Systems for electrostatic discharge protection

In one example, a system includes a radio frequency port coupled to an external connector and a microstrip line coupled to the radio frequency port and one or more components mounted on a printed circuit board. The system further includes a short coupled to the microstrip line and a ground reference, wherein the short is coupled to the microstrip line proximate the radio frequency port.

BACKGROUND

Electrostatic discharge (ESD) is a hazard that can endanger equipment located in close proximity to operable RF and DC signal circuits and transmitters. For example, when an antenna is decoupled from the antenna port of operating transceiver electronics, electrostatic charges can develop at the antenna port. If equipment comes within a sufficient proximity of the electrostatically charged antenna port, a path to ground may be created that allows a discharge current to flow through the equipment causing substantial harm. In order to attempt to mitigate such hazards, ESD protection diodes have been coupled to a transmitter's output to shunt ESD to ground. However, such techniques introduce a capacitance onto the antenna port that reduces transmission performance, particularly for higher power applications (for example, 2 Watts).

SUMMARY

In one example, a system includes a radio frequency port coupled to an external connector and a microstrip line coupled to the radio frequency port and one or more components mounted on a printed circuit board. The system further includes a short coupled to the microstrip line and a ground reference, wherein the short is coupled to the microstrip line proximate the radio frequency port.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be used and that logical, mechanical, and electrical changes may be made. The following detailed description is, therefore, not to be taken in a limiting sense.

The example systems described herein provide better ESD protection for equipment while maintaining low insertion loss and return loss. The ESD protection circuit in the example systems includes a microstrip line from one or more components of a printed circuit board (PCB) to a radio frequency port. The ESD protection circuit also includes a short coupled to the microstrip line and a ground reference, and the short is positioned proximate to the radio frequency port. The example systems described herein are not limited to particular RF system architectures, but may be used in conjunction with wireless network access points (for example, IEEE 802.11 (Wi-Fi) access points), distributed antenna systems, RF repeaters, cellular communications base stations, small cell base stations, or other RF signal transport, processing, or transceiver devices.

FIG.1is a top view of an example ESD protection circuit100that can be included in a device. In the example ofFIG.1, the ESD protection circuit100includes a microstrip line102, a radio frequency port104, and a short106coupled to a ground reference108. While a single instance of each component is shown inFIG.1, it should be understood that this is for ease of illustration and the device can include one or more of the components shown inFIG.1. For example, a device may include multiple ESD protection circuits100or a single ESD protection circuit100could include more than one of the components discussed above.

The microstrip line102is coupled to one or more components112of a PCB and the radio frequency port104. In some examples, the microstrip line102is configured to have a characteristic impedance matched to the system impedance (for example, 50 Ohms). In some examples, the microstrip line102includes one or more mitered bends or corners. For example, the microstrip line102shown inFIG.1includes two mitered bends. In some examples, the one or more components112of the PCB include RF transmitter or receiver circuits and/or other RF signal processing or DC electronics mounted to the PCB. The microstrip line102can function as a transmission line from the one or more components112of the PCB to the radio frequency port104.

The radio frequency port104is coupled to the end of the microstrip line102opposite the one or more components112of the PCB. In some examples, the radio frequency port104is coupled to an external connector114, which could be an external RF connector. In some examples, the external connector114is configured to be coupled to an antenna or other RF device (not shown). In some examples, the radio frequency port104is an output port of the device. In some examples, the radio frequency port104is an input port of the device. As discussed above, the external RF connector is a potential source of ESD, particularly when it is being coupled or decoupled.

In order to prevent ESD from damaging the one or more components112of the PCB, the short106of the ESD protection circuit100is coupled to the microstrip line102at a point that is proximate to the radio frequency port104. In some examples, the short106is coupled to the microstrip line102as close as possible to the radio frequency port104. The other end of the short106is coupled to a ground reference108. In some examples, the ground reference108is a ground pin of the radio frequency port104or the ground pin of another input port or output port of the device. In some examples, the ground reference108is also positioned as close as possible to the radio frequency port104of the device.

In some examples, the short106is configured to have a higher characteristic impedance than the microstrip line102. For example, if the microstrip line102has a characteristic impedance of 50 Ohms, the short106can be configured to have a characteristic impedance that is greater than 50 Ohms (for example, 75 Ohms). In some examples, the short106is configured to have a length that is a quarter wavelength of the operating frequency of the RF signals transmitted or received via the radio frequency port104. In some examples, the short106is configured to operate as an open circuit for the operating frequency of the RF signals transmitted or received via the radio frequency port104. For example, the width and length of the short can be chosen during design such that the short106operates as an open circuit for the operating frequency of the RF signals transmitted or received via the radio frequency port104.

