US-12627053-B1 - Patch antenna element with reactive areal loading

US12627053B1US 12627053 B1US12627053 B1US 12627053B1US-12627053-B1

Abstract

A patch antenna element has a plurality of patches that are coplanar, each having a length along a resonant dimension that is no greater than one-quarter of a wavelength of a maximum operating frequency of the patch antenna element. The antenna element also includes one or more discrete reactive elements. For each pair of neighboring patches of the plurality of patches, the pair forms an electrically insulating space therebetween. At least one discrete reactive element lies within the electrically insulating space and is electrically connected to both of the neighboring patches of the pair. A patch antenna combines the patch antenna element with a counterpoise that is parallel to, and displaced from, the patch antenna element. Each discrete reactive element may be an inductor or capacitor, either planar or non-planar. The patch antenna may be configured as a dual-polarization patch antenna or quarter-wave patch antenna.

Inventors

Dean Paschen
Lars Grimsrud

Assignees

FIRST RF CORPORATION

Dates

Publication Date: 20260512
Application Date: 20220419

Claims (17)

1 . A patch antenna element, comprising: a plurality of radiating patches that are coplanar, each of the plurality of radiating patches having a length along a resonant dimension of the patch antenna element, the length being no greater than one-half of a wavelength of a maximum operating frequency of the patch antenna element; and one or more passive inductors; wherein for each pair of neighboring patches of the plurality of radiating patches: the pair of neighboring patches forms an electrically insulating space therebetween; at least one passive inductor of the one or more passive inductors lies within the electrically insulating space; and each passive inductor of the at least one passive inductor is directly electrically connected to both of the pair of neighboring patches such that no circuit element is electrically connected between the passive inductor and each of the pair of neighboring patches; wherein the patch antenna element is disposed above a counterpoise and has a smaller footprint than a conventional single-patch half-wave air-loaded patch antenna sized to resonate at the maximum operating frequency.
2 . The patch antenna element of claim 1 , wherein for each pair of neighboring patches: a first patch of the pair of neighboring patches has a first edge nearest a second patch of the pair of neighboring patches; and the second patch has a second edge that is nearest the first patch, parallel to the first edge, and displaced from the first edge to create the electrically insulating space.
3 . The patch antenna element of claim 2 , wherein: the first edge is parallel to a first radiating edge of the plurality of patches; and the second edge is parallel to a second radiating edge of the plurality of patches.
4 . The patch antenna element of claim 2 , wherein for each pair of neighboring patches, the at least one passive inductor comprises a plurality of passive inductors that are uniformly spaced along a direction parallel to the first and second edges.
5 . The patch antenna element of claim 1 , each of the one or more passive inductors being a planar inductor that is coplanar with the plurality of radiating patches.
6 . The patch antenna element of claim 1 , the one or more passive inductors including a planar inductor.
7 . The patch antenna element of claim 1 , the plurality of radiating patches being identically shaped and regularly spaced along the resonant dimension.
8 . The patch antenna element of claim 1 , the plurality of radiating patches being identically shaped and regularly spaced along (i) the resonant dimension and (ii) a dimension that is perpendicular to the resonant dimension and parallel to a plane of the plurality of radiating patches.
9 . The patch antenna element of claim 1 , wherein: the plurality of radiating patches includes a first patch and a second patch; and the second patch fully surrounds the first patch in a plane of the plurality of radiating patches.
10 . A patch antenna comprising: the patch antenna element of claim 1 ; and the counterpoise of claim 1 , the counterpoise being parallel to the patch antenna element and at least partially underneath the patch antenna element.
11 . The patch antenna of claim 10 , further comprising a substrate between the patch antenna element and the counterpoise; wherein the patch antenna element is located on a first side of the substrate and the counterpoise is located on a second side of the substrate that is opposite to the first side.
12 . The patch antenna of claim 11 , the substrate comprising one or more layers of a printed circuit board.
13 . The patch antenna of claim 10 , further comprising a feed that electrically connects to one of the plurality of radiating patches.
14 . The patch antenna of claim 10 , further comprising: a first feed electrically connecting to a first patch of the plurality of radiating patches; and a second feed electrically connecting to a second patch of the plurality of radiating patches, the second patch being different from the first patch; wherein: the patch antenna, when driven via the first feed, emits radiation polarized in a first direction; and the patch antenna, when driven via the second feed, emits radiation polarized in a second direction that is perpendicular to the first direction.
15 . The patch antenna of claim 10 , further comprising a magnetodielectric material at least partially located between the patch antenna element and the counterpoise.
16 . The patch antenna of claim 10 , wherein a gap between the patch antenna element and the counterpoise is filled with air.
17 . The patch antenna of claim 10 , one of the plurality of radiating patches having a distal widthwise edge that is electrically shorted to the counterpoise.

