WO2023245274A1

WO2023245274A1 - Tightly-coupled antenna array and method thereof

Info

Publication number: WO2023245274A1
Application number: PCT/CA2022/051002
Authority: WO
Inventors: Amir BORJI; Nazanin RAHMATI; Safieddin Safavi-Naeini; Peter Chun; Pengyong CHEN; Liangsheng LIU; Xianbiao WANG
Original assignee: Huawei Technologies Canada Co., Ltd.
Priority date: 2022-06-22
Filing date: 2022-06-22
Publication date: 2023-12-28

Abstract

A tightly-coupled antenna array has a plurality of tightly-coupled antenna elements configured to transmit or receive electromagnetic waves. The plurality of antenna elements include a plurality of active antenna elements for being excited by a plurality of excitation sources and a plurality of passive antenna elements. Each active antenna element is configured to be excited by a respective one of the plurality of excitation sources. Each passive antenna element is terminated by a finite passive impedance. Each antenna element of the array is adjacent a plurality of other antenna elements of the array and is spaced from each of the plurality of other antenna elements by a spacing of no more than half a wavelength of the electromagnetic waves.

Description

TIGHTLY-COUPLED ANTENNA ARRAY AND METHOD THEREOF

TECHNICAL FIELD

The present disclosure relates to the field of wireless communications and radar systems, and in particular to a tightly-coupled antenna array.

BACKGROUND

The rapid growth of mobile network technology has led to the need for multi-band or ultra-wideband phased array antennas that can cover all required frequency ranges. In order to provide greater capacity, the 5G frequency band has been extended to mm-wave frequencies above 20 GHz and up to 71 GHz. Furthermore, due to relatively higher transmission loss at these frequencies, an ultra- wideband phased array antenna with fairly high directivity and adaptive beam scanning capability, both in the base station and the mobile terminal, may be required.

The application of ultra-wideband antennas is not limited to wideband 5G communication technology. For example, another fast-growing area of application for such antenna arrays is automotive radars. For any multi-functional antenna system, a low-profile ultra-wideband antenna array with wide scan capability and high polarization purity is in great demand. Consolidating multiple antennas into a single ultra-wideband or multi-band radiating aperture that fulfills all the requirements is challenging but can lead to smaller and cheaper antenna devices.

Tightly-coupled arrays (TCAs) tend to be planar, ultra-wideband antenna arrays that are good candidates for wideband applications where the available space for the antenna is limited but the required gain is not very high. TCA elements are closely-spaced or tightly-coupled instead of being isolated by half a wavelength spacing as is commonly used in ordinary antenna arrays. Strong capacitive mutual coupling among neighboring elements makes TCAs a good candidate for extremely wide Voltage Standing Wave Ratio bandwidth while being low-profile enough to be used in applications such as cell-phone devices. Moreover, TCAs are capable of steering the beam to wide scanning volumes with low cross-polarization levels, since the unit cell dimension is smaller than half of the wavelength at the highest frequency of operation of the array.

The most challenging and expensive part in the design and manufacture of any phased array antenna, including TCAs, is the design of the feed network and the integration of active and passive circuit components that are required for excitation of each individual element. Compared to a conventional narrow-band phased array antenna, this becomes more challenging and expensive in the case of TCAs because of the significantly larger number of elements that must fit into the same aperture area. SUMMARY

According to one aspect of this disclosure, there is provided a tightly-coupled antenna array comprising: a plurality of tightly-coupled antenna elements configured to transmit or receive electromagnetic waves, the plurality of antenna elements comprising: a plurality of active antenna elements each for being excited by an excitation source; and a plurality of passive antenna elements each being terminated by a finite passive impedance; each antenna element of the array is adjacent a plurality of other antenna elements of the array and is spaced from each of the plurality of other antenna elements by a spacing of no more than half a wavelength of the electromagnetic waves.

In some embodiments, the excitation source comprises a transmitter, a receiver, or a transceiver.

