AN91445

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www.cypress.com Document No. 001-91445 Rev. *B 1 AN91445 Antenna Design Guide Author: Tapan Pattnayak Associated Part Family: CY8C4XX7 -BL, CY8C4XX8 -BL, CYBL10X6X , CYBL10X7X Related Application Notes: None To get the latest version of this application note and the associated Gerber file, please visit http://www.cypress.com/go/AN91445 AN91445 explains antenna design in simple terms and recommen ds two Cypress -tested PCB antennas that can be implemented at a very low cost for use with the Bluetooth Low Energy (BLE) solutions that are part of Cypress’s PRoC™ and PSoC® families. The PRoC BLE and PSoC 4 BLE 2.4 -GHz radio must be carefully matched to its antenna for optimum performance. It concludes by showing how to tune the antenna in the final product.

Contents

11 Effect of Enclosure and Ground Plane on

1 Introduction

An antenna is a critical component in a wireless system that transmits and receives electromagnetic radiation in free space. 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 range s using the same silicon and the same power but different layout and antenna -design practice. This application note describes the best practices, layout guidelines, and an antenna-tuning procedure to get the widest range with a given amount of power. This is an important consideration for BLE system which has to operate from a tiny power source. Below Figure show s the critical compo nents of a wireless system both at the Transmitter (TX) and Receiver (RX).

Figure 1. Typical Short-Range Wireless System from the radio, the larger the distance it can cover for a given packet error rate (PER) and receiver sensitivity. Similarly, a well-tuned radio in the receiver side can work with minimal radiation incident at the antenna.

2 Antenna Basics

fed to antenna is radiated into free space. Figure 2. Dipole Antenna Basic

1 See “harmonic antenna operation”

current standing waves are formed across the length of the conductor, as shown in Figure 2. which has an impendence of 377 Ω2. boards achieve the same performance by having a /4-length conductor in a particular way. See Figure 3. Figure 3. Quarter-Wave Antenna

1. Shape and size of the ground plane and the return path

2 Impedance of Free Space if there is no material nearby

3 We will see the effect of this return path later. This is a very important aspect in PCB layout of the antenna and the antenna feed.

3 Antenna Types

1. Wire Antenna: This is a piece of wire extending over the PCB in free space with its length matched to /4 over a
2. PCB Antenna: This is a trace drawn on the PCB. This can be a straight trace, inverted F-type trace, meandered

antenna, the antenna becomes a two-dimensional (2D) structure in the same plane of the PCB; see Figure 5. but is cheaper. It has easy manufacturability and has the wireless range acceptable for a BLE application. Figure 5. PCB Antenna 4 The feed is generally of 50 ohm in most RF PCB catering to low -power wireless applications. However, other impedance values are possible.

5 Please refer to the section on MIFA and IFA on page 7

1. Chip Antenna: This is an antenna in a small form -factor IC that has a conductor packed inside. This is useful

cent is coin is given below. Figure 6. Cypress EZ BLE Module (10 mm × 10 mm) with Chip Antenna

4 Choosing an Antenna

The selection of an antenna depends on the application, the available board size, cost, RF range, and directivity. around 20 ft in an indoor setup and a data rate of 64 kbps. transmitted and a high throughput without packet loss is required.

5 Antenna Parameters

The following section gives some key antenna performance parameters. convenient to use this value. Return loss indicates how much of the incident power is reflected by the antenna due to mismatch (Equation 1). An ideal antenna when perfectly matched will radiate the entire energy without any reflection. dB) is considered sufficient. Table 1 relates the return loss (dB) to the power reflected from the antenna (percent). A return loss of 10 dB signifies that the 90% of the incident power goes into the antenna for radiation.

more radiation and which have less. This information helps to orient the antenna properly in an application. the receiver. As expected, the contours are not exactly circle, as the antenna is not isotropic. Figure 9. Radiation Pattern