The higher characteristic impedance of the short106helps to avoid additional insertion loss on the microstrip line102, which can function as the output transmission line of the device. It has been observed that the ESD protection circuit100shown inFIG.1, through the inductive impact of the short106, has better matching to 50 Ohms for the operating frequency of the RF signals transmitted or received via the radio frequency port104than if the short106were not included. Further, the ESD protection circuit100has a less negative effect on passive intermodulation (PIM) performance of the device like previous designs using ESD protection diodes.

FIG.2is a graph illustrating simulated insertion loss and return loss for an ESD protection circuit. In particular,FIG.2illustrates simulation results for a 3.55-3.7 GHz Citizens Broadband Radio Service (CBRS) band with an ESD protection circuit as shown inFIG.1. The output 50 Ohm line has a low insertion loss (approximately 0.08 dB) for the 50 Ohm line and 0.03 dB additional loss for the ESD protection for approximately 0.11 dB of total loss. In some examples, the short106is also configured to suppress one or more harmonics of an operating frequency for the RF signals transmitted via the radio frequency port104. With this additional suppression of harmonics provided by the short106, the size of output filters, loss, and power consumption could be reduced for the device. In the example results shown inFIG.2, the harmonic suppression is greater than 10 dB at 7.1-7.4 GHz.

In some examples, the ESD protection circuit100is mounted to the same circuit board as the one or more components112. In other examples, the ESD protection circuit100is mounted to a different circuit board than the one or more components112shown inFIG.1. For example, the one or more components112could be mounted to a first circuit board and the components of the ESD protection circuit100could be mounted on a second circuit board. In some examples, the first circuit board and the second circuit board each include compatible edge connector interface hardware that electrically couple the one or more components112to the ESD protection circuit100.

In some examples, the PCB that includes the ESD protection circuit100is a multi-layer PCB. In such examples, the ESD protection circuit100includes a plurality of ground vias110, which are included from the top layer to the bottom layer to keep the ESD pulses energy within a restricted area close to the radio frequency port104. In some examples, the plurality of ground vias110are positioned around the perimeter of portion of the circuit board on which the ESD protection circuit100is mounted.

As mentioned above, the ESD protection circuit100described herein can be used in conjunction with any number of RF circuits and system architectures such as, but not limited to: wireless network access points, distributed antenna systems, RF repeaters, cellular communications base stations, and small cell base stations.

FIG.3is a block diagram of an example distributed antenna system (DAS)300that includes the ESD protection circuit100in one or more components of the DAS300. In the example ofFIG.3, the DAS300includes one or more master units302(also referred to as “host units” or “central area nodes” or “central units”) and one or more remote antenna units304(also referred to as “remote units” or “radiating points”) that are communicatively coupled to the one or more master units302. In this example, the DAS300comprises a digital DAS, in which DAS traffic is distributed between the master units302and the remote antenna units304in digital form. The DAS300can be deployed at a site to provide wireless coverage and capacity for one or more wireless network operators. The site may be, for example, a building or campus or other grouping of buildings (used, for example, by one or more businesses, governments, or other enterprise entities) or some other public venue (such as a hotel, resort, amusement park, hospital, shopping center, airport, university campus, arena, or an outdoor area such as a ski area, stadium or a densely-populated downtown area).

The master unit302is communicatively coupled to the plurality of base stations306. One or more of the base stations306can be co-located with the respective master unit302to which it is coupled (for example, where the base station306is dedicated to providing base station capacity to the DAS300). Also, one or more of the base stations306can be located remotely from the respective master unit302to which it is coupled (for example, where the base station306is a macro base station providing base station capacity to a macro cell in addition to providing capacity to the DAS300). In this latter case, a master unit302can be coupled to a donor antenna using an over-the-air repeater in order to wirelessly communicate with the remotely located base station.