In some embodiments, the antenna elements of the array are configured to transmit or receive electromagnetic waves of different wavelengths; and the spacing is, from among the different wavelengths, no more than half a smallest wavelength of the electromagnetic waves.

In some embodiments, the antenna elements of the array comprises a patch antenna.

In some embodiments, the antenna elements of the array comprises a linear dipole antenna.

In some embodiments, the antenna elements of the array comprises a bowtie antenna.

In some embodiments, the bowtie antenna comprises: a first conductive layer with one or more slots formed therein; and a second, parasitic conductive layer with one or more slots formed therein and separated from the first conductive layer by a dielectric.

In some embodiments, the antenna elements of the array are configured to transmit or receive electromagnetic waves at a frequency from 20 GHz to 80 GHz.

In some embodiments, each active antenna element of the array is configured to transmit or receive the electromagnetic waves according to a first polarization and according to a second polarization orthogonal to the first polarization.

In some embodiments, each active antenna element is configured to be excited by the respective excitation source through a respective impedance matching circuit.

According to one aspect of this disclosure, there is provided a method comprising: determining a radiation pattern to be generated by a tightly-coupled antenna array; determining, based on the radiation pattern, an excitation voltage of an excitation source for each of a plurality of active antenna elements of the antenna array and a finite passive impedance of each of a plurality of passive antenna elements of the antenna array; and making the antenna array such that: each passive antenna element is terminated by the finite passive impedance determined for the passive antenna element; and each antenna element of the antenna array is adjacent a plurality of other antenna elements of the antenna array and is spaced from each of the plurality of other antenna elements by a spacing of no more than half a wavelength of the electromagnetic waves.

In some embodiments, the excitation source comprises a transmitter, a receiver, or a transceiver. In some embodiments, said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array comprises: using one or more genetic algorithms for determining the excitation voltage of the excitation source for each the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array.

In some embodiments, the method further comprises: operating the antenna array by driving each active antenna element according to the excitation voltage of the corresponding excitation source determined for the active antenna element.

In some embodiments, said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array comprises: for each of a plurality of frequencies at which the active antenna elements are to be excited: determining, for a broadside angle, the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array.

In some embodiments, said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array comprises: for each of a plurality of frequencies at which the active antenna elements are to be excited: determining, for non-broadside angles, the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array by fixing the determined finite passive impedances.

In some embodiments, each finite passive impedance of each passive antenna element comprises one or more lumped or distributed circuit components; the method further comprises, for each passive antenna element: determining, based on the finite passive impedance determined for the passive antenna element, a value for each lumped or distributed circuit component; and said making the antenna array comprises: for each finite passive impedance, making the finite passive impedance according to each lumped or distributed circuit component and according to the value determined for each lumped or distributed circuit component.

In some embodiments, said making the antenna array comprises making each antenna element such that each antenna element is configured to transmit or receive electromagnetic waves of different wavelengths; and the spacing is, from among the different wavelengths, no more than half a smallest wavelength of the electromagnetic waves.

In some embodiments, said making the antenna array comprises making each antenna element such that each antenna element of the antenna array comprises a patch antenna, a linear dipole antenna, or a bowtie antenna. In some embodiments, the bowtie antenna comprises: a first conductive layer with one or more slots formed therein; and a second, parasitic conductive layer with one or more slots formed therein and separated from the first conductive layer by a dielectric.

In some embodiments, said making the antenna array comprises making each antenna element such that each active antenna element of the antenna array is configured to transmit or receive the electromagnetic waves according to a first polarization and according to a second polarization orthogonal to the first polarization.

In some embodiments, said making the antenna array comprises making each antenna element such that: each active antenna element is configured to be excited by the respective one of the plurality of excitation sources through a respective impedance matching circuit.

