Introduction

When designing an RF transmitter or receiver, choosing an amplifier (or amplifiers!) is one of the most critical tasks for ensuring that it functions optimally. If it’s your first time, though, it can be difficult to parse through all of the information provided on datasheets to try and find an optimal part, especially if you don’t really know what your looking for. This article is going to focus on RF amplifiers, and how you can ensure that you’re choosing a good one for your transmitter or receiver.

To help you choose an amplifier, I’m going to go step-by-step through several of the more important characteristics you’ll need to know. This is by no means an exhaustive list, but in broad strokes you can go through this list one by one, in order, to narrow down your search.

1. Frequency Range
2. Characteristic Impedance
3. Gain
4. Is it a LNA or a power amplifier?
   1. Noise Figure
   2. P1dB
   3. Psat
5. Power Added Efficiency & Heat dissipation
6. Maximum Input Power
7. Temperature Range/Stability
8. Input/Output VSWR
9. Operating Bias Voltage
10. Operating Current
11. Form Factor/Case Suitability

Prerequisite Reading

1. Overview of Key Terms – Antennas
2. Noise Figure and the Friis Formula for Noise
3. Noise Floor

Important Information

It’s important to note a few assumptions before getting into the weeds. In this article I’m focusing on amplifiers for the most common types of transmitters/receivers used on CubeSats today, single center frequency, with constant envelope modulation schemes. If you’re planning on building a multi-frequency system or one with a modulation scheme that isn’t constant envelope (like On-Off Keying or Amplitude Modulation), you’ll probably need to do a bit of extra legwork in order to make sure the parts you’re choosing will satisfy your requirements. That being said many of these terms and factors of merit are still relevant, so read on, just be aware that this article isn’t going to go as in-depth as you may need it to.

When explaining a few of these items on the list above, I’ll be referencing a Mini-Circuits component datasheet for ease of understanding, referenced in the “References” section at the bottom. It’s important to note that not all of these parameters will always be available in every part’s datasheet. Sometimes you’ll have to calculate them yourself based on other information that’s in the datasheet, and sometimes manufacturer’s just don’t include what you’re looking for. Here I want to emphasize, as with all things in the CubeSat world, the importance of testing. Always make sure you have time to test the device you’re building thoroughly, as the real world doesn’t always jive perfectly with what you find in datasheets!

1. Frequency Range

The frequency range is the most important and easiest way to narrow down your search for an amplifier, and it’s as simple as it sounds. Determine the operating frequency of your transmitter/receiver, and make sure that it’s within the operating frequency range of the radio you’re trying to build. On the example datasheet shown in Figure 1, note the frequency range circled in green and marked with a “1”.

2. Characteristic Impedance

The characteristic impedance (or Z₀) of an amplifier is the impedance which it’s designed to be fed by and output to. If you don’t remember what an impedance is, check this article for a refresher. Almost all high frequency electronic components these days are designed to have 50 ohms as their characteristic impedance. 75 ohms was once commonly used for things like broadcast television sets, but it’s becoming rarer. Because of their ubiquity and low cost, I’d recommended that you stick with 50 ohm components unless you have a very pressing reason to switch. The characteristic impedance is circled in Figure 1 and labeled with the number “2”.

3. Gain

An amplifier’s gain describes the ratio of the signal power output from the amplifier to the input power while the power is within the amplifier’s linear region (more on that in section 4).

G = \frac{P_o}{P_i}

The equation above is for linear gain G, where output power is P_o and input power is P_i. You can use any units for power, as long as input and output power use the same units. Gain, being a ratio, is a unitless quantity.

As with most quantities in communications, you’ll often see gain listed as a logarithmic quantity with units of decibels (dB). You can convert from linear gain to logarithmic gain using the equation

G_{dB} = 10*log_{10}(G_{linear})

Correspondingly, you can convert from logarithmic gain to linear gain using

G_{linear} = 10^{\frac{G_{dB}}{10}}

The gain is labelled in Figure 2 with the number “3”.

ADDENDUM ON DATASHEETS

In the specifications section (Figure 2), note that there are several columns. This section is a quick explanation on each.

Condition (GHz) – The frequency the parameter is measured at (in this case, in GHz).

Vd=5.0V/Vd=3.0V – Indicates that values were measured using a 5 Volt or 3 Volt bias voltage

Min./Typ./Max. – Minimum/Typical/Maximum measured values within acceptable production variation range. You can normally design using the typical value, but beware that each part may have some variance within the minimum/maximum range.