The base stations306can be implemented in a traditional manner in which a base band unit (BBU) is deployed at the same location with a radio head (RRH) to which it is coupled, where the BBU and RRH are coupled to each other using optical fibers over which front haul data is communicated as streams of digital IQ samples (for example, in a format that complies with one of the Common Public Radio Interface (CPRI), Open Base Station Architecture Initiative (OBSAI), and Open RAN (O-RAN) families of specifications). Also, the base stations306can be implemented in other ways (for example, using a centralized radio access network (C-RAN) topology where multiple BBUs are deployed together in a central location, where each of BBU is coupled to one or more RRHs that are deployed in the area in which wireless service is to be provided. Also, the base station306can be implemented as a small cell base station in which the BBU and RRH functions are deployed together in a single package.

The master unit302can be configured to use wideband interfaces or narrowband interfaces to the base stations306. Also, the master unit302can be configured to interface with the base stations306using analog radio frequency (RF) interfaces or digital interfaces (for example, using a CPRI, OB SAI, or O-RAN digital interface). In some examples, the master unit302interfaces with the base stations306via one or more wireless interface nodes (not shown). A wireless interface node can be located, for example, at a base station hotel, and group a particular part of a RF installation to transfer to the master unit302.

Traditionally, a master unit302interfaces with one or more base stations306using the analog radio frequency signals that each base station306communicates to and from a mobile device308(also referred to as “mobile units” or “user equipment”) of a user using a suitable air interface standard. Although the devices308are referred to here as “mobile” devices308, it is to be understood that the devices308need not be mobile in ordinary use (for example, where the device308is integrated into, or is coupled to, a sensor unit that is deployed in a fixed location and that periodically wirelessly communicates with a gateway or other device). The DAS300operates as a distributed repeater for such radio frequency signals. RF signals transmitted from each base station306(also referred to herein as “downlink RF signals”) are received at the master unit. In such examples, the master unit302uses the downlink RF signals to generate a downlink transport signal that is distributed to one or more of the remote antenna units304. Each such remote antenna unit304receives the downlink transport signal and reconstructs a version of the downlink RF signals based on the downlink transport signal and causes the reconstructed downlink RF signals to be radiated from an antenna416coupled to or included in that remote antenna unit304.

In some aspects, the master unit302is directly coupled to the remote antenna units304. In such aspects, the master unit302is coupled to the remote antenna units304using cables321. For example, the cables321can include optical fiber or Ethernet cable complying with the Category 5, Category 5e, Category 6, Category 6A, or Category 7 specifications. Future communication medium specifications used for Ethernet signals are also within the scope of the present disclosure.

A similar process can be performed in the uplink direction. RF signals transmitted from mobile devices308(also referred to herein as “uplink RF signals”) are received at one or more remote antenna units304via an antenna416. Each remote antenna unit304uses the uplink RF signals to generate an uplink transport signal that is transmitted from the remote antenna unit304to a master unit302. The master unit302receives uplink transport signals transmitted from one or more remote antenna units304coupled to it. The master unit302can combine data or signals communicated via the uplink transport signals from multiple remote antenna units304(for example, where the DAS300is implemented as a digital DAS300, by digitally summing corresponding digital samples received from the various remote antenna units304) and generates uplink RF signals from the combined data or signals. In such examples, the master unit302communicates the generated uplink RF signals to one or more base stations306. In this way, the coverage of the base stations306can be expanded using the DAS300.

As noted above, in the example shown inFIG.3, the DAS300is implemented as a digital DAS. In a “digital” DAS, signals received from and provided to the base stations306and mobile devices308are used to produce digital in-phase (I) and quadrature (Q) samples, which are communicated between the master unit302and remote antenna units304. It is important to note that this digital IQ representation of the original signals received from the base stations306and from the mobile units still maintains the original modulation (that is, the change in the amplitude, phase, or frequency of a carrier) used to convey telephony or data information pursuant to the cellular air interface protocol used for wirelessly communicating between the base stations306and the mobile units. Examples of such cellular air interface protocols include, for example, the Global System for Mobile Communication (GSM), Universal Mobile Telecommunications System (UMTS), High-Speed Downlink Packet Access (HSDPA), Long-Term Evolution (LTE), Citizens Broadband Radio Service (CBRS), and fifth generation New Radio (5G NR) air interface protocols. Also, each stream of digital IQ samples represents or includes a portion of wireless spectrum. For example, the digital IQ samples can represent a single radio access network carrier (for example, a 5G NR carrier of 40 MHz or 400 MHz) onto which voice or data information has been modulated using a 5G NR air interface. However, it is to be understood that each such stream can also represent multiple carriers (for example, in a band of frequency spectrum or a sub-band of a given band of frequency spectrum).