www.cypress.com Document No. 001-91445 Rev. *B 8

6 Antennas for Cypress PRoC/PSoC BLE

One of the product objective for Cypress BLE is to have an antenna design within the tight area that requires no more than two external components for tuning. Tuning is the process that ensures that near-maximum power is sent to the antenna while transmitting over the working band of frequencies. This is ensured by making the return loss in the band of interest greater than 10 dB. When the impedance seen looking into the antenna and the chip output impedance are the same, maximum power is transferred to the antenna; the same rule holds true for receiving too. Antenna tuning ensures that the antenna impedance is matched to 50 Ω looking towards the antenna . Radio tuning ensures that the impedance looks 50 Ω, looking towards the chip, when the chip is in the receive mode. The integrated balun inside PRoC/PSoC BLE is not exactly 50 -Ω impedance and may require two components for tuning. For a low -data-rate and low -RF-range application, the PCB antenna Cypress recommends does not require any component for antenna tuning. For high-data-rate applications like voice recognition over remote control, at least four components for the matching network are recommended. Two of these will be used for radio tuning and two will be used for antenna tuning. It may be possible to do the tuning with two components if the resulting bandwidth is acceptabl e. Having an 6extra component footprint is a wise design choice for future mitigation of 7EMI radiation in a new product. Filters can be implemented for out-of-band operation using those components. Cypress PRoC/PSoC devices can also be employed in applications such as indoor positioning, smart home, smart appliances, and sensor hub. Because these applications may not have space constraint s, you can employ an antenna with a better RF range and radiation pattern. The wire antenna can be a perfect fit for suc h an application where the ID (Industrial Design) can have some height to fit a wire. In some application like wearable ultra small form factor is required. The chip antenna usually takes less space compared to a PCB antenna, The chip antenna is more p opular in this application category. Cypress recommends a few guideline for using the ultracompact chip antennas. There are many applications that directly embed a Cypress module in the host PCB for wireless connectivity. For such applications, a very-low-cost, FCC-passed, tiny module is desired. Cypress has come up with EZ -BLE module for such application. The Cypress EZ-BLE module uses Johansson chip antenna 2450AT18B100E. Though there are multiple antennas for the 2.4 -GHz band , most BLE applications a re catered by two Cypress- Proprietary PCB Antennas . Cypress recommends using two proprietary PCB antennas, meandered inverted -F antenna (MIFA) and inv erted-F antenna (IFA), which are characterized and simulated extensively for BLE applications. MIFA in particular is useful to most of the applications. However, you can choose any antenna described in this document to suit your application requirements.

7 Cypress-Proprietary PCB Antennas

Cypress recommends IFA and MIFA types of PCB antennas. The low data rate and typical range requirement in a BLE application make these antennas extremely useful. These antennas are inexpensive and easy to design, because they are a part of the PCB, and provide good performance in the 150-250 MHz bandwidth range. MIFA is recommended for applications that require a minimum PCB area such as a wireless mouse and presenter. IFA is recommended for applications where one of the ante nna dimensions is required to be much shorter than the other such as a heart-rate monitor. Most BLE applications are catered by MIFA antennas.

7.1 Meandered Inverted-F Antenna (MIFA)

The MIFA is a popular antenna widely used in human interface devices (HIDs) because it occupies a small PCB area. Cypress has designed a robust MIFA that offers an excellent performance with a small form factor. The antenna size is 7.2 mm × 11.1 mm (284 mi ls × 437 mils), making it suitable for HID applications such as a wireless mouse, keyboard, or presenter. Figure 10 shows the layout details of the rec ommended MIFA, both top layer and bottom layer in a two -layer PCB. The antenna trace -width is 20 mils throughout. The main parameter that would change, depending on the PCB stack spacing, is the value of “W,” the RF trace (transmission line) width. 6 Extra components before the antenna is a recommended practice that helps in implementing filters for EMI reduction in future. 7 EMI is electro-magnetic interference regulation that sets limit for radiated power for public health.

Figure 10. MIFA Layout

7.2 Antenna Feed Consideration

Table 2. Value of “W” for FR4 PCB: Thickness Between Antenna Layer and Adjacent RF Ground Layer Figure 11. Clarification of PCB Thickness the trace width feeding the antenna is not as wide as recommended in Table 2. Figure 12. Antenna Feed Width for Short Trace width “W” over a bottom ground plane for the feed. Figure 13 plots S11 of the MIFA. The MIFA has a bandwidth (S11 ≤ –10 dB) of 230 MHz around 2.44 GHz.

www.cypress.com Document No. 001-91445 Rev. *B 12 From the radiation patterns , we can infer that the maximum radiation happens across a 30 -degree cone around the X-axis. This can be explained as the MIFA is no longer a strictly horizontal or a vertical antenna in the XY plane. Both the vertical legs and the tip contribute to the radiation and result in a slanted radiation pattern.

7.3 Antenna Length Considerations

Depending on the PCB thickness, the MIFA antenna should be length -adjusted to adjust the antenna radiation impedance and frequency selectivity. Cypress recommends the values listed in Table 3 for antenna lengths for various board thicknesses.

Figure 15. Length of MIFA Table 3. Leg and Tip length for adjusting the length of the MIFA antennas for a specific board thickness.

