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Radiocrafts Practical Radio design Practical Antennas PCB-layout for optimum performance UART-extentions: Pairing Radiocrafts modules with other equipment.

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Presentation on theme: "Radiocrafts Practical Radio design Practical Antennas PCB-layout for optimum performance UART-extentions: Pairing Radiocrafts modules with other equipment."— Presentation transcript:

1 Radiocrafts Practical Radio design Practical Antennas PCB-layout for optimum performance UART-extentions: Pairing Radiocrafts modules with other equipment

2 Radiocrafts Practical Antennas Quarterwave whip coated with plastic Quarterwave copper on FR-4 laminate Yagi: Increased directivity Helical

3 Radiocrafts Practical Antennas The most easy way to reduce range is by thinking about antenna as any piece of wire EM-waves are travelling along the antenna conductor and we want to radiate as much as possible of the power (when we transmit) or receive as much as possible (when we receive) To achieve this, the wire should be as long as possible while maintaining resonance to the centre frequency. Radiation is prevented by; Nearby grounding, metal obstacles (like metal enclosures…). Shorted antennas always reduces range but sometimes is required due to available space

4 Radiocrafts Practical Antennas It is important that the antenna has correct length which is a multiple of a quarter wave. When so, the impedance will be purely resistive in the feeding point, and we will get max power transfer from a resistive source (usually 50 ohm) Feeding point λ = c / f x 0.95

5 Radiocrafts Antenna classes Monopole: Usually λ/4 or 5/8λ. Electric field dominates Dipole: Usually λ/2 (can also be 5/8λ). El. field dominates Loop (magnetic field dominates). Not covered. Helical (combination of electric and magnetic) Antennas containing elements of the above 5/8 λ: Can be either monopole or dipole (Note: serial inductor is needed for impedance match). Yagi: Extra Directive antennas (lobe in one direction). Has one Dipole antenna element and directors + reflectors

6 Radiocrafts Monopole vs. dipole Monopole quarterwave Dipole halfwave

7 Radiocrafts Radiation patterns Gain: 0 dBi 5.15 dBi 5/8λ: 8.2 dBi 2.15 dBi 5/8λ: 5.2 dBi 5-10 dBi (or more)

8 Radiocrafts Practical Antenna guidelines Use quarter-wave stubs with sufficient ground plane extension Sufficient ground: Preferably the longest length the same as the antenna length Can be considered as a wire, either in the shape of a whip antenna or a PCB-trace. Length should be L=(c/f) / 4 x 0.95, i.e: 2.9 cm (2.4 GHz), 8.2cm (910MHz), 7.8cm (868MHz) or 16.4cm (434MHz). Coated whip antennas:

9 Radiocrafts Radiocrafts Range measurement setup Antenna quarterwave, from RC1240DK, approximately 17cm Cu-side FR4 board size 24x24 cm or at least 15x15cm, antenna placed in center Coax-cable with conducting SMA-connector fastened tightly to adaptor and connecting to Cu-plane SMA-SMA adaptor in drilled hole in PCB

10 Radiocrafts Shortened antennas If not available space, shorter antennas can be used but an inductor (or more complex matching) must be added at the base to achieve better impedance match. Radiates less! Measure impedance! Dielectric antennas: Ceramic material where λ gets shorter. Maintains resonance (see datasheet for req. match) but radiates less. Available for all frequencies MHz (www.fractus.com, )www.fractus.com PCB-antennas: Can be made more area-efficient by folding the antenna, which also is good for receiving different polarizations. Width: 3mm is OK (the broader the width, the lower the resistive loss)

11 Radiocrafts PCB antenna example, 2 layer PCB, λ/4-monopole Large groundplane Free space inside, both layers. Total length of antenna 16.4 cm Do NOT route antenna close to ground or metallic parts Note; There is NO gnd in layer 2 under antenna- trace!!

12 Radiocrafts Helical antenna at 433/868 MHz Radiates in the direction normal to the axis Can be seen as monopole antenna shorted by coiling up the whip Resonance can be achieved for a much shorter construction Higher gain than with a non-helical structure of the same size

13 Radiocrafts Helical antenna at 433/868 MHz

14 Radiocrafts PIFA-Planar Inverted F-antenna (2.4 GHz) Feeding point, 50ohm line Ground, GND

15 Radiocrafts Practical Antennas cont. Usually, FR-4 laminate is used; Thickness and material does not affect length (as the antenna is a wire, not a transmission line) If orientation varies (equipment is used both vertical and horizontal), make a 90 degrees bend at the middle If there is any length from RF pin of module, use 50ohm trace in PCB until antenna launches (connector or solder joint).

16 Radiocrafts Routing guidelines GND CTS RTS CONFIG TXD RXD GND RC1xx0/RC2x00/RC220x RF SMA 50ohm trace; Width is 1.8 x h for typical FR-4 material. See litterature for general calculations of characteristic impedance ALL vias to ground in entire design; As close to the pad as possible. One via per ground-pad (do not share with others as this tends to increase length of trace, increasing inductance/impedance to ground) Gnd-plane in inner- or bottom layer, as large as possible, as un-penetrated as possible. Remember NO ground under PCB-antennas!! RC-MODULE h=board thickness Via to ground Layer 1 RF routing PCB Antenna feeding point or coax launch to external antenna

17 Radiocrafts RF Basics The higher the frequency, the higher the loss in the air, the lower the range The higher the data rate, the lower the range (bandwidth is high=wider internal filter=receiver receives more natural electromagnetic noise, masking a weak signal) The higher the frequency, the more straight line the EM signal is following Reflections: All EM-signals are reflected, giving local field minimums or maximums. As frequency increases, these min/max occur more frequently

18 Radiocrafts UART extentions

19 Radiocrafts UART extentions II

20 Radiocrafts UART extentions III


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