Units – The units of the measured value.

4. Use-Case Dependent Quantities

Amplifiers are used in many places in a CubeSat communication system. Two of the most common uses are Low-Noise Amplifiers (LNAs) in receivers and Power Amplifiers (PAs) in transmitters. The actual construction of amplifier circuits is beyond the scope of what we cover on Crashcube, but essentially you’ll need to know two things. LNAs are designed, as you might expect based on their name, to have a low noise figure. PAs, on the other hand, are designed to have their linear regions extend up to higher output power values.

4-1. Noise Figure

All amplifiers are inherently imperfect, and each will introduce some amount of noise into the signal it’s amplifying. The noise figure of an amplifier is a quantity that describes how much noise is in the signal at the output of the amplifier relative to the noise at the input. This is quantified as a signal to noise ratio (SNR). The noise figure of an amplifier is defined as the ratio of the input to output signal-to-noise ratios (a ratio of ratios, I know that’s a little bit confusing). Similarly to the way gain can be expressed as a logarithmic quantity, noise figure is also often expressed in decibels.

NF = \frac{SNR_i}{SNR_o}

NF_{dB} = 10*log_{10}(\frac{SNR_i}{SNR_o}) = 10*log_{10}(SNR_i) - 10*log_{10}(SNR_i)

If you look closely, you’ll notice that noise figure has the input and output values inverted compared to the equation for gain. This is because we want to have positive values for noise figure (due to both common convention and to make some of the equations we use it in easier to manage), and because an amplifier will ALWAYS have a lower SNR at its output compared to its input.

Why is this, though? It’s important to remember that, while we distinguish between the signal and the noise when doing analysis, to an amplifier they both appear together as a single input current and voltage. There’s no way for it to distinguish or separate the two. This means that when a signal (with some amount of noise) goes into an amplifier, it amplifies both signal and noise equally. Since in reality, all amplifiers will also add some additional amount of noise to the signal they amplify, this means that the noise value at the output will ALWAYS be higher than at the input.

The noise figure of an amplifier is more important in the case of LNAs than it is for PAs. This is because typically an LNA is being used in a receiver to amplify a very weak signal that is closer to the noise floor. As an example, let’s say your input power is -90 dBm and you have a noise floor power of -110 dBm. If you have an amplifier with a noise figure of 12 dB, your output SNR after amplification is only 8 dB. Depending on what modulation and error correction methods you’re using on your satellite link, this may not be enough to decode it properly! If you use an LNA with a lower noise figure, such as 3 dB, it may be possible to decode that same signal properly since its output SNR would then be much higher at 17 dB.

For a PA, this is less important because the input power to the amplifier is often far higher than the noise floor. As an example, a typical power amplifier might have 30 dB of gain and be fed with a signal that’s been generated by a transceiver at 0 dBm. If the noise floor power for this example system is -80 dBm before amplification, an amplifier with a noise figure of 12 dB would increase the signal power to 30 dBm and the noise power to -38 dBm. This increase will have very little impact on the quality of the transmitted signal. The SNR in this case would be reduced from 80 dB at the input to 68 dB at the output.

Once the signal travels all the way across space to a receiver on the ground, both the signal and the noise will be greatly reduced in power due to geometric spreading out of the power density. Let’s assume that the geometric spreading losses are 120 dB and that the receiver has a similar noise floor power to the one in the first half of this example, -110 dBm. Our hypothetical receiver now has a signal input power of -90 dBm, above the noise power floor, but the noise that was amplified by the PA at the beginning is now at -158 dBm, far below the level that is inherently within the receiver from external noise sources.

Table 1 below shows numerically what was described above.

4-2. P1dB Compression Point

Amplifiers are generally linear devices, but only up to a point. By a linear device, I mean that the gain of an amplifier is not affected by the input power of the signal. For a 20 dB amplifier whose linear range encompasses both, for example, a -50 dBm input signal and a -20 dBm input signal should both be amplified equally (to -30 dBm and 0 dBm output, respectively).

The linear range of an amplifier is defined as the range of output power values where the amplifier will operate as a linear device. Typically, an amplifier will operate linearly for all power values up to the point where it becomes compressed (i.e. there’s no relevant lower bound other than the noise floor). The P1dB compression point is used as the upper bounding point of the linear region, and refers to the output power when the amplifier loses 1 dB of linearity (also sometimes denoted as OP1dB).

