.05, tanδe = 0.02, and V = 2720 mm3) are inserted into the FR-4 substrate. Three topologies are investigated: one ferrite layer, two ferrite layers, and three ferrite layers. For each topology, the volume of the ferrite remains the same. For the cases with more than one ferrite layer, the inner-most layer has a constant V = 600 mm3, and the remaining volume is divided equally among the outer layers. Antenna performance results are summarized in Table 1. For one ferrite layer, 16.7% miniaturization is achieved, but the PRG decreases by 14.1 dBi. However, as the number of layers increases to two, 49.8% miniaturization is achieved with a decrease in PRG of 5.6 dBi. For three layers, 49.3% miniaturization is observed with a 5.6 dBi decrease in PRG. Compared to the case with the all-ferrite substrate (V = 9800 mm3), the patch antenna with two ferrite layers has a 4.4 dBi higher PRG. Ferrite and dielectric substrate contributes remarkably to antenna size reduction.  Fig. 1. Design and specifications of (a) baseline patch antenna, (b) ferrite-dielectric layering, and (c) multi-layer patches  Table 1. Comparison of antenna performance results