This summary does not necessarily describe the entire scope of all aspects. Other aspects, features, and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described in detail in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic diagram of a tightly-coupled antenna array, according to an embodiment of the disclosure;

FIG. 2 is another schematic diagram of a tightly-coupled antenna array, according to an embodiment of the disclosure;

FIGS. 3A and 3B show two examples of RLC circuits for the passive impedances of passive antenna elements of a tightly-coupled antenna array, according to an embodiment of the disclosure;

FIGS. 4A and 4B are schematic diagrams of dual-polarized, tightly-coupled arrays with circular and square patch antenna elements, respectively, according to embodiments of the disclosure;

FIGS. 5A and 5B show perspective and cross-sectional views, respectively, of a bowtie antenna element, according to an embodiment of the disclosure;

FIG. 6 shows upper and lower layers of the bowtie antenna element of FIGS. 5A and 5B; and

FIG. 7 is a flow diagram of a method of making a tightly-coupled antenna array according to an embodiment of the disclosure;

FIG. 8 shows an example of a directivity pattern of a tightly-coupled antenna array and a desired directivity pattern of an idealized tightly-coupled antenna array; and

FIG. 9 shows an example of a directivity pattern of a tightly-coupled antenna array according to an embodiment of the disclosure and a desired directivity pattern of an idealized tightly-coupled antenna array. DETAILED DESCRIPTION

The present disclosure seeks to provide an improved tightly-coupled antenna array that benefits from lower cost and manufacturing complexity, without an unacceptable loss of performance. While various embodiments of the disclosure are described below, the disclosure is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the disclosure which is to be limited only by the appended claims.

In prior implementations of TCAs, each antenna element is excited and thus requires a number of circuitry components (for example, a matching network, phase shifter, amplifier, and diplexer) in order to be excited. This can be difficult to accommodate because of the very small size of the unit cell that is inherent in TCAs. This problem is exacerbated as the operational frequency of the TCA moves toward mm-waves.

Therefore, in order to address this problem, embodiments of the disclosure reduce the number of “active” elements in the TCA while maintaining the performance of the parameters of the array as whole, as well as maintaining the characteristics of the radiation pattern within acceptable ranges. Reducing the number of “active” elements in the TCA in turn reduces the total number of active and passive circuitry components (including baluns, matching networks, phase shifters, and amplifiers) that are required for the array as a whole. This in turn may reduce the cost and complexity of the phased array antenna.

According to embodiments of the disclosure, instead of actively feeding or exciting every antenna element in the array, only a subset of antenna elements is actively fed, while the remaining antenna elements are terminated with correctly-designed passive impedances. Throughout this disclosure, an antenna element that is driven by an excitation voltage of an excitation source may be referred to as an “active antenna element”, whereas an antenna element that is terminated by a finite, passive impedance may be referred to as a “passive antenna element”. In various embodiments, such an excitation source may be, for example, a transmitter module (or simply a “transmitter”), a receiver module (or simply “receiver”), or a transceiver module.

Because of the relatively close spacing between the antenna elements, the passive antenna elements experience a strong mutual coupling between themselves and the active antenna elements. As a result, currents are induced on the passive antenna elements such that the passive antenna elements contribute to the radiation pattern. By properly designing the excitation voltages that drive the active antenna elements, and by properly designing the circuit components for the passive impedances of the passive antenna elements, an acceptable radiation pattern with specified gain and side lobe level may be achieved. The excitation voltages that drive the active antenna elements, and the passive impedances that terminate the passive antenna elements, may be designed and optimized using a genetic algorithm in order to satisfy the required characteristics of the radiation pattern. The resulting tightly-coupled array can operate in a wide range of frequencies without significant appearance of any grating lobes. As a result, embodiments of the disclosure may result in phased antenna arrays that maintain the performance of the array within design specifications, while reducing the overall cost of the array.

Turning to FIG. 1 , there is shown a schematic diagram of a “partially excited” TCA 100 with printed dipole antenna elements. In this context, “partially excited” refers to the fact that only a subset of the total number of antenna elements is driven by excitation voltages of excitation sources, whereas the remainder are terminated in passive impedances and are therefore “passive antenna elements”. As described above, such excitation sources may be, for example, transmitters, receivers, and/or transceivers.

