|Publication number||US20060089115 A1|
|Application number||US 10/817,416|
|Publication date||Apr 27, 2006|
|Filing date||Apr 2, 2004|
|Priority date||Apr 3, 2003|
|Also published as||US7027833|
|Publication number||10817416, 817416, US 2006/0089115 A1, US 2006/089115 A1, US 20060089115 A1, US 20060089115A1, US 2006089115 A1, US 2006089115A1, US-A1-20060089115, US-A1-2006089115, US2006/0089115A1, US2006/089115A1, US20060089115 A1, US20060089115A1, US2006089115 A1, US2006089115A1|
|Original Assignee||Goodman Daniel J|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (50), Referenced by (5), Classifications (14), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application No. 60/514,596, filed on Oct. 20, 2003 and the benefit of U.S. Provisional Application No. 60/459,651, filed on Apr. 3, 2003, the disclosures of each of which are incorporated by reference in their entireties.
This invention relates in general to a receiver for receiving electromagnetic energy over a wide frequency band and converting the energy to an intermediate frequency.
Radar systems use a wide variety of frequencies and signal shapes. In many environments, it is desired to be able to determine that a radar source is operational, and to identify the type of radar system which is transmitting energy into the environment. For example, aircraft traveling in a region may wish to be able to identify the type of radar systems operational in an area.
Radar detectors have been produced which are tuned for a specific, relatively narrow energy band. Other radar detectors can receive signals at a few discrete frequencies. For example, U.S. Pat. No. 5,606,736 to Hasler et al. discloses a receiver for receiving signals from both GPS satellites and GLOSNASS satellite, each of which transmits at a different frequency.
Commonly assigned U.S. Pat. No. 6,029,054 to Lemley, the disclosure of which is incorporated by reference herein in its entirety, discloses a receiver that is suitable for receiving energy over a band of frequencies from 0.5 GHz to 18 GHz and converts the received frequency to an intermediate frequency of either 160 MHz or 400 MHz. Lemley discloses using image rejection mixers and filters at the input to reduce image problems. Attention is also drawn to an example of a superheterodyne receiver discussed in Microwave Receivers with Electronic Warfare Applications, James Bao-Yen Tsui, 1992, which discloses using filters before the first mixer stages to reduce image problems.
One embodiment of a superheterodyne receiver suitable receiving RF energy in an upper frequency band and a lower frequency band and for translating the received RF energy to an output frequency includes a first input for receiving the RF energy, a second input for receiving the RF energy, and at least one attenuator for attenuating the RF energy received through the first input or the second input. The receiver also includes a first mixer arranged for mixing a first local oscillator signal with the RF energy in the lower frequency band to produce a signal at a first intermediate frequency, a second mixer arranged for mixing the first local oscillator signal with the RF energy in the upper frequency band to produce a signal at a second intermediate frequency, and a switch configured to direct the first local oscillator signal either to the first mixer or to the second mixer. The receiver also includes a third mixer for mixing a second local oscillator signal with the signal at the first intermediate frequency or the signal at the second intermediate frequency to produce a signal at the output frequency.
Other advantages and features of the invention will become apparent from the following detailed description of the preferred embodiments and the accompanying drawings.
The invention will now be described with reference to certain preferred embodiments thereof and the accompanying drawings.
The receivers described herein are useful in electronic surveillance or intelligence systems that identify the type of radar transmitter based on the transmitted signal.
Superheterodyne receivers generally convert the incoming signal to a known output frequency, typically called an “intermediate frequency”, for further processing by electronics optimized for that particular frequency. The following description uses “output frequency” to refer to the frequency of the output signal of the superheterodyne receiver, and “intermediate frequency” to refer to the frequency of the signal after the initial mixing stage and before the second mixing stage.
Most or all of the receiver components can be surface mount radio frequency semiconductor functional-elements, and the entire RF receiver can be incorporated on printed circuits and housed in small modules.
The receiver 100 is dual-band receiver, meaning it has components arranged to process an upper frequency band input and a lower frequency band input, although the receiver can also be adapted to process more than two frequency bands. The receiver 100 has two input connectors 102 and 104 for receiving signals intercepted with a low frequency antenna and a high frequency antenna, respectively. Alternatively, the input signal can be from a single antenna, and a splitter can be used to divide the signal into an upper and a lower frequency bands.
The receiver 100 performs conversion of a wide band of frequencies at low cost and in a simple, compact, lightweight receiver package. As will be discussed in later paragraphs, the wideband first-conversion approach of the receiver requires no pre-selection filtering of the input signals. In contrast, and as discussed in Tsui's Microwave Receivers with Electronic Warfare Applications, other superheterodyne receivers position a bandpass filter in front of the first stage mixer (between the antenna and the mixer).
In the embodiment illustrated in
The receiver 100 can be housed in two modules 110 and 150, where a converter module 110 contains the RF receiver components such as converters, filters, gain blocks, and attenuators, and a local oscillator module 150 contains the local oscillators used for frequency tuning. This allows the receiver 100 to be configured as a single or coherent multiple-channel RF receiver. For coherent processing, one local oscillator module 150 can provide signals to two or more converter modules 110, allowing the two converter modules to provide outputs which can then be coherently processed by follow-on electronics.
