The 5G millimeter wave frequency band has a large signal propagation attenuation. Therefore, in addition to the use of active power components, a large number of antennas must be used to achieve high gain transmission. The microstrip patch antenna is a common unit form that constitutes a millimeter wave antenna array. This structure has Low profile and high gain characteristics have attracted much attention in applications.

As the 5G millimeter wave communication system needs to overcome the propagation attenuation of this frequency band, it is necessary to increase the Equivalent Isotropic Radiated Power (EIRP) value of the overall system operation to achieve communication that meets the transmission distance and coverage requirements Link signal-to-noise ratio specifications. Active power components can be used to increase the transmission signal strength, but the current millimeter wave frequency power amplifier components still face problems such as excessive power consumption and high cost. Therefore, how to effectively use the antenna array to achieve energy focusing is the most cost-effective approach. Due to the small wavelength of the millimeter wave frequency band, the required resonance length of the antenna is about less than 1 cm , and it is easy to realize the design of a huge antenna array under an acceptable product size. For the selection of the antenna unit, it is necessary to adopt a structure with a simple structure and easy control of the radiation mode, so as to take into account the combined field pattern and beam scanning characteristics at the same time.

Figure 1 shows the common forms of microstrip patch antennas. Generally speaking, the shape of microstrip patch antennas is mostly round or square. The reason is that it can be analyzed through mathematical models. However, there are several important design considerations for the microstrip patch antenna, including the size and shape of the patch antenna, the feeding method, and the thickness of the substrate and the dielectric coefficient. Microstrip patch antennas also have related design parameters that can be used for analysis and evaluation, such as formulas (A)~(G) , including patch width (W p ) , patch length (L p ) , equivalent dielectric coefficient ( ε) Reff ) , effective patch length (L eff ) , substrate length (L s ) and substrate width (W s ) and other parameters are calculated, which can be used as design reference without relying on full-wave simulation software analysis.

In addition, in addition to feeding the patch from the side, the feeding method can also be back-fed patch connection through the probe method, or use the slot coupling patch method to achieve energy excitation. Choose a suitable feed structure according to different antenna layouts, assembly methods, and convenience of back-end circuit integration.

Figure 1. Millimeter-wave microstrip patch antenna unit architecture and feeding method

Figure 2 shows the use of microstrip patch antenna elements to form a 1x4 linear array antenna structure, and energy is fed to the antenna end through a one-to-four power splitter to achieve high-gain design. Since the feed side edges of the patch have a higher characteristic impedance, and therefore, the parallel transfer of power through the demultiplexer easily parallel to a low impedance, and by the gradient (Taper) manner gradual impedance conversion.

Figure 2. 1x4 millimeter wave microstrip patch antenna array

Figure III is a 1x4 composite field pattern of the linear array antenna, can be observed at 27GHz the measured frequency, the H-plane and E-plane beam width angle of approximately 68 [deg.] And 20 is [deg.], The gain up type field 13dBi , belonging to the sector The fan beam field pattern is suitable for fan-shaped service cell coverage. At present, in 5G millimeter wave communications, microstrip patch antenna arrays are used at both the base station and the terminal. For example , the Qualcomm AiP antenna module used on 5G terminal devices is composed of four microstrip patch antennas. The beamforming transceiver chip used in the base station also integrates this architecture on the RF front-end circuit.

Figure 3. H-plane of 1x4 millimeter wave microstrip patch antenna array

And E-plane radiation field type (27GHz)