As can be seen in the example of FIG. 1 , two of every three columns comprise passive antenna elements 20 while every third column comprises alternative active antenna elements 10 and passive antenna elements 20. Each active antenna element 10 is actively fed by excitation circuitry 15 (denoted by V~), whereas each passive antenna element 20 is terminated in a finite, passive impedance 25 (denoted by R + jX). FIGS. 3A and 3B show two examples of RLC circuits, including a number of lumped circuit components, that may be used to implement the passive impedances of passive antenna elements 20.

While in FIG. 1 the antenna elements are printed dipoles, the antenna elements may be any of a variety of other types of elements (such as microstrip patches or bowtie dipole antennas). In FIG. 1 , each antenna element is printed on a dielectric substrate. Active antenna elements 10 are connected to a transmitter or a receiver. In FIG. 1 , TCA 100 is shown in transmitting mode. If the array were in receiving mode, then instead of voltage sources 15 each active antenna element 10 would comprise receiver frontends. Whether in transmitting or receiving mode, each active antenna element 10 is connected to a number of circuit components including a phase shifter, amplifier, impedance matching circuit, and diplexer (not shown) in order to control/vary the amplitude and phase of the signal input to or received by the active antenna element.

In order for passive antenna elements 20 to benefit from mutual coupling with active antenna elements 10, the inter-element distance or spacing separating the antenna of each active antenna element 10 from the antenna of each adjacently-located passive antenna element 20 is much smaller than conventional antenna arrays, and in particular is no more than half a wavelength of the highest frequency of operation of TCA 100 in some embodiments. In some other embodiments, the interelement spacing may be preferably half of the wavelength of the highest frequency of operation of TCA 100.

It shall be noted that the pattern of active and passive antenna elements 10, 20 shown in FIG. 1 is only one example of a pattern that may be used to form a tightly-coupled array according to the embodiments described herein. For example, according to some embodiments, the spacing between antenna elements in the H-plane (Y-axis in FIG.1 ) can be much smaller than the spacing in the E-plane (X-axis in FIG.1 ). As a result, according to some embodiments, one in every three antenna elements in each column may be active. Any other symmetrical or even asymmetrical design pattern may be used. For instance, FIG. 2 shows an example in which active antenna elements 10 are randomly distributed in array 200. Generally, there is a limit to the number of passive antenna elements that may be positioned between any two successive active antenna elements in a given row or column of the array. This is because, past a certain point, it may become too impractical to prevent the appearance of grating lobes in the radiation pattern if the distance between every two active antenna elements becomes too large.

While FIG. 1 shows printed dipole antenna elements, other types of antenna elements may be used. For example, as can be seen in FIGS. 4A and 4B, each antenna element 30, 40 may comprise a circular patch antenna (FIG. 4A) or a square patch antenna (FIG. 4B). In FIGS. 4A and 4B, the Xs denote the locations of polarized antenna elements that are excited. For instance, in FIGS. 4A and 4B, active antenna elements 30, 40 each comprise a first antenna element 35a, 45a configured to transmit or receive electromagnetic waves according to a first polarization, and a second antenna element 35b, 45b configured to transmit or receive electromagnetic waves according to a second polarization orthogonal to the first polarization.

Other types of antenna elements that may be used include slot antennas and other types of planar multilayer antennas, depending on the application. As in the case of FIGS. 4A and 4B, each antenna element may provide either single or dual polarization.

