US-12627060-B2 - Low-profile antenna for below-grade applications

US12627060B2US 12627060 B2US12627060 B2US 12627060B2US-12627060-B2

Abstract

A capacitively coupled below-grade antenna is provided. The antenna includes a housing; a cap detachable from the housing, the cap having a top surface; a feeding element coupled to a radio module; and a radiating element provided on the cap along the top surface such that the radiating element is capacitively coupled with the feeding element.

Inventors

Umesh Navsariwala

Assignees

PCTEL, INC.

Dates

Publication Date: 20260512
Application Date: 20230912

Claims (14)

1 . An antenna comprising: a housing that is substantially below grade level; a cap detachable from the housing, the cap having a top surface, the cap configured to be above grade level, wherein the cap comprises a radiating element, wherein the housing comprises a feeding element and a radio module, and wherein the radiating element is capacitively coupled with the feeding element.
2 . The antenna of claim 1 , wherein the feeding element extends along a first axis, the first axis is substantially parallel to the top surface.
3 . The antenna of claim 1 , wherein the radio module extends along a second axis, the second axis is substantially perpendicular to the first axis.
4 . The antenna of claim 1 , wherein the feeding element is provided at an end of the radio module, the feeding element is directly connected to the radio module at the end.
5 . The antenna of claim 4 , wherein the feeding element is directly connected to the radio module through solder.
6 . The antenna of claim 1 , wherein the radio module is coupled to the feeding element at a location proximal to a center of the feeding element.
7 . The antenna of claim 1 , wherein the feeding element is formed of a stamped metal part.
8 . The antenna of claim 1 , wherein the radiating element is provided along the top surface of the cap.
9 . The antenna of claim 1 , wherein the radiating element further comprising a first surface that is substantially parallel with the feeding element.
10 . The antenna of claim 9 , wherein the radiating element further comprising a second surface facing a different direction than the first surface.
11 . The antenna of claim 1 , wherein the radiating element is attachable to the cap.
12 . The antenna of claim 1 , wherein the radiating element is insert molded into the cap.
13 . The antenna of claim 1 , wherein the radiating element is provided along the top surface and a side surface of the cap.
14 . A below-grade antenna comprising: a housing; a cap detachable from the housing, the cap having a top surface; a feeding element coupled to a radio module; and a radiating element provided on the cap along the top surface, wherein the radiating element is capacitively coupled with the feeding element, wherein the feeding element is provided at an end of the radio module; and wherein the feeding element extends along a first axis substantially parallel to the top surface, and the radio module extends along a second axis substantially perpendicular to the first axis.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 63/406,893 filed Sep. 15, 2023, entitled, “Low-Profile Antenna For Below-Grade Applications”, which is hereby incorporated by reference as if fully set forth herein. TECHNICAL FIELD This disclosure generally relates to an antenna. More specifically, this disclosure relates to a low-profile antenna suitable for below-grade applications. BACKGROUND In many applications where the device and radio are below-grade, such as underground or below ground level, it is challenging to get sufficient gain from an antenna to establish a communication link with a base station or access point. For example, the radio could be part of a water meter that monitors water flow inside an underground vault or pit. Since the pit is underground and the pit and the lid covering the pit are typically metal, the pit and lid block all signals. As a result, the radio has to be connected to an antenna that is above ground level in order to establish a reliable communication link. To address these issues, a typical practice is to use an antenna that is mounted remotely somewhere other than the radio. However, this type of solution is not practical in many scenarios, like walkways or pathways, where antennas are often located. There are, however, restrictions on the size of above-ground devices and antennas, especially when these are deployed on walkways or pathways. In particular, there are several regulations that govern the height and size of the device, including the antenna, that can protrude above the level surface. For example, Americans with Disabilities Act (ADA) enforces a profile of the device above grade level that cannot exceed a certain profile and has to be less than ½ inch in height. Due to these restrictions, the antenna therein has an extremely small radiating volume or aperture, and consequently, the gain and bandwidth of the antenna are very low. In addition, there is a general need for aesthetic deployment, One approach has been to use an antenna, like a surface-mounted chip antenna on a printed circuit board assembly (PCBA) of the device as shown in FIGS. 1 and 2, with the antenna poking into the allowable above-grade volume. In this type of device, an underground pit can include the underground device and with a lid over a pit. The underground device in the pit has a printed circuit board (PCB) with a radio coupled to the PCB. A chip antenna then extends upward from the radio PCB, poking through the lid and above ground. In FIGS. 1 and 2, the chip antenna can be located in a housing of the device and a cap can be provided on the housing. The cap can be attached to the housing from the outside, and a nut (not shown) can be used on the inside to hold the cap in position. Thereby, the apparatus can be used with lids of various thicknesses and compositions. As mentioned before, these types of solutions, however, suffer from extremely small bandwidths, low efficiency, or both. FIG. 3 illustrates antenna efficiency versus frequency of a chip antenna in various scenarios of materials for the lid and with or without a pit. The antenna efficiency represents the average of the signal strength from the antenna in all directions. As shown in FIG. 3, there is a drop in antenna efficiency in the low-frequency band when the device is mounted on a metal lid placed on a metal pit. In particular, for frequencies between 824 MHz and 960 MHz (i.e., LTE Bands 5 and 8), this antenna shows a drop in efficiency of over 20 decibels (dB) in terms of signal strength as compared to a performance outside of the metal pit and lid. In terms of power, the drop of 20 dB would be 100 times less power. In most situations, this drop in efficiency would translate to a complete lack of a communication signal from the device to the base station or access point. Also as shown in FIG. 3, even with a composite lid placed on a metal pit, there is a substantial drop in efficiency or signal, e.g., about 10 dB. Another approach that has been used with limited success is to change the lids of the vault or pit from a metal to a composite or plastic. While this solution does give some benefits over the previous solutions, it comes at a very high cost, both for the expensive composite lid as well as the labor and logistics involved in deploying these. There may also be additional concerns about maximum load handling limits for lids of larger sizes. Further, there is still a substantial drop in efficiency or signal with such an approach. Another approach that has been attempted is to use antennas tuned to different bands to attempt to obtain better performance in a very specific band. Again, this has limited success and is an expensive solution as well from a logistical perspective. Thus, there is a need for a low-profile antenna for below-grade applications with higher efficiency. BRIEF SUMMARY As described above, an antenna embedded