Figure 3 below illustrates the linear region and where it breaks down near the P1dB compression point, becoming non-linear. You’ll notice that on this plot there are a few other points labelled, the second-order and third-order intercept points. These (particularly the third-order intercept, IP3) are used for measuring and quantifying the linearity of devices. They are more complicated to explain conceptually than the P1dB compression point, so I won’t do so in this article, however I highly recommend this video from Rohde & Schwarz [3] that I think explains them very well.

The P1dB compression point is more relevant to power amplifiers used in transmitters than it is for the amplifiers used in receivers. This is because in almost all cases you’ll want to have a high transmit power to make it easier to close your link budget. It’s important to choose an amplifier whose P1dB compression point is at or above your desired output power so it won’t be stressed trying to amplify an already too-strong signal. Stressing parts more than they need to be is a quick and easy way to cause them to fail, and for something as critical as your transmitter, having an amplifier fail could mean your whole satellite fails!

4-3. Psat

Sometimes datasheets for amplifiers will also include a value P_{sat} that refers to the saturated power point. This is the absolute maximum output power level of an amplifier, where the slope of the input-output curve becomes horizontal. It is always above (at a higher power level than) the P1dB compression point.

While it’s generally preferable to operate an amplifier below the P1dB point, if using a modulation with a constant power envelope (such as BPSK or QPSK, among others), it is possible to operate closer to the saturation region with careful design. Generally though, it’s better to avoid it when designing smallsat systems. The extra margin of error you get from being a bit more conservative is almost always worth it when it comes time to test your devices.

5. Power Added Efficiency (PAE) and Heat Dissipation

Power Added Efficiency refers to how efficient the amplifier is while taking into account the gain of the amplifier, and can be described by the below equation, where P^{RF}_{out} is the output RF power, P^{RF}_{in} is the input RF power, and P^{DC}_{in} is the DC power consumption/dissipation. It’s important here to note that P^{RF}_{out} - P^{RF}_{in} will NOT equal the gain of the amplifier! This is because you need to use linear power units (such as milliwatts, Watts, etc.) instead of logarithmic ones for this equation to be valid.

PAE = 100 \cdot \frac{P^{RF}_{out} - P^{RF}_{in}}{P^{DC}_{in}}

In the datasheet in Figure 2 I’ve circled the absolute maximum power dissipation and labelled it with a “5”, which you can use as a conservative estimate for the DC power consumption when calculating PAE. PAE is important primarily because a cubesat will have a limited ability to generate power using solar cells and it’s important to use that power efficiently, but it is also important for another reason. Every milliwatt of heat that’s generated by using power has to be managed by your cubesat’s thermal control system. It could be a good or bad thing to generate more heat, depending on your design, but either way it’s an important systems engineering consideration.

Generally, PAE and heat dissipation are more relevant to the choice of PAs for transmitters versus LNAs for receivers. It is important in both cases to be efficient, but LNAs will often be consuming much less power overall, so an inefficient ampifier using 100 mW of DC power will be much less of a concern than one using 5 W of DC power.

As a good rule of thumb, a power amplifier with reasonable PAE for a cubesat transmitter will be somewhere in the 20% to 40% range. Amplifiers will also generally be more efficient at lower frequencies vs. higher ones. You may be able to find an inexpensive amplifier in the VHF band with a 40% PAE relatively easily, but amplifiers for S-band above 25% may be much more expensive or difficult to locate.

6. Maximum Input Power

In Figure 2, the maximum input power is circled and labelled with a “6”. Maximum Input Power (CW) refers to the maximum power input that an amplifier can sustain without damage. This is a value that only indicates whether or not an amplifier will be damaged by an input signal at that level. It does not indicate whether or not an input signal will be effectively amplified without distortion or intermodulation problems, so using this value together with the gain can’t be used as a shortcut to properly determining whether or not your signal will be compressed.

The (CW) in the label refers to power using a Continuous Wave modulation scheme. This means that the power is valid for modulation schemes have a consistent amplitude, such as phase modulation and frequency modulation. Modulation schemes that vary the amplitude of the signal are referred to as pulsed wave or pulsed modulation schemes (like on-off keying or the amplitude modulation used for AM radio). Most modulation schemes used for satellite communication are continuous wave, though, since they tend to be more spectrally efficient. Pulsed modulation likely isn’t something you’ll need to worry too much about unless you’re tracking aircraft using ADS-B [4].

7. Temperature Range

As mentioned in Section 5, thermal considerations are important for cubesat systems engineering, and therefore must be taken into account when choosing parts. Both of the temperatures labelled as “7” in Figure 2 refer to the temperature at the mounting points or leads of the package, not the temperature of the package itself. There are two temperatures listed.