Turning to FIGS. 5A, 5B, and 6, there is shown another example design of an antenna element that may be used with a tightly-coupled antenna array according to the present embodiments. In order to cover the three millimeter-wave bands that are allocated for 5G wireless communications, the example antenna element of FIGS. 5A and 5B comprises a dual-polarized, slotted bowtie antenna element 200. Antenna element 200 comprises a first conductive layer 210 with a number of slots 212 formed therein, spaced from a second conductive layer 220 with slots 214 formed therein. In particular, first conductive layer 210 is separated from second conductive layer 220 by a dielectric 205 of thickness d2. Slots 212 and 214 prolong the path of the current flowing through conductive layer 210 and conductive layer 220, and may therefore create resonances at appropriate frequency bands. By optimizing the shape, dimensions, and locations of slots 212 and 214, different resonances can be created at different frequencies, in order to result in a multi-band antenna. Conductive layer 220 is used to produce additional resonances at the lower end of the frequency band of operation. Conductive layer 210 and conductive layer 220 are placed on a dielectric substrate 215 of thickness d1 on top of a ground plane 215.

One advantage of the bowtie antenna element 200 of FIGS. 5A, 5B, and 6 is that bowtie antenna element 200 may occupy a relatively small area while being operable over a relatively wide frequency range. Using a wideband antenna element may simplify the design (described in further detail below) of the tightly-couple antenna array, since the use of wideband antenna elements may lead to improved frequency behavior of the terminating passive impedances of the passive antenna elements. According to embodiments of the disclosure, the terminating passive impedances of the passive antenna elements, and the excitation voltages driving the active antenna elements, may be optimized using any of various genetic algorithms in order to achieve an acceptable directivity and side lobe level (SLL). Typically, for each steering angle of the array, a mask that specifies the acceptable directivity and SLL is provided, and the optimization attempts to obtain proper impedances and excitation voltages such that the radiation pattern of the array does not violate the mask.

In particular, at each frequency at which the array is set to operate, the terminating impedances are fixed at the optimized values obtained for the broadside steering angle, and only the excitation voltages are optimized for other, non-broadside steering angles. As a result, the optimized impedances are only a function of frequency and do not change when steering the beam. A different set of optimized excitation voltages may be required for each frequency and for each steering angle.

In order to design the terminating impedances of each passive antenna element, different topologies of lumped or distributed circuit elements can be used (as can be seen, for example, in FIGS. 3A and 3B). The value of each lumped or distributed circuit component can be obtained according to either of two ways. According to a first method, optimization techniques may be used to obtain the value of each lumped or distributed circuit component such that the impedance of the circuit, over the frequency band of the antenna, is close to what was obtained from the above-described antenna optimization. According to a second method, a rational function may be fitted to the impedance data and then conventional circuit synthesis methods may be used to extract the value of each lumped or distributed circuit component.

Turning to FIG. 7, there will now be described a flow diagram of a method of making a tightly-coupled antenna array according to an embodiment of the disclosure.

At block 302, at initial frequency is selected, and a scan angle of 0° is selected.

At block 304, an initial terminating, passive impedance for each passive antenna element is selected.

At block 306, an initial excitation voltage for each active antenna element is selected.

At block 308, the current on each antenna element (passive and active) is calculated, for example using the impedance matrix of the array.

At block 310, the radiation pattern of the array is calculated, for example by multiplying the array factor by the radiation pattern for each antenna element. The radiation pattern for each element is calculated by assuming the element is embedded in the array environment (rather than being a single isolated element).

At block 312, the radiation pattern calculated at block 310 is compared to a predefined mask, and a cost function is calculated based on the comparison.

At block 314, the cost function is compared to a preset tolerance. If the cost function is greater than the preset tolerance, and if the scan angle is currently set to 0, then the excitation voltages and passive impedances are modified using a genetic algorithm, and the process returns to block 308.

If the cost function is greater than the preset tolerance, and if the scan angle is not currently set to 0, then the excitation voltages are modified using a genetic algorithm, and the process returns to block 308.

If the cost function is less than the preset tolerance, then at block 320 it is determined whether the optimization has been performed for all scan angles.

If the optimization has not been performed for all scan angles, then at block 326 a next scan angle is selected, at block 328 the passive impedances are kept fixed, and the process returns to block 306.

