Design investigation of microstrip antenna using loading circuit (LC) method for amateur satellite communication UHF band

This paper presents a design investigation of microstrip antennas by using inserting a resistive load (loading circuit method) that it is called as loading circuit (LC) microstrip antenna. The aim of inserting of a resistive load is to reduce dimensions of conventional one that is relatively large in size for UHF bands. The antenna material uses PCB FR-4 Epoxy, in which there is a dielectric substrate with dielectric constant (εr = 4.7, tan δ = 0.02), height h = 1.6 mm. As a comparator, first a conventional square microstrip antenna is designed with a certain dimension. To generate a resonant frequency, the feed point of the antenna is placed at the vertices of the diagonal line at a certain position. Next, the microstrip antennas is designed by using the same material at the same operating frequency as conventional one and adding resistive loads. At this stage, an effect of the position of the feeding point and value of the loads to the antenna characteristics is investigated. In addition, value of the loads are varied from: shorting circuit (pin), low resistive resistor 1.0 Ω, 1.1 Ω, 1.2 Ω, and also the impact of slit to produce a size reduction with the expected specifications. The design specifications of both microstrip antennas (a conventional and loading circuit) are operating frequency of 435 MHz to 438 MHz according to amateur radio frequency band for satellite, with design frequency of 435.9 MHz, bandwidth of 3 MHz, with 50 Ω input impedance, VSWR is smaller than 2.0, and bandwidth more than 3 MHz. Circularly polarized antenna with axial ratio is less than 3 dB, and the radiation pattern produced is direction. All the design process of this antenna using CST Microwave Studio.