The Operating Temperature is the range of temperatures that the amplifier can safely operate at while powered on and in use.

The Storage Temperature is the range of temperatures that the amplifier can be exposed to while powered off with no current flowing through it.

8. Input/Output VSWR

The VSWR, or Voltage Standing Wave Ratio, is an important characteristic for determining how much of the power of a signal is transmitted through an amplifier, and how much is reflected at its input and output ports. In figure 2, it is labelled with an “8”. For a more detailed explanation on VSWR, see this article.

Essentially, for more optimal matching and therefore power transfer, we want the VSWR to be as close to 1:1 as possible. A value of 1.5:1 corresponds to 96% of the power being transferred to the amplifier, and 4% being reflected. A value of 2:1 corresponds to approximately 90% throughput, 10% reflection. A value of 3:1 corresponds to approximately 75% throughput, 25% reflection. To calculate this value, you can use this handy online calculator from All About Circuits, and then convert the Mismatch Loss from dB to a linear value [5].

This is an especially important value if you have multiple amplifiers and are using them together. If the reflected portion of the signal bounces between the output of the first amplifier and the input of the second, you can quickly end up with an unstable system that leads to overload and failure. This is why engineers will often put a small value attenuator (1 or 2 dB) of the same characteristic impedance as the amplifiers between them. While it does slightly decrease efficiency, it’s an easy way to impedance match the two amplifiers better over a wide range of frequencies and often doesn’t waste much power or decrease link budget significantly, due to the way that system noise temperature is cascaded [a more detailed article on this subject is in progress].

9. Operating Bias Voltage

The operating bias voltage is the DC voltage that will be applied to the amplifier in order to power it. Most of the time, an amplifier will expect a very particular voltage, and so the supplied bias voltage must be regulated to that value.

Power subsystems can be designed in several ways, either providing regulated or unregulated voltages to the various units/boards that make up the subsystem. If you have certain regulated voltages available, it is often preferable to choose an amplifier that uses one of those voltages, as otherwise you’ll have to convert the voltage a second time. Each voltage conversion stage introduces inefficiencies, and if you are using a switched mode converter like a buck, boost, or buck-boost, you can also introduce noise into your signal that will have to be filtered out.

The operating bias voltage is labelled in Figure 2 with a “9”.

10. Operating Current

Operating current is the current that the amplifier draws when operated at a bias voltage. This is an important consideration, since the power subsystem will have to be able to supply an appropriate amount of current, and the PCB you design for the radio will likewise need to handle it appropriately. In most cases, you won’t require more than 1 or 2 Amps for power amplifiers and even less for LNAs. This is marked in Figure 2 with a “10”.

11. Form Factor/Case Suitability

The form factor of the amplifier tells you what size it is, how many electrical connections it requires, and what the layout and dimensions of those connection points to a PCB are, also called a footprint.

The device footprint is labelled as “11” in Figure 1 at the top of the page. Many components will use industry standard packaging, and be described simply as such. This component, for example uses the SOT-343 package. The benefit of using these standardized packages is that many devices that have a similar size and number of electrical contacts, even if they have different functions, can use the same footprint. This makes life much easier for PCB designers using the components, as they don’t have to draw a custom footprint for each and every part.

More information on the footprint of most standard packages can be found online. The SOT-343 package has information available from Infineon Technologies, for instance [6].

Conclusion

I hope this article was helpful for any aspiring cubesat communication engineers. If you find any errors or important omissions in the information presented here, we encourage you to submit feedback via the comments and we will endeavour to correct anything that needs correction or clarification. Happy orbiting!

References

1. Mini-Circuits PSA4-5043+ Low Noise Amplifier Datasheet. Retrieved on Feb 3, 2020. URL: https://www.minicircuits.com/pdfs/PSA4-5043+.pdf
2. RF Wireless World, “IIP3 vs. OIP3”. https://www.rfwireless-world.com/Terminology/IIP3-vs-OIP3.html
3. Rohde & Schwarz, “Understanding Third Order Intercept”. https://youtu.be/m-2H8ddSwTI
4. https://www.mathworks.com/help//comm/ug/airplane-tracking-using-ads-b-signals.html
5. All About Circuits, “VSWR/Return Loss Calculator”. https://www.allaboutcircuits.com/tools/vswr-return-loss-calculator/
6. Infineon Technologies, “SOT343 Package Overview”. https://www.infineon.com/dgdl/SOT343-Package_Overview.pdf?fileId=5546d462580663ef015806a5338d04ef

Introduction

This article will give you an introduction to some of the key terms used by spacecraft engineers when designing and analyzing antennas. While this article doesn’t require any prior knowledge of spacecraft engineering, some knowledge of circuit theory as well as mathematical concepts including logarithms and complex numbers are used.