7.4 Inverted-F Antenna (IFA)

layer PCB. The trace width is 24 mils. The IFA is designed with a size of 4 mm × 20.5 mm (157.5 mils × 807 mils) for an FR4 PCB with a 1.6-mm thickness. The IFA has a larger aspect ratio (width to height) than the MIFA.

Figure 16. IFA Layout file at www.cypress.com/go/AN91445.

8 Chip Antennas

Figure 19. Chip Antenna tuning, increasing the BOM expense even further. such applications, Cypress recommends the Johansson Technology antennas mentioned below. mils × 196 mils but provides a better RF performance.

1. Ground clearance around the antenna
2. Antenna placement for optimal radiation
3. Antenna feed consideration
4. Antenna matching network for bandwidth extension

2450AT42B100E. See their website for detailed guidelines for these antennas.

Figure 22. Radiation Pattern from Chip Antenna

9 Wire Antennas

rise from the PCB plane and protrude to free space over a ground plane. have the most isotropic radiation pattern. various shapes according to the enclosure. Figure 23. Wire Antenna Layout 8 Only Johansson antenna is characterized; others are not.

www.cypress.com Document No. 001-91445 Rev. *B 19 A wire antenna is the best in RF performance. They have the best antenna efficiency and directivity compared to other antennas. See Figure 24 for the qualitative radiation pattern out of wire antenna. Figure 24. Qualitative Radiation Pattern Out of Wire Antenna

10 Antenna Comparison

Use Table 5 as a quick reference to select the appropriate antenna for your application. Table 5. Comparison of MIFA, IFA, Chip, and Wire Antennas

Applications

(Mouse, Keyboard, Presenter) Height Constrain (Heart Rate Monitor) Small Area (Nano Dongle, BLE Module) More Height (6 mm) (3D) (Sensor Hub) Dimensions (mils) 284 × 437 157.5 × 807 126 × 63 250 × 1200 Gerber File Web Web Refer to datasheet Cost (US$) Minimal Minimal 0.1–0.5 0.1 Bandwidth (MHz) (S11 ≤ –10 dB) 230 220 230 200 Gain (dBi) 1.6 1.1 0.5 2

11 Effect of Enclosure and Ground Plane on Antenna Performance

reduce the resonant frequency.

11.1 Effect of Ground Plane

As explained before, a monopole PCB antenna requires a ground plane for proper operation. varies from 20 mm × 20 mm to 50 mm × 50 mm. there is hardly enough space for ground clearance. Figure 25. Effect of PCB Ground Plane Size

11.2 Effect of Enclosure

the wireless mouse, and then measurements are made for radiation pattern and return loss.

Figure 26. Effect of Plastic Casing  The resonant frequency shifts to a lower frequency when the antenna is placed near the plastic casing. to bring it to the desired band. For antenna tuning, see Guidelines for Enclosure and Ground Plane. antenna by approximately 100 MHz to 200 MHz.

12 Guidelines for Enclosure and Ground Plane

 The battery cable or mic cable should not cross the antenna trace on the PCB on the same side of the antenna. shield, the casing should not cover the antenna. No metal is allowed in the antenna near-field. maximized in the desired direction.

 There should not be any ground directly below the antenna. See Figure 14. This applies for all antennas. have a minimum width. See Figure 10, Figure 15, and Figure 20.

13 Antenna Tuning

receives the received signal from antenna. network analyzer. Please refer to Appendix B for matching network design reference. Figure 27. Reference for Tuning and Matching Network instruments are suited for 50 ohm port impedance. attain 50-ohm impedance. In most applications using Cypress MIFA the ant enna is made 50 ohm by correct length.

www.cypress.com Document No. 001-91445 Rev. *B 23

13.1 Tuning Procedure

As explained in Effect of Enclosure and Ground Plane on Antenna Performance, the effect of enclosure and ground detunes the antenna from the desired band and affects the return loss. Thus, antenna tu ning is a two -step process where the bare PCB is tuned for the desired band first, and then in the second phase after the industrial design is finalized, the tuning is checked with the plastic enclosure and human body contact. A basic familiarity with Smith Chart is required for antenna tuning by Network Analyzer. Without loss of generality the readers are encouraged to read a bout Smith chart. The antenna tuning is checked with a network analyzer. A network analyzer is an instrument which characterizes the s parameter, such as S11 and S21. The S11 is a indication of return loss and S21 is the forward transmission ratio. Interested readers are encouraged to refer any of the link provided below. As the first step, the network analyzer is calibrated, and then the antenna is tuned by adjusting the matching network components and verifying the tuning in the Smith chart. The tuning procedure uses the following:  Agilent 8714ES network analyzer (calibrated)  Cypress CY5682 kit mouse as DUT  A semi-rigid cable with 50 ohm characteristic impedance up to 5GHz  A high-Q RF component (this example uses Johanson kit P/N: L402DC) The following major steps are required to tune the antenna: 1. Prepare the ID 2. Set up and Calibrate Network Analyzer 3. Tune the Bare PCB Antenna 4. Adjust Tuning with Plastic and Human Body Contact for Antenna 5. Tune the Radio Side by Putting the Chip in Receive Mode

