What Is a Rhombic Antenna?

A diamond antenna is a wideband antenna. It consists of a horizontal rhombus suspended on four pillars, one acute angle of the rhombus is connected to the feeder, and the other acute angle is connected to a terminating resistor equal to the characteristic impedance of the rhombus antenna. Its maximum emission direction is in a vertical plane pointing to the direction of the terminal resistance, and it is unidirectional.

A diamond antenna is connected with four long wires longer than the wavelength. It is suspended horizontally or obliquely on four pillars, fed at an acute angle of the rhombus, and connected at another acute angle to an absorption resistance equal to the characteristic impedance of the antenna. This antenna was proposed in 1931. It is a strong directional traveling wave antenna, which can be seen as two V-shaped wires connected at the open end, and its working principle is similar to that of a V-shaped traveling wave antenna. The four arms carrying the traveling wave current are equal in length, and their radiation patterns are exactly the same. Proper selection of the side length L and the vertex angle A of the rhombus can make the lobes a, a , a , a of each arm superimpose in the same direction in the diagonal direction of the rhombus, and other lobes interfere with each other to form the side lobe. The main lobe direction is the acute diagonal direction from the feed point to the absorption resistance, and there are more and stronger side lobes in other directions. When the apex angle A is between the maximum of the two main lobes of each side wire When the angle 2 is equal, the main lobe direction of the antenna is located in the rhombus plane and coincides with the acute diagonal; when A <2, the main lobe direction is at an angle with the rhombus plane and lies in the major plane perpendicular to the rhombus plane; when A When> 2, the main lobe of the antenna is split. The horizontal diamond antenna mounted on the ground is interfered by the ground reflection. The vertical plane beam is split into multiple beams. The shape of the pattern is determined by the height of the antenna and the operating wavelength. , The lobe direction of the lobe forms a certain elevation angle with the ground. Therefore, the performance of the diamond antenna depends on three parameters: L / , , and H / . ^[1]

Based on the analysis of the structure and working principle of the diamond antenna, in order to reduce the size of the antenna structure and improve the direction and gain characteristics of the antenna, a stacked double diamond antenna with a reflecting plate with a working frequency of 2.4 GHz is designed. During the design process, VB software was used to make an interactive antenna calculator to facilitate the calculation and optimization of antenna size parameters, and 4NEC software was used to build the antenna model and simulation optimization. The antenna was tested on the antenna test platform using PNA3621 network analyzer. The measurement results show that the antenna pattern is better in the frequency range of 2.35GHz to 2.45GHz, which is in good agreement with the simulation results. The voltage standing wave ratio and return loss of the antenna input are ideal. In order to improve the direction and gain characteristics of the diamond antenna, In the form of an antenna array, the design improves a stacked dual-link antenna structure. The two double-diamond antennas are stacked one above the other, and the double-diamond connected to the feeder is called a radiating oscillator, which is used to radiate energy. The other double-diamond overlapping with the radiating oscillator is called a directional oscillator, which mainly radiates energy in a certain direction. The device adopts the bridge method to test the load, return loss, standing wave and other reflection characteristics of the antenna; the rotating antenna method can be used to test the gain and directionality of the antenna: the antenna to be tested is fixed on the test turntable, and the direction controller is used The control antenna is rotated 360 ° in the horizontal plane, and the receiving antenna receives the field strength from the transmitting antenna on the gimbal, and the test result is obtained after processing. While the network analyzer instrument panel displays the results, through the network analyzer serial interface, the relevant graph curves and data of the measurement can be displayed on the computer. The reason is that there will be a certain error in the manufacturing accuracy of the antenna, and the impedance mismatch caused by the welding of the antenna and the feeder connection. As can be seen from the pattern diagram, the dual-diamond antenna has good directivity and symmetry. Its main lobe width is 56 °, but the level of the first side lobe is large, which is slightly different from the simulation result. The pattern is not smooth and jagged because the space test environment of the laboratory is limited, which causes the radio waves to enter the test antenna after multiple reflections. ^[3]