In the example shown inFIG.3, the master unit302can be configured to interface with one or more base stations306using an analog RF interface (for example, via the analog RF interface of an RRH or a small cell base station). In some examples, the base stations306can be coupled to the master unit302using a network of attenuators, combiners, splitters, amplifiers, filters, cross-connects, etc., which is referred to collectively as a point-of-interface (POI)307. This is done so that, in the downlink, the desired set of RF carriers output by the base stations306can be extracted, combined, and routed to the appropriate master unit302, and so that, in the uplink, the desired set of carriers output by the master unit302can be extracted, combined, and routed to the appropriate interface of each base station306. In other examples, the POI307can be part of the master unit302.

In the example shown inFIG.3, in the downlink, the master unit302can produce digital IQ samples from an analog signal received at radio frequency (RF) by down-converting the received signal to an intermediate frequency (IF) or to baseband, digitizing the down-converted signal to produce real digital samples, and digitally down-converting the real digital samples to produce digital in-phase (I) and quadrature (Q) samples. These digital IQ samples can also be filtered, amplified, attenuated, and/or re-sampled or decimated to a lower sample rate. The digital samples can be produced in other ways. Each stream of digital IQ samples represents a portion of radio frequency spectrum output by one or more base stations306. Each portion of radio frequency spectrum can include, for example, a band of wireless spectrum, a sub-band of a given band of wireless spectrum, or an individual wireless carrier.

Likewise, in the uplink, the master unit302can produce an uplink analog signal from one or more streams of digital IQ samples received from one or more remote antenna units304by digitally combining streams of digital IQ samples that represent the same carriers or frequency bands or sub-bands received from multiple remote antenna units304(for example, by digitally summing corresponding digital IQ samples from the various remote antenna units304), digitally up-converting the combined digital IQ samples to produce real digital samples, performing a digital-to-analog process on the real samples in order to produce an IF or baseband analog signal, and up-converting the IF or baseband analog signal to the desired RF frequency. The digital IQ samples can also be filtered, amplified, attenuated, and/or re-sampled or interpolated to a higher sample rate, before and/or after being combined. The analog signal can be produced in other ways (for example, where the digital IQ samples are provided to a quadrature digital-to-analog converter that directly produces the analog IF or baseband signal).

In the example shown inFIG.3, the master unit302can be configured to interface with one or more base stations306using a digital interface (in addition to, or instead of) interfacing with one or more base stations306via an analog RF interface. For example, the master unit302can be configured to interact directly with one or more BBUs using the digital IQ interface that is used for communicating between the BBUs and an RRHs (for example, using the CPRI serial digital IQ interface).

In the downlink, the master unit302terminates one or more downlink streams of digital IQ samples provided to it from one or more BBUs and, if necessary, converts (by re-sampling, synchronizing, combining, separating, gain adjusting, etc.) them into downlink streams of digital IQ samples compatible with the remote antenna units304used in the DAS300. In the uplink, the master unit302receives uplink streams of digital IQ samples from one or more remote antenna units304, digitally combining streams of digital IQ samples that represent the same carriers or frequency bands or sub-bands received from multiple remote antenna units304(for example, by digitally summing corresponding digital IQ samples received from the various remote antenna units304), and, if necessary, converts (by re-sampling, synchronizing, combining, separating, gain adjusting, etc.) them into uplink streams of digital IQ samples compatible with the one or more BBUs that are coupled to that master unit302.

In the downlink, each remote antenna unit304receives streams of digital IQ samples from the master unit302, where each stream of digital IQ samples represents a portion of wireless radio frequency spectrum output by one or more base stations306. Each remote antenna unit304generates, from the downlink digital IQ samples, one or more downlink RF signals for radiation from the one or more antennas coupled to that remote antenna unit304for reception by any mobile devices308in the associated coverage area. In the uplink, each remote antenna unit304receives one or more uplink radio frequency signals transmitted from any mobile devices308in the associated coverage area, generates one or more uplink streams of digital IQ samples derived from the received one or more uplink radio frequency signals, and transmits them to the master unit302.

Each remote antenna unit304can be communicatively coupled directly to one or more master units302or indirectly via one or more other remote antenna units304and/or via one or more intermediate units316(also referred to as “expansion units” or “transport expansion nodes”). The latter approach can be done, for example, in order to increase the number of remote antenna units304that a single master unit302can feed, to increase the master-unit-to-remote-antenna-unit distance, and/or to reduce the amount of cabling needed to couple a master unit302to its associated remote antenna units304. The expansion units are coupled to the master unit302via one or more cables421.