If the optimization has been performed for all scan angles, then at block 322 it is determined whether the optimization has been performed for all frequencies.

If the optimization has not been performed for all frequencies, then at block 330 a next frequency is selected and the scan angle is set to 0, and the process returns to block 304.

If the optimization has been performed for all frequencies, then at block 324 the optimization ends.

FIGS. 8 and 9 show directivity patterns of a tightly-coupled antenna array according to embodiments of the disclosure (dotted line) and desired directivity patterns of an idealized tightly-coupled antenna array (solid line) wherein all antenna elements would be excited, at 50 GHz when the main beam is scanned to 0=30°, <p=0°. FIG. 8 shows the directivity in the E-plane (the plane being parallel to the dipoles), whereas FIG. 9 shows the directivity in the H-plane (the plane that is perpendicular to the dipoles).

In FIGS. 8 and 9, the tightly-coupled antenna array according to embodiments of the disclosure is an array of 32x13 elements, with 77 active elements and 339 passive elements.

As can be seen from the above, an advantage of the tightly-coupled arrays described herein is that the array may benefit from a significantly lower number of active antenna elements when compared to more traditional phased arrays. By taking advantage of the strong coupling between the antenna elements in order to induce appropriate currents on the passive antenna elements by properly tuning the terminating, passive impedances at the passive elements, the complexity and cost of the tightly- coupled phased array decreases substantially compared to a conventional fully-excited array. Furthermore, as described above, the current distributions on the passive and active elements may be tuned such that the radiation pattern of the array maintains the specified gain and side lobe level.

Embodiments of the tightly-coupled array disclosed herein may be used in mobile and fixed stations in 5G mm-wave wireless communication systems. However, by no means are the embodiments limited to such applications. For example, embodiments of the tightly-coupled array disclosed herein can be used in any application where a wideband or a multiband phased array antenna is needed. For example, millimeter-wave automotive radars may benefit from the embodiments described herein. Other local millimeter-wave wireless networks in the automotive industry (for example, permanent networks inside a vehicle or ad-hoc networks formed from multiple vehicles in motion) may also benefit from the embodiments described herein.

The word “a” or “an” when used in conjunction with the term “comprising” or “including” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one” unless the content clearly dictates otherwise. Similarly, the word “another” may mean at least a second or more unless the content clearly dictates otherwise.

The terms “coupled”, “coupling” or “connected” as used herein can have several different meanings depending on the context in which these terms are used. For example, as used herein, the terms coupled, coupling, or connected can indicate that two elements or devices are directly connected to one another or connected to one another through one or more intermediate elements or devices via a mechanical element depending on the particular context. The term “and/or” herein when used in association with a list of items means any one or more of the items comprising that list.

As used herein, a reference to “about” or “approximately” a number or to being “substantially” equal to a number means being within +/- 10% of that number.

While the disclosure has been described in connection with specific embodiments, it is to be understood that the disclosure is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the disclosure.

It is furthermore contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.

Claims

CLAIMS:

1 . A tightly-coupled antenna array comprising: a plurality of tightly-coupled antenna elements configured to transmit or receive electromagnetic waves, the plurality of antenna elements comprising: a plurality of active antenna elements each for being excited by an excitation source; and a plurality of passive antenna elements each being terminated by a finite passive impedance; wherein each antenna element of the array is adjacent a plurality of other antenna elements of the array and is spaced from each of the plurality of other antenna elements by a spacing of no more than half a wavelength of the electromagnetic waves.

2. The array of claim 1 , wherein the excitation source comprises a transmitter, a receiver, or a transceiver.

3. The array of claim 1 or 2, wherein: the antenna elements of the array are configured to transmit or receive electromagnetic waves of different wavelengths; and the spacing is, from among the different wavelengths, no more than half a smallest wavelength of the electromagnetic waves.