13.1.1 Prepare the ID

This is a very important step as the placement of the coaxial cable can show variation s in S11 by up to 3 dB. The ground connection of the coaxial cable shield should be as close to the transmission line return pat h as possible. The basic steps of ID preparation are given below. 1. Open the plastic casing and remove the batteries or power supplies. 2. Connect the coaxial cable close to the RF out pin from the chip. Remove the connection from the chip. If not, the balun will load the coaxial cable in addition to the antenna. See Figure 28. 3. Ensure that there is an exposed ground near to the tip of the coax ial cable. Connect the sheath or the shield of the cable to ground. While connecting the shield/sheath to ground, ensure that it is as short as possible. The shorter the distance, the better the tuning accuracy . There can be 3 -dB differences in return -loss measurement depending on where the coaxial cable is connected to ground. 4. Connect a 10-pF capacitor from the first pad going from the 50-Ω reference point to the antenna tip. There should always be a capacitor between the coax ial cable and the antenna. This blocks the DC to and from the network analyzer.

Figure 28. Coax Connection Point

13.1.2 Set up and Calibrate Network Anal yzer

1. Connect the 3.5-mm calibration kit for calibration and then press the ‘cal’ button on the Agilent 8714ES network

calibration kit such as a type N calibration kit.

1. Press the frequency button and set the start and stop freq uency to 2 GHz and 3 GHz respectively , and then set
2. Press the cal button, select S11 on the network analyzer. and then set it to ‘user 1 port calibration’.
3. When prompted to connect the ‘open’ load, c onnect the “O pen fixture” to the VNA and press ‘measure
4. Connect the “Short Fixture” and press measure standard.
5. Connect the “B roadband load ” fixture and press ‘measure standard ’. After this , the network analyzer will
6. Connect the tuning coaxial cable and set the electrical delay by pressing the ‘scale’ button and setting the

www.cypress.com Document No. 001-91445 Rev. *B 25

13.1.3 Tun e the Bare PCB Antenna

There are two methods to tune the antenna to bring it near 50 ohm. 1. Length adjustment of the antenna if it is a PCB trace or a wire antenna, by cutting off the extra length 2. Use of a matching network (recommended practice) For PCB trace antennas or wire antenna s, it is often easier to adjust the length of the PCB trace antenna by scrapping off the extra length at the end of the antenna trace. For this, it is advised to keep the length of the antenna a little longer than the Cypress-recommended length and later cu t the length to get the resonance around 2.4 GHz. This is a crude method and does not require any additional components. However, the matching network method is the most widely used method as it gives the flexibility in future to implement additional filt ering for passing EMI/EMC and has a better repeatability. However , the matching network method requires expertise. Contact Cypress Technical support for tuning support for high-volume manufacturing. Use the following procedure to tune the bare PCB using matching network method. This section below describes the steps required to tune the antenna or the radio using matching network components. The reader is assumed to have some familiarity with Smith Chart. 1. Connect an 8.2-pF or 10-pF capacitor in series with the antenna. In the band of interest, it acts as 0 Ω. This gives the antenna impedance. The impedance of antenna is at (100.36 –j34.82), shown as a dot in the Smith chart. Figure 29: Smith Chart of Antenna Only 2. After determining the antenna impedance, use L-C components to bring it to 50 -Ω impedance by performing an impedance transformation. 3. Impedance transformation networks are networks that transform one impedance to the required impedance without con suming any power. Refer to the impedance transformation property of the L and C resonating networks. Without going to the detail of the matching networks , we can state that m ost of the matching networks (Figure 30) for cypress MIFA or IFA can be met by two components.

Figure 34. Smith Chart with Real Components close to the (50,0) point on the Smith chart. This shows a good match. Figure 35. Return Loss with Real Components As seen Figure 35, the return loss is greater than 15 dB for the marker 1, 2 and 3.

13.1.4 Adjust Tuning with Plastic and Human Bod y Contact for Antenna

antenna, there are very high chances of objects in its near field disturbing the antenna.

plastic, simulating a user’s operation of the device. The effect on return loss was observed to be minimal. Figure 36. Smith Chart with Plastic Assembly, Illustration of Connecting with ID

13.1.5 Tune the Radio Side b y Putting the Chip in Receive Mode

Analyzer by the use of Smith Chart.

