A transmitter comprising a planar antenna including a ground plane and first and second spiral radiating elements wrapping around the ground plane, and a driving circuit. Proximal ends of the spiral radiating elements terminate near points located along a perimeter of the ground plane. Exactly one of the first and second spiral radiating elements are electrically isolated from the ground plane. The first and second spiral radiating elements are wound in the same direction for approximately a single turn and increase in thickness for approximately three-fourths of the turn. The driving circuit drives one of the first and second spiral radiating elements.

BACKGROUND

Many types of sensors require a remote connection to the internet to compile data and allow for remote monitoring. Long range radio technology (e.g., LoRa® radio technology) is a relatively recent development that allows connection of remote sensors to the internet because of its ability to transmit at distances of over 1 km using adequately reduced power levels that enable battery-operated sensors to operate for months or longer without a battery change. Long range radio technology as described in U.S. Pat. No. 7,791,415, incorporated by reference in its entirety herein, uses a fractional-N phase-locked-loop to allow a modulated frequency that differs in up-frequency rate from down-frequency rate with great accuracy, thus allowing much longer range and lower power usage than standard transmission technology.

Long range radio technology switches between a number of channels when transmitting in order to decrease the possibility of data collisions with nearby long range radio transmitters. The number of channels required depends on the number of nearby transmitters and the rate at which the transmitters transmit information. The range of frequencies over which a transmitter is required to transmit information may comprise, for example, a 2:1 ratio.

Many antenna designs are optimized for use at a single frequency or a very small band of frequencies around a center frequency. Such antennas are poorly adapted for use with long range radio technology since most long range radio applications must transmit at a multitude of channels and therefore require a large frequency range.

Applications that can benefit from long range radio technology often require very compact transmitters. For example, tags on animals or inventory items may need to be flat, light, and small. Such applications also require a built-in power source such as a battery or a super capacitor. These applications therefore need to use a compact combination of a power source, an antenna, and a driver that operates over a wide frequency range.

Planar spiral antennas such as log-periodic spiral antennas and Archimedean Spiral Antennas are well-known as a means to achieve very large bandwidth in a planar antenna. Spiral antennas employ two radiating elements that wrap around each other in a spiral pattern which terminates at a point in the center of the two spirals. In order to achieve very high bandwidth, spiral antennas often reside in a stand-alone plane. Driving circuits and power sources must be located outside of the immediate vicinity of the plane of a traditional spiral antenna and connect to the center of the antenna through a coaxial cable. Otherwise, the ground plane of the driving circuit or the large surface area of the battery may interfere with transmission. A traditional complete circuit that includes a spiral antenna and a driver thus requires a relatively large volume and is poorly suited to many long range radio applications.

SUMMARY OF THE INVENTION

The present invention solves the above-described problems and provides a distinct advance to compact circuits appropriate for use in applications that employ long range radio transmitters. Specifically, the present invention includes a transmitter comprising a planar antenna that includes a centralized ground plane and first and second spiral radiating elements which wrap around the centralized ground plane and are composed of a first conducting material. A proximal end of the first spiral radiating element terminates near (at or in the vicinity of), but may be electrically isolated from, a first termination point located along the perimeter/circumference of the centralized ground plane. A proximal end of the second spiral radiating element terminates near, but may be electrically isolated from, a second termination point located along the perimeter/circumference of the centralized ground plane. The first termination point and second termination point may be 180 degrees apart from each other on (e.g. on opposite sides of) the centralized ground plane.

Exactly one of the proximal end of the first spiral radiating element and the proximal end of the second spiral radiating element may be electrically isolated from the centralized ground plane. The first and second spiral radiating elements may be wound in the same direction (either both clockwise or both anti-clockwise) around the centralized ground plane. The first and second spiral radiating elements each circle the centralized ground plane approximately a single turn (e.g., between 0.9 and 1.1 turns). The first and second spiral radiating elements may increase in width for at least ¾ths of a turn (i.e., at least 270 degrees) from their proximal ends.

The transmitter may also comprise a driving circuit configured to drive one of the first and second spiral radiating elements. In another embodiment, the transmitter may further comprise a planar battery configured to be confined within a horizontal footprint of the centralized ground plane and further configured to be affixed directly or indirectly to the centralized ground plane and provide electrical power to the driving circuit.

DETAILED DESCRIPTION

A plan view of an embodiment of Transmitter100is shown inFIGS.1and2.FIG.1andFIG.2show the same embodiment, except that the drawing inFIG.1depicts conductive material (such as copper) in solidly filled areas andFIG.2is a line drawing depicting boundaries between conducting and non-conducting material. Transmitter100comprises an Antenna105including Radiating Elements120and130and Ground Plane110. In some embodiments, the Ground Plane110may be in the shape of a rectangle in which the corners have been trimmed or rounded, an oval, or a circle.

Radiating Element120terminates via its proximal end near (at or in the vicinity of) First Termination Point123of Ground Plane110. Radiating Element130terminates via its proximal end near Second Termination Point133of Ground Plane110. As can be seen fromFIGS.1and2, the termination near First Termination Point123comprises an electrically conductive material whereas the termination near Second Termination Point133is non-conducting—that is, Radiating Element120is electrically connected to Ground Plane110while Radiating Element130is not electrically connected to Ground Plane110. Note that Ground Plane110is depicted as a solid region inFIG.1; however, in some embodiments Ground Plane110is not entirely solid. For example, Ground Plane110may be the ground plane of a multi-layer circuit board, and thus may have small cut-outs coinciding with through-holes, vias, and circuit board traces.

