# Calibration of a Low-Cost 8\(\times\)8 Active Phased Array Antenna
## 1 Introduction  
The new requirement for 5G satellite communications for future mobile communications encourages the investigation of new technologies to meet market demand for latency reduction, higher speed of communications and flexibility [1]. The revolution is in development in markets such as automotive, energy, entertainment and defense that want to benefit from the capabilities of 5G technology to fulfill the demands of businesses and consumers [1, 2, 3]. The main advantage of 5G satellite communication is its non-geographic dependency; it is capable of providing connectivity anywhere, by sea or air, for mobile devices, planes, ships and high-speed trains [1, 4, 5]. The use of a millimeter band and phased array antenna is the key to fulfilling these requirements in the future [5, 6, 7]. The millimeter band provides a wider bandwidth to offer a higher transmission speed; planar phased array antenna is the most efficient solution for compensating high free space losses, canceling interference and correcting beam-steering electronically without the need for a mechanical motor, highlighting its ease of integration in any type of surface, vehicle or IoT device [6, 7, 8, 9]. In order to electronically steer the antenna, the key factor is the beamformer. Depending on the application, the beamformer can be analog, hybrid or fully digital. One of the solutions can be an integrated circuit (IC) which includes all elements of the beamforming circuit: an amplifier, phase shifter, switch, filter, analog to digital converter (ADC) or digital to analog converter (DAC) [6, 10, 11, 12, 13, 14]. The integrated circuit (IC), depending on the technology, can be GaAs, CMOS, BiCMOS [6]. The advantage of the integrated circuit is that it carries all the elements mentioned previously, but the disadvantage is that, dependingon the architecture of the integrated circuit, the errors in each response can be critical for further integration with the antenna. To correct for array beamformer errors, antenna manufacturing errors, temperature variation, connector integration and wiring errors, an array calibration is necessary to minimize all the previously mentioned errors to obtain an accurate array response [14]. There are different antenna calibration procedures. As mentioned in [14], they can be divided into four subgroups: the near-field or far-field probing method, the peripheral-fixed probe method, the mutual coupling method and the built-in network method [13; 14]. The different methods can also be divided depending on the calibration approach, which can be offline, on-site or online [14]. To make an on-site or online calibration, extra radiating elements are necessary to make these calibrations, which increases the size of the antenna. The offline calibration is the most accurate method for calibrating the antenna, but an extra facility, as well as additional measurement equipment, is required [13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. In [16], the comparison of three offline calibration methods is presented for a 4 \(\times\) 8 rectangular array; the amplitude-only method yields the worst results in the calibration. In contrast, the rotating-element electric-field vector (REV) and the complex amplitude calibration method demonstrate considerable accuracy. After the previous analysis, a 64-element lineal polarized phased array antenna divided into eight subcolumns is used to analyze the different calibration methods mentioned in [14; 16]. The radiating elements are manufactured separately to analyze possible manufacturing errors. The chosen beamformer is an 8 channels commercial IC provided by Chengdu Xphased Technology Co., Ltd. (Chengdu, China). The passive antenna and the beamformer are connected by RF cables to test different methods of offline calibration. The structure of this paper is divided into four sections. In Section 2, the architecture of the phased array antenna is explained; the passive antenna, the IC structure and the measurement facilities are also detailed in this section.