In the example DAS300shown inFIG.3, a remote antenna unit304is shown having another co-located remote antenna unit305(also referred to herein as an “extension unit”) communicatively coupled to it. Subtending a co-located extension remote antenna unit305from another remote antenna unit304can be done in order to expand the number of frequency bands that are radiated from that same location and/or to support MIMO service (for example, where different co-located remote antenna units radiate and receive different MIMO streams for a single MIMO frequency band). The remote antenna unit304is communicatively coupled to the “extension” remote antenna units305using a fiber optic cable, a multi-conductor cable, coaxial cable, or the like. In such an implementation, the remote antenna units305are coupled to the master unit302of the DAS300via the remote antenna unit304.

In some examples, one or more components of the DAS300include the ESD protection circuit100as described above. For example, the master unit302and/or remote antenna units304,305can include the ESD protection circuit100in order to prevent damage to components of the master unit302and/or remote antenna units304,305. In some examples, an ESD protection circuit100is positioned in the uplink path and/or downlink path in the master unit302. In some examples, an ESD protection circuit100is positioned in the uplink path and/or downlink path in one or more remote antenna units304,305.

Other types of radio frequency distribution systems can also benefit from the ESD protection circuit described above.FIG.4illustrates an example of a single-node repeater400that includes the ESD protection circuit100as discussed above.

In the exemplary embodiment shown inFIG.4, the single-node repeater400is coupled to one or more base stations402using a donor antenna430.

The single-node repeater400comprises a first duplexer406having a common port that is coupled to the donor antenna430via a cable432, a downlink port that is coupled to downlink circuitry408, and an uplink port that is coupled to uplink circuitry410. The single-node repeater400comprises a second duplexer412having a common port that is coupled to the coverage antenna416, a downlink port that is coupled to the downlink circuitry408, and an uplink port that is coupled to the uplink circuitry410.

In general, the single-node repeater400is configured to receive one or more downlink signals from one or more base stations402. Each base station downlink signal includes one or more radio frequency channels used for communicating in the downlink direction with user equipment414over the relevant one or more wireless air interfaces. The downlink circuitry408is configured to amplify the downlink signals received at the repeater400and re-radiate the amplified downlink signals via the coverage antenna416. As a part of doing this, the downlink circuitry408can be configured to filter the downlink signals to separate out the individual channels, individually amplify each filtered downlink channel signal, combine the individually amplified downlink channel signals, and re-radiate the resulting combined signal.

Similar processing is performed in the uplink. The single-node repeater400is configured to receive one or more uplink signals from mobile device414. Each mobile device uplink signal includes one or more radio frequency channels used for communicating in the uplink direction with one or more base stations402over the relevant one or more wireless air interfaces. The uplink circuitry410is configured to amplify the uplink signals received at the repeater400and re-radiate the amplified uplink signals via the donor antenna430. As a part of doing this, the uplink circuitry410can be configured to filter the uplink signals to separate out the individual channels, individually amplify each filtered uplink channel signal, combine the individually amplified uplink channel signals, and re-radiate the resulting combined signal.

The single-node repeater400can be configured to implement one or more features to provide sufficient isolation between the donor antenna430and the coverage antenna416. These features can include gain control circuitry and adaptive cancellation circuitry. Other features can be implemented. These features can be implemented in one or more of the downlink circuitry408and/or the uplink circuitry410. These features can also be implemented in separate circuitry.

The single-node repeater400can also include an ESD protection circuit100as described above. The single-node repeater400can include one or more ESD protection circuits100in order to prevent damage to components of the single-node repeater400. In some examples, an ESD protection circuit100is positioned between the donor antenna430and the duplexer406and/or an ESD protection circuit100is positioned between the duplexer412and the coverage antenna416.

In various aspects, system elements, method steps, or examples described throughout this disclosure (such as the distributed antenna system, repeater, or components thereof, for example) may be implemented on one or more computer systems, field programmable gate array (FPGA), application specific integrated circuit (ASIC) or similar devices comprising hardware executing code to realize those elements, processes, or examples, said code stored on a non-transient data storage device. These devices include or function with software programs, firmware, or other computer readable instructions for carrying out various methods, process tasks, calculations, and control functions.