This article is a bit of a work in progress that we’ll be adding to continuously, so there are a few sections that aren’t yet completed. These are marked with a [TBC] for “To Be Completed”.

Prerequisite Knowledge

1. Frequency domain, (video)

Background

This section will introduce many of the theoretical and conceptual terms you will come across on Crash Cube on pages related to antennas and electromagnetics.

Electric Field

An electric field, commonly abbreviated as an E-field, is a field generated by electrical charges (such as electrons) or by a magnetic field that changes with time. It is one half of the force of electromagnetism, one of the four fundamental forces of nature. The strength of an electric field (E) is given as the force (F) exerted per unit charge (q) and is often measured in units of volts per meter, or electric potential per distance. Electric field is a vector quantity, meaning that direction is important in determining its effect.

\overrightarrow{E} = \frac{\overrightarrow{F}}{q}

Dimensional Analysis:

\frac{Newton}{Coulomb} = \frac{N*m}{C*m} = \frac{J}{C*m} = \frac{V}{m}

Convention is to define electric field lines generated by a positive charge as emanating from the charge, outward.

Magnetic Field

A magnetic field, commonly abbreviated as an B-field, is one generated by a moving electric charges (such as an electric current) or by an electric field that changes with time. It is the other half of the force of electromagnetism along with the electric field.

It is convention to define the direction of the field as perpendicular to the direction of the current generating it, following the right-hand rule.

Electromagnetic Wave

An electromagnetic wave is a paired, sinusoidally oscillating electric field and magnetic field that travels through space, either through vacuum, air, or some other non-conducting material. In almost all typically used materials, including PCB substrates and vacuum, the electric and magnetic fields are perpendicular to both each other and the direction of travel of the wave. They follow the right hand rule such that the cross product of the E field and the B field is in the direction of propagation.

The direction of Figure 1 shows an illustration of an electromagnetic wave, with the electric field (E) in blue oscillating in the x-axis, the magnetic field (B) in red oscillating in the y-axis. The z-axis is the direction the wave is travelling in.

Polarization

An electromagnetic wave can oscillate in different axes, or multiple axes simultaneously. This is called the polarization, essentially how the wave oscillates in the plane perpendicular to its axis of propagation.

In Figure 1 for example, the electric field is oscillating in the x-axis. If the wave was projected into the x-y plane, the tip of the arrow would trace out a line over time, only moving in the x-axis. This is an example of linear polarization. If the ground is in the y-z plane in that image, this could also be called vertical polarization. If the wave was rotated 90 degrees to either side, it would be an example of horizontal polarization. It is also possible for a linearly polarized wave to be rotated at an arbitrary angle around the axis of propagation (z in this example).

A wave can also be polarized in more than one axis simultaneously. A common form of this in the space industry is circular polarization, in which the electric field oscillates in both the vertical and horizontal axis with the same magnitude, 90 degrees out of phase with each other. If the oscillations are of differing magnitudes or have different phasing, the polarization is called elliptical. Figure 2 shows an example of linear, circular, and elliptical polarization.

Frequency

The frequency of an electromagnetic wave is the rate at which the phase of the wave changes per time. All electromagnetic waves oscillate sinusoidally. Frequency is commonly measured in Hertz (abbreviated Hz), or cycles per second. In antenna engineering, however, it is also common to measure frequency using angular measurements, radians per second. Recall that for each 360° phase cycle of a sine wave, there are 2π radians. Frequency is often abbreviated using the symbol f.

Wavelength

The wavelength of an electromagnetic wave is the distance between the peaks of the wave, represented by the symbol λ. In vacuum, this is equal to the speed of light divided by the frequency.

\lambda_0 = \frac{c_0}{f}

The subscript 0 (often pronounced “naught”) is used to indicate that the wavelength is that measured in vacuum. In materials other than vacuum, the frequency of a wave remains the same. The wavelength, however, will change based on the material’s properties since the speed of light in a material other than vacuum is lower than the speed of light in vacuum.