The local oscillator module 150 has a local oscillator 152 that provides the 9-15 GHz local oscillator signal to both the Band A mixer 116 and the Band B mixer 126. The local oscillator frequency is varied by a computer controller from 9.0 to 15 GHz. The local oscillator signal is switched between Bands A and B by a diode switch 134 in the converter module 110.
In the 1 GHz receiver 100, the converter module 110 includes components for first conversion of the input signals in the lower frequency band, Band A, components for first conversion of the input signals in the upper frequency band, Band B, and common components for the second mixing statge. The input signals are converted by the second mixer to a common 1 GHz output frequency. The 1 GHz output signal can then be transferred by an output connector 108 to a signal processor for analog to digital conversion or other processing.
As seen in
After attenuation, the Band A RF signal enters the I Port of the first RF mixer 116. A signal from the first local oscillator (LO1) 152 within the 9.0 to 15.0 GHz range is injected into the L port of the mixer 116, and the RF Band A input signal is converted to an intermediate frequency (IF1) signal at 9 GHz. The Band A 9 GHz signal then passes from the R port of the mixer 116 through a bandpass filter 118 having a 500 MHz bandwidth, then through gain blocks 120 and 122 into a switch 124, which selectively forwards either this Band A 9 GHz signal or the Band B 3 GHz signal to the second mixing stage.
As seen in
Once converted to 3 GHz, the Band B signal is passed through a printed circuit bandpass filter 132 having a bandwidth centered approximately at the 3 GHz intermediate frequency and having a 500 MHz bandwidth that is small enough to substantially block mixer spurs. Details of the mixing plan are discussed later paragraphs and illustrated in
The pre-packaged MMIC switch 124 feeds either the 9 GHZ IF signal from Band A or the 3 GHz IF signal from Band B to the R Port of a second stage mixer 136. The mixer 136 downconverts the 3 GHz or 9 GHz input to a 1 GHz signal at its I port output by applying a second local oscillator signal to the L port of the mixer 136.
The receiver 100 can be set to provide either a 8.0 GHz or a 10 GHz local oscillator signal (LO2) to the downstream mixer 136 when the switch 124 directs the Band A 9 GHz signal to the mixer 136, depending on whether low side mixing or high side mixing is desired. Similarly, the receiver can be set to provide either a 2.0 or 4.0 GHz local oscillator signal to the second stage mixer 136 when the switch 124 directs the Band B 3 GHz signal to the mixer 136, depending on whether low side mixing or high side mixing is desired. A switch 158 is used to select the correct oscillator source and frequency for the mixer 136. The switch 158 can be, for example, a surface-mounted, MMIC, single pole double throw (SPDT) switch. A dielectric resonance oscillator (DRO) 162 can provide the 8.0 and 10.0 GHz signal and a phase-locked loop synthesizer 160 can provide the 2.0 or 4.0 GHz signal, although other alternative sources can be used.
The 1 GHz output signal from the downstream mixer 136 of
Thus, as seen in
The gain blocks 120 and 122, as well as the other gain blocks in the receiver 100, are preferably prepackaged MMIC gain blocks. Fixed-bias resistors (not shown) that feed a DC voltage to the gain blocks can be varied to adjust the overall receiver gain. For the
An advantage of including the attenuator 114 before the first mixer 106 is that the attenuator increases the dynamic range control of the receiver 200 without the use of high dynamic-range conversion components. For example, the receiver in
The bandpass filters can be selected to provide a desired amount of group delay. For example, the filter 142 of the
Although the input frequency bands are broad (0.1 to 6 GHz and 6 to 18 GHz), the receiver 100 does not require a bandpass filter or amplifier positioned before either of the first mixers 116 and 126 to prevent image frequencies from generating outputs in the mixers. This is the result of the spectrum inversion mixing plan discussed in the following paragraphs and illustrated in
As seen in
Spectrum inversion or non-inversion can therefore be selected by the operator by choosing either high side mixing or low side mixing for the second mixing stage. As will be discussed in later paragraphs, the receiver also produces an inverted 1 GHz output that Band B inputs in the 6-12 GHz range, and non-inverted outputs for Band B inputs above 12 GHz. Because low-side mixing in mixer 136 can result in mixer spurs in some parts of the filter's passband, the high side mixing plan in
The next mixer 136 then converts the 3 GHz intermediate frequency to an output frequency of 1.0 GHz by either low side mixing (
One advantage of the receiver 100 described herein is that the mixing profile reduces images and other interfering frequencies that might be generated in the mixers. Some examples follow.