These instructions are typically stored on any appropriate computer readable medium used for storage of computer readable instructions or data structures. The computer readable medium can be implemented as any available media that can be accessed by a general purpose or special purpose computer or processor, or any programmable logic device. Suitable processor-readable media may include storage or memory media such as magnetic or optical media. For example, storage or memory media may include conventional hard disks, Compact Disk-Read Only Memory (CD-ROM), volatile or non-volatile media such as Random Access Memory (RAM) (including, but not limited to, Synchronous Dynamic Random Access Memory (SDRAM), Double Data Rate (DDR) RAM, RAMBUS Dynamic RAM (RDRAM), Static RAM (SRAM), etc.), Read Only Memory (ROM), Electrically Erasable Programmable ROM (EEPROM), and flash memory, etc. Suitable processor-readable media may also include transmission media such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link.

Example Embodiments

Example 1 includes a system, comprising: a radio frequency port coupled to an external connector; a microstrip line coupled to the radio frequency port and one or more components mounted on a printed circuit board; and a short coupled to the microstrip line and a ground reference, wherein the short is coupled to the microstrip line proximate the radio frequency port.

Example 2 includes the system of Example 1, wherein the short is configured to have a higher characteristic impedance than the microstrip line.

Example 3 includes the system of any of Examples 1-2, wherein a length of the short is a quarter wavelength of an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 4 includes the system of any of Examples 1-3, wherein the ground reference comprises a ground pin of the radio frequency port.

Example 5 includes the system of any of Examples 1-4, wherein the short is configured to operate as an open circuit for an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 6 includes the system of any of Examples 1-5, wherein the short is configured to suppress one or more harmonics of an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 7 includes the system of any of Examples 1-6, wherein the one or more components mounted on the printed circuit board include at least one of: a power amplifier; or a duplexer.

Example 8 includes the system of any of Examples 1-7, wherein the microstrip line includes one or more mitered corners between the radio frequency port and the one or more components mounted on the printed circuit board.

Example 9 includes the system of any of Examples 1-8, wherein the printed circuit board is a multi-layer printed circuit board comprising a plurality of ground vias.

Example 10 includes a unit of a repeater system, comprising: downlink circuitry configured to receive downlink signals sourced from a base station and to output a gain-adjusted downlink signal to one or more user equipment in a coverage area of the repeater system; uplink circuitry configured to receive uplink signals from one or more user equipment in the coverage area of the repeater system and to output a gain-adjusted uplink signal to the base station; a radio frequency port coupled to an external connector; a microstrip line coupled to the radio frequency port and the downlink circuitry and/or the uplink circuitry; and a short coupled to the microstrip line and a ground reference, wherein the short is coupled to the microstrip line proximate the radio frequency port.

Example 11 includes the unit of Example 10, wherein the unit is a single-node repeater.

Example 12 includes the unit of any of Examples 10-11, wherein the unit is a master unit of a distributed antenna system, wherein the master unit is communicatively coupled to one or more remote antenna units that are located remotely from the master unit.

Example 13 includes the unit of any of Examples 10-12, wherein the unit is a remote antenna unit of a distributed antenna system, wherein the distributed antenna system comprises a master unit communicatively coupled to the remote antenna unit, wherein the remote antenna unit is located remotely from the master unit.

Example 14 includes the unit of any of Examples 10-13, wherein the short is configured to have a higher characteristic impedance than the microstrip line.

Example 15 includes the unit of any of Examples 10-14, wherein a length of the short is a quarter wavelength of an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 16 includes the unit of any of Examples 10-15, wherein the ground reference comprises a ground pin of the radio frequency port of the unit.

Example 17 includes the unit of any of Examples 10-16, wherein the short is configured to operate as an open circuit for an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 18 includes the unit of any of Examples 10-17, wherein the short is configured to suppress one or more harmonics of an operating frequency for radio frequency signals transmitted or received via the radio frequency port.

Example 19 includes the unit of any of Examples 10-18, wherein the downlink circuitry and/or the uplink circuitry is mounted on the printed circuit board, wherein the microstrip line includes one or more mitered corners between the radio frequency port and the downlink circuitry and/or uplink circuitry mounted on the printed circuit board.

Example 20 includes the unit of any of Examples 10-19, wherein the downlink circuitry and/or the uplink circuitry is mounted on the printed circuit board, wherein the printed circuit board is a multi-layer printed circuit board comprising a plurality of ground vias.