Modulation

An electromagnetic wave is sinusoidal, but it is impossible to encode any information onto a pure sinusoid without changing it over time. By changing the sinusoid in some way that is detectable, we can encode information. Changes to the wave over time to encode information can take many forms, from changing the phase at specific intervals, to changing the frequency, to shutting the wave on and off. These changes, which can be decoded by a receiver as 0’s and 1’s, are called modulation.

Bandwidth

An unmodulated signal with one frequency appears as a single value on a frequency spectrum plot (see prerequisite reading #1). When a signal is modulated it is no longer a pure sinusoid, instead it’s power spreads out wider in the frequency spectrum in a manner that is dependent on the type of modulation that’s being used and the rate at which the signal is being modulated.

Bandwidth is the range of frequencies under which most of the power of the signal resides. It can be defined in a couple of ways most commonly 98% power (for signal bandwidths), -3 dB off-peak insertion loss (for filter bandwidths), or -10 dB return loss (for antenna bandwidths), but it’s possible to define it however is relevant to your specific application.

Essentially, it boils down to the difference between the minimum significant frequency component and the maximum frequency component of your signal. A modulated signal that has a minimum frequency component of 10 MHz and a maximum frequency component of 15 MHz has a bandwidth of 5 MHz.

Rather than defining a signal by the minimum and maximum frequency components, its common to describe it using the point in between them, called the center frequency, and the bandwidth (in this example 12.5 MHz and 5 MHz, respectively).

Decibels

Decibels, often abbreviated as dB, are a logarithmic unit of measurement for measuring relative quantities. Most often you’ll see them used to describe quantities like gain (dBi, decibels relative to an isotropic antenna), power (dBm, decibels relative to one milliwatt), or voltage (dBV, decibels relative to one volt), but it can be used to describe any measurement. The purpose of using decibels for many quantities in communications is twofold. First, they allow representations of both extremely large and extremely small values in a manner that’s easy to represent and perform mathematical operations with. Second,

For example, 50 mW can be represented as 17 dBm. If a 1 GHz signal is transmitted over 50 km, the amount of power at a receiver is 2.3*10^-14 of what was originally transmitted, or -106.4 dB. Rather than multiply these two numbers together to find the amount of power at the receiver (1.15*10^-9 mW), by using decibels the two values can simply be added together. This becomes far more convenient, especially when many different gains and losses need to be taken into account in an equation.

To convert a value x to decibels, for linear quantities such as voltage, use the following formula.

20\log_{10}x

For nonlinear quantities such as power or gain (which is itself a measure of relative power), use the following formula.

10\log_{10} x

Impedance

The impedance of an electromagnetic wave is the ratio between the amplitudes of its electric and magnetic fields. In a circuit, the impedance describes the ratio between the voltage and current of a wave travelling in the circuit. It is measured in units of ohms, similarly to resistance, and can be a complex value. Impedance is important because, as a wave reaches the boundary between two mediums or transmission lines (such as transitioning between a coaxial cable and a an antenna), if the impedances aren’t matched, some of the energy gets reflected resulting in inefficiencies.

The two relationships that impedance describes are related. If you wish to learn about them in more detail, check out Chapter 2 in [3], an excellent textbook on the fundamentals of electromagnetics.

VSWR and Reflection Coefficient

[TBC] – While we continue work on this article, here is an external link covering the concept we haven’t gotten around to yet.

https://www.electronics-notes.com/articles/antennas-propagation/vswr-return-loss/what-is-vswr.php

Directivity, Gain, Realized Gain

[TBC]

Radiation Pattern

When an antenna radiates, it does not do so equally in all directions. Based on the shape, size, and material composition of an antenna, the amplitudes of the fields radiated in different directions will be different. By plotting the strength of the fields relative to the direction in which they emanate, a radiation pattern can be generated. The radiation pattern is one of the most useful tools for an antenna engineer.

A radiation pattern can be generated for several different quantities, most of which are what is called far-field quantities, i.e. they are the values that would be measured if an observer was very far away from an antenna, such that the entire antenna essentially appears as a point source. Typical quantities measured using a radiation pattern are directivity, gain, realized gain, and axial ratio. An example of a 2D radiation pattern (normalized to the peak value, 9 dBi) is shown below in Figure 3.

Further Reading

1. [TBC]

References

[1] – By SuperManu – Self, based on Image:Onde electromagnetique.png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2107870

[2] – R. Nave, Classification of Polarization. [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html. [Accessed: 12-Jan-2021].

[3] – Ulaby, Fundamentals of Applied Electromagnetics

[4] – https://commons.wikimedia.org/wiki/File:Patch_antenna_pattern.gif