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With the rapid development of the Internet of Things, more and more intelligent products such as intelligent home, intelligent transportation, intelligent city and so on have emerged in the market. These terminals rely on wireless transceiver module to realize information transmission and reception. As a result, we know that wireless modules are indispensable in the use of the Internet of Things.Wireless modules often need a backplane to match them, enabling them to perform better in their application.So the design of our backplane is particularly important. How to design is our concern. Today, let's briefly talk about how to design the backplane of our wireless module. Most importantly, we should pay attention to the space reserved for wireless modular antennas. Our most common antennas are ceramic antennas, PCB loaded antennas, and external antennas (just a generic name here). External Antenna Fig.1 is a typical external antenna-based wireless module backplane design.From Fig.1, Fig.2, we can see that on the left are USB interface, LDO, plug-in interface, Jing Zhen, USB-TTTL chip, module bottom without components and line. When we design the module, we try not to walk high-speed lines and place components sensitive to RF signals. The module is placed in a separate area to prevent interference with other functional modules from causing communication problems. The outboard antenna SMA is on the far right, preventing the effects of RF signals on other sensitive devices after they are radiated through the antenna. As we can see from Fig.3, when we draw the RF line from the base plate to the outside SMA head, the RF line needs to have an accompanying hole, which allows a vortex between the RF signal and the ground, a circuit in space, to absorb part of the radiated signal, thereby reducing the effect of radio-frequency signal radiation on other signals inside the plate.Another reason is the Faraday shield, together with a hole that effectively prevents other signals from interfering with it. Ceramic Antenna, PCB Board Antenna Ceramic antennas and PCB loaded antennas are similar in design. This is the unified explanation here. From Fig.4, we can see that the left side is the same design as Fig.1. This is no longer the case here, but focus on the placement of the right antenna. We can see that when we are designing, we need to place ceramic antennas at the edge of the board (sometimes because of some restrictions, the antenna needs to be placed inside the backplane, then we need to carve out the position of the antenna and hang the antenna outside the backplane so that the antenna can radiate out the radio signal better and communicate better. Of course, there are more factors involved in baseplate design, which requires a combination of actual conditions and often a compromise.
Introduction Antenna design and RF layout are critical in a wireless system . The wireless range that an end-customer gets out of an RF product with a current-limited power source such as a coin-cell battery depends greatly on the antenna design, the enclosure, and a good PCB layout. It is not uncommon to have a wide variation in RF ranges for designs that use the same silicon and the same power but a different layout and antenna-design practice. Other important general layout considerations for RF trace, power supply decoupling, via holes, PCB stackup, and antenna and grounding . An antenna is basically a conductor exposed in space. If the length of the conductor is a certain ratio or multiple of the wavelength of the signal1 , it becomes an antenna. This condition is called “resonance”, as the electrical energy fed to antenna is radiated into free space. Types of Antenna Wire Antenna , pcb Antenna, Chip Antenna Wire Antenna: This is a piece of wire extending over the PCB in free space with its length matched to /4 over a ground plane. This is generally fed by a 50-Ω 4 transmission line. PCB Antenna: This is a trace drawn on the PCB. This can be a straight trace, inverted F-type trace, meandered trace, circular trace, or a curve with wiggles depending on the antenna type and space constraints. In a PCB antenna, the antenna becomes a two-dimensional (2D) structure in the same plane of the PCB Chip Antenna: This is an antenna in a small form-factor IC that has a conductor packed inside. This is useful when there is limited space to print a PCB antenna or support a 3D wire antenna Antenna Parameters Return loss: The return loss of an antenna signifies how well the antenna is matched to the 50- transmission line (TL), shown as a signal feed in Figure 7. The TL impedance is typically 50 , although it could be a different value. The industry standard for commercial antennas and testing equipment is 50- impedance, so it is most convenient to use this value. Bandwidth: Bandwidth indicates the frequency response of an antenna. It signifies how well the antenna is matched to the 50-Ω transmission line over the entire band of interest, that is, between 2.40 GHz and 2.48 GHz for BLE applications Radiation efficiency: A portion of the non-reflected power gets dissipated as heat or as thermal loss in the antenna. Thermal loss is due to the dielectric loss in the FR4 substrate and the conductor loss in the copper trace. This information is characterized as radiation efficiency. A radiation efficiency of 100 percent indicates that all non-reflected power is radiated to free space. For a small-form-factor PCB, the heat loss is minimal. Radiation pattern: Radiation pattern indicates the directional property of radiation, that is, which directions have more radiation and which have less. This information helps to orient the antenna properly in an application Gain: Gain indicates the radiation in the direction of interest compared to the isotropic antenna, which radiates uniformly in all directions. This is expressed in terms of dBi—how strong the radiation field is compared to an ideal isotropic antenna. Antenna Feed Consideration Here this parameter is specifically explained for PCB antenna For the small length of PCB trace that feeds the antenna, the width requirement can be relaxed. Ensure that the antenna trace width and the antenna feed connection have the same width . However, if it is a long transmission line approximately 1 cm from the matching network to antenna it is recommended a transmission line (TLine) type of layout, having a specific width “W” over a bottom ground plane for the feed S = space between main RF trace and ground plane W = RF trace width H = Height of substrate ER = material used Dielectric constant T = Thickness of top layer copper And there are different cross sections available for making transmission line, among Coplanar waveguide is in common practice as it provides good isolation from other signals . CPW is similar to Edge Coupled Microstrip Zo even can be calculated with below equation One can use online calculators for calculating parameters https://www.eeweb.com/toolbox/edge-coupled-microstrip-impedance/ So in above parameters T and H are dependent on stackup available with pcb fabrication house