Mixers produce intermediate frequencies according to the equation IF=(N fR)±(M fLO), where N and M are integers, fR and fLO are the frequencies of the input signal and the local oscillator to be mixed, and IF is the resulting intermediate frequency. The largest amplitude signals result when both N and M are equal to 1, e.g., at IF=2fR−fL and IF=fR+fL. Traditional mixers have specific image problems at the frequency 2fL−fR when up converting, and at 2fR when downconverting. The mixing plan of the present receiver 100 eliminates these image problems. For example, when mixer 116 upconverts the a 6 GHz input signal to a 9 GHz IF (
A few examples are provided to illustrate other advantages of the receiver's mixing plan. Referring again to mixer 116 in
If the RF input to the mixer 116 is 1 GHz, a LO frequency of 8 GHz would also produce a 9 GHz intermediate frequency. However, the local oscillator 152 produces signals between 9 and 15 GHz, so a 8 GHz signal will not be generated.
With a 1 GHz RF input and a 10 GHz local oscillator signal, a 9.0 GHz and a 11 GHz signal can be produced (N=1 and M=1). However, the bandpass filter 118 that follows the mixer has a bandwidth that will allow the desired 9.0 GHz frequency to pass, but will reject a 11.0 GHz signal. For example, the bandpass filter 118 has a 9.0 GHz center frequency and a 275 MHz bandwidth, thus excluding signals with a frequency outside of the 8.86 to 9.14 GHz passband of the filter 118.
For a local oscillator frequency of 9.1 GHz (
At the upper end of the Band A input range, when an RF input of 6.0 GHz is mixed with a 15 GHz LO1, two main signal components will be produced having frequencies of 9 GHz and 21 GHz. The 21 GHz frequency component is outside the passband of the filter 118 and will not pass through the filter 118. For the 15 GHz LO1, the possible inputs that will produce a 9 GHz IF include 6 GHz and 24 GHz. The 24 GHz input frequency is outside of the frequency of the Band B input band, so will not pass to the mixer.
In this arrangement, each local oscillator signal has only one RF input within the RF input band that will result in a large amplitude IF at the output of the following bandpass filter. Thus, as the local oscillator is tuned through its frequency range, when an IF signal is produced at the output of the mixer, the input frequency can be readily determined by its correspondence with the local oscillator frequency.
After filtering and amplification, the Band A 9 GHz intermediate frequency signal 206 is then downconverted in the mixer 136 by either low-side mixing with a 8 GHz local oscillator signal (LO2) or high side mixing with a 10 GHz local oscillator signal. The choice of high-side mixing or low-side mixing can be either made by the operator or preset into the controller for the LO2 source. The resulting output signal from the mixer 136 is passed through a second bandpass filter 142 with a bandwidth that includes, and preferably is centered on the desired output frequency. For example, the bandpass filter 142 in the
The receiver 100 shown in
To change the synthesizer frequency, thus tuning the receiver, a serial synchronous data word 338 is sent into the data port of the PLL 323 by a controller 330 such as a personal computer or field programmable gate array (FPGA). These words 338 adjust the frequency dividers within the PLL 323 to step the frequency through the tuning range.
The components in the converter 110 and local oscillator 150 modules can be selected to have any desired degree of reliability. For example, using special reliability components for all the active devices can produce a receiver which is spacecraft-qualified.
Each module discussed in previous paragraphs can be housed within a an outer housing formed of metal or another suitable material. The housings can be affixed to each other in a compact receiver package approximately 2″ by 2″ by 3″ in size, and weighing approximately 12 ounces. Power connections and inter-module connectors arranged at the ends of the housings. If desired, the receiver can be ruggedized by using rugged packaging of the receiver, in which the housing is slightly larger, and includes waterproofing seals, EM interference seals, and special sealed connectors.
While the receiver 100 is shown in
For the second mixing stage of the receiver 500, the R port of the mixer 536 receives a 3 GHz signal or a 9 GHz signal from the switch 524. A local oscillator signal is provided to the L port of the mixer 536, to produce an output signal with a frequency of 160 MHz.
The local oscillator module 550 is identical to the
In addition, the bandpass filter 542 that follows the second stage mixer 536 preferably has a narrower passband than the filter 142 in the
Consider next possible image frequencies. For a local oscillator signal at 8.840 GHz, an input IF signal of 8.68 GHz could also result in an output signal having a 160 MHz frequency. However, as can be seen in
Turning next to
Note that for
The mixers 116 and 126 of the
Spectrum inversion can be compensated by program software if desired. For example, a computer can re-invert the inverted signal after digitization of the output frequency. In some applications, non-inversion is desired to provide quick inter-changeability with other receivers without having concern on toggling the computer. Simple internal module replacement by the manufacturer is possible to select either inversion or non-inversion choices.
The invention has been described with reference to certain preferred embodiments thereof. It will be understood, however, that modification and variations are possible within the scope of the appended claims.
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|U.S. Classification||455/189.1, 455/280, 455/323, 455/313|
|International Classification||H04B15/00, H04B1/26, H04B1/18, H04B1/28|
|Cooperative Classification||H04B1/005, H04B1/28, H04B1/406|
|European Classification||H04B1/00M, H04B1/28, H04B1/40C4|
|Aug 11, 2004||AS||Assignment|
Owner name: NAVY, THE UNITED STATES OF AMERICA AS REPRESENTED
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:GOODMAN, DANIEL J.;REEL/FRAME:015004/0416
Effective date: 20040402
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