Description

RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application 63/176,802, filed Apr. 19, 2021, which is incorporated herein by reference in its entirety. BACKGROUND The characteristic impedance Z(ω) of an infinitely-long transmission line is the ratio of the voltage to the current of a sinusoidal wave of frequency ω travelling along the transmission line. Since the transmission line is infinitely-long, the sinusoidal wave will not produce any reflections. It is frequently assumed that the transmission line has no series resistance (per unit length) and infinite shunt resistance (also per unit length). In this case, the characteristic impedance is essentially independent of frequency (i.e., Z(ω)≈Z0, where Z0 is a constant) and independent of length. Thus, the characteristic impedance Z0 also applies to finite-length sections of the transmission line. Common values of Z0 include 50Ω (e.g., RG-58 coaxial cable), 7502 (e.g., RG-6 coaxial cable), 900 (e.g., USB), and 1000 (e.g., Ethernet). SUMMARY Disclosed herein are techniques that use discrete reactive elements (i.e., capacitors and inductors) to increase the impedance of a transmission line. These techniques are particularly useful for planar transmission lines (e.g., microstrip, stripline, coplanar waveguide, etc.), where the characteristic impedance Z0 increases as the effective width weff of the strip decreases. Due to limitations in processing and manufacturing (e.g., printed circuit boards, lithography, etc.), there is a smallest effective width weff that can be reliably and repeatedly fabricated. This smallest effective width weff limits the characteristic impedance Z0 to typically less than a couple hundred ohms. However, for many applications, it would be advantageous (e.g., less insertion loss, higher bandwidth, improved energy efficiency, reduced component count, etc.) to fabricate higher-impedance planar transmission lines. The impedance-increasing techniques disclosed herein are also applicable to other types of transmission lines, such as coaxial and twisted-pair. In some embodiments, a high-impedance transmission line includes a sequence of transmission-line segments, each having a characteristic impedance Z0. These segments are disjoint in that their signal conductors do not make direct electrical contact with each other. Each segment has a length (along a transmission direction) that is no greater than λmax/2, where λmax is the maximum wavelength of a maximum operating frequency fmax of the high-impedance transmission line. At least one discrete reactive element or component electrically connects each segment to its nearest neighbor. The reactive elements may be planar (e.g., a planar capacitor or inductor), in which case they may be fabricated simultaneously with planar transmission-line segments. Alternatively, the reactive elements may be non-planar (e.g., a helical coil, surface-mount component, etc.). These reactive elements are “discrete” to differentiate them from the continuously-distributed properties of the transmission-line segments. Advantageously, the plurality of transmission-line segments may be fabricated using conventional techniques, and therefore may have a relatively low characteristic impedance Z0 (e.g., 500 or 75Ω). Accordingly, planar implementations of the high-impedance transmission line can utilize the same techniques currently used to fabricate planar transmission lines. The discrete reactive elements are selected such that the high-impedance transmission line has a characteristic impedance Z0′ that is greater than Z0. In many of the present embodiments, the reactive elements are inductors. The self-resonant frequencies of these inductors may be close to, or exceed, the maximum operating frequency fmax. However, one or more of the discrete reactive elements may be a capacitor. More generally, the discrete reactive elements can be any combination of inductors and capacitors. Microstrip patch antennas are devices whose performance can be improved using the impedance-increasing techniques described herein. For example, consider a conventional half-wave patch antenna having a single patch of length l≈λc/2, where λc is the wavelength of a resonant frequency fc of the patch antenna. The single patch is located over a counterpoise that is parallel to the single patch and vertically displaced from the counterpoise by a small gap. This patch antenna can be modeled as a transmission line of length l and characteristic impedance Z0. The two lengthwise radiating edges can be modeled as radiation resistances R that load both ends of the modeled transmission line. Typically R is at least ten times greater than Z0. Due to this impedance mismatch, the reflectivities of the electrical signal at the radiating edges are large, i.e., the patch antenna has a large Q, which results in low electrical efficiency and small bandwidth. To improve the performance of the conventional patch antenna, the single patc