14 Summary

15 Appendix A: Checklist

You can use the checklist in Table 6 while designing the antenna to track your progress. Table 6. Checklist for Optimal Antenna Design Decide on the PCB antenna type based on the application at hand: MIFA, IFA, wire antenna, or chip antenna. See Table 5. Comparison of MIFA, IFA, Chip, and Wire Antenna. Note the chosen antenna layout (dimension). Download the Gerber files from www.cypress.com/go/AN91445. Orient the antenna suitably for maximum radiation in the desired direction. For MIFA, see Figure 14. 3D Radiation-Gain Pattern for MIFA. For IFA, see Figure 18. Qualitative 2D Radiation Gain Pattern for IFA. Determine the “W” value to be used in the antenna layout, based on the PCB thickness (stack). Select the antenna tip length or leg length for MIFA, Figure 15. Ground width for better s11. Please look at the layout pictures. Make sure that Antenna feed has a solid Gnd plane below it. Make sure that the RF output of the chip is routed like a Tline. Calibrate the VNA (one-port calibration is sufficient). Measure S11 (dB) with the complete product casing present. See Figure 35. Return Loss with Real Components. Tune by matching network S11 (dip) shifts to the desired 2.44 GHz with the bare PCB and with complete product casing present. Figure 36. Smith Chart with Plastic Assembly. Note the final matching network components of the antenna and use them for volume production.

www.cypress.com Document No. 001-91445 Rev. *B 31

16 Appendix B: References

The following references provide further detailed information.

16.1.1 Antenna Basics

 Constantine A. Balanis, Antenna Theory: Analysis and Design, 3rd edition. Wiley - Interscience, 2005 (Chapters 2 and 5).  Antenna with multiple fold, Philip Pak-Lin Kwan, Paul Beard, US Patent 7936318 B2  AN48610, Cypress Semiconductor, Design and layout guideline for matching network and antenna for wireless USB

16.1.2 Smith Chart Basics

 David M. Pozar, “Microwave Engineering,” 4th edition, Wiley, 2011 (Chapters 2, 4, and 5).  Christopher Bowick, John Blyler, Cheryl Ajluni, “RF Circuit Design,” 2nd edition, Newnes, 2007 (Chapter 4).  Smith v3.10, Bern Institute

16.1.3 Useful Free Online Software

 Transmission line calculator: Grounded CPW (air gap = 12 mil, r = 4.3 for FR4): www1.sphere.ne.jp/i-lab/ilab/tool/cpw_g_e.htm  Smith Chart based matching: L or Pi matching:  Smith Chart Bern Institute http://www.fritz.dellsperger.net/

16.1.4 Chip Antenna La yout

http://www.johansontechnology.com/datasheets/antennas/2450AT42B100.pdf

www.cypress.com Document No. 001-91445 Rev. *B 32 Document History Document Title: AN91445 – Antenna Design Guide Document Number: 001-91445 Revision ECN Orig. of Change Submission Date Description of Change ** 4468573 GOWB 08/07/2014 New Spec *A 4565905 TAPI 11/10/2014 Updated all figures and sections. Corrected sections. De-prioritized length cutting. Added Chip antenna layout guideline *B 4768767 TAPI 06/18/2015 Module characterization results with chip antenna referred. Added the following sections: Chip antenna layout, wire antenna layout, antenna length cutting for a quick churn, description about far field and near field Edits throughout the document Sunset review Updated template

www.cypress.com Document No. 001-91445 Rev. *B 33 Worldwide Sales and Design Support Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find the office closest to you, visit us at Cypress Locations. Products Automotive cypress.com/go/automotive Clocks & Buffers cypress.com/go/clocks Interface cypress.com/go/interface Lighting & Power Control cypress.com/go/powerpsoc cypress.com/go/plc Memory cypress.com/go/memory PSoC cypress.com/go/psoc Touch Sensing cypress.com/go/touch USB Controllers cypress.com/go/usb Wireless/RF cypress.com/go/wireless PSoC® Solutions psoc.cypress.com/solutions PSoC 1 | PSoC 3 | PSoC 4 | PSoC 5LP Cypress Developer Community Community | Forums | Blogs | Video | Training Technical Support cypress.com/go/support PSoC is a registered trademark and PSoC Creator is a trademark of Cypress Semiconductor Corp. All other trademarks or registered trademarks referenced herein are the property of their respective owners. Cypress Semiconductor

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