4. The array of any one of claims 1 to 3, wherein the antenna elements of the array comprises a patch antenna.

5. The array of any one of claims 1 to 4, wherein the antenna elements of the array comprises a linear dipole antenna.

6. The array of any one of claims 1 to 4, wherein the antenna elements of the array comprises a bowtie antenna.

7. The array of claim 6, wherein the bowtie antenna comprises: a first conductive layer with one or more slots formed therein; and a second, parasitic conductive layer with one or more slots formed therein and separated from the first conductive layer by a dielectric. The array of any one of claims 1 to 7, wherein the antenna elements of the array are configured to transmit or receive electromagnetic waves at a frequency from 20 GHz to 80 GHz. The array of any one of claims 1 to 8, wherein each active antenna element of the array is configured to transmit or receive the electromagnetic waves according to a first polarization and according to a second polarization orthogonal to the first polarization. The array of any one of claims 1 to 9, wherein: each active antenna element is configured to be excited by the respective excitation source through a respective impedance matching circuit. A method comprising: determining a radiation pattern to be generated by a tightly-coupled antenna array; determining, based on the radiation pattern, an excitation voltage of an excitation source for each of a plurality of active antenna elements of the antenna array and a finite passive impedance of each of a plurality of passive antenna elements of the antenna array; and making the antenna array such that: each passive antenna element is terminated by the finite passive impedance determined for the passive antenna element; and each antenna element of the antenna array is adjacent a plurality of other antenna elements of the antenna array and is spaced from each of the plurality of other antenna elements by a spacing of no more than half a wavelength of the electromagnetic waves. The method of claim 11 , wherein the excitation source comprises a transmitter, a receiver, or a transceiver. The method of claim 11 or 12, wherein said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array comprises: using one or more genetic algorithms for determining the excitation voltage of the excitation source for each the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array. The method of any one of claims 11 to 13, further comprising: operating the antenna array by driving each active antenna element according to the excitation voltage of the corresponding excitation source determined for the active antenna element. The method of any one of claims 11 to 14, wherein said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array comprises: for each of a plurality of frequencies at which the active antenna elements are to be excited: determining, for a broadside angle, the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array and the finite passive impedance of each of the plurality of passive antenna elements of the antenna array. The method of any one of claims 11 to 15, wherein said determining the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array comprises: for each of a plurality of frequencies at which the active antenna elements are to be excited: determining, for non-broadside angles, the excitation voltage of the excitation source for each of the plurality of active antenna elements of the antenna array by fixing the determined finite passive impedances. The method of any one of claims 11 to 16, wherein: each finite passive impedance of each passive antenna element comprises one or more lumped or distributed circuit components; the method further comprises, for each passive antenna element: determining, based on the finite passive impedance determined for the passive antenna element, a value for each lumped or distributed circuit component; and said making the antenna array comprises: for each finite passive impedance, making the finite passive impedance according to each lumped or distributed circuit component and according to the value determined for each lumped or distributed circuit component. The method of any one of claims 11 to 17, wherein: said making the antenna array comprises making each antenna element such that each antenna element is configured to transmit or receive electromagnetic waves of different wavelengths; and the spacing is, from among the different wavelengths, no more than half a smallest wavelength of the electromagnetic waves. The method of any one of claims 11 to 18, wherein said making the antenna array comprises making each antenna element such that each antenna element of the antenna array comprises a patch antenna, a linear dipole antenna, or a bowtie antenna. The method of claim 19, wherein the bowtie antenna comprises: a first conductive layer with one or more slots formed therein; and a second, parasitic conductive layer with one or more slots formed therein and separated from the first conductive layer by a dielectric. The method of any one of claims 11 to 20, wherein said making the antenna array comprises making each antenna element such that each active antenna element of the antenna array is configured to transmit or receive the electromagnetic waves according to a first polarization and according to a second polarization orthogonal to the first polarization. The method of any one of claims 11 to 21 , wherein said making the antenna array comprises making each antenna element such that: each active antenna element is configured to be excited by the respective one of the plurality of excitation sources through a respective impedance matching circuit.