# Tech Chat | Understanding Antenna Phase Center & Its Calculation

In satellite positioning, the original calculated coordinates is the location of the GNSS antenna phase center (APC). To accurately determine the coordinates of the measured point, it's essential to understand the relationship between the APC and the measured point, and how to calculate this conversion. In today's blog, we'll delve into what the antenna phase center is, how it's calculated, and why it matters for your field operations.

**What is the Antenna Phase Center?**

The **antenna phase center** (APC) refers to the central point of the electric field intensity phase distribution in an antenna's radiation field. This is a critical parameter for measuring antenna performance, especially in high-precision applications like GNSS surveying, wireless communications, radar, and remote sensing. The accuracy of your positioning and overall system stability heavily depends on understanding and correctly determining the APC.

**The Concept of Antenna Phase Center:**

When electromagnetic waves radiate from an antenna, they form a spherical wavefront at a certain distance. The center of this sphere is considered the** equivalent phase center** of the antenna. In an ideal scenario, this phase center would be a single, precise point from which all signals are emitted. However, in practice, the phase center is an area rather than a point due to the imperfections in real-world antenna design.

**Antenna Phase Center Position Calculation Formula:**

To convert the APC to the measured point, we can calculate the position of the phase center using the following formula:

**φ**: Phase center offset distance.**λ**: Operating wavelength.**εr**: Relative dielectric constant.**d**: Distance from the antenna vertex to the reference plane.**r**: Antenna radiation resistance.

**Calculating the Phase Center in SingularXYZ Products**

**Abbreviations Explained:**

**ARP: Antenna Reference Point**– Typically, this is where the bottom of the receiver antenna intersects with the center axis of the antenna.**APC: Antenna Phase Center**– The central point from which the antenna radiates its signals, crucial for accurate position calculation.**L1/L2: L1/L2 Phase Center**– Refers to the phase centers for the L1 and L2 frequency bands, important for dual-frequency GNSS measurements.**H:**Distance from ARP to receiver mark.**HL1, HL2:**Distance from receiver mark to the phase center of the L1, L2 frequency bands.

Since the ARP is normally the center point of the receiver bottom, it's easy to convert to the measure point by adding the range pole height to the ARP. So here let's use the X1-Series and Y1 as examples to illustrate how to convert the APC to the ARP. And the method for calculating the APC is slightly different between them.

**1. X1-Series Models**

Distance from ARP to APC = H + HL1 = 1.968m - 1.9m = 0.068m

**2. Y1 Model**

Distance from ARP to APC = H + (HL1 + HL2) / 2 = 0.0634m

Though the calculations differ between the two products, both methods are accurate and appropriate for their respective systems.

Understanding the concept of the antenna phase center and its accurate positioning is crucial for ensuring the high performance and stability of your GNSS surveying. Whether you're using SingularXYZ's X1 or Y1 model, knowing how the APC is calculated helps in achieving precise results in your fieldwork.

Learn more about SingularXYZ GNSS receivers