In one embodiment such as the one shown inFIGS.1and2, at least one of Radiating Elements120and130terminates at Ground Plane110without making a physical electrical connection to Ground Plane110. The non-electrical termination can be accomplished by a number of means. For example, the non-electrical termination can be accomplished by removing a thin sliver of conducting material around the radiating element (resulting in the structure shown inFIGS.1and2), or it can be accomplished by offsetting the radiating element from the plane of Ground Plane110and placing an insulating material (such as standard circuit board material) between the radiating element and Ground Plane110. Furthermore, in another embodiment, either or both of Radiating Elements120and130may be non-permanently electrically disconnected from Ground Plane110. For example, each of Radiating Elements120and130can terminate at Ground Plane110via switches (such as Switches208and210described below and shown inFIG.5) such that the switches alternately electrically connect Radiating Elements120and130to (and isolate the other radiating element from) Ground Plane110. Importantly, at any given time, exactly one of Radiating Elements120and130is electrically coupled to Ground Plane110.

Radiating Elements120and130wrap around each other as well as wrap around Ground Plane110. As can be seen inFIGS.1and2, Radiating Elements120and130form spirals in an anti-clockwise direction. Radiating Elements120and130could also form spirals in a clockwise direction rather than an anti-clockwise direction. What is important is that Radiating Elements120and130wrap around Ground Plane110and wrap around each other in the same direction.

Radiating Elements120and130each form spirals of approximately one turn (e.g., between 0.9 and 1.1 turns). The exact number of turns may be adjusted from exactly one turn due to the difference between the speed of electricity in the conducting material that forms Radiating Elements120and130(e.g. copper) and the speed of light, as well as adjustments necessary due to capacitance of nearby structures in the enclosure of the Antenna105.

As shown inFIGS.1and2, Radiating Elements120and130may increase in width as they spiral out from Ground Plane110. The lower or lowest frequency in the transmitting frequency range of the Transmitter100is determined by the outside perimeter of the Radiating Elements120and130and the upper or uppermost frequency in the transmitting frequency range of the Transmitter100is determined by the inside perimeter of the Radiating Elements120and130. It is therefore critical in certain embodiments that the width of the Radiating Elements120and130increase as the radiating elements120and130spiral outward from Ground Plane110in order to yield a large operating frequency range. The outer terminations of Radiating Elements120and130may not be able to support a large width due to space constraints on the Antenna105. It is adequate for the width of the Radiating Elements120and130to increase for approximately ¾ths of a turn (i.e., approximately 270 degrees of rotation) beginning at the proximal ends spiraling out from the centralized Ground Plane110as shown inFIGS.1and2.

Turning now toFIGS.3and4,FIG.3shows the same plan view embodiment of Transmitter100asFIGS.1and2, except thatFIG.3includes dotted line300which defines a vertical cross-section of the Transmitter100that is shown inFIG.4.

As best seen inFIG.4, a Driving Circuit410configured to drive Radiating Elements120and130is located on top of Ground Plane110. Ground Plane110may form an integral part of a two or more layer printed circuit board integral to the Driving Circuit410.

Insulator490may be the insulation material of a printed circuit board. A copper layer above Insulator490comprises Radiating Elements120and130as well as Ground Plane110. The copper layer comprising Radiating Elements120and130corresponds to the solid regions shown inFIG.3, which are intersected by dotted line300.

Insulator411is located above Ground Plane110. Insulator411may be the insulation material of a printed circuit board such as FR-4 material. Conducting layer412is located above Insulator411. Conducting Layer412may be an etched layer of copper forming printed circuit board pads on which electronic components are soldered as well as copper traces forming connections between pins of the electronic components.

Component Layer413comprises electronic components which may be soldered to appropriate places on Conducting Layer412. Note that while Ground Plane110is depicted as a solid region of copper, small areas of Ground Plane110may be etched away to allow, for example, placement of electrical traces for the purpose of completing electrical circuits, and while Insulator411is depicted as a solid insulator, small electrical vertical runs of copper may be placed within Insulator411, for example, for the purpose of electrically connecting various pins from Components Layer413to Ground Plane110.

Driving Circuit410comprises the components in Component Layer413in tandem with Conducting Layer412, Insulator411, and Ground Plane110and is configured to drive the Antenna105which comprises Radiating Arms120and130and Ground Plane110. More specifically, Driving Circuit410drives whichever one of Radiating Arms120and130is not electrically coupled to Ground Plane110. What is presented inFIG.4is thus a planar transmitter configured to operate over a broad range of frequencies.

FIG.4also shows Planar Battery450under Insulator490. Planar Battery450is configured to be electrically coupled to and power the Driving Circuit410that is formed by the components in Component Layer413through small vertical wires which may comprise vertical copper traces within Insulators411and490. Planar Battery450may be further configured to be confined within a horizontal footprint of Ground Plane110.

FIG.5shows typical dimensions of an exemplary embodiment of a broadband Transmitter200configured to transmit signals according to a LoRaWAN standard. The overall length of transmitter is 98 mm and the overall width is 79 mm. The height of the Transmitter200may be about 10 mm without a battery, or 13 mm with a battery. The Transmitter200also includes switches208and210that alternately electrically connect Radiating Elements204and206to Ground Plane202. Importantly, at any given time, exactly one of Radiating Elements204and206is electrically coupled to Ground Plane202, and the other radiating element is not electrically coupled to Ground Plane. Note that Switches208and210are shown schematically and may be any suitable electronic or electrical switches.

FIG.6shows a plot of return loss (RL) and standing wave ratio (SWR) of the embodiment inFIG.5over a range of frequencies, andFIG.7shows a table of some data points in the plot ofFIG.6. Curve601is the return loss and Curve602is the standing wave ratio. Results show that the embodiment inFIG.5demonstrates good performance in a range of frequencies from 779 MHz to 929 MHz, which is a range of frequencies appropriate for long range radio applications.

Having thus described one or more embodiments of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: