Nowadays, Beidou antennas are used more and more in our lies, such as persona location snice’s, when you enter an unfamiliar place, you can use mobile phones or car satellite, navigation device. equipped with Beidou antennas to provide us with the route to go; Although the Beidou antenna makes our life more convenient but its performance indicator we have to pay attention to, because these performance indicators determine its function, then what are the performance indicator of the Beidou antenna.

Beidou antenna input impedance: input impedances the ratio of voltages current at the feed point of the Beidou antenna. The input impedance of the general Beidou antenna is complex and the real part is called the input resistance, expressed in rt: The imaginary part is called the input reactance, expressed in xi, and the input impedance of the Beidou antenna is related to factors such as the antenna's geometry. Size feed point location operating wave length and surrounding environment. Directional diagram: The directional diagram is a graphic representation of the directional function, which can vividly describe the spatial distribution of the electric (magnetic field strength. The general power warning width is commonly used to express the degree the direction map, because the direction of the Beidou antenna is determined by the far field area, so it is also called the far field pattern.

3 gain in the case of the same input power of the Beidou antenna. the square of the filed strength generated at the same place as an ideal non- directional point source it quantitively describes the degree of concentrated radiation of a beidou input power. And the gain level is closely related to the antenna pattern, the narrower the main lobe, the smaller the secondary storage, the higher the gain, usually expressed in decibels, the symbol is dB.

Polarization: The Polarization characteristic of Beidou antenna is defined by the space orientation of the electric field intensity vector in the maximum radiation direction of the electromagnetic wave radiated by the Beidou antenna. Since the electric field has a constant relationship, the spatial direction of the electric field vector generally used as the polarization direction of the electromagnetic wave radiated by the Beidou antenna generally divided into line polarization and fine polarization.

standing wave coefficient (VSWR): standing wave coefficient is a characteristic parameter on the key line ofthe Beidou antenna. which inverts the matching degree of the antenna input impedance and the feeder characteristics, defined as the ratio of the maximum voltage to the minimum voltage on the feeder. If the value of SWR is equal to 1, it means that the radio waves transmitted to the Beidou antenna are not reflected, and al are transmitted, which is the most ideal situation. If the SWR value is greater than 1,it means that some of the radio waves are reflected back and eventually become